Solder Joint Reliability

1. Flux Reactions and Solderability.- 1.1 Flux History.- 1.2 Solderability Tests.- 1.2.1 Visual Assessment.- 1.2.2 Area of Spread Test.- 1.2.3 Edge Dip and Capillary Rise Tests.- 1.2.4 Globule Test.- 1.2.5 Rotary Dip Test.- 1.2.6 Surface Tension Balance Test.- 1.3 Flux Action from Solderability Measurements.- 1.4 Flux Types.- 1.4.1 Mechanistic Studies for Inorganic Fluxes.- 1.4.2 Mechanistic Studies for Rosin-based Fluxes.- References.- 2. Solder Paste Technology and Applications.- 2.1 Chemical and Physical Characteristics.- 2.2 Fluxing and Fluxes.- 2.3 Solder Alloys.- 2.4 Solder Powder.- 2.5 Paste Formulation.- 2.6 Paste Rheology.- 2.7 Rheology Behavior Characterization.- 2.8 Viscosity and Measurement.- 2.9 Printing Technique.- 2.10 Dispensing Technique.- 2.11 Soldering Principle.- 2.12 Solderability.- 2.13 Soldering Methods.- 2.14 Controlled Atmosphere Soldering.- 2.15 Solvent Cleaning.- 2.16 Aqueous Cleaning and Aqueous Cleaning Paste.- 2.17 No-clean Paste.- 2.18 Fine Pitch Paste.- 2.19 Quality.- 2.20 Conclusion.- References.- 3. Technical Considerations in Vapor Phase and Infrared Solder Reflow Processes.- 3.1 Introduction to Surface Mount Reflow Soldering.- 3.2 Type I.- 3.3 Soldering Requirements for Surface Mount Technology.- 3.4 Reflow Process Phases.- 3.5 Reflow Equipment.- 3.5.1 Infrared.- 3.5.2 Vapor Phase.- 3.5.3 Convection.- 3.5.4 Conductive Belt.- 3.5.5 Laser Soldering.- 3.6 Prereflow Solder Paste Bake.- 3.7 Maximizing Solder Joint Yield.- 3.8 Reflow Processing.- 3.8.1 Vapor Phase.- 3.8.2 Infrared.- 3.8.3 Cost Comparison.- 3.9 SMT Reliability.- References.- 4. Optimizing the Wave Soldering Process.- 4.1 Basic Wave Soldering Process Overview.- 4.2 Wave Soldering Process Hardware.- 4.2.1 Fluxing.- 4.2.2 Fluxers.- 4.2.3 Fluxer Measurement Parameters.- 4.2.4 Fluxer Optimization.- 4.2.5 Preheating.- 4.2.6 Preheaters.- 4.2.7 Preheat Measurement Parameters.- 4.2.8 Preheat Optimization.- 4.2.9 Wave Soldering.- 4.2.10 Solder Waves.- 4.2.11 Solder Wave Measurement Parameters.- 4.2.12 Wave Soldering Optimization.- 4.2.13 Solidification.- 4.2.14 Conveyors.- 4.3 Wave Soldering Process Parameter Optimization.- 4.3.1 Optimization Procedure Test Study.- 4.4 Results.- 4.5 Conclusion.- References.- 5. Post-Solder Cleaning Considerations.- 5.1 Purpose and Chapter Description.- 5.2 Environmental Concerns.- 5.3 Definition of Soldering Flux.- 5.4 Specifications.- 5.4.1 Test Methods.- 5.4.2 Institute for Interconnecting and Packaging Electronic Circuits (IPC).- 5.4.3 U.S. Military.- 5.4.4 Telecommunications.- 5.5 Flux Materials and Associated Cleaning.- 5.5.1 Rosin.- 5.5.2 Water Soluble.- 5.5.3 Synthetic Activated.- 5.5.4 Low Solids (No-Clean).- 5.5.5 Controlled Atmosphere Soldering.- 5.6 Flux Application Methods.- 5.6.1 Wave.- 5.6.2 Foam.- 5.6.3 Spray.- 5.6.4 Rotating Drum Spray.- 5.6.5 Application Issues for Low Solids Fluxes.- 5.7 Process Issues Associated with Reliability.- 5.7.1 Flux Residue.- 5.7.2 Solder Ball Formation.- 5.7.3 Top-Side Fillet Formation.- 5.7.4 Conformal Coating Compatibility.- 5.8 Non-Liquid Fluxes.- 5.8.1 Core Solder Material.- 5.8.2 Solder Paste Material.- 5.9 Trends.- References.- Additional Readings.- 6. Scanning Electron Microscopy/Energy Dispersive X-Ray (SEM/EDX) Characterization of Solder-Solderability and Reliability.- 6.1 Scanning Electron Microscopy/Energy Dispersive X-ray Analysis.- 6.2 Other Methods-WDX.- 6.3 Detection Modes.- 6.4 Sample Preparation.- 6.5 Different Phases in Alloys.- 6.6 Intermetallics.- 6.7 Scope of the Chapter.- 6.8 SEM/EDX Characterization-General.- 6.8.1 Tin-Lead Solders.- 6.8.2 Two Percent Silver Solder.- 6.8.3 Gold-and Silver-Based Solders.- 6.8.4 Indium Solders.- 6.8.5 Bismuth Solders.- 6.8.6 Miscellaneous.- 6.9 Solderability Issues.- 6.9.1 Maintaining Solderability.- 6.9.2 Inadequate Tin Protective Coatings.- 6.9.3 The Dangers of "Forcing" Poor Solderability.- 6.10 Reliability Issues-Leaching of Substrate.- 6.11 Reliability Issues Gold Embrittlement.- 6.12 Reliability Issues-Fatigue.- References.- 7. The Role of Microstructure in Thermal Fatigue of Pb-Sn Solder Joints.- 7.1 Experimental Details.- 7.2 Eutectic Microstructures.- 7.2.1 Lamellar Eutectics.- 7.2.2 Degenerate Eutectics.- 7.2.3 Solder Joint Microstructures.- 7.2.4 Effects of Composition.- 7.2.5 Recrystallized Pb-Sn Microstructure.- 7.2.6 Coarsening Behavior.- 7.3 Mechanical Properties.- 7.3.1 Eutectic Structures.- 7.3.2 Deformation Mechanisms.- 7.4 Microstructural Evolution under Thermal Fatigue.- 7.4.1 Thermal Fatigue in Shear.- 7.4.2 Microstructural Mechanisms of Thermal Fatigue.- 7.4.3 Other Microstructures.- 7.5 Conclusion.- 7.6 Acknowledgments.- References.- 8. Microstructure and Mechanical Properties of Solder Alloys.- 8.1 Thermal Cycling Fatigue.- 8.2 Precipitation and Dissolution in Pb-Sn Alloys.- 8.3 Discussion.- References.- 9. The Interaction of Creep and Fatigue in Lead-Tin Solders.- 9.1 Current Approaches to Accelerated Testing.- 9.2 Damage by Fatigue and Creep Mechanisms.- 9.3 Assessing Actual Joint Damage.- 9.3.1 In-service Testing.- 9.4 Understanding the Damage Mechanisms.- 9.4.1 Creep and Tensile Test Results.- 9.4.2 Cyclic Creep.- 9.4.3 Hold Time Effects.- 9.5 Interpretation for Packaging Applications.- 9.5.1 Deformation.- 9.5.2 Thermomechanical Test Guidance.- 9.6 Concluding Remarks.- References.- 10. Creep and Stress Relaxation in Solder Joints.- 10.1 Ideal Expansivity of a Substrate.- 10.1.1 No Temperature Gradients, No Transients.- 10.1.2 Power Dissipation in the Component.- 10.1.3 Z-Gradients in the Substrate.- 10.1.4 In-Plane Gradients.- 10.1.5 Temperature Shock.- 10.1.6 Solder-Substrate Expansivity Mismatch.- 10.1.7 Overall Judgment.- 10.2 Creep and Stress Relaxation.- 10.3 Solder Properties.- 10.4 Constitutive Relations.- 10.5 Temperature Cycling.- 10.5.1 Small Temperature Range Cycling.- 10.6 Larger Temperature Cycles.- 10.7 Acknowledgments.- References.- 11. Effects of Strain Range, Ramp Time, Hold Time, and Temperature on Isothermal Fatigue Life of Tin-Lead Solder Alloys.- 11.1 Definition of Failure, Specimen Design, and Mode of Loading.- 11.2 Effect of Strain Range on Fatigue Life.- 11.3 Effect of Frequency on the Fatigue Life.- 11.4 Effect of Hold Time on Fatigue Life.- 11.5 Effect of Temperature on Isothermal Fatigue of Solders.- 11.6 Conclusion.- References.- 12. A Damage Integral Methodology for Thermal and Mechanical Fatigue of Solder Joints.- 12.1 Inelastic Deformation and Stress Calculation.- 12.1.1 Governing Equation for Solder Stress.- 12.1.2 Inelastic Deformation Behavior and Constitutive Relations.- 12.1.3 Stress Calculation.- 12.2 Damage Rate Formulation.- 12.2.1 Damage Mechanisms.- 12.2.2 A Phenomenological Formulation for Crack Growth Rates.- 12.3 Damage Integration and Failure Criterion Effects.- 12.3.1 Thermal Fatigue Life Estimation.- 12.3.2 Failure Criterion Effects.- 12.4 Discussion and Conclusions.- 12.5 Acknowledgments.- References.- 13. Modern Approaches to Fatigue Life Prediction of SMT Solder Joints.- 13.1 Mechanical Testing.- 13.1.1 Determination of Elastic Properties.- 13.1.2 Mechanical Properties.- 13.2 Life Prediction Techniques.- 13.2.1 Fatigue Models.- 13.3 Hybrid Life Prediction Techniques.- 13.3.1 Strain Range Partitioning Rule.- 13.4 Model Joints.- 13.4.1 Quality Control.- 13.4.2 Lap Joint Specimens.- 13.4.3 Straddle Board Specimens.- 13.5 Expert Systems.- 13.6 Conclusions.- 13.7 Acknowledgments.- References.- 14. Predicting Thermal and Mechanical Fatigue Lives from Isothermal Low Cycle Data.- 14.1 Low Cycle Fatigue (LCF).- 14.2 Low Cycle Fatigue of Solders-Influence of the Definition for Failure.- 14.3 Influence of the Temperature.- 14.4 Influence of Hold Times and Cycling Frequency.- 14.5 Influence of the Environment.- 14.6 Microstructural Changes.- 14.7 Determination of the Displacement and Strain Distribution in a Solder Joint.- 14.8 Prediction of the Fatigue Life of Solder Joints.- 14.9 Inherent Limitations to Fatigue Life Predictions.- 14.10 Necessary Further Work.- 14.11 Acknowledgments.- References.- 15. Static and Dynamic Analyses of Surface Mount Component Leads and Solder Joints.- Stiffness of Gull-Wing and J Leads and Solder Joints for Surface Mounted Chip Carriers.- 15.1 Boundary-Value Problem.- 15.2 Finite Element Methods.- 15.3 Stiffness of Gull-Wing Lead and Solder Joint.- 15.4 Stiffness of J Lead and Solder Joint.- 15.4.1 Unit Displacement (0.0001 in.) in the 1-Direction.- 15.4.2 Unit Displacement and Rotation in Other Directions.- 15.4.3 Comparison of the Stiffness Matrices between the PQFPs and PLCCs.- Solder Joint Reliability Under Shock and Vibration Conditions.- 15.5 Free Vibration of Soldered and Unsoldered Leads.- 15.5.1 Vibration Results for Wide SOICs.- 15.5.2 Vibration Results for Narrow SOICs.- 15.5.3 Vibration Results for PLCCs.- 15.5.4 Vibration Results for PQFPs.- 15.5.5 Experimental Verification.- 15.6 Free Vibration of a Constrained PCB with a SMC.- 15.7 Acknowledgments.- References.- 16. Integrated Matrix Creep: Application to Accelerated Testing and Lifetime Prediction.- 16.1 General Form of the Constitutive Relation.- 16.2 Development of the Constitutive Relation.- 16.2.1 Description of Data.- 16.2.2 Steady-State Creep Strain Component.- 16.2.3 Elastic Strain Component.- 16.2.4 Time Independent Plastic Strain Component.- 16.3 Summary of Constitutive Equation.- 16.4 Comparison of the Steady-State Creep Equation to Published Data.- 16.5 Application of Constitutive Equation to Data of Reference 2.- 16.5.1 Description of Numerical Procedures.- 16.5.2 Results.- 16.6 Multiaxial Stress States.- 16.6.1 Derivation of Constitutive Equation in Three Dimensions.- 16.7 Fatigue Calculations and Mechanical Shear Tests.- 16.7.1 Correlation of the Data of Reference 2.- 16.7.2 Correlation of the Data of Wild and Solomon.- 16.8 Analysis of Leaded Solder Joints.- 16.8.1 Extension of Matrix Creep Failure Indicator to General Case.- 16.8.2 Description of Model.- 16.8.3 Results.- 16.9 Conclusions.- 16.10 Acknowledgments.- References.- 17. Solder Joint Reliability, Accelerated Testing, and Result Evaluation.- 17.1 The Reliability of Electronic Assemblies and Solder Joint Reliability.- 17.1.1 "Bathtub" Reliability Curve-Hazard Rate Model.- 17.2 Solder Joint Loading Conditions and Reliability.- 17.3 Reliability and Accelerated Tested-Overview.- 17.4 The Thermal Expansion Mismatch Problem.- 17.4.1 Solution 1: CTE-Tailoring to Reduce Expansion Mismatch.- 17.4.2 Solution 2: Attachment Compliancy to Accommodate Expansion Mismatch.- 17.5 Analytical Model of Solder Shear Fatigue.- 17.5.1 Solder Joint Fatigue.- 17.5.2 Leadless Solder Attachments.- 17.5.3 Leaded Solder Attachments.- 17.5.4 Acceleration Transform.- 17.5.5 Failure Statistical Considerations.- 17.6 Accelerated Fatigue Reliability Testing.- 17.6.1 Testing Considerations.- 17.6.2 Accelerated Test Conditions.- 17.6.3 Test Vehicle Design.- 17.6.4 Sample Statistics and Solder Joint Defects.- 17.6.5 Test Vehicle Assembly and Conditioning.- 17.6.6 Failure Definition and Detection.- 17.7 Prediction of SM Solder Joint Reliability.- 17.7.1 Simple Cyclic Load Histories.- 17.7.2 Multiple Cyclic Load Histories.- 17.8 Acknowledgments.- References.- 18. Surface Mount Attachment Reliability and Figures of Merit for Design for Reliability.- 18.1 Mechanics and Fatigue of SM Solder Joints.- 18.1.1 SM Leadless Attachments.- 18.1.2 SM Leaded Attachments.- 18.1.3 Failure Distribution.- 18.2 Figures of Merit for Attachment Reliability.- 18.2.1 Derivation of FM Formulas.- 18.2.2 FMs for Multiple Thermal Fluctuations.- 18.2.3 Graphical Interpretation and Reliability Charts.- 18.3 Examples.- 18.3.1 Example 18-1: Chip Components on FR-4 Printed Wiring Boards.- 18.3.2 Example 18-2: 50-Mil Pitch Ceramic Leaded Devices on FR-4.- 18.3.3 Example 18-3: 25- and 50-Mil Pitch Plastic Leaded Components on FR-4.- 18.4 Concluding Remarks.- 18.5 Acknowledgments.- Appendix 18-A FM Formulas and Scaling Constants.- Appendix 18-B FMs for Multiple Thermal Fluctuations.- References.- Authors' Biographies.