Cleaning Printed Wiring Assemblies in Today's Environment

ISBN-13: 9789401169691 / Angielski / Miękka / 2012 / 225 str.

L. Hymes

Opis

The impetus to create this book originated from several concerns. One of these was the perceived value to the industry of a collection in one volume of a wide range of information pertinent to the reasons and techniques for de fluxing printed wiring assemblies (PWAs). This book is expected to be of use not only to those engaged in the electronics packaging industry but also to those in related fields seeking information concerning viable methods of dealing with one of the en- vironmental issues of our time: the destruction of the ozone layer surrounding and protecting the planet with which we have been entrusted. The volume of information relative to providing PW As free of residues ad- versely impacting operation, reliability, and life of electronic products is grow- ing, and it will continue to expand at an accelerated rate as we seek to match our technology needs and desires with our environmental responsibilities. At the time ofthis writing, which has spanned the latter portion of 1989 and early 1990, the issue of choosing a new approach to producing PW As free of detrimental residues while using environmentally acceptable manufacturing techniques ap- peared to be the major concern of the vast majority of those involved in the printed wiring assembly industry. To many this meant the use of different clean- ing media and/or process or equipment enhancements; to others it meant the elimination of the need to clean through materials or process changes.

Spis treści

1 Design and Process Considerations.- 1.1 Overview.- 1.2 Assembly Packaging.- 1.2.1 Throughhole Mounted Technology.- 1.2.2 Surface Mounted Technology.- 1.3 Component Packaging.- 1.3.1 Materials.- 1.3.2 Package and Mounting Configuration.- 1.4 The Printed Wiring Assembly.- 1.4.1 Substrate and Solder Mask.- 1.4.2 Component Placement.- 1.5 Assembly and Solder Process.- 1.5.1 Assembly Aids.- 1.5.2 Component Mounting Adhesives.- 1.5.3 Soldering Cycles and Fluxes.- 1.5.4 Conformal Coating.- 1.6 Cleaning Operation.- 1.6.1 Cleaning Solution Properties.- 1.6.2 Process Enhancements.- 1.7 Summary.- References.- 2 Flux Considerations with Emphasis on Low Solids.- 2.1 Introduction.- 2.1.1 Purpose and Chapter Description.- 2.1.2 Definition of Soldering Flux.- 2.2 Specifications.- 2.2.1 Test Methods.- 2.2.2 IPC.- 2.2.3 U. S. Military.- 2.2.4 Telecommunications.- 2.2.5 Summary.- 2.3 Flux Materials.- 2.3.1 Rosin.- 2.3.2 Water Soluble.- 2.3.3 Synthetic Activated.- 2.3.4 Low Solids (No-Clean).- 2.3.5 Controlled Atmosphere Soldering.- 2.4 Application Methods.- 2.4.1 Wave.- 2.4.2 Foam.- 2.4.3 Spray.- 2.4.4 Application Issues for LSFs.- 2.5 Monitoring Techniques.- 2.5.1 Specific Gravity.- 2.5.2 Acid Number (Titration).- 2.5.3 Weight Measurements.- 2.5.4 Monitoring for LSFs.- 2.6 Process Issues.- 2.6.1 Flux Residue.- 2.6.2 Solder Ball Formation.- 2.6.3 Top Side Fillet Formation.- 2.6.4 Conformal Coating Compatibility.- 2.7 Nonliquid Fluxes.- 2.7.1 Core Solder Material.- 2.7.2 Solder Paste Material.- 2.7.3 Specifics for LSFs.- 2.8 Importance of Soldering Parameters.- 2.8.1 Wave Soldering.- 2.8.2 Hand Soldering.- 2.8.3 Reflow Soldering.- 2.8.4 Specifics for LSFs.- 2.9 Summary and Trends.- 2.9.1 Summary.- 2.9.2 Trends.- References.- 3 Solvent Defluxing of Printed Wiring Board Assemblies and Surface Mount Assemblies: Materials, Processes, and Equipment.- 3.1 The Need for Cleaning.- 3.1.1 The Bare Board and Assembly Process—An Overview.- 3.1.2 Types of Contaminants.- 3.1.3 Results of Different Types of Contaminants on Printing Wiring/.- 3.2 The Cleaning Process.- 3.2.1 Solvents for Cleaning.- 3.2.2 Bipolar Solvent Cleaning.- 3.2.3 Equipment for Cleaning.- 3.2.4 The Defluxing Process.- 3.2.5 Solvent Conservation and Reclamation.- 3.3 Testing for Cleanliness.- 3.3.1 Overview of Contamination Testing.- 3.3.2 Testing for Ionics.- 3.3.3 Testing for Nonionics.- 3.3.4 Surface Insulation Resistance (SIR) Test.- 3.3.5 Electromigration (EM) Test.- 3.4 Environmental Concerns of Solvents.- 3.4.1 The Ozone Depletion Problem.- 3.4.2 The Benchmark/Phase 2 Test.- 3.4.3 Alternative Defluxing Solvents.- 3.5 Conclusion.- References.- 4 Aqueous Defluxing: Materials, Processes, and Equipment.- 4.1 Introduction.- 4.1.1 Why Aqueous?.- 4.1.2 Plusses and Minuses.- 4.2 Design Considerations.- 4.2.1 Layout.- 4.2.2 Component Choice.- 4.2.3 Surface Mount versus Throughhole.- 4.2.4 Process/Materials Considerations.- 4.2.5 Summary.- 4.3 Process Considerations.- 4.3.1 Cleaning Materials.- 4.3.2 Equipment.- 4.4 Process Qualification and Control.- 4.4.1 Qualification Strategies.- 4.4.2 Cleanliness Evaluation Techniques.- 4.5 Environmental Concerns.- 4.5.1 Heavy Metals.- 4.5.2 pH.- 4.5.3 BOD.- 4.5.4 Summary.- References.- 5 Alternative Defluxing: Materials, Processes, and Equipment.- 5.1 Introduction.- 5.2 Methods and Equipment.- 5.2.1 Acoustical (Ultrasonic) Cleaning.- 5.2.2 Spray Equipment.- 5.2.3 Centrifugal Cleaning Equipment.- 5.3 Materials.- 5.3.1 Performance.- 5.3.2 Environmental Acceptability and Safety Considerations.- 5.3.3 Economics.- 5.3.4 Specific Material Descriptions.- 5.3.5 Use of Semi-Aqueous Materials in Military Electronics.- References.- 6 Defluxing for High Reliability Applications and General Environmental Issues.- 6.1 Introduction.- 6.2 Background.- 6.3 Cleanliness Requirements.- 6.3.1 Necessity for Cleanliness.- 6.3.2 Military Requirements.- 6.4 Cleaning Materials.- 6.4.1 Solvents.- 6.4.2 Aqueous.- 6.4.3 New Alternatives.- 6.4.4 Acceptance of Alternatives.- 6.5 Cleaning Equipment.- 6.5.1 Batch Cleaners.- 6.5.2 Inline Cleaners.- 6.6 Cleanliness Verification.- 6.6.1 Ionic Test Methods.- 6.6.2 Organic Residue Test Methods.- 6.7 Environmental Issues.- 6.7.1 Atmospheric Impact.- 6.7.2 Montreal Protocol.- 6.7.3 CFC Solvent Availability.- 6.8 The Future of Cleaning.- 6.8.1 Unilateral CFC Reductions.- 6.8.2 Alternative CFC Cleaning Materials.- 6.9 Conclusions.- References.