Surface Mount Technology

Surface Mount Technology is not a technology of tommorrow but a technology of today. It provides a quantum jump in the packaging tech­ nology to produce state-of-the-art miniaturized electronic products. How­ ever, in order to take advantage of this technology, a complete infrastruc­ ture must be put in place. This requires considerable investment in human and capital resources. Intel corporation has made these investments to keep its customers for components and systems on the leading edge of technology. Based on the experience of putting this infrastructure in place for system products, this book is written for managers who need to manage the risk during its implementation, and the practicing engineers who need to improve the design and manufacturing processes for improved yield and cost reduction. To accomplish this task, I have not only culled the infor­ mation from published materials, but have also depended on input from both my colleagues in Intel and such outside organizations as the Institute of interconnecting and Packaging electronic Circuits (IPC) , the Electronics Industries Association (EIA), and the Surface Mount Council. But the underlying basis for this book has been my first-hand experience in im­ plementing this technology for Intel Systems Group and my experience at Boeing, my previous employer. In a fast-changing technology like SMT, it is very easy to have obsolete information even before the book is published. For this reason, I have concentrated on the basic principles and practice of the technology.

One Introduction to Surface Mounting.- 1 Introduction to Surface Mounting.- 1.0 Introduction.- 1.1 Types of Surface Mounting.- 1.2 Benefits of Surface Mounting.- 1.3 SMT Equipment Requiring Major Capital Investment.- 1.3.1 Pick-and-place equipment.- 1.3.2 Solder paste screen printer.- 1.3.3 Curing/baking oven.- 1.3.4 Reflow soldering equipment.- 1.3.5 Solvent cleaning.- 1.3.6 Wave soldering equipment.- 1.3.7 Repair and inspection equipment.- 1.4 When to Use Surface Mounting.- 1.5 Technical Issues in Surface Mounting.- 1.6 Trend in Surface Mounting.- 1.7 The Future.- 1.7.1 Chip-and-wire (chip-on-board) Technology.- 1.7.2 Tape-automated bonding (TAB).- 1.7.3 Flip chip or controlled collapse bonding:.- 1.8 Summary.- 2 Implementing Surface Mount Technology.- 2.0 Introduction.- 2.1 Setting the Implementation Strategy.- 2.2 Building the SMT Infrastructure.- 2.2.1 Developing internal SMT infrastructure.- 2.2.2 Influencing external SMT infrastructure.- 2.3 Setting In-House Manufacturing Strategy.- 2.4 Selecting an Outside SMT Assembly House.- 2.4.1 Evaluation and qualification of subcontractors.- 2.4.2 The various stages of subcontractor qualification.- 2.4.3 Questionnaires for rating of subcontractors.- 2.4.3.1 Technology questions.- 2.4.3.2 Manufacturing questions.- 2.4.3.3 Business questions.- 2.4.3.4 Quality assurance questions.- 2.5 Managing the Risk: Pilot to Production.- 2.6 Summary.- Two Designing with Surface Mounting.- 3 Surface Mount Components.- 3.0 Introduction.- 3.1 Surface Mount Component Characteristics.- 3.2 Passive Surface Mount Components.- 3.2.1 Surface mount discrete resistors.- 3.2.2 Surface mount resistor networks.- 3.2.3 Ceramic capacitors.- 3.2.4 Tantalum capacitors.- 3.2.5 Tubular passive components.- 3.3 Active Components: Ceramic Packages.- 3.3.1 Leadless ceramic chip carriers.- 3.3.2 Ceramic leaded chip carriers (preleaded and postleaded).- 3.4 Active Components: Plastic Packages.- 3.4.1 Small outline transistors.- 3.4.2 Small outline integrated circuits.- 3.4.3 Plastic leaded chip carriers.- 3.4.4 Small outline J packages.- 3.4.5 Fine pitch packages.- 3.5 Miscellaneous Components.- 3.6 Future Components.- 3.7 Major Issues in Components.- 3.7.1 Lead coplanarity.- 3.7.2 Lead configuration.- 3.7.3 Standardization.- 3.8 Component Procurement Guidelines.- 3.9 Summary.- 4 Substrates for Surface Mounting.- 4.0 Introduction.- 4.1 Glass Transition Temperature (Tg).- 4.2 X, Y, and Z Coefficients of Thermal Expansion.- 4.3 Selection of Substrate Material.- 4.3.1 CTE compatibility considerations in substrate selection.- 4.3.2 Process considerations in substrate selection.- 4.4 Ceramic Substrates.- 4.4.1 Porcelainized steel substrates.- 4.5 Constraining Core Substrates.- 4.5.1 Copper-invar-copper constraining core substrates.- 4.5.2 Graphite epoxy constraining core substrates.- 4.6 Compliant Layer Substrate.- 4.7 Glass-Epoxy Substrates.- 4.7.1 Types of glass epoxy substrate.- 4.7.2 Operating temperatures for glass epoxy boards.- 4.7.3 Fabrication of glass epoxy substrates.- 4.8 Plating Processes.- 4.8.1 Copper plating.- 4.8.2 Gold plating.- 4.8.3 Nickel plating.- 4.8.4 Lead-tin solder plating.- 4.9 Solder Mask Selection.- 4.9.1 Wet versus dry film solder masks.- 4.9.2 Photoimageable solder masks.- 4.10 Via Hole Cracking Problems in Substrates.- 4.11 Summary.- 5 Surface Mount Design Considerations.- 5.0 Introduction.- 5.1 System Design Considerations.- 5.2 Form, Fit, and Function.- 5.3 Real Estate Considerations.- 5.4 Manufacturing Considerations.- 5.5 Cost Considerations.- 5.5.1 Printed circuit board cost.- 5.5.2 Component cost.- 5.5.3 Assembly cost.- 5.6 Thermal Considerations.- 5.7 Package Reliability Considerations.- 5.7.1 Package cracking mechanism.- 5.7.2 Solutions to package cracking.- 5.7.3 Reliability tests for package cracking.- 5.8 Solder Joint Reliability Considerations.- 5.8.1 Solder joint reliability tests.- 5.9 Interconnect Considerations.- 5.10 CAD Layout Considerations.- 5.11 Summary.- 6 Surface Mount Land Pattern Design.- 6.0 Introduction.- 6.1 General Considerations for Land Pattern Design.- 6.2 Land Patterns for Passive Components.- 6.2.1 Land pattern design for rectangular passive components.- 6.2.2 Land pattern design for tantalum capacitors.- 6.3 Land Patterns for Cylindrical Passive (MELF) Devices.- 6.4 Land Patterns for Transistors.- 6.5 Land Patterns for Plastic Leaded Chip Carriers.- 6.6 Land Patterns for Leadless Ceramic Chip Carriers.- 6.7 Land Patterns for Small Outline Integrated Circuits and R-Packs.- 6.8 Land Patterns for SOJ (Memory) Packages.- 6.9 Land Patterns for DIP (Butt Mount) Packages.- 6.10 Land Patterns for Fine Pitch, Gull Wing Packages.- 6.11 Land Patterns for Solder Paste and Solder Mask Screens.- 6.12 Summary.- 7 Design for Manufacturability, Testing, and Repair.- 7.0 Introduction.- 7.1 Design Guidelines, Rules, the Role of the Designer.- 7.2 Standard Form Factor Considerations.- 7.3 Component Selection Considerations for Manufacturability.- 7.4 Soldering Considerations.- 7.5 Component Orientation Consideration.- 7.6 Interpackage Spacing Considerations.- 7.6.1 Assumptions in interpackaging spacing requirements.- 7.6.2 Interpackage spacing requirements.- 7.7 Via Hole Considerations.- 7.8 Solder Mask Considerations.- 7.9 Repairability Considerations.- 7.10 Cleanliness Considerations.- 7.11 Testability Considerations.- 7.11.1 Guidelines for ATE testing.- 7.12 Summary.- Three Manufacturing with Surface Mounting.- 8 Adhesive and Its Application.- 8.0 Introduction.- 8.1 Ideal Adhesive for Surface Mounting.- 8.1.1 Precure properties.- 8.1.2 Cure properties.- 8.1.3 Postcure properties.- 8.2 General Classification of Adhesives.- 8.3 Adhesives for Surface Mounting.- 8.3.1 Epoxy adhesives.- 8.3.2 Acrylic adhesives.- 8.3.3 Other adhesives for surface mounting.- 8.4 Conductive Adhesives for Surface Mounting.- 8.5 Adhesive Application Methods.- 8.5.1 Screening.- 8.5.2 Pin transfer.- 8.5.3 Syringing.- 8.6 Curing of Adhesives.- 8.6.1 Thermal cure.- 8.6.1.1 Thermal cure profile and bond strength.- 8.6.1.2 Adhesive cure profile and flux entrapment.- 8.6.2 UV/Thermal cure.- 8.7 Evaluation of Adhesives with Differential Scanning Calorimetry.- 8.7.1 Basic principles of DSC analysis.- 8.7.2 DSC characterization of an epoxy adhesive.- 8.7.3 DSC characterization of an acrylic adhesive.- 8.8 Summary.- 9 Solder Paste and Its Application.- 9.0 Introduction.- 9.1 Solder Paste Properties.- 9.1.1 Metal composition.- 9.1.2 Metal content.- 9.1.3 Particle size and shape.- 9.1.4 Flux activators and wetting action.- 9.1.5 Solvent and void formation.- 9.1.6 Rheological properties.- 9.1.6.1 Viscosity.- 9.1.6.2 Slump.- 9.1.6.3 Working life and tackiness.- 9.1.7 Solder balls.- 9.1.8 Printability.- 9.2 Solder Paste Printing Equipment.- 9.3 Solder Paste Printing Processes.- 9.3.1 Screen printing.- 9.3.2 Stencil printing.- 9.3.3 Screen printing versus stencil printing.- 9.3.4 Dispensing.- 9.4 Paste Printing Defects.- 9.5 Paste Printing Variables.- 9.5.1 Solder paste viscosity.- 9.5.2 Print thickness.- 9.5.3 Squeegee wear, pressure, and hardness.- 9.5.4 Print speed.- 9.5.5 Mesh tension.- 9.5.6 Board warpage.- 9.6 Summary.- 10 Metallurgy of Soldering and Solderability.- 10.0 Introduction.- 10.1 Phase Diagrams.- 10.2 Metallization Leaching in Passive Surface Mount Components.- 10.3 Solder Alloys and Their Properties.- 10.4 Solderability.- 10.4.1 Wetting.- 10.4.2 Nonwetting.- 10.4.3 Dewetting.- 10.5 Various Approaches for Ensuring Solderability.- 10.6 Solderability Test Methods and Requirements.- 10.7 Recommendations for Solderability Test Methods and Requirements.- 10.8 Effect of Substrate Surface Finish on Solderability.- 10.9 Effect of Component Lead or Termination Finish on Solderability.- 10.10 Summary.- 11 Component Placement.- 11.0 Component Placement.- 11.1 Manual Placement of Parts.- 11.2 Automated Placement of Parts.- 11.3 Selection Criteria for Placement Equipment.- 11.3.1 Maximum substrate size handling capacity.- 11.3.2 Maximum feeder input or slot capacity.- 11.3.3 Placement rate and flexibility.- 11.3.4 Placement accuracy/repeatability.- 11.3.5 Vision capability.- 11.3.6 Adhesive dispensing capability.- 11.3.7 Other important selection criteria.- 11.4 Selection of Feeders for Placement Equipment.- 11.4.1 Tape and reel feeders.- 11.4.2 Bulk feeders:.- 11.4.3 Tube or stick feeders.- 11.4.4 Waffle packs.- 11.5 Available Placement Equipment.- 11.5.1 Equipment with low flexibility and high throughput.- 11.5.2 Equipment with high flexibility and low throughput.- 11.5.3 Equipment with medium flexibility and throughput.- 11.5.4 Equipment with low cost and throughput but high flexibility.- 11.6 Summary.- 12 Soldering of Surface Mounted Components.- 12.0 Introduction.- 12.1 Wave Soldering.- 12.1.1 Design and process variables in wave soldering.- 12.1.2 Process and equipment variables in wave soldering.- 12.2 Types of Wave Soldering for Surface Mounting.- 12.2.1 Dual-wave soldering.- 12.2.2 Vibrating wave soldering.- 12.2.3 Modified wave soldering.- 12.3 Wave Versus Reflow Soldering.- 12.4 Single-Step Soldering of Mixed Assemblies.- 12.5 Single-Step Soldering of Double-Sided SMT Assemblies.- 12.6 Vapor Phase Soldering.- 12.6.1 The Heat transfer mechanism in vapor phase soldering.- 12.7 Infrared Reflow Soldering.- 12.7.1 The Heat transfer mechanism in infrared soldering.- 12.7.2 Convection/IR versus near IR.- 12.8 Vapor Phase Versus Infrared Reflow Soldering.- 12.8.1 Cost and flexibility.- 12.8.2 Solder profile development.- 12.8.2.1 Heating rate.- 12.8.2.2 Peak temperature in preheat zone.- 12.8.2.3 Time above solder melting point.- 12.8.2.4 Peak reflow temperature.- 12.8.2.5 Cooling rate and duration above glass transition temperature.- 12.8.3 Solder defects.- 12.8.4 Solder opens (wicking).- 12.8.5 Tombstoning and part movement.- 12.8.6 Thermal shock on components.- 12.8.7 Solder mask discoloration.- 12.9 Laser Reflow Soldering.- 12.10 Miscellaneous Reflow Soldering Methods.- 12.11 Selecting The Appropriate Soldering Method.- 12.12 Summary.- 13 Flux and Cleaning.- 13.0 Introduction.- 13.1 Concerns in Surface Mount Cleaning.- 13.2 The Function of Flux.- 13.3 Considerations in Flux Selection.- 13.4 Flux Classification.- 13.4.1 Inorganic fluxes.- 13.4.2 Organic acid fluxes.- 13.4.3 Superactivated fluxes (SRA and SA).- 13.4.4 Rosin fluxes.- 13.5 Contaminants and Their Effects.- 13.5.1 Particulate contaminants.- 13.5.2 Nonpolar contaminants.- 13.5.3 Polar contaminants.- 13.6 Major Considerations in Solvent Selection.- 13.7 Commonly Used Solvent Types.- 13.8 Solvent Cleaning Equipment.- 13.8.1 Batch solvent cleaning equipment.- 13.8.2 In-line solvent cleaning equipment.- 13.8.3 Ultrasonic cleaning equipment.- 13.9 Aqueous Cleaning.- 13.9.1 Aqueous cleaning equipment.- 13.10 Cleanliness Test Methods and Requirements.- 13.10.1 Visual examination.- 13.10.2 Solvent extraction.- 13.10.3 Surface Insulation Resistance (SIR).- 13.10.3.1 SIR measurement test conditions.- 13.10.3.2 Application of the SIR test.- 13.11 Designing for Cleaning.- 13.12 Summary.- 14 Quality Control, Repair, and Testing.- 14.0 Introduction.- 14.1 Statistical Quality Control.- 14.2 Application of SQC: A Case History.- 14.2.1 Implementing statistical process control.- 14.3 Defects Related to Materials and Process Defects.- 14.3.1 Substrate-related defects.- 14.3.2 Component-related defects.- 14.3.3 Adhesive-related defects.- 14.3.4 Defects related to solder paste.- 14.3.5 Process-related defects.- 14.4 Solder Joint Quality Requirements.- 14.5 Solder Joint Inspection.- 14.6 Repair Equipment and Processes.- 14.6.1 Repair requirements.- 14.6.2 Soldering irons for surface mount repair.- 14.6.3 Hot air systems for surface mount repair.- 14.6.4 Rework profiles.- 14.7 Assembly Testing.- 14.7.1 Fixtures for ATE testing.- 14.7.2 Issues in ATE testing.- 14.8 Summary.- Appendix A Surface Mount Standards.- Appendix B Detailed Questionnaire for Evaluating Pick-and-Place Equipment for Surface Mounting.- Appendix C Glossary.