High Reliability Magnetic Devices (Electrical Engineering & Electronics, 115)

HIGH RELIABILITY MAGNETIC DEVICES Design and Fabrication

COLONEL WM. T. MCLYMAN Kg Magnetics, Inc. Idyllwild, California

M A R C E L

H

MARCEL DEKKER, INC.

D E K K E R

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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Library of Congress Cataloging-in-Publication Data McLyman, Colonel William T. High reliability magnetic devices: design and fabrication/Wm. T. McLyman p. cm.—(Electrical and computer engineering; 115) ISBN 0-8247-0818-0 (alk. paper) 1. Magnetic devices—Design and construction—Quality control. 2. Electric inductors. 3. Electronic transformers. I. Title. II. Electrical engineering and electronics; 115 TK454.4.M3 .M35 2002

621.31'4-Kic21

2002073408

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ELECTRICAL AND COMPUTER ENGINEERING A Series of Reference Books and Textbooks

FOUNDING EDITOR Marlin O. Thurston Department of Electrical Engineering The Ohio State University Columbus, Ohio

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

Rational Fault Analysis, edited by Richard Saeks and S. R. Liberty Nonparametric Methods in Communications, edited by P. Papantoni-Kazakos and Dimitri Kazakos Interactive Pattern Recognition, Yi-tzuu Chien Solid-State Electronics, Lawrence E. Murr Electronic, Magnetic, and Thermal Properties of Solid Materials, Klaus Schroder Magnetic-Bubble Memory Technology, Hsu Chang Transformer and Inductor Design Handbook, Colonel Wm. T. McLyman Electromagnetics: Classical and Modern Theory and Applications, Samuel Seely and Alexander D, Poulahkas One-Dimensional Digital Signal Processing, Chi-Tsong Chen Interconnected Dynamical Systems, Raymond A. DeCaho and Richard Saeks Modern Digital Control Systems, Raymond G. Jacquot Hybrid Circuit Design and Manufacture, Roydn D. Jones Magnetic Core Selection for Transformers and Inductors: A User's Guide to Practice and Specification, Colonel Wm. T. McLyman Static and Rotating Electromagnetic Devices, Richard H. Engelmann Energy-Efficient Electric Motors: Selection and Application, John C. Andreas Electromagnetic Compossibility, Heinz M. Schlicke Electronics: Models, Analysis, and Systems, James G. Gottling Digital Filter Design Handbook, FredJ. Taylor Multivariable Control: An Introduction, P. K. Sinha Flexible Circuits: Design and Applications, Steve Gurley, with contributions by Carl A. Edstrom, Jr., Ray D. Greenway, and William P. Kelly Circuit Interruption: Theory and Techniques, Thomas E. Browne, Jr. Switch Mode Power Conversion: Basic Theory and Design, K. Kit Sum Pattern Recognition: Applications to Large Data-Set Problems, Sing-Tze Bow Custom-Specific Integrated Circuits: Design and Fabrication, Stanley L. Hurst Digital Circuits: Logic and Design, Ronald C. Emery Large-Scale Control Systems: Theories and Techniques, Magdi S. Mahmoud, Mohamed F. Hassan, and Mohamed G. Darwish Microprocessor Software Project Management, Eli T. Fathi and Cedric V. W. Armstrong (Sponsored by Ontario Centre for Microelectronics) Low Frequency Electromagnetic Design, Michael P. Perry Multidimensional Systems: Techniques and Applications, edited by Spyros G. Tzafestas AC Motors for High-Performance Applications: Analysis and Control, Sakae Yamamura Ceramic Motors for Electronics: Processing, Properties, and Applications, edited by Relva C. Buchanan Microcomputer Bus Structures and Bus Interface Design, Arthur L Dexter End User's Guide to Innovative Flexible Circuit Packaging, Jay J. Miniet Reliability Engineering for Electronic Design, Norman B. Fuqua Design Fundamentals for Low-Voltage Distribution and Control, Frank W. Kussy and Jack L. Warren Encapsulation of Electronic Devices and Components, Edward R. Salmon Protective Relaying: Principles and Applications, J. Lewis Blackburn Testing Active and Passive Electronic Components, Richard F. Powell Adaptive Control Systems: Techniques and Applications, V. V. Chalam Computer-Aided Analysis of Power Electronic Systems, Venkatachari Rajagopalan

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97. Robust Control System Design: Advanced State Space Techniques, Chia-Chi Tsui 98. Spatial Electric Load Forecasting, H. Lee Willis 99. Permanent Magnet Motor Technology: Design and Applications, Jacek F. Gieras and Mitchell Wing 100. High Voltage Circuit Breakers: Design and Applications, Ruben D. Garzon 101. Integrating Electrical Heating Elements in Appliance Design, ThorHegbom 102. Magnetic Core Selection for Transformers and Inductors: A User's Guide to Practice and Specification, Second Edition, Colonel Wm. T. McLyman 103. Statistical Methods in Control and Signal Processing, edited by Tohru Katayama and Sueo Sugimoto 104. Radio Receiver Design, Robert C. Dixon 105. Electrical Contacts: Principles and Applications, edited by Paul G. Slade 106. Handbook of Electrical Engineering Calculations, edited byArun G. Phadke 107. Reliability Control for Electronic Systems, Donald J. LaCombe 108. Embedded Systems Design with 8051 Microcontrollers: Hardware and Software, Zdravko Karakehayov, Knud Smed Christensen, and Ole Winther 109. Pilot Protective Relaying, edited by Walter A. Elmore 110. High-Voltage Engineering: Theory and Practice, Second Edition, Revised and Expanded, Mazen Abdel-Salam, Hussein Anis, Ahdab EI-Morshedy, and Roshdy Radwan 111. EMI Filter Design: Second Edition, Revised and Expanded, Richard Lee Ozenbaugh 112. Electromagnetic Compatibility: Principles and Applications, Second Edition, Revised and Expanded, David Weston 113. Permanent Magnet Motor Technology: Design and Applications, Second Edition, Revised and Expanded, Jacek F. Gieras and Mitchell Wing 114. High Voltage Circuit Breakers: Design and Applications, Second Edition, Revised and Expanded, Ruben D. Garzon 115. High Reliability Magnetic Devices: Design and Fabrication, Colonel Wm. T. McLyman

Additional Volumes in Preparation Practical Reliability of Electronic Equipment and Products, Eugene R. Hnatek

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1926-1993

Dedicated to C. Harris Adams Graduated from California Institute of Technology

1949

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Preface This book is intended to provide guidelines and behind-the-scenes background to system and transformer engineers for the design and manufacturing of transformers and inductors of high reliability. There are many applications in which high reliability is a byword, such as manned space vehicles, spacecraft, satellites, flight control systems, missiles, and surveillance drones. Reliability is mandatory because of the high cost of component failure. Pursuing reliability in the manufacturing of transformers and inductors primarily involves attention to detail, coupled with close control in all phases of manufacturing.

I worked at the Jet Propulsion Laboratory (JPL) for almost 30 years as their magnetics design specialist. I have seen all types of vendors and magnetic components, some good and some bad.

Frequently,

components that were rejected were rejected because specifications were not followed. Shortcuts were taken thinking they would save time. Also, in many cases the design engineer would neglect to open the design manual that was provided. The engineer would design and fabricate the transformer or inductor the way he or she had done it on a previous job.

At JPL the guidelines used to design and fabricate high reliability magnetic components were previously found in the DM 509306, Volumes I, II, and III. These books are informative and I still have my original set. The required data is strung out in three volumes, making it very cumbersome to quickly locate anything in them, if one is not familiar with them. JPL finally updated them into a single volume, called JPL D-8208, which is still being revised.

With this book I have tried to bring together all of the existing pertinent literature into one volume. The information in this book comes from many sources: JPL DM 509306, Volumes I, II, and III, JPL D-8208, Mil-STD-981, Mil-T-27, NAVMAT P4855-1A, selected IEEE publications, and discussions with those with years of experience working with these components. Many of the lessons learned by these people have not been captured before in written form. It is hoped that this book will help in achieving standardization and aid in the reduction of the cost of high reliability and the need for custom magnetics. Hopefully it will also provide assistance in preventing design, manufacturing and/or testing mistakes.

The main goal of this book is to provide a comprehensive guide for every aspect of producing a high reliability magnetic component, from choosing the raw materials and construction techniques to in-process inspection, end item testing, and quality assurance recommendation. Colonel Wm. T. McLyman

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Acknowledgements I worked at the Jet Propulsion Laboratory (JPL) for almost 30 years. I am proud to say that I worked on almost every major space endeavor that JPL was part of. I had many opportunities to work with Project Manager Tom Gavin, who would use my expertise as the magnetic specialist. It was here that I saw the need for a book that would explain the design and fabrication of high reliability magnetic components. In gathering the material for this book, I have been fortunate in having the assistance and cooperation of JPL, several other companies, and many colleagues. I wish to express my gratitude to all of them.

Jet Propulsion Laboratory Earl A. Cherniack, James C. Arnett, Paul N. Bowerman, Charles J. Bodie, Deputy Section Manager J. K. "Kirk" Bonner, Ph.D. Roberta Certa, Group Lead Fabrication Services Magnetics, Inc. Lowell M. Bosley Mike W. Horgan Scott D. Schmidt Todd A. Wuchevich Micrometals Corp. Dale Nicol Rodon Products, Inc. Steve Freeman Coast Magnetics Satya Dosaj Jai Dosaj Sherwood Associates Edward Sherwood Linear Magnetics Corp. Richard L. Ozenbaugh Fridenberg Research Inc. Jerry Fridenberg

Allen Adams, President

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Contents Preface Acknowledgements A History of High Reliability Custom Magnetic Components, 1950 to the Present C. Harris Adams Introduction

James C. Arnett

Symbols

Chapter 1 Transformer and Inductor Design Philosophy Chapter 2 Magnetic Materials Chapter 3 Magnetic Cores Chapter 4 Window Utilization, Magnet Wire, and Insulation Chapter 5 Coil Winding Layer, Foil, and Toroidal Chapter 6 Soldering and Magnet Wire Terminations Chapter 7 Packaging, Enclosures, Mounts, and Headers Chapter 8 Polymeric Impregnate, Embedment, and Adhesives Chapter 9 High Voltage Design Guidelines Chapter 10 Testing, Evaluation, and Quality Assurance

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A History of High Reliability Custom Magnetic Components, 1950 to the Present In the years immediately following World War II, the military services recognized the need for and the wisdom of coordinating hardware specifications. During the War each service was procuring hardware using its own specifications. Many specifications were of very similar content. This plurality of similar, but not identical, specifications complicated all aspects of procurement including stocking and quality assurance.

Joint Army-Navy specifications (JAN specs) were first written to coordinate separate

specifications. Then came the Military specifications (MIL) intended for use by all services. This paper traces the history of MIL-T-27, a military specification covering custom magnetic devices. Although MIL-T-27 was initially intended only as a specification for high-grade military magnetics, it has, over the years, come to be used as the document around which "high reliability" magnetic components are specified.

Such procurements used MIL-T-27 in conjunction with other specifications, which imposed

additional requirements. Specification MIL-T-27 (no revision) was issued in September 1949. It was the first issue of an Army, Navy, Air Force joint document covering custom magnetic devices. MIL-T-27 had two parents. These were the Army document 71-4942 and the Navy document 16T30. These documents were those used prior to the issue of MIL-T-27 to specify custom magnetic devices. Since 1949 MIL-T-27 has been subjected to several revisions leading up to the current Revision E. Table 1 lists the progressive revision sequence. Revisions over the years addressed, among other aspects, materials, construction, testing and quality assurance. Since the focus of this paper is directed primarily towards reliability, it is interesting to note that in the "A" revision (1955) the concept of life expectancy was added to the specification. Life expectancies of 10,000, 2500, and <500 hours were included. The thinking here was that in many applications, i.e., ordinance, the required life was seconds or minutes and that long term reliability was not needed. Table 1 MIL-T-27 Rev. Initial Revision A Revision B Revision C Revision D Revision E

Issue Date September, 1949 March, 1955 September, 1963 June, 1968 April, 1974 April, 1985

Published with permission from Allen Adams, Coast/ACM, Los Angeles, California.

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It did not take long to recognize that, in most applications (high voltage perhaps excepted), it was not possible to design a magnetic component with a short life. Ultimate failure was brought about by external factors such as heat or physical destruction, not by a designed short life. With the issuance of Revision D, in 1974, the "life" concept was abandoned and replaced by a design goal of 10,000 hours minimum life, a requirement buried deep within the revision (Par. 4.8.22). The fact of the matter is, though, that to have a high yield of parts lasting 10,000 hours, the average life must be many times greater than this. There are several matters scheduled to be addressed in the future Revision F if and when funding becomes available. It needs to be recognized that in dealing with MIL-T-27 that, by inference, also included are the other custom magnetic components which comprise the MIL-T-27 family: MIL-C-15305, MIL-T-21038, MIL-T55631, and MIL-C-83446. The history of these other documents parallels the evolution of MIL-T-27. Also, MIL-T-27 provides for "standard" parts. These parts are covered by individual specification sheets called "slash sheets." These parts differ from other MIL-T-27 custom parts only in that they are subject to listing on a Qualified Parts List (QPL). A slash sheet part is placed on the QPL whenever a supplier provides to the Government qualification for that part. The part may then be ordered from that supplier with minimum quality assurance for the three year valid period of the listing. QPL parts constitute a small percentage of magnetic devices built to MIL-T-27 and few new slash sheets are issued currently. It goes without saying that two of the objectives of a military specification are to insure suitability and reliability. Magnetic components built to MIL-T-27 have always been quite reliable in the general sense. It was with the arrival of Sputnik and the following decades of space flight, including manned flight and including satellites needing long service life, that the term "high reliability" came to be applied to hardware destined for use in such applications. The problem with which specifiers struggled over the years was how to define the word "high" in "high reliability." Magnetic devices built to MIL-T-27 from day one were pretty high in reliability. There are undoubtedly thousands upon thousands of devices built in the 50's and 60's, which are still functioning perfectly today.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The quest for "high reliability" was spearheaded by NASA since they were initially the users of devices for space applications. The growth of manned space flight has necessitated that NASA still be the leader in this effort. The military services and particularly the communications industry have welcomed and followed the NASA efforts.

Reliability in all components is needed to protect the staggering investment required to

build and orbit military and communication satellites.

Early efforts to specify "high reliability" magnetic components (what was really meant by higher reliability) came through user documents.

These documents often detailed the construction of the component.

Screening was added to eliminate so called "early failures". Thus reliability was enhanced by establishing tighter manufacturing controls and by conducting more rigorous inspection. This approach worked quite well as is evidenced by the success of most of the early satellites (electronically speaking).

There was another approach that was initiated in the 1960's. Since testing, no matter how rigorous, cannot absolutely guarantee how a component will fare over a long period of time, the concept of "established reliability" was suggested as a better way to "establish" reliability. The idea here was to demonstrate reliability statistically. Statistics can show the likelihood of failure of a large number of exact or very similar components.

This established reliability method has come to be the principal way reliability is established for components built in large quantities. These include resistors, capacitors and certain classes of inductors and EMI filters using inductors and capacitors. These components are used in such quantity that service life data can easily include the millions of hours needed to statistically demonstrate very high levels of reliability. MIL-STD-975, first issued in 1976, is demonstrated statistically. Each component had its own previously developed and detailed specification, but MIL-STD-975 was the "overseer" document.

MIL-STD-690

describes the statistical processes. In the early days of the "established reliability" movement there was an attempt to bring "custom" magnetic devices into the fold. A document that was an established reliability version of MIL-T-27 was issued in 1964. It was called MIL-T-39013 and was bora with great expectations.

MIL-T-39013 was hailed as the answer to specifying "high reliability" magnetics. Managers were delighted and issued requisitions to their purchasing departments for 10, 20, or even 100 pieces of devices built to

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

MIL-T-39013.

Purchasing dutifully sent out requests for quotation (RFQ's).

What happened, with

hindsight, is easy to understand. With 2,000,000-plus hours of operation required to establish a space level reliability, most suppliers did not bid. Those who, tongue-in-cheek, went along entered a quote for 10, 20, or 100 parts with a quality assurance charge including 1000 parts in a 2000 hour life test regime, carefully burdened with an insurance policy. The outcome is easy to picture.

To the best of the author's knowledge, no procurement was ever placed to this document and it was retired ignominiously in 1971. It might be called a noble attempt but it should have been cleared upfront that the "established reliability" concept was not economically practical for any component built in small quantities and destined for a single application.

Following the demise of MIL-T-39013, the industry had no choice but to fall back on previously used methods of procuring higher reliability components:

1. Adding to MIL-T-27 additional quality enhancing requirements. 2. Generating a stand-alone, m-house document package.

In either case a complete document package would, or would not, include a detailed manufacturing requirement.

Some users felt more comfortable if they controlled the design along with workmanship.

Other users were happy with the supplier's design but controlled workmanship.

Rigorous electrical,

physical and environmental testing were a part of the specifications in either case.

Of significance, from an economic viewpoint, was the fact that with no standards there were major differences between the quality assurance provisions of users.

The cost of the preparation of these specifying documents and the cost of accommodating widely varying quality assurance programs dramatically increased the cost of the hardware.

In the early 1980's NASA recognized that there would be an increasing need for custom magnetic components and that costs for custom space level magnetic components must be controlled.

What might

do the job, it was envisioned, would be a new specification, that, when used with MIL-T-27, would provide the required reliability. Hopefully, this new specification would be adopted by all users. The continuing cost of writing new user specifications would be avoided. From this need was born MIL-STD-981.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The philosophy of MIL-STD-981 was based on what was, by then, obvious to users and suppliers: reliability of custom magnetic devices cannot be demonstrated statistically at any affordable cost. The alternative was that the required reliability must somehow be inherent in the design and manufacture. MILSTD-981 was written with this intent. Its desired future was that it could eventually replace the increasing number of separate user specifications which had essentially the same objectives. The economies of this seemed quite clear.

MIL-STD-981, though, had a grander concept. It wanted to make its primary objective "build parts that will not fail in service" to an absolute (sic) fulfillment. A secondary objective, just as important from an administrative standpoint, was to engender a confidence among potential users that the primary objective could be realized. Otherwise, users would not adopt MIL-STD-981.

To accomplish its primary objective, MIL-STD-981 directs in minute detail standards for material, manufacture, workmanship, process control, and quality assurance. While MIL-T-27 remains the primary document for specifics of design and test, MIL-STD-981 imposes additional controls and workmanship standards. The documentation required by MIL-STD-981, in a sense, replaces the statistical records of established reliability parts, and provides objective evidence of reliability in its own way.

MIL-STD-981 has been revised twice, now at Revision B. Revisions have been the result of NASA-usersupplier conferences. At these conferences it was most gratifying to feel the camaraderie that existed among government and non-government participants.

Clearly, each attendee had a sincere interest in

helping the document to meet its objectives.

It is pleasing to note that MIL-STD-981 is rapidly gaining acceptance as the document of choice for space level magnetics. Magnetic components for the Space Station are being procured to MIL-STD-981. Other programs are espousing the document at an increasing pace.

Many users are abandoning in-house

documents and using MIL-STD-981. It clearly appears that MIL-STD-981 will be just as successful, and widely-used to specify high reliability custom magnetics, as are the established reliability documents now used to specify other passive components.

C. Harris Adams

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Transformers designed for operating in the environment of space must meet stringent requirements of high reliability, minimum size and weight, and high efficiency, due to unattended operation for a long period of time. Unlike terrestrial transformers, cooling of which is readily achieved by a combination of radiation and convection in the air at atmospheric pressure, the mode of cooling space transformers is conduction through the coil to the core and thence, by means of the mounting brackets, to a controlled heat sink. A relatively minor portion of the heat loss is transferred by radiation to surrounding objects or directly to space. Any voids or interference in the heat flow path, under vacuum conditions, will be disastrous to thermal resistance and will contribute to an excessive increase in temperature. To achieve high reliability, it is mandatory to employ materials of construction that offer the maximum in thermal stability at the highest operating temperature, in order to ensure consistency of physical and electrical properties over the life of the system. Certain combinations of flux density, frequency and magnetic material available to the designer can result in a smaller transformer, and therefore in lower copper losses and lighter weight. Since heat conduction through the core is a major mode of heat transfer in space transformers, the thermal conductivity of the core material is a major factor in rising temperatures of the transformer. Most space transformers are required to operate in air at atmospheric pressure for a period of time for preflight test purposes and hence the design criteria are those for a transformer operating in air and moisture. Operating in air is accomplished by impregnation and encapsulation of the coil, and in most instances, the entire transformer is encapsulated.

The insulating material and resins used should possess negligible

outgassing characteristics. Desirable properties of the resin are low viscosity, low shrinkage on cure, low coefficient of expansion, low temperature cure and good thermal conduction characteristics. Processing includes baking out the coil to remove moisture, treating under vacuum for several hours to remove occluded gasses, introduction of the resin under a vacuum, and then soaking the coil in heated resin for a time sufficient enough to allow the liquid to impregnate the coil.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

While careful selection of materials and the use of the appropriate manufacturing processes and procedures are key contributors to long life and reliable performance, it is also important that the design, fabrication and application of transformers for space be supported by an effective product assurance program. Reliability, availability, maintainability, configuration control and environmental testing and qualification requirements must be defined early in the design and development process.

The manufacturing cycle

should be controlled and monitored by a conscientious quality assurance program, which includes appropriate in-process inspection points, and testing activities to prevent workmanship defects and assure delivery of a highly reliable end product.

James C. Arnett Reliability Engineering Section Jet Propulsion Laboratory Pasadena, California

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Symbols a

regulation, %

AC

effective cross section of the core, cirr

Ap

area product, cnv

At

surface area of the transformer, crn^

Aw

wire area, cm^

AW(B)

bare wire area, cirr

A

insulated wire area, cirr

w(I)

primary wire area, cmr secondary wire area, cirr AWG

American Wire Gage

B

alternating current flux density, tesla

ac

AB

change in flux, tesla

Bdc

direct current flux density, tesla

Bm

flux density, tesla

Bmax

maximum flux density, tesla

Br

residual flux density, tesla

Bs

saturation flux density, tesla

DAWG

wire diameter, cm

E

voltage

Energy

energy, watt-second

T!

efficiency

f

frequency, Hz

F

fringing flux factor

F.L.

full load

G

winding length, cm

8

skin depth, cm

H

magnetizing force, oersteds

I

current, amps charge current, amps

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AI

delta current, amps

Ij n

input current, amps

Im

magnetizing current, amps

I0

load current, amps

Ip

primary current, amps

Is

secondary current, amps

J

-^ current density, amps per cm^

Ke

electrical coefficient

Kf

waveform coefficient

KO

core geometry coefficient

Ku

window utilization factor

L

inductance, henry

A.

density, grams per crrr

lg

gap, cm

lm

magnetic path, cm

MLT

mean length turn, cm

MPL

magnetic path length, cm

fi l

initial permeability

u^

incremental permeability

um

core material permeability

ur

relative permeability

u^

effective permeability

n

turns ratio

N

turns

N.L.

no load

Np

primary turns

Ns

secondary turns

P

watts

Pcu

copper loss, watts

Pfe

core loss, watts

o

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Pg

gap loss, watts

Pj n

input power, watts

Po

output power, watts

Pp

primary copper loss, watts

PS

secondary copper loss, watts

P£

total loss (core and copper), watts

Pt

total apparent power, watts

R

resistance, ohms

Rac

ac resistance, ohms

Rcu

copper resistance, ohms

R^c

dc resistance, ohms

Ro

load resistance, ohms

Rp

primary resistance, ohms

Rs

secondary resistance, ohms

Rt

total resistance, ohms

p

resistivity, ohm-cm

Si

conductor area/wire area

82

wound area/usable window

83

usable window area/window area

84

usable window area/usable window area + insulation area

T

total period, seconds

Tr

temperature rise, degrees C

VA

volt-amps

VG

control voltage, volts

Vjj

diode voltage drop, volts

Vj n

input voltage, volts

VQ

output voltage, volts

Vp

primary voltage, volts

Vs

secondary voltage, volts

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AVp

delta primary voltage, volts

AV S

delta secondary voltage, volts

W

watts

Wa

•y window area, cmz

w-s

watt-seconds

W tcu

copper weight, grams iron weight, grams

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

HIGH RELIABILITY MAGNETIC DEVICES

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 1

Transformer and Inductor Design Philosophy

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2.

Power-Handling Ability

3.

Transformer Design

4.

Transformers with Multiple Outputs

5.

Regulation

6. Relationship Kg to Power Transformer Regulation Capability 7. Relationship A p to Transformer Power Handling Capability 8. Inductor Design 9.

Fundamental Conditions in Designing Inductors

10. Fringing Flux 11. Toroidal Powder Core Selection 12. Relationship Kg to Power Inductor Regulation Capabilit 13. Relationship Ap to Inductor Energy Handling Capability 14. Transformer Losses 15. Inductor Losses 16. Eddy Current Losses, Skin Effect 17. Eddy Current Losses, Proximity Effect 18. Temperature Rise and Surface Area

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction The conversion process in power electronics requires the use of transformers, and components which frequently are the heaviest and bulkiest items in the conversion circuits. They also have a significant effect upon the overall performance and efficiency of the system. Accordingly, the design of such transformers has an important influence on overall system weight, on the power conversion efficiency and cost. Because of the interdependence and interaction of parameters, judicious tradeoffs are necessary to achieve design optimization.

Power-Handling Ability For years, manufacturers have assigned numeric codes to their cores; these codes represent the powerhandling ability. This method assigns to each core, a number, which is the product of its window area, (W a ), and core cross-section area, (Ac), and is called, "Area Product," A p .

These numbers are used by core suppliers to summarize dimensional and electrical properties in their catalogs. They are available for laminations, C-cores, pot cores, powder cores, ferrite toroids, and toroidal tape-wound cores.

The regulation and power-handling ability of a core is related to the core geometry, Kg. Every core has its own inherent, Kg. The core geometry, Kg, is a relatively new for magnetic cores. Manufacturers do not list this coefficient.

Because of their significance, the area product, Ap, and core geometry, Kg, are treated extensively in this book. A great deal of other information is also presented for the convenience of the designer. Much of the material is in tabular form to assist the designer in making the tradeoffs, best-suited for his particular application, in a minimum amount of time.

These relationships can now be used as new tools to simplify and standardize the process of transformer design. They make it possible to design transformers of a lighter weight and smaller volume, or to optimize efficiency without going through a cut and try, design procedure. While developed specifically for aerospace applications, the information has a wider utility, and can be used for the design of non-aerospace transformers, as well.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Transformer Design

The designer is faced with a set of constraints which must be observed in the design of any transformer. One of these is the output power, PQ, (operating voltage multiplied by maximum current demand), which the secondary winding must be capable of delivering to the load within specified regulation limits. Another relates to minimum efficiency of operation which is dependent upon the maximum power loss, which can be allowed in the transformer. Still another defines the maximum permissible temperature rise for the transformer, when used in a specified temperature environment.

Other constraints relate to volume occupied by the transformer, particularly, in aerospace applications, and weight, since weight minimization is an important goal in the design of space flight electronics. Lastly, cost effectiveness is always an important consideration.

Output power, (P0), is of greatest interest to the user. To the transformer designer it is the apparent power, (P t ), which is associated with the greater important geometry of the transformer. Assume, for the sake of simplicity, the core of an isolation transformer has only two windings in the window area, (Wa), a primary and a secondary. Also, assume that the window area, (W a ), is divided up in proportion to the power handling capability of the windings, using equal current density. This includes the primary winding handles, Pj n , and the secondary handles, P0, to the load. Since the power transformer has to be designed to accommodate the primary, P in and P0, then:

By definition:

P > = — , [watts]

The primary turns can be expressed using Faraday's law:

N /' = —^ A D

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

f

— , [turns]

IS

The winding area of a transformer is fully utilized when:

By definition the wire area is:

Rearranging the equation shows:

Now, substitute in Faraday's equation:

AcBiicfKfj Rearranging shows:

The output power, P0, is:

^ = ^ / , , [watts] The input power, Pin, is:

Then:

[watts]

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Substitute in P,

W A=

BiJJK,Ku

By definition, A p , equals: Ap=WaAc,

[cm 4 ]

Then:

A

., [cm 4 ]

The designer must be concerned with the apparent power, handling capability, P t , of the transformer core and windings. P^ may vary by a factor, ranging from 2 to 2.828 times the input power, P^, depending upon the type of circuit in which the transformer is used. If the current in the rectifier transformer becomes interrupted, its effective RMS value changes. Thus, transformer size, is not only determined by the load demand, but also, by application, because of the different copper losses incurred, due to the current waveform. For example, for a load of one watt, compare the power handling capabilities required for each winding, (neglecting transformer and diode losses, so that Pj n = P o ) for the full-wave bridge circuit of Figure 1-1, the full-wave center-tapped secondary circuit of Figure 1-2, and the push-pull, center-tapped full-wave circuit in Figure 1-3, where all the windings have the same number of turns, (N).

o

Figure 1-1. Full-Wave Bridge Secondary. The total apparent power, P,, for the circuit shown in Figure 1-1 is 2 watts. This is shown in the following equation: P,=Pin+Pn, [watts]

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

< R,

Pt=2PiH,

[watts]

Figure 1-2. Full-Wave, Center-Tapped Secondary.

O (-

CRl

Qi

Cl

JE

i

N

' i—

s~ -N

HP

i

Q2 \—i

Figure 1-3. Push-Pull Primary, Full- Wave, Center-Tapped Secondary. The total power, Pt, for the circuit shown in Figure 1-2, increased 20.7%, due to the distorted wave form of the interrupted current flowing in the secondary winding. This is shown in the following equation: P,=Pin+P0j2,

[watts]

Pf=Pin(l+j2),

[watts]

The total power, Pt, for the circuit is shown in Figure 1-3, which is typical of a dc to dc converter. It increases to 2.828 times Pjn, because of the interrupted current flowing in both the primary and secondary windings. Pr=P:nj2+Poj2,

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[watts]

Pt=2Pin^2, [watts]

Transformers with Multiple Outputs

This is an example of how the apparent power, P t , changes with a multiple output transformers.

Circuit center tapped V^ = diode drop ~ 1 V 15 V(o), 1A

full wave bridge V^ = diode drop = 2 V

Efficiency = 0.95

Figure 1-4. Multiple Output Converter.

The output power seen by the transformer in Figure 1-4 is:

^,=(K,,+K/)(/»,).

[watts]

P0, = ( 5 + l)(lO), [watts] pg] = 60,

[watts]

and: ^=(^+^)(/J, Po2 = ( 1 5 + 2)(1.0), /

J

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

o ; =17,

[watts]

[watts] [watts]

o

£ R,

o

< R,

Because of the different winding configurations the apparent power, Pt, the transformer will have to be summed to reflect this. When a winding has a center tap and produces a discontinuous current, then, the power in that winding, be it primary or secondary, has to be multiplied by the factor, U. The factor, U, corrects for the rms current in that winding, if the winding has a center tap, then, the factor U is equal to 1.41. If not, the factor, U, is equal to 1. For an example, summing up the output power of a multiple output transformer, would be:

then:

/ > = 60(1.41) + 17(1), [watts] />=101.6,

[watts]

After the secondary has been totaled, then the primary power can be calculated.

P +P

/> = -2!-21,

(60) P =V / (0.95) f> n =81,

[watts] , L[watts]J

[watts]

Then, the apparent power, Pt, equals:

P^

[watts]

/?=(81)(1.41) + (101.6),

[watts]

P,=215.S, [watts]

Regulation The minimum size of a transformer is usually determined either by a temperature rise limit, or by allowable voltage regulation, assuming that size and weight are to be minimized. Figure 1-5 shows a circuit diagram of a transformer with one secondary. Note that a = regulation (%).

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Secondary

Primaiy n = Ns/Np = 1

Figure 1-5. Transformer Circuit Diagram.

The assumption is that distributed capacitance in the secondary can be neglected because the frequency and secondary voltage are not excessively high. Also, the winding geometry is designed to limit the leakage inductance to a level, low enough to be neglected under most operating conditions.

Transformer voltage regulation can now be expressed as:

.., V (F.L.)

.

-(100), V '

[%]

in which, V O (N.L.), is the no load voltage and, V O (F.L.), is the full load voltage. For the sake of simplicity, assume the transformer in Figure 1-5, is an isolation transformer, with a 1:1 turns ratio, and the core impedance, Re, is infinite. If the transformer has a 1:1 turns ratio, and the core impedance is infinite, then:

R,,=R5, [ohms] With equal window areas allocated for the primary and secondary windings, and using the same current density, J,

A I/, = /,.„/?,, = A F = I 0 R f , Regulation is then:

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[volts]

Multiply the equation by currents, I:

Vs Io

VpI .in Primary copper loss is:

Pp=&ypI.H,

[watts]

Ps=&VsIo,

[watts]

Secondary copper loss is:

Total copper loss is:

Then, the regulation equation can be rewritten to:

a ="-(100),

[%]

Regulation can be expressed as the power lost in the copper. A transformer, with an output power of 100 watts and regulation of 2%, will have a 2 watt loss in the copper:

Pa

Prc =-2—,

"

Pcl =

(100)(2) A ; 100

Pcu = 2,

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[watts]

100

,

[watts]

[watts]

Relationship Kpo to Power Transformer Regulation Capability Transformers Although most transformers are designed for a given temperature rise, they can also be designed for a given regulation. The regulation and power-handling ability of a core is related to two constants:

rv — (J.

2KgKc

a = Regulation (%) The constant, *Kg, is determined by the core geometry, which may be related by the following equations:

-

WaA;KH , —-, [cm'] MLT

The constant, Ke, is determined by the magnetic and electric operating conditions, which may be related by the following equation:

K =

Where: Kf = waveform coefficient 4.0 square wave 4.44 sine wave From the above, it can be seen that factors, such as flux density, frequency of operation, and waveform coefficient, have an influence on the transformer size.

The derivation for these equations is set forth, in detail, by the author in the book, "Transformer and Inductor Design Handbook," Marcel Dekker, Inc., New York, 1988.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Relationship Ap to Transformer Power Handling Capability Transformers According to the newly developed approach, the power handling capability of a core is related to its area product, *Ap, by an equation which may be stated as:

A= - -'—, [cm 4 ]

Where: Kf= waveform coefficient 4.0 square wave 4.44 sine wave From the above, it can be seen that factors, such as flux density, frequency of operation, and window utilization factor Ku, defines the maximum space which may be occupied by the copper in the window.

The area product, Ap, of a core is the product of the available window area, Wa, of the core in square centimeters, (cirr), multiplied by the effective, cross-sectional area, Ac, in square centimeters, (cirr), which may be stated as:

Ap=WaAc,

[cm 4 ]

Figures 1-6 through Figure 1-8 show, in outline form, three transformer core types that are typical of those shown in the catalogs of suppliers.

The derivation for these equations is set forth in detail by the author in the book "Transformer and Inductor Design Handbook," Marcel Dekker, Inc., New York, 1988.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

W, G

D

Figure 1-6. C, Core.

Ar

G

D

Figure 1-7. EE Core.

OD

Figure 1-8. Toroidal Core.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Inductor Design The designer is faced with a set of constraints which must be observed in the design of any inductor. One of these constraints is copper loss. The winding must be capable of delivering current to the load within specified regulation limits. Another constraint relates to minimum efficiency of operation, which is dependent upon the maximum power loss that can be allowed in the inductor. Still another defines the maximum permissible temperature rise for the inductor, when used in a specified temperature environment. The gapped inductor has three loss components. They are copper loss, Pcu, core loss Pfe, and gap loss, Pg. Maximum efficiency is reached in an inductor, as in a transformer, when the copper loss, Pcu, and the iron loss, Pf e , are equal, but only, when the core gap is zero. The loss does not occur in the air gap itself, but is caused by magnetic flux fringing around the gap, and re-entering the core in a direction of high loss. As the air gap increases, the fringing flux increases more and more. Some of the fringing flux strikes the core perpendicular to the lamination, and sets up eddy currents, which cause additional loss. Designing with molypermalloy powder core, the gap loss is minimized because the powder is insulated with a ceramic material, which provides an uniformly distributed air gap. Also designing with ferrites, the gap loss is minimized because ferrite materials have such high resistivity.

Other constraints relate to volume occupied by the inductor, and weight, since weight minimization is an important goal in the design of space flight electronics. Lastly, cost effectiveness is always an important consideration.

Fundamental Conditions in Designing Inductors The design of a linear reactor depends upon four related factors:

1.

Desired inductance, L.

2.

Direct current, Idc.

3.

Alternating current, AI.

4.

Power loss and temperature rise, Tr.

With these requirements established, the designer must determine the maximum values for, Bdc, and for, Bac, which will not produce magnetic saturation. The designer must make tradeoffs, which will yield the highest inductance for a given volume. The core material, which is chosen, dictates the maximum flux density which can be tolerated for a given design. The basic equation for maximum flux is:

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

0.471 N(I, + A / ( l ( T 4 )

-

[tesla]

/'

The inductance of an iron-core inductor, carrying dc and having an air gap, may be expressed as:

0.47t/V 2 /f (10 8 ) L

-

•

[henrysl

Inductance is dependent on the effective length of the magnetic path, which is the sum of the air gap length, (l g ), and the ratio of the core mean length to relative permeability, (l m /u r ).

When the core air gap, (lg), is larger, compared to relative permeability, (l m /u r ), because of the high relative permeability (u r ), variations in (u r ) do not substantially effect the total effective magnetic path length, or the inductance. The inductance equation, then reduces to:

L=

0.471 N2 A , ( l 0 8 )

, [henrys]

Final determination of the air gap size requires consideration of the effect of fringing flux, which is a function of gap dimension, the shape of the pole faces, and the shape, size and location of the winding. Its net effect is the shorting of the air gap.

Fringing Flux Fringing flux decreases the total reluctance of the magnetic path and, therefore, increases the inductance by a factor, F, to a value greater than that calculated from inductance equation. Fringing flux is a larger percentage of the total for larger gaps. The fringing flux factor is:

/

2G

Inductance, L, computed, does not include the effect of fringing flux. The value of inductance, L, corrected for fringing flux is:

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

A F(lO 8 )

2

[henrys]

MPL

Distribution of fringing flux is also affected by another aspect of core geometry, the proximity of coil turns to the core, and whether, there are turns on both legs.

OAnNFU, + —

lO~ 4

The fringing flux is around the gap and re-entering the core in a direction of high loss as shown in Figure 1 9.

Eddy currents

N

©0©©© ©©©©©

Fringing Flux Magnetic Path

Figure 1-9. Fringing Flux Around the Gap of an Inductor Design with a C Core. Effective permeability may be calculated from the following expression: Urn

1 + A,

MPL

After establishing the required inductance and the dc bias current which will be encountered, dimensions can be determined. This requires consideration of the energy handling capability, which is controlled by the size of the inductor. The energy handling capability of a core is:

Energy =

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

LI2

, [watt-second]

Toroidal Powder Core Selection The design of an inductor, also, frequently involves consideration of the effect of its magnetic field on other devices near where it is placed. This is especially true in the design of high-current inductors for converters and switching regulators used in spacecraft, which may also employ sensitive magnetic field detectors. For this type of design problem, it is frequently imperative that a toroidal core be used. The magnetic flux in a powder toroid, (core), can be contained inside the core more readily, than in a lamination, or C type core, as the winding covers the core along the whole magnetic path length.

The author has developed a simplified method of designing optimum, dc carrying inductors with powder cores. This method allows the correct core permeability to be determined, without relying on trial and error.

With these requirements established, the designer must determine the maximum values for, Bac, and for Bac, which will not produce magnetic saturation, and must make tradeoffs that will yield the highest inductance for a given volume. The chosen core permeability dictates the maximum dc flux density, which can be tolerated for a given design. Powder cores come in a range of permeability. Figure 1-10 shows how the required permeability changes with dc bias. As the magnetizing force (dc bias) is increased, the permeability will start to drop. When the permeability has reached 90% of its initial value, as shown in Figure 1-10, the permeability falls off, relatively fast.

1.0

10 100 DC Magnetizing Force, (Oersteds)

Figure 1-10. Typical Permeability Versus dc Bias for Powder Cores.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1000

If an inductance is to be constant with an increasing direct current, there must be a negligible drop in inductance over the operating current range. Then the maximum, H, is an indication of a core's capability. The magnetization force, H, is in oersteds:

,, 0.471 NI H = , MPL

r

oersteds

Inductance decreases with increasing flux density and magnetizing force for various materials of different values of permeability. The selection of the correct permeability for a given design is made after solving for the energy handling capability: ^ = g m (MPL)(l0 4 )

JK. It should be remembered that maximum flux density depends upon, Idc + AI/2, in the manner shown in Figure 1-11. Different powder cores materials, with different permeability, will operate with a high or lower dc bias. Table 1-1 shows the different types of powder cores that are offered to the design engineer.

0.471

//C+

MPL

4

)

-,

[tesla]

H (oersteds)

Figure 1-11. Flux Density Versus 1^ + AI.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 1-1

Powder Cores MPP

Hugh Flux

Kool Mu

Iron Powder

14 - 550

14- 160

60- 125

10- 100

Flux Density

Mi Bm

0.7T

1.4T

LOT

1.03- 1.4T

Density

5

8.5

8

6.15

6.5-7

Materials Initial Permeability

Relationship KK to Power Inductor Regulation Capability Inductors Inductors, like transformers, are designed for a given temperature rise. They can also be designed for a given regulation. The regulation and energy handling ability of a core is related to two constants:

a =

(Energy)'

KK.,

a = Regulation (%) The constant, *Kg, is determined by the core geometry:

,

MLT

The constant, K e , is determined by the magnetic and electric operating conditions:

Where: Po = output power A D

B max = B,(tc + — ," [tesla] L J From the above, it can be seen that flux density is the predominant factor, governing the size.

*The derivation for these equations are set forth in detail by the author in the book, "Transformer and Inductor Design Handbook," Marcel Dekker, Inc., New York, 1988.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Relationship Ap to Inductor Energy Handling Capability Inductors According to the newly developed approach, the energy handling capability of a core is related to its area product, *Ap, by an equation, which may be stated as follows:

AP =

2(Energy)(lQ 4 )

K..BJ

, [cm 1

From the above, it can be seen that factors, such as flux density, Bmax, window utilization factor, K u , (which defines the maximum space, which may be occupied by the copper in the window), and the current density, J. All have an influence on the inductor area product. The area product Ap of a core is the product of the available window area, Wa, of the core in square centimeters, (cmr), multiplied by the effective, cross-sectional area, Ac, in square centimeters, (cn~r), which may be stated as:

Ap=WaAc,

[cm 4 ]

Figures 1-6 through 1-8 show, in outline form, three transformer core types that are typical of those shown in the catalogs of the suppliers.

*The derivation for these equations are set forth in detail by the author in the book, "Transformer and Inductor Design Handbook," Marcel Dekker, Inc., New York, 1988.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Transformer Losses Transformer efficiency, regulation, and temperature rise are all interrelated. Not all of the input power to the transformer is delivered to the load. The difference between the input power and output power is converted into heat. This power loss can be broken down into two components: core loss and copper loss. The core loss is a fixed loss, and the copper loss is a variable loss that is related to the current demand of the load. Copper loss increases by the square of the current and is also termed quadratic loss. Maximum efficiency is achieved when the fixed loss is equal to the quadratic loss at the rated load. Transformer regulation is the copper loss, Pcu, divided by the output power, Po: P*=Pcu+Pfc,

[watts]

Inductor Losses The losses in an inductor are made up of three components: (1) copper loss, Pcu; (2) iron loss, Pf e ; and (3) gap loss, Pp. The copper loss and iron loss have been previously discussed. Gap loss is independent of core material thickness and permeability. Maximum efficiency is reached in an inductor, as in a transformer, when the copper loss, P cu , and the iron loss, P te , are equal, but only when the core gap is zero. The loss does not occur in the air gap itself, but is caused by magnetic flux fringing around the gap and reentering the core in a direction of high loss. As the air gap increases, the flux across the gap fringes more and more. Some of the fringing flux strikes the core, perpendicular to the strip or tape, and sets up eddy currents, which cause additional losses in the core. If the gap dimension gets too large the fringing flux will strike the copper winding and produce eddy currents, generating heat, just like an induction heater. The fringing flux will jump the gap and produce eddy currents, in both the core and winding, as shown in Figure 1-12. p

v = Pcu + Pe + p»'

[watts]

Eddy currents Core Winding Fringing Flux

L/2

Magnetic Path

Figure 1-12. Fringing Flux Around the Gap of an Inductor Design with a C Core.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Eddy Current Losses, Skin Effect As the frequency increases, there are additional losses that occur in the winding, due to eddy currents induced in the conductors by the magnetic fields within the winding. Skin effect is caused by eddy currents, induced in a wire by the magnetic field of the current carried by the wire itself. Skin depth is defined as the distance below the surface, where the current density has fallen to, 1/e, or 37 percent of its value at the surface. Skin depth of copper at 20°C is:

6.62 e=-7=r>

[cm]

Skin effect is illustrated in Figure 1-13. The required wire size is a number 17, magnet wire. The operating frequency is 100 kHz. The skin depth is 0.0209 centimeters. A number 17 magnet wire, operating at 100 kHz, will yield an unused area of 0.00422 cm2, as shown in Figure 1-13. If you take the skin depth s, and, assume it to be the radius of the wire, then, you can calculate the minimum wire area. Take this area and match it with the closest, AWG. Then, take the area of the AWG, and divide it into the required area, and that will be the number of strands. Frequency = 100 kHz #17 Required, area = 0.010398 cm2 Area not used = 0.00422 cm2 8 #26, area = 0.00128 cm2 x 8 = .01024 cm2

Skin depth

Figure 1-13. Skin Depth Illustration. Eddy Current Losses, Proximity Effect Proximity effect is caused by eddy currents induced in a wire, due to the alternating magnetic field of other conductors in the vicinity. Proximity effect is more serious than skin effect because skin effect can be overcome by going to a smaller diameter wire. In the proximity effect, eddy currents, caused by adjacent layers, increase exponentially in amplitude, as the number of layers increases. Proximity effect, skin effect and high frequency together will cause the transformer, with multiple layers, to have losses that are excessive, due to current crowding from the skin effect. With each additional layer, the I2R losses in that layer, increase by the square of the current of the previous layer. Selecting the correct AWG, as well as the winding geometry, is very important in keeping the losses down. The proximity effect can be reduced, significantly, by interleaving the primary and secondary, as shown in Figures 1-14 and Figure 1-15. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Spatial Illustration 0, mmf

Core

OOO0OOO0

Secondary-layer 2 Secondary-layer 1 Primary-layer 2 — Primary-layer 1

O0000000

Insulation

Bobbin

Magnet wire Center leg

Figure 1-14. Primary and Secondary are Separated.

Core Secondary-layer 2 - —*• Primaiy-layer 2 — —*• Secondary-layer 1 - —*• Primary-layer 1 —

Spatial Illustration (), mmf

00000000

\^

®00@®0O® 00000000 ©0®<S©®©®

^ \^

-y / / Insulation Bobbin

^

Magnet wire Center leg

Figure 1-15. Primary and Secondary are Interleaved. Temperature Rise and Surface Area The heat, generated by the core loss, copper loss, gap loss, and the losses due to the skin effect and proximity effect, produces a temperature rise, which must be controlled to prevent damage to, or the failure of the windings by the breakdown of the insulation at elevated temperatures. This heat is dissipated from the exposed surfaces of the transformer or inductor by a combination of radiation and convection. Therefore, the dissipation is dependent upon the total, exposed surface area of the core and windings. Temperature rise in a transformer winding cannot be predicted with complete precision, despite the fact that many techniques are described in the literature for its calculation. One, reasonably accurate method for open core and winding construction is a homogeneous method. It is also based upon the assumption that the core and winding losses may be lumped together as: Transformer: /> = pcu + / ? / 5

[watts]

Inductor: p

- = Pcu + Pfc + P*'

[watts]

Also, The assumption is made that the thermal energy is dissipated uniformly throughout the surface area of the core and winding assembly. The effective surface area, A,, required to dissipate heat, (expressed as watts dissipated per unit area), is:

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

4 = ^ , [cm 2 ] "y" is the power density of the average power, dissipated per unit area from the surface of the transformer and, Pv, is the total power lost or dissipated.

The temperature rise that can be expected for various levels of power loss is shown in Figure 1-16. It is based on data obtained from Blume, (1938), for heat transfer, effected by a combination of 55% radiation and 45% convection, from surfaces having an emissivity of 0.95, in an ambient temperature of 25°C, at sea level. Power loss, (heat dissipation), is expressed in watts per square centimeter of the total surface area. Heat dissipation, by convection from the upper side of a horizontal flat surface, is on the order of 15-20% more than from a vertical surface. Heat dissipation, from the underside of a horizontal flat surface, depends upon surface area and conductivity. Below are two, prominently used power loss factors, expressed in watts per square centimeter of the total surface area.

y =0.03^/cm 2 @25°C rise y/ = 0.07H / /cm 2 @25°C rise

1.0 Ambient Temperature

0.1

0.01

I 00

Emissivity 0.95 45% Convection 55% Radiation

0.001 10° C 100° C AT = Temperature Rise, °C Tr =450

Figure 1-16. Temperature Rise Versus Surface Dissipation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 2

Magnetic Materials

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2.

Saturation

3.

Remanence Flux, Br, and Coercivity Hc

4.

Permeability, ju

5.

Hysteresis Loss, Resistivity, p, (core loss)

6.

Introduction to Silicon Steel

7.

Introduction to Thin Tape Nickel Alloys

8.

Introduction to Metallic Glass

9.

Introduction to Soft Ferrites

10. Manganese-Zinc Ferrites 11. Nickel-Zinc Ferrites 12. Introduction to Molypermalloy Powder Cores 13. Introduction to Iron Powder Cores 14. Core Loss

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction The magnetic material is the paramount player in the design of magnetic components. The magnetics design engineer has three standard words when making the normal design trade-off study: cost, size, and performance. The engineer will be happy to stuff any two in the bag. The magnetics design engineer is now designing magnetic components that operate from below the audio range to the megahertz range. He is normally asked to design for maximum performance, with the minimum of his parasitic friends' capacitance and leakage inductance. Today, the magnetic materials, the engineer has to work with, are silicon steel, nickel iron (permalloy), cobalt iron (permendur), amorphous metallic alloys, and ferrites. These also have spin-off material variants, such as moly-permalloy powder, sendust powder, and iron powder cores. From this group of magnetic materials, the engineer will make trade-offs with the magnetic properties for his design. These properties are: saturation Bs, permeability u, resistivity p (core loss), remanence Br, and coercivity Hc.

Saturation A typical hysteresis loop of a soft magnetic material is shown in Figure 2-1. When a high magnetizing force is encountered, a point is reached where further increase in H does not cause, useful increase in B. This point is known as the saturation point of that material. The saturation flux density, Bs, and the required magnetizing force, Hs, to saturate the core is shown with dashed lines.

B

Figure 2-1. Typical B-H or Hysteresis Loop of a Soft Magnetic Material. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Remanence Flux, Br, and Coercivity Hc The hysteresis loop in Figure 2-1 clearly shows the remanence flux density, B r . The remanence flux is the polarized flux remaining in the core after the excitation has been removed. The magnetizing force, -Hc is called coercivity. It is the amount of magnetizing force required to bring the remanence flux density back to zero.

Permeability, ji The permeability of a magnetic material is a measure of the ease in magnetizing the material. Permeability ji, is the ratio of the flux density, B, to the magnetizing force, H.

u = — , [permeability]

The relationship between B and H is not linear, as shown in the hysteresis loop in Figure 2-1. Then it is evident that the ratio, B/H (permeability) also varies. The variation of permeability with flux density B is shown in Figure 2-2. It also shows the flux density at which the permeability is at a maximum.

Bs

u, Permeability

0

Magnetizing Force Figure 2-2. Variation in Permeability ii with B and H.

Hysteresis Loss, Resistivity, p, (core loss) The enclosed area within the hysteresis, shown in Figure 2-1, is a measure of the energy lost in the core material during that cycle. This loss is made up in two components: (1) the hysteresis loss and (2) eddy current loss. The hysteresis loss is the energy loss when the magnetic material is going through a cycling state. The eddy current loss is caused when the lines of flux pass through the core, inducing electrical currents in it. These currents are called eddy currents and produce heat in the core. If the electrical resistance of the core is high, the current will be low; therefore, a feature of low-loss material is high

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

electrical resistance. In the norm, when designing magnetics components the core loss is a major design factor. Core loss, can be controlled by selecting the right material and thickness. Selecting the correct material, and operating within its limits, will prevent overheating that could result in damage to the wire insulation and/or the potting compound.

Introduction to Silicon Steel Silicon steel was one of the first alloys to be used in transformers and inductors. It has been greatly improved over the years and is probably, pound for pound, the most, widely used magnetic material. One of the drawbacks in using steel in the early years was, as the material became older, the losses would increase. With the addition of silicon to the steel, the advantages were twofold: it increased the electrical resistivity, therefore, reducing the eddy current losses, and it also improved the material stability with age.

Silicon steel offers high saturation flux density, a relatively good permeability at high flux density, and a moderate loss at audio frequency. One of the important improvements made to the silicon steel was in the process called cold rolled, grain-oriented, AISI type M6. This M6 grain oriented steel has exceptionally low losses and high permeability. It is used in applications requiring high performance and the losses will be at a minimum.

Introduction to Thin Tape Nickel Alloys High permeability metal alloys are based primarily on the nickel-iron system. Although Hopkinson investigated nickel-iron alloys as early as 1889, it was not until the studies by Elmen, starting in about 1913, on properties in weak magnetic fields and effects of heat-treatments, that the importance of the Ni-Fe alloys was realized. Elmen called his Ni-Fe alloys, "Permalloys," and his first patent was filed in 1916. His preferred composition was the 78 Ni-Fe alloy. Shortly after Elmen, Yensen started an independent investigation that resulted in the 50Ni-50Fe alloy, "Hipernik," which has lower permeability and resistivity but higher saturation than the 78-Permalloy, (1.5 tesla compared to 0.75 tesla), making it more useful in power equipment. Improvements in the Ni-Fe alloys were achieved by high temperature anneals in hydrogen atmosphere, as first reported by Yensen. The next improvement was done by using grain-oriented material and annealing it, in a magnetic field, which was also in a hydrogen atmosphere. This work was done by Kelsall and Bozorth. Using these two methods, a new material, called Supermalloy, was achieved. It has a higher permeability, a lower coercive force, and about the same flux density as 78-Permalloy. Perhaps the most important of these factors is the magnetic anneal, which, not only increases permeability, but also provides a "square" magnetization curve, important in high frequency power conversion equipment. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

In order to obtain high resistance, and therefore, lower core losses for high frequency applications, two approaches have been followed: (1) modification of the shape of metallic alloys and (2) development of magnetic oxides. The result was the development of thin tapes and powdered alloys, in the 1920's, and thin films in the 1950's. The development of thin film has been spurred by the requirements of aerospace power conversion electronics from the mid 1960's to the present. The Ni-Fe alloys are available in thicknesses of 2 mil, 1 mil, 0.5 mil, 0.25 and 0.125 mil. The material comes with a round or square B-H loop. This gives the engineer a wide range of sizes and configurations from which to select for his/her design. The iron alloy properties for some of the most popular materials are shown in Table 2-1. Also given in Table 2-1 is the Figure number for the B-H loop of each of the magnetic materials.

Table 2-1 Magnetic Properties for Selected Iron Alloys Materials.

Iron Alloy Material Properties Material Name

Silicon

Composition

3% Si

Initial

Flux Density

Curie

dc, Coercive

Density

Typical

Permeability

Tesla

Temperture

Force, He

grams/cm

B-H Loop

Of~*

Oersteds

5

Figures

Hi

Bs

1.5 K

1.5-1.8

750

0.4-0.6

7.3

(2-3)

0.8 K

1.9-2.2

940

0.15-0.35

8.15

(2-4)

2K

1.42-1.58

500

0.1-0.2

8.24

(2-5)

12 K-100 K

0.66-0.82

460

0.02-0.04

8.73

(2-6)

10K-50K

0.65-0.82

460

0.003-0.008

8.76

(2-7)

97% Fe

Supermendur*

49% Co 49% Fe 2%V

Orthonol

50%Ni 50% Fe

Permalloy

79% Ni 1 7% Fe 4% Mo

Supermalloy

78%Ni 1 7% Fe 5% Mo

* Field Anneal

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

B, tesla l.O~

1.2-

Magnesil sil ^steresis Loop

: /" /

0.80.4-

| 1 1.6

- 0.4 1.2

0.8

).4

-

0.8

1.2

1

H, oersteds

- 0.4

1

~ 0.8

^y :

~ 1.2 1.6

Figure 2-3. Silicon B-H Loop: 97% Fe 3% Si.

1.6 Supermendur DC Hysteresis Loop

1.2 0.8 0.4 0.4

1.6

1.2

0.8

0.4

0.8

1.2

1.6

H, oersteds

0.4 0.8 1.2 1.6

Figure 2-4. Supermendur B-H Loop: 49% Fe 49% Co 2% V.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

B, tesla -r

1.6

1.2

Orthonol DC Hysteresis Loop 0.8 0.4 0.2 0.8

0.6

0.4

0.:

0.4

0.4

0.6

0.!

H, oersteds

0.8 1.2 1.6

Figure 2-5. Orthonol B-H loop: 50% Fe 50% Ni.

B, tesla 0.8 -r

Square Permalloy 80 DC Hysteresis Loop

0.12 0.16

Figure 2-6. Square Permalloy 80 B-H loop: 79% Ni 17% Fe 4% Mo.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Supermalloy DC Hysteresis Loop

0.04 0.08 0.12 0.16

Figure 2-7. Supermalloy B-H Loop: 78% Ni 17% Fe 5% Mo.

Introduction to Metallic Glass The first synthesis of a metallic glass, drawing wide attention among material scientists, occurred in 1960. Klement, Willens and Duwez reported that a liquid, AuSi alloy, when rapidly quenched to liquid nitrogen temperature, would form an amorphous solid. It was twelve years later that Chen and Polk produced ferrous-based metallic glasses in useful shapes with significant ductility. Metallic glasses have since survived the transition from laboratory curiosities to useful products, and currently, are the focus of intensive technological and fundamental studies.

Metallic glasses are generally produced, by liquid quenching, in which a molten metal alloy is rapidly cooled, at rates on the order of 10* degrees/sec.; through the temperature, at which crystallization normally occurs. The basic difference between crystalline, (standard magnetic material), and glassy metals is in their atomic structures. Crystalline metals are composed of regular, three-dimensional arrays of atoms, which exhibit long-range order. Metallic glasses do not have long-range structural order. Despite their structural differences, crystalline and glassy metals of the same compositions exhibit nearly the same densities.

The electrical resistivities of metallic glasses are much larger, (up to three times higher), than those of crystalline metals of similar compositions. The magnitude of the electrical resistivities and their temperature coefficients in the glassy and liquid states are almost identical. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Metallic glasses are quite soft magnetically. The term, "soft," refers to a large response of the magnetization to a small-applied field. A large magnetic response is desirable in such applications as transformers and inductors. The obvious advantages of these new materials are in high frequency applications with their high induction, high permeability and low core loss. There are four amorphous materials that have been used in high frequency applications: 2605SC, 2714A, 2714AF and Vitroperm 500F. Material 2605SC offers a unique combination of high resistivity, high saturation induction, and low core loss, making it suitable for designing high frequency dc inductors. Material 2714A is a cobalt material that offers a unique combination of high resistivity, high squareness ratio Br/Bs, and very low core loss making it suitable for designing high frequency aerospace transformers and mag-amps. The Vitroperm 500F is an iron based material with a saturation of 1.2 tesla and is wellsuited for high frequency transformers and gapped inductors. The high frequency core loss for the nanocrystal E 2000 is much lower than ferrite, even operating at a high flux density. The amorphous properties for some of the most popular materials are shown in Table 2-2. Also given in Table 2-2 is the Figure number for the B-H loop of each of the magnetic materials.

Table 2-2. Magnetic Properties for Selected Amorphous Materials.

Amorphous Material Properties Material

Major

Initial

Flux Density

Curie

dc, Coercive

Name

Composition

Permeability

Tesla

Temp.

Force, He

Hi

B5

°C

Oersteds

5

Figures

1.5K

1.5-1.6

370

0.4-0.6

7.32

(2-8)

0.8K

0.5-0.65

205

0.15-0.35

7.59

(2-9)

2K

0.5-0.65

205

0.1-0.2

7.59

(2-10)

30K-80K

1.0-1.2

460

0.02-0.04

8.73

(2-11)

2605SC

8 1 % Fe

Density

Typical

grams/cm" B-H Loop

13.5%B 3. 5% Si

2714A

66% Co

E 1000

15% Mo 4% Fe

2714AF

66% Co 15% Mo 4% Fe

Nanocrystal Vitroperm 500F*

* Vitroperm is the trademark of Vacuumschmelze.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

B, Tesla 1.6 T Metglas Type 2605SC DC Hysteresis Loop

1.2 0.8 0.4

H, oersted H

1

1

0.6

1

f-

0.4

0.2

0.2 0.4 0.6 0 4 H, oersted

1.2 - 1.6

Figure 2-8. Amorphous 2605SC B-H Loop: 78% Ni 17% Fe 5% Mo.

B, Tesla

0.6 0.5 ( - r Metglas Type 2714A DC Hysteresis Loop

0.4

-

0.3 0.2

-

o.i 1

1

0.05

1

1

0.03

i

1

0.01 I

0.01 . Q i

i

0.03 t

t

0.05 i

i

H, oersted

- 0.2 - 0.3 - 0.4

J- ) 0.5

- n^

Figure 2-9. Amorphous 2714A B-H Loop: 78% Ni 17% Fe 5% Mo.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tesla

Metglas Type 2714AF DC Hysteresis Loop

Figure 2-10. Amorphous 2714AF B-H Loop: 78% Ni 17% Fe 5% Mo.

Vitroperm 500F 10 Hz

Figure 2-11. Vitroperm 500F B-H loop: 78% Ni 17% Fe 5% Mo.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction to Soft Ferrites In the early days of electrical industry, the need for the indispensable magnetic material was served by iron and its magnetic alloys. However, with the advent of higher frequencies, the standard techniques of reducing eddy current losses, (using laminations or iron powder cores), was no longer efficient or cost effective. This realization stimulated a renewed interest in "magnetic insulators," as first reported by S. Hilpert, in Germany, in 1909. It was readily understood that, if the high electrical resistivity of oxides could be combined with desired magnetic characteristics, a magnetic material that was particularly well-suited for high frequency operation would result. Research to develop such a material was being performed in various laboratories all over the world, such as, by V. Kato, T. Takei, and N. Kawai in the 1930's in Japan, and by J. Snoek of the Philips' Research Laboratories in the period 1935-1945, in the Netherlands. By 1945, Snoek had laid down the basic fundamentals of the physics and technology of practical ferrite materials. In 1948, the Neel Theory of ferromagnetism provided the theoretical understanding of this type of magnetic material. Ferrites are ceramic, homogeneous materials composed of oxides; iron oxide is their main constituent. Soft ferrites can be divided into two major categories; manganese-zinc and nickel-zinc. In each of these categories, changing the chemical composition or manufacturing technology can manufacture many different Mn-Zn and Ni-Zn material grades. The two families of Mn-Zn and Ni-Zn ferrite materials complement each other and allow the use of soft ferrites from audio frequencies to several hundred megahertz. Manufacturers do not like to handle manganese-zinc in the same area, or building with nickelzinc, because one contaminates the other, which leads to poor performance yields. The basic difference between Manganese-Zinc and Nickel-Zinc is shown in Table 2-3. The biggest difference is ManganeseZinc has a higher permeability and Nickel-Zinc has a higher resistibility. Shown in Table 2-4 are some of the most popular ferrite materials. Also, given in Table 2-4, is the Figure number for the B-H loop of each of the materials. Table 2-3. Comparing Manganese-Zinc and Nickel-Zinc Basic Properties.

Basic Ferrite Material Properties Materials Manganese Zinc Nickel Zinc

Tesla

Curie Temperture, °C

dc, Coercive Force, H c Oersteds

0.3-0.5 0.3-0.5

100-300 150-450

0.04-0.25 0.3-0.5

Initial Permeability

Flux Density P D

Hi 750-15 K 15-1500

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max

Resistivity Q - cm 10-100

106

Manganese-Zinc Ferrites This type of soft femte is the most common, and is used in many more applications than the nickel-zinc ferrites. Within the Mn-Zn category, a large variety of materials are possible. Manganese-zinc ferrites are primarily used at frequencies less than 2 MHz.

Nickel-Zinc Ferrites This class of soft ferrite is characterized by its high material resistivity, several orders of magnitude higher than Mn-Zn ferrites. Because of its high resistivity, Ni-Zn ferrite is the material of choice for operating from 1-2 MHz to several hundred megahertz. The material permeability, u ni , has little influence on the effective permeability, ue, when the gap dimension is relatively large, as shown in Table 2-5.

Table 2-4. Magnetic Properties for Selected Ferrite Materials.

Ferrites Material Properties Magnetic

Initial

Material

Permeability

Tesla

Name

Hi

K

Flux Density Residua! Flux

Curie

dc, Coercive

Density

Typical

Tesla

Temperture

Force, He

grams/cm

B-H Loop

Bs(o; 1 5 Oe

Br

O/"~*

Oersteds

5

Figures

1500

0.48T

0.08T

>230

0.2

4.7

(2-12)

R

2300

0.50T

0.12T

>230

0.18

4.8

(2-13)

P

2500

0.50T

0.12T

>230

0.18

4.8

(2-13)

F

5000

0.49T

0.1 OT

>250

0.2

4.8

(2-14)

W

10,000

0.43T

0.07T

>125

0.15

4.8

(2-15)

H

15,000

0.43T

0.07T

>125

0.15

4.8

(2-15)

Table 2-5. Permeability, and its Effect on Gapped Inductors.

Com] taring Material Permeabilities Material K R P F *Core , ETD44

Urn

1500 2300 2500 3000

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Gap, inch 0.04 0.04 0.04 0.04

Gap, cm 0.101 0.101 0.101 0.101

*MPL, cm 10.4 10.4 10.4 10.4

He

96 98 99 100

Bm, Tesla

K Material

0.5

1.0 25 °C

1.5

2.0

2.5

Bm = 0.460T (a) 15 oersted

100 °C Bm = 0.3 SOT @ 15 oersted

Figure 2-12. Ferrite B-H loop, K Material at 25 and 100°C.

P & R Material

0.2

25 °C Bm = 0.500T (u) 15 oersted 100 °C Bm = 0.375T (g> 15 oersted

Figure 2-13. Ferrite B-H loop, P & R Material at 25 and 100 °C.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Bm, Tesla 0.5 T F Material

Figure 2-14. Fernte B-H loop, F Material at 25 and 100 ° C.

W & H Material

0.2

100 ''C Bm - 0 220T in' 15 oersted

Figure 2-15. Ferrite B-H loop, W & H Material at 25 and 100 ° C.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 2-6. Ferrite Materials, Manufacturers' Cross Reference.

Ferrite Material Cross Reference 1500 Power

Permeability Application

3000 5000 2500 Power Filter Power Material Designation

2300 Power

Manufacturer's Magnetics Thomson LCC Philips Comp. Fair-Rite

1

K 3F4

Siemens

N47

TDK Corp. MMG Ceramic Mag Tokin Ferrite Int.

PC50 MN67

2

R

L2 3F3 78 N67 PC44 F44 MN80 HBM

3

P B2 3C85 77 N27 PC44 F5 2500B TSF-05

F Bl 3C81 N41 H7A F5C MN8CX 3100B TSF-10

J A4 3E2A 75 T35 HP5 F-10 MN60 5000B TSF-15

10,000 Filter

15,000 Filter

W A2 3E5 76 T38 H5C2 F-39 MC25 12001H

H

T46 H5D

1. High Frequency power material 250 kHz & up. 2. Lowest loss at 80°-100°C, 25 kHz to 250 kHz. 3. Lowest loss at 60°C-80°C.

Introduction to Molypermalloy Powder Cores The nickel-iron (Ni-Fe) high permeability magnetic alloys (permalloy) were discovered in 1923, and in 1927. Permalloy alloys were successfully used in powder cores, greatly contributing to the carrier wave communications of the time.

In the early 1940's, a new material, trademarked molybdenum permalloy powder, (MPP), was developed into cores by the Bell Telephone Laboratory and the Western Electric Company. This new material was developed for loading coils, and filtering coils, and transformers at audio and carrier frequencies in the telephone facility. The use of such cores has been extended to many industrial and military circuits. The stability of permeability and core losses, with time, temperature, and flux level, are particularly important to engineers designing tuned circuits and timing circuits. This new material has given reliable and superior performance over all past powder core materials.

Molybdenum permalloy powder, [2 Molybdenum (Mo)-82 Nickel (Ni)-16 Iron (Fe)], is made by grinding hot-rolled and embrittled cast ingots; then, the alloy is insulated and screened to a fineness of 120 mesh for use in audio frequency applications, and 400 mesh for use at high frequencies. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

In the power conversion field, the MPP core has made its greatest impact in switching power supplies. The use of MPP cores and power MOSFET transistors has permitted increased frequency, resulting in greater compactness and weight reduction in computer systems. The power supply is the heart of the system. When the power supply is designed correctly, using a moderate temperature rise, the system will last until it becomes obsolete. In these power systems there are switching inductors, smoothing choke coils, common mode filters, input filters, output filters, power transformers, current transformers and pulse transformers. They cannot all be optimally designed, using MPP cores. But, in some cases, MPP cores are the only ones that will perform in the available space with the proper temperature rise.

Introduction to Iron Powder Cores The development of compressed iron powder cores as a magnetic material for inductance coils stemmed from efforts of Bell Telephone Laboratory engineers to find a substitute for fine iron-wire cores. The use of iron powder cores was suggested by Heaviside, in 1887, and again, by Dolezalek in 1900.

The first iron powder cores of commercially valuable properties were described by Buckner Speed, in U.S. Patent No. 1274952, issued in 1918. Buckner Speed and G.W. Elman published a paper in the A.I.E.E. Transactions, "Magnetic Properties of Compressed Powdered Iron," in 1921. This paper describes a magnetic material, which is well-suited to the construction of cores in small inductance coils and transformers, such as those used in a telephone system. These iron powder cores were made from 80 Mesh Electrolytic Iron Powder. The material was annealed, then, insulated by oxidizing the surface of the individual particles. In this way, a very thin and tough insulation of grains of iron was obtained; this did not break down when the cores were compressed. A shellac solution was applied to the insulated powder as a further insulator and binder. This was how toroidal iron powder cores were manufactured by Western Electric Company, until about 1929. Today's iron powder cores are manufactured much the same way, using highly pure iron powder and a more exotic insulator and binder. The prepared powder is compressed under extremely high pressures to produce a solid-looking core. This process creates a magnetic structure with a distributed air-gap. The inherent high saturation flux density of iron combined with the distributed air-gap produces a core material with initial permeability of less than 100, and with high-energy storage capabilities.

The dc current does not generate core loss, but an ac or ripple current does generate core loss. Iron powder material has higher core loss than some other more expensive core materials. Most dc-biased inductors have a relatively small percentage of ripple current and, thus, core loss will be minimal. However, core loss will sometimes become a limiting factor in applications with a relatively high percentage of ripple current at

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

very high frequency. Iron powder is not recommended for inductors with discontinuous current or transformers with large ac flux swings.

Low cost, iron powder cores are typically used in today's, low and high frequency power switching conversion applications, for differential-mode, input and output power inductors. Because iron powder cores have such low permeability, a relatively large number of turns are required for the proper inductance, thus keeping the ac flux at a minimum. The penalty for using iron powder cores is usually found in the size and efficiency of the magnetic component.

There are four standard powder materials available for power magnetic devices: Molypermalloy (MPP) Powder Cores with a family of curves, as shown in Figure 2-20; High flux (HF) Powder Cores with a family of curves, as shown in Figure 2-21; Sendust Powder Cores, (Kool Mu), with a family of curves, as shown in Figure 2-22; and Iron Powder Cores, with a family of curves, as shown in Figure 2-23. The powder cores come in a variety of permeabilities. This gives the engineer a wide range in which to optimize the design. The powder core properties for the most popular materials are shown in Table 2-7. Also, given in Table 27, is the Figure number for the B-H loop of each of the powder core materials. In Table 2-8 is a listing of the most popular permeabilities for each of the powder core materials.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 2-7. Powder Core Material Properties.

Powder Core Material Properties Material Name MPP

High Flux Sendust (Kool Mu) Iron Powder

Initial Flux Density dc, Coercive Curie Composition Permeability Temperture Force, He Tesla Oersteds °C Bs Hi 14-550 0.7 0.3 80% Ni 450 20% Fe 1 14-160 50% Ni 1.5 360 50% Fe 26-125 85% Fe 1 0.5 740 9% Si 6% Al 5.0-9.0 4.0- 100 0.5 - 1.4 770 100%Fe

grams/cm 5 8.5

Typical B-H Loop Figures (2-16)

8

(2-17)

6.15

(2-18)

3.3 - 7 . 2

(2-19)

Density

Table 2-8. Standard Powder Core Permeabilities.

Standard Powder Core Permeabilities Powder Material

MPP

High Flux

Sendust (Kool Mu)

Iron Powder

Initial Permeability, a,

10 14 26 35 55 60 75 90 100 125 147 160 173 200 300 550

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X X X

X X

X

X

X

X X X

X X X X X X X

X X X

X

X X X X X

Molypermalloy MPP 125 Perm

50 100 150 200 250 I 250 200 150 100

50

Figure 2-16. Molypermalloy Powder Core, 125 Perm.

Tesla High Flux HF 125 Perm

50 100 150 200 250 i 1 1 250 200 150 100

50

Figure 2-17. High Flux Powder Core, 125 Perm.

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Kool Mu 125 Perm

50 250 200 150 100

100 150 200 250

50

Figure 2-18. Sendust (Kool Mu) Powder Core, 125 Perm.

Tesla Iron Powder-52 75 Perm

50 100 150 200 250 200 150 100

50

Figure 2-19. Iron Powder (-52) Core, 75 Perm.

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250

i i i i i i i MPP Powder Cores

100

i

i

i

DC Magnetizing Force (Oersteds) i i i i i i i i i i i i i

1000

100 Figure 2-20. Permeability Versus dc Bias for Molypermalloy Powder Cores.

i i

I I I I I I I I High Flux Powder Cores

DC Magnetizing Force (Oersteds)

1000 Figure 2-21. Permeability Versus dc Bias for High Flux Powder Cores. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

i I i i I I I I I I Sendust Powder Cores (Kool Mu)

100

80

OJ

60

I CM 13

40

a

20 DC Magnetizing Force (Oersteds) I I I I i I I I I I I I I

1.0

100

10

1000

Figure 2-22. Permeability Versus dc Bias for Sendust Powder Cores.

I 1 I I I I II Iron Powder Cores

100

80

S v.

60

o» CH

13 40

20 DC Magnetizing Force (Oersteds) I

I I

I I I

1.0

L

10

i

i

1 I 1 I I

100

Figure 2-23. Permeability Versus dc Bias for Iron Powder Cores. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

I

I

I I I I I

1000

Core Loss The designer of power magnetic components, such as transformer and inductors, requires specific knowledge about the electrical and magnetic properties of the magnetic materials used in these components. There are two magnetic properties that are of interest to the design engineer, the dc and the ac. The dc, B-H hysteresis loop is a very useful guide for comparing the different types of magnetic materials. It is the ac, magnetic properties that are of interest to the design engineer. One of the most important ac properties is the core loss. The ac core loss is a function of the magnetic material, magnetic material thickness, magnetic flux density Bac, frequency f, and operating temperature. The choice of the magnetic material is, thus, based upon achieving the best characteristic, using the standard trade-off, such as cost, size, and performance.

All manufacturers do not use the same units when describing their core loss. The user should be aware of the different core loss units when comparing different magnetic materials. A typical core loss graph is shown in Figure 2-24. The vertical scale is core loss and the horizontal scale is flux density. The core loss data is plotted at different frequencies, as shown in Figure 2-24.

100

Frequency #1 Frequency #2 Frequency #3

10

o -J

o U 1.0

0.1 0.01

0.1

1.0 Flux Density

Figure 2-24. Typical Graph for Plotting Core Loss at Different Frequencies. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Vertical Scale Here is a list of core loss units used by manufacturers: 1.

watts per pound

2.

watts per kilogram

3.

milliwatts per gram

4.

milliwatts per cubic centimeter (cm1)

Horizontal Scale Here is a list of flux density units used by manufacturers: 1.

gauss

2.

kilogauss

3.

tesla

4.

millitesla

The data can be plotted or presented in either hertz or kilohertz. Manufacturers are now presenting the core loss in an equation form such as: watts/kilogram = k f ( m ] B ( " ] Here, again, the units will change from one manufacturer to another.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 3

Magnetic Cores

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. Core Type and Shell Type Construction 3. Types of Core Materials 4. Eddy Currents and Insulation 5. Laminations 6. Annealing and Stress-Relief 7. Stacking Laminations and Polarity 8. Flux Crowding 9. Exciting Current 10. Tape Wound C, EE, and Toroidal Cores 11. Tape Toroidal Cores 12. Toroidal, Powder Core 13. Dimensional Outline for El Laminations 14. Dimensional Outline for UI Laminations 15. Dimensional Outline for LL Laminations 16. Dimensional Outline for DU Laminations 17. Dimensional Outline for Three Phase Laminations 18. Dimensional Outline for Tape Wound C, EE, and Toroidal Cores 19. Dimensional Outline for EE and El, Ferrite Cores 20. Dimensional Outline for EE and El Planar, Ferrite Cores 21. Dimensional Outline for EC, Ferrite Cores 22. Dimensional Outline for ETD, Ferrite Cores 23. Dimensional Outline for ETD/(low profile), Ferrite Cores 24. Dimensional Outline for ER, Ferrite Cores 25. Dimensional Outline for EFD, Ferrite Cores 26. Dimensional Outline for EPC, Ferrite Cores 27. Dimensional Outline for PC, Ferrite Cores 28. Dimensional Outline for EP, Ferrite Cores 29. Dimensional Outline for PQ, Ferrite Cores 30. Dimensional Outline for PQ/(low profile), Ferrite Cores 31. Dimensional Outline for RM, Ferrite Cores 32. Dimensional Outline for RM/(low profile), Ferrite Cores

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

33. Dimensional Outline for DS, Ferrite Cores 34. Dimensional Outline for UUR, Ferrite Cores 35. Dimensional Outline for UUS, Ferrite Cores 36. Dimensional Outline for Toroidal, Ferrite Cores 37. Dimensional Outline for Toroidal, MPP Powder Cores 38. Dimensional Outline for Toroidal, Iron Powder Cores

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction The key ingredient in a magnetic device is the magnetic field (flux) created when current is passed through a coiled wire. The ability to control (channel, predict, conduct), the magnetic field (flux) is critical to controlling the operation of the magnetic device.

The ability of a material to conduct magnetic flux is defined as permeability. A vacuum is defined as having a permeability of 1.0 and the permeability of all other materials is measured against this baseline. Most materials, such as air, paper, and wood are poor conductors of magnetic flux, in that they have low permeability. If wire is wound on a dowel, it exhibits a magnetic field exactly, as shown in Figure 3-1. There are a few materials, such as iron, nickel, cobalt, and their alloys that have high permeabilities, sometimes ranging into the hundreds of thousands. These materials and their alloys are used as the base materials for all core materials.

Coil

Dowel

Figure 3-1. Air Core with an Intensified Magnetic Field. The main purpose of the core is to contain the magnetic flux and create a well defined, predictable path for the flux. This flux path, and the mean distance covered by the flux within the magnetic material, is defined as the magnetic path length (MPL) (see Figure 3-2). The magnetic path length and permeability are vital keys in predicting the operation characteristic of a magnetic device. Selection of a core material and geometry are usually based on a compromise between conflicting requirements, such as size, weight, temperature rise, flux density, core loss, and operating frequency.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnetic Path Length

Flux,

Magnetic Core

Figure 3-2. Magnetic Core Confines the Magnetic Field. Core Type and Shell Type Construction There are two types of construction for magnetic cores, core type and shell type. The shell type construction is shown in Figure 3-3 and the core type construction is shown in Figure 3-4. In the shell type of construction, shown in Figure 3-3, the core surrounds the coil. In the shell type of construction the magnetic fields are around the outside of the coil. The advantage of this configuration is that it requires only one coil. In the core type of construction, shown in Figure 3-4, the coils are outside of the core. A good example of this is a toroid, where the coil is wound on the outside of a core.

E-I Core

Flux,

Coil

Figure 3-3. Shell Type Construction: the Core Surrounds the Coil.

C Core

Flux, Coils

\

\

Figure 3-4. Core Type Construction the Coil Surrounds the Core. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Types of Core Materials Magnetic cores are made of three basic materials. The first is the bulk metal, the second is the powdered materials, and the third is ferrite. The bulk metals are processed from the furnace into ingots. Then, the material is put into a process of hot and cold rolling. The rolling process produces a sheet of material with a thickness ranging from 0.004 to 0.031 mils that can be punched into laminations. It can be further rolled to a thickness ranging from 0.002 to 0.000125 mils, then slit and wound into tape cores, such as C cores, E cores and toroids.

The powder cores, such as powder molypermalloy and powdered iron materials, are die-pressed into toroids, EE cores and slugs. Powder core processing starts at the ingot, then, goes through various steps of grinding until the powder is the right consistency for the required performance. Normally, powder cores are not machined after processing. Ferrites are ceramic material of iron oxide, alloyed with oxides or carbonate of manganese, zinc, nickel, magnesium, or cobalt. Alloys are selected and mixed, based on the required permeability of the core.

Then, these mixtures are molded into the desired shape with pressure of approximately 150-200 tons per square inch and fired at temperatures above 2000 degrees F. After the parts are made, they are usually tumbled to remove burrs and sharp edges, which are characteristic of this process. Ferrites can be machined to almost any shape to meet the engineer's needs.

Eddy Currents and Insulation Transformers operating at moderate frequency require the reduction of eddy current losses in the magnetic material. To reduce the eddy current losses to a reasonable value requires electrical steel to have adequate resistivity. Also, it needs to be rolled to a specific thickness, and it needs effective electrical insulation or coating of the magnetic material.

If an alternating voltage is applied to the primary winding, as shown in Figure 3-5, it will induce an alternating flux in the core. The alternating flux will, in turn, induce a voltage on the secondary winding. This alternating flux also induces a small alternating voltage in the core material. These voltages produce currents called eddy currents, which are proportional to the voltage. The magnitude of these eddy currents is also limited by the resistivity of the material. The alternating flux is proportional to the applied voltage. Doubling the applied voltage will double the eddy currents. This will raise the core loss by a factor of four. Eddy currents not only flow in the lamination itself, but could flow within the core as a unit, if the lamination is not properly stamped, and if the lamination is not adequately insulated, as shown in Figure 3-6. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnetic Core Applied Voltage

Secondary Voltage

Flux, (() Figure 3-5. Applied Alternating Voltage Induces an Alternating Flux. There are two eddy currents, as shown in Figure 3-6, Ia and It,. The intralaminar eddy current, Ia, is governed by flux, per lamination and resistance of the lamination. It is, therefore, dependent on lamination width, thickness, and volume resistivity. Insulation, (Coating)

Figure 3-6. Using Insulation Between Laminations to Reduce Eddy Currents. The interlaminar eddy current, Ib, is governed by total flux and resistance of the core stack. It is primarily dependent upon stack width and height, the number of laminations, and the surface insulation resistance, per lamination. The magnetic materials used for tape cores and laminations are coated with an insulating material. The insulating coating is applied to reduce eddy currents. The American Iron and Steel Institute (AISI) have set up insulation standards for transformer steels used in different applications. High permeability nickel-iron cores are very strain sensitive. Manufacturers of these cores normally have their own proprietary, insulating material. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Laminations Laminations are available in scores of different shapes and sizes. The punch press technology for fabricating laminations has been well developed. Most lamination sizes have been around forever. The most commonly used laminations are the El, EE, FF, UI, LL, and the DU as shown in Figure 3-7. The laminations differ from each other by the location of the cut in the magnetic path length. This cut introduces an air gap, which results in the loss of permeability. To minimize the resulting air gap, the laminations are generally stacked in such a way the air gaps in each layer are staggered.

El, Laminations

EE, Laminations

FF, Laminations

UI, Laminations

LL, Laminations

DU, Laminations

Figure 3-7. Commonly Used Lamination Shapes. There are bobbins and brackets for almost all standard stacking dimensions. Most of the El lamination is the scrapless. The name, scrapless, is derived from shapes that are punched with minimum waste, as shown in Figure 3-8.

A

El, Laminations

E, Laminations

A

I, Laminations

Figure 3-8. Typical, Scrapless El Lamination. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Annealing and Stress-Relief One of the most important parameters in transformer steels is permeability. Any stress or strain of the magnetic materials will have an impact on the permeability. The resulting stress could cause higher magnetizing current, or a lower inductance. When the transformer is being assembled (in the stacking process) and a lamination is bent, (does not return to its original shape), that lamination has been stressed and should be replaced. Some of the important magnetic properties are due to stress and strain after stamping, shearing and slitting. These properties that have been lost or seriously reduced, can be restored to the magnetic materials by annealing. Basically, stress relief is accomplished by heating (annealing) the magnetic material to prescribed temperature, (depending on the material), followed by cooling to room temperature. The entire annealing process is a delicate operation. The annealing must be done under controlled conditions of time, temperature and the ambient atmosphere that will avoid, even minute, adverse changes in the chemistry of the steel.

Stacking Laminations and Polarity The edges of the magnetic material that have been stamped, sheared, or slit, will have a burr, as shown in Figure 3-9. The quality of the equipment will keep the burr to a minimum. This burr now gives the lamination a polarity. When a transformer is being stacked, the lamination build is normally sized by dimensions, or it just fills the bobbin. Lamination Worn Die

Expanded View

Bun-

=^

Figure 3-9. Expanded View, Showing Lamination Burr. If the laminations are stacked correctly, all of the burred ends will be aligned. If the laminations are stacked randomly, such as the burr ends facing each other, then, the stacking factor would be affected. The stacking factor has a direct impact on the cross-section of the core. The end result would be less iron. This could lead to premature saturation, as increase in the magnetizing current, or a loss of inductance. There are several methods used in stacking transformer laminations. The most common technique used in stacking laminations is the alternate method. The alternate method is where one set of laminations, such as an E and an I, are assembled. Then the laminations are reversed, as shown in Figure 3-10. This technique, used in stacking, provides the lowest air gap and the highest permeability. Another method for stacking Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

laminations is to interleave two by two also shown in Figure 3-10. The second method of stacking would be in groups of two or more. This is done to cut assembly time. The loss in performance in stacking, other than one by one, is the increase in magnetizing current and a loss of permeability.

Laminations E and I

Interleave 1 x 1

Interleave 2 x 2

Figure 3-10. Methods for Stacking Laminations. Flux Crowding When laminations are stacked, as shown in Figure 3-11, there is flux crowding. This flux crowding is caused by the difference in spacing between the E, I, and the adjacent lamination. The adjacent lamination has a minimum air gap, which translates into a higher permeability.

Laminations E and I

Flux Crowding

)

\ \

Minute Air Gap Flux

Interleave 1 x 1 Figure 3-11. Flux Crowding when Lamination are Interleaved.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Exciting Current The flux will skirt the low permeability, air gap and migrate into the adjacent lamination, causing flux crowding in that lamination. Eventually, this crowding will cause saturation in that portion of the lamination, and the excitation current will rise. After that portion of the lamination has saturated, the flux will migrate back to the lower permeability segment of the lamination from, where it left. This effect can be easily viewed by observing the B-H loops at low and high flux densities and comparing them with a toroidal core of the same material, with a minimum air gap, as shown in Figure 3-12. The B-H loop along with the magnetizing current Im of a toroidal core, is shown in Figure 3-12A. The toroidal core, with its inherit minimum air gap, will have almost a square of current. Using the same material in lamination form will exhibit a B-H loop, and a magnetizing current, Im, similar to Figure 3-12B operating at low flux densities. Increasing the excitation will cause premature saturation of the lamination, as seen by the nonlinear, exciting current as shown in Figure 3-12C

B

rn AB H A

Figure 3-12. Comparing the Exciting Currents and Three B-H Loops. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Most finished transformers or inductors will have some sort of bracket, such as an L bracket, end bells, a channel bracket or maybe a bolt through the mounting holes to the chassis. When transformers are being assembled, there is a certain amount of attention that has to be used to get proper performance. The insulation material used to coat the lamination is normally very durable, but it can be scratched off and degrade the performance. When brackets are used in the transformer assembly, as shown in Figure 3-13 care must be taken on how the bolts and brackets are put together. The transformer assembly bolts, shown in Figure 3-13 should be the recommended size for the mounting hole and use all of the required hardware. This hardware should include the correct bolt size and length, and correct surface washer, lock washer and nut. Also, included in this hardware, should be fiber shoulder washers and proper sleeving to cover the bolt threads. If insulating hardware is not used, there is a good chance of a partial, shorted turn. The continuity for this partial turn can be created through the bolts and bracket, or the bolts, bracket, and the chassis. This partial shorted turn will downgrade the performance of the transformer.

Sleeving

Laminations Shoulder Washer

Bolt Air Gap Material

Fringing Flux Mounting Bracket

Mounting Bracket Flux

Butt Stack

Figure 3-13. Lamination Mounting Hardware.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tape Wound C, EE, and Toroidal Cores Tape wound cores are constructed by winding around a mandrel, a magnetic material in the form of a preslit tape, as shown in Figure 3-14. This tape material comes in all of the iron alloys, plus the amorphous materials. The tape thickness varies from 0.0005 inch (0.0127 mm) to 0.012 inch (0.305 mm). The advantage of this type of construction is that the flux is parallel with the direction of rolling of the magnetic material. This provides the maximum utilization of flux with the minimum of magnetizing force. There are two disadvantages in this type of construction. When the core is cut in half, as shown in Figure 3-15, the mating surface has to be ground, lapped, and then, acid-etched. This is done to provide a smooth mating surface with the minimum of air gap and the maximum of permeability. The other disadvantage is when the cores are reassembled, the method used is normally done with a band and buckle, and this procedure requires a little skill to provide the right alignment and correct tension, as shown in Figure 3-16. The C cores are impregnated for strength, prior to being cut. The cut C core can be used in many configurations in the design of a magnetic component, as shown in Figure 3-17. The EE cores are constructed in the same way as C cores, but they have an additional overwind, as shown in Figure 3-18. The assembled, three phase transformer is shown in Figure 3-19.

Magnetic Material (Tape)

Magnetic Material (Tape)

C Core Construction

Toroidal Core Construction

Mandrel

Mandrel

Figure 3-14. Tape Cores Being Wound on a Mandrel.

Cut C Core Mating Surface

Figure 3-15. Two Halves of a Cut C Core. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Banding Material

Figure 3-16. Banding the Cut C Core.

Single Core Single Coil

(

Core

^ Coil

V

J

Single Core Dual Coils

r GO Coil

^

re

Dual Cores Single Coil

(

Core

^

\

Core

Coil

Coil

j

\[

V

A

}

Figure 3-17. Three Different C Core Configurations.

Overwind C Core Coil

Coil

Coil

WindowCore

Figure 3-18. Three Phase Cut EE Core.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

J

Figure 3-19. Typical, Assembled EE Cut Core.

Tape Toroidal Cores Tape toroidal cores are constructed in the same way as tape C cores, by winding the magnetic material around a mandrel, in the form of a preslit tape. This tape material comes in all of the iron alloys, plus the amorphous materials. The tape thickness varies from 0.000125 inch (0.00318 mm) to 0.012 inch (0.305 mm). The tape toroid is normally offered in two configurations, cased and encapsulated as shown in Figure 3-20. The cased toroid offers superior electrical properties and stress protection against winding. The encapsulated cores are used when not all of the fine magnetic properties are important to the design, such as in power transformers.

Enclosure Cased Toroid

Caseless Toroid

Figure 3-20. Outline of a Cased and a Caseless Toroidal Core.

Toroidal, Powder Core Powder cores as shown in Figure 3-21 are very unique. They give the engineer another tool that speed the initial design. Powder cores have a built-in air gap. They come in a variety of materials and are very stable with time and temperature. The cores are manufactured with good engineering aids. Manufacturers provide catalogs for their cores that list, not only the size, but also permeability and Millihenrys per 1000 turns. The data is presented to the engineer in such a way that it takes the minimum amount of time to have a design that will function.

OD

Figure 3-21. Outline of a Powder Toroidal Core. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Dimensional Outline for El Laminations Laminations are still one of the most widely-used cores in power conversion. The dimensional outline for El laminations is shown in Figure 3-22. The assembled transformer is shown in Figure 3-23. A listing of common El lamination sizes is shown in Table 3-1. E, Laminations

I, Laminations

w. G

D

Figure 3-22. El Lamination Outline.

V

Lamination

-

1

/ Channel Bracket

Coil Mounting Foot Dt *

Figure 3-23. El Lamination Assembled with Channel Bracket. Table 3-1. Standard 14 mil El Laminations.

El, Laminations Part Number EI-375 EI-021 EI-625 El-750 EI-875 EI-100 EI-112 EI-125 EI-138 EI-150 EI-175 EI-225

D cm 0.953 1.270 1.588 1.905 2.223 2.540 2.857 3.175 3.493 3.810 4.445 5.715

E cm 0.953 1.270 1.588 1.905 2.223 2.540 2.857 3.175 3.493 3.810 4.445 5.715

F cm 0.794 0.794 0.794 0.953 1.111 1.270 1.429 1.588 1.746 1.905 2.223 2.858

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

G cm 1.905 2.064 2.381 2.857 3.333 3.810 4.286 4.763 5.239 5.715 6.668 8.573

wa Ac

1.754 1.075 0.418 0.790 0.789 0.790 0.789 0.789 0.789 0.789 0.789 0.789

Ac

cm" 0.862

1.523 2.394 3.448 4.693 6.129 7.757 9.577 11.588 13.790 18.770 31.028

wa 2

cm 1.512 1.638 1.890 2.723 3.705 4.839 6.124 7.560 9.148 10.887 14.818 24.496

A

P 4

cm 1.303 2.510 4.525 9.384 17.384 29.656 47.504 72.404 106.006 150.136 278.145 760.064

K* cm 0.067 0.188 0.459 1.153 2.513 4.927 8.920 15.162 24.492 37.579 81.656 288.936

Dimensional Outline for UI Laminations The dimensional outline for UI laminations is shown in Figure 3-24. The assembled transformer is shown in Figure 3-25. A listing of common UI lamination sizes is shown in Table 3-2.

o

0

i ir i

•^*~

H

G

o F.

0

i ii i,H

D

F

F

Figure 3-24. UI Lamination Outline. Mounting Hardware Bolt, Washer, Nut Sleeving Shoulder Washer

0 UI, Laminations

Coil#l

Coil#2

e Side View

End View

Figure 3-25. UI Lamination Assembled with Coils and Hardware.

Table 3-2. Standard 14 mil UI Laminations.

Part

D

E

F

UI, Standard Laminations G H wa A c

2

wa

AP 4 cm 7.414

Kg 5 cm 0.592

Number

cm

cm

cm

cm

cm

Ac

50UI

1.270 1.429

1.270

3.810

1.270

60UI

1.270 1.429

2.223

5.398

1.429

3.159 6.187

1.939

cm 4.839 11.996

23.263

1.839

75UI

1.905

1.905

1.905

5.715

3.157

3.448

10.887

37.534

4.614

100UI

2.540

2.540

2.540

7.620

1.905 2.540

3.158

6.129

19.355

118.626

19.709

125UI

3.175

3.175

3.175

9.525

3.175

3.158

9.577

30.242

289.614

60.647

15 GUI 180UI

3.810 4.572

3.810 4.572

3.810 4.572

11.430

3.158 2.632

13.790

43.548

600.544

150.318

11.430

3.810 4.572

19.858

52.258

1037.740

313.636

240UI

6.096

6.096

6.096

15.240

6.096

2.632

35.303

92.903

3279.770

1331.997

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

cm 1.532

Dimensional Outline for LL Laminations The dimensional outline for LL laminations is shown in Figure 3-26. The assembled transformer is shown in Figure 3-27. A listing of common lamination sizes is shown in Table 3-3.

o

o I

1r H

It ^

G

o

o

-^ ^-

-^ ^-

-^ ^-

c

K

c

\r i 1! H D

Figure 3-26. LL Lamination Outline.

LL, Laminations

e -^>

e

Coil#l

e

Side View Figure 3-27.


&>

Mounting Hardware Bolt, Washer, Nut Sleeving Shoulder Washer

Coil

Coil#2

e

End View

4 ^ LL Lamination Assembled with Coils and Hardware.

Table 3-3. Standard 14 mil LL Laminations.

LL, Standard Laminations Number

D cm

E cm

F cm

G cm

141L

0.635

0.635

2.858

108L 250L

1.031

1.031 1.031

1.270 0.874 0.874

5.239

101L 7L

1.111 1.270

1.111

1.588

2.858

1.270

1.270

3.810

4L 104L

1.270

1.270 1.270 1.270

3.810 5.555

105L

1.270 1.270

1.905 1.984

102L 106L

1.429 1.429

107L

1.588

Part

1.031

3.334

H cm 0.635

1.111 1.111

wa

Ac

Kg cm 0.043 0.201 0.316

9.473

cm 0.383

cm 3.629

2.884

1.010

4.532

1.010

2.913 4.577

AP 4 cm 1.390 2.943 4.624

3.867

4.536

5.322

0.340

4.839

7.414

0.592

Ac

7

7

1.111 1.270

3.159

1.173 1.532

1.270

4.737

1.532

7.258

11.121

0.785

1.270 1.270

7.193 8.488

1.532

11.020

16.885

1.176

1.532

13.004

19.925

4.419 6.187

1.939 1.939

8.569

16.617

1.407 1.462

11.996

23.263

1.839

5.474

2.394

13.105

31.375

2.946

1.905

6.826

1.429 1.429

1.588 2.223

5.398 5.398

1.429 1.429

1.588

2.064

6.350

1.588

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

wa

Dimensional Outline for DU Laminations The dimensional outline for DU laminations is shown in Figure 3-28. The assembled transformer is shown in Figure 3-29. A listing of common DU laminations sizes is shown in Table 3-4.

ii H

0

0

o

o

o

o

0

0

\r i

i

G ir t H

k

ir

-^ E

F

E -«-

Figure 3-28. DU Lamination Outline.

DU, Laminations

e — +*

Coil #1 Coil #2

e

Side View

is

c

e

Mounting Hardware Bolt, Washer, Nut Sleeving Shoulder Washer

Coil

e

fc

C

End View

Figure 3-29. DU Lamination Assembled with Coils and Hardware. Table 3-4. Standard 14 mil DU Laminations.

DU, Standard Laminations Part Number DU-63 DU-124 DU-18 DU-26 DU-25 DU-1 DU-39 DU-37 DU-50 DU-75 DU-1 125 DU-125

D cm

E cm

G cm

H cm

wa

cm

0.159 0.318 0.476 0.635 0.635 0.635 0.953 0.953 1.270 1.905 2.858 3.175

0.159 0.318 0.476 0.635 0.635 0.635 0.953 0.953 1.270 1.905 2.858 3.175

0.318 0.476 0.635 0.635 0.953 0.953 0.953 1.905 2.540 3.810 5.715 3.175

0.794 1.191 1.588 1.905 2.064 3.810 2.858 3.810 5.080 7.620 11.430 9.525

0.318 0.635 0.953 1.270 1.270 1.270 1.905 1.905 2.540 3.810 5.715 3.175

10.500 5.906 4.688 3.159 5.133 9.634 3.158 8.420 8.422 8.420 8.421 3.158

F

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Ac

Ac

cm2 0.024 0.096 0.215 0.383 0.383 0.383 0.862 0.862 1.532 3.448 7.757 9.577

wa cm 0.252 0.567 1.008 1.210 1.966 3.690 2.722 7.258 12.903 29.032 65.322 30.242

Ap 4

cm 0.006 0.054 0.217 0.463 0.753 1.390 2.346 6.256 19.771 100.091 506.709 289.614

Kg cm5 0.00003 0.0009 0.0057 0.0180 0.0260 0.0479 0.1416 0.2992 1.2524 9.7136 74.8302 60.6474

Dimensional Outline for Three Phase Laminations The dimensional outline for three phase laminations is shown in Figure 3-30. The assembled transformer is shown in Figure 3-31. A listing of common three phase laminations sizes is shown in Table 3-5. 1t

E

*r i

F

0

i

O

^r

O v v """ W a

Ar

0

G

D

E

o

O

Figure 3-30. El Three Phase Laminations Outline.

Laminations -

Side Vie w

e —^

e

e

Coil #1

Coil #2

©

©

Coil #3

©

<

|»

Mounting Hardware Bolt, Washer, Nut Sleeving Shoulder Washer

Coil

\

Ba End View

Figure 3-31. Three Phase Lamination Assembled with Coils and Hardware. Table 3-5. Standard 14 mil El Three Phase Laminations.

3Phase, Standard Laminations Part Number 25E1 375EI 50E1 562EI 625EI 875EI 100EI 120E! 150EI 180E1 240E1 360EI

D cm 0.635 0.953 1.270 1.427 1.588 2.223 2.540 3.048 3.810 4.572 6.096 9.144

E cm 0.635 0.953 1.270 1.427 1.588 2.223 2.540 3.048 3.810 4.572 6.096 9.144

F cm 0.871 1.270 1.588 1.588 1.984 2.779 3.810 3.048 3.810 4.572 6.096 9.144

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

G cm 2.858 3.175 3.493 5.398 5.634 6.111 7.620 7.620 9.525 11.430 15.240 22.860

wa 2A C 3.251 2.339 1.810 2.213 2.334 1.809 2.368 1.316 1.316 1.316 1.316 1.316

Ac

cm"

0.383 0.862 1.532 1.936 2.394 4.693 6.129 8.826 13.790 19.858 35.303 79.432

wa 2

A

P 4

K g

cm cm cm 2.490 1.430 0.051 4.032 5.213 0.289 5.544 12.743 0.955 8.569 24.881 2.187 11.176 40.135 3.816 16.982 119.531 16.187 29.032 39.067 266.908 61.727 23.226 307.479 36.290 187.898 750.680 52.258 1556.609 470.453 92.903 4919.656 1997.995 209.032 24905.750 15174.600

Dimensional Outline for Tape Wound C, EE, and Toroidal Cores The dimensional outline for C cores is shown in Figure 3-32. The dimensional outline for EE cores is shown in Figure 3-33. The dimensional outline for C cores is shown in Figure 3-34.

W, G

D Figure 3-32. Tape C Core Dimensional Outline.

A, D Figure 3-33. Tape EE Core Dimensional Outline.

W,

Figure 3-34. Tape Toroidal Core Dimensional Outline. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Dimensional Outline for EE and El, Ferrite Cores The dimensional outline for EE and El ferrite cores is shown in Figure 3-35. A listing of common lamination sizes is shown in Table 3-6.

A

B

W,

G

D

Figure 3-35. Dimension Outline for EE, El Ferrite Cores.

Table 3-6. Standard EE Ferrite Cores.

EE, Ferrite Cores (Magnetics) Part Number EE-187 EE-2425 EE-375

EE-21 EE-625 EE-75

A cm 1.930 2.515 3.454 4.087 4.712 5.657

B cm 1.392 1.880 2.527 2.832 3.162 3.810

C cm 1.620

1.906 2.820 3.300 3.940 4.720

D cm 0.478 0.653 0.935 1.252 1.567 1.880

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

E cm 0.478 0.610 0.932 1.252 1.567 1.880

G cm 1.108 1 .250 1.930 2.080 2.420 2.420

wa AC

2.223 2.062

1.832 1.081 0.806 0.669

Ac

wa

cm" 0.228 0.385 0.840 1.520 2.390 3.490

cm 0.506 0.794 1.539 1.643 1.930 2.335

A

P 4 cm 0.115 0.306 1.293 2.498 4.613 8.150

K

g cm 0.0028 0.0095 0.0654 0.1875 0.4700 1.0195

Dimensional Outline for EE and El Planar, Ferrite Cores The dimensional outline for EE and El planar ferrite cores is shown in Figure 3-36. A listing of EE, El planar cores are shown in Table 3-7.

c ii

Matting Set E or I

^-

-—

1 ^

A

-AC

B

1

\r --— -^-

D Figure 3-36. Dimension Outline for EE, El Planar Ferrite Cores. Table 3-7. Standard EE, El Planar Ferrite Cores.

EE&EI/LP, Ferrite Cores (Magnetics) Part Number 41805-EI 41805-EE 42216-EI 42216-EE 43208-EI 43208-EE 43618-EI 43618-EE

A cm 1.800 1.800 2.160 2.160 3.175 3.175 3.556 3.556

B cm 1.370 1.370 1.610 1.610 2.450 2.450 2.720 2.720

C cm 0.598 0.796 0.826 1.144 0.908 1.270 0.635 1.270

D cm 1.000 1.000 1.590 1.590 2.032 2.032 1.780 1.780

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

E cm 0.398 0.398 0.508 0.508 0.635 0.635 0.762 0.762

G cm 0.188 0.367 0.297 0.594 0.318 0.636 0.241 0.482

wa Ac

0.227 0.456 0.203 0.406 0.224 0.447 0.175 0.350

Ac 2

cm 0.401 0.401 0.806 0.806 1.290 1.290 1.350 1.350

wa cm 2 0.091 0.183 0.164 0.327 0.289 0.577 0.236 0.472

Ap 4

cm 0.036639 0.073277 0.131899 0.263799 0.372275 0.744549 0.318518 0.637035

K

g cm 0.001240 0.002484 0.006507 0.013014

0.021846 0.043692 0.019618 0.039235

Dimensional Outline for EC, Ferrite Cores The dimensional outline for EC ferrite cores is shown in Figure 3-37. A listing of EC cores is shown in Table 3-8.

Figure 3-37. Dimension Outline for EC Ferrite Cores.

Table 3-8. Standard EC Ferrite Cores.

EC, Ferrite Cores Part Number EC-35 EC-41 EC-52 EC-70

A

B

cm

cm

C cm

3.450 4.060 5.220

2.270 2.705 3.302

7.000

4,45

D

E

cm

cm

3.460 3.901 4.841

0.950

0.950

1.161 1.340

1.161 1.340

6.900

1.683

1.683

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

G cm

H

wa

Ac

cm

Ac 2.220

cm" 0.710

2.380 2.697

NA NA

1.960

1.060

3.099

NA

2.160

1.410

4.465

NA

2.970

2.110

wa cm" 1.580 2.080 3.040 6.280

AP cm4 1.119 2.208 4.286 13.246

Kg 5

cm 0.051

0.125 0.267

0.966

Dimensional Outline for ETD, Ferrite Cores The dimensional outline for ETD ferrite cores is shown in Figure 3-38. A listing of ETD cores is shown in Table 3-9.

A

Ar

B

G

D

Figure 3-38. Dimension Outline for ETD Ferrite Cores.

Table 3-9. Standard ETD Ferrite Cores.

ETD, Ferrite Cores Part Number ETD-29 ETD-34 ETD-39 ETD-44 ETD-49 ETD-54 ETD-59

A cm

B cm

C cm

2.980 3.500 4.000 4.500 4.980 5.450 5.980

2.270 2.560 2.930 3.250 3.610 4.120 4.470

3.360 3.460 3.960 4.460 4.940 5.520 6.200

G

wa

cm 0.980 1.110 1.280 1.520

E cm 0.980 1.110 1.280 1.520

cm 2.200 2.420 2.920 3.300

Ac 1.910

1.670 1.890 2.165

1.670 1.890 2.165

3.620 4.040 4.400

D

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1.925 2.052 1.742 1.767 1.609 1.382

Ac

W *' a

cm" 0.761 0.974

cm2 1.452

1.252 1.742 2.110 2.800 3.677

1.875 2.569 3.036 3.729 4.505 5.082

AP 4 cm 1.1050 1.8270 3.2171 5.2890

Kg cm5 0.0536 0.0994

0.1925 0.3897 7.8673 0.6383 12.6129 1.2106 18.6860 2.1347

Dimensional Outline for ETD/(low profile), Ferrite Cores The ETD/lp cores offer a low profile to be used with printed circuit board (PCB) designs. The dimensional outline for ETD/lp ferrite cores is shown in Figure 3-39. A listing of ETD/lp cores is shown in Table 3-10.

B

A

Ar

G

W,

D

Figure 3-39. Dimension Outline for ETD/lp Ferrite Cores.

Table 3-10. Standard ETD/lp Ferrite Cores.

ETD/lp, Ferrite Cores Part

A

B

Number

cm

cm

ETD34(lp)

3.421

ETD39(lp)

3.909

2.631 3.010 3.330 3.701

ETD44(lp)

4.399

ETD49(lp)

4.869

C cm 1.804 1.798 1.920 2.082

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

D cm 1.080 1.250 1.481 1.631

E cm 1.080 1.250 1.481 1.631

G cm

Wa

0.762

0.609

0.762

0.559

vv

Ac

0.762

0.407

0.762

0.374

AC

wa

2

cm

cm" i 0.591 0.970

1.200 f 0.671 1.730 0.704 2 . 1 1 0 0.789

AP cm 0.5732

Kg cm 0.0310

0.8047

0.0461

1.2187

0.0894

1 .6640

0.1353

Dimensional Outline for ER, Ferrite Cores SMD The dimensional outline for ER ferrite cores is shown in Figure 3-40. A listing of ER ferrite cores is shown in Table 3-11.

C

B

'A,

D

Figure 3-40. Dimension Outline for ER Ferrite Cores. Table 3-11. Standard ER Ferrite Cores.

ER, Ferrite Cores (Philips) Part Number ER9.5 ER 11 ER35 ER42 ER48 ER54

A cm 0.950 1.100 3.500 4.200 4.800 5.350

B cm 0.750 0.870 2.615 3.005 3.800 4.065

C cm 0.490 0.500 4.140 4.480 4.220 3.660

D cm 0.500

E cm 0.350

0.600 1.140 1.560 2.100 1.795

0.425 1.130 1.550 1.800 1.790

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

G cm 0.320 0.300 2.950 3.090 2.940 2.220

Wa

Ac

Ac

cm" 0.0760 0.1270 1.0700 1.9400 2.5500 2.5000

0.842 0.526 2.470 1.159 1.153 1.010

wa

K P S cm5 cm" cm 0.0640 0.00486 0.000054 0.0668 0.00848 0.000136 2.1904 2.34370 0.137777 2.2480 4.36107 0.371338 2.9400 7.49700 0.662096 2.5253 6.31313 0.556146 A

Dimensional Outline for EFD, Ferrite Cores

SMD The EFD cores (Economic Flat Design) offer a significant advance in power transformer circuit miniaturization. The dimensional outline for EFD ferrite cores is shown in Figure 3-41. A listing of EFD cores is shown in Table 3-12.

D

-(

1i 1

I

iL

) k V>

A

B

E

1r

\ ir

V\

r

^ 'W,

\

-* H -»

AcP

(

Figure 3-41. Dimension Outline for EFD Ferrite Cores. Table 3-12. Standard EFD Ferrite Cores.

EFD, Ferrite Cores Part Number EFD-10 EFD-15 EFD-20 EFD-25 EFD-30

A

B

C

D

E

G

H

wa

cm

cm

cm

cm

cm

cm

Ac

1.050

0.765

0.145

1.610

1.100 1.540

1.500 2.000

0.455 0.530 0.890

0.750

1.500 2.000 2.500 3.000

0.270 0.465 0.665

cm 1.040

1.100 1.540

0.240 0.360

2.090 1.610

1.870

0.910 0.910

1.140 1.460

1.860 2.240

0.520 0.490

1.170

2.240

2.500 3.000

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1.266

^A c cm"

wa cm"

0.072 0.150 0.310

0.116

0.580 0.690

0.679 0.874

0.314 0.501

A

P

Kg

4

cm cm" 0.00836 0.00013

0.04702 0.00105 0.15515 0.00506 0.39376 0.01911 0.60278 0.03047

Dimensional Outline for EPC, Ferrite Cores SMD The dimensional outline for EPC ferrite cores is shown in Figure 3-42. A listing of ECP cores is shown in Table 3-13.

C

D

A

B

Ar

H

G

Figure 3-42. Dimension Outline for EPC Ferrite Cores. Table 3-13. Standard EPC Ferrite Cores.

EPC, Ferrite Cores (TDK) Part

A

B

C

D

E

G

H

wa

Number

cm

cm

cm

cm

cm

cm

cm

EPC- 10

1.020

0.760

0.340

0.810

0.500

0.530

0.190

Ac 0.734

cm" cm 0.0939 0.0689

cm 0.006470

EPC-13

1.325

1.050

0.460

1.320

0.560

0.900

0.205

1.765

0.1250 0.2205

0.027562

0.000549

EPC- 17

1.760

1.430

0.600

1.710

0.770

1.210

0.280

1.751

0.2280 0.3993

0.091040

0.002428

Ac 1

wa

Ap

Kg cm 0.000128

EPC- 19

1.910

1.580

0.600

1.950

0.850

1.450

0.250

2.334

0.2270 0.5293

0.120140

0.002981

EPC-25

2.510

2.080

0.800

2.500

1.150

1.800

0.400

1.804

0.4640 0.8370

0.388368

0.014533

EPC-27

2.710

2.160

0.800

3.200

1.300

2.400

0.400

1.890

0.5460 1.0320

0.563472

0.024036

EPC-30

3.010

2.360

0.800

3.500

1.500

2.600

0.400

1.832

0.6100 1.1180

0.681980

0.030015

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Dimensional Outline for PC, Ferrite Cores The dimensional outline for PC ferrite cores is shown in Figure 3-43. A listing of PC cores is shown in Table 3-14.

C

B

A

X G

Figure 3-43. Dimension Outline for PC Ferrite Cores. Table 3-14. Standard PC Ferrite Cores.

PC, Ferrite Cores (Magnetics) Part

A

B

C

E

G

wn

wa

A

0.650

crrf 0.100

cm 0.065

P cm4 0.00652

K \ cm" 0.000134

0.559

0.631

0.249

0.157

0.03904

0.001331

0.720

0.697

0.429

0.299

0.11413

0.005287

0.940

0.920

0.612

0.639

0.391

0.24985

0.014360

1.610

1.148

1.102

0.576

0.931

0.536

0.49913

0.035114

1.880

1.350

1.300

0.549

1.360

0.747

1.01660

0.088001

2.200

1.610

1.460

0.498

2.020

1.007

2.03495

0.220347

2.960

1.770

2.040

0.686

2.660

1.826

4.85663

0.600289

Number

cm

cm

cm

cm

cm

Ac

PC-40905

0.914

0.749

0.562

0.388

0.361

PC-41408

1.400

1 . 1 60

0.848

0.599

PC-41811

1.800

1.498

1.067

0.759

PC-42213

2.160

1.790

1.340

PC-42616

2.550

2.121

PC-43019

3.000

2.500

PC-43622

3.560

2.990

PC-44229

4.240

3.560

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

AC

2

Dimensional Outline for EP, Ferrite Cores The EP ferrite cores are typically used in transformer applications. The shape of the assembly is almost cubical, allowing high package densities on the PCB. The dimensional outline for EP ferrite cores is shown in Figure 3-44. A listing of EP cores is shown in Table 3-15.

D

A

B

A

c

Figure 3-44. Dimension Outline for EP Ferrite Cores. Table 3-15. Standard EP Ferrite Cores.

EP, Ferrite Cores Part Number EP-7 EP-10 EP-13 EP-17 EP-20

A cm 0.940 1.150 1.280 1.800 2.400

B cm 0.720 0.940 0.970 1.200 1.650

C cm 0.650 0.760 0.900 1.100 1.500

D cm 0.750 1.020 1.300 1.680 2.140

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

E cm 0.340 0.330 0.450 0.570 0.880

G cm 0.500 0.740 0.900 1.140 1.440

wa Ac

0.987 1.997 1.344 1.066 0.704

Ac

wa

cm" 0.1080 0.1130 0.1950 0.3370 0.7870

cm 0.1066 0.2257 0.2622 0.3591 0.5544

AP cm4 0.01151 0.02550 0.05112 0.12101 0.43631

KB cm 0.00027 0.00053 0.00165 0.00540 0.03261

Dimensional Outline for PQ, Ferrite Cores The PQ ferrite cores (Power Quality) feature round center legs with rather small cross-sections. The dimensional outline for PQ femte cores is shown in Figure 3-45. A listing of PQ cores is shown in Table

3-16.

Ar

Figure 3-45. Dimension Outline for PQ Ferrite Cores. Table 3-16. Standard PQ Ferrite Cores.

PQ, Ferrite Cores Part

A

B

D

C

E

G

wa

Number

cm

cm

cm

cm

cm

cm

Ac

PQ20/16 PQ20/20 PQ26/20 PQ26/25 PQ32/20 PQ32/30 PQ35/35 PQ40/40 PQ50/50

2.050 2.050 2.650 2.650 3.200 3.200 3.510 4.050 5.000

1.800 1.800 2.250 2.250 2.750 2.750 3.200 3.700 4.400

1.620 2.020 2.015 2.475 2.055 3.035 3.475 3.975 4.995

1.400 1 .400 1.900 1.900 2.200 2.200 2.600 2.800 3.200

0.880 0.880 1.200 1.200 1.345 1.245 1.435 1 .490 2.000

1.030 1.430 1.150 1.610 1.150 2.130 2.500 2.950 3.610

0.764 1.061 0.507 0.724 0.475 0.930 1.126 1.622 1.321

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Ac 2

cm 0.620 0.620 1.190 1.180 1.700 1.610 1 .960 2.010 3.280

wa cm" 0.474 0.658 0.604 0.854 0.808 1.496 2.206 3.260 4.332

AP 4 cm4 0.294 0.408 0.717 0.997 1.373 2.409 4.324 6.552 14.210

Kg cm 0.0167 0.0232 0.0161 0.0855 0.1401 0.2327 0.4511 0.6281 1.8123

Dimensional Outline for PQ/(low profile), Ferrite Cores The PQ/lp cores are a cut down version of the standard PQ cores. The PQ/lp cores have a substantially reduced total height. The dimensional outline for PQ/lp ferrite cores is shown in Figure 3-46. A listing of PQ/lp cores is shown in Table 3-17.

G

r— j i

~\ 1L

^\

\\

B

\

1r

A \ \

\r -^ (—i

Figure 3-46. Dimension Outline for PQ Ferrite Cores.

Table 3-17. Standard PQ Ferrite Cores.

PQ/lp, Ferrite Cores (Ferrite International) Part Number PQ20/20/lp PQ26/20/lp PQ32/20/lp PQ35/35/lp PQ40/40/lp

A cm 2.125 2.724 3.302 3.612

B cm 1.801

C cm 2.702

D cm 1.400

E cm 0.884

G cm 1.524

2.250 2.751 3.200

1.900 2.200 2.601

1.199

1.524 1.524 1.524

4.148

3.701

3.260 3.342 3.474 3.566

2.799

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1.348 1.435 1.491

1.524

wa

Ac

2

Ac 1.127

cm 0.620

0.673 0.629 0.686 0.838

1.190 1.700 1.960 2.010

wa 2

cm 0.699 0.801 1.069 1.345 1.684

A

P cm4 0.433 0.953 1.817 2.636 3.385

K

g cm5 0.024 0.080 0.185 0.275 0.324

Dimensional Outline for RM, Ferrite Cores The RM cores (Rectangular Modular) were developed for high printed circuit board (PCB) packing densities. The dimensional outline for RM ferrite cores is shown in Figure 3-47. A listing of RM cores is shown in Table 3-18.

A

Figure 3-47. Dimension Outline for RM Ferrite Cores.

Table 3-18. Standard RM Ferrite Cores.

RM, Ferrite Cores B cm

C cm

D

E

G

H

wa

Ac

wa

cm

cm

cm

cm

Ac

0.815

1.04

NA

0.38

0.72

NA

1.12

cm' 0.157

1.04 1.265

1.04 1.24

NA

0.48

NA

0.63

0.65 0.82

NA

RM-6

0.963 1.205 1.44

cm" 0.14

0.768 0.71

RM-7

1.685

1.34

NA

0.71

NA

1.64

NA

0.84

1.86

NA

2.35 2.88

NA NA

1.07 1.26 1.47

0.865 1.1 1.27

Part Number RM-4 RM-5

A cm

RM-8

1.935

1.508 1.73

RM-10

2.415

2.165

RM-12 RM-14

2.925 3.42

2.55 2.95

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1.71 2.1 1

A

P 4 cm 0.0219

Kg cm" 0.0006

0.0431 0.0953

0.0016 0.0044

0.159

0.00802 0.01911

NA

0.75 0.76

0.237 , 0 . 1 8 2 0.26 0.366 0.46 0.345 0.64 0.489

NA

0.71

0.695

0.681

1.103 1.556

1.544 2.77

NA

NA NA

0.98 0.788 ' 1.4 0.874 1.78

0.313

0.05098 0.139 0.2744

Dimensional Outline for RM/(low profile), Ferrite Cores SMD The RM/lp ferrite cores are a cut down version of the standard RM cores. The dimensional outline for RM/lp ferrite cores is shown in Figure 3-48. A listing of RM/lp cores is shown in Table 3-19.

A

Figure 3-48. Dimension Outline for RM/lp Ferrite Cores.

Table 3-19. Standard RM/lp Ferrite Cores.

RM/lp, Ferrite Cores (Ferrite International) Part Number PQ20/20/!p PQ26/20/!p PQ32/20/lp PQ35/35/lp PQ40/40/lp

A cm 2.126 2.725 3.302 3.612 4.148

B cm 1.801 2.250 2.751 3.200 3.701

C cm 2.702 3.260 3.342 3.474 3.566

D cm 1.400 1.900 2.200 2.601 2.799

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

E cm 0.884

1.199 1.348 1.435 1.491

G cm 1.524 1.524 1.524 1.524 1.524

wa Ac 1.127 0.673 0.629 0.686 0.838

Ac 7

cm" 0.620 1.190 1.700 1.960 2.010

wa

•> cm" 0.699 0.801 1.069 1.345 1.684

A

Kg P 4 cm5 cm 0.43323 0.02412 0.95303 0.08022 1.81744 0.18514 2.63606 0.27494 3.38488 0.32431

Dimensional Outline for DS, Ferrite Cores The DS ferrite cores are similar to standard Pot Cores. These cores have a large opening to bring out many strands of wire, which is convenient for high power and multiple outputs. The dimensional outline for DS ferrite cores is shown in Figure 3-49. A listing of DS cores is shown in Table 3-20.

Figure 3-49. Dimension Outline for DS Ferrite Cores.

Table 3-20. Standard DS Ferrite Cores.

DS, Ferrite Cores (Magnetics) Part

A

B

C

D

E

G

wa

Ac

wa

Number

cm

cm

cm

cm

cm

cm

AC

DS-42311

2.286

1.793

1.108

1.540

0.990

0.726

0.568

DS-42318

2.286

1.793

1.800

1.540

0.990

1.386

0.960

DS-42316

2.550 3.000

2.121

1.610 1.880

1.709

1.148

1.102

2.500

1.709

1.351

1.300

0.696 0.638

3.561

2.985

2.170

2.385

1.610

1.458

0.672

4.240

3.561

2.960

2.840

1.770

2.042

0.875

cm 0.512 0.580 0.770 1.170 1.490 2.090

cm" 0.291 0.557 0.536 0.747 1.002 1.828

DS-42319 DS-42322 DS-42329

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

AP 4 cm 0.14920 0.32275 0.41281 0.87381 1.49354 3.82179

Kg cm 0.00674 0.01624 0.02402 0.06506 0.11942 0.37109

Dimensional Outline for UUR, Ferrite Cores The UUR ferrite cores feature round legs with rather small cross sections. The round legs allow easy winding with either wire or foil. U cores are used for power, pulse and high-voltage transformers. The dimensional outline for UUR ferrite cores is shown in Figure 3-50. A listing of UUR cores is shown in Table 3-21.

C

A

Figure 3-50. Dimension Outline for UUR Ferrite Cores. Table 3-21. Standard UUR Ferrite Cores.

UUR, Ferrite Cores (Magnetics) Part Number UUR-44121 UUR-44119 UUR-44125 UUR-44130

A cm 4.196 4.196 4.196 4.196

C cm 4.120 4.180 5.080 6.100

D cm 1.170 1.170 1.170 1.170

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

F cm 1.910 1.910 1.910 1.910

G cm 2.180 2.680 3.140 4.160

wa Ac

4.215 5.619 6.070 8.O43

AC

wa

cm" 0.988 0.911 0.988 0.988

cm" 4.164 5.119 5.997 7.946

AP cm 4 4.114

4.663 5.925 7.850

Kg cm 0.202 0.211 0.291 0.386

Dimensional Outline for UUS, Ferrite Cores The UUS ferrite cores feature square or rectangular legs. U cores are used for power, pulse and highvoltage transformers. The dimensional outline for UUS ferrite cores is shown in Figure 3-51. A listing of UUS cores is shown in Table 3-22.

A

D

G

Figure 3-51. Dimension Outline for UUS Ferrite Cores.

Table 3-22. Standard UUS Ferrite Cores.

UUS, Ferrite Cores (Philips) Part Number UUS-10 UUS-20 UUS-25 UUS-30 UUS-67 UUS-93

F

G

wa

AC

wa

cm

D cm

cm

cm

Ac

1.640 3.120 3.920

0.290 0.750 1.270

0.435 0.640 0.840

1.000

5.179

1.660

1.896 1.841

cm" 0.084 0.560

cm" 0.435 1.062

5.060 5.400 15.200

1.600 1.430

1.050

A

C

cm 1 .000

2.080 2.480 3.130

6.730 9.300

4.800

3.880 3.620

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2.280 2.980 2.540 9.600

1 .040

1.915

4.831

1.610 2.040

3.129 9.855

7.757

4.480

34.752

1.943

A

P 4 cm 0.0365

Kg 5 cm 0.000549

0.5949 1.9918 5.0377 20.1046 155.6889

0.030612 0.135668 0.430427 1.321661 12.808331

Dimensional Outline for Toroidal, Ferrite Cores The toroidal ferrite core has the best possible shape from the magnetic point of view. The magnetic flux path is completely enclosed within the magnetic structure. The toroidal structure fully exploits the capabilities of a ferrite material. The dimensional outline for toroidal ferrite cores is shown in Figure 3-52. A listing of toroidal cores is shown in Table 3-23.

HT.

I.D

Figure 3-52. Dimension Outline for Toroidal Ferrite Cores.

Table 3-23. Standard Toroidal Ferrite Cores.

Toroidal, Ferrite Cores (Magnetics) Part Number TC-40705 TC-41206 TC-42206 TC-42908 TC-43806 TC-43610 TC-43813 TC-48613

OD cm 0.762 1.270 2.210 2.900

3.810 3.600 3.810 8.570

ID cm 0.318 0.516

1.370 1.900 1.900 2.300

1.900 5.550

HT cm 0.478 0.635 0.635 0.749 0.635 1.000 1.270 1.270

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

wa

wa

Ac 0.806 0.946 5.896 7.919 4.974

cm 0.098

cm" 0.079

0.221

0.209

AP cm4 0.007783 0.046215

0.250

1.474

0.368528

0.358

2.835

1.015032

Kg cm5 0.000222 0.002011 0.013237 0.041312

0.570

2.835

1.616112

0.090668

6.616

0.628

0.146301

1.150 1.870

4.155 2.835 24.192

2.609185

2.465

3.260577

0.295249

45.239426

3.807278

12.937

Ac

2

7

Dimensional Outline for Toroidal, MPP Powder Cores The dimensional outline for toroidal MPP powder cores is shown in Figure 3-53. A listing of toroidal cores is shown in Table 3-24.

OD

Figure 3-53. Dimension Outline for Toroidal Powder Cores.

Table 3-24. A Small List of Standard Toroidal MPP Powder Cores.

MPP Powder Cores, Magnetics 60 mu (coated) ID

HT

MPL

wa

Ac

wa

Number

OD cm

cm

cm

cm

Ac

cm"

cm"

55021

0.699

0.229

0.343

1.36

0.877

0.047

0.041

55281

1.029

0.427

0.381

2.18

1.900

0.075

0.143

55291

1.029

0.427

0.457

2.18

1.512

0.095

0.143

55041

1.080

0.457

0.457

2.38

1.640

0.100

0.164

55131

1.190

0.589

0.472

2.69

3.013

0.091

0.273

55051

1.346

0.699

0.551

3.12

3.360

0.114

0.383

55121

1.740

0.953

0.711

4.11

3.714

0.192

0.713

55381

1.803

0.902

0.711

4.14

2.750

0.232

0.638

55848

2.110

1.207

0.711

5.09

5.044

0.226

1.140

55059

2.350

1.339

0.838

5.67

4.260

0.331

1.410

55351

2.430

1.377

0.970

5.88

3.840

0.388

1.490

55894

2.770

1.410

1 . 1 99

6.35

2.385

0.654

1.560

55071

3.380

1.930

1.161

8.15

4.360

0.672

2.930

55586

3.520

2.260

0.983

8.95

8.833

0.454

4.010

55076

3.670

2.150

1.128

8.98

5.369

0.678

3.640

55083

4.070

2.330

1.537

9.84

3.983

1.072

4.270

55439

4.760

2.330

1.892

10.74

2.146

1.990

4.270

55090

4.760

2.790

1.613

11.63

4.560

1.340

6.110

55716

5.170

3.090

1.435

12.73

5.995

1.251

7.500

55110

5.800

3.470

1 .486

14.300

6.565

1.444

9.480

Part

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

A

P 4 cm 0.001930 0.010746 0.013504

0.016400 0.024734 0.043662 0.136896 0.148016 0.257640 0.466710 0.578120 1 .020240 1.968960 1.820540 2.467920 4.577440 8.497300 8.187400 9.382500 13.689120

Kg cm 0.000040 0.000252

0.000357 0.000432 0.000603 0.001225 0.004787 0.006030 0.009730 0.020153 0.028639 0.070381 0.124886 0.087356 0.154082 0.389064 1.034038 0.717932 0.762526 1.212742

AL mh/lOOON 24 25 32 32 26 27 35 43 32 43 51 75 61 38 56 81 135 86 73 75

Dimensional Outline for Toroidal, Iron Powder Cores The dimensional outline for toroidal iron powder cores is shown in Figure 3-54. A listing of toroidal cores is shown in Table 3-25.

OD

Figure 3-54. Dimension Outline for Toroidal Iron Powder Cores.

Table 3-25. A Small List of Standard Toroidal Iron Powder Cores.

Iron Powder Cores, Micrometals 75 mu (coated) OD Part Number cm T20-26 0.508 T25-26 0.648 T26-26 0.673 T30-26 0.780 T37-26 0.953 T38-26 0.953 T44-26 1.120 T50-26 1.270 1.520 T60-26 1.750 T68-26 2.020 T80-26 T94-26 2.390 T90-26 2.290 T 1 06-26 2.690 T 130-26 3.300 T132-26 3.300 T131-26 3.300 T141-26 3.590 T 150-26 3.840 Tl 75-26 ^4.450

ID cm 0.224

0.305 0.267 0.384 0.521 0.445 0.582 0.770 0.853 0.940 1.260 1.420 1.400 1.450 1.980 1.780 1.630 2.240 2.150 2.720

HT cm

MPL cm

wa

0.178 0.244 0.483 0.325 0.325 0.483 0.404 0.483 0.594

1.15 1.50 1.47 1.84 2.31 2.18 2.68 3.19 3.74

1.713 1.974 0.622

0.483 0.635 0.792 0.953 1.110 1.110 1.110 1.110 1.050 1.110 1.650

4.23 5.14

3.875 5.395 4.373 3.895 2.504 4.409 3.090 2.357 5.844 4.091 4.334

5.97 5.78 6.49 8.28 7.96 7.72 9.14 9.38 11.200

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Ac

1.929 3.329 1.364 2.686 4.156 3.054

Ac

cm 0.023 0.037 0.090 0.060 0.064 0.114 0.099 0.112 0.187 0.179 0.231 0.362 0.395 0.659 0.698 0.805 0.885 0.674 0.887 1.340

wa 2

cm 0.039 0.073 0.056 0.116 0.213 0.155 0.266 0.465 0.571 0.694 1.246 1.583 1.539 1.650 3.078 2.487 2.086 3.939 3.629 5.808

A

P 4 cm 0.000906 0.002702

0.005037 0.006945 0.013637 0.017721 0.026324 0.052128 0.106809 0.124159 0.287887 0.573000 0.607747 1.087655 2.148105 2.002191 1.845815 2.654762 3.218624 7.782377

Kg cm5 0.000014

0.000053 0.000154 0.000158 0.000308 0.000572 0.000760 0.002174 0.003938 0.007187 0.010389 0.016164 0.030827 0.113914 0.141056 0.151249 0.152983 0.164023 0.246891 0.715820

AL mh/lOOON 18.5 24.5 57 33.5 28.5 49 37 33 50 43.5 46 60 70 93 81 103 116 75 96 105

Chapter 4

Window Utilization, Magnet Wire, and

Insulation

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1.

Window Utilization Factor, K u

2.

Sj, Wire Insulation

3.

S2, Fill Factor

4.

S3, Effective Window

5.

S4, Insulation Factor

6.

Circular mil and Square mil

7.

Summary

8.

Magnet Wire

9.

Magnet Wire, Film Insulation

10. Wire Table 11. Solderable Insulation 12. Bondable Magnet Wire 13. Base Film Insulation 14. Bonding Methods 15. Miniature Square Magnet Wire 16. Multistrand Wire and Skin Effe 17. Multistrand Litz Wire 18. Specialty Wire 19. Triple Insulated Wire 20. Triple Insulated Litz 21. Polyfilar Magnetic Wire 22. Standard Foils 23. The Use of Foils 24. Calculating, MLT 25. Calculating, MLT (toroid) 26. Copper Resistance 27. Copper Weigh 28. Electrical Insulating Materials 29. References

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Window Utilization Factor, Ku

The window utilization factor is the amount of copper that appears in the window area of the transformer or inductor. The window utilization factor is influenced by five main factors:

1.

Wire insulation, S|.

2.

Wire lay fill factor, layer or random wound, S2.

3.

Effective window area (or, when using a torrid, the clearance hole for passage of the shuttle), S3.

4.

Insulation required for multiplayer windings, or between windings, S4.

5.

Workmanship, (quality).

These factors, multiplied together, will give a normalized window utilization of Ku = 0.4, as shown in Figure 4-1.

Core Window Area Area Taken By: Bobbin Tube Margin Wrapper Insulation Layer Insulation Magnet Wire Insulation Fill Factor

Copper Area

Figure 4-1. Window Area Occupied by Copper.

The window utilization factor, K u , of the available core window space, that will be occupied by the winding, (copper), is calculated from areas, S,, S2, S3, and S4:

J^jj — O| X 02 X 03 X 04

Where: 51 - conductor area/wire area 52 = wound area/usable window area 53 = usable window area/window area 54 = usable window area/usable window area + insulation Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

In which: Conductor area, A W ( B ) = copper area. Wire area, Avv = copper area + insulation area. Wound area = number of turns x wire area of one turn. Usable window area - available window area - residual area, that results from the particular winding technique used. Window area = available window area. Insulation area = area used for winding insulation.

Si, Wire Insulation In the design of high-current or low-current transformers, the ratio of the conductor area to the total wire area can vary from 0.941 to 0.673, depending on the wire size. In Figure 4-2, the thickness of the insulation has been exaggerated to show how the insulation impacts the overall area of the wire.

It can be seen, in Figure 4-2, that, by using multi-strands of fine wire to reduce the skin effect, it will have a significant impact on the window utilization factor, K u . Si is not only dependent upon wire size, but it is also dependent upon insulation coating. Table 4-1 shows the ratio of bare magnet wire to the magnet wire with insulation for single, heavy, triple, and quad insulation. When designing low-current transformers, it is advisable to re-evaluate, Si, because of the increased amount of insulating material. Si = A W( B/A W

Insulation 0.00965 cm

0.00787 cm

AWG #40

0.268 cm

0.259 cm

AWG #10

Figure 4-2. Comparing Insulation with Different Wire Gauges.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 4-1

Magnetic Wire Data (Nominal) Size AWG 10 15 20 25 30 35 40

Bare Area (cm") 0.1019 0.0571 0.0320 0.0179 0.0100 0.0056 0.0031

Ratio Bare/Single 0.961 0.939 0.917 0.878 0.842 0.815 0.784

Ratio Bare/Heavy 0.930 0.899 0.855 0.793 0.743 0.698 0.665

Ratio Bare/Triple 0.910 0.867 0.812 0.733 0.661 0.588 0.544

Ratio Bare/Quad 0.880 0.826 0.756 0.662 0.574 0.502 0.474

S2, Fill Factor S2 is the fill factor, or the wire lay, for the usable window area. When winding a large number of turns tightly on a smooth surface, the winding length exceeds the calculated value from the wire diameter by 10 to 15%, depending on the wire gauge. See Figure 4-3. The wire lay is subjected to wire tension, and wire quality, such as continuous wire diameter and the winding technique depending on the skill of the operator. The wire lay factor relationship for various wire sizes is shown in Table 4-2, for layer wound coils, and in Table 4-3, for random wound coils. The tables list the outside diameter for heavy film magnetic wire, 10 -

44 AWG.

Table 4-2

Wire Lay Factor For Layer Wound Coils Insulated Wire OD (inch) 0.1051 -0.0199 10 to 25 0.0178-0.0116 26 to 30 0.0105-0.0067 31 to 35 0.0060 - 0.0049 36 to 38 39 to 40 0.0043 - 0.0038 41 to 44 0.0034 - 0.0025 Heavy film magnetic wire

AWG

Insulated Wire OD (cm) 0.2670-0.0505 0.0452 - 0.0294 0.0267-0.0170 0.0152-0.0124 0.0109-0.0096 0.00863 - 0.00635

Wire Lay Factor 0.90 0.89 0.88 0.87 0.86 0.85

Table 4-3

Wire Lay Factor For Random Wound Coils Insulated Wire OD (inch) 10 to 22 0.1051 -0.0276 23 to 39 0.0623-0.0109 40 to 44 0.0038 - 0.0025 Heavy film magnet wire.

AWG

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Insulated Wire OD (cm) 0.267 - 0.0701 0.0249 - 0.0043 0.0096 - 0.00635

Wire Lay Factor 0.90 0.85 0.75

Calculated turns Actual turns

ooooooooooooo Winding Length

Figure 4-3. Capable Turns per Unit Length.

There are two ideal winding arrangements shown in Figure 4-4 and Figure 4-5. The square winding is shown in Figure 4-4 and the hexagonal winding is shown in Figure 4-5. The simplest form of winding is done by a coil being wound, turn-by-turn and layer-upon-layer, as shown in Figure 4-4. The square winding pattern has a theoretical fill factor of 0.785.

Wire Area = 0.785

Winding Build

Figure 4-4. Theoretically, the Square Winding Pattern Fill Factor 0.785.

A seemingly better fill factor can be achieved by using the hexagonal winding in Figure 4-5, compared to the square winding in Figure 4-4. In this type of winding, the individual wires do not lie exactly above each other, as in the square winding pattern. Instead, the wires lie in the grooves of the lower layer, as shown in Figure 4-5. This style of winding produces the tightest possible packing of the wire. The hexagonal style of winding will yield a theoretical fill factor of 0.907.

The fill factor, using the square winding pattern of 0.785, would be nearly impossible to achieve by hand winding without some layer insulation. Any layer insulation will reduce the fill factor even further. The fill factor, using the hexagonal winding pattern of 0.907, is just as hard to get. Hand winding, using the hexagonal technique, will result in the following: The first layer goes down with almost complete order. In

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

0.866(D)

Winding Build

Figure 4-5. Theoretically, the Hexagonal Winding Pattern Fill Factor 0.907.

the second layer, some disordering has occurred. With the third and fourth layer, disordering really sets in and the winding goes completely awry. This type of winding performs well with a small number of turns, but, with a large number of turns, it becomes randomly wound.

The ideal winding on a rectangular bobbin is shown in Figure 4-6. Then, when winding rectangular bobbins or tubes, the actual winding height in the region covered by the core, will be greater than the calculated winding height or build, due to the bowing of the windings. See Figure 4-7. The amount of bowing depends on the proportions of the winding and the height of the winding. Usually, the available winding build should be reduced by 15 to 20%, or 0.85x the winding build. When winding on a round bobbin or tube, this bowing effect is negligible.

The conclusion is, in comparing the square winding pattern used in the layer wound coil with its insulation, with the hexagonal winding pattern and its awry winding pattern, both seem to have a fill factor of about 0.61. But there is always the hundred to one exception, such as, when a design happens to have the right bobbin, the right number of turns, and the right wire size. This normally only happens when the design is not critical.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Build

Figure 4-6. Ideal Winding on a Rectangular Bobbin. To minimize this bowing effect and to insure a minimum build for either random or layer winding, the round bobbin, shown in Figure 4-8, will provide the most compact design. It can be seen, in Figure 4-8 that the round bobbin provides a uniform tension, all 360 degrees around the bobbin, for both layer and random windings. The other benefit, in using a round bobbin, is the reducing and minimizing of the leakage inductance caused from the bowing.

Winding Build Rectangular Core

Bowing

Figure 4-7. Bowing in Transformer Windings. Winding Build

Round Core

Figure 4-8. A Round Bobbin Insures Minimum Bowing.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

S3, Effective Window The effective window, S3, defines how much of the available window space may actually be used for the winding. The winding area available to the designer depends on the bobbin or tube configuration. Designing a layer winding that uses a tube will require a margin, as shown in Figure 4-9. The margin dimensions will vary with wire size. See Table 4-4. It can be seen, in Figure 4-9 and Table 4-4, how the margin reduces the effective window area. When transformers are constructed, using the layer winding technique, there is an industry standard for layer insulation thickness. This thickness is based on the diameter of the wire as shown in Table 4-5. Tube

Layer Insulation Wrapper

Winding Length Margin Figure 4-9. Transformer Windings with Margins. Table 4-4

Winding Margins Versus AWG Margin

AWG 10-15 16-18 19-21 22-31 32-37 38-up

cm 0.635 0.475 0.396 0.318 0.236 0.157

inch 0.25 0.187 0.156 0.125 0.093 0.062

Table 4-5

Layer Insulation Thickness AWG 10- 16 17- 19 20-21 22-23 24-27 28-33 34-41 42-46 Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Insulation Thickness cm inch 0.02540 0.01000 0.01780 0.00700 0.01270 0.00500 0.00760 0.00300 0.00510 0.00200 0.00381 0.00150 0.00254 0.00100 0.00127 0.00050

A single bobbin design, as shown in Figure 4-10, offers an effective area, Wa, between 0.835 to 0.929 for laminations, and 0.55 to 0.75 for ferrites, while a two bobbin configuration, as shown in Figure 4-11, offers an effective area, W a , between 0.687 to 0.873 for the tape C cores.

The toroid is a little different. The term, S3, defines how much of the available window space can actually be used for the winding. In order to wind the toroidal core, there has to be room to allow free passage of the shuttle. If half of the inside diameter is set aside for the shuttle, then, there will be 75% of the window area, (Wa), left for the design which is a good value for the effective window area factor, S3 — 0.75, as shown in Figure 4-12. The toroid would fall into all of the above categories.

Bobbin

Channel Bracket

Coil Mounting Foot

Lamination

Figure 4-10. Transformer Construction with Single Bobbin.

Bobbin

Coil #1

Coil #2

Tape C Core Mounting Bracket

Figure 4-11. Transformer Construction with Dual Bobbins.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

0.5 ID Clearance For Shuttle Effective Window Area Core Effective Window area Wa(eff) = (0.75)(7i)(ID)2/4 Figure 4-12. Effective Winding Area of a Toroidal Core.

S4, Insulation Factor The insulation factor, S4, defines how much of the usable window space is actually being used for insulation. If the transformer has multiple secondaries with significant amounts of insulation, S4 should be reduced by 5 to 10% for each additional secondary winding, partly because of the added space occupied by insulation and, partly because of the poorer space factor.

The insulation factor, S4, is not taken into account in Figure 4-12. The insulation factor, S4, is to be 1.0. The window utilization factor, Ku, is highly influenced by insulation factor, S4, because of the rapid buildup of insulation in the toroid, as shown in Figure 4-13.

In Figure 4-13, it can be seen that the insulation buildup is greater on the inside, than, on the outside. For example, in Figure 4-13, if 1.27 cm (1/2") wide tape was used with an overlap of 0.32 cm (1/8") on the outside diameter, the overlap thickness would be four times the thickness of the tape. It should be noted that the amount of overlap depends greatly on the size of the toroid and the required tape. In the design of toroidal components, and using the 0.5 ID remaining for passage of the shuttle, there is normally enough room for the wrapper.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Dacron Wrapper

Wound Ht.

Figure 4-13. Wrapped Toroid.

Circular mil and Square mil There are engineers that use circular mils/amp or square mils/amp. This is the reciprocal current density. The norm is to use amps/cm", which is a true current density. There have been some requests to define circular mils and square mils. First of all, let's define a mil, which is .001 inch. Figure 4-14 shows the area of a square mil, and the area of a circular mil.

One Square mil =

0.001

0.001

One Circular mil =

Figure 4-14. Comparing Circular-Mils and Square-Mils.

To convert Square mils to Circular mils , multiply by 1.2732. To convert Circular mils to Square mils , multiply by 0.7854. To convert Circular mils to Square centimeters , multiply by 5.066x10""To convert Square mils to Square centimeters , multiply by 6.45x10""

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Summary I hope I have cleared up some of the mystery of how the window utilization factor, Ku, was derived. I hope the magic of 0.4 is now clear. I have tried to bring together all of the different parts that make up the window utilization and then, explain each one. I hope I have simplified for you the complexity of the window utilization factor. I hope I have not confused you more. As stated at the beginning of this chapter, a good approximation for the window utilization factor is Ku = 0.4.

S, = conductor area/wire area = 0.855, #20 AWG S2 = wound area/usable window area = 0.61 83 = usable window area/window area - 0.75 S4 = usable window area/usable window area + insulation = 1

Ku — S] S2 8^ S4 Ku = (0.855)(0.61)(0.75)(1.0) = 0.391« 0.4 Being a very conservative number, it can be used in most designs. It is an important factor in all designs of magnetic components.

Magnet Wire Standard magnet wire is available in three different materials, as shown in Table 4-6. The most common is copper, but aluminum and silver are available. Aluminum magnet wire is one-third the weight of copper for the same size conductor and one-half the weight for the same conductivity. Aluminum magnet wire is a little more difficult to terminate, but it can be done. Silver magnet wire has the highest conductivity, easy to solder to, and weighs 20% more than copper. Table 4-6

Magnet Wire Material Properties Density

Resistivity

Weight

Resistance

Temperature

Material

Symbol

grams/cm5

uQ/cm

Factor

Factor

Coefficient

Copper Silver Aluminum

Cu

8.89

1.72

1

1

Ag Al

10.49 2.703

1.59

1.18

0.95

2.83

0.3

1.64

0.00393 0.00380 0.00410

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnet Wire, Film Insulation It is the design engineer's responsibility to ensure that the selected magnet wire, used in the design, is compatible with the environmental and design specification. The environmental specification will set the ambient temperature. The maximum operating temperature of the magnet wire is obtained by summing the maximum, ambient temperature, plus the temperature rise of the magnetic component. After the maximum temperature has been obtained then see Table 4-7 for the Temperature Class. The magnet wire insulation guide listing, in Table 4-7, is only a partial list from NEMA, Standard MW 1000. The maximum operating temperature is the, "Achilles Heel" to the magnet wire. Standard magnet wire is rated by temperature. The range is from 105°C to 220°C, as shown in Table 4-7. The insulation film of the magnet wire is on the surface of the copper wire. This insulation film is the most vulnerable to thermal overloads, so the selection of the insulation film is very critical for long life. When magnet wire is subjected to thermal overloads, or a high, ambient temperature above its rated temperature, the life of the magnet wire is greatly reduced, as shown in Figures 4-15 and 4-16. The engineer must be very careful of hot spots so as not to degrade the service life of the magnetic component. Table 4-7

Magnet Wire Insulation Guide NEMA Temperature

Insulation

Class

Type

Dielectric Constant

105°C 105°C

Polyurethane* Formvar

6.20 3.71

130°C

Polyurethane -Nylon*

MW-79-C

Standard MW 1000

MW-2-C MW-15-C MW-28-C

155°C

Polyurethane- 155

6.20 6.20

180°C

Polyester Solderable*

3.95

MW-77-C

200°C

Polyester-amid-imide

4.55

MW-35-C

220°C

Polyimide (ML)

3.90

MW-16-C

*Solderable insulations

Wire Table Table 4-8 is the wire table for AWG, 10 to 44, heavy film wire. The bare wire area is given in cm2, in column 2, and the circular mils is given in column 3 for each wire size. The equivalent resistance in microohms per centimeter (uQ/cm or 10"6 Q/cm and in wire length for each wire size. Columns 5 through 13 relate to heavy, insulated film coating. The weight of the magnet wire is found in column 13, in grams, per centimeter. Table 4-9 provides the maximum outside diameter for magnet wire with single, heavy, triple, and quad film insulation. The dimensional data is in centimeters and inches, for AWG 10 through 44.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 4-8

Wire Table Resistance Bare Area Area AWG f^Q/cm cm2(10~3) cir-mil 20°C cm2(10~3) cir-mil 1 2 4 3 5 6 32.7 55.9000 11046.00 10 52.6100 10384.00 41.4 44.5000 8798.00 11 41.6800 8226.00 12 33.0800 6529.00 52.1 35.6400 7022.00 65.6 28.3600 5610.00 13 26.2600 5184.00 14 20.8200 4109.00 82.8 22.9500 4556.00 104.3 18.3700 3624.00 15 16.5100 3260.00 16 13.0700 2581.00 131.8 14.7300 2905.00 17 10.3900 2052.00 165.8 11.6800 2323.00 18 209.5 9.3260 1857.00 8.2280 1624.00 263.9 7.5390 1490.00 19 6.5310 1289.00 20 332.3 6.0650 1197.00 5.1880 1024.00 21 812.30 418.9 4.8370 954.80 4.1160 531.4 3.8570 761.70 22 3.2430 640. 1 0 23 666.0 3.1350 620.00 2.5880 510.80 24 842.1 2.5140 497.30 2.0470 404.00 1062.0 2.0020 396.00 25 320.40 1.6230 1345.0 1.6030 316.80 26 1.2800 252.80 27 1687.0 1.3130 259.20 1.0210 201.60 28 158.80 2142.0 1.0515 207.30 0.8046 29 2664.0 0.8548 169.00 0.6470 127.70 30 100.00 3402.0 0.6785 134.50 0.5067 79.21 31 4294.0 0.5596 110.20 0.4013 32 5315.0 0.4559 90.25 64.00 0.3242 50.41 6748.0 0.3662 33 72.25 0.2554 34 8572.0 0.2863 39.69 56.25 0.2011 10849.0 0.2268 35 31.36 44.89 0.1589 36 13608.0 0.1813 36.00 25.00 0.1266 37 16801.0 0.1538 30.25 20.25 0.1026 38 16.00 21266.0 0.1207 24.01 0.0811 39 27775.0 0.0932 18.49 12.25 0.0621 14.44 40 9.61 35400.0 0.0723 0.0487 41 7.84 43405.0 0.0584 11.56 0.0397 42 54429.0 0.0456 6.25 9.00 0.0317 4.84 43 70308.0 0.0368 7.29 0.0245 44 0.0202 4.00 85072.0 0.0316 6.25

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Heavy Synthetics Turns-Per Diameter cm Inch cm Inch 7 10 9 8 10 0.2670 0.105 3.9 0.094 0.2380 4.4 1 1 0.2130 0.084 4.9 12 0.1900 0.075 5.5 13 0.1710 0.068 6.0 15 0.1530 0.060 6.8 17 0.054 0.1370 19 7.3 0.1220 0.048 8.2 21 0.1090 0.043 9.1 23 0.0980 0.039 10.2 26 0.0879 0.035 11.4 29 0.0785 0.031 12.8 32 0.0701 0.028 14.3 36 0.0632 0.025 15.8 40 0.0566 0.022 17.6 45 0.0505 0.020 19.8 50 0.0452 0.018 22.1 56 0.0409 0.016 24.4 62 0.0366 0.014 27.3 69 0.0330 0.013 30.3 77 0.0294 0.012 33.9 86 0.0267 0.011 37.5 95 0.0241 0.010 41.5 105 0.0216 0.009 46.3 118 0.0191 0.008 52.5 133 0.0170 0.007 58.8 149 0.0152 0.006 62.5 167 0.0140 0.006 71.6 182 0.0124 0.005 80.4 204 0.0109 0.004 91.6 233 0.0096 0.004 103.6 263 0.0086 0.003 115.7 294 0.0076 0.003 131.2 333 0.0069 0.003 145.8 370 0.0064 0.003 157.4 400

Turns-Per crrf Inch2 11 12 11 69 13 90 17 108 21 136 26 169 211 33 41 263 331 51 64 415 515 80 638 99 800 124 1003 156 1234 191 239 1539 300 1933 2414 374 2947 457 3680 571 702 4527 884 5703 6914 1072 8488 1316 10565 1638 13512 2095 17060 2645 21343 3309 25161 3901 4971 32062 6437 41518 53522 8298 10273 66260 13163 84901 16291 105076 18957 122272

Weight gm/cm 13 0.46800 0.37500 0.29770 0.23670 0.18790 0.14920 0.11840 0.09430 0.07474 0.05940 0.04726 0.03757 0.02965 0.02372 0.01884 0.01498 0.01185 0.00945 0.00747 0.00602 0.00472 0.00372 0.00305 0.00241 0.00189 0.00150 0.00119 0.00098 0.00077 0.00059 0.00046 0.00038 0.00030 0.00023 0.00020

Table 4-9

Dimensional Data for Film Insulated Magnetic Wire Wire Size AWG 10 II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Single-Insulation Inches Centimeters 0.1054 0.2677 0.9410 2.3901 0.2134 0.0840 0.0750 0.1905 0.1702 0.0670 0.0599 0.1521 0.0534 0.1356 0.1214 0.0478 0.0426 0. 1 082 0.0382 0.0970 0.0341 0.0866 0.0306 0.0777 0.0273 0.0693 0.0244 0.0620 0.0554 0.0218 0.0195 0.0495 0.0174 0.0442 0.0156 0.0396 0.0139 0.0353 0.0126 0.0320 0.0112 0.0284 0.0100 0.0254 0.0091 0.0231 0.0081 0.0206 0.0072 0.0183 0.0064 0.0163 0.0058 0.0147 0.0052 0.0132 0.0047 0.0119 0.0041 0.0104 0.0094 0.0037 0.0084 0.0033 0.0030 0.0076 0.0066 0.0026 0.0024 0.0061

Maximum Diameter Triple-Insulation Heavy-Insulation Centimeters Inches Centimeters Inches 0.2720 0.1084 0.2753 0.1071 0.0969 0.2461 0.0957 0.2431 0.2172 0.2202 0.0855 0.0867 0.1971 0.0765 0. 1 943 0.0776 0.1765 0.0684 0.1737 0.0695 0.1557 0.0624 0.1585 0.0613 0.1392 0.1417 0.0548 0.0558 0.0502 0.1275 0.0492 0.1250 0.0440 0.1143 0.1118 0.0450 0.1026 0.0395 0. 1 003 0.0404 0.0362 0.0919 0.0897 0.0353 0.0317 0.0805 0.0326 0.0828 0.0742 0.0284 0.0721 0.0292 0.0668 0.0255 0.0648 0.0263 0.0229 0.0582 0.0602 0.0237 0.0544 0.0206 0.0523 0.0214 0.0192 0.0488 0.0185 0.0470 0.0165 0.0419 0.0172 0.0437 0.0394 0.0155 0.0148 0.0376 0.0134 0.0340 0.0141 0.0358 0.0120 0.0305 0.0127 0.0323 0.0292 0.0274 0.0115 0.0108 0.0249 0.0105 0.0267 0.0098 0.0224 0.0241 0.0095 0.0088 0.0084 0.0198 0.0213 0.0078 0.0193 0.0070 0.0178 0.0076 0.0160 0.0175 0.0063 0.0069 0.0062 0.0157 0.0057 0.0145 0.0142 0.0051 0.0130 0.0056 0.0114 0.0127 0.0045 0.0050 0.0044 0.0102 0.0112 0.0040 0.0036 0.0091 0.0040 0.0102 0.0032 0.0037 0.0094 0.0081 0.0084 0.0074 0.0033 0.0029 0.0027 0.0076 0.0069 0.0030

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Quad-Insulation Inches Centimeters 0.1106 0.2809 0.2517 0.0991 0.0888 0.2256 0.2022 0.0796 0.1816 0.0715 0.0644 0.1636 0.0577 0.1466 0.0520 0.1321 0.0468 0.1189 0.0422 0.1072 0.0379 0.0963 0.0342 0.0869 0.0782 0.0308 0.0709 0.0279 0.2520 0.6401 0.0579 0.0228 0.0206 0.0523 0.0185 0.0470 0.0166 0.0422 0.0152 0.0386 0.0137 0.0348 0.0124 0.0315 0.0287 0.0113 0.0102 0.0259 0.0091 0.0231 0.0082 0.0208 0.0074 0.0188 0.0067 0.0170 0.0152 0.0060 0.0053 0.0135 0.0047 0.0119 0.0043 0.0109 0.0097 0.0038 0.0035 0.0089 0.0032 0.0081

20,000

10,000 52

Formvar 105°C Insulation MW15-C

o ffi

-a c W

1,000

100 100

200

300

Film Insulation Temperature, °C Figure 4-15. Thermal Endurance, for 105°C Formvar Insulation. 20,000 10,000 o ffi if

Polyimide (ML) 220°C Insulation MW16-C

8 I

w Is

1,000

100 100

200

300

Film Insulation Temperature, °C Figure 4-16. Thermal Endurance for 220°C Polyimide Insulation (ML).

Solderable Insulation Solderable insulation is a special film insulation that is used on magnet wire in low cost, high volume applications. The magnet wire, with this solderable insulation, is wrapped around the terminal or pin, as shown in Figure 4-17. Then the terminal can be dip-soldered at the prescribed temperature, without prior stripping. The ambient temperature range for this type of film insulation is 105°C to 180°C. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

There are drawbacks in using some of the solderable insulation magnet wire. Prior to using, check your application with the wire manufacturer. Some solderable film insulation is not recommended where severe overloads may occur. Some solderable film insulations are susceptible to softening, due to prolonged exposure to strong solvents, such as alcohol, acetone, and methylethy Ike tone.

Terminal Dipped Solder Connection Strain Relief Solderable Insulation

Figure 4-17. Solderable Insulation on a Dip Solder Terminal.

Bondable Magnet Wire Bondable, magnet wires are a film-coated, copper or aluminum, with an additional coating of a thermoplastic adhesive. See Figure 4-18. They are used in applications where it is desirable to have the bonding agent such as a solvent, which will hold the coil form, until it is oven-baked. Most adhesive coatings can be softened with solvents or heat. If a coil is wound with an irregular shape, held in a form, and then, raised to the appropriate temperature, the coil will retain its shape. Bondable magnet wires, have applications, such as armatures, field coils, and self-supporting coils.

Bondable Thermoplastic Adhesive Film Insulation Copper Wire

Figure 4-18. Typical Cross-Section of a Bondable Magnet Wire.

Base Film Insulation All conventional film insulations may be adhesive-coated to achieve a bondable wire. However, care should be taken in selecting wires, which are insulated with high temperature films, since the adhesive coating may not withstand the equally high temperatures. See Table 4-10. The temperatures in Table 4-10 are for reference only. It is wise to always check with the manufacturer for the latest in materials and application notes. The addition of the adhesive coating over the film insulation will result in an increase in the finished diameter, by the same magnitude, as if going from a single to a heavy insulation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 4-10

Bondable Overcoats Operating Temperature

Heat Activation Temperature

105°C

120°- 140°C

Epoxy

130°C

130°- 150°C

Polyester

130°C

130°- 150°C

Methylethylketone Acetone Methylethylketone

Nylon

155°C

180°-220°C

None

Type Polyvinyl Butryal

Solvents Activating Agents Alcohol

Bonding Methods Heat Bonding may be accomplished by the use of a temperature-controlled oven. Small components can use a controlled hot air blower to bond the wires. In either case, caution should be used, when handling the coil while it is still hot, since deformation can take place.

Resistance Bonding is a method where a current is passed through the winding to achieve the desired bonding temperature. This method generates a very even, heat distribution resulting in a good bonding throughout the winding. Many coils can be resistance-bonded at the same time. The current required for one coil, will be the same current required when many are connected in series. Just solder the coils in series, then, adjust the applied voltage, until the same current is reached. Solvent Bonding is a method where the solvent activates the bonding material. This can be done, by passing the wire through a solvent-saturated felt pad, or a light spray application. There are many activating solvents that can be used: denatured ethyl alcohol, isopropyl alcohol, methylethylketone and acetone. The solvents should always be checked on with the manufacturer for the latest in materials and application notes.

Miniature Square Magnet Wire When product miniaturization calls for more copper in a given area, MWS Microsquare film, insulated magnet wire allows design of compact coils that deliver more power in less space. See Table 4-11. Microsquare magnet wire is available in both copper and aluminum. It is also available in a range of solderable and high temperature, film insulation. A cross-section of a number 26, heavy build, microsquare magnet wire is shown in Figure 4-19.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Film Insulation Copper Wire

0.0445 cm

0.0445 cm

Figure 4-19. Cross-Section of a 26, Heavy, Microsquare Magnet Wire.

Table 4-11

Micro-Square Magnetic Wire (Nominal Dimension) Wire

Bare

Bare

Wire

Size

Width

Width

Area

AWG

cm

Inch

15 16

cm" 0.1450 0.0571 0.019614

Wire

Copper

Aluminum

Single

Heavy

Area

Resistance

Resistance

Width

Width

Q/cm 0.000144

cm

3041

Q/cm 0.0000879

cm

0.1483 0.1514

sq-mils

0.1290 0.0508

0.015228

2361

0.0001132

0.000186

0.1323 0.1354

17

0.1151 0.0453

0.011816

1832

0.0001459

0.000239

0.1184 0.1212

18

0.1024 0.0403

0.009675

1500

0.0001782

0.000293

0.1054 0.1080

19

0.0912 0.0359

0.007514

1165

0.0002294

0.000377

0.0940 0.0968

20

0.0813 0.0320

0.006153

954

0.0002802

0.000460

0.0841 0.0866

21

0.0724 0.0285

0.004786

742

0.0003602

0.000591

0.0749 0.0772

22

0.0643

0.003935

610

0.0004382

0.000719

0.0668 0.0688

23

0.0574 0.0226 0.003096

480

0.0005568

0.000914

0.0599 0.0620

24

0.0511 0.0201

0.002412

374

0.0007147

0.001173

0.0536 0.0556

25

0.0455 0.0179

0.002038

316

0.0008458

0.001388

0.0480

26

0.0404 0.0159

0.001496

232

0.0011521

0.001891

0.0427 0.0445

27

0.0361

0.0142 0.001271

197

0.0013568

0.002227

0.0389

0.0409

28

0.0320 0.0126

0.001006

156

0.0017134

0.002813

0.0348

0.0366

29

0.0287 0.0113 0.000787

122

0.0021909

0.003596

0.0312 0.0330

0.0029372

0.004822

0.0277 0.0295

30

0.0253

0.0254 0.0100 0.000587

91

0.0498

Multistrand Wire and Skin Effect Electronic equipment are now operating at higher frequencies, and the predicted efficiency is altered, since the current carried by a conductor is distributed uniformly across the conductor, cross-section only, with direct current, and at low frequencies. The flux generated by the magnet wire is shown in Figure 4-20. There is a concentration of current near the wire surface at higher frequencies, which is termed the skin effect. This is the result of magnetic flux lines that generate eddy currents in the magnet wire, as shown in Figure 4-21.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

External Flux, <j> Internal Flux, (j) Magnet Wire Current, I

Figure 4-20. Flux Distribution in a Magnet Wire.

Eddy currents setup by the internal flux, (j), field.

Magnet wire cross-section

Note: The main current shown in the center is being cancelled by the eddy currents. This forces the current to the surface, which causes surface crowding of the magnet wire.

Main current direction

Figure 4-21. Eddy Currents Generated in a Magnet Wire. Skin effect accounts for the fact that the ratio of effective, alternating current resistance to direct current is greater than unity. The magnitude of this effect, at high frequency on conductivity, magnetic permeability, and inductance is sufficient to require further evaluation of conductor size, during design. The skin depth is defined as the distance below the surface, where the current density has fallen to 1/e or 37 percent of its value at the surface.

£=

6.62

k

V7J

cm

e, is the skin depth /, is frequency in hertz K, is equal to 1 for copper When selecting the wire for high frequency, select a wire, so that the relationship between the ac resistance and the dc resistance is 1. /?„

R-de Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

i

Using this approach, select the largest wire, operating at 100 kHz.

e = -T=r k' [cm]

8 =

6.62 /100,000

(1), [cm]

8 = 0.0209, [cm] Then, the wire diameter is: £ W c = 2 ( e ) , [cm] 0^=2(0.0209), [cm] 0^=0.0418, [cm] Then, the bare wire area A w(B) is

-,

[cm2]

(3.14)(0.0418) A^B) =0.00137,

,

[cm2 ]

[cm 2 ]

A graph of skin depth, as a function of frequency, is shown in Figure 4-22. The relationship of skin depth to AWG radius is shown in Figure 4-23, where R ac /R dc =l is plotted on a graph of AWG versus frequency.

1.0 :

o.i C

0.01

0.001 IK

10K

100K

Frequency, Hz Figure 4-22. Skin Depth Versus Frequency.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

IMeg

50 40

Skin depth is more than the wire radius.

30

O

20 10

Skin depth is less than the wire radius.

0

10K 100K Frequency, Hz

IK

IMeg

Figure 4-23. AWG Versus Frequency at Which Skin Depth Equals the Radius.

To illustrate how the AWG, ac/dc resistance ratio changes with frequency, see Table 4-12.

Table 4-12

AWG ac/dc Resistance Ratio at Common Converter Frequencies 25kHz D(AWG)

8

50kHz Rac

AWG cm cm Rdc 12 0.041868 1.527 0.20309 14 0.16132 1.300 0.041868 0.12814 16 0.041868 1.136 18 0.041868 1.032 0.10178 1.001 20 0.041868 0.08085 1.000 22 0.041868 0.06422 1.000 24 0.05101 0.041868 1.000 0.04052 26 0.041868 1.000 0.041868 28 0.03219 0.041868 1.000 30 0.02557 AWG Copper, skin depth is at 20°C

200kHz

100 kHz

8 cm

Rac

8

Rac

8

Rac

Rdc

cm

Rdc

cm

Rdc

0.029606 0.029606 0.029606 0.029606 0.029606 0.029606 0.029606 0.029606 0.029606 0.029606

2.007 1.668 1.407 1.211 1.077 1.006 1.000 1.000 1.000 1.000

0.020934 0.020934 0.020934 0.020934 0.020934 0.020934 0.020934 0.020934 0.020934 0.020934

2.704 2.214 1.829 1.530 1.303 1.137 1.033 1.001 1.000 1.000

0.014802 0.014802 0.014802 0.014802 0.014802 0.014802 0.014802 0.014802 0.014802 0.014802

3.699 2.999 2.447 2.011 1.672 1.410 1.214 1.078 1.006 1.000

In Table 4-12, it can be seen that when a converter operates at 100 kHz, the largest wire that should be used is a number 26, with an ac/dc resistance ratio of 1.001.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Multistrand Litz Wire The term litz wire is extracted from the German word, meaning woven wire. Litz wire is generally defined, as a wire constructed of individually, film insulated wires, braided together in a uniform pattern of twists and length of lay. This multistrand configuration minimizes the power losses, otherwise encountered, in a solid conductor, due to the skin effect. The minimum and maximum number of strand for standard litz wire is shown in Table 4-13. Magnet wire suppliers will supply larger, twisted magnet wire on request.

Table 4-13

Standard Litz Wire AWG 30 32 34 36 38 40 41 42 43 44 45 46 47 48

Minimum Strands j 3

Maximum Strands 20 20 20 60 60 175 175 175 175 175 175 175 175 175

Approximate AWG 25 27 29 31 33 35 36 37 38 39 40 41 42 43

-> -> -5

3 -> J>

3 3 3 3 3 3 3

Approximate AWG 17.0 19.0 21.0 18.5 20.5 18.0 18.5 19.5 21.0 21.5 22.5 23.5 25.0 25.5

Specialty Wire There are a lot of new ideas out in the wire industry, if only the engineer had the time to evaluate these new concepts to build confidence and apply them.

Triple Insulated Wire Transformers designed to meet the IEC/VDE safety specification requirements for creepage and clearance must adhere to one of the following specifications: 1. VDE0805

2. IEC950

3. EN60950

4. UL1950-3e

5. CSA 950-95

The engineer must be aware that one specification does not encompass all applications. For example the IEC has specifications for office machines, data-processing equipment, electromedical equipment, appliances, and others.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Originally these IEC specifications were developed around linear 50 and 60 Hz transformers, and were not, always, conducive to optimal designs for high frequency, such as switching power transformers. The complexity of a standard, high frequency switching type transformer, designed to the IEC/VDE safety specification, is shown in Figure 4-24. In any switching transformer, coupling has the highest priority because of the leakage flux.

Wrapper Insulation Winding Area "^ ~

Bobbin Flange Secondary

Winding Area

Primary 3 Layers Insulation Minimum Positive Tape Barrier

Figure 4-24. Bobbin Cross-Section Design to Meet IEC/VDE Specifications.

The triple, insulated wire was developed to meet the above specification and eliminate the need for three layers of insulating tape between primary and secondary. Also, the triple, insulated wire eliminates the need for the creepage margin, and now, the whole bobbin can be used for winding. This wire can also be used as hook up wire, from the primary or secondary, to the circuits, without the use of sleeving or tubing.

The construction of the triple, insulated wire is shown in Figure 4-25. The temperature range for this type of wire is from 105°C to 180°C. The dimensions for triple, insulated wire are shown in Table 4-14, using a 0.002 inch coat per layer. Other thicknesses are available. The manufacturer, Rubadue Wire Company, is listed in the Reference section on page 4-34.

^v

x

Copper conductor 1st insulation layer 2nd insulation layer 3rd insulation layer

Figure 4-25. Triple, Insulated Wire Construction.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 4-14

Triple Insulated Wire (.002) Material Area

AWG 16 18 19 20 21 22 23 24 25 26 27 28 29 30 32 34 36 38

cm 2 (10~ 3 ) 13.0700 8.2280 6.5310 5.1880 4.1160 3.2430 2.5880 2.0470 1.6230 1.2800 1.0210 0.8046 0.6470 0.5067 0.3242 0.2011 0.1266 0.0811

Bare Wire Diameter Diameter inch mm 0.0508 1.2903 0.0403 1.0236 0.0359 0.9119 0.0320 0.8128 0.0285 0.7239 0.0253 0.6426 0.0226 0.5740 0.0201 0.5105 0.0179 0.4547 0.0159 0.4039 0.0142 0.3607 0.0126 0.3200 0.0113 0.2870 0.0100 0.2540 0.0080 0.2032 0.0063 0.1600 0.0050 0.1270 0.0040 0.1016

Resistance |LiQ/cm 132 166 264 332 419 531 666 842 1062 1345 1687 2142 2664 3402 5315 8572 13608 21266

With Insulation Diameter Diameter inch mm 1.5951 0.0628 1.3284 0.0523 1.2167 0.0479 1.1176 0.0440 0.0405 1.0287 0.9474 0.0373 0.0346 0.8788 0.0321 0.8153 0.7595 0.0299 0.7087 0.0279 0.0262 0.6655 0.6248 0.0246 0.0233 0.5918 0.0220 0.5588 0.0200 0.5080 0.0183 0.4648 0.0170 0.4318 0.4064 0.0160

Triple Insulated Litz High frequency litz wire, shown in Figure 4-26, is also available, triple insulated wire from manufacturers. The insulation, layers' thickness for litz wire comes in 0.002 and 0.003 inches.

1st insulation layer 2nd insulation layer 3rd insulation layer

Figure 4-26. Triple, Insulated Litz Wire.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Copper conductor Film Insulation

Polyfilar Magnetic Wire Poly or multiple strands of magnet wire, bonded together, can be used in many high frequency transformer and inductor applications. Round polyfilar magnet wire is shown in Figure 4-27, and square polyfilar is shown in Figure 28. Both can be used in place of foil in some applications. Polyfilar magnet wire can be used as a foil type winding, such as a low voltage, high current, or even a faraday shield. The polyfilar, magnet wire strip width can be easily increased or decreased, by adding, or removing wires to provide the proper strip width to fit a bobbin. It is relatively easy to wind. Polyfilar wire has complete insulation, and it does not have the sharp edge problem that could cut insulation in the way foil does. It is not recommended to wind a transformer with polyfilar magnet wire, in order to have an exact center tap, unless it is just a few turns, because of the penalty in capacitance. If the use of polyfilar is necessary, then use a magnet wire with a film insulation that has a low dielectric constant. See Table 4-7.

Bondable Thermal Adhesive Copper conductor Film Insulation

Figure 4-27. Polyfilar, Strip-Bonded, Round Magnet Wire.

Bondable Thermal Adhesive Copper conductor Film Insulation

Figure 28. Polyfilar, Strip-Bonded, Square Magnet Wire. Standard Foils The biggest advantage for using foil over magnet wire is the fill factor. The design of a high current, high frequency, dc to dc converter is common place. The main reason for going to high frequency is the reduction in size. The power transformer is the largest component in the design. When designing high frequency transformers, the design equations relate to a very small transformer. When operating transformers at high frequencies, the skin effect becomes more and more dominate, and requires the use of smaller wire. If larger wire is required, because of the required current density, then, more parallel strands of wire will have to be used (litz wire). The use of small wire has a large effect on the fill factor.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

When using foil, the gain in the fill factor is the biggest improvement over htz. To make a comparison, a litz design is shown in Figure 4-29, and a foil design is shown in Figure 4-30. In the litz design, there is a percentage of the winding area, which cannot be used for the conductors. This lost area is made up of voids, space between the wires, and the insulation film on the wire. The foil wound coil, shown in Figure 4-35 can be designed to make optimum use of the available winding area. Each turn of the foil can extend within limits, edge-to-edge of the bobbin or tube. The insulation required between layers is at a minimum, as long as the foil has been rolled to remove the sharp burr.

Winding Build

Winding Length

Figure 4-29. Layer Winding, Using Litz Magnet Wire.

Winding Build

t

Winding Length

Figure 4-30. Layer Winding, Using Foil with Insulation.

The Use of Foils Designing transformers and inductors, with foil, is a very laborious task, especially if the engineer only does it now and then. A monumental job, in itself, is finding out where to get the materials. Foil has its advantages, mainly, in high current, high frequency, and a high density environment.

The window utilization factor, K u , can be greater than 0.6, under the right conditions, without a lot of force. The standard foil materials used, by transformer engineers, are copper and aluminum. The engineer has a good selection of standard thicknesses as shown: 1.0 mil, 1.4 mil, 2.0 mil, 5.0 mil, and 10 mil

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The engineer will find other thicknesses, available, but standard thicknesses should be considered first. Be careful of using a nonstandard thickness. What you might be using could be from an overrun, and could create problems for you. Foil comes in standard widths, in inches, as shown:

0.25, 0.375, 0.50, 0.625, 0.75, 1.0, 1.25, 1.50, 2.00, 2.50, 3.00, 4.00

(inches)

Standard widths are the widths that are most readily available. There are also different styles of pre-fab foils, as shown in Figures 4-31, 4-32, and 4-33.

Cuffed Conductor

Backed Conductor

Figure 4-31. Pre-fab Foils.

p-TsSssssssss.i-3

Backed Multiple Conductor

Sandwiched Conductor

Figure 4-32. Pre-fab Foils.

Jacketed Conductor

Jacketed Multiple Conductor

Figure 4-33. Pre-fab Foils.

Although special slitting is done all the time, there is normally a minimum buy. When slitting is done, special care must be attended to, with the sharp edges, as shown in Figure 4-34. The cut edge should be Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

rolled after slitting it, at least two times, to remove the sharp burrs that could cut through the insulation. It is wise, not to use insulation between layers of less than 1 mil.

Sharp edge caused by slitting.

Figure 4-34. Foil with Sharp Edge Burrs after Slitting.

When winding transformers or inductors with foil, special care must be taken with lead finishing. One of the biggest problems about using foil is solder wicking. This wicking will puncture the insulation, resulting in a shorted turn. The normal insulation used for foil is very thin. Winding with foil, the coil is still subjected to bowing, only more so, as shown in Figure 4-7.

Foil used for winding transformers and inductors should be dead soft. There is another shortcoming about using foil, and that is, the inherit capacitance build-up, as shown in Figure 4-35.

Wrapper

nnnmrn Layer Capacitance

Figure 4-35. Foil Capacitance Equation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The capacitance build up is expressed:

'K(N-I)(MLT:)(G)} } ^ -^-f-

C = 0.0885] —^

K - Dielectric Constant

d

)I

[pfd]

MLT = Mean Length Turn

N = Number of Turns

G = Foil Width, cm

d = Layer Insulation Thickness, cm

The dielectric constant K for different materials can be found in Table 4-15.

Table 4-15

Dielectric Constants Material Kapton Mylar Kraft Paper Fish Paper Nomex

K 3.2-3.5 3-3.5 1.5-3.0 1.5-3.0 1.6-2.9

Calculating, MLT The mean length turn, (MLT), is required to calculate the winding resistance and weight for any given winding. The winding dimensions, relating to the mean length turn, (MLT), for a tube or bobbin coil are shown in Figure 4-36.

Calculating, MLT (toroid) It is very difficult to calculate the mean length turn (MLT) for a toroidal core that would satisfy all conditions. There are just too many ways to wind a toroid. If the toroid were designed to be wound by machine, then, that would require a special clearance for a wire shuttle. If the toroid were designed to be hand-wound, then, the wound, inside diameter would be different. The fabrication of a toroidal design is weighted heavily on the skill of the winder. A good approximation for a toroidal core, mean length turn, (MLT), is shown in Figure 4-37.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

F = Winding tube thickness (MLT)j, first winding (MLT), single winding (MLT)2, second winding

MLT

2F)+TiA,

MLT,

single winding

+ 7rB, first winding

MLT

C),

second winding

Figure 4-36. Dimensions, Relating to the Winding Mean Length Turn, (MLT).

Mean Length Turn (MLT) Wound Toroid Toroidal Core

}Ht

\ '

<

1

v

-" J

Toroidal Core OD 2(/// 1 )), approximation

Figure 4-37. Toroidal Mean Length Turn, (MLT), is an Approximation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Copper Resistance The dc resistance calculation of a winding requires knowing the total length, 1, of the conductor, the crosssectional area, A w , of the conductor, and the resistivity, p, of the conductor material. The value for the resistivity, p, in uQ per cm for three different conductor materials can be found in Table 4-7.

Copper Weight The weight calculation of a winding requires knowing the total length, 1, of the conductor, the crosssectional area, A w , of the conductor, and the density, A, of the conductor material. The value for the density, X, in grams per cm3 for three different conductor materials, can be found in Table 4-7. Wt=UAw,

[grams]

Electrical Insulating Materials The reliability and life span of a magnetic component depends on the stress level put upon the insulating materials. If the design or workmanship is not incorporated, then, insulation will not help you.

References B.C. Snelling, Soft Ferrites, CRC Press, Iliffe Books Ltd., 42 Russell Square, London, W.C.I, 1969. Werner Osterland, "The Influence of Wire Characteristics on the Winding Factor and Winding Method," WIRE, Coburg, Germany. Issue 97, October 1968. H. A. George, "Orthocyclic Winding of Magnet Wire Without Interleaving Materials," Insulation/Circuits, August 1976. MWS Wire Industries, "Wire Catalog," Revised June, 1992, 31200 Cedar Valley Drive, Westlake Village, CA 91362. Alpha-Core Inc. (Special Foils), 915 Pembroke Street, Bridgeport, CT 06608 Phone: (203) 335 6805.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Industrial Dielectrics West, Inc., (Special Foils), 455 East 9th Street, San Bernardino, CA 92410 Phone: (909)381 4734. Rubadue Wire Company, Inc., (Triple Insulated Wire), 5150 E. LaPalma Avenue, Suite 108, Anaheim Hills, CA 92807 Phone: (714) 693 5512, Email: www.rubaduevvire.com.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 5

Coil Winding Layer, Foil, and Toroidal

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. Documentation Requirements 3. Winding Facilities and Work Stations 4. Recommended Work Stations, Tools, and Materials 5. Removing the Enamel 6. Coil Winding Equipment 7. Winding Tension Device 8. Crossed Wires 9. Wire Breaks 10. Traveler 11. In-process Inspection 12. Recommended Winding Procedure for Layer Wound Coils 13. Tube Layer Windings 14. Recommended Winding Procedure for Bobbin Wound Coils 15. Single and Multilayer Bobbin Winding 16. Slotted Bobbins 17. Recommended Winding Procedure for Foil Wound Coils 18. Electrostatic Shield 19. Foil Wound Coils 20. Recommended Winding Procedure for Toroidal Wound Coils 21. Single and Multiple Toroidal Winding 22. Hand Shuttle 23. Marlinespike Tool 24. Woven Glass Sleeving 25. Toroid Self Lead 26. External Toroid Leads 27. Progressive or Bank Winding

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Reliability is accomplished through control of design, materials, techniques, and processes. There are many applications where reliability is supreme. Programs that demand this type of reliability are spacecraft, aircraft, missile guidance, and internal medicine. A failure in any one of these programs cannot be tolerated. Fabrication The fabrication of a Hi-Rel magnetic component, such as a transformer and/or inductor, must be controlled from ordering of the parts through final inspection. The documentation to fabricate any magnetic component must be exact in every detail. Not one detail should be left to memory or standard operating procedure. Construction Transformers and inductors should be constructed according to the latest, signed engineering drawings. A complete up-to-date bill of materials should accompany, or be a part of, the engineering drawings. Materials Only materials specified by the engineering drawing should be used in the construction of transformers and inductors. Traceability of all materials is required, including shelf-life certification for materials with limited, life expectancy.

Documentation Requirements Documentation shall contain all information necessary to fabricate and inspect flight-rated electronic equipment: physical, electrical, environmental, and process criteria. Drawing Standards All drawings shall conform to JPL, STD-00001 and ANSI Y14.5 for reproducibility. Assembly Drawing The assembly drawing provides eight major types of information: A. A detailed drawing will show the package outline, terminals or lead location, mounting, and marking. See Figure 5-1. B. The schematic diagram will show the sequence for all windings. The winding nearest the core would be W l . The next winding would be W2 and continues until the last winding. The schematic diagram will also show wire gauge, number of turns, and start and finish of each winding. See Figure 5-2. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

\

4,

^

_/ (

~"^O

"^9

1

2

Height

\ Manufacturer Part Number Serial Number

Width Length

Teflon Lead Wire 6 inches Long Type xxxx

Mounting (4) 6-32 Inserts

Figure 5-1. Typical Transformer Package Outline.

Lead Number Terminal Number Electrical Start Wl SOT #30

Wire Size, AWG Winding Number /

2T W4 100T #33

\ Number of Turns 7T

Figure 5-2. Typical Transformer Schematic Diagram.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

C. The Winding Information is shown step-by-step: Toroids A winding location, a winding type, which is continuous or progressive, a multifilar winding, insulation, wrapper, and lead wire breakout is shown in Figures 5-3 and 5-4.

Bobbins and Layer Windings A winding type that is, either layered or random, a multifilar winding, insulation, wrapper, and lead wire breakout is shown in Figure 5-5.

D. Winding instructions are required in the step-by-step approach from start to finish. These instructions would include: wrapping the core, placement of the winding on the toroid, the use of fiberglass sleeving over the start and finish lead, the number of turns, if it is layer wound, the turns per layer, the wire gauge, (AWG), including single strand or multifilar, and the required insulation. Each winding will be labeled for start and finish. See Table 5-1.

E. A complete electrical specification, is required which will include: dc resistance, winding inductance, turns ratio, magnetizing current, and the resonant frequency, and a schematic diagram of the test circuit and test equipment used.

F.

A detailed drawing is required, showing the internal construction details, such as terminations, splices, lead dressing, bonding and potting. See Figure 5-6.

G. Assembly notes are required in a step-by-step process from start to finish. After the transformer is wound and tested, then, place it in the cup, bond it, terminate the leads, and make it ready for inprocess testing. The last steps would be details on impregnating, embedment, and the final test and inspection. See Table 5-2.

H. The Parts' List will include: item number, quantity required, part number, Mil or industrial specification, nomenclature or description, material specification, and material suppliers. See Table 5-3.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

180

Start

Finish

Start

270

180

90

270

90

270

Finish First Winding, 350°

0

0

Second Winding, 180°

Third Winding, Continuous 360°+

Figure 5-3. Toroidal transformer winding locations.

Wound Ht Dacron Wrapper

Lead Identification

Part Number

Figure 5-4. Finished toroidal transformer.

Lead Identification

Wrapper Part Number

Wrapper

Figure 5-5. Layer and bobbin wounding coil assemblies.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

"X,

Table 5-1. Example of Step-by-Step Winding Instructions.

Step-by-Step Winding Instructions 1

Description Wrap the toroidal core, Item 1 , with mylar tape, Item 2. Overlap is required, Secure the end with, Item 3. See References.

2

There are 4 windings, 2 single and 1 bifilar winding. The start and finish of each winding are distributed around the core, as shown in Figure 5-3.

Step No.

3

4

5

6

7

8 9

10 11 12

References Table 5-3 Figure 5-70 Figure 5-2 Figure 5-3

(Wl ) Wind the core, Item 1 , with 50 turns of #30 AWG magnet wire, Item 4. Place the winding, as shown in Figure 5-3. Progressively wind, 350°, and label Start 1 and Finish 2. Fiberglass sleeving, Item 7, will be used to cover the Start and Finish leads.

Figure 5-2 Figure 5-3 Table 5-3

Perform the required electrical test. (W2, W3) Wind bifilar the core, Item 1, with 10 turns of #33 AWG magnet wire, Item 5. Place the winding, as shown in Figure 5-2 and Figure 5-3. Wind progressively, 180°, and label Strand 1 as Start 3 and Finish 4. Label Strand 2 as Start 5 and Finish 6. Fiberglass sleeving, Item 7, will be used to cover the start and finish leads.

Assembly Drawing Table 5-3 Figure 5-2 Figure 5-3

Perform the required electrical test. (W4) Wind the core, Item 1 , with 100 turns of #33 AWG magnet wire, Item 5. Place the winding as shown in Figure 5-3. Wind continuously 360°+ and label as Start 6 and Finish 7. Fiberglass sleeving, Item 7, will be used to cover the start and finish leads.

Assembly Drawing Figure 5-2 Figure 5-3 Table 5-3

Perform the required electrical test. Peripheral wrap, with mylar tape, Item 3. Dress the magnet wire leads to appropriate lead breakout locations. See Figure 5-4.

Assembly Drawing Table 5-3 Figure 5-4

Wind the Dacron insulating tape, Item 6, 360°, progressively around the core, and secure the end with item 3. Coil is ready for final assembly.

Figure 5-4 Figure 5-6 Fiberglass Enclosure Bifurcated Terminals

(4) Spot Bonding

Fastener Tube

Dacron, Covered Toroid (5) Teflon Leads, 6 Inches Long

Figure 5-6. Transformer Top View of Assembly showing the Internal Construction. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 5-2. Example of a Step-by-Step Assembly Procedure.

Step-by-Step Assembly Step No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Description Remarks Check potting Cup, Part Number. Check potting cup (QA) approval. Check finished winding, magnet component, test data. Spot bond, terminal board in potting cup, using Stycast 1095. Mix-Sample Spot bond, magnetic component in position, using Stycast 1095. Inspection (QA). Cure Stycast 1095. Dress the leads of the magnetic component, as shown in the assembly drawing. Attach leads from the magnetic component to the terminals. Install and attach the external, teflon leads to the terminals. Solder all connections. Inspection (QA). Do final test before potting. Preheat magnet assembly for 3 hours at 70°C. (Bake out the moisture.) Fill the magnetic assembly with vacuum-degassed, impregnating material. When the magnetic assembly is completely covered with impregnating material, then, vacuum the Mix-Sample complete assembly. After vacuuming the impregnation, pour out the remaining impregnating material. Fill the magnetic assembly with vacuum-degassed embedment material. When the magnetic assembly is completely covered with the embedment material, then, vacuum Mix-Sample the complete assembly. Cure the embedment for 16 to 20 hours, at 94°C. Perform a final electrical test and visual inspection. Place in Bonded Stores

Table 5-3. Typical Parts List.

Parts' List Ll Drawing Number 0001234 Item Qty Part Specification No. Reqd Number 1 1 55059-A2 2 AR MH-I-G31 3 AR No. 1298 4 AR #30 AWG ST12281-30 5 AR #33 AWG ST12281-33 6 AR 7500 7 AR No. 24 SI 600 8 280 AR 9 AR 281 10 AR QQ-S-571 11 AR Mil-W-22759 12 1 1234

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Nomenclature or Description Molypermalloy Powder Core Tape Mylar Film Non-Adhesive 1 mil Tape Mylar Film Adhesive 3 mil Magnet Wire Solderable 155°C Magnet Wire Solderable 155°C Tape Dacron (3/8 inch, 5 m i l ) Flexible Fiberglass Sleeving Epoxy Impregnant Epoxy Embedment Solder, Type SN63 Stranded Wire, 26 AWG, Teflon Fiberglass Cup

Page 1 Material Specification Powder Mylar MW-80-C MW-80-C Fiberglass Epoxy Filled-Epoxy SN63, Type R Clear G10

Material Supplier Magnetics Dupont 3M MWS MWS Fralock Varflex Scotchcast Scotchcast Kester Dorco

Winding Facilities and Work Stations The winding work areas and workbenches should be maintained in a clean, well-ventilated, orderly manner, and have lighting which is adequate for the necessary detail of the required operations. The work area must be cleaned with alcohol dampened Kimwipes, each day, prior to starting a job. There should be no smoking, eating, or drinking permitted within three meters (ten foot) radius. Prior to handling parts and/or materials, the operator should thoroughly clean his or her hands. The use of any hand lotion is forbidden. Anyone working with or handling parts and/or materials must wear clean gloves and/or finger cots. Gloves must be changed when they show signs of contamination, and finger cots must be replaced, when they are torn or contaminated.

Recommended Work Stations, Tools, and Materials The following tools are required for lead attachment, soldering, anchoring, and cutting insulating tape. 1.

Needle nose pliers (non-serrated)

2.

Tweezers, (fine point)

3.

Cutters, (full flush cut)

4.

Scissors

5.

Orange stick

6.

Wire scrapers

7.

Gloves

8.

3-5X magnification with light.

9.

Dial or vernier calipers

10. Ruler 11. Soldering iron (temperature controlled) 12. Alcohol burner The following materials are required as an aid in the lead attachment, soldering, anchoring, and cleaning. Only those materials that are, "Program Approved," should be allowed in the work area. All materials in the work area are required to have traceability data. 1.

Solder, type S/N 60 or 63

2.

Alcohol, Isopropyl grade A

3.

Liquid flux conforming to Mil-F-14256

4.

Sandpaper (emery), 220, 280, 320 grit

5.

Kimwipes

6.

Cotton swabs

7.

Acid brushes (cleaning)

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Removing the Enamel

Magnet Wire Stripping, (See Chapter 6) The enamel on magnet wire can be stripped in many ways: 1. Solder pot can be used for tinning when special solderable insulations are used. 2. Abrasive, fiberglass wheels are used to perform the stripping. 3. The removal of enamel insulation can be done with flame by charring the enamel, then, using an emery paper to clean. 4. Chemicals are used for stripping enamel wire. They are very toxic and cumbersome to use and are not recommended for use in space, unless tightly controlled. See Figure 5-7.

Solder Pot

Abrasives

Flame

Chemical

Figure 5-7. Methods Used to Remove Enamel from Magnet Wire.

Chemical Wire Stripping To strip insulation from magnet wire by the use of chemicals, a step-by-step procedure must be submitted and approved, before starting. Stripping insulation, with the use of chemicals, will only be approved if there is not another way.

Coil Winding Equipment Coil winding equipment used for the fabrication of magnetic items should have inspection records for both layer type and toroidal type winding machines. Winding equipment controls, settings, and set-up records should be permanently documented for that machine. Records should be available to the operator prior to placing the winding on a core, tube or bobbin. The coil winding machines shall have a complete, seethrough, dust cover. Layer and Bobbin Winders Layer and bobbin winders should have, at least, a pre-set counter and a wire dereeler, capable of tension adjustment. A simple tube and bobbin winder is shown in Figure 5-8. Toroidal Winders The shuttle rings and slider on the toroidal winding machine must be inspected prior to winding. This inspection will look for nicks, burrs and rough spots. After each winding the toroid will be inspected in place for nick and scrapes. Toroidal winders will have a pre-set counter. A simple toroidal winder is shown in Figure 5-9.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Counter Reset

Counter Set

Bobbin

Hand Friction Wheel

Platform

Wire Direction

Figure 5-8. Simple Tube and Bobbin, Manually Operated Winder.

Shuttle Slider

Toroidal Core Shuttle Drive

Platform

Control Switches

Speed Control

Foot Peddle Speed Control Figure 5-9. Simple Toroidal, Manually Operated Winder.

Winding Tension Device Magnet wire is supplied on spools and reels. The spool size will depend on the wire size and the quantity ordered. As the winding machine is using the wire, the reels are subjected to starts, stops and speed changes. This non-linear action puts stress on the magnet wire. This excessive tension on magnet wire, during the winding process, will result in damage to the insulation, and increased resistance to the finished coil, due to stretching the wire. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The winding tension device is normally a compensating, mechanical arm with an adjustable spring, which maintains proper tension on the wire, independent of its linear velocity through a system of pulleys, lever arms, and breaks. Winding tension devices must be adjusted and calibrated to the proper wire gauge.

There are basically two types of tension devices. Each tension device has advantages over the other in their application. The tension device, shown in Figure 5-10, allows the wire to be extracted from the spool at almost any speed. The wire supply spool sits on a platform and remains stationary inside a shielded cone.

Wire Guide Spring Tension Adjustment

Shield

Wire Spool Platform

Figure 5-10. Twist Type De-Spooler and Tension Device. The wire is wound completely around the wire guide whose resistance to turning is controlled by the tension of the spring on the wire guide. This pressure can be varied by means of an adjustable screw. It should be noted, in this type of de-spooling, there should be one twist to the wire for each turn of wire that is removed from the spool. This is because the spool is stationary. There is an, "Anti-Kink Disk," accessory, shown in Figure 5-11, that is used along with the twist type, tension devices. When the anti-kink disk is placed on top of the spool of wire, as shown, it will prevent the wire from dropping off the spool, and becoming entangled. This entanglement could lead to kinking and breaking of the fine wire. This anti-kink disk is available for a wide range of wire sizes and spool sizes.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Anti-Kink Disk

Magnet Wire Spool

Figure 5-11. Anti-Kink Disk.

The demand type of tension device is shown in Figure 5-12. The demand type is dependent on winding speed and spool weight. The wire spool turns during the winding process. The wire runs over the freeturning wire guide, which is mounted at the end of the lever arm to obtain mechanical advantage over the spring-loaded friction device. The lever arm causes a delay action in releasing the spool, thus providing a constant amount of tension. When the winding demand goes to zero, the spool will stop automatically.

Wire Guide Magnet Wire

Friction Device

Wire Spool Tension Adjustment Tension Spring

Figure 5-12. Demand Type, Tension Device.

It is always advisable to check the calibration of the tension device before its use. The biggest problem that is encountered is stretching, and distorting, which results in producing the wrong resistance. The nominal and maximum tension range for magnet wire, both copper and aluminum, is shown in Table 5-4. The material properties for copper and aluminum magnet wire are shown in Table 5-5.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 5-4

Machine Winding Tension Table AWG Size 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Copper Nominal Maximum Tension Tension 103 Ib 61.5 Ib 81.4 48.9 64.5 38.7 51.2 30.7 40.5 24.3 32.2 19.3 25.5 15.3 20.2 12.1 16.1 9.7 12.8 7.7 10.1 6.0 8.0 4.8 6.3 3.8 5.0 3.0 4.0 2.4 3.2 1.9 2.5 1.5 2.0 1.21b 1.6 430 gm 1.3 340 1.0 270 360 gm 220 280 170 220 130 180 110 140 84 110 68 87 51 69 40 56 32 45 25 35 20 29 17

Aluminum Nominal Maximum Tension Tension 30.8 Ib 20.5 Ib 16.3 24.4 19.4 12.9 15.4 10.2 8.1 12.2 6.4 9.7 7.7 5.1 4.0 6.1 3.2 4.8 2.6 3.8 2.0 3.0 2.4 1.6 1.3 1.9 1.0 1.5 1.2 360 gm 290 430 gm 230 340 180 270 140 210

Table 5-5

Magnet Wire Material Properties Density Material Copper Aluminum

Symbol Cu Al

grams/cm 8.89 2.703

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Resistivity uQ/cm 1.72 2.83

Weight Factor 1 0.3

Resistance Factor 1 1.64

Temperature Coefficient 0.00393 0.0041

There is a relatively simple way to check the wire tension, by using a calibrated spring scale, as shown in Figure 5-13. When the tension device is setup with the correct spool of wire, and the wire has been laced through all the rollers and guides, then pull the wire tight via one end of the scale until the wire spool starts to turn or rotate. Then use the tension adjustment screw to adjust for the proper force. Next, take a reading on the spring scale. That will be the force, either in pounds or grams. Also, there are wire tension devices available with built-in scales for calibration.

Wire Guide

Wire Spool Tension Adjustment Tension Spring Force

Figure 5-13. Simple, Wire Tension Test. Crossed Wires Winding shall be even and smooth. In the insulated, interleaved layer-wound coils, no uninsulated turn shall cross over other turns. In toroidal and cylindrical, or random wound bobbin coils wound in segments, there shall be no uninsulated crossover of any one turn to the adjacent winding segment. All situations, where the voltage stress exceeds the ability of the magnet wire insulation to withstand it, shall be avoided.

Wire Breaks There shall be no wire breaks for any winding within the coil. The winding operation can be considered complete, only when the coil has been made with an unbroken winding. Should the magnet wire break during winding operation, the magnet wire may be unwound and rewound. In no case may a broken coil wire be repaired. If magnet wire opens after assembly, the entire device shall be rejected. Those devices, that are as multi-series, connected windings, are not to be identified as wire breaks within the definition of the paragraph.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Traveler A lot traveler, specifying each operation in the sequence, shall be provided with each lot. The initialing or stamping of the individual traveler, by the operator or inspector, prior to moving to the next work station shall be required for each operation in the manufacturing process. A sample traveler card is shown in Figure 5-14a and 5-14b.

In-process Inspection All critical, in-process operations, used in the manufacturing of these devices, shall be inspected by an adequately, trained inspector. If circumstances preclude inspections, after the process is complete, the inspection shall occur during the process. These inspection stations shall be defined in the manufacturing process.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Traveler-Transformers, Inductors and Coil Assemblies (Front) Program Machine Specification No.

Assembly No. Drawing No. & Rev. Serial No. Part Number

Material

IR/PAT

Type

Tech

Date

QA

Date

Core Bobbin/Tube Wire Hook Up Tape Adhesive Tape Cloth Poly Shielding Banding Strap Seal Strap Air Gap Material Mylar Housing Terminal Board Sleeving

Figure 5-14a. A Sample Front Page of a Traveler Card.

Traveler- Transformers, Inductors and Coil Assemblies (Back) Winding Number

Wire AWG

Turns

IR/PAT

1 2 3 4 5 6 7 8 9 10 Inspection Prior to Solding Solder Wires and Inspect Electrical Test Encapsulation Serial No. Marking Part No. Assembly No. A. Magnetizing Current Test to Perform

*Test

Tech.

B. Turns Ratio

Date

Date

C. See Winding Specification

Figure 5-14b. A Sample Back Page of a Traveler Card. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

QA

Recommended Winding Procedure for

Layer Wound Coils

Note 1: Minimize The Use of Mylar Tape There are two good reasons why the use of Mylar tapes of any kind should be kept to a minimum. First, since Mylar is not porous, impregnation must go around. If the tape is wound too tightly, there may be an air trap within the transformer. Secondly epoxies do not bond well to Mylar. An incipient, fracture plane is produced in the impregnation.

Note 2: Woven Glass Sleeving It has been found that the use of woven glass sleeving over the magnet wire improves the reliability. This sleeving is not merely slipped on after the unit is wound. It is actually placed over the lead as soon as the lead is brought out. The sleeving serves several purposes: it helps take the stress off the lead, it prevents sharp bending, and it prevents abrasions of the insulation. See Figure 5-16.

Note 3: Parallel Winding A parallel winding is a winding of two or more wires wound simultaneously and adjacent with each turn, consisting of the specified number of wires. The parallel wires are joined at the ends to form a single conductor winding.

Note 4: Bifilar and Multifilar Winding A bifilar or a multifilar winding is a winding of two or more wires, as in a parallel winding, except the wires are not connected. The wires could be left unconnected resulting in two separate windings, or connected in a series, and parallel, to form a single multifilar, center-tapped winding.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tube Layer Windings Start Leads Anchor Tapes Anchor tapes for start leads are shown on tube type windings. See Figure 5-15. Start Leads with Woven Glass Sleeving Starting leads are shown using woven glass sleeving. See Figure 5-16.

Cut 0.375 inch Magnet Wire Fold Back

Winding Start

t

Locking tape to be used on 27 AWG and larger. Figure 5-15. Layer Winding Start Lead Using Tape. Loose Pigtail for Ease of Anchoring

Anchor Tape

Woven Glass Sleeving Magnet Wire Winding Start Figure 5-16. Layer Winding Start Lead Using Woven Glass Sleeving. Start Lead Using Tape Applying the start lead, using tape, is shown in Figure 5-17, 5-18, and 5-19. Adhesive Side

^—^_

, _ Anchor 1 ape

Winding Tube Winding Start Figure 5-17. Step 1, for the Start Lead, Using Tape. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tape Folded Back

Anchor Tape

Magnet Wire

Winding Tube Winding Start Figure 5-18. Step 2, for the Start Lead, for Folding the Anchor Tape.

Anchor Tape

Winding Tube Winding Start Figure 5-19. Step 3, for the Start for Lead, Locking the Anchor Tape. Start Lead for Using Woven Glass Sleeving Applying the start lead, using woven glass sleeving, is shown in Figure 5-20, 5-21, and 5-22.

Anchor Tape 1 Magnet Wire

Anchor Tape 2 Adhesive Side ^•B.

Woven Glass Sleeving

Winding Tube Winding Start Figure 5-20. Step 1, for the Start Lead, Using Woven Glass Sleeving. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Anchor Tape 1 Anchor Tape 2

Magnet Wire Woven Glass Sleeving

Winding Tube Winding Start Figure 5-21. Step 2, for the Start Lead, for Folding the Anchor Tape. Magnet Wire

Wind Over Tape

Woven Glass Sleeving

\ Winding Tube Winding Start Figure 5-22. Step 3, for the Start Lead, for Locking the Anchor Tape. Interlayer Insulation Interlayer Insulation shall be held in place with an approved tape and meet the requirements of the assembly drawing, as shown in Figure 5-23 for tape, and Figure 5-24 for woven glass sleeving.

Magnet Wire

Winding Tube Layer Insulation Figure 5-23. Step 1, Applying the Interlayer Insulation and Taping. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Woven Glass Sleeving Magnet Wire

Winding Tube Layer Insulation

Figure 5-24. Step 2, Applying the Interlayer Insulation and Taping.

Tap Leads Using Tape Tap leads in a tube windings shall be insulated from the windings, using an approved tape. Tape over and under the tap lead, as shown in Figures 5-25, 5-26, and 5-27.

Tap Leads Using Woven Glass Sleeving Tap leads in a tube windings shall be insulated from the windings using an approved tape. Tape over and under the sleeving, as shown in Figures 5-28, 5-29, and 5-30.

Adhesive Side of Tape Winding Tap Adhesive Side of Tape

Winding Start

Layer Insulation

Figure 5-25. Tap Lead Using Tape: Step 1, Showing the Exploded View.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Tap

Adhesive Side of Tape

Winding Start

Layer Insulation Figure 5-26. Tap Lead Using Tape: Step 2, Showing the Compressed View.

Tap in Position Winding Start

A/r +w Winding Tap Magnet Wire . Layer Insulation Figure 5-27. Tap Lead Using Tape: Step 3, Showing the Tap Lead in Place.

Woven Glass Sleeving Adhesive Side of Tape Winding Tap Adhesive Side of Tape

Winding Start

Layer Insulation Figure 5-28. Tap Lead: Step 1, Showing the Exploded View, Using Sleeving.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Woven Glass Sleeving

Adhesive Side of Tape

Winding Tap Winding Start

Layer Insulation Figure 5-29. Tap Lead: Step 2, Showing the Compressed View, Using Sleeving. Tap in Position

Winding Start Magnet Wire Winding Tap

Layer Insulation

Woven Glass Sleeving

Figure 5-30. Tap Lead: Step 3, Showing the Tap Lead in Place, Using Sleeving. Crossover Tap Leads Using Tape Tap leads in layer windings shall be insulated from the windings, using an approved tape. Tape over and under the tap lead, as shown in Figure 5-31. Crossover Tap Leads Using Woven Glass Sleeving Tap leads in tube windings shall be insulated from the windings, using an approved tape. Tape over and under the sleeving, as shown in Figure 5-32. Tap in Position

•X

Winding Tap

Approved Tape Winding Start

X Magnet Wire Layer Insulation Figure 5-31. Tap Lead Crossing Over a Winding. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tap in Position

X

Winding Tap

Woven Glass Sleeving Winding Start Magnet Wire Layer Insulation Figure 5-32. Tap Lead Crossing Over a Winding, Using Sleeving. Parallel and Bifilar Windings The start of a parallel winding shall be treated as a single magnet wire. The start of a bifilar winding shall be treated as a separate magnet wire. Parallel wires can be brought out together. Bifilar wires have to be brought out separately. Multifilar windings can be brought out with a combination of both. Parallel and bifilar windings shall be wound during fabrication, as shown in Figures 5-33, 5-34, 5-35, and 5-36.

Fold Anchor Tape Winding Start Magnet Wire

Parallel and Bifilar Windings Winding Tube Figure 5-33. Start Lead Positioning for Parallel and Bifilar Windings, Using Tape.

Fold Anchor Tape

Woven Glass Sleeving Winding Start Magnet Wire

Parallel and Bifilar Windings Winding Tube Figure 5-34. Start Lead Positioning for Parallel and Bifilar Windings, Using Sleeving. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Crossovers There will be no crossovers in bifilar or multifilar windings, as shown in Figures 5-35 and 5-36.

Approved Tape Winding Start Parallel and Bifilar Windings Magnet Wire Winding Tube

There will be no crossovers in the winding.

Figure 5-35. Parallel and Bifilar Windings Shall Not Have Crossovers, Using Tape.

V/oven Glass Sleeving Winding Start Magnet Wire

Parallel and Bifilar Windings Winding Tube

There will be no crossovers in the winding.

Figure 5-36. Parallel and Bifilar Windings Shall Not Have Crossovers, Using Sleeving.

Wrapper Insulation The wrapper insulation will be the same width as the interlayer insulation, as shown in Figure 5-37. The anchor tape will secure the wrapper.

Completed Coil Figure 5-37 shows a view of a finished layer, wound coil ready for the next assembly procedure. Note A: Any of the leads closer than 0.09 inches, or 0.23 cm to the inside of the coil, shall be insulated by tape, or if approved, by woven glass sleeving.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Wrapper Support Tapes

Winding Tube Woven Glass Sleeving

Magnet Wire

Note A

Figure 5-37. Completed Layer, Wound Coil Assembly.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Recommended Winding Procedure for

Bobbin Wound Coils Note 1: Minimize The Use of Mylar Tape There are two good reasons why the use of Mylar tapes of any kind should be kept to a minimum. First, since Mylar is not porous, impregnation must go around it, and if the tape is wound too tightly, there may be an air trap within the transformer. Secondly, if epoxies do not bond well to Mylar, an incipient fracture plane is produced in the impregnation.

Note 2: Woven Glass Sleeving It has been found that the use of woven glass sleeving over the magnet wire improves the reliability. This sleeving is not merely slipped on after the unit is wound. It is actually placed over the lead as soon as the lead is brought out. The sleeving serves several purposes: it helps take the stress off the lead, it prevents sharp bending, and it prevents abrasions of the insulation. See Figure 5-16.

Note 3: Parallel Winding A parallel winding is a winding of two or more wires wound simultaneously and adjacent with each turn consisting of the specified number of wires. The parallel wires are joined at the ends to form a single conductor winding.

Note 4: Bifilar and Multifilar Winding A bifilar or a multifilar winding is a winding of two or more wires, as in a parallel winding, except the wires are not connected. The wires could be left unconnected resulting in two separate windings or connected in a series and parallel to form single multifilar, center-tapped winding.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Single and Multilayer Bobbin Winding Single and multilayer bobbin windings shall be fabricated, as follows: Start Lead Non-Slot Bobbins (Step 1 of 2) The start lead should be attached using the support tape, as shown in Figure 5-38.

Support Tape 1

Bobbin

Magnet Wire

Figure 5-38. Secure Start Lead on a Non-Slot Bobbin. Start Lead Non-Slot Bobbins (Step 2 of 2) Place the anchor tape over the support tape and continue winding as shown in Figure 5-39.

Support Tape 1 Anchoring Tape 1 Magnet Wire

Figure 5-39. Start Lead on a Non-Slot Bobbin. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Bobbin

Interlayer Insulation (Step 1 of 2) Bobbin mterlayer insulation shall be held in place with an approved tape, and meet the requirements of the assembly drawing, as shown in Figure 5-40.

Start — Bobbin

Support Tape 1 Anchor Tape Interlayer Insulation

Magnet Wire

Figure 5-40. Applying the Interlayer, Insulation and Taping. Interlayer Insulation (Step 2 of 2) The interlayer insulation should be wrapped around the winding and overlap the interlayer insulation start. The anchor tape can be removed after the interlayer insulation has been secured with the winding-, as shown in Figure 5-41.

Tape

Start Support Tape 1

Bobbin Interlayer Insulation

Magnet Wire

Figure 5-41. Securing the Interlayer Insulation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Tap (Step 1 of 2) The winding tap is placed on the bobbin, as shown in Figure 5-42.

Self Tap Start Bobbin

Support Tape 1

Magnet Wire

Figure 5-42. Positioning Winding Tap.

Winding Tap (Step 2 of 2) The support and anchor tape is placed on the self tap lead, as shown in Figure 5-43.

Self Tap Start Support Tape 1 Anchoring Tape 2

Magnet Wire Bobbin

Figure 5-43. Winding Tap with Anchor Tape.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Tap with Over-Wind (Step 1 of 3) The winding tap is positioned on the bobbin, as shown in Figure 5-44.

Tap

Start Support Tape 1 Interlayer Insulation

Bobbin

Magnet Wire

Figure 5-44. Positioning the Over-Wind Tap.

Winding Tap with Over-Wind (Step 2 of 3) The winding tap is insulated and supported with tape 2, as shown in Figure 5-45.

Tap Start Support Tape 1

Support and Insulating Tape 2

Interlayer Insulation Magnet Wire

Figure 5-45. Over-Wind Tap with Insulating Tape.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Bobbin

Winding Tap with Over-Wind (Step 3 of 3) The winding tap is placed on the bobbin, as shown in Figure 5-46.

Tap

Start Support Tape 1

Support and Insulating Tape 2

Bobbin Magnet Wire Interlayer Insulation

Figure 5-46. Over-Winding Tap Insulation.

Winding Tap with Opposite End Exiting (Step 1 of 3) The winding tap is positioned on the bobbin, as shown in Figure 5-47.

Second Tap Support and Insulating Tape Magnet Wire

Start

Interlayer Insulation

Figure 5-47. Positioning the Opposite End Tap.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Tap with Opposite End Exiting (Step 2 of 3) The winding tap with applied support tape, is shown in Figure 5-48.

Support Tape Support and Insulating Tape Magnet Wire

Start

Interlayer Insulation

Figure 5-48. Insulating Winding Tap.

Winding; Tap with Opposite End Exiting (Step 3 of 3) Insulating the winding tap and then continuing the winding is shown in Figure 5-49.

Second Tap Support and Insulating Tape

Magnet Wire Support and Insulating Tape Start

Figure 5-49. Tap Winding Continues After Insulating Tape.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Finish Lead (Step 1 of 2) Position the finish lead, then, use the support and insulating tape, as shown in Figure 5-50.

Finish

Tap Start Support and Insulating Tape

Support and Insulating Tape

Bobbin

Figure 5-50. Positioning the Finish Lead.

Finish Lead Exiting Opposite End (Step 2 of 2) Apply the support tape and insulating tape, as shown in Figure 5-51.

Tap Start Support and Insulating Tape

Support and Insulating Tape 2

Finish

Bobbin

Figure 5-51. Exiting the Finish Lead at Opposite End.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Crossovers There will be no crossovers in the windings, as shown in Figure 5-52.

Support and Insulating Tape Support and Insulating Tape

Wind Without Crossovers Bobbin

Figure 5-52. Layer Windings Shall Not Have Crossovers.

Slotted Bobbins Bobbins, with slots in the end plates, shall have the lead wires sleeved with woven glass sleeving, as shown in Figure 5-53.

Start Woven Glass Sleeving Magnet Wire

Bobbin

Figure 5-53. Start Lead on a Slotted Bobbin, Using Woven Glass Sleeving.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Slotted Bobbins (Step 1 of 6) Bobbins, with slots in the end plates, shall have the start lead wires sleeved with woven glass sleeving, as shown in Figure 5-54.

Start — Woven Glass Sleeving

Slots

Sleeving Pigtail Magnet Wire

Bobbin

Figure 5-54. Slotted Bobbin with Sleeved Start Lead.

Finish Lead (Step 2 of 6) Position the finish lead at the slot, as shown in Figure 5-55.

Slots Sleeving Pigtail Woven Glass Sleeving

Bobbin

Figure 5-55. Slotted Bobbin with Sleeved Finish Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Finish Lead (Step 3 of 6) Position the finish lead, then use anchor tape, as shown in Figure 5-56.

Woven Glass Sleeving

Bobbin

Figure 5-56. Slotted Bobbin, Anchoring the Finish Lead.

Interlayer Insulation (Step 4 of 6) Bobbin interlayer insulation shall be held in place with an approved tape, and meet the requirements of the assembly drawing, as shown in Figure 5-57.

Start — Woven Glass Sleeving

Bobbin

Anchor Tape Interlayer Insulation

Magnet Wire

Figure 5-57. Applying the Interlayer Insulation and Taping.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Slotted Bobbins with Tap Leads (Step 5 of 6) Slotted bobbins, with tap leads using woven glass sleeving, shall be installed, as shown in Figure 5-58.

Start Woven Glass Sleeving

Tape on Both Sides of Sleeving Bobbin

Interlayer Insulation Magnet Wire

Figure 5-58. Insulating the Tap Lead with Woven Glass sleeving.

Slotted Bobbins with Interim Leads (Step 6 of 6) Slotted bobbins, with interim leads using woven glass sleeving and shrink tubing, shall be installed, as shown in Figure 5-59.

Slots

Interim Lead

Shrink Tubing Interim Lead

Magnet Wire

Bobbin Wrapper

Figure 5-59. Slotted bobbins, with interim leads.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Recommended Winding Procedure for

Foil Wound Coils Note 1: Minimize The Use of Mylar Tape There are two good reasons why the use ol Mylar tapes of any kind should be kept to a minimum. First, since Mylar is not porous, impregnation must go around and if the tape is wound too tightly, there may be an air trap within the transformer. Secondly, epoxies do not bond well to Mylar. An incipient fracture plane is produced in the impregnation. Note 2: Woven Glass Sleeving It has been found that the use of woven glass sleeving over the magnet wire improves the reliability. This sleeving is not merely slipped on after the unit is wound; it is actually placed over the lead as soon as the lead is brought out. The sleeving serves several purposes: it helps take the stress off the lead, it prevents sharp bending, and it prevents abrasions of the insulation. See Figure 5-16.

Note 3: Parallel Winding A parallel winding is a winding of two or more wires wound simultaneously and adjacent with each turn consisting of the specified number of wires. The parallel wires are joined at the ends to form a single conductor winding.

Note 4: Bifilar and Multifilar Winding A bifilar or a multifilar winding is a winding of two or more wires, as in a parallel winding, except the wires are not connected. The wires could be left unconnected resulting in two separate windings or connected in series and parallel to form single multifilar center-tapped winding.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Electrostatic Shield Foil Material Foil shall be inspected to be sure there are no slitting burrs, as shown in Figure 5-60.

Foil

Foil with sharp edge after slitting

Foil sharp edge removed after rolling

Figure 5-60. Copper Foil with the Burr Removed After Rolling. Exiting Leads All exiting leads, starts, taps, and finishes will be sweat-soldered to the foil. The exiting lead or foil will make contact to, at least, 70 to 80% of the copper foil. There will be no solder-wicking at the solder joint, as shown in Figure 5-61.

Exiting Lead Copper Foil

Sweat Solder Copper Foil

Exiting Foil

Sweat Solder

Figure 5-61. Attaching the Lead to the Copper Foil. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Electrostatic Shield (Faraday Shield) The electrostatic shield (copper foil) must cover the complete winding. There shall be insulation material to cover both sides of the electrostatic shield. There shall be insulating material to overlap the start of the electrostatic shield. The lead that is soldered to the electrostatic shield must be soldered to the center or at an equal distance from each end. The application of the electrostatic shield is shown in Figure 5-62 for the bobbin, and Figure 5-63, for the tube layer, winding type.

Finish Tap

Final Wrapper Insulation

Start

Electrostatic Shield

Shield Anchoring Tape

Wrapper Insulation

Overlap Insulating Material Bobbin Electrostatic Shield Lead is Attached to the Center of the Copper Foil. Electrostatic Shield (Copper Foil)

Figure 5-62. Bobbin Winding, with an Electrostatic Shield.

Final Wrapper Insulation Anchor Tape Overlap Insulation Copper Foil

Winding Tube Electrostatic Shield (Copper Foil) The Electrostatic Shield Lead is Attached to the Center of the Foil.

Figure 5-63. Tube Winding, with an Electrostatic Shield.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Foil Wound Coils Start Lead (Step 1 of 5) The anchor tape shall overlap the start lead completely, as shown in Figure 5-64.

Anchor Tape Shall Overlap Start Lead Anchor Tape

Start Lead

Copper Foil Winding Tube

Figure 5-64. Anchor Tape Overlaps the Start Lead.

Interlayer Insulation (Step 2 of 5) The anchor tape for the insulation shall not overlap the foil, as shown in Figure 5-65. The interlayer insulation shall overlap the edge of the foil, but not extend beyond, the edge of the winding tube. The end view of Figure 5-65 is shown in Figure 5-66.

Exiting Lead Interlayer Insulation

Anchor Tape for Insulation

Foil

Winding Tube

Figure 5-65. Attaching the Lead to the Copper Foil.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Anchor Tape for Insulation

Interlayer Insulation J ^~

Exiting Lead

Foil

Anchor Tape for Foil Winding Tube

Figure 5-66. End View of Figure 5-65.

Tap Lead (Step 3 of 5) The anchor tape shall overlap the tap lead completely, as shown in Figure 5-67. Before the application of the anchor tape, the exiting lead will be inspected for solder wicking or sharp points at the surface solder joint.

Start Lead Interlayer Insulation

Winding Tube

Figure 5-67. The Anchor Tape Overlaps the Tap Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Finish Lead (Step 4 of 5) The anchor tape shall overlap the finish lead completely, as shown in Figure 5-68. Before the application of the anchor tape, the exiting lead will be inspected for solder wicking or sharp points at the surface solder joint.

Finish Lead

Interlayer Insulation

Winding Tube

Anchor T ipe for the Finish Lead

Figure 5-68. The Anchor Tape Overlaps the Finish Lead.

Wrapper Insulation (Step 5 of 5) The wrapper insulation will be the same width as the interlayer insulation, as shown in Figure 5-69. The anchor tape will secure the wrapper.

Anchor Tape

Tap Lead

Wrapper Start Lead Finish Lead Winding Tube

Figure 5-69. Finished Foil Winding with a Wrapper.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Recommended Winding Procedure for

Toroidal Wound Coils Note 1: Minimize The Use of Mylar Tape There are two good reasons why the use of Mylar tapes of any kind should be kept to a minimum. First, since Mylar is not porous, impregnation must go around and if the tape is wound too tightly, there may be an air trap within the transformer. Secondly, epoxies do not bond well to Mylar; an incipient fracture plane is produced in the impregnation.

Note 2: Woven Glass Sleeving It has been found that the use of woven glass sleeving over the magnet wire improves the reliability. This sleeving is not merely slipped on after the unit is wound; it is actually placed over the lead as soon as the lead is brought out. The sleeving serves several purposes: it helps take the stress off the lead, it prevents sharp bending, and it prevents abrasions of the insulation. See Figure 5-16.

Note 3: Parallel Winding A parallel winding is a winding of two or more wires wound simultaneously and adjacent with each turn consisting of the specified number of wires. The parallel wires are joined at the ends to form a single conductor winding.

Note 4: Bifilar and Multifilar Winding A bifilar or a multifilar winding is a winding of two or more wires, as in a parallel winding, except the wires are not connected. The wires could be left unconnected resulting in two separate windings or connected in a series and parallel to form single multifilar center-tapped winding.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Single and Multiple Toroidal Windings

Single and multiple windings shall be fabricated as follows: 1.

All toroidal leads will be anchored on the periphery of the wound core.

2.

Splices and solder joints shall be prohibited within the winding.

3.

A magnetic device, wound with 33 AWG or smaller wire sizes, shall be joined with an intermediate lead, per Table 5-6.

4.

All solder joints will conform to the solder connection, as shown in Figure 5-80. There will be a minimum of three turns of insulated magnet wire, wrapped tightly, for stress relief. There will be a minimum of two turns of magnet wire, visibly soldered.

5.

Splicing is acceptable, only, when the number of turns specified, requires more wire than the shuttle can hold.

Strain Relief Loop A Strain Relief Loop shall be provided for all spliced lead breakouts.

Bend Radii The wire, Bend Radii, shall be greater than five times the wire diameter, except for one-time bends around terminals and wire splices.

Winding Tension The Winding Tension, used in the winding, shall be the minimum required to pull the wire into position.

Wire Lay The Wire Lay shall be smooth and uniform, unless, otherwise required, by the detailed winding instructions. Splicing Splicing shall not be made because of a broken wire. If a winding has a broken wire, then, the entire winding shall be replaced. The only winding splice that can be made is if the toroidal winding shuttle does not hold enough wire for the required number of turns.

Toroid Core Taping All toroids, including tape cores, powder cores, and ferrites, shall have the core wrapped with Mylar polyester, prior to winding. The tape shall be either adhesive-coated, or if uncoated, the ends shall be secured with adhesive coated tape. See Figure 5-70.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Figure 5-70. Mylar-Wrapped, Toroidal Core. Hand Shuttle A hand shuttle is normally used to put on windings of very few turns. The shuttle, shown in Figure 5-71, is a typical handheld shuttle, that is normally patterned and fabricated to the size of the toroidal core and the wire size.

rui

Hand Shuttle

Magnet Wire

Figure 5-71. Typical Hand Shuttle for Winding Small Number of Turns.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Marlinespike Tool

A marlinespike is a tool used to expand the window of a wound toroidal transformer or inductor, as shown in Figure 5-72. Care must be taken when using this tool, as to not exert too much pressure that could break or distort the windings.

Marlinespike

Toroid

Toroid

Gentle But Firm

Figure 5-72. Expanding Tool, Similar to a Marlinespike to Open the Window on Toroids.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Intermediate Wire Leads Magnetic devices, wound with AWG 33 or smaller wire sizes, shall be joined with an intermediate lead per Table 5-6.

Table 5-6. Intermediate Lead Wire Size.

Intermediate Lead Magnet Wire Size AWG #32 and larger #33 to #40 #41 and smaller

Intermediate Wire Size None #26 #32

Woven Glass Sleeving Place unimpregnated, woven glass sleeving over all leads from AWG 24 to AWG 33, coming from the magnetic devices, as shown in Figure 5-73.

Woven Glass Sleeving

Small Hole to Insert Magnet Wire

Standard no Pigtail Magnet Wire

Loose Pigtail for Ease of Anchoring

Figure 5-73. Magnet Wire Lead with Woven Glass Sleeving.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Toroid Self Lead Toroid Self-Start Lead The Toroid Self-Start Lead on a toroidal core shall be fabricated, as shown in Figure 5-74.

Anchoring Tape Winding Start Magnet Wire Woven Glass Sleeving Magnet Wire

Figure 5-74. Toroid, Self-Start Lead with Woven Glass Sleeving.

Toroid Self-Finish Lead The Toroid Self-Finish Lead shall be fabricated, as shown in Figure 5-75.

Self-Finish lead

Woven Glass Sleeving

Tape

Figure 5-75. Toroid, Self-Finished Lead with Woven Glass Sleeving.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Toroid Self-Tapping Lead (Step 1 of 3) The Toroid Self-Tapping Lead shall be fabricated with a loop, as shown in Figure 5-76.

Magnet Wire

1

Self-Tapping Loop

Figure 5-76. Breakout Loop for Self-Tapping Lead.

Toroid Self-Tapping Lead (Step 2 of 3) The Toroid Self-Tapping Lead is anchored with tape, as shown in Figure 5-77.

Anchoring Tapes

Twist 2 or 3 times to make one lead

Figure 5-77. Anchor Tape the Breakout Loop for Self-Tapping Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Toroid Self-Tapping Lead (Step 3 of 3) The Toroid Self-Tapping Lead shall be fabricated, as shown in Figure 5-78.

Magnet Wire

Woven Glass Sleeving

Anchoring Tape

Figure 5-78. Breakout Loop with Woven Glass Sleeving.

Solder Joints Solder joints are prohibited within the winding. All splicing, including the interim leads, must be placed on the periphery toroid after it is wound, as shown in Figure 5-79.

Periphery Insulation

Interim Lead

Figure 5-79. Soldering and Finishing the Interim Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

External Toroid Leads External Toroid Leads (vertical) The External Interim Lead Wire shall be fabricated, as shown in Figures 5-80, 5-81, and 5-82.

Strain relief requires three minimum turns with the insulated magnet wire wrapped tightly.

External lead wire Strain relief Anchoring Tape 2 Support Tape 1 A minimum of two turns are soldered. The magnet wire lead needs to be visible beneath the solder.

Soldered wire

Figure 5-80. Soldering the Interim Lead.

Finished External Toroid Lead (Vertical) The External Interim Lead Wire shall be finished, as shown in Figure 5-81.

External lead wire Strain relief Support Tape 1 Anchoring Tape 2 Finish Cover Tape 3

Figure 5-81. Finished, Vertical Interim Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

External Toroid Lead (Horizontal) The External Interim Lead Wire shall be fabricated, as shown in Figure 5-82.

External Lead Wire Magnet Wire may run on either side. Anchoring Tape 2 Support Tape 1 Cover Tape 4 over entire splice Anchoring Tape 3 through the toroid Strain relief, requires three minimum turns, with the insulated magnet wire wrapped tightly A minimum of two turns are soldered. The magnet wire lead needs to be visible beneath the solder

Figure 5-82. Finished, Horizontal Interim Lead.

Winding Requiring Interim Lead (Step 1 of 11) Secure the Start Lead with Anchor Tape, as shown in Figure 5-83.

Anchor Tape Magnet Wire Self Start Lead

Figure 5-83. Securing the Start Lead with Anchor Tape.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Requiring Interim Lead (Step 2 of 11) Securing the Finish Lead with Anchor Tape, as shown in Figure 5-84.

Finish Lead

Anchoring Tape 1 Start Lead

Figure 5-84. Securing the Finish Lead with Anchor Tape.

Winding Requiring Interim Lead (Step 3 of 11) Positioning the Start and Finish Leads with Anchor Tape 1, as shown in Figure 5-85.

Anchor Tape Self Start Lead

Self Finish Lead

Figure 5-85. Positioning the Start and Finish Leads.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Requiring Interim Lead (Step 4 of 11) Securing the Finish Lead with Anchor Tape 2, as shown in Figure 5-86.

Anchoring Tape 2 Anchoring Tape 1 Start Lead

Finish Lead

Figure 5-86. Securing the Finish Lead.

Winding Requiring Interim Lead (Step 5 of 11) Attach Interim Leads No. 1 and No. 2 with Anchor Tape 3 and Solder, as shown in Figure 5-87.

No. 1 Interim Lead

No. 2 Interim Lead Sleeving Anchor Tape 3 Finish Lead

Start Lead

Soldered connection

Figure 5-87. Attach Interim Leads.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Requiring Interim Lead (Step 6 of 11) Insulate the solder connections with the Finish Cover Tape 4, as shown in Figure 5-88.

No. 1 Interim Lead

No. 2 Interim Lead Finish Cover Tape 4

Figure 5-88. Insulate the Solder Connections with Tape.

Winding Requiring Interim Lead (Step 7 of 11) Breakout the loop for Self-tapping Lead, as shown in Figure 5-89.

Self-Tapping

Loop

Magnet Wire

Figure 5-89. Breakout the Loop for Self-Tapping Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Requiring Interim Lead (Step 8 of 11) Anchor tape the Self-tapping Lead, as shown in Figure 5-90.

Twist 2 or 3 times to make one lead

Anchoring Tapes

Figure 5-90. Anchor Tape the Self-Tapping Lead.

Winding Requiring Interim Lead (Step 9 of 11) Securing the Self-tapping lead with Anchor Tape 3, as shown in Figure 5-91.

Interim Wire with Woven Glass Sleeving Anchoring Tape 3

Figure 5-91. Securing the Self-Tapping Lead.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Winding Requiring Interim Lead (Step 10 of 11) Secure the Interim Lead with Anchor Tape 4 and solder, as shown in Figure 5-92.

Interim Lead with Woven Glass Sleeving Anchoring Tape 4 Soldered Wire

Figure 5-92. Securing the Interim Lead.

Winding Requiring Interim Lead (Step 11 of 11) Insulate the solder connection with Anchor Tape 5, as shown in Figure 5-93.

Interim Wire with Woven Glass Sleeving Finish Cover Tape 5

Figure 5-93. Finished Interim Lead, with Insulating Tape.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Progressive or Bank Winding The winding is placed on the core in sections. A tape barrier is placed around the core for the start. The start of the first section is at the tape barrier, as shown in Figure 5-94. Then, after so many turns, the second section is started. The start of the second section will overlap the first. This continues around the core for about 350°, as shown in Figure 5-95. An overview is shown of how the winding should look when it is finished. The number of overturns, each section has, is dependent on the design engineer, as shown in Figure 5-95. Second Section

A11

subsequent sections are like the second section. o-^o-*-o-*-o+-o-K} O+-O+-O+-O+-

First Section •O*O+O

-*o*o CL

HD/CL

Toroidal Core

Figure 5-94. A Side View of a Progressive Wound Toroid.

Section 4 & 5 Overlap

Section 3 & 4 Overlap

Section 5

Section 3

Section 5 & 6 Overlap

Section 2 & 3 Overlap

Section 6

Section 2

Section 6 & 7 Overlap

Section 1 & 2 Overlap

Section 7 ' / 4 \

' Section 1

Finish | Start Tape Barrier

Figure 5-95. A Top View of a Progressive Wound Toroid.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 6

Soldering and

Magnet Wire Terminations

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. Facilities and Work Station 3.

Hand Tools

4. Soldering Irons 5. Temperature 6. Soldering Preparation 7. Heat Sink or Shunt 8. Soldering 9. Solder Joint 10. Excess Solder Removal 11. Removing Insulation from Magnet Wire 12. Solder Pot 13. Magnet Wire Stripping Using an Abrasive Wheel 14. Removing Insulation from Stranded Wire 15. Thermal and Mechanical Wire Strippers 16. Tinning and Retinning 17. Solder Pot Tinning 18. Soldering Iron Tinnin 19. Terminal Soldering 20. Terminal Connections 21. Preparing Interim Magnet Wire for Soldering 22. Preparing Interim Stranded Wire for Soldering 23. Splicing Magnet Wire 24. Enclosures with Antirotation Terminals

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Reliability is accomplished through control of design, materials, techniques, and processes. There are many applications where reliability is supreme. Programs that demand this type of reliability are spacecraft, aircraft, missile guidance, and internal medicine. A failure in any one of these programs cannot be tolerated. Fabrication The fabrication of a Hi-Rel magnetic component, such as a transformer and/or an inductor, must be controlled from ordering the parts through final inspection. The documentation to fabricate any magnetic component must be exact in every detail. Nothing is left to memory or standard operating procedure. Construction Transformers and inductors shall be constructed according to the latest, signed engineering drawings. A complete up-to-date bill of materials will accompany, or be a part of the engineering drawings. Materials Only materials specified by the engineering drawing shall be used in the construction of transformers and inductors. Traceability of all materials is required, including shelflife certification for materials with limited life expectancy.

Facilities and Work Stations Soldering Facility (Clean Room) The general assembly and soldering area shall have a controlled environment, which limits the entry of contaminations. The temperature and humidity in the soldering area shall be monitored and maintained within the comfort zone, as shown in Figure 6-1. The enclosed soldering facility, will maintain a positive pressure, unless the soldering area is not in an air-conditioned, clean room. Lighting The lighting at the working surface for soldering and solder pot operations shall have a minimum illumination of 100 foot-candles.

Handling Parts Prior to handling parts and/or materials, the operator shall thoroughly clean his/her hands; the use of any hand lotion is forbidden. Anyone working or handling parts, and/or materials must wear clean gloves and/or finger cots. Gloves must be changed when they show signs of contamination, and finger cots must be replaced when they are torn or contaminated.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Work Area The work areas and workbenches shall be maintained in a clean and orderly manner. At the start of each workday, the work stations shall be free of visible dirt, grime, grease, flux or solder splatters, and other foreign materials. Restrictions There will be no smoking, eating, or drinking permitted at the workstations. Cosmetics Hand cream, ointments, perfumes, cosmetics, and other materials, not essential to the fabrication operation shall not be permitted at the work station. ESP Protection Requirement Supplier shall establish and maintain a documented program for the control of Elect-Static Discharge (ESD) during fabrication and handling of such devices. The program shall comply with the requirements of MIL-STD- 1686. Hand Tools Hand tools shall be checked daily for proper condition, operation, performance, and cleanliness.

Recommended Work Stations Tools and Materials The following tools are required for lead attachment, soldering, anchoring, and cutting insulating tape. 1.

Needle nose pliers (non-serrated).

2.

Tweezers, (fine point).

3.

Cutters, (full flush cut).

4.

Scissors.

5.

Orange stick.

6.

Wire scrapers.

7.

Gloves.

8.

3-1 OX magnification, (with a light is preferred).

9.

Dial or vernier calipers.

10. Ruler. 11. Soldering iron (temperature-controlled). 12. Alcohol burner. The following materials are required as an aid in lead attachment, soldering, anchoring, and cleaning. Only those materials that are "Program Approved" are allowed in the work area. All materials in the work area are required to have traceability data. 1.

Solder, type S/N 60 or 63.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

2.

Alcohol, Isopropyl grade A.

3.

Liquid flux conforming to Mil-F-14256.

4.

Sandpaper (emery), 220, 280, 320 grit.

5.

Kimwipes.

6.

Cotton swabs.

7.

Acid brushes (cleaning).

90°F 30°C

80 °F S 25°C ex S 70°F 20°C

60°F 40 60 Relative Humidity, (%)

20

80

100

Figure 6-1. Temperature and Humidity in the Soldering Area. Soldering Irons Soldering Irons and Soldering Irons Tips Only a temperature, controlled soldering iron shall be used, similar to the one shown in Figure 6-2. The tip idling temperature shall be checked with a calibrated device, at least once a day, and as often as necessary to assure that the requirements are adhered to.

Temperature For all solder joints, except those containing "solder-through" magnet wire, the tip idling temperature shall be controlled to 315°C +/- 20°C (600 +/- 35°F). For solder joints containing "solder-through" magnet wire, the tip idling temperature shall be controlled to 370°C +/- 20°C [700 +/- 35°F). Grounding The soldering iron shall have a NEMA, three wire power plug. There will be less than 2 ma leakage to the local ground and 2 ohms resistance, tip-to-ground. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Melting Capacity Select the correct soldering iron tip size, and the proper tip geometry for the soldering application. The soldering iron tip must be of a size and configuration to provide the capability to melt solder on a wire or joint, within a maximum of three seconds. Cleaning Plated soldering iron tips shall not be filed. The surface of plated soldering irons tips shall be polished, only if the plated tip was not tinned in the, "as received," condition, or if de wetting is evident. If the soldering iron tips need to be polished to remove the dewetting, either an emery cloth or aluminum oxide cloth, 320 grit, shall be used. If the dewetting cannot be easily removed, or there are signs that the soldering iron tip is eroding, as shown in Figure 6-3, the tips shall be replaced.

Temperature Controlled Soldering Iron

Soldering Iron Holder

Temperature Control Dial

Three Wire NEMA Plug

Figure 6-2. Temperature Controlled, Soldering Iron.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Eroded Tip

Soldering Surface Dewettin Plated Tip

Collar

Shank

Figure 6-3. Soldering Iron Tips.

Soldering Preparation Preparing Leads for Tinning The enamel magnet wire must be stripped and made ready for tinning (See Chapter 5). Abrasive cleaning shall not be used on tinned, or plated leads.

Fluxing It is recommended that liquid flux be applied to component leads and component terminals, prior to the application of heat, even when using flux cored solder.

Heat Sink or Shunt A component lead heat sink or shunt is shown in Figure 6-4. It is used to absorb, or delay, the heat from traveling up the lead being soldered which will cause damage. The size, shape, and material of the heat sink shall be adequate to provide enough heat sink protection to heat sensitive parts or components. The heat sink shall not scratch or damage a component lead or wire. Tension Spring

Clamp Jaws

Figure 6-4. Typical, Commercially Available, Component Lead Heat Sink.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Solder Tinning Tin the soldering iron tip by applying a rosin, cored solder. Remove excess solder by wiping the tip with either a moist sponge, or a tissue, before each soldering operation. The tinned surface shall be continuous, smooth, and without inclusions. It shall not show evidence of either non-wetting or dewetting. The strands of stranded wire shall be visible under the solder coating. There shall not be any wicking of solder under the insulation of the insulated wire. The lay of the tinned wire shall not be disturbed.

Connection For those terminations, which require the conductor to be formed, use a smooth, or round jaw pliers to prevent damaging the conductor. Then, trim the end off to the required length using flush-cut type cutters.

Soldering Acceptable Soldering An acceptable solder joint shall be continuous, smooth, and without inclusions, with fillets, that are either straight or concave, feathered to a fine edge. There shall be no evidence of dewetting or non-wetting. The cut end of the wires shall be covered with solder, and the contour of the soldered conductors shall be visible after soldering. During the time the joint is heated, and until the solder has solidified, the lead shall be immobilized to prevent movement of the solder joint. Heat-sensitive leads shall be protected with suitable heat sink, during soldering. Flux Removal After Soldering After soldering, flux residues shall be completely removed, using an approved, flux removal solvent, and an acid brush.

Solder Joint All solder joints should be well-formed, and positioned, and should not show any of the following characteristics, when inspected under a magnification of 3X to 10X: 1.

Solder joints with sharp (tips, peaks).

2.

Excessive solder, which obscures the connection configuration, except connections of a AWG 38 or smaller magnet wire.

3.

Swelling of stranded leads, due to excessive wicking.

4.

Loose wire, (except stress relief wraps).

5.

Foreign or extraneous material, embedded in the solder.

6.

Fractures, cracks, or pinholes.

7.

Bare conductor or dewetting within the solder joint area.

8.

Protrusion of the bare wire end, of stranded wire out of the solder joint.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

9.

Necking down of the magnet wire at the joint.

10. Pitting or voids in the corona free ball connections.

Excess Solder Removal Excess solder shall be removed from a joint by the use of a vacuum or with an approved pre-flux wicking braid, as shown in Figure 6-5. Wick the solder from the lead or terminal, by placing the braid in contact with the solder joint. Apply the soldering iron tip to the wicking braid, as shown Figure 6-6. Limit the time on the joint to 5 to 6 seconds to avoid any damage. After all the solder has been removed from the solder joint, clean the area with an approved flux removal solvent.

Solder Wicking Dispenser

Flux Impregnated Copper Braid

Static Dissipative Material

Figure 6-5. Commercially Prepared, Copper Wicking Braid.

Soldering Iron

Flat Side of Solder Tip Flux Impregnated Copper Braid

Bifurcated Terminal

] Insulated Lead Wire

Figure 6-6. Solder Wicking, Using Flux-Impregnated Copper Braid.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Removing Insulation from Magnet Wire

Solder Pot A typical solder pot for tinning solderable magnet wire is shown in Figure 6-1. The solder pot shall have a molten solder capacity of, at least, 1 pound (453.6 grams) minimum. The solder used shall be SN63 from a solid bar, with a composition as shown in Table 6-1. The solder pot capacity shall be maintained to, at least, 90%. The solder pot temperature shall be controlled at 260°C +/-20°C (500°F +/-25°F), when measured below the solder surface, and near the center of the solder mass away from the walls. The solder pot shall have a sufficient quantity of solder to minimize the temperature drop of the molten solder, when dip tinning. Prior to dip soldering, the dross* on the solder surface shall be removed using a stainless steel paddle. When the solder composition exceeds the contamination levels of Table 6-1, the solder shall be discarded and replaced with fresh solder.

Calibration Records Records shall be maintained to ensure solder pot conformance with solder, temperature, and contamination.

Grounding The soldering iron shall have a NEMA, three wire power plug. There will be less than 2 ma leakage to local ground, and 2 ohms resistance, tip-to-ground.

Three Wire NEMA Plug

Temperature Control Dial F

Figure 6-7. Typical Temperature Controlled Solder Pot.

* dross Oxide and other contaminants, which form on the surface of the molten solder.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 6-1

SN63 Solder Elements

Basic Elements Impurity Limits Maximum Limits

Tin 60-65 Aluminum 0.01 1 Antimony 1 Bismuth Cadmium 0.01 Copper 0.5 Gold 0.2 Iron 0.02 Magnesium 0.01 Sulfur 0.02 Zinc 0.01 * Others 0.1 Lead Remainder *Total of all others (except lead remainder)

Magnet Wire Stripping Using Flame

The removal, of enamel insulation on magnet wire, having a diameter 0.295 mm, (0.01 16 inches 30 AWG), or smaller, can be done with a flame. Using an alcohol burner as shown in Figure 6-8, and placing the magnet wire in the upper portion of the flame, the insulation can be carefully burned black to the desired length. After the insulation has been blackened, the magnet wire should be immediately quenched in to water to regain temperature. Emery paper can now be applied to the blackened area on the magnet wire to remove the black residue left from burning. After the magnet wire has been cleaned and inspected, the wire is ready to be tinned.

Flame Flame Adjustment

Clear Beaker Alcohol Burner Distilled Water

Figure 6-8. Typical Alcohol Burners, with Distilled Water for Quenching.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnet Wire Stripping Using an Abrasive Wheel Abrasive wheel stripping normally involves the use of two wheels of various materials to remove the magnet wire insulation. The wire is inserted between two rotating wheels to perform the stripping. The two most common materials used for the stripping wheels are fiberglass and wire. The fiberglass material, in the wheels, wipes away the insulation, thus leaving the magnet wire clean and polished. The cone type of fiberglass strippers, shown in Figure 6-9A, is normally used for very fine wire, from 0.046 - 0.25 mm, (30-45 AWG). For medium wire, from 0.25 - 1.45 mm, (15-30 AWG), a pair of round fiberglass wheels, like those in Figure 6-9B, would be used to strip the insulation from the magnet wire. For large wire, from 0.81-7.34 mm, (1-20 AWG), a pair of round wire wheels, like those in Figure 6-9C, would be used to strip the insulation from the magnet wire. Care must be taken when selecting the correct wire wheel. Selecting the wrong wire wheel could cause a rough surface in that it would cause the removal of some of the copper conductor.

Fiberglass Cones

Round Wheels

Wire Wheels

Direction of Rotation A B C Figure 6-9. Typical Abrasive, Magnet Wire Strippers. There is not one abrasive stripper for all sizes of magnet wire. Different abrasive wheels have to be used with different ranges of wire sizes and different types of insulation. It is necessary to choose the correct wheel type and grade, (roughness), for the gauge of wire and insulation type to be stripped. If the abrasive wheels are not adjusted with the proper tension, it will lead to grabbing and breaking of the magnet wire. Chemical Stripping Magnet Wire, (Very Toxic) Chemical stripping involves the use of a chemical reaction to break down the insulation and to remove it from the magnetic wire. There are several types of chemical strippers available that may be used. They are all very toxic. The chemical strippers are available in cream or paste, gel, and liquid. A typical chemical stripping procedure is shown in Figure 6-10. (1) The magnet wire is placed in the toxic stripper until the insulation separates from the magnet wire. Then, it is wiped clean with a kimwipe. (2) The magnet wire is then placed in the distilled water, stirred, removed, scrubbed with an acid brush, and rinsed again. (3) Then the magnet wire is placed in the neutralizer solution, stirred, removed, and scrubbed with an acid brush, after which it is wiped clean with a kimwipe. (4) The magnet wire is then placed in

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

the distilled water, stirred, removed, and scrubbed with an acid brush. (5) Then magnet wire is placed in the alcohol, stirred, removed, and scrubbed with an acid brush, after which it is wiped clean with a kimwipe. The magnet wire is then ready to be inspected and tinned. The time required to remove the magnet wire insulation with chemical strippers will vary with insulation type and wire size. There are occasions when the requirements specify that the stripping to be performed does not put physical stress on the magnet wire. Chemical stripping is the only way. Chemical stripping is not a preferred method as it creates a hazardous work station requiring ventilation, special equipment, and safety training for skilled operators. The operators should be wearing special aprons, gloves, and goggles for their protection. Records shall be maintained to ensure the traceability for the manufacturers' lot and date. All Beakers are Clear Glass

V

-r

1 Toxic Stripper

V

v

2

3

4

Distilled Water

1vfeutralizer Solution

Distilled Water

Alcohol

Figure 6-10. Typical, Chemical-Stripping Procedures for Magnet Wire. Magnet Wire Stripping Summarized The above paragraphs have described four ways to strip or remove the enamel insulation from magnet wire: solder pot, flame (burning), abrasive wheel, and chemical. After reviewing all four enamel stripping methods one does not stand out over the rest. Each of the stripping methods has its own advantages and disadvantages. There is not a clear-cut winner. All of the wire stripping methods, have their own unique process to remove the enamel from the magnet wire. Each method of wire stripping is unique in itself. However, they all have the following requirements, in common: 1.

They all require a work station.

2.

They all require special equipment.

3.

They all require special setup.

4.

They all require special adjustment.

5.

They all require control of records.

Any of the above wire stripping methods requires skilled operators. There has to be a written, a complete, and a thorough procedure for each of the above wire stripping methods. The operator must be capable of fine-tuning the equipment, and then be able to demonstrate the performance. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Removing Insulation from Stranded Wire Stranded Hookup Wire The wire used for breakout leads shall be a stranded, hookup wire, per MIL-W-16878. The insulation shall be 600 volt, unpigmented, bondable virgin TFE. For stranded hookup wire, see Table 6-2.

Table 6-2. Design Standard for Teflon Hookup Wire.

Teflon Insulated, 200°C Hookup Wire AWG 16 18 20 22 24 26

JPL Standard ST11478-16ET ST11478-18ET ST11478-20ET ST11478-22ET ST11478-24ET ST11478-26ET

MIL-W-16878E Strands AWG 19 29 19 30 19 32 19 34 19 36 7 34

Wire Stripping When using an approved wire stripper strip, approximately 0.2 inch, (0.5 cm) of insulation from the wire to be tinned. Remove any tag, or icicle ends of wire insulation as shown in Figure 6-11. Use a pair of flush cutters or clippers.

Wire Insulation

Wire Strands

Tag Ends or Icicles Figure 6-11. Stripped, Insulated Stranded Wire with Icicles. If the lay of the outer wire strands has been disturbed, restore the lay by twisting the strands in the direction of the original lay. Do not handle the strands with bare fingers. Use either gloves, finger cots, or the equivalent. Do not over twist the strands, as this tends to increase the outer diameter of the conductor and may prevent insertion of the tinned wire into the bifurcated terminal. Do not attempt to restore the lay of the wires that have disturbed inner strands. Cut off the length containing the disturbed inner strands and restrip the wire. Reject wires with nicked or broken strands.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Thermal and Mechanical Wire Strippers Only approved thermal or mechanical wire strippers should be used. A typical, thermal wire stripper is shown in Figure 6-12 and a mechanical stripper is shown in Figure 6-13. Mechanical strippers require finer adjustment to get the performance, without having cuts, nicks or a broken serve, as shown in Figure 6-22.

Control Lamp Temperature Control Dial Stripping Elements Hand Held Thermal Wire Strippers

Three Wire NEMA Plug

Figure 6-12. Typical, Thermal Wire Strippers.

Acme Insulatated Wire Stripper

Wire Insertion Port Strip Length Adjustment Blade Depth Adjustment

Oliree Wire NEMA Plug

Figure 6-13. Typical, Mechanical Wire Stripper. The damage to wires, caused by the insulation stripping process, is restricted as follows:

1.

Stranded conductors shall not have cracked or severed strands.

2.

The conductor insulation shall not be punctured, crushed, or otherwise damaged, to such an extent, that the wire could not pass the dielectric acceptance requirement of the wire. The ends of the insulation shall be cut square and clean, except for a few remaining fibrous strands. Do not bend the conductor strands for the purpose of removing excess fibrous strands.

3.

The conductor strands shall not have evidence of plastic film deposit resulting from the thermal stripping operation.

4.

The wire insulation shall not be blistered or swollen, but, a slight discoloration is acceptable when using thermal strippers.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

5.

The illustrated examples of acceptable and unacceptable wire stripping are shown in Figure 6-14 through 6-18 for thermal strippers, and Figure 6-19 through 6-22 for mechanical strippers.

Figure 6-14. Acceptable, Thermally Stripped, Square and Clean Insulation.

Figure 6-15. Unacceptable, Thermally Stripped, Smeared Insulation.

Figure 6-16. Unacceptable, Thermally Stripped, Insulation with Icicles.

Figure 6-17. Unacceptable, Thermally Stripped, Excess Heat, Globular Appearance.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Figure 6-18. Unacceptable, Thermally Stripped, Irregular Cut Exceeding OD/4.

Mechanically Stripped

Figure 6-19. Acceptable, Mechanically Stripped, Clean Appearance.

Figure 6-20. Acceptable, Mechanically Stripped, Minor Burnishing.

Figure 6-21. Unacceptable, Mechanically Stripped, Nicked and/or Severed Strands.

Figure 6-22. Unacceptable, Mechanically Stripped, Broken Serve.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Tinning and Retinning General Tinning shall be accomplished, prior to parts-to-parts installation and joint assembly. Terminals and solder-through types of magnet wire are not required to be tinned or retinned. Tinned Surface A tinned surface shall be continuous, smooth, without inclusions, and shall not show evidence of either nonwetting or dewetting. The strands of stranded wire shall be visible under the solder coating. There shall not be any wicking of solder under the insulation of the insulated wire. The lay of the tinned wire shall not be disturbed. Insulation Gap Prior to tinning, insulated wires and leads that require an insulating gap, (distance between insulation and the assembled joint), shall be stripped to a length which will afford an insulated gap, (0.30 to 0.90), inch as shown in Figure 6-23. If damaged, the lay shall be carefully restored. Damaged wire, (nicked or broken strands), or damaged insulation shall not be allowed.

Lead Wire Insulation

., _ , Solder Tinned

0

Insulation Gap

Figure 6-23. Solder Tinned, Insulated Lead Wire.

Solder Pot Tinning

Preferred Tinning The preferred method for tinning insulated wires and leads is the hot solder dip. Dip about 1/3 of the length of the conductor to be tinned into the liquid rosin flux. After the lead end has been coated with liquid flux, then, dip the fluxed length of the conductor into the temperature-controlled solder pot, leaving adequate space for the insulation gap, and dwell for 3 seconds, See Figure 6-24. Then slowly withdraw the conductor vertically from the solder pot. Remove solder residues with an approved flux removal solvent using a brush or swab. If the contour of the wire strands is not visible after tinning, there is an excess of solder on the wire. Remove this excess solder from the wire by repeating the dip tinning procedure. Repeat the cleaning process.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Molten Solder Lead Wire Enlarged For Clarity Insulation

Stranded Wire

X

Insulation Gap Liquid Flux

Figure 6-24. Using the Solder Pot to Dip Tin Leads.

Solder Pot Tinning Characteristics Tinned components shall satisfy the following requirements: 1.

All soldered surface are smooth, and completely, wetted with solder.

2.

Lack of projections, bridging, fractures, porosity, and inclusions.

3.

No flux residue on the solder joint after the cleaning process.

Insulation Damage The tinning process shall not damage the wire insulation.

Wire Lay The lay of the wire shall be undisturbed by the tinning process, as shown in Figure 6-23.

Soldering Iron Tinning Soldering Iron Tinning Dip about 1/3 of the length of the conductor to be tinned into a non-activated liquid, rosin flux. Place a clean, and well-tinned, soldering iron tip on the conductor near the center of the area to be tinned, and apply solder. Remove the soldering iron tip from the conductor by sliding the tip down the conductor, and finally, off the end, as shown in Figure 6-25. Remove solder residues with an approved flux, removal solvent using a brush or swab. If the contour of the wire strands is not visible after tinning, there is an excess of solder on the wire. Remove this excess solder from the wire by fluxing the wire and then, reheating and sliding the tip down the wire and off the cut end, without applying additional solder. Repeat the cleaning process. If excess solder is still present, reject the wire.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Soldering Iron

Stranded Wire Lead Wire Insulation

Insulation Gap Figure 6-25. Using the Soldering Iron to Tin Insulated Leads.

Terminal Soldering All Solder Joints For all solder joints, except those containing, "solder-through," magnet wire, the soldering iron tip idling temperature shall be controlled to 315°C +/- 20°C (600°F +/- 35°F), and frequently checked by actual measurement. For solder joints containing, "solder-through", magnet wire, the tip temperature shall be controlled to 370°C +/- 20°C (700°F +/- 35°F), and frequently checked by actual measurement. Solder Flow The assembled joint shall be heated to, or above, the melting point of the solder, before the solder is applied to the assembled joint. The use of a small amount of solder, between the junction of the tip and the assembled joint, is permissible to improve heat flow. Add solder to cover any exposed ends of wire or leads and then add solder to the assembled joint. Solder may be applied at more than one point to a solder joint to provide control on the fillet size, and fill openings, as required. Immobilized Leads During the time the joint is heated, and until the solder has solidified, leads shall be immobilized to prevent movement of the soldered joint.

Acceptable Solder Joint An acceptable solder joint shall be continuous, smooth, and without inclusions, with fillets that are either straight or concave, and feathered to a fine edge. There shall be no evidence of dewettmg or non-wetting. The cut end of wires shall be covered with solder, and the contour of the soldered conductors shall be visible, after soldering. Final Solder Joint All excess solder not required, flux, and soldering residues shall be removed. Solder joints shall not exhibit stress lines, fractures, or cracks.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Typical Terminal Solder Joint The lead shall enter the bifurcated terminal at 90° +/-150 to the plane of the tine, as shown in Figure 6-26, and shall meet the preferred solder profile in the above paragraphs.

Wire End View

^

Pre-tinned Insulated, Stranded Wire

Smooth, Solder Flow

Bifurcated Terminal

Figure 6-26. Bifurcated, Terminal Lead Entrance.

Terminal Connections Terminal Modification Any modification of the terminal and conductor shall be prohibited.

Bifurcated Terminals (1) The lead or wire shall enter the terminal at 90° +/-150 to the plane of the tines and shall meet the preferred solder profile, as shown in Figure 6-27.

90°±15C

90°±15C

Figure 6-27. Bifurcated, Terminal Lead Entrance. Bifurcated Terminals (2) Magnet wire leads are attached to the bifurcated terminals, as shown in Figure 6-28. The wire shall enter the terminal at 90° +/-150 to the plane of the tines, and shall meet the preferred solder profile. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

33 AWG

32 AWG and Larger

X^Vj, «

180° Hook Straight Lead

Tinned Magnet Wire

V

/

Tinned Magnet Wire

Figure 6-28. Magnet Wire Lead Attachment to Bifurcated Terminals.

Insulation Gap 0.030-0.090"

Terminal Board

t

\ Dimensions are in Inches Figure 6-29. Magnet Wire Lead Attachment to Bifurcated Terminals.

Bifurcated Terminals (3) Bifurcated terminals, using the standard side lead routing, is shown in Figure 6-29.

b

/rr\ Bifurcated Terminal

Insulation Gap 0.030-0.090

0.030

Terminal Board

Dimensions are in Inches

li

K

li il

Figure 6-30. Bifurcated Terminal Side Routed.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Bifurcated Terminals (4) Bifurcated terminals, using the non-standard bottom lead routing, is shown in Figure 6-30.

Multiple Terminations The top lead or wire, soldered in a terminal, shall have less than one-half of its diameter above the tines, as shown in Figure 6-30.

Turret Terminals Turret solder joints shall meet the requirements of Figure 6-33 and 6-34 in its mechanical configuration and its preferred solder profile.

Bifurcated Terminal Terminal Board

Insulation in contact with with swage area of terminal. Dimensions are in Inches.

Figure 6-31. Bifurcated, Terminal Bottom Routed.

Bifurcated Terminals

The body of the last stranded wire, added to the bifurcated terminal, shall not protude more than 50% above the tines.

Terminal Board

Figure 6-32. Bifurcated Terminal with Multiple Terminations. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

h Insulation Gap

f ) j ) 180°+/- 15° Turret Terminal

0.030-0.090

Terminal Board

Dimensions are in Inches.

Figure 6-33. Dual, Turret Terminal, Solder Profile.

/- 15°

Insulation Gap

0.030-0.090 Turret Terminal

h

Terminal Board

Dimensions are in Inches.

Figure 6-34. Single, Turret Terminal, Solder Profile.

Larger Than 2D

Entrance Angle of Lead is Optional

0.015 Max

Dimensions are in Inches.

Figure 6-35. Wrapped Eyelet Terminal Joint.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Insulation Gap - 0.030 - 0.090

2D or Smaller

4»- 0.010 - 0.030

Insulation Gap 0.030 - 0.090 Dimensions are in Inches.

Figure 6-36. Not Wrapped, Eyelet Terminal Joint.

2D or Smaller

0.010 - 0.030

Insulation Gap 0.030 - 0.090 Dimensions are in Inches. Figure 6-37. Not Wrapped, Hook Terminal Joint.

Larger Than 2D

D

Insulation Gap 0.030 - 0.090 •

0.015 Max Dimensions are in Inches.

Figure 6-38. Wrapped Hook, Terminal Joint.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Preparing Interim Magnet Wire for Soldering Interim Lead (Magnet Wire or Bus Wire) Interim lead, wire splices shall conform to Figure 6-39. The strain relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The magnet wire, lead outline shall be visible beneath the solder. There shall be no overlapping of either the strain reliefer the solder turns, as shown in Figure 6-40. There shall be no protruding pigtails, as shown in Figure 6-41.

Stress Relief, with a Minimum of Three Turns. The Magnet Wire is Wrapped Tightly.

Magnet Wire or Bus Wire A Minimum of Two Turns, Soldered. Magnet Wire Figure 6-39. Acceptable Splice, with Smooth, Even Wrap. Stress Relief, with a Minimum of Three Turns. The Magnet Wire is Wrapped Tightly.

Magnet Wire or Bus Wire

X No Overlapping, Smooth Wrap.

Magnet Wire Figure 6-40. Unacceptable Splice with Overlap. Stress Relief, with a Minimum of Three Turns. The Magnet Wire is Wrapped Tightly.

Magnet Wire or Bus Wire ••••••^^^^^^^

No Protruding Pigtails, Smooth Wrap.

Magnet Wire ' Figure 6-41. Unacceptable Splice with Protruding Pigtail.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Interim Leads with Two Magnet Wires Interim lead wire, with two magnet wires spliced, shall conform to Figure 6-42. This interim splice shall also conform to Figure 6-40 and Figure 6-41, regarding overlapping and protruding pigtails. Stress Relief, with a Minimum of Three Turns. The Magnet Wire is Wrapped Tightly.

A Minimum of Two Turns Each, Soldered. ^^•••B^^'-

Two Magnet Wire

*

Figure 6-42. Acceptable Splice with Two Magnet Wires.

U Style Interim Lead (Magnet Wire or Bus Wire) U style interim lead, wire splices shall conform to Figure 6-43. The strain relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The magnet wire, lead outline shall be visible beneath the solder. There shall be no overlapping of either the strain relief or the solder turns, as shown in Figure 6-40. There shall be no protruding pigtails, as shown in Figure 6-41.

A Minimum of Two Turns, Soldered

Stress Relief, with a Minimum of Three Turns. Magnet Wire is Wrapped Tightly Magnet Wire

Magnet Wire or Bus Wire

Figure 6-43. U Style, Acceptable Splice, with Smooth, Even Wrap.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Preparing Interim Stranded Wire for Soldering Interim Lead (Insulated Stranded Lead Wire) Interim lead, wire splices shall conform to Figure 6-44. The strain relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The outlines of both the insulated, stranded lead wire and the magnet wire lead shall be visible beneath the solder. There shall be no overlapping of either the strain reliefer the solder turns, as shown in Figure 6-45. There shall be no protruding pigtails, as shown in Figure 6-46.

Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly.

Insulated Stranded Lead Wire _ A Minimum of Two Turns, Soldered. •m^^^^" Magnet Wire / Figure 6-44. Acceptable Splice, with Smooth, Even Wrap. Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly.

Insulated Stranded Lead Wire Magnet Wire

Overlapping Not Acceptable

X

Figure 6-45. Unacceptable Splice with Overlap. Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly.

Insulated Stranded Lead Wire ^^^•••^^^ # Magnet Wire

Pigtail Not Acceptable

Figure 6-46. Unacceptable Splice with Protruding Pigtail.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Interim Lead (Insulated Stranded Lead Wire) with Two Magnet Wires Interim lead wire, with two magnet wires spliced, shall conform to Figure 6-47. This interim splice shall also conform to Figures 6-45 and Figures 6-46, regarding overlapping and protruding pigtails. Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly.

Insulated Stranded Lead Wire A Minimum of Two Turns, Soldered. Two Magnet Wire Figure 6-47. Acceptable Splice with Two Magnet Wires. Interim Lead (Insulated Stranded Lead Wire with Shrink Sleeving) Interim lead, wire splices using shrink sleeving shall conform to Figure 6-48. The strain relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The outlines of both the insulated stranded lead wire and the magnet wire lead shall be visible beneath the solder. There shall be no overlapping of either the strain reliefer the solder turns, as shown in Figure 6-45. There shall be no protruding pigtails, as shown in Figure 6-46. Care must be exercised when using the heat shrink sleeving to avoid the concentration of heat at the soldered joint. Heat shall be controlled in accordance with the sleeving manufacturers' stated, recommended conditions and procedures.

Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. Insulated Stranded Lead Wire

\

Clear Shrink Tubing ^*

Magnet Wire

,/

^"

A Minimum of Two Turns, Soldered.

Figure 6-48. Acceptable Splice using Heat Shrink Tubing. U Style Interim Lead (Insulated Stranded Lead Wire) U style, interim lead, wire splices shall conform to Figure 6-49. The strain relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The magnet wire, lead outline shall be visible beneath the solder. There shall be no overlapping of either the strain relief or the solder turns, as shown in Figure 6-45. There shall be no protruding pigtails, as shown in Figure 6-46. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

A Minimum of Two Turns, Soldered

Stress Relief, with a Minimum of Three Turns. Magnet Wire Wrapped Tightly Magnet Wire

Insulated Stranded Lead Wire

Figure 6-49. U Style Acceptable Splice, with Smooth, Even Wrap.

Splicing Magnet Wire Internal Connection and/or Splice (20 AWG and Larger) Terminating an internal connection or making an internal splice is shown in Figures 6-50 through 6-52. The magnet wires are brought together, cut and tinned, as shown in Figure 6-50. The wires are then wrapped with a number 24 AWG bus wire, with a minimum of 4 turns and soldered. Magnet Wire or Bus Wire

Solder Tinned Figure 6-50. Splicing Multiple Strands of Magnetic Wire. Magnet Wire or Bus Wire

Wrap Tightly with a Minimum of 4 Turns.

Solder Tinned

Figure 6-51. Splicing Multiple Strands of Magnetic Wire with Anchor Wrap.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnet Wire or Bus Wire

A Minimum of 4 Turns, Soldered.

Solder Tinned

Figure 6-52. Acceptable Splice, with Smooth, Even Wrap.

Enclosures with Antirotation Terminals Magnet Wire to Terminal Lug The terminals used within the magnetic package must have antirotation features, as shown in Figures 6-53 through 6-57. The flattened or dimpled area thickness shall be no less than one-half the lead diameter and shall not exhibit sharp edges. The radius, R, shall not be greater than twice, or less than one times the diameter of the terminal lead. This radius shall be formed prior to soldering.

The stress relief will consist of a minimum of three turns of magnet wire wrapped tightly, then, two turns, minimum, to be soldered. The magnet wire, lead outline shall be visible beneath the solder. There shall be no overlapping of either the strain reliefer the solder turns, as shown in Figure 6-53.

Fiberglass Enclosure

A Minimum of Two Turns, Soldered. Stress Relief with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. Solder Foot

Figure 6-53. Typical, Solder Terminal on a Surface Mount Device.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Fiberglass Enclosure

A Minimum of Two Turns, Soldered. Stress Relief with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. The radius, R, shall be no greater than twice, or less than one times the diameter of the terminal lead. Solder Pin

Figure 6-54. Z-Bend Solder Terminal.

Fiberglass Enclosure

A Minimum of Two Turns, Soldered. Stress Relief with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. The dimpled area thickness shall be no less than one-half the lead diameter, D.

Dimple Solder Pin

Figure 6-55. Dimpled Solder Terminal. Fiberglass Enclosure

A Minimum of Two Turns, Soldered. Stress Relief with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. The flattened area thickness shall be no less than one-half the lead diameter, D. Solder Pin

Figure 6-56.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Flattened Solder Terminal.

Fiberglass Enclosure

A Minimum of Two Turns, Soldered. Stress Relief with a Minimum of Three Turns. Magnet Wire Wrapped Tightly. The radius, R, shall be no greater than twice, or less than one times the diameter of the terminal lead.

Solder Pin

Figure 6-57. Wire Bend Solder Terminal.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 7

Packaging, Enclosures, Mounts, and Headers

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. Material 3. Enclosur 4. Enclosure Cover 5. Fastener Tube 6. Threaded Fasteners 7. Terminal Board 8. Terminals and Leads 9. Terminal Installation 10. Damaged Terminals 11. Measles 12. Leads 13. Magnetic Wire Termination 14. External Leads 15. Installing the Magnetic Component 16. Terminating the Leads 17. Surface Mounts for High-Rel, Power Magnetics 18. Introductio 19. Selecting the Best Plastic for Your Application 20. Through-Hole Toroid Mounts 21. Horizontal Toroid Mounts 22. Vertical Toroid Mounts 23. Surface Mount, Toroid Mounts 24. Referenc

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Scope This chapter covers the packaging to be used for the transformers and inductors in rectangular and cylindrical, epoxy fiberglass cups. These fiberglass cups will have terminals and/or flexible leads exiting for use in electrical circuits. The transformer and inductor will be referred to as, "magnetic component," throughout this chapter. Application When selecting the enclosure (package), electrical performance of the magnetic component must have first priority. The magnetic component must function in the circuit with rated electrical conditions at extreme, environmental conditions. The magnetic component enclosure must be designed to meet electrical, environmental conditions and be able to remove the heat generated by the magnetic component, if required. The amount of polymeric material used for impregnating and embedment must be kept to a minimum. Minimizing the amount of polymeric material used to encapsulate the magnetic component will keep undue pressure on the magnetic component to a minimum.

Material Material All magnetic components shall be protected from direct exposure to the physical environment by the use of epoxy-glass enclosures. The enclosures for magnetic components shall be fabricated from epoxy-glass laminate, per MIL-P-18177, Type GEE, flame retardant Grade 4, or MIL-P-13949, Type GF (flame retardant).

Enclosure Enclosure Cup Magnetic devices shall be protected by properly shaped enclosures designed to maintain structural integrity, provide a conductive heat path to the mounting surface, if required, and anchor the external leads to prevent stresses being applied to the terminals and the magnet wire leads. Typical enclosures are shown in Figure 7-1. Fastener Tubes

Enclosure Wall Figure 7-1. Typical, Enclosure for a Magnetic Component. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Enclosure Cover Enclosure Cover A cover shall be optional for a magnetic device with radial lead routing. Enclosure covers shall be required on all magnetic components, utilizing the separate impregnating and embedment processes. The enclosure covers shall be enclosed by the cup and be flush with the cup's inner edge. The cover thickness shall be as specified in Table 7-1. The cover shall have holes, as required, to accept the applicable number of fastener holes. The cover shall have two embedment fill holes of 0.125 of an inch in diameter for covers with a maximum dimension of 1.00 inch, and holes of 0.250 of an inch in diameter for covers greater than 1.00 inch. The embedment, fill hole centers shall be located, as shown in Figure 7-2 and Figure 7-3.

Fastener Tube Holes

Cover

Fill Holes Figure 7-2. Location of the Embedment Fill Holes for a Circular Cover.

Fastener Tube Holes

Figure 7-3. Location of the Embedment Fill Holes for a Rectangular Cover. Dimensions The enclosure dimensions shall provide a clearance of 0.020 of an inch minimum to 0.10 of an inch maximum to the winding and core assembly, except for the bonding of the winding assembly to the terminal assembly or base. The wall and cover thickness for different enclosure sizes is given in Table 7-1.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 7-1

Enclosure Material Thickness OD Width or Length < 1.5 inches <38mm > 1.5 inches >38mm * *

Cover Wall Thickness Thickness 0.02 inches 0.0 15 inches 0.51 mm 0.51 mm 0.02 inches 0.025 inches 0.64 mm 0.51 mm 0.031 inches (min) 0.03 1 inches (min) 0.80 mm (min) 0.80 mm (min) * Magnetic device mounted by bracket, a clamp, or a similar device.

Type Fastener Screw Screw Screw Screw Bracket Bracket

Selecting the Enclosure The enclosure must be selected to best fit the magnetic device. There must be ample room for the terminal board, and space to route the leads. The selected enclosure should provide ease of assembly and inspection. If the selected enclosure is larger than it needs to be, then additional embedment would be required to fill these voids. See Figure 7-4 and Figure 7-5. Always select an enclosure that requires a minimum of embedment. Too much embedment will put undue stress on the magnetic device.

Fastener Tube Fasteners The fastener tube wall thickness shall be 0.031 of an inch (0.08 cm), minimum, for all magnetic devices. The fastener tube length shall be identical to the height of the enclosure and extend through the base and cover or spacer, as applicable in all applications. The ID of the fastener tube shall be 0.125 of an inch when, a 4-40 screw is specified and 0.144 of an inch when a 6-32 is the specified screw for single fastener tube application. Fastener tubes are shown in Figure 7-1. Where two or more fastener tubes are used, the internal diameter shall be 0.138 of an inch when, a 4-40 screw is specified and 0.151 of an inch when a 632 is the specified screw. Excessive Amount of Embedment Material

L: 3:

C Core

J Inserts Acceptable

Unacceptable

Figure 7-4. Comparing Enclosures C Cores. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Excessive Amount of Embedment Material

Toroid

Inserts

Fastener Tube Acceptable

Unacceptable Figure 7-5. Comparing Enclosures C Cores.

Threaded Fasteners Threaded Fasteners Threaded Fasteners, embedded in the encapsulation material, shall be of the blind type. The threaded fasteners will be secured in place with a 360 degrees bead of epoxy adhesive. The threaded fasteners or blind type inserts are shown in Figure 7-6. Epoxy Adhesive

Threaded Fastener

Enclosure Wall Figure 7-6. Enclosures with Blind Type Threaded Fasteners.

Terminal Board Terminal Board Material The internal terminal boards shall be fabricated from epoxy-glass laminate, per MIL-P-18177, Type GEE, flame retardant Grade 4, or MIL-P-13949, Type GF (flame retardant).

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Terminal Board Position The terminal board shall be positioned as follows: 1.

Bonded to the wall of a rectangular cup, as shown in Figure 7-7.

2.

Bonded to the wall of a round cup, as shown in Figure 7-8.

3.

Bonded to the core, as shown in Figure 7-9.

Bifurcated Terminals

C Core

Terminal Board

\

Fiberglass Enclosure

Inserts Figure 7-7. Terminal Boards, Bonded to the Wall of Rectangular Cup.

Bifurcated Terminals

,/

.Terminal Board

Fastener Tube Toroid Fiberglass Enclosure

Figure 7-8. Terminal Boards, Bonded to the Wall Round Cup. Bifurcated Terminals

Terminal Board

C Core

Inserts

Fiberglass Enclosure Figure 7-9. Terminal Board, Bonded to the C Core.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Terminal Board Outline The terminal board shall have embedment, flow-through holes. The holes shall be 0.125 to 0.25 of an inch in diameter and shall number four to each square inch of board surface. The holes shall be located a minimum of 0.050 of an inch from any edge or installed terminal. See Figure 7-10.

Bifurcated Terminals Terminal Board

0.015 of an inch minimum 15-20 mils Thick

0.060 of an inch minimum

\

Q p O QIQ O 0.050 of an inch minimum Embedment Flows Through Holes.

End View This part of the board is cut away to clear breakout of interconnecting leads.

Figure 7-10. Terminal Board.

Terminals and Leads Terminal Description Terminals shall be bifurcated or turret, solderable, and capable of being permanently fastened to epoxy glass board. Terminals shall be procured, to the latest Mil Spec. It is common for a single bifurcated terminal to handle multiple terminations. See Figure 7-11. The terminal selected must be able to handle the required number of connecting lead wires.

Terminal Installation Terminal Installation Terminals shall be swaged using the force, specified in Table 7-2.

Bifurcated Terminals

The body of the last stranded wire, added to the bifurcated terminal, shall not protude more than 50% above the tines.

Terminal Board

Figure 7-11. Terminal Board. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 7-2. Swage Force for Terminals.

Swaging Force for Terminals Units

*Nominal Force (pounds/kilograms)

Maximum Force (pounds/kilograms)

pounds

80

100

kilograms

36

45

pounds

130

150

Approximate Size Swage Barrel

0.041 0.062 0.078

0.09 0.112

kilograms

59

68

pounds

200

225

kilograms

102

pounds

91 250

300

kilograms

113

136

pounds

500

800

kilograms

227

363

This is the force which is required to just meet minimum, roll-over requirements.

Terminal Flange The swage flange of the terminal shall be seated and then, there will be sufficient tightness to assure that the terminal will not move. Maximum permissible height of the terminal swage above the plane of the wiring board shall be 0.012 of an inch and the edge of the rollover shall not be more than 0.004 of an inch above the board surface.

Damaged Terminals Damaged Terminals Damage to the funnel type swage and loose terminals is unacceptable. See Figure 7-12. 1.

Acceptable

2.

More than two cracks in the terminal flange are unacceptable.

3.

A loose terminal, as a result of insufficient swage force, is unacceptable. An edge of rollover, more than 0.004 of an inch above the board surface is unacceptable.

4.

Funnel type swage is unacceptable.

Bifurcated Terminals Installation The bifurcated terminals shall show no evidence of damage caused by the swaging tools. See Figure 7-13. 1.

Acceptable

2.

If the installation is not perpendicular to the plane of terminal area, it is unacceptable.

3.

Bent tines are unacceptable.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Figure 7-12. Terminal Swaging.

Figure 7-13. Bifurcated Terminal Installation. Turret Terminals Installation The turret terminals shall show no evidence of damage caused by the swaging tools. See Figure 7-14. 1.

Acceptable

2.

If the installation is not perpendicular to the plane of terminal area, it is unacceptable.

3.

Bent terminals are unacceptable.

1

2

3

Figure 7-14. Turret Terminal Installation.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Measles Terminal Installation (measles) Small white spots, or "measles", caused by terminal installation, shall be acceptable provided they do not form a continuous path between terminals, as shown in Figure 7-15. The small white spots, or "measles" can appear after time or temperature. 3

Unacceptable

Acceptable Ideal

Figure 7-15. Terminal Board with Spots Called, "measles."

Leads Terminal Leads A stranded, insulated terminal lead, with a minimum length to facilitate testing and assembly, shall be used for connection to the magnetic device. External Wire Size The external lead wire size shall be equal to, or greater than, the area of the magnet wire used in the magnetic device. The minimum external conductor size shall be 26 AWG, stranded wire. Bifurcated terminals, or solder ferrules shall provide the solder interconnection between the coil and external leads for Wire 15, AWG, and smaller. The solder interconnection for wire sizes, 14 AWG, and larger, shall be soldered directly to the external lead by the use of a ferrule appropriately sized. Stranded Lead Wire

Ferrule

Magnetic Wire X

Solder

Solder

Figure 7-16. Ferrule Connection Using Stranded and Magnetic Wire. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnetic Wire Termination Small Leads Winding leads of 33 AWG, shall be wrapped around a tine of the terminal, a maximum of 180°. See Figure

7-17.

180° Hook Bifurcated Terminals

Magnet Wire Figure 7-17. Winding Lead Termination for a 33 AWG. Large leads Winding leads of 32 AWG up to 15 AWG, shall be terminated without wrapping. See Figure 7-18.

Straight Lead

Bifurcated Terminals

Magnet Wire Figure 7-18. Winding Lead Termination for a 32 to 15 AWG. Magnetic Component Lead Preparation (Pattern) If the spec control drawing (SCD) does not call out the length of the finish leads, then do the following: Using an enclosure with terminals as a pattern, place the magnetic device in the enclosure, and align the leads with the terminals. With the magnetic device in place, route the leads to provide suitable strain relief, plus sufficient length to rework the solder joint once. See Figure 7-19.

Tinned Magnet Wire (finished leads) Dacron Wrapper

Woven Glass Sleeving

Figure 7-19. Toroidal Winding Leads Breakout. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

External Leads External Lead Connection External leads connected to an internal board shall extend through a separate opening in the enclosure, or encapsulation material, with spacing of 0.125 of an inch minimum on the centers, as shown in Figure 7-20. The external leads shall emerge, evenly spaced within a 90° sector or side, unless minimum spacing limits require a larger angle, as shown in Figure 7-21. If the number of leads is greater than that which can be accommodated around the periphery, the leads may be aligned in two rows. The external lead length will be six inches long, unless otherwise specified in the spec control drawing (SCD). 0.125 Inch Maximum Cover O

O

Lead Exit Holes 0.125 Inch Minimum

O

t

Fiberglass Enclosure

Figure 7-20. External Leads Breakout Location.

Bifurcated Terminals Fiberglass Enclosure Terminal Board

External Insulated Leads

Figure 7-21. Top View Showing Leads Breakout.

Installing the Magnetic Component Installation of Magnetic Device The magnetic component shall be placed into the enclosure in the location specified on the drawing. If the location is not specified, the magnetic device shall be located, as centrally in the enclosure cavity as practicable. The magnetic device may be spot-bonded in place, when properly located. See Figure 7-22. For an approved spot bonding material, refer to Chapter 8. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Bifurcated Terminals Sleeved Magnet Wire

Fiberglass Enclosure

Fastener Tube

(4) Spot Bonding

Toroid

Figure 7-22. Spot Bonding the Toroid.

Terminating the Leads Terminating the Leads After the magnet wire leads are terminated, with suitable strain relief, the external leads are attached to the terminals and soldered. The design of the enclosure and internal terminal boards shall be such that flexing of external lead wires, prior to encapsulation, shall not apply appreciable strain to the terminals. The standard length for lead wires is 6 inches; if the external lead wire is to be longer, it must be called out in the spec control drawing (SCD). After the lead wires have been soldered, a verification is done of the lead wire numbers, with the numbers on the magnetic device being the same, then the solder joints will be inspected. After inspection of solder joints and lead numbers, the magnetic device is ready for a pre-pot test. See Figure 7-23.

Fiberglass Enclosure Bifurcated Terminals (4) Spot Bonding Dacron, Covered Toroid Lead Markers (5) Teflon Leads, 6 Inches Long

Figure 7-23. Magnetic Device in Final Assembly.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Fastener Tube

Surface Mounts for High-Rel, Power Magnetics The surface mount carrier (SMC) is a means of attaching a component to a printed circuit board (PCB). There are many types of packages, and headers for mounting magnetic components to printed circuit boards. These mountings come in different configurations and styles. There are horizontal, vertical, open, and surface mounting, all of which are designed for the printed circuit board. The design engineer must select which configuration will best fulfill the design requirement. There are five areas to investigate when selecting a surface mount carrier (SMC) for use in a Hi-Rel environment: (1) molding material; (2) mechanical integrity; (3) terminal material; (4) solderability; (5) inspectability.

Introduction Mounting and packaging for magnetic components have become more important in recent years because the size of the power converter has become smaller. The reduction in size of the magnetic component is due to the higher operating frequency, and the power demand required by new scientific instruments and microprocessors. The surface mount carrier (SMC) is ideally suited for high frequency converters. However, using standard packaging has its drawbacks, such as a limited number of sizes for a given configuration. This could lead to design trade-offs, in order to get an adequate fit. Another factor is the current carrying capacity of the surface mount carrier pins. The output power of the converter has drop, but the output current could remain the same. The conductor material of the pins should be of high conductance for a minimum voltage drop. Even with copper pins, the cross section of the pin is not enough to handle the current capacity, and pins have to be paralleled to minimize the voltage drop.

Selecting the Best Plastic for Your Application Plastics used in molding toroid mounts and headers come in two broad categories: thermoset and thermoplastic. Thermoset plastics include epoxies, phenolics, and diallyl phthalate, (DAP), which are known for their environmental stability, and ability to tolerate over 400°C (750°F) without melting. Thermoplastics include nylon, polypropylene, polycarbonate, polyester, (Valox, Rynite), LCP (Vectra), and PPS (Ryton), which will begin to melt if they experience temperatures much above 260°C (500°F) for an extended period. The chemistry that gives thermoplastics a lower melting point also makes it less expensive to mold, giving it a cost advantage over the thermoset plastics. Thermoplastics are widely used in applications that do not experience temperatures above 260°C (500°F), except for a few seconds during the winding lead to terminal, and component to a PCB soldering process. Thermoset plastics, on the other hand, are popular in magnetic applications when they are used in conjunction with self-stripping magnetic wire. The unstripped and untinned magnetic wire is wrapped around the terminal, molded into a thermoset header or toroid mount, and then, dipped into a 400°C (750°F) solder pot. The high temperature solder will burn off the wire's insulation, tin the wire, and solder it to the terminal in a cost-effective way, without melting the mount. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

There are trade-offs between the two plastic types that must be considered. Parts molded from thermoplastic, will require pretinning the winding leads, and careful heat management while soldering the leads to the mount, and soldering the mount to the circuit board. The thermoset parts can be used with selfstripping magnetic wire. Several terminations can be soldered at once. This type of termination makes it ideal for fine insulated, magnet wire.

Through-Hole Toroid Mounts Through-hole headers and mounts connect components to a printed-circuit board by inserting a terminal or lead through a hole in the board and soldering it to the opposite side. Through-hole headers and mounts have two basic configurations, horizontal or vertical.

Horizontal Toroid Mounts Horizontal through-hole headers or toroid mounts are widely used as a platform or holder for mounting wound toroids on their side. They are usually molded from plastic, with the size, shape, and number of termination points specific to the wound toroid. They are most often either a platform, as shown in Figure 7-24, or cup-shaped, like Figure 7-25. The molding of either configuration will typically include standoffs, which allows the printed circuit board's, cleaning solutions to easily flow under the component. The minimum standoff is usually 0.0015 in.

The leads from the toroidal winding are attached to the mount's terminals, usually by soldering. Once the toroid is attached to the mount, this component is ready for insertion into a printed circuit board. Magnetic components are heavy, and the mechanical characteristics of the solder connection are as important as the electrical integrity. Printed circuit boards, with unplated through holes using heavy components, may require a clinched terminal, as described in Figure 7-26. Printed circuit boards, with printed through holes, offer good mechanical integrity without clinching, providing a successful intermetallic bond. This bond is created during the board solder process, as shown in Figure 7-27.

The toroids can be attached to the mount with either adhesives or mechanical means. Cup-shaped toroid mounts can be filled with a potting or encapsulation compound to both adhere and protect the wound toroid. Horizontal mounting offers both a low profile and a low center of gravity in applications that will experience shock and vibration. As the toroid's diameter gets larger, horizontal mounting begins to use up valuable circuit board real estate. If there is room in the enclosure, vertical mounting is used to save board space.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Header

Top View

Toroid

Solder Terminals

mm/

Side View

Standoffs Pads

Figure 7-24. Horizontal Platform with Through Hole.

Toroid Bottom View

Solder Pins

S •N • •

»* * »* *

|'

iriV

Side View

s ,X „ ~

rapIF

IT~l

Standoffs Pads

Figure 7-25. Horizontal Cup with Through Hole. Toroid

\

1

Header •M^H

J

Terminals Cut to Length

>

^r

^

^

V^/

A

V/'

1

? -^ — Printed Circuit Boarc Solder

Plated Solder Pad

Figure 7-26. Clinched Terminals. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Toroid

K

Header Terminals Cut to Length

/

Printed Circuit Board Plated Through Holes and Pad

Solder Figure 7-27. Clinched Terminals.

Vertical Toroid Mounts Toroids using vertical through-hole headers and vertical cups, are used to save circuit board real estate. As, with horizontal mounts, vertical mounts are usually molded from plastic, with the size, shape, and number of termination points specific to the application. The molding of either configuration will typically include standoffs, which allow the printed circuit board cleaning solutions to flow easily under the component. The minimum standoff is usually 0.015 in. Vertical toroid mounts come in many configurations, several of which are shown in Figures 7-28 and Figure 7-29. Much of their structure is devoted to supporting the vertical toroid and creating a stable base for connection to the printed circuit board.

Vertical Mount

Toroid Vertical Support

Standoff Pads

Solder Pins

Figure 7-28. Vertical Mount with Through Hole.

Vertical Cup

Standoff Pads

Toroid

Solder Pins

Figure 7-29. Vertical, Open Cup with Through Hole.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The leads from the toroidal winding are attached to the mount's terminals, by soldering, as shown in Figure 7-28. The toroids can be attached to the mount with either adhesives or mechanical means, or by encapsulation. The cup-shaped toroid mounts shown in Figure 7-29 and Figure 7-30, can be filled with a potting or encapsulation compound to both adhere and protect the wound toroid.

Toroid Vertical Cup Standoff Pads Solder Pins Figure 7-30. Vertical Cup with Through Hole. Vertical mounting saves circuit board real estate when a toroid's diameter gets larger, but it creates a component height issue. Vertical mounting also raises the component's center of gravity, making it vulnerable to shock and vibration.

Surface Mount, Toroid Mounts Surface mount components are a direct response to smaller size magnetic components and improved circuit board real estate. Instead of a pin or terminal passing through a printed circuit board, and being soldered on the opposite side, surface mount components utilize a flat solderable surface that is soldered to a flat solderable pad on the face of the printed circuit board. See Figures 7-31 and 7-32. For ease of manufacturing, the circuit board is usually coated with a paste-like formulation of solder and flux. With careful placement, surface mount style components on solder paste will stay in position until temperatures are elevated, usually from an infrared oven. The temperature melts the solder paste and solders the mount's flat terminals to the circuit board's pad. Surface Mount Header

Component Solder Pins

Standoff Pads

Figure 7-31. Gull Wing Surface Mount Carrier (SMC). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

r

^-^ Component Solder Pm —— *-—. Gull Wing Surface Mount

'

.} (

7^

11

11

\ 1

^N.

Printed Circuit Board /^= \r^> , ., mSS\\\\\1
s

/-\

1

J

—i

Solder Pad

^.y

;fa£

Figure 7-32. End View of a Soldered in Gull Wing.

Component Solder Pins

Surface Mount Header Solder Pad

Standoff Pads

Figure 7-33. "J" Type Lead Surface Mount Carrier (SMC).

Toroid

/

-\

/

/

\,

V,

]

s~\

ier Pin —1

f

\

\

•\

^ ^

t ^s^

Printed Circuit Board rd

X

S

I

J

J ^

^k. r

j.

~ ) v

^

J

1

"l ,

Snider Pad

^JLA

Figure 7-34. End View of a Soldered in, "J" Type.

Because the mount's leads lay on the printed circuit board, it is important that all the mount's leads are flat and on the same plane. If one or several of the leads are out of position, or not on the same plane as the others, the solder connection can be defective. The industry specification for lead "co-planarity" allows a tolerance of 0.004 of an inch from the plane of the printed circuit board. The use of a holding fixture is imperative when mounting the toroid.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The most familiar styles are either gull wing, as shown in Figure 7-31, or "J" lead, as shown in Figure 7-32. Both are horizontal surface mount devices. The gull wings are flexible to withstand thermal expansion and contraction, and it is easy to inspect the integrity of the gull wing lead to circuit board solder connection. The "J" lead also has wide acceptance because it uses up less board real estate than the gull wing. However, the "J" lead to the board solder connections is hidden from inspection, and the leads are more difficult to form. Once the toroids are attached to the mount, with either adhesives or mechanical means, or by encapsulation, the winding leads are soldered to the mount's terminations. Both the gull wing and "J" lead are subject to co-planarity problems, if packaging for shipment and production handling is not carefully considered.

There is another surface mount technique called the "Lunar Lander," which is shown in Figures 7-35 and 736. The "Lunar Lander" incorporates a lead style that is more rigidly supported by the plastic molding. This style is very robust, and will tolerate handling and shipping with little or no effect on the co-planarity. This style solders well with the mount to board connections mostly visible for inspection. Figure 7-35 shows the Lunar Lander lead style incorporated with a cup-shaped mount. This can be filled with a potting or encapsulation compound to both adhere and protect the wound toroid.

Toroid

Surface Mount Header

Component Solder Pins Bottom View Side View

Solder Pad

Standoff Pads

Figure 7-35. Lunar Lander Surface Mount Carrier (SMC).

'up —>• Inverted Cup

k

Component Solderr Pin 3oard \

^

J

:

/ K, ^r* t

Figure 7-36. End View of a Soldered Lunar Lander.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Lander Terminal

^—• C/~v1/-1oiooiaer Do/4 r aa

\

Reference Lodestone Pacific 4769 Wesley Drive, Anaheim, CA 92807 Phone: (800) 694-8089, Fax: (714) 970-0800 Web page: www.loadestonepacific.com

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 8

Polymeric Impregnate, Embedment, and Adhesives

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. Applicable Documents 3.

Specifications

4.

Standard

5. Impregnation/Embedment, (The Two Step Process) 6. Part Preparation 7. Impregnation Using Scotchcast 280 or 235 8. Embedment Using Scotchcast 281 or 241 9.

Quality Assurance

10. Impregnation/Embedment, (The Single Step Process) 11. Part Preparation 12. Embedment Using Scotchcast 281 or 241 13. Quality Assurance 14. Preparing Polymeric Materials 15. Preparing Scotchcast 280 for Impregnation 16. Preparing Scotchcast 235 for Impregnation 17. Preparing Scotchcast 281 for Embedment 18. Preparing Scotchcast 241 for Embedment 19. Preparing Stycast 1095/9 for Spot Bonding 20. Preparing Epoxy-Polyamide Adhesive EC-2216 B/A 21. Preparing Silicone Rubber Compound (RTV 566 A/B) 22. Application and Storage 23. Cut "C" Core and "E" Core Assembly Preparation 24. Cut Cores with Stress Relief Coating RTV-566 25. Polymeric Mixing Record Form 26. Tools and Aids

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Function This chapter covers the procedures to be used for the impregnation and embodiment of transformers and inductors used in electrical circuits. This process provides electrical insulation, together with moisture and mechanical protection for these parts. The transformer and inductor will be referred to as, "magnetic component," throughout this chapter. Materials Covered (See Table 8-1) The complete procedure shall consist of impregnation, (Scotchcast 280), followed by embedment, (Scotchcast 281), unless either, "impregnation only," or, "embedment only," is specified on the engineering drawing. Scotchcast 280 and 281 are high temperature materials, (Class F, 155°C). Scotchcast 235 and 241 are for low temperature impregnation and embedment. Scotchcast 235 is the impregnate and 241 is the embedment, to be used at lower temperature, (Class B, 130°C). Also, included are the gap adhesive cements, EC2216 A and B, the stress relief materials, RTV566A and B for the magnetic core, and the spot bonding material, Stycast 1095/9. Application and mixing procedures are given for all materials.

Table 8-1. Polymeric Materials.

Polymeric Materials Application

Manufacturer

Transformer Gap Cement

Emerson Cuming, Inc.

Transformer Stress Relief Open Cores Transformer Spot Bonding

GE

Emerson Cuming, Inc.

Impregnation

3M

Materials and Mix Ratio Cure (2) Polymeric Ratio (1) EC2216A 140(+/-1) Min. cure 24 hrs. at room temp. EC2216B 100(+/-1) Full cure, 7 days at room temp. 3 hrs. at65°C(150°F) RTV566A 100(+/-1) Min. cure, 24 hrs. at room temp. Full cure, 7 days at room temp. RTV566B 0.1 Stycast 1095 Catalyst

100(+/-1) 9(+/-l)

24 hrs. at room temp.

Cured Control Sample A-93 (+/-3)

A-47

>D-65

Transformers and Inductors, (potting) Scotchcast 235A Scotchcast 235B Embedment 3M Scotchcast 241 A Scotchcast 24 IB Impregnation 3M Scotchcast 280A Scotchcast 280B Embedment 3M Scotchcast 281 A Scotchcast 28 IB 1 . All ratios are parts-by- weight (pbw). 2. Specimens being produced to provide proof of cure. 3. Shore Hardness per ASTM D-2240.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1 2 1 2 2 3 2 3

16 to 20 hrs. at 94°C (200°F)

D-50 or higher

16 to 20 hrs. at 94°C (200°F)

D-60 or higher

16 to 20 hrs. at 94°C (200°F)

D-60 or higher

16 to 20 hrs. at 94°C (200°F)

D-60 or higher

Applicable Documents The following documents are specified, as the controlling specification herein:

Specifications 3M Company,

Material Specification, Epoxy Resin Encapsulant (Scotchcast 281 A/B).

3M Company,

Material Specification, Epoxy Resin Encapsulant (Scotchcast 280 A/B).

3M Company,

Material Specification, Epoxy Resin Encapsulant (Scotchcast 241 A/B).

3M Company,

Material Specification, Epoxy Resin Encapsulant (Scotchcast 235 A/B).

Emerson Gumming,

Material Specification, Epoxy Resin Bonding (Stycast 1095/9)

3M Company,

Material Specification, Epoxy-Polyamide Adhesive (EC-2216 A/B)

General Electric,

Material Specification, Silicone Rubber Adhesive (RTV-566 A/B)

Federal O-T-620

1,1,1 Trichlorethane (Inhibited) Methyl Chloroform

Standard American Society for Testing Materials ASTM-D-1706-61 Indentation Hardness of Plastic by Means of a Durometer

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Impregnation/Embedment, (The Two Step Process) Part Preparation Potting Cups Clean the potting cups as shown in Figure 8-1, by immersing them in 1,1,1 trichlorethane, and brushing them with a No. 1 acid brush as shown in Figure 8-2. Allow the potting cups to air dry for a minimum of five minutes before using then: Do not touch the interior of the cups with bare hands after they have been cleaned. All personnel required to handle these parts shall wear clean, white, cotton gloves, when handling parts after surface preparation. Fastener Tubes

Enclosure Wall Figure 8-1. Typical Enclosures for a Magnetic Device.

Figure 8-2. Typical, Acid-Cleaning Brush. Magnetic Components Visually inspect the parts to be sure the lead ends are identified with EZ code labels, or equivalent and that they are free of grease or dirt. If grease or dirt is present, clean the parts by wiping with a clean cloth, wet with 1,1,1 trichlorethane. Dry the parts in a vacuum oven, for one hour at 100° +/-3°C, (212° +/-10°F), and at 2 ±0.5 mm Hg pressure to remove any entrapped moisture. If a vacuum oven is not available, the parts may be dried in an air-circulating oven at 100° +/-5°C, (212° +/-10°F), for three hours. Leave the parts in the oven until they are ready to be processed.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Impregnation Using Scotchcast 280 or 235 Application I Impregnate the magnetic component using either of the following procedures: The first procedure, A, which uses a vacuum oven or tank, has provisions for the introduction of material under vacuum. The second procedure, B, permits introduction of the material at ambient pressure, followed by the application of a vacuum to accomplish the impregnation. A. Procedure-Vacuum Application Place the warm, predried magnetic component in a suitable container and then place the container in a heated vacuum oven or tank, which has provisions for the introduction of material under vacuum. Preheat and maintain the vacuum oven or tank at a temperature of 60°+/-3°C, (140° +/-5°F). With the vacuum oven maintained at this temperature, lower the pressure to less than 10 mm, Hg. Hold this pressure for 15 minutes. Without releasing the vacuum, allow the warm, degassed resin to flow rapidly into the container until the parts are covered. Maintain the vacuum for an additional 20 minutes. Gradually return the vacuum oven or tank, (within one minute), to room pressure and maintain at this pressure for 10 minutes. Evacuate the chamber, again, to less than 10 mm, Hg, and hold this pressure for an additional 20 minutes. Release the vacuum slowly to room ambient pressure. Remove parts from the liquid resin and allow the excess material to drain off. Remove additional material by wiping with a clean cloth or tissue. B. Procedure - Ambient Pressure Application Place the warm, predried transformer or inductor into a suitable container. Fill the container, at ambient pressure, with the warm 60°C, (140°F), degassed resin until the parts are covered. Where possible, preheat the vacuum chamber to a temperature of 60°+/-6°C, (140° +/-10°F). Place the container of parts and resin into the vacuum chamber and evacuate to less than 10 mm Hg and maintain this vacuum for 20 minutes. Gradually, return the chamber, (within one to two minutes), to room pressure and maintain at this pressure for 5 to 10 minutes. Repeat this procedure of evacuating the vacuum chamber, maintaining the vacuum for 20 minutes and then, return the chamber to ambient pressure. Remove the parts from the liquid resin and allow the excess material to drain off, as shown in Figure 8-3 and Figure 8-4. Magnetic Component

Impregnate Dram '

Teflon Stick

Figure 8-3. Draining the Magnetic Component Before Curing.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Coil Assembly

i I

Impregnate Drain

Teflon Stick

Figure 8-4. Draining the Wound Coil Assemblies, Before Curing. Cure Place the impregnated parts into an air circulating oven and cure at 75° +/-3°C, (167° +/-5°F), for 15 to 20 hours. Inspect the part and remove the excess resin with a Q-tip, clean cloth or tissue during the first hour of cure. Inspection (QA) (It is time to inspect the work in process.) "C", "U", or "E" Cores See Cut "C" Cores and "E" Cores Assembly Preparation.

Spot Bonding with Stycast 1095/9 The terminal board will be installed into the cup, as shown in Figure 8-5, at the location specified on the Spec Control Drawing, (SCD). Terminal Board

Bifurcated Terminals

Bifurcated Terminals

Fastener Tube

Inserts Fifberglass Enclosure Figure 8-5. Terminal Boards, Bonded to the Wall. Inspection (QA) (It is time to inspect the work in process.) Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Terminal Board

Installing the Magnetic Component The magnetic component will be placed into the cup as shown in Figure 8-6, in the location specified on the spec control drawing, (SCO). The magnetic component will be spot-bonded in place, when properly located. Spot Bonding

C Core

Toroid

Figure 8-6. Spot-Bonding the Magnetic Component. Inspection (QA) (It is time to inspect the work in process.) Leads, Termination, and Sealant Route and terminate all leads, as required by the spec control drawing, (SCO). Verify that all solder joints have been inspected. Seal all leads, leaving the cup with RTV 3116, to prevent leakage of the embedment material. Apply the sealant around the exit of each wire, or around a group of wires, if a number of them exit within a small area, as shown in Figure 8-7. Cure the RTV 3116 for 10 minutes at room temperature. Fiberglass Enclosure Bifurcated Terminals (4) Spot-Bonding

Fastener Tube

Dacron, Covered Toroid Lead Markers (5) Teflon Leads, 6 Inches Long

RTV 3116 Sealant

Figure 8-7. Typical, Magnetic Component in Final Assembly. Inspection (QA) (It is time to inspect the work in process.)

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Potting Cups Without Lids Wrap a length of Permacel, No. 248 tape around the periphery of the potting cup, so that it projects above the level of the cup to a potting well, so the potting cup may be completely filled with the embedment material, as shown in Figure 8-8.

Tape -

RTV Sealant I— Potting Cup External Leads -

Figure 8-8. Potting Cup with Periphery Tape. Potting Cups with Lids Check all wire routing and terminations, prior to bonding lids in place. Use only lids with two holes, through which the embedment material is poured. Bond the lid in place in accordance with the applicable, engineering drawing. Modify two plastic syringes to serve as a funnel for pouring the embedment material into the cup. The funnel can also serve as a reservoir for excess material. Use Biggs, 10 cc, plastic syringes that reduce to a small diameter at the tip. Cut part of the tip off, so that the diameter of the portion remaining is only slightly larger than the hole in the lid. Cut the barrel of the syringe so that approximately two inches remain, as shown on Figure 8-9. Locate a modified syringe above each hole. Seal and hold in place, with RTV 3116 placed around the junction of the syringe and the lid, as shown in Figure 8-10. This method is not suitable if the holes in the lids are smaller than 3.2 mm, (0.125 inches) in diameter. In this case, refer to Application II.B (page 8-11), for the correct procedure.

2 Inches

Cut off the end so that it is larger than potting hole.

Figure 8-9. A Funnel Made from a Modified Plastic Syringe. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Potting Funnels

Figure 8-10. Potting Filling Ports. Embedment Using Scotchcast 281 or 241 Application II Embed the assembled part using one of the following procedures: The first procedure, A, which uses a vacuum oven or tank, has provisions for the introduction of material under vacuum, is preferred. The second procedure, B, permits introduction of the material at ambient pressure, followed by the application of a vacuum, to accomplish the impregnation. Use of the second procedure, B, is required if the holes in the lid of the potting cup are less than 3.2 mm, (0.125 inches) in diameter.

A. Procedure-Vacuum Application Place the assembled potting cup in a heated vacuum oven or tank which has provisions for the introduction of material under vacuum. Locate the potting cup so that the embedment material can flow from the material reservoir into the cup or modified syringe leading into the cup. Preheat and maintain the vacuum oven or tank at a temperature of 60° +/-3°C, (140° +/-5°F). With the vacuum oven maintained at this temperature, lower the pressure to less than 10 mm Hg, and hold this pressure for 15 minutes. Without releasing the vacuum, allow the warm, degassed Scotchcast 281/241 to flow, (by means of the modified syringe), into the potting cup. Fill the potting cup until the material rises in the other modified syringe. Fill the potting cups without lids, above the level of the cup. See Figure 8-8. Maintain the vacuum for an additional 20 minutes. Gradually return the vacuum oven or tank, (within one minute), to room pressure and maintain this pressure for 5 to 10 minutes. Evacuate the chamber, again, to less than 10 mm Hg, and hold this pressure for 20 minutes. Release the vacuum slowly to room ambient pressure. Remove any excess embedment material from the exterior of the potting cup by wiping with a cloth wet with methylene chloride. Do not remove the plastic syringes before curing.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

B. Procedure-Ambient Pressure Application Fill the assembled potting cup with the warm, degassed Scotchcast 281/241. For potting cups with lids having holes less than 3.2 mm (0.125 inches) in diameter, use an unmodified 10 cc syringe for filling the cup. Where possible, preheat the vacuum chamber to a temperature of 60°+/-6°C, (140° +/-10°F). Place the potted unit into the vacuum chamber and evacuate to less than 10 mm Hg, and maintain this vacuum for 20 minutes. Gradually, return the chamber, (within one to two minutes), to room pressure and maintain at this pressure for 5 to 10 minutes. Repeat this procedure of evacuating the vacuum chamber, maintaining the vacuum for 20 minutes, and then, returning the chamber to ambient pressure. Remove the assemblies, and use a cloth wet with methylene chloride to remove any material from the exterior of the potting cup. Cure Place the embedded unit into an air circulating-oven and cure at 75°+/-3°C, (167° +/-5°F), for 15 to 20 hours. Inspect the surface of the material, where possible, for bubbles during the first hour of cure. Break any bubbles with a toothpick or any other sharp probe. CAUTION To avoid damage, the oven shall have two independent temperature control devices; one to control and record the temperature to the predetermined setting, and the second control device to turn off the heat if the desired temperature is exceeded by more than 11°C, (20°F).

Cleanup Remove all RTV 3116 used as a sealing material. If cured embedment material or a portion of the polyethylene syringe adheres to the potting cup lid, cut the syringe with a razor blade so the material remaining is flush with the lid. Remove all masking tape applied to potting cups without lids. Use a cloth, wet with methylene chloride, to remove any tape residue from the exterior surfaces of the potting cup. Dimensions Check all completed assemblies for conformance with the dimensional requirement, as shown on the spec control drawing, (SCO). Remove any excess material protruding above the level of the potting cup, (primarily, cups without lids). Hold the part firmly and remove any excess material by filing, sawing or sanding. Inspection (QA) (It is time to inspect the work in process.) CAUTION During machining, avoid excessive vibration, which may cause damage.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Quality Assurance Inspection Quality Assurance shall inspect the procedures, materials, and equipment, in accordance with the requirements specified herein. Acceptance Criteria The acceptance criteria for impregnated and embedded transformers or inductors shall be as follows. The finished part shall be unacceptable if any of the following occurs:

a.

If the incorrect type of process or material was used.

b.

If the cured impregnating or embedment material is soft, tacky, or has any other indication of an improper cure.

c.

If there are cracks, voids, cavities, discolorations, or any other evidence of unsatisfactory blending or application.

d.

If there is unsatisfactory bonding of the cured material to an epoxy fiberglass potting cup.

e.

If the cured material is torn, burned or crumbling.

f.

If compound is on the exterior surface of the potting cup.

g.

If the dimensional requirements are not complied with.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Impregnation/Embedment, (The Single Step Process) Part Preparation Potting cups Clean potting cups, as shown in Figure 8-11, by immersing them in 1,1,1 trichlorethane and brushing them with a No. 1 acid brush, as shown in Figure 8-12. Allow the potting cups to air dry for a minimum of five minutes before using. Do not touch the interior of the cups with bare hands after they have been cleaned. All personnel required to handle these parts shall wear clean, white, cotton gloves, when handling parts after surface preparation. Fastener Tubes

Enclosure Wall Figure 8-11. Typical, Enclosures for Magnetic Device.

Figure 8-12. Typical Acid Cleaning Brush. Magnetic Components Visually inspect the parts to be sure that the lead ends are identified with EZ code labels, or equivalent and they are free of grease or dirt. If grease or dirt are present, clean the parts by wiping with a clean cloth wet with 1,1,1 trichlorethane. Dry the parts in a vacuum oven for one hour at 100° +/-5°C, (212° +/-10°F), and at 2 ±0.5 mm Hg, pressure to remove any entrapped moisture. If a vacuum oven is not available, the parts may be dried in an air circulating oven at 100 +/-5°C, (212° +/-10°F), for three hours. Leave the parts in the oven until they are ready to be processed. "C", "U". or "E" Cores See the Table of Contents for, Cut "C" Cores and "E" Cores Assembly Preparation. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Spot Bonding with Stycast 1095/9 The terminal board will be installed into the cup, as shown in Figure 8-13, at the location specified on the spec control drawing, (SCD). Terminal Board

Bifurcated Terminals

Terminal Board

Bifurcated Terminals

Fastener Tube

Inserts

^

Fifberglass Enclosure

Figure 8-13. Terminal Boards, Bonded to the Wall. Inspection (QA) (It is time to inspect the work in process.) Installing the Magnetic Component The magnetic component will be placed into the cup, as shown in Figure 8-14, in the location specified on the spec control drawing, (SCD). The magnetic component will be spot-bonded in place, when properly located. Spot-Bonding

Toroid

C Core

Figure 8-14. Spot-Bonding the Magnetic Component. Inspection (QA) (It is time to inspect the work in process.) Leads, Termination and Sealant Route and terminate all leads, as required by the spec control drawing, (SCD). Verify that all solder joints have been inspected. Seal all leads leaving the cup, with RTV 3116, to prevent leakage of the embedment material. Apply the sealant around the exit of each wire, or around a group of wires, if a number of them exit within a small area, as shown in Figure 8-15. Cure the RTV 3116 for 10 minutes at room temperature.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Fiberglass Enclosure Bifurcated Terminals (4) Spot-Bonding

Fastener Tube

Dacron, Covered Toroid Lead Markers (5) Teflon Leads, 6 Inches Long

RTV 3116 Sealant

Figure 8-15. Typical Magnetic Component in Final Assembly. Inspection (QA) (It is time to inspect the work in process.) Potting Cups Without Lids Wrap a length of Permacel, No. 248 tape around the end of the potting cup, so that it projects above the level of the cup to a potting well, so that the porting cup may be completely filled with the embedment material, as shown in Figure 8-16.

Tape -

RTV Sealant I— Potting Cup External Leads Figure 8-16. Potting Cup with Periphery Tape. Potting Cups with Lids Check all wire routing and terminations prior to bonding the lids in place. Use only lids with two holes, through which the embedment material is poured. Bond the lid in place in accordance with the Spec Control Drawing, (SCO). Modify two plastic syringes to serve as a funnel for pouring the embedment material into the cup. The funnel can also serve as a reservoir for excess material. Use Biggs, 10 cc, plastic syringes that reduce to a small diameter at the tip. Cut part of the tip off so that the diameter of the portion remaining is only slightly larger than the hole in the lid. Cut the barrel of the syringe so that approximately two inches remain, as shown on Figure 8-17. Locate a modified syringe above each hole. Seal and hold in place with RTV 3116 placed around the junction of the syringe and the lid, as shown in Figure 8-18.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

2 Inches

Cut off the end so that it is larger than potting hole. Figure 8-17. A Funnel Made from a Modified Plastic Syringe.

Pottmc Funnels

Potting Holes

Figure 8-18. Potting Filling Ports.

Embedment Using Scotchcast 281 or 241 Application Embed the assembled part using one of the following procedures: The first procedure, A, which uses a vacuum oven or tank, that has provisions for the introduction of material under vacuum. The second procedure, B, permits introduction of the material, at ambient pressure, followed by application of a vacuum, to accomplish the impregnation. Use of the second procedure, B, is required if the holes in the lid of the potting cup are less than 3.2 mm, (0.125 inches), in diameter.

A. Procedure-Vacuum Application Place the assembled potting cup in a heated vacuum oven or tank which has provisions for the introduction of material under vacuum. Locate the potting cup so that the embedment material can flow from the material reservoir into the cup or modified syringe leading into the cup. Preheat and maintain the vacuum oven or tank at a temperature of 60° +/-3°C, (140° +/-5°F). With the vacuum oven maintained at

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

this temperature, lower the pressure to less than 10 mm Hg, and hold this pressure for 15 minutes. Without releasing the vacuum, allow the warm, degassed Scotchcast 281/241 to flow (by means of the modified syringe) into the potting cup. Fill the potting cup until the material rises in the other modified syringe. Fill the potting cups without lids, above the level of the cup. See Figure 8-16. Maintain the vacuum for an additional 20 minutes. Gradually return the vacuum oven or tank, (within one minute), to room pressure and maintain this pressure for 5 to 10 minutes. Evacuate the chamber, again, to less than 10 mm Hg and hold this pressure for 20 minutes. Release the vacuum slowly to room ambient pressure. Remove any excess embedment material from the exterior of the potting cup by wiping with a cloth wet with methylene chloride. Do not remove the plastic syringes before curing.

B. Procedure-Ambient Pressure Application Fill the assembled potting cup with the warm, degassed Scotchcast 281/241. For potting cups with lids having holes less than 3.2 mm, (0.125 inches), in diameter, use an unmodified 10 cc syringe for filling the cup. Where possible, preheat the vacuum chamber to a temperature of 60°+/-6°C, (140° +/-10°F). Place the potted unit into the vacuum chamber and evacuate to less than 10 mm Hg, and maintain this vacuum for 20 minutes. Gradually, return the chamber, (within one to two minutes), to room pressure and maintain at this pressure for 5 to 10 minutes. Repeat this procedure of evacuating the vacuum chamber, maintaining the vacuum for 20 minutes, and then, returning the chamber to ambient pressure. Remove the assemblies, and use a cloth wet with methylene chloride to remove any material from the exterior of the potting cup.

Cure Place the embedded unit into an air circulating oven and cure at 75° +/-3°C, (167° +/-5°F), for 15 to 20 hours. Inspect the surface of the material, where possible, for bubbles during the first hour of cure. Break any bubbles with a toothpick or any other sharp probe.

CAUTION To avoid damage, the oven shall have two independent temperature control devices; one to control and record the temperature to the predetermined setting, and the second control device to turn off the heat if the desired temperature is exceeded by more than 11°C, (20°F).

Cleanup Remove all RTV 3116 used as a sealing material. If cured embedment material or a portion of the polyethylene syringe adheres to the potting cup lid, cut the syringe with a razor blade so the material remaining is flush with the lid. Remove all masking tape applied to potting cups without lids. Use a cloth, wet with methylene chloride to remove any tape residue from the exterior surfaces of the potting cup.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Dimensions Check all completed assemblies for conformance with the dimensional requirement as shown on the Spec Control Drawing, (SCO). Remove any excess material protruding above the level of the potting cup (primarily, cups without lids). Hold the part firmly and remove any excess material by filing, sawing or sanding.

CAUTION During machining, avoid excessive vibration, which may cause damage.

Quality Assurance Inspection Quality Assurance shall inspect the procedures, materials and equipment, in accordance with the requirements specified herein.

Acceptance Criteria The acceptance criteria for impregnated and embedded transformers or inductors shall be as follows. The finished part shall be unacceptable if any of the following occurs:

a.

If the incorrect type of process or material was used.

b.

If the cured impregnating or embedment material is soft, tacky, or has any other indication of an improper cure.

c.

If there are cracks, voids, cavities, discolorations, or any other evidence of unsatisfactory blending or application.

d.

If there is unsatisfactory bonding of the cured material to an epoxy fiberglass, potting cup.

e.

If the cured material is torn, burned or crumbling.

f.

If compound is on the exterior surface of the potting cup.

g.

If the dimensional requirements are not complied with.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Preparing Polymeric Materials Proof of Cure All polymeric materials used in the processing of magnetic devices shall have proof of cure established by testing the hardness of a sample of the material that has been processed concurrently with the magnetic devices. The hardness of the sample shall meet the hardness specified by the manufacturer of the material.

Preparing Scotchcast 280 for Impregnation Control Specification for Scotchcast 280 A/B. 3M Product Information, use Electrical Resin Scotchcast 280 A/B to the latest revision.

Mixing Scotchcast 280 Material Preparation and Control Heat Part A and Part B of Scotchcast 280 to a temperature of 60° +/-5°C, (140° +/-10°F) prior to mixing, in order to reduce the viscosity. Heat the material, by either placing the containers in a oven, or by partially immersing them in hot water. Do not heat them on a hot plate, or over an open flame. Mix the materials thoroughly in their original containers. Weigh the separate parts to within two percent accuracy, using the proportions as follows: 1) Scotchcast 280, Part A: 2 parts by weight. 2) Scotchcast 280, Part B: 3 parts by weight. Weigh the materials on a balance scale, accurate to 0.10 grams. Use either a glass or metal round bottom, (without corners), container, suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients, using a stainless steel spatula, until the color is absolutely uniform, or a homogeneous mixture is obtained. This information should now be recorded on the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Degassing Scotchcast 280 Place the container of warm, mixed Scotchcast 280 into a vacuum chamber that has been preheated to 60°C (140°F). Lower the pressure in the vacuum chamber to less than 10 mm Hg, and degas the material until foaming ceases. Do not subject the material to a vacuum of less than one mm Hg, or, for more than 15 minutes. The container's sidewalls should be four times the height of the liquid resin to contain the foaming that takes place in a vacuum.

Control Sample, Scotchcast 280 For each mixed batch of Scotchcast 280, make a control sample by transferring a portion of the degassed material into an aluminum foil dish to a depth of approximately 6.4 mm (0.25 inches). Identify the control sample by writing the mixture record number and date on the outside of the bottom of the dish. Place the Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

control sample in the same vacuum oven or tank that will be used for processing the parts. Subject the control sample to the same process conditions that the parts will undergo. After exposure to the actual processing conditions, cure the control sample for 15 to 20 hours at a temperature of 75° +/-3°C, (167° +/5°F). The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample, after cure, per ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness shall be a minimum of 60. Determine tackiness by pressing a clean polyethylene film on the surface of the sample. The film shall not adhere to the surface. If any control samples fail to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing Scotchcast 280 Cure Scotchcast 280 in a air circulating oven at 75° +/-3°C, (167 +/-5°F), for 15 to 20 hours.

Preparing Scotchcast 235 for Impregnation Control Specification for Scotchcast 235 A/B 3M, Product Information, use Electrical Resin Scotchcast 235 A/B to the latest revision.

Mixing Scotchcast 235 Material Preparation and Control Heat Part A and Part B of Scotchcast 235 to a temperature of 60° +/-5° C, (140° +/-10 0 F), prior to mixing, in order to reduce the viscosity. Heat the material by either placing the containers in a oven or by partially immersing them in hot water. Do not heat them on a hot plate or over an open flame. Mix the materials thoroughly in their original containers. Weigh the separate parts to within two percent accuracy using the proportions as follows: 1) Scotchcast 235, Part A: 1 part by weight. 2) Scotchcast 235, Part B: 2 parts by weight. Weigh the materials on a balance scale, accurate to 0.10 grams. Use either a glass or metal round bottom, (without corners) container suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients, using a stainless steel spatula, until the color is absolutely uniform, or a homogeneous mixture is obtained. This information should now be recorded on the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Degassing Scotchcast 235 Place the container of warm, mixed Scotchcast 235 into a vacuum chamber that has been preheated to 60°C, (140°F). Lower the pressure in the vacuum chamber to less than 10 mm Hg, and degas the material until foaming ceases. Do not subject the material to a vacuum of less than one mm Hg, or, for more than 15

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

minutes. The container's sidewalls should be four times the height of the liquid resin to contain the foaming that takes place in a vacuum.

Control Sample Scotchcast 235 For each mixed batch of Scotchcast 235, make a control sample by transferring a portion of the degassed material into an aluminum foil dish to a depth of approximately 6.4 mm (0.25 inches). Identify the control sample by writing the mixture record number and date on the outside of the bottom of the dish. Place the control sample in the same vacuum oven or tank that will be used for processing the parts. Subject the control sample to the same process conditions that the parts will undergo. After the exposure to the actual processing conditions, cure the control sample for 15 to 20 hours at a temperature of 75° +/-5°C, (167° +/5°F). The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample after cure, per ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness of 50 shall be the minimum. Determine tackiness by pressing a clean polyethylene film on the surface of the sample. The film shall not adhere to the surface. If any control samples fail to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing Scotchcast 235 Cure Scotchcast 235 in a air circulating oven at 75° +/-3°C, (167° +/-5°F), for 15 to 20 hours.

Preparing Scotchcast 281 for Embedment Control Specification for Scotchcast 281 A/B 3M Product Information, use Electrical Resin Scotchcast 281 A/B to the latest revision.

Mixing Scotchcast 281 Material Preparation and Control Heat Part A and Part B of Scotchcast 281 to a temperature of 60° +/-5°C, (140° +/-10°F), prior to mixing in order to reduce the viscosity. Heat the material by either placing the containers in a oven or by partially immersing them in hot water. Do not heat them on a hot plate or over an open flame. Mix the materials thoroughly in their original containers. Weigh the separate parts to within two percent accuracy using the proportions as follows: 1) Scotchcast 281, Part A: 2 parts by weight. 2) Scotchcast 281, Part B: 3 parts by weight. Weigh the materials on a balance scale, accurate to 0.10 grams. Use either a glass or metal round bottom, (without corners), container suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients, using a stainless steel spatula, until the color is absolutely uniform, or a homogeneous mixture is obtained. This information should now be recorded on the Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Degassing Scotchcast 281 Place the container of warm, mixed Scotchcast 281 into a vacuum chamber that has been preheated to 60°C, (140°F). Lower the pressure in the vacuum chamber to less than 10 mm Hg, and degas the material until foaming ceases. Do not subject the material to a vacuum of less than one mm Hg, or, for more than 15 minutes. The container's sidewalls should be four times the height of the liquid resin to contain the foaming that takes place in a vacuum.

Control Sample Scotchcast 281 For each mixed batch of Scotchcast 281, make a control sample by transferring a portion of the degassed material into an aluminum foil dish to a depth of approximately 6.4 mm (0.25 inches). Identify the control sample by writing the mixture record number and date on the outside of the bottom of the dish. Place the control sample in the same vacuum oven or tank that will be used for processing the parts. Subject the control sample to the same process conditions that the parts will undergo. After exposure to the actual processing conditions, cure the control sample for 15 to 20 hours at a temperature of 75° +/-3°C, (167° +/5°F). The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample after cure, per ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness of 60 shall be the minimum. Determine tackiness by pressing a clean polyethylene film on the surface of the sample. The film shall not adhere to the surface. If any control samples fails to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing Scotchcast 281 Cure Scotchcast 281 in a circulating air oven at 75° +/-3°C, (167° +/-5°F), for 15 to 20 hours.

Preparing Scotchcast 241 for Embedment Control Specification for Scotchcast 241 A/B 3M Product Information, use Electrical Resin Scotchcast 241 A/B to the latest revision.

Mixing Scotchcast 241 Material Preparation and Control Heat Part A and Part B of Scotchcast 241 to a temperature of 60° +/-5°C, (140° +/-10°F) prior to mixing in order to reduce the viscosity. Heat the material by either placing the containers in a oven or by partially immersing them in hot water. Do not heat them on a hot plate or over an open flame. Mix the materials thoroughly in their original containers. Weigh the separate parts to within two percent accuracy using the proportions as follows:

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

1) Scotchcast 241, Part A: 1 part by weight. 2) Scotchcast 241, Part B: 2 parts by weight. Weigh the materials on a balance scale, accurate to 0.10 grams. Use either a glass or metal round bottom, (without corners), container suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients, using a stainless steel spatula, until the color is absolutely uniform, or a homogeneous mixture is obtained. This information should now be recorded on the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Degassing 241 Place the container of warm, mixed Scotchcast 241 into a vacuum chamber that has been preheated to 60°C, (140°F). Lower the pressure in the vacuum chamber to less than 10 mm Hg, and degas the material until foaming ceases. Do not subject the material to a vacuum of less than one mm Hg, or, for more than 15 minutes. The container's sidewalls should be four times the height of the liquid resin to contain the foaming that takes place in a vacuum.

Control Sample Scotchcast 241 For each mixed batch of Scotchcast 241, make a control sample by transferring a portion of the degassed material into an aluminum foil dish to a depth of approximately 6.2 mm, (0.25 inches). Identify the control sample by writing the mixture record number and date on the outside of the bottom of the dish. Place the control sample in the same vacuum oven or tank that will be used for processing the parts. Subject the control sample to the same process conditions that the parts will undergo. After the exposure to the actual processing conditions, cure the control sample for 15 to 20 hours at a temperature of 75° +/-3° C (167° +/-5° F). The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample after cure, per ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness of 60 shall be the minimum. Determine tackiness by pressing a clean polyethylene film on the surface of the sample. The film shall not adhere to the surface. If any control samples fail to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing Scotchcast 241 Cure Scotchcast 241 in a circulating air oven at 75° +/-3°C, (167° +/-5°F) for 15 to 20 hours.

Preparing Stycast 1095/9 for Spot Bonding Control Specification for Stycast 1095/9 Emerson and Cuming, Inc., Mixing Bulletin for Stycast 1095 and Catalyst No. 9, to the latest revision.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Mixing Stycast 1095/9 Material Preparation and Control Warm the Stycast 1095 in its original container to approximately 54°C, (130°F), in order to reduce the viscosity and facilitate mixing. Thoroughly blend the ingredients using a stainless steel spatula until a homogeneous mixture is obtained. Cool the Stycast 1095 to room temperature before mixing with Catalyst 9. Weight out 100 +/-1 parts, by weight, of Stycast 1095, and add 9 +/- 0.1 parts, by weight, of Catalyst 9. Weigh the materials on a balance scale accurate to 0.10 grams. Use either a glass or metal round bottom, (without corners) container, suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Do not mix more than 100 grams of resin and 9 grams of catalyst at any one time. Mix the ingredients thoroughly keeping the end of the mixing blade below the mixture level. Avoid any whipping motion, which would tend to introduce air into the mixture. This information should now be recorded in the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Pot Life of Stycast 1095/9 The useful life of the mixed material is approximately 30 minutes, after adding the catalyst. The end of useful life is indicated by the lack of wetting and adhesion, or excessive thickening of the mixed material. Any mixed material, exhibiting these characteristics, shall be discarded immediately, regardless of the time at which it was first mixed.

Control Sample Stycast 1095/9 For each mixed batch of Stycast 1095/9, make a control sample by transferring a portion of the material into an aluminum foil dish to a depth of approximately 1/8 inch. Identify the control sample, by writing the mixture record number and date on the outside, of the bottom of the small aluminum dish. Cure the control sample, overnight, at room temperature. The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample after cure, per ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness of 65 shall be the minimum. If any of the control samples fail to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing Stycast 1095/9 Allow Stycast 1095/9 to cure for four hours, minimum, at ambient temperature, before cleaning or extensive handling.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Preparing Epoxy-Polyamide Adhesive EC-2216 B/A Control Specification for Epoxy-Polyamide Adhesive EC-2216 B/A Emerson and Cuming, Inc., use Mixing Bulletin for Epoxy-Polyamide Adhesive EC-2216 B/A, to the latest revision.

Mixing Epoxy-Polyamide Adhesive EC-2216 B/A Material Preparation and Control Use either a glass or metal round bottom, (without corners), container suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients, using a stainless steel spatula, until a homogeneous mixture is obtained. CAUTION Excessive loss of adhesive liquid may result in incomplete adhesive curing and reduced bonding strength. To minimize the possible loss of adhesive liquid through absorption, paper, wood, fiber, or other porous materials shall not be used when preparing the mixture. In addition, keg-lined cans or wax-coated cups shall not be used. WARNING The materials used in this process may cause injurious effects to allergic personnel. Avoid contact with the adhesive material, and perform the mixing procedure in a well, ventilated area. It is advisable to wash your hands thoroughly with soap and warm water, prior to, and after working with the adhesive material. Measure the required amount of adhesive past, in a ratio of 100 +/-1 parts by weight of EC-2216 of component B, (base), to 140 +/-1 parts, by weight, of EC-2216 component A, (hardener), in the container. Weigh the materials on a balance scale, accurate to 0.10 grams. Use either a glass or metal round bottom (without corners), container, suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Measure more adhesive, than actually required, to allow for waste. Mix the ingredients thoroughly, keeping the end of the mixing blade below the mixture level. Avoid any whipping motion, which would tend to introduce air into the mixture. This information should now be recorded on the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Pot Life of EC-2216 B/A The useful life of the mixed material is approximately 1.5 hours at 24°C (75°F). The end of the useful life is indicated by the lack of wetting and adhesion or excessive thickening of the mixed material. Any mixed material exhibiting these characteristics shall be discarded immediately, regardless of the time at which it was first mixed. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Control Sample EC-2216 B/A For each mixed batch of EC-2216 B/A, make a control sample by transferring a portion of the material into an aluminum foil dish to a depth of approximately 1/8 inch. Identify the control sample by writing the mixture record number and date on the outside of the bottom of the small aluminum dish. Cure the control sample in the oven along with the parts to be bonded. The cured sample shall be of a uniform appearance and tack free. Determine the hardness of the sample after cure per, ASTM-D-1706-61, using a Shore D Durometer. The Shore D hardness of 95 shall be the minimum. If any control samples fails to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing EC-2216 B/A Cure EC-2216 B/A at room temperature 24° +/-3°C (75° +/-5°F) for a period of 168 hours. Curing at a elevated temperature requires an air-circulating oven, and cure at a temperature of 66° +/-5°C, (150° +/10°F), for a period of three hours.

Preparing Silicone Rubber Compound (RTV 566 A/B) Control Specification for Silicone Rubber Compound RTV 566 A/B General Electric Company, use Mixing Bulletin for Silicone Rubber Compound RTV 566 A/B, to the latest revision.

Mixing RTV 566 A/B Material Preparation and Control Use either a glass or metal round bottom, (without corners), container suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Thoroughly blend the ingredients using a stainless steel spatula, until a homogeneous mixture is obtained. CAUTION To minimize the possible loss of catalyst through absorption, paper, wood, fiber, or other porous materials shall not be used when preparing the mixture. In addition, keg-lined cans or wax-coated cups shall not be used. Weigh the required amount of silicone rubber into a clean mixing container. Add the required amount of catalyst at a ratio of 0.1 parts, by weight, to 100 parts by weight of silicone rubber. The catalyst may be added, dropwise, from a calibrated medicine dropper, or an equivalent. For example, for 20 gms of Part A, add one drop* of Part B. *(Measure from a conventional-type medicine dropper, one drop is approximately 0.02 gms). Use volumetric addition and syringe, when more precise measurements are required. Deareate in a vacuum of 10 torr or better at 24° +/-3°C, (75° +/-5°F). The vacuum shall be applied until the material

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

rises in the container and breaks. Then the application of the vacuum shall be continued for an additional 0.5 to 1.0 minute. Weigh the materials on a balance scale accurate to 0.10 grams. Use either a glass or metal round bottom (without corners) container, suitable for weighing and mixing. Determine the tare weight of the container and stirring rod. Mix the ingredients thoroughly keeping the end of the mixing blade below the mixture level. Avoid any whipping motion, which would tend to introduce air into the mixture. This information should now be recorded on the Mixing Record Form. See Figure 8-25 (or use an equivalent), noting all applicable data for each batch.

Pot Life of RTV-566 A/B The useful life of the mixed material is approximately 20 minutes at 24°C, (75°F), when mixed with 0.1% catalyst.

Control Sample RTV-566 A/B For each mixed batch of RTV-566 A/B, make a control sample by transferring a portion of the material into an aluminum foil dish to a depth of approximately 3.2 mm (0.125 inches). Identify the control sample by writing the mixture record number and date on the outside of the bottom of the small aluminum dish. Cure the control sample in the same area, along with the parts that have been coated. Allow the RTV-566 A/B to cure for a minimum of 25 hours at 24° +/-3°C, (75° +/-5°F), and 50% +/-5% relative humidity. The cured sample shall be of a uniform appearance, free of soft areas and tackiness. Determine the hardness of the sample after cure, per ASTM-D-1706-6,1 using a Shore D Durometer. The Shore D hardness of 95 shall be the minimum. If any control samples fail to meet the above requirements, reject all parts processed with that particular batch of material. Record all the results in the remarks section of the Mixing Record Form.

Curing RTV-566 A/B Cure the RTV-566 A/B for a minimum of 25 hours at 24° +/-3°C, (75° +/-5°F), and 50% +1-5% relative humidity.

Application and Storage Method of Application For convenience in using, polymeric materials may be placed in a syringe for application. Using a syringe the polymeric technician has better control with the application and the amount applied, as shown in Figure 8-19. There are several types of syringes that are used with the application of polymeric materials. When large quantities of bonding or adhesives are being dispensed, then, the one of choice would be the Semco gun with a cartridge. Smaller amounts of polymeric materials can be dispensed using a heavy-duty syringe, with a 10 cc tapered or blunt needle, or a No. 10, Polyethylene Syringe, as shown in Figure 8-20.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Fastener Tube

Toroid

Fiberglass Enclosure

10%to20%ofD

\

Figure 8-19. Bonding a Toroid into Position.

Toroid

Bonding Fillets

No. 10 Polyethylene Syringe

Figure 8-20. Applying Bonding Material with a Syringe. Method of Storage Polymeric materials can be prepared in advance, and the material placed in syringes. The material can then be frozen in liquid nitrogen, (LN 2 ) for long periods of time for later use. The thaw time for 10 cc syringe of the material is about 19 to 25 minutes. This method of storage does have an effect on pot life after thawing. The end of useful life, after thawing, is exhibited by a significant increase in the pressure required to extrude the material from the syringe, and a lack of wetting and adhesion, or excessive thickening, of the mixed material. Any material exhibiting these characteristics will be discarded immediately, regardless of the time at which it was first mixed.

Cut "C" Core and "E" Core Assembly Preparation Cut Core Preparation Prior to banding the core halves, the mating surfaces shall be coated with an approved epoxy. A thin layer

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

of EC 2216 B/A, adhesive shall be applied over both mating surfaces, as shown in Figure 8-21. Bond line thickness for optimum properties shall be in the range of 0.076 to 0.254 mm (0.003 to 0.010 inches). Sufficient adhesive shall be applied to allow a bead of excess adhesive to be squeezed out when pressure is applied.

Note: Providing sufficient adhesive to obtain a squeeze-out bead will minimize adhesive voids, and will allow the air, entrapped in the adhesive during mixing, to be squeezed out. The squeezed-out bead shall be kept to a minimum size, because it will be difficult, or impossible to remove, when assembled. Banding Cut Cores Cut cores that require a narrow gap shall be banded with phosphor-bronze banding material. The gapping material inserted into the air gap shall use, either Mylar or Kapton, depending on the temperature. Cut cores that require no air gap shall be banded with solderable, tin-coated, low-carbon steel bands. Bands and Seals for cut "C" cores, "U" cores, and "E" cores will be selected from Table 8-2. The bands shall be evenly spaced around the core, as shown in Figure 8-22. If the design requires two bands, then the seals shall be staggered, as shown in Figure 8-23.

Note: There will be a magnetizing current test or inductance test, prior to banding. The test will be conducted with the core halves firmly in place with moderate pressure. The magnetizing current or the inductance measurement should not vary more than +/-5%, from the initial measurement with dry mating surfaces to the mating surface, with adhesive compound. See the Spec Control Drawing (SCD).

Seal .

Impregnated Coils

Seal

. Seal

V

Core Mating Surface C Core

Mating Surface E Core

Figure 8-21. Mating Surface with Adhesive Epoxy. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table 8-2. C Core Banding Data.

C Core Banding Data Core Dimensions (1 leg) Seal Band *Banding Force Dimension Bands D Size AC Required (Inch) (Pounds) (kilograms) (Inch) (cm) (cm2) 1 17 37.5 0.188x0.25 0.188x0.006 Any 1.21 or Less 34 75 0.375x0.375 0.375 x 0.006 0.953 or Larger 1.21 to 2.42 1 1 0.375x0.375 68 150 0.375x0.012 2.42 to 4.84 0.953 to 3. 81 34 75 0.375x0.375 0.375 x 0.006 2 4.13 or Larger 1 68 150 0.375x0.375 0.375x0.012 4.84 to 9.68 1.27x2.86 68 150 0.375x0.375 0.375x0.012 2 3.175 or Larger This force must be reduced from 30% to 50% when banding nickel-iron or supermendur cores.

Centered Band

V

Cross Section \

C Core

J^> Figure 8-22. C Core, Banding Location.

Staggered Seals

C Core Cross Section \

D

Figure 8-23. C Core with dual Bands.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Cut Cores with Stress Relief Coating RTV-566 Stress Relief Coating Stress relief coating will be applied to all cut "C" cores and "E" cores prior to potting in a rigid material as shown in Figure 8-24. The RTV-566 can be applied with a brush and/or dipped, see Figure 8-24.

Impregnated Coils

C Core Band

Both Ends RTV Stress Relief

Figure 8-24. C Core, Coated with RTV Stress Relief Material. Cured Material Allow the RTV coating to cure for a minimum of 24 hours at room temperature, before handling, or, before any post curing. The cured coating shall be of a uniform appearance, free of soft areas and tackiness.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Polymeric Mixing Record Form Mixing Record Form All applicable data must be recorded on the mixing record form as shown in Figure 8-25.

Mixing Record

Date

Mixture S/N

Project

Hardward I.D.

Work Order No.

Material Type

Specification No.

Drawing No.

Manufacturer Spec.

Ambient Temperature

Mixture Ingredients Item 1 2 3 4 5 6 7 8 9

Ingredient

Manufacturer

No

Exp. Date

% By Wt

Wt. Grams

Total Weight Grams Material Conditioning Yes No Describe:

Degassing Performed Describe:

Yes

Time Mixed Cure Cycle

Syringes # Control Sample Data Required Shore A Hardness Shore B Hardness Other Inspection Report Number

Storage Temperature Control Sample Data Actual Shore A Hardness Shore B Hardness Other

Remarks

Name

Phone Number

Bldg

Requester Polymerics Technician Quality Assurance Figure 8-25. Typical, Polymeric Material Mixing Form.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Room

Tools and Aids Aluminum Disk All polymeric materials shall have a control sample made for each batch of mixed materials and this control sample shall meet the requirement of Table 8-1. The control sample materials shall be stored in a clean aluminum dish, similar to the one in Figure 8-26.

Figure 8-26. Proof of Cure Sample Container. RTV Sealant RTV 3116 is a silicone rubber sealant. It is applied around all exiting leads to prevent leakage of the embedment material. Mix RTV 3116, in proportions of 10 grams RTV 3116 to 4 drops of Nuocure 28 catalyst. Cure the RTV 3116 for 10 minutes at room temperature. Polyethylene Syringe The No. 10 syringe may be used for the application of some epoxies. The outline is shown in Figure 8-27.

Figure 8-27. No. 10, Polyethylene Syringe.

Temperature Chamber (oven) A hot, air-circulating oven, capable of maintaining 40° to 150°C +/-3°C, (100° to 300°F +/-5°F), shall be used. The oven shall be equipped with two temperature controllers. The first shall regulate the oven temperature. The second shall turn off the oven, whenever, the temperature exceeds the regulated temperature by more than 10°C, (20°F). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Balance Scales Use a balance scale, with a capacity 1 to 500 grams minimum, with an accuracy range of+/- 0.25 grams. A typical balance scale is shown in Figure 8-28.

Figure 8-28. Typical Balance Scale Used to Measure Polymeric Materials. Cotton Swabs Cotton swabs are a handy device for removing epoxy droplets, globule, and material that does not drain from cracks and crevices of the magnetic device. A cotton swab is shown in Figure 8-29.

Figure 8-29. Typical Cotton Swabs Used for Cleaning. Razor Blade Industrial razor blades are a handy device for removing potting funnels and epoxy droplets from the magnetic device. A typical industrial razor blade is shown in Figure 8-30.

Figure 8-30. Typical Industrial Razor Blade Used for Cleaning. Clean White Gloves Prior to handling parts and/or materials, the polymeric technician shall thoroughly clean his/her hands; the use of any hand lotion is forbidden. Anyone working with or handling parts and/or materials must wear clean gloves, and/or finger cots. Gloves must be changed when they show signs of contamination, and finger cots must be replaced when they are torn or contaminated.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Paper Cup A six ounce, unwaxed paper cup is a handy device for transferring bulk epoxy resins from storage containers to the mixing bowls for measuring. A typical paper cup is shown in Figure 8-31.

Figure 8-31. Typical Paper Cup used for Measuring Epoxy Resins.

Acid Brush The industrial acid brush type No. 1 (0.375 inch), is a handy tool for cleaning with solvents, for applying coating, and a host of other uses. A typical industrial acid brush is shown in Figure 8-32.

Figure 8-32. Typical Industrial Acid Brush Type No. 1.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 9

High Voltage Design Guidelines

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents

1. Introduction 2. High Voltage Design Guidelines 3. High Voltage Problem Areas 4.

Means of Reducing High Field Density

5. High Voltage Solder Connections 6. High Voltage Solder Joints 7. Means of Reducing Voltage Gradients 8.

Separation of High Voltage and Low Voltage Circuits

9. Component Spacing 10. Grounding 11. High Voltage Transformer Insulating Materials 12. Terms Used

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction The use of high voltage transformers in power converters in space, for power processing, require special attention, in regards to insulation. These transformers usually operate with a square wave voltage on the primary, and boost the voltage from 1 to 10 kv, or even higher. At this voltage level, corona degradation becomes a serious limitation on reliability. Corona is a particularly serious problem in all solid dielectric high voltage transformers. In order to assure the success of high voltage encapsulated transformers, the design must follow proven guidelines. There are many unusual problems that arise when high voltage is operating at critical pressure, and not all of the basic mechanisms are well-understood. The art of building high voltage transformers has developed to the point where guidelines can be given to help the new designer avoid old problems. (See Terms Used at the end of this chapter).

High Voltage Design Guidelines All electronic equipment to be exposed to the critical pressure region and employing voltages above the minimum require special attention to avoid failures, caused by corona and arcing. The intent of this chapter is to provide guidelines for high voltage fabrication. High Voltage Limits Guidelines presented here are on constructing and fabricating hi-rel, high voltage electronic equipment with circuit conductors having instantaneous voltage, (with respect to other circuit conductors to the common ground, or to the subchassis), in excess of 250 volts peak. This limit is applicable to frequencies, from dc to 60 Hz, and shall be reduced, in accordance with Figure 9-1, for frequencies above 60 Hz. At voltages, lower than that specified in Figure 1, compliance may be desirable for one or more of the following reasons: Number 1 The conductive plasmas generated by a corona or arc, or other mechanisms, such as passage of equipment through, low pressure gaseous environments, can drift across bare conductors carrying much lower voltages, (e.g., 24 volts), initiating arcing in these circuits, also. Number 2 The theoretical, breakdown voltage minimum of 270 volts peak is for air; other gases, especially the noble ones, even in trace quantities, can cause breakdown to occur at much lower voltages. Number 3 Other conditions being the same, reduction of large voltage gradients, by suitable gradient control techniques, will markedly improve the long-term reliability of high voltage circuits.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

10 MHz

1 MHz -

100 kHz N

ac

cr

10 kHz -

1 kHz -

100 Hz

25

50

75

100

125

150

175

200

225

Voltage, (Peak Volts) Figure 9-1. Lower Voltage Breakdown Limit versus Frequency.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

250

High Voltage Problem Areas The design of high voltage equipment, is heavily influenced by the following problem area:

Means of Reducing High Field Density Field Density Field lines should be spread out as evenly as possible to minimize the local field density, and not allow the field lines to concentrate, as is the case at sharp points. The field density can be improved by having smooth, round surfaces compared to a sharp point, as shown in Figure 9-2.

100 80 Sparkgap Breakdown

60 40

£ 20 o

3 PL,

10 8 6 4

1 0.01

0.02

0.040.06 0.1 0.2 Gap Length in Inches

0.4 0.6

1.0

Figure 9-2. Comparing Sparkgap, Breakdown Voltage with a Sphere and Needle Point.

High Voltage Solder Connections Terminals Terminals used, for high voltage will be a smooth, rounded swage mount, as shown in Figure 9-3.

/rr\ HV Bifurcated Terminal

HV Type A Terminal

HV Type B Terminal

Figure 9-3. Hemispherical High Voltage Terminals. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Flush Leads The ends of the component leads shall be flush with the edge of the terminal. After part leads are installed, the terminals, at voltages above 1.0 kv, will have excess length of the bifurcated terminal trimmed off, as shown in Figure 9-4. A smooth solder joint will be made to enclose all cut ends of the component leads and trimmed tines of the bifurcated terminal to reduce the voltage gradient. A smooth solder ball or other conductive material, shown in Figure 9-4, is allowable for high voltage terminals. For circuits above 1.0 kv, the terminals will have a hemispherical conducting cap to reduce the voltage gradient at the edge of the swage, as shown in Figure 9-4.

Tines Trimmed Solder Ball

0 to 0.76 mm (0.03 Inch) Ends of Leads Flush to -0.76 mm (-0.030 Inch) From Diameter of Terminal.

Modified Bifurcated Terminal Conducting Cap (Bonded or Pressed in).

Slightly Larger Than Swage Diameter

Figure 9-4. High voltage Solder Terminal.

Minimum Terminals The use of terminals will be kept to a minimum in high voltage circuits. Sharp Points Circuit conductors, electronic parts and mechanical parts, either in the high voltage circuit, grounded, or insulated electrically but located at a distance that is less than twice conductor spacing (CS), from the high voltage conductors, will be designed or laid out in a manner that avoids sharp points, sharps corners, and abrupt changes in dimensions. Smooth Conductors Smooth curves, rather than sharp corners, will be used for changes in directions of all conductors, both in printed circuit (PC) traces and wire.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

High Voltage Solder Joints Inline Solder Joint Inline solder connections shall be assembled using a tinned or soldered-plated, thin wall metal sleeve, (ferrule), as shown in Figure 9.5. Insulated Wire Inline Splice

Metal Ferrule (Thin Wall Sleeve)

Gap Distance 0.030-0.090" Joint after Soldering Smooth without Pits or Air Bubbles Figure 9-5. Inline Solder Connection. Parallel Solder Joint Parallel solder connections shall be assembled using a tinned or soldered-plated thin, wall metal sleeve (ferrule), as shown in Figure 9.6. Insulated Wire

Metal Ferrule (Thin Wall Sleeve)

Gap Distance 0.030-0.090" Joint after Soldering Smooth without Pits or Air Bubbles.

Parallel Splice

Figure 9-6. Parallel Solder Connection. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Assembly of Solder Joint Teflon sleeving shall be used over each required terminal to assist in forming a spherical, shaped solder joint. Each length of sleeving shall be notched, as shown in Figure 9-7, to allow clearance for the wire being soldered to the terminal. Only newly cut, Teflon sleeving will be used.

Teflon Sleeving

Wire Clearance Notch

Figure 9-7. Teflon Sleeving, Soldering Mold.

Modified Holding Tweezers Specially modified tweezers, as shown in Figure 9-8, are designed to help to hold the Teflon sleeving during soldering. The tweezers are used to secure the Teflon mold in place, while soldering.

Reverse Action Tweezers

Modified Tweezers Holding Clamp Figure 9-8. Modified Tweezers, Used as a Holding Clamp.

Assembly of HV Solder Joints Prior to assembly, all parts of the connection shall be cleaned with ethyl alcohol. Wire insulation shall be removed from the ends of wires to provide a gap of 0.76 to 2.3 mm (0.03 to 0.09 inch), between the insulation and the terminal shoulder. In order to minimize the amount of solder in the high voltage solder joint, unused sections of the turret shall be filled with tinned copper wire. Wire ends shall not protrude past the terminal. The soldering tip shall be kept as short as possible, and small enough to fit inside the Teflon sleeving surrounding the high voltage solder joint. The solder on top of the terminal should appear round, or approximately round, but not flat, as shown in Figures 9-9 through Figures 9-11. The finished high voltage terminal assembly is shown in Figure 9-12.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Soldering Iron Bifurcated Terminal Teflon Sleeving Insulated Wire Modified Tweezers

Terminal Board Figure 9-9. Standard, Bifurcated Terminal in a High Voltage Assembly. Soldering Iron High Voltage Bifurcated Terminal

Insulated Wire Modified Tweezers

Terminal Board Figure 9-10. High Voltage, Bifurcated Terminal Assembly. Soldering Iron

Turret Terminal Filler Wire Teflon Sleeving

Modified Tweezers

Terminal Board Figure 9-11. Turret Terminal in a High Voltage Assembly. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Terminal After Soldering Smooth without Pits or Air Bubbles

Solder Dome

Insulated Wire

Terminal Board Figure 9-12. A Finished, High Voltage Terminal Assembly. Means of Reducing Voltage Gradients Voltage gradient should be as low as possible. Attempt to spread the applied voltage to minimize the unit voltage gradient linearly over, or within, the total available insulating media. Increase the insulating distance, when possible, or utilize insulating media with a greater dielectric strength, or both. Determination of Voltage Gradient The distance or thickness between high voltage conductors shall be measured in a straight line from the point of closest approach, including worst tolerance buildup. Then the voltage gradient will be calculated by dividing the peak voltage by the insulating distance thickness in mm, or (mils). Voltage Gradient Limits The thickness of insulation provided as a function of the voltage, shall be 40 volts/mil or ten percent of the actual breakdown voltage for the thickness of the insulation used in the design, whichever voltage gradient is less. This is the linear gradient, calculated by dividing the peak volts by the distance in mils. If the geometry is one in which calculation of the maximum gradient is possible, the maximum gradient allowable shall be 100 volts/mil, or 25 percent of the actual breakdown voltage for the same thickness, whichever is less. Conductor Spacing (CS) The minimum high voltage carrying conductor separation, (CS), on the same side of the printed wiring or terminal boards shall be as calculated by: i

CS =

= [mm]

= [inches]

The minimum separation shall be 3 mm (0.125 inch). Distances shall be measured along the surface between the conductor and shall be the minimum distance possible. Layout of the high voltage circuitry should consider gradient reduction by placing conductors in order of decreasing voltages, if such locations do not cause adverse effects on the performance of the circuit. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

High Voltage Pulse Circuit The minimum conductor separation (CS), as specified in the above equation, can be reduced when the conductor is carrying pulses. The conductor separation (CS), can be reduced by a multiplying factor K. The pulse duty cycle shall be less than five percent for this reduction to apply, where t is the pulse width in microseconds.

K=

Separation of High Voltage and Low Voltage Circuits

Separation of High Voltage Circuits Circuits employing high voltage shall be physically separated from low voltage circuits with a minimum common boundary, when located on the same printed wiring or terminal board, as shown in Figure 9-13 through Figure 9-15.

Low Voltage Circuit Protection A ground bus shall be located between high and low voltage circuitry to prevent possible creepage currents or arcs causing premature damage of failure to the low voltage circuits, as shown in Figure 9-13 through Figure 9-15. Where the high voltage circuit is physically separated from the low voltage circuit board, a ground bus around the perimeter of the high voltage board shall be used to prevent a possible arcing to the low voltage circuits. Where high voltage exists on both sides of the printed wiring or terminal board, the ground bus shall be on both sides, preferably superimposed one above the other, as shown in Figure 9-16. This ground bus should about a 4 mm (0.15 inch) conductor to provide a low impedance return path in case of an arc. A ground bus shall be used in each layer of a multilayer circuit board to isolate the high voltage circuit from the low voltage circuit. In selected areas, the ground buses may be staggered instead of superimposed to allow conductors to pass between the high and low voltage areas by transferring from one layer to an adjacent one; or a ground bus on a given layer may be interrupted to allow passage of such conductors. The connection to the ground point for this bus shall be so that the currents from a possible arc will not be coupled into the ground returns of any other circuits.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Insulating Gap

Ground Bus

High Voltage Transformer and Circuitry

Figure 9-13. Preferred Combine Layout, High and Low Voltage Circuitry. Ground Bus

Insulating Gap

High Voltage Transformer and Circuitry

Figure 9-14. Acceptable Combine Layout, High and Low Voltage Circuitry. Ground Bus

Insulating Gap

High Voltage Transformer and Circuitry

Low Voltage Circuitry

Figure 9-15. Unacceptable Combine Layout, High and Low Voltage Circuitry.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

High Voltage Components on this Side of Bus Double Side Ground Bus

LH Encapsulant

HJUH

High Voltage Terminals

Figure 9-16. Circuit Board with Double Sided Ground Bus.

Component Spacing Spacing from Edge The minimum distance of the conductor from the edge of the printed wiring or terminal board shall be 1.5 times conductor spacing (CS), as shown in Figure 9-17 and Figure 9-18. See page 9-10 for an explanation. High Voltage Components on this Side of Bus Double Side Ground Bus Spacing from Edge

CS

1.5CS

CS

1.5CS

1.5CS

CS = Conductor or Component Spacing, HV = High Voltage, Gnd = Ground

Figure 9-17. Minimum Distance for High Voltage Circuitry from Board Edge.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

High Voltage Components on this Side of Bus Double Side Ground Bus

Chassis

Encapsulant

CS

HV

CS

HV

1.5CS

CS = Conductor or Component Spacing, HV = High Voltage, Gnd = Ground Figure 9-18. Minimum Distance for High Voltage Circuitry Between Terminal and Ground.

Grounding Chassis ground leads shall be separate from signal and power returns leads to prevent corona or arc currents from adversely affecting or damaging other circuits. The connection to the ground point for this bus shall be so that currents from a possible arc will not be coupled into the ground returns of any other circuits. The random grounding, shown in Figure 9-19, is not recommended. The recommended grounding is shown in Figure 9-20. Ground leads shall be such that ground loops are not permitted. Low Voltage Components on this Side of Bus

High Voltage Components on this Side of Bus

Ground Bus Figure 9-19. Circuit Grounding to the Ground Bus.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Low Voltage Components on this Side of Bus

High Voltage Components on this Side of Bus Circuit Gnd

-0-

2. 9

Ground Bus Figure 9-20. Isolated Circuit Grounds from the Ground Bus.

High Voltage Transformer Insulating Materials Dielectric Strength Insulating materials, having the higher dielectric strengths, shall be used in high voltage applications when other properties or characteristics pertinent to the application are similar. Materials, with dielectric strength of less 400 volts/mil measured between parallel plates at the thickness required, should be avoided. Dielectric Constant Insulating materials with low dielectric constants shall be selected for insulation of ac voltages. Where two different insulating materials are in contact, they should be selected so that the difference in their dielectric constant is minimal. Materials, with dielectric constant greater than five shall be avoided. Air Dielectric Strength For the purpose of equipment design, in accordance with this chapter, air shall be assumed to have zero dielectric strength in the critical pressure region. High Frequency Applications Insulating materials, selected for use in the high frequency, (nominally above 1 MHz), application, shall have the dielectric constant and dielectric losses small enough, so that blistering, delamination, or other internal damage caused by internal heating, will not occur during normal operation. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Foams Expanded or syntactic foam materials, or materials that are porous, shall not be used for high voltage, insulation applications. Low Arc Resistant Materials Organic insulating materials, which have a tendency to sustain arcing under any pressure condition, or which deteriorate, or outgas under arcing conditions, shall not be used in contact with bare conductors emerging from the insulating material, and exposed to the ambient pressure. Inorganic insulating materials, which do not sustain arcing, shall be used to provide the interface of an emerging bare conductor from the encapsulent or conformal coating, as shown in Figure 9-21.

Inorganic Insulator Imbedded in Organic Encapsulant Organic Encapsulant

«* rH hi

^^^^^^^?<^^^^cs^^^x^^^^^^

High Voltage Terminal

HV Transformer

(ft (n>

Figure 9-21. Using Inorganic Insulators in Organic Encapsulating Material.

Magnet Wire Insulation The thickness of the magnet wire insulation coat and winding technique shall be such that the maximum possible voltage gradient between any two adjacent wires in a winding shall be. in accordance with the voltage gradient limit, and, in no case, greater than 40 volts peak, as shown in Figure 9-22. Voltage, at termination of winding, and between wires in excess of this value, shall employ additional insulation in accordance with the voltage gradient limit requirements for high voltage equipment. In high voltage pulse transformers, with pulse widths of 10 us or less, the allowable voltage limit between wires can be 200 volts peak.

40 volts peak, Max. Voltage Gradient Between Turns Magnet Wire Turn

Magnet Wire Insulation Insulation Magnetic Core Figure 9-22. Maximum Voltage Gradient Between Turns.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Magnetic Core Connection Electrically conductive cores, insulated from the mounting base of the transformer or inductor, shall have an auxiliary lead brought out to facilitate hi-pot testing between core and the windings, as shown in Figure

9-23.

Enclosure Primary

Secondary

Shield

Core

Figure 9-23. Transformer with External Lead Attached to the Core. Cores, that are exempt from this requirement, are toroidal powder cores, toroidal ferrites and tape toroidal cased cores, providing that they are wrapped with an insulating material that meets the high voltage insulation material requirements, and that the low voltage winding is located between the high voltage windings and the core. Interwinding Insulation Insulation between windings shall meet the high voltage, insulation material requirements and shall be capable of withstanding, without damage, the equipment test requirements.

Winding Embedment Windings shall be impregnated, and then, encapsulated with materials that meet the high voltage insulation material requirements so that all the wires are securely anchored and no voids are present. Winding Termination Winding termination into insulated lead wires shall be embedded with materials that meet the high voltage insulation material requirements. Terminals employed for termination of transformer or inductor windings shall meet the same requirements as the high voltage printed circuit boards terminals. The conformal coating, or encapsulant material, shall be compatible with the lead wire insulation and achieve a thorough bond, so that creepage paths from the conductor to the outside of the module will not occur. The length of the path from the conductor to the outside shall be 6.35 mm (0.25 inch), for voltage less than 1.0 kv. Voltages, greater than 1.0 kv, use the equation that is used for component spacing (CS):

CS = 6.35 Jkv. ;/t) = [mm] CS = Q.25jkvlpk) = [inches] Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Provisions shall be made to anchor the wire as it emerges from the encapsulant, or other precautions shall be taken so that subsequent handling does not mechanically stress the bond between the encapsulant and the wire insulation.

Terms Used High Voltage Circuit conductors having instantaneous voltages, (with respect to other circuit conductors, to the common ground, or to the subchassis), in excess of 250 volt peak ac. This limit is applicable to frequencies from dc

to 60 Hz. Critical Pressure The range of pressure through which the dielectric strength of the air reduces to 20 percent or less of the dielectric strength of 20°C (68°F) and at sea level pressure, will be the critical pressure for the purpose of this chapter. Nominal limits of the critical pressure region in air are 50 torr 18.3 kilometers, (60,000 feet altitude), to 5 x 10"4 torr 94.5 kilometers (310,000 feet altitude). Arcing A complete voltage breakdown of dielectric between two conductors, with currents on the order of milliamperes or higher, limited only by power supply impedance, or the total number of ionized gas molecules or atoms available. Corona An incomplete or partial voltage breakdown of the air or gas adjacent to one or both electrodes or conductors resulting in a current flow of the order of 10~ 7 to 10"6 amperes rms. Voltage Breakdown As used in this chapter, voltage breakdown refers to either arcing or corona. Noble Noble refers to a group of chemically inert gases, such as helium, neon, argon, krypton, and xenon. torr It is a unit of pressure that is equal to approximately 1.316 x 10" atmosphere. 1 atmosphere = 14.7 pounds per square inch. Conductor Separation (CS) The distance between conductors and terminals is: CS = 6.35 /A:v (M) = [mm] CS = 0.25^Av (M) = [inches] Plasma Plasma is the electrical discharge generated by a corona or arc that has ionized gas, that is electrically neutral.

CDN Corona Detection Network is used in testing the presence of corona. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Chapter 10

Testing, Evaluation, and Quality Assurance

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Table of Contents 1. Introduction 2.

Electrical Tests

3.

Electrical Tests to Perform

4.

Fabrication Tests

5. Fabrication Tests to Perform 6. Environmental Tests 7.

Test Guidelines

8.

Test Conditions

9. Turns Ratio Test 10. Turns Ratio Test Using Voltage 11. Primary Inductance and Leakage Inductance Measurements Using a Bridge 12. Primary Inductance and Leakage Inductance Measurements Using Current 13. Inductance Measurement with DC 14. Resistance Measurement Using a Bridge 15. Resistance Measurement Using Current 16. Testing for Transformer Resonance 17. Phase Testing 18. Insulation Resistance Test 19. Voltage Breakdown Test 20. Primary to Secondary Capacitance Measurement 21. Testing Core Permeability 22. Turns Ratio Test on Multi-Winding Inductors with Large Gaps 22. Testing the Dynamic B-H Loop 23. High Voltage Testing 24. High Voltage Test Equipment 25. Quality Assurance 26. Introduction 27. Assumptions Prior to Fabrication 28. Facility and Work Stations 29. Before the Start of Fabrication 30. Documentation 31. In-Process Inspection 32. Unit Specification Verification

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Transformer testing is the only way to determine verification of how effective the design and fabrication is. Transformer tests can be grouped into two categories: a functional test and a reliability test. Functional tests are those that verify the design criteria and specification requirements, while reliability tests are defined as those, which determine the adequacy of the mechanical and insulation system.

Electrical Tests The electrical tests performed on a magnetic component are to insure that they will meet the overall specification. A transformer or inductor is designed to meet a specific requirement, such as a primary inductance magnetizing current. The transformer is also required to provide a specified voltage and current with the proper phasing. Some transformers are required to operate over a wide frequency range. There are many electrical tests that have to be performed to insure that the transformers that are fabricated, will meet the specification. The electrical tests are used to catch things such, as a wrong or bad core, a wrong wire size, (AWG), incorrect turns, and winding procedure.

Electrical Tests to Perform Magnetizing Current The magnetizing current is an indication on whether the transformer or inductor has the correct core, the correct core material, and/or the correct gap. Inductance Measurement The inductance measurement is an indication on whether the transformer or inductor has the correct core, the correct core material, and/or the correct gap. Turns-Ratio The turns-ratio test will assure the proper terminal voltage. Winding Resistance The winding resistance test is to insure the correct wire size and the proper winding procedure was used. Phasing Phase testing is a very important parameter in many transformer applications. Resonant Frequency The resonant frequency is an indication of how the transformer is wound and what material is used. It also is an indicator regarding, whether or not the correct core, the correct core material, and/or the correct gap was used. Primary to Secondary Capacitance The primary to secondary capacitance is an indication of the winding method and materials used. Voltage Breakdown The voltage breakdown test is an indication on whether the transformer has the correct insulation and lead dressing. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Fabrication Tests The fabrication tests performed on a magnetic component are used to insure that the construction and workmanship procedures have been followed. Fabrication procedures must be followed to minimize contamination from preservatives, such as oils and grease, that could collect foreign objects. If transformers or inductors are to be handled, then gloves should be worn to minimize contamination from body oils and salts. There are other contaminations, such as flux, and/or solder splashes that could lead to a premature failure.

Fabrication Tests to Perform Megger Test The Megger Test is an insulation resistance test. This test is to detect any leakage resistance caused by contamination. The Megger Test is performed, at either 50 or 500 volts dc, depending on the requirement. The Megger Test is normally performed between all combinations of isolated elements, such as the primary, secondaries, the core, shields, enclosures, and mounting hardware. The normal insulation reading is about 20,000 meg-ohms. Hi-Pot Test The Hi-pot Test is an electrical strength test. This test is to check for voltage breakdown caused by poor or inadequate insulation, lead dressing, and/or foreign particles. The Hi-pot test is normally performed with a potential of twice the operating voltage, plus 1000 volts ac, depending on the requirement. The Hi-pot test is performed between all combinations of isolated elements, such as the primary, secondaries, the core, shields, enclosures, and mounting hardware. The Hi-pot voltage is normally applied for one minute.

Environmental Tests The Environmental Test, such as shock, vibration, temperature range, temperature shock, and temperature burn-in, (life test), is normally set by project.

Test Guidelines B-H Loops Testing transformers and inductors always stays within the linear portion of the B-H loop, as shown in Figure 10-1. Frequency Evaluation testing of transformers and inductors should be done at more than one frequency and at more than one voltage level.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

B (tesla) B(sat)

B (tesla)

Bop

H (oersted)

Figure 10-1. Operating in the Linear Portion of the B-H Loop. Test Fixture There should be a special test fixture for testing and evaluating transformer and inductors. This test fixture should be permanent and not torn down after each test. This way, if the test has to be run again, it is always best to use the same components to duplicate the test. Breadboard Components It is not wise to impregnate or pot the original set of breadboard magnetic components used to evaluate the design. The reason is the potting material could have an influence on the performance of the magnetic components and the performance of the circuit they are used in. Once they are potted, going back to the original set of conditions is impossible. It is best to have an additional set wound to impregnate and pot, and leave the originals alone.

Test Conditions Applied Voltage The test voltages and conditions for the magnetic component should be in the specification control drawing, (SCO). If there is no reference to voltage or test conditions, then the test engineer should consult with the cognizant engineer. If this is not feasible, and the magnetic component is of a simple design, then, the test engineer should calculate the required applied voltage. The test should be performed at a frequency of 1.0 kHz, and a flux level of about 0.05 tesla. The applied voltage during the test of the magnetic component should be a clean and undistorted sine wave at all times. Equipment Care must be taken when interpreting test results. There is always a chance for a misapplication, where a piece of equipment is used beyond its capacity. An example would be an instrument bridge being used to excite an inductor, with a large gap requiring more power, beyond the instruments deliverable capability. Reading the manual is important to be sure the test instrument is operating within its capability. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Turns Ratio Test

Power Audio Oscillator

Turns Ratio Tester

Frequency

Voltage Ratio

1 1 1 1 1 1 M in 1 1 1 1 1 1 Voltage Nr II I I I I I I I I I HITTTTI

O

O O P

O

Measurement at Connections.

Enclosure UUT

Figure 10-2. Test Setup for a Turns Ratio Test.

Equipment 1.

Power Audio Oscillator

2.

Voltage Ratio Meter

Test (See the information on Test Conditions). The test setup for making turns ratio test is shown in Figure 10-2. Apply the voltage to Terminals, (1-2) and the read secondary on terminals, (3-4):

Ratio =

N

125 75 Ratio = 1.6666

Ratio =

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Turns Ratio Test Using Voltage Power Audio Oscillator

Digital Voltmeter

Frequency

Voltage "in iiiiinrrrmi

fral O

O

Measurement at Terminals.

Enclosure

UUT Figure 10-3. Test Setup for a Turns Ratio Test, Using Voltage. Equipment 1.

Power Audio Oscillator

2.

Voltage Meter

3.

SI, DPST (break before make)

Test (See the information on Test Conditions). There are two methods to accomplish this type of turns ratio test shown in Figure 10-3: 1. Apply a voltage equal to the primary turns, such as 0.75 volts. Then, read the secondary voltage of 1.25 as turns, directly. 2. Apply the voltage to terminals, (1-2), and read the secondary voltage, (3-4). Use a calculator and divide the primary voltage into the secondary.

N V Ratio = IJL = l£. 125 1.666 75 1 Ratio = 1.666 Ratio =

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Primary Inductance and Leakage Inductance Measurements Using a Bridge

Inductance Bridge

RCL Meter

O O

OO Four Wire RCL Bridge I

Sense Lead

Short Secondaries Sense Lead Shortest possible leads. — Enclosure

UUT

Figure 10-4. Inductance Measurements, Using a Four-Wire Bridge.

Equipment 1.

Four-Wire, RCL Bridge

Test (See the information on Test Conditions). Connect the leads to terminals, (1-2), as shown in Figure 10-4, and read the inductance directly on the RCL meter. The two sense leads will compensate for the long leads. This way, the bridge will measure right at the terminals. Instruments of this type, with four leads coming from the instrument, provide a more accurate reading.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Primary Inductance and Leakage Inductance Measurements Using Current Power Audio Oscillator

Digital Voltmeter

Frequency rriTTTmnnTUTT Voltage

Voltage

O

Rw = Winding Resistance

Short (3 and 4) for Leakage Test.

Figure 10-5. Test Setup for Measuring Magnetizing Current. Equipment 1.

Power Audio Oscillator

2.

Digital Voltmeter

3.

SI, 2 pole 3 position (break before make)

4.

S2, SPST

5.

R1, 0.1OQ, 1 .OQ, 1OQ, 1 % wire wound (non-inductive)

6.

Winding Resistance, Rw

Test (See the information on Test Conditions). Place the switch, S2, in position E, and apply the input voltage V^, as shown in Figure 10-5. Place switch, SI, in a position that provides the best voltage reading with the lowest resistance value of Rl. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Test Specification Frequency, f = 1 kHz Vin = 6 volts Rl = 1 Q Rw - 2 Q V R I = 0.150 volts Step 1. Calculate the input current, Ij n . 7

m

= - ,

[amps]

OJ5

1 4=0.150,

[amps]

Step 2. Calculate the circuit impedance, Z. Z = -^, /.in

[ohms]

Z =

, [ohms] 0.15 Z = 40, [ohms] Step 3. Calculate the equivalent resistance, Rx. RX=R\ + RW, /?,=! + 2, Rx = 3,

[ohms]

[ohms]

[ohms]

Step 4. Calculate the reactance, XL. XL = Jz2 - R] ,

[ohms]

^=>/(40)2-(3)2,

[ohms]

A^ = 39.9, [ohms] Step 5. Calculate the inductance, L.

, _ ^ , [henrys] 2n / (39.9) , [henrys] (6.28)(1000) I = 0.00635,

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[henrys]

Inductance Measurement with DC Power Audio Oscillator

Digital Voltmeter

DC Power Supply

O

O

Constant Current

O

Short (3 and 4) for Leakage Test. Rw = Winding Resistance

Figure 10-6. Test Setup for Measuring Magnetizing Current. Equipment 1.

Power Audio Oscillator

2.

Digital Voltage Meter

3.

DC Power Supply, 0 - 1 0 amps

4.

SI, 2 pole, 3 position, (breakbefore make)

5.

S2, SPST

6.

Rl, 0.1 OQ, l.OQ, 10Q, 1% Wire Wound (non-inductive)

7.

Winding Resistance, Rw

8.

Cl, dc Blocking Capacitor

9.

LI, ac Isolation Inductor is designed to minimize the ac current driven back into the power supply.

Test (See the information on Test Conditions). Place switch, S2, in position E and apply the input voltage, Vin, as shown in Figure 10-6. Place switch, SI, in a position that provides the digital voltmeter with the best resolution with lowest resistance value of Rl. Adjust the constant current, power supply to the current as specified in the Specification Control Drawing, (SCD). Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Test Specification Frequency, f = 50 kHz Vin = 3 volts Rl = 1 Q RW = 0.15Q V R 1 = 0.250 volts Idc = 3 amps Step 1 . Calculate the input current, I in . /,=—, '" Rl

[amps]

°'25

/,.„ = 0.250,

[amps]

Step 2. Calculate the circuit impedance, Z.

V. Z = -^,

[ohms]

in

Z - - , [ohms] 0.25 Z = 12, [ohms] Step 3. Calculate the equivalent resistance, R x . /?,=/?! + /?„.,

[ohms]

^ = 1 + 0.15,

[ohms]

/?, =1.15,

[ohms]

Step 4. Calculate the reactance, X L . XL = ^Z2 -R;, [ohms] XL = ^(12) 2 -(1.15) 2 , XL . = 1 1 . 9 ,

[ohms]

[ohms]

Step 5. Calculate the inductance, L.

X L = —-^-, [henrys] 271 /

(11.9) (6.28)(50000) L = 0.0000379,

L = 37.9, L"h]

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[henrys]

[henrys]

Resistance Measurement Using a Bridge (Measure Resistance >1Q)

Inductance Bridge

RCL Meter

oo

99 (!)

UUT

Figure 10-7. Resistance Measurements, Using a Four-Wire Bridge.

Equipment 1.

Four Wire RCL Bridge

Test (See the information on Test Conditions). Connect the leads to terminals, (1-2), as shown in Figure 10-7, and read the resistance, directly on the RCL meter. The two sense leads will compensate for the long leads. This way, the bridge will measure directly at the terminals. Instruments, that use four leads for measurement, will provide a more accurate reading.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Resistance Measurement Using Current (Measuring Resistance, < 1.0 Q) Current Set, Typically at (1.0 and 0.10 amps). Digital Voltmeter

Measurement at Terminals

Figure 10-8. Resistance Measurements, Using a Constant Current Power Supply.

Equipment 1.

DC Power Supply

2.

Digital Voltmeter

3.

Rl, Calibration Resistor 1 fi, 1% Wire Wound 5-10 Watt. The calibration resistor is used to provide an accurate current reference, in case the power supply is not capable of it.

Test (See the information on Test Conditions). Connect the leads to terminals (1-2), as shown in Figure 10-8, and read the voltage, directly on the digital voltmeter. Using a current value of 1 amp will provide a direct resistance reading. Caution High currents on fine wire could cause overheating and damage.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Testing for Transformer Resonance Dual Channel Oscilloscope

Power Audio Oscillator Vert. #1, VI Vert. #2, V2

UUT

Vert #2 Input Voltage Figure 10-9. Circuit for Measuring Transformer or Inductance Self Resonates. Equipment 1.

Wide Band Power Oscillator

2.

Dual Beam Oscilloscope

3.

Rl m , Sense Resistor 250 - 1000 Q, 5% Carbon 1 Watt.

Test (See the information on Test Conditions). Connect the circuit, as shown in Figure 10-9. The voltage, VI, will be held constant and go to a vertical input, #1, of the oscilloscope. The voltage, V2, will go to a vertical input, #2, of the oscilloscope, starting at about 1 kHz sweep through the frequency, while keeping the voltage, VI, constant. The oscilloscope will monitor, VI and V2. The voltage, V2, will change in amplitude, as the frequency is changed. As the frequency is increased, the voltage, V2, will start to rise and reach a peak value, and then start to decay. At this peak voltage, the transformer is at resonance.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Phase Testing

Oscilloscope

Power Audio Oscillator Frequency TTTTirTTTTTTTTTTT

Voltage

Black Test Probe Enclosure UUT

Figure 10-10. Test Circuit for Measuring the Transformer Winding Phase. Equipment 1.

Power Oscillator

2.

Oscilloscope with Both Vertical and Horizontal Input.

Test (See the information on Test Conditions). Connect the circuit, as shown in Figure 10-10. The voltage, V I , will be held constant and go to a horizontal input of the oscilloscope. The voltage, V2, will go to a vertical input of the oscilloscope. Place the, V2, Red Test Probe on the input, VI, Red. The oscilloscope will show a deflection to the left, indicating a start phase condition. If the trace is deflected in the other direction, then the phase is reversed.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Insulation Resistance Test (Megger Test) Insulation Resistance Tester (Megger) Voltage

Resistance Meg Q

50 V dc High Voltage O

500 V dc

d

Arc Lamp

Core

Primary

- Secondaries

- Enclosure Shield Mounting Hardware

Figure 10-11. Setup for the Insulation, Resistance Test. Equipment (Caution High Voltage) 1.

Insulation, Resistance Tester (Megger)

Test (See the information on Test Conditions). An insulation resistance test circuit is shown in Figure 10-11. The Megger Test is performed at either 50 or 500 volts dc, depending upon the requirement. The Megger Test is normally performed between all combinations of isolated elements, such as primary, secondaries, core, shields, enclosures, and mounting hardware. The normal insulation reading is about 20,000 meg-ohms. The test voltages and conditions for the magnetic component should be in the Specification Control Drawing, (SCD). If there is no reference to voltage or test conditions, then the test engineer should consult with the cognizant engineer.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Voltage Breakdown Test (Hi-Pot Test) Voltage Breakdown Tester (Hi-Pot) Applied Voltage

1000 Vac Variable

b High Voltage O O

Arc Lamp

Core

Primary

Secondaries

Enclosure Shield Mounting Hardware

Figure 10-12. Setup for the Voltage Breakdown Test.

Equipment (Caution High Voltage) 1.

Voltage Breakdown Tester, (Hi-pot)

Test (See the information on Test Conditions). Voltage breakdown test circuit is shown in Figure 10-12. The Hi-pot Test is normally performed with a potential of twice the operating voltage, plus 1000 volts ac, depending on the requirement. The Hi-pot Test is performed between all combinations of isolated elements, such as primary, secondaries, core, shields, enclosures, and mounting hardware. The Hi-pot voltage is normally applied for one minute. The test voltages and conditions for the magnetic component should be in the specification control drawing, (SCD). If there is no reference to voltage or test conditions, then the test engineer should consult with the cognizant engineer.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Primary to Secondary Capacitance Measurement

Digital Voltmeter

Power Audio Oscillator Frequency

iiiiiiiinnTTTn

Voltage

Voltage

Gnd.O

Shield

\ •J 1—1

1 >

< <

f

<

~l

1 (r c Rl

V/ i

UUT

Enclosure

Figure 10-13. Test Circuit for Measuring Primary to Secondary, ac, Leakage Current. Equipment 1.

Power Audio Oscillator

2.

Digital Voltmeter

Test (See the information on Test Conditions). Connect the leakage current test circuit, as shown in Figure 10-13. The test voltages and conditions for the magnetic component should be in the Specification Control Drawing, (SCD). If there is no reference to voltage or test conditions, then the test engineer should consult with the cognizant engineer.

Test Specification Frequency, f = 1.0 kHz Vin = 10 volts V0 = 100 micro-volts R1=50Q

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Step 1. Calculate the reactance of the capacitor, Xc. If y \

X =/?! \ I -^ _i ir \ c

[ohms]

L

Xc=(W\l-—\-\, ' V 7VV0.005j A', = 2236,

J

[ohms]

[ohms]

Step 2. Calculate the circuit capacitance, C x . C = , [farads] •' 2nfXc Cv =

] . . , [farads] w (6.28)(1000)(2236)

Cv =7.12(10 8 ) , [farads] C, =712,

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

[pf]

Testing Core Permeability Inductance Bridge

RCL Meter

O O

OO Four-Wire RCL Bridge 4

Sense Lead

Sense Lead

Figure 10-14. Inductance Measurements, Using a Four-Wire Bridge. Equipment 1.

Four Wire RCL Bridge

Test (See the information on Test Conditions). Connect the leads to terminals, (1-2), as shown in Figure 10-14, and read the inductance directly on the RCL meter. The two sense leads will compensate for the long leads. This way the bridge will measure directly at the terminals. Instruments, that use four leads for measurement, will provide a more accurate reading. Testing the permeability of magnetic cores can best be done on toroidal cores. Steps include: winding a few turns, measuring the inductance, and then simply calculating the millihenrys per 1000 turns. Testing power cores for permeability, by winding only a few turns, will not yield the correct permeability. The permeability, given by the manufacturers, is based on a fully- wound core. The error is caused by the fringing flux, due to the distributed gap. The error in permeability can be greater than 10%.

Ln = inductance for N turns (mh) - nominal inductance (millihenry per 1000 turns) 0.471 N2A u l O ~ 8 L=

(MPL)

0.4;r/V2/l Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

, [henrys]

, [permeability]

Turns Ratio Test on Multi-Winding Inductors with Large Gaps Power Audio Oscillator

Ill

Digital Voltmeter

Mill

Voltage

Measurement at Terminals

Test turns are 360 degrees around the core.

Figure 10-15. Test Setup for a Turns Ratio Test, Using a Tertiary Winding. Equipment 1.

Power Audio Oscillator

2.

Digital Voltmeter

3.

S1, DPST (break before make)

An accurate turns-ratio test on a multi-winding inductor is very difficult, due to winding resistance and leakage inductance. If the primary inductance is low, it results in a high excitation current, depending on the frequency. The test-operating frequency must stay well-below the resonant frequency. The resultant voltage drop, V R , due to the primary resistance, is caused by a high excitation current, and the voltage drop, V L , due to the leakage inductance, does not get transferred by the primary, as shown in Figure 10-16.

Figure 10-16. Primary Circuit and its Parasites.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Test (See the information on Test Conditions). Add a tertiary winding. An example would be: Wind 10 turns, N x , preferably 360 degrees around the core. This will be the reference winding. Place SI in position 1. Then apply the input voltage, V in , to terminals, (1-2), and read the tertiary voltage, V x , at (X1-X2). Adjust the applied input voltage, V in , until the voltage, V x , equals 1 volt. Place SI in position 2 and read the secondary voltage, Vs. The turns-ratio can be calculated using the tertiary winding, as shown below. The reverse has to be done to check the primary,

Np.

yv

v

N

V

Ratio = ^L = ^L

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Testing the Dynamic B-H Loop Oscilloscope

Power Audio Oscillator Frequency T T I M I I T T n I I I I I ITI

Voltage II

Ill M i l l I I I III

7^31

O O

Vert -O

Horiz O-

Gnd.

Gnd. UUT

Rl

*

R2 s/VNA

Enclosure

O

Figure 10-17. B-H Loop Test Circuit. The test circuit, that is most commonly used to display the B-H loop on an oscilloscope, is shown in Figure 10-17. The dynamic hysterestis, or B-H loop, contains very important information about the magnetic component. The area within the B-H loop relates to losses, and the amplitude relates to flux density, as shown in Figure 10-18. B (tesla) B

H (oersteds)

B The flux level in tesla. Br The remanence flux in tesla Bc The saturated flux in tesla. H Magnetizing force in oersteds. HS The magnetizing force at saturation in oersteds. Hc The coercivity force in oersteds.

Figure 10-18. Typical B-H Loop. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

The excitation current, Im, causes a magnetic force in the magnetic component:

H(MPL) / m = —---, L [amps] F J 0.4u/V The voltage drop across R2 is proportional to the excitation current, as long as the current through Rl and

Cl is: IRC RC - -^~ 1 0 Q »•>

L[amps] FJ

The voltage drop, V2, should be very small compared to Vac:

= , [volts]

22

100

Then: = - - , [ohms] 100/_

The series network of Rl and Cl perform the integration of the applied voltage. The resistance should be very large compared to the impedance of the capacitor at the operating frequency:

Rl = —, coC

[ohms]

Then:

The measurement of the B-H loop is then:

'"

4A4NAC

And Tr

H =

n

,

r

—- L [oersteds]

The voltage, Vc, across the capacitor, Cl, is directly proportional to the, Bm, in tesla. The voltage, V2, across the resistor, R2, is directly proportional to H in oersteds. The oscilloscope will have to be calibrated with a known, magnetic material.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

High Voltage Testing Transformer and Inductor Test (Magnetic Component) Test voltage shall be applied to the magnetic component undergoing the test in a vacuum chamber, at room pressure. Corona detection networks, as shown in Figure 10-19, shall be used in appropriate leads to monitor for corona or arcing. Typical corona and arcing waveforms are shown in Figure 10-20. With the voltage continuously applied, the air pressure shall be reduced to the lower limit, 5.0 x 10"4 torr, and then raised to 50 torr. This pressure shall be varied between the upper and lower limits several times for a minimum length of one hour in the critical pressure region. At the conclusion of the test, the voltage shall be removed, and the magnetic component shall be brought back to ambient room pressure. During the test, any evidence of corona or arcing shall be cause for rejection.

Input Return

; • ' Corona ia LI

}

11

1

LB2 Arc

L2

Figure 10-19. Corona Detection Network Schematic (CDN). Parts' List Cl = 300 pf 400 volt mica capacitor. LI = 2.6 mh+/-20%, 40 ohms air-core. L2 = 3.0 h+/-20%, 225 ohms. LB1= NE-2 Neon, AC/DC visual corona indicator. LB2= NE-2 Neon, AC/DC visual arc indicator. SI - SPST, Bypass switch. VTVM, AC/DC corona detector. Scope, AC corona indicator.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Oscilloscope

Corona Burst

AC Supply Frequency Abrupt breaks in the scope trace or burst amplitudes, >5 volt pk-pk, indicates arcing, rather than corona. Figure 10-20. Typical Oscilloscope, Corona Burst Pattern. Test Configuration The configuration for testing magnetic components shall be shown, as in Figure 10-21 and Figure 10-22. Electrical connectors and wire leads shall be corona proof, when the pressure is in the critical pressure region. Transformer Mounting Magnetic components, undergoing tests, shall be mounted in a similar manner to that in the subsystem, especially, with regards to, adjacent metallic surfaces, terminals, etc. Potting, coating or encapsulation shall be similar to that applied to the magnetic component part in the complete subsystem. Interwinding Insulation The insulation integrity between windings, between the winding and the core, and between the winding and the case, if one is used, or between windings and mounting inserts, if used, shall be tested by applying a voltage between the various windings, cores, etc., in accordance with Figure 10-21 and Table 10-1. The voltage shall be applied for a minimum time of 5 +/- 1 seconds. Table 10-1 Working Voltage (dc plus peak ac)

Test (rms)

250 to 700 volts

2.8x working voltage

Above 700 volts

1.4x working voltage plus 1000

Intrawinding Insulation Magnetic components shall be subjected to a voltage to cause twice the rated voltage to appear across all windings at the critical pressure region. The test voltage may be applied to any winding, as shown in Figure 10-22. Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Vacuum Chamber or Bell Jar Transformer Under Test (TUT)

Mounting Plate

Insulator

High Voltage Feed Through Low Voltage Feed Through

High Voltage Return CDN = Corona Detection Network

Figure 10-21. Transformer Interwinding, Voltage Breakdown Test.

Note: 1.

Switch, SI, in the Corona Detection Network, shall be closed for this test.

2.

Grounding type selector switch may be used with one Corona Detection Network.

3.

CDN = Corona Detection Network. See Figure 10-19.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Vacuum Chamber or Bell Jar Transformer Under Test (TUT) \

Mounting Plate

Insulator

High Voltage Feed Through

/

Low Voltage Feed Through

CDN = Corona Detection Network

Figure 10-22. Transformer Intrawinding, Voltage Breakdown Test. Note: 1.

Resistors are loading, R's, for the secondary winding. (They may be located outside of the chamber).

2.

Switch, SI, in the Corona Detection Network, shall be closed for this test.

3.

The power supply, ac voltage, shall be twice-rated voltage for the winding, energized with the frequency raised, so that the ac current flowing is equal to, or less than the rated current.

4.

The grounding type selector switch may be used with one Corona Detection Network.

5.

CDN = Corona Detection Network. See Figure 10-19.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Care must be taken to terminate all of the magnetic components terminals so that external corona or arcing is prevented. Mountings and windings shall be grounded as they would be in service. The test frequency shall be far enough from any resonant frequency, so that voltages, more than twice rated, will not occur in any winding. Twice the rated voltage shall be applied across a winding at approximately twice the normal frequency, or in a manner that will not exceed twice rated current.

Examination During and After Test Magnetic components, undergoing the tests, shall show no internal corona or arcing during the test. After the test, the magnetic component shall be examined for evidence of arcing, flashover, breakdown of insulation, and damage. Visible damage or detection of voltage breakdown or corona, by insulation, shall be cause for rejection.

High Voltage Test Equipment Corona Detection Network Detection of corona or arcing shall be by a current, or series type network, as shown in Figure 10-19. Insert the Corona Detection Network in series with the ground, or return of the high voltage circuit being tested. Indicators, LB-1, and LB-2, shown in Figure 10-19, serve the dual purpose of corona and arc indication, and over voltage protection. Inductance LI and L2 are in series and provide a significant ac impedance, from audio frequencies to nearly 0.5 MHz respectively, which is the significant frequency range of corona voltage. The function of the capacitor, Cl, is to attenuate the ac supply frequency to a sufficient degree, but pass the corona burst pulses, so the maximum sensitivity of the oscilloscope may be utilized. The power supply waveform, appearing on the oscilloscope, shall serve as a reference for corona bursts, as shown in Figure 10-20. Thus corona bursts can be distinguished from extraneous noise in the circuit. Vacuum Chamber The vacuum equipment shall have sufficient capacity to pump down to the critical region in 20 minutes with the chamber air and outgassing loads present. Switching Switching of the magnetic component, high voltage leads shall be accomplished externally to the vacuum system. Oscilloscope The frequency response of the vertical amplifiers of the oscilloscope shall be flat to 1.0 MHz. Deflection sensitivity of the trace shall be 10 millivolts/cm or less. The zero trace of the oscilloscope shall be blanked out visually by opaque tape, so that the intensity can be turned up sufficiently to see the trace.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Quality Assurance

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Introduction Pursuing reliability in the manufacturing of transformers and inductors primarily involves attention to details, coupled with close controls in all phases of manufacturing. The manufacturing cycle should be controlled and monitored by a conscientious Quality Assurance (QA) program, which includes appropriate in-process inspection points, and testing activities to prevent workmanship defects and assures delivery of a high reliable end product.

Quality Assurance Requirements Assumptions Prior to Fabrication Vendor Survey A vendor survey had been performed and all open items had been closed.

Facility and Work Stations Facility (Clean Room) The general assembly and soldering area shall have a controlled environment, which limits the entry of contaminations. The temperature and humidity in the soldering area shall be monitored and maintained within the comfort zone, as shown in Figure 10-23. The enclosed soldering facility will maintain a positive pressure, unless the soldering area is not in an air-conditioned, clean room. 90°F 30°C

80°F 2 25°C

ex S 70°F 20°C

60°F

20

40 60 Relative Humidity, (%)

Figure 10-23. Temperature and Humidity in the Soldering Area. Lighting The lighting at the working surface for soldering and solder pot operations shall have a minimum illumination of 100 foot-candles.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Handling Parts Prior to handling parts and/or materials, the operator shall thoroughly clean his/her hands; the use of any hand lotion is forbidden. Anyone working or handling parts and/or materials must wear clean gloves and/or finger cots. Gloves must be changed when they show signs of contamination, and finger cots must be replaced when they are torn or contaminated. Work Area The work areas and workbenches shall be maintained in a clean and orderly manner. At the start of each workday, the work stations shall be free of visible dirt, grime, grease, flux or solder splatters, and other foreign materials. Restrictions There will be no smoking, eating, or drinking permitted at the work stations. Cosmetics Hand cream, ointments, perfumes, cosmetics, and other materials unessential to the fabrication operation shall not be permitted at the work station. ESP Protection Requirement Supplier shall establish and maintain a documented program for the control of Elect-Static Discharge, (ESD), during fabrication and handling of such devices. The program shall comply with the requirements of MIL-STD- 1686. Certified Personnel All certified personnel must have up-to-date, valid training certificates before fabrication can begin. In-House Fabrication Procedures All fabrication drawings and procedures must be signed off by the cognizant engineer before work can begin. There shall no red line drawings in the magnetic component assembly area. Purchase Order The purchase order or contract has to be issued between the company and vendor, before any parts are ordered or the beginning of fabrication. The purchase order, or contract, defines the test that will be performed, the manufacturing, and the quality assurance requirements. Fabrication Review A fabrication review will have been conducted between the company and the vendor to assure that the vendor is ready to begin fabrication and testing.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Engineering Model (EM) or Prototype After the engineering model, (EM), has been tested for form, fit, and function, a review panel that will involve the vendor and the Company Quality Assurance, and the cognizant engineer will be setup to access the magnetic component for practicality, reliability, and fabrication.

Before the Start of Fabrication Procedures Quality Assurance personnel shall review, inspect, and give their concurrence on: (a) assembly drawings, (b) test procedures, (c) potting procedures, (d) inspections, (travelers), and (e) shipping. Materials Quality Assurance personnel shall review, inspect, and issue a Part Acceptance Tag (PAT tag), as shown in Figure 10-24, on all materials such as: (a) wire, both magnet and insulated, (b) insulation material, (c) magnetic cores, (d) enclosures, (e) terminals, and (f) solder type. Equipment Quality Assurance personnel shall review, inspect, and give their concurrence on: (a) the winding machine, (b) the tension device, (c) the soldering iron, (d) the solder pot, (e) hand tools, and (f) aids.

Part Acceptance Tag

No. 35002

Part Number

Revision

Lot Number

P.O./W.O. Number

Inspection Report No.

Cert. Number

Supplier

Quantity

Date Received

Cert. Number

Date Inspected

Inspection Stamp

Figure 10-24. Typical, Quality Assurance, Part Acceptance Tag.

Documentation Materials Certification Manufacturers of the materials shall supply certification of conformance for the required and applicable specification. Traceability 100% traceability of all parts and materials shall be maintained throughout the process from the receiving, or source inspection, to the final tests.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Reverse-Traceability The information content of each document shall be sufficient to provide reverse-traceability. Manufacturing and Inspection Records All manufacturing and inspection checks shall be recorded on an approved, (Traveler). See Figures 10-25 and 10-26. The approved fabrication instructions will accompany each deliverable item, which will provide an accurate history of the part. Deliverable Package A documentation package shall be maintained for each deliverable piece of electronic equipment, and will include approved fabrication instructions, inspection reports, deviation reports, and all Material Review Board, (MRB), evaluations. This package will also include a Certificate of Compliance, serialized test data, and the traceability information.

In-Process Inspection In-Process Inspection The Company Quality Assurance personnel shall set up mandatory in-process inspection points after the vendor supplies assembly and test flow charts. Discrepancies Any discrepancies, with respect to the specification, drawing or inspection standards, defined in the contract, shall be written up on an Inspection Report, (IR). The, (IR), will be submitted to the company, cognizant engineer for disposition. Parts, that have been written up on an Inspection Report, (IR), will be assessed for impact to form fit or function. Common Problems In the fabrication of magnetic components, the most common problems found over the years are: (a) cold solder joints, (b) nicked magnet wire, (c) magnet wire lead dressing, and (d) magnet wire lead fatigue.

Unit Specification Verification Test Demonstration Verification, by testing, is accomplished by subjecting the magnetic component to a set of conditions under the control of the approved test plan, procedures, and test equipment which will provide the accurate test data. The results of the test are compared with the specification control drawings.

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Test Discrepancies Any discrepancies in the test results, when compared to the specification requirements, shall be written up by the company Quality Assurance. This information will be submitted to the cognizant, company engineer for disposition. The parts will be assessed for impact to form fit or function.

Visual Inspection The magnetic component shall be measured/inspected to verify that the construction, the physical dimensions, the correct markings, cleanliness, and the workmanship are in accordance with the specification, control drawings.

Traveler-Transformers, Inductors and Coil Assemblies (Front) Assembly No. Drawing No. & Rev. Serial No.

Prograrr Machine Specific ation No.

Material Part Number

IR/PAT

Type

Tech

Date

QA

Core Bobbin / Tube Wire Hook Up Tape Adhesive Tape Cloth Poly Shielding Banding Strap Seal Strap Air Gap Material Mylar Housing Terminal Board Sleeving Remarks Figure 10-25. Typical, Transformer, Inductor Inspection Traveler Card, (Front).

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Date

Traveler-Transformers, Inductors and Coil Assemblies (Back) Wire AWG

*Test Tech. IR/PAT Turns I 2 3 4 5 6 7 8 9 10 Inspection Prior to Soldering Solder Wires and Inspect Electrical Test Encapsulation Serial No. Marking Part No. Assembly No. A. Magnetizing Current B. Turns Ratio Test to Perform Winding Number

Date

QA

C. See Winding Specification

Figure 10-26. Typical, Transformer, Inductor Inspection Traveler Card, (Rear).

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

Date