Solder Paste in Electronics Packaging : Technology and Applications in Surface Mount, Hybrid Circuits, and Component Assembly

One of the strongest trends in the design and manufacture of modern electronics packages and assemblies is the utilization of surface mount technology as a replacement for through-hole tech­ nology. The mounting of electronic devices and components onto the surface of a printed wiring board or other substrate offers many advantages over inserting the leads of devices or components into holes. From the engineering viewpoint, much higher lead counts with shorter wire and interconnection lengths can be accommo­ dated. This is critical in high performance modern electronics packaging. From the manufacturing viewpoint, the application of automated assembly and robotics is much more adaptable to high lead count surface mounted devices and components. Indeed, the insertion of high lead count parts into fine holes on a substrate might often be nearly impossible. Yet, in spite of these surface mounting advantages, the utilization of surface mount technology is often a problem, primarily due to soldering problems. The most practical soldering methods use solder pastes, whose intricacies are frequently not understood by most of those involved in the engineering and manufacture of electronics assemblies. This publication is the first book devoted exclusively to explanations of the broad combination of the chemical, metallurgical, and rheological principles that are critical to the successful use of solder pastes. The critical relation­ ships between these characteristics are clearly explained and pre­ sented. In this excellent presentation, Dr. Hwang highlights three impor­ tant areas of solder paste technology.

I—Overview.- 1 Introduction.- 1.1 Purpose of the Book.- 1.2 Electronics Industry in General.- 1.3 Electronics Packaging and Market.- 1.4 Surface Mount Technology.- 1.5 Surface Mount Technology Market.- 1.6 Surface Mount Components.- 1.7 Surface Mount Land Patterns.- 1.8 Surface Mount Processes.- 1.9 Surface Mount Device Reliability.- 1.10 Utility of the Book.- 2 Interdisciplinary Approach.- 2.1 Basic Function.- 2.2 Materials.- 2.3 Compositional Constitution.- 2.4 Technology.- 2.5 Interplay of Technology.- II—Basic Technologies.- 3 Chemical and Physical Characteristics.- 3.1 Performance Parameters.- 3.2 Physical Properties.- 3.3 Fluxes and Fluxing.- 3.4 Flux Chemistry.- 3.5 Rosin Chemistry.- 3.6 Tackiness and Adhesion.- 3.7 Thermal Properties.- 3.8 Dryability.- 3.9 Residue.- 3.10 Solderability.- 3.11 Solderability: Components.- 3.12 Metal Load Acceptability.- 3.13 Flow Properties.- 3.14 Exposure Life.- 3.15 Formulation.- 4 Metallurgical Aspects.- 4.1 Alloys in General.- 4.2 Solder Alloy.- 4.3 Phase Diagrams.- 4.4 Phase Diagrams: Solder Alloys.- 4.5 Wetting and Spreading.- 4.6 Solidification.- 4.7 Heat Treatment and Thermal Excursion.- 4.8 Metal Powder.- 4.9 Solder Powder Characteristics.- 4.10 Physical Properties of Solder Alloys.- 4.11 Mechanical Properties of Solder Alloys.- 5 Rheology of Solder Pastes.- 5.1 Requirements and Driving Forces.- 5.2 Flow Behavior: TheoreticalBackground.- 5.3Elastic Behavior: TheoreticalBackground.- 5.4 Mechanical Models.- 5.5 Flow Characteristics.- 5.6 Elastic Characteristics.- 5.7 Characterization Versus Performance.- 5.8 Single Point Viscosity Measurement.- 5.9 Viscosity Versus Temperature andOther Factors.- III—Methodologies and Applications.- 6 Application Techniques.- 6.1 Introduction.- 6.2 Printer.- 6.3 Printing Mode.- 6.4 Screen Hardware.- 6.5 Screen Artwork and Patterns.- 6.6 Screen Cleaning and Maintenance.- 6.7 Squeegee System.- 6.8 Snap-off.- 6.9 Printing Principles.- 6.10 Printing Variables.- 6.11 Printing Operation.- 6.12 Considerations for Printing ParameterSelection.- 6.13 Differential Thickness Printing.- 6.14 Printing Environment and PasteHandling.- 6.15 Pneumatic Dispensing.- 6.16 Positive Displacement Dispensing.- 6.17 Dispensing Operation.- 6.18 Pin Transfer.- 7 Soldering Methodologies.- 7.1 Introduction.- 7.2 Thermal Conduction.- 7.3 Thermal Radiation.- 7.4 Thermal Convection.- 7.5 Reflow Methods.- 7.6 Conduction Reflow.- 7.7 Infrared Reflow: Furnace Type.- 7.8 Infrared Reflow Dynamics.- 7.9 Infrared Reflow Profile.- 7.10 Infrared Reflow Operation.- 7.11 Temperature Monitoring.- 7.12 Vapor Phase Reflow.- 7.13 Convection Reflow.- 7.14 Hot Gas Reflow.- 7.15 Resistance Reflow.- 7.16 Laser Reflow.- 7.17 Intelligent Laser Soldering.- 7.18 Induction Reflow.- 7.19 Temperature Profiling Versus PastePerformance.- 7.20Temperature Profiling VersusComponent.- 7.21Temperature Profiling Versus SolderingProblems.- 7.22Comparison of Reflow Methods.- 8 Cleaning.- 8.1 Solder Paste Residue.- 8.2 What Is Cleaning?.- 8.3 Cleaning Principle.- 8.4 Factors of Cleaning Efficiency.- 8.5 Solvent.- 8.6 Solubility Parameters.- 8.7 Solvent Cleaning Technique andEquipment.- 8.8 Ultrasonic Cleaning.- 8.9 Aqueous Cleaning.- 8.10 White Residue.- 8.11 Solder Ball Removal.- 8.12 Cleanliness Measurement.- 8.13 Safety and Health.- 8.14 Ozone Depletion.- IV—Reliability, Quality Control, and Tests.- 9 Solder Joint Reliability and Inspection.- 9.1 Introduction.- 9.2 Factors of Solder Joint Integrity.- 9.3 Creep.- 9.4 Fatigue.- 9.5 Thermal Fatigue.- 9.6 Intrinsic Thermal Expansion Anisotropy.- 9.7 Corrosion-Enhanced Fatigue.- 9.8 Coating Considerations.- 9.9 Intermetallic Compounds.- 9.10 Solder Joint Voids.- 9.11 State-of-the-Art Studies.- 9.12 Solder Joint Appearance.- 9.13 Solder Joint Inspection.- 10 Special Topics in Surface Mount Soldering Problems and Other Soldering-RelatedProblems.- 10.1 Surface Mount J-Lead Wicking.- 10.2 Inserted Lead Wicking.- 10.3 Clip-on Lead Wicking.- 10.4 Tombstoning.- 10.5 Solder Balling.- 10.6 Residue Cleaning.- 10.7 Pad Bridging.- 10.8 Paste Tack Time.- 10.9 Paste Open Time.- 10.10 Lot-to-Lot Consistency.- 10.11 Electromigration.- 10.12 Leaching.- 10.13 Solderability.- 10.14 Solder Joint Integrity.- 11 Quality Assurance and Tests.- 11.1 Quality.- 11.2 Appearance.- 11.3 Metal Content.- 11.4 Density.- 11.5 Viscosity.- 11.6 Viscosity Versus Shear Rate.- 11.7 Cold Slump.- 11.8 Hot Slump.- 11.9 Molten Flow.- 11.10 Tack Time.- 11.11 Dryability.- 11.12 Dispensability.- 11.13 Printability.- 11.14 Shelf Stability.- 11.15 Handling and Safety.- 11.16 Water Extract Resistivity.- 11.17 Copper Mirror.- 11.18 Chloride and Bromide.- 11.19 Acid Number.- 11.20 Infrared Spectrum Fingerprint andOther Spectroscopies.- 11.21 Alloy Composition.- 11.22 Particle Size—Sieve.- 11.23 Particle Size Distribution—SediGraph.- 11.24 Particle Shape.- 11.25 Particle Surface Condition.- 11.26 Dross.- 11.27 Melting Range.- 11.28 Solder Ball.- 11.29 Solderability.- 11.30 Exposure Time.- 11.31 Soldering Dynamics.- 11.32 Cleanliness.- 11.33 Surface Insulation Resistance.- 11.34 Other Post-Reflow Examinations andTests.- 11.35Required Tests.- V—Future Tasks and Emerging Trends.- 12 Future Developments.- 12.1 Quality-Driven.- 12.2 Mirror and Marriage.- 12.3 Conductive Adhesive.- 12.4 Tasks and Issues.- 12.5 Conclusion.- VI—Appendix.- I. Federal Specification QQ-S-571E and Amendment 4.- II. Ternary Phase Diagram: Pb-Ag-Sn, Sn-Pb-Bi.- III. Military Specification MIL-P-28809A: PrintedWiring Assemblies.- IV.Quantitative Determination of Rosin Residues onCleaned Electronics Assemblies.