Cleaning Printed Wiring Assemblies in Today’s Environment

237 Pages·1991·5.471 MB·English

by  Les Hymes (auth.), Les Hymes P.E. (eds.)

CLEANING PRINTED
WIRING ASSEMBLIES
IN TODAY' S ENVIRONMENT
CLEANING PRINTED
WIRING ASSEMBLIES
IN TODA Y'S ENVIRONMENT
Edited by
Les Hymes, P.E.
~ VAN NOSTRAND REINHOLD
~ ____ New York
DISCLAIMER
We believe the information provided in this work is reliable and useful, but it is furnished
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provision of the information. herein.
Copyright © 1991 by Van Nostrand Reinhold
Softcover reprint of the hardcover 1st edition 1991
Library of Congress Catalog Card Number 90-43405
ISBN-13: 978-94-011-6969-1 e-ISBN-13: 978-94-011-6967-7
001: 10.1007/978-94-011-6967-7
All rights reserved. No part of this work covered by the copyright hereon may be reproduced or
used in any form or by any means-graphic, electronic, or mechanical, including photocopying,
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Published by Van Nostrand Reinhold
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16 15 14 13 12 II 10 9 8 7 6 5 4 3 2
Library of Congress Cataloging-in. Publication Data
Cleaning printed wiring assemblies in today's environment / edited by Les Hymes.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-94-011-6969-1
I. Printed circuits--Cleaning. I. Hymes, Les.
TK7868.P7C56 1990 90-43405
621.381 '531--dc20 CIP
FOR MY PARENTS, BROTHERS, AND CHILDREN
AND IN APPRECIATION OF THE SUPPORT
FROM BARBARA
Books are but piles of stone set up to show coming travelers
where other minds have been, but no amount ofw ordm aking
could make a single soul to truly know the mountains. One
days exposure to the mountains is better than mountains of
books.
John Muir
John of the Mountains: The Unpublished Journals of John
Muir, p. 94 (University of Wisconsin Press, 1938).
Contents
Preface/xi
} Design and Process Considerations/}
Les Hymes, P.E., GE Medical Systems, Waukesha, Wisconsin
1.1 Overviewll
1.2 Assembly Packagingl2
1.2.1 Throughhole Mounted Technology/3
1.2.2 Surface Mounted Technology/4
1. 3 Component Packaging/6
1.3.1 Materials/6
1.3.2 Package and Mounting Configurationl8
1.4 The Printed Wiring Assembly/13
1.4.1 Substrate and Solder Mask/13
1.4.2 Component Placement/15
1.5 Assembly and Solder Processl17
1. 5.1 Assembly Aidsll7
1.5.2 Component Mounting Adhesivesl17
1.5.3 Soldering Cycles and Fluxes/18
1.5.4 Conformal Coating121
1.6 Cleaning Operationl21
1.6.1 Cleaning Solution Properties122
1.6.2 Process Enhancements122
1. 7 Summary/24
References/24
2 Flux Considerations with Emphasis on Low Solids/26
Leslie Adler Guth, AT&T Bell Labs
2. 1 Introductionl26
2.1.1 Purpose and Chapter Descriptionl26
vii
viii CONTENTS
2.1.2 Definition of Soldering Flux127
2.2 Specifications127
2.2.1 Test Methods128
2.2.2 IPCl35
2.2.3 U.S. Military/36
2.2.4 Telecommunications/37
2.2.5 Summary/38
2.3 Flux Materials/38
2.3.1 Rosinl40
.2.3.2 Water Soluble/42
2.3.3 Synthetic Activatedl43
2.3.4 Low Solids (No-Clean)/44
2.3.5 Controlled Atmosphere Soldering/49
2.4 Application Methods/50
2.4.1 Wave/51
2.4.2 Foam/51
2.4.3 Spray/52
2.4.4 Application Issues for LSFs/54
2.5 Monitoring Techniques/56
2.5.1 Specific Gravity/56
2.5.2 Acid Number (Titration)/56
2.5.3 Weight Measurements/56
2.5.4 Monitoring for LSFs/57
2.6 Process Issues/57
2.6.1 Flux Residue/57
2.6.2 Solder Ball Formationl57
2.6.3 Top Side Fillet Formationl58
2.6.4 Conformal Coating Compatibility/58
2.7 Nonliquid Fluxes/59
2.7.1 Core Solder Material/59
2.7.2 Solder Paste Material/59
2.7.3 Specifics for LSFs/60
2.8 Importance of Soldering Parameters/60
2.8.1 Wave Soldering/61
2.8.2 Hand Soldering/61
2.8.3 Reftow Soldering/61
2.8.4 Specifics for LSFs/61
2.9 Summary and Trends/62
2.9.1 Summary/62
2.9.2 Trends/62
References/63
CONTENTS ix
3 Solvent Defluxing of Printed Wiring Board Assemblies and Surface Mount
Assemblies: Materials, Processes, and Equipmenti65
1.K. "Kirk" Bonner
3.1 The Need for Cleaning/65
3.1.1 The Bare Board and Assembly Process-An Overview/65
3.1. 2 Types of Contaminants/68
3.1.3 Results of Different Types of Contaminants on Printing Wiring/
80
3.2 The Cleaning Process/83
3.2.1 Solvents for Cleaning/84
3.2.2 Bipolar Solvent Cleaning/87
3.2.3 Equipment for Cleaning/88
3.2.4 The Defiuxing Process/9l
3.2.5 Solvent Conservation and Reclamationl93
3.3 Testing for Cleanliness/94
3.3.1 Overview of Contamination Testing/94
3.3.2 Testing for Ionics/95
3.3.3 Testing for Nonionics/99
3.3.4 Surface Insulation Resistance (SIR) Test/l03
3.3.5 Electromigration (EM) Test/105
3.4 Environmental Concerns of Solvents/105
3.4.1 The Ozone Depletion Problem/106
3.4.2 The Benchmark/Phase 2 Test/108
3.4.3 Alternative Defiuxing Solvents/Ill
3.5 Conclusionll16
References/l 17
4 Aqueous Defluxing: Materials, Processes, and Equipmenti120
Gregory C. Munie
AT&T Bell Laboratories, Naperville, Illnois
4.1 Introductionl120
4.1.1 Why Aqueous?/120
4.1.2 Plusses and Minuses/12l
4.2 Design Considerationsl123
4.2.1 Layout/I 24
4.2.2 Component Choice/125
4.2.3 Surface Mount versus Throughhole/126
4.2.4 Process/Materials Considerationsl126
4.2.5 Summary/126
4.3 Process Considerations/126
x CONTENTS
4.3.1 Cleaning Materials/129
4.3.2 Equipmentl132
4.4 Process Qualific.ation and Control/136
4.4.1 Qualification Strategies/136
4.4.2 Cleanliness Evaluation Techniquesl138
4.5 Environmental Concems/145
4.5.1 Heavy Metals/146
4.5.2 pH/146
4.5.3 BOD/146
4.5.4 Summary/147
Referencesl147
5 Alternative Defluxing: Materials, Processes, and Equipment/151
Michael E. Hayes-Petroferm, Inc.
Kathi Johnson-Hexacon Electric Co.
5. 1 Introduction/151
5.2 Methods and Equipmentl152
5.2.1 Acoustical (Ultrasonic) Cleaningl152
5.2.2 Spray Equipmentl158
5.2.3 Centrifugal Cleaning Equipmentl159
5.3 Materials/160
5.3.1 Performance/162
5.3.2 Environmental Acceptability and Safety
Considerations/165
5.3.3 Economicsl172
5.3.4 Specific Material Descriptions/ 174
5.3.5 Use of Semi-Aqueous Materials in Military Electronicsl181
References/181
6 Defluxing for High Reliability Applications and General
Environmental Issues/183
Joe R. Felty
Texas Instruments, Inc.
6.1 Introduction/183
6.2 BackgroundJ183
6.3 Cleanliness Requirements/184
6.3.1 Necessity for Cleanlinessl184
6.3.2 Military Requirements/185
6.4 Cleaning Materials/186
6.4.1 Solvents/186
CONTENTS xi
6.4.2 Aqueousll87
6.4.3 New Alternatives/I88
6.4.4 Acceptance of Aiternativesll88
6.5 Cleaning Equipment/I92
6.5.1 Batch Cleanersll92
6.5.2 Inline Cleaners/I 92
6.6 Cleanliness VerificationlI96
6.6.1 Ionic Test Methodsll96
6.6.2 Organic Residue Test Methods/I98
6.7 Environmental Issues/I99
6.7.1 Atmospheric Impact/200
6.7.2 Montreal Protocol/20I
6.7.3 CFC Solvent Availability/203
6.8 The Future of Cleaning!203
6.8.1 Unilateral CFC Reductions/204
6.8.2 Alternative CFC Cleaning Materials/204
6.9 Conclusions!209
References!209
Bibliography!2IO
Index!219