Lead-Free Solder Process Development
March 2011, Wiley-IEEE Press
Discusses the growth mechanisms of tin whiskers and the effective mitigation strategies necessary to reduce whisker growth risks
This book covers key tin whisker topics, ranging from fundamental science to practical mitigation strategies. The text begins with a review of the characteristic properties of local microstructures around whisker and hillock grains to identify why these particular grains and locations become predisposed to forming whiskers and hillocks. The book discusses the basic properties of tin-based alloy finishes and the effects of various alloying elements on whisker formation, with a focus on potential mechanisms for whisker suppression or enhancement for each element. Tin whisker risk mitigation strategies for each tier of the supply chain for high reliability electronic systems are also described.
- Discusses whisker formation factors including surface grain geometry, crystallographic orientation-dependent surface grain boundary structure, and the localization of elastic strain/strain energy density distribution
- Examines how whiskers and hillocks evolve in time through real-time studies of whisker growth with the scanning electron microscope/focused ion beaming milling (SEM/FIB)
- Covers characterization methods of tin and tin-based alloy finishes such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD)
- Reviews theories of mechanically-induced tin whiskers with case studies using pure tin and other lead-free finishes shown to evaluate the pressure-induced tin whiskers
Mitigating Tin Whisker Risks: Theory and Practice is intended for the broader electronic packaging and manufacturing community including: manufacturing engineers, packaging development engineers, as well as engineers and researchers in high reliability industries.
1. Regulatory and Voluntary Drivers for Environmental Improvement: Hazardous Substances, Lifecycle Design and End of Life (John Hawley).
1.2 Substances of Environmental Concern.
1.3 Design for Environment/Energy Efficiency.
1.4 Recycling and Take-back.
2. Lead-free Surface Mount Technology (Jasbir Bath, Jennifer Nguyen and Sundar Sethuraman).
2.2 No-clean and Water-soluble Lead-free Pastes.
2.3 Solder Paste Handling.
2.4 Board and Stencil Design.
2.5 Screen Printing and Printability of Lead-free Solder Pastes.
2.6 Paste inspection.
2.7 Component Placement (Paste Tackiness).
2.8 Reflow Soldering and the Reflow Profile.
2.9 Effect of Nitrogen versus Air Atmosphere during Lead-free Reflow.
2.10 Head-in-Pillow Component Soldering Defect.
2.11 Solder Joint Visual Inspection.
2.12 AOI (Automated Optical Inspection).
2.13 X-ray Inspection.
2.14 ICT/Functional Testing.
2.16 Future Work.
3. Lead-free Wave Soldering (Dennis Barbini and Jasbir Bath).
3.1 Wave soldering process boundaries.
3.2 Soldering temperatures on the chip and main soldering waves.
3.3 Alloys for Lead-free Wave Soldering.
3.4 The function of nitrogen in wave soldering.
3.5 The effect of PCB Design on wave solder joint formation.
3.6 Standards related to wave soldering.
3.8 Future work.
4. Lead-free Rework (Alan Donaldson).
4.2 Surface Mount Technology (SMT) Hand Soldering/Touch-up.
4.3 BGA/CSP Rework.
4.4 BGA Socket Rework.
4.6 Through-hole Hand Soldering Rework.
4.7 Through-hole Mini-pot/Solder Fountain Rework.
4.8 Best Practices and Rework Equipment Calibrations.
4.10 Future Work.
5 Lead-Free Alloys for BGA/CSP Components (Gregory A. Henshall).
5.2 Overview of New Lead-Free Alloys.
5.3 Benefits of New Alloys for BGAs and CSPs.
5.4 Technical Concerns .
5.5 Management of New Alloys.
5.6 Future Work.
5.7 Summary and Conclusions.
6 Growth Mechanisms and Mitigation Strategies of Tin Whisker Growth (Peng Su).
6.2 Role of stress in whisker growth.
6.3 Understanding standard acceleration tests.
6.4 Plating process optimization and other mitigation strategies.
6.5 Whisker growth on board-mounted components.
7. Testability of Lead-Free Printed Circuit Assemblies (Rosa D.Reinosa and Aileen M. Allen).
7.2 Contact Repeatability of Lead-Free Boards.
7.3 Probe Wear and Contamination.
7.4 Board Flexure.
8. Board-Level Solder Joint Reliability of High Performance Computers under Mechanical Loading (Keith Newman).
8.2 Establishing PWB Strain Limits for Manufacturing.
8.3. SMT Component Fracture Strength Characterization.
8.4 PWB Fracture Strength Characterization.
8.5 PWB Strain Characterization.
8.6. Solder Joint Fracture Prediction – Modeling.
8.7. Fracture Strength Optimization.
9. Lead-Free Reliability in Aerospace/Military Environments (Thomas A. Woodrow and Jasbir Bath).
9.2 Aerospace/Military Consortia.
9.3 Lead-Free Control Plans for Aerospace/Military Electronics.
9.4 Aerospace/Military Lead-Free Reliability Concerns.
9.5 Summary and Conclusions.
10. Lead-Free Reliability in Automotive Environments (Richard D. Parke).
10.1 Introduction to Electronics in Automotive Environments.
10.2 Performance Risks and Issues.
10.3 Legislation Driving Lead-Free Automotive Electronics.
10.4 Reliability Requirements for Automotive Environments.
10.5 Failure Modes of Lead-free Joints.
10.6 Impact to Lead-free Component Procurement and Management.
10.7 Change versus Risks.
10.8 Summary and Conclusions.
JASBIR BATH is the owner of Bath Technical Consultancy LLC in Fremont, California. He has over fifteen years' experience in research, design, development, and implementation in the areas of soldering, surface mount, and packaging technologies working for companies including Flextronics International/Solectron Corporation and ITRI (International Tin Research Institute). Bath has been chair of various iNEMI lead-free consortia involving OEMs, EMS, and component and material supplier companies on alloy selection, assembly, and rework.
CAROL A. HANDWERKER is the Reinhardt Schuhmann Jr. Professor of Materials Engineering at Purdue University, Indiana. Previously, she was chief of the Metallurgy Division at the National Institute of Standards and Technology (NIST), where she participated in the NCMS (National Center for Manufacturing Sciences) Lead-Free Solder Project and co-chaired the iNEMI Lead-Free Alloy Selection Team. Dr. Handwerker is currently active on the iNEMI Technical, Research, and Environmental Leadership Steering Committees, as well as a participant in a range of iNEMI project teams.