IPC-AJ-820A ® Assembly and Joining Handbook Developed by theAssembly and Joining Subcommittee (7-35) of the ProductAssurance Committee (7-30) of IPC Supersedes: Users of this publication are encouraged to participate in the IPC-AJ-820 -April 1997 development of future revisions. Contact: IPC 3000LakesideDrive,Suite309S Bannockburn,Illinois 60015-1249 Tel847615.7100 Fax847615.7105 February2012 IPC-AJ-820A Table of Contents 1 SCOPE ...................................................................... 1 3.3.1 Component Orientation ...................................... 21 1.1 Assembly and Joining Technology ...................... 1 3.3.2 Accessibility ....................................................... 22 1.2 Through-Hole Technology ................................... 1 3.3.3 Design Envelope ................................................ 22 1.3 Surface Mount Technology .................................. 1 3.3.4 Clearances .......................................................... 23 1.4 Related Documents .............................................. 2 3.3.5 Physical Support ................................................ 23 1.4.1 Joint Industry Standards ...................................... 2 3.4 Design forAutomatedAssembly ....................... 23 1.4.2 IPC -Association Connecting Electronics 3.4.1 Fiducial Marks ................................................... 23 Industries Documents ........................................... 4 3.4.2 Automated Through HoleAssembly ................. 23 1.4.3 United States Government Documents ............. 10 3.4.3 Automated Surface MountAssembly ................ 23 1.4.4 American Society of Mechanical Engineers ..... 11 3.4.4 Automated Mixed-TechnologyAssembly ......... 24 1.4.5 ASTM International ........................................... 11 3.5 Through HoleAssembly .................................... 24 1.4.6 SAE International ............................................... 12 3.5.1 Lead Configuration ............................................ 24 1.4.7 FederalAviation Regulations (FARs) ................ 12 3.5.2 Lead/Hole Relationships .................................... 28 1.4.8 Underwriters Laboratories ................................. 12 3.5.3 Through Hole Land Patterns ............................. 28 1.4.9 IEC Standards .................................................... 12 3.6 Surface MountAssembly ................................... 29 1.4.10 Independent Distributors of Electronics 3.6.1 Basic Printed Board Features ............................ 29 Association (IDEA) ............................................ 12 3.6.2 ManufacturingAllowances ................................ 29 1.4.11 Electrostatic DischargeAssociation ................... 13 3.6.3 SMT Land Pattern Details ................................. 29 2 HANDLING ELECTRONICASSEMBLIES ............. 13 3.6.4 SMTAssembly Processing ................................ 30 2.1 Definitions .......................................................... 13 4 PRINTED CIRCUIT BOARDS ................................. 32 2.1.1 Electrostatic Discharge (ESD) ........................... 13 4.1 General Considerations ...................................... 32 2.1.2 Electrostatic Discharge Sensitive Components (ESDS) .......................................... 13 4.2 Design Issues ...................................................... 34 2.1.3 Electrical Overstress (EOS) ............................... 13 4.2.1 Structures ............................................................ 34 2.2 Handling of ESDS Items (Components 4.2.2 Leaded vs. Leadless Components ...................... 34 and/orAssemblies) ............................................. 13 4.2.3 CTE Issues ......................................................... 34 2.2.1 Electrical Overstress (EOS) Damage 4.3 PCB Materials .................................................... 34 Prevention ........................................................... 14 4.3.1 Thermosetting Base Resins ................................ 34 2.2.2 Electrostatic Discharge (ESD) Damage 4.4 Printed Boards with Non-Metallic Prevention ........................................................... 14 Constraining Cores ............................................. 36 2.3 Physical Handling .............................................. 15 4.5 Base Conductors ................................................ 36 2.3.1 Handling after Soldering .................................... 15 4.5.1 Metallic Foils ..................................................... 36 2.4 Contamination .................................................... 15 4.5.2 Electrodeposited Copper Foil ............................ 37 2.5 Processing Moisture Sensitive Components ..... 15 4.5.3 Rolled-Annealed Copper Foil ............................ 37 2.6 Classification of Non-IC Electronic 4.5.4 Additive Circuit Plating ..................................... 37 Components forAssembly Processes (ECA/IPC/JEDEC J-STD-075) .......................... 16 4.6 Plating and Surface Finishes ............................. 37 4.6.1 Electroless Copper Plating ................................. 37 3 DESIGN CONSIDERATIONS .................................. 19 4.6.2 Semi-Conductive Coatings ................................ 37 3.1 Background and Theory ..................................... 19 4.6.3 Electrolytic Copper Plating ................................ 37 3.2 Basic Considerations .......................................... 19 4.6.4 Gold Plating ....................................................... 38 3.2.1 End-Product Usage ............................................ 19 4.6.5 Immersion Silver ................................................ 41 3.2.2 Performance and Reliability .............................. 20 4.6.6 Immersion Tin .................................................... 42 3.2.3 Designing for Producibility ............................... 20 4.6.7 Organic Solderability Preservative (OSP) ......... 42 3.3 Packaged-ComponentAssembly Considerations .................................................... 21 4.6.8 Nickel Plating ..................................................... 43 v IPC-AJ-820A February2012 4.6.9 Tin/Lead Plating ................................................. 44 6.6 Printed Wiring Board Weak Knee Phenomena ......................................................... 56 4.6.10 Solder Coating .................................................... 44 6.7 Troubleshooting a Solderability Problem .......... 57 4.6.11 Other Metallic Coatings for Edge Printed Board Contacts ................................................... 45 6.8 Solderability Tests .............................................. 57 4.7 Printed Board Handling and Storage 6.8.1 IPC J-STD-002 ................................................... 57 Guidelines ........................................................... 45 6.8.2 Force Measurement ............................................ 58 6.9 IPC J-STD-003 ................................................... 59 5 ELECTRONIC CIRCUIT COMPONENTS ............... 45 6.10 The Importance of Flux Material in 5.1 Lead/Termination Finishes ................................. 46 Solderability Testing .......................................... 60 5.2 Moisture Sensitivity ........................................... 46 5.3 Components ........................................................ 46 7 ASSEMBLYAND JOINING MATERIALS ............... 61 7.1 Introduction ........................................................ 61 5.3.1 Active versus Passive Components ................... 46 7.2 Presoldering Chemicals ...................................... 62 5.3.2 Discrete versus Integrated Components ............ 46 7.2.1 Metal SurfaceActivating Solutions ................... 62 5.4 Through Hole versus Surface Mount Components ........................................................ 46 7.2.2 Solder Mask ....................................................... 63 5.4.1 Through Hole Lead Components ...................... 47 7.2.3 Protective Coatings ............................................ 63 5.4.2 Surface Mount - Leadless Components ............ 47 7.3 Solder Fluxes ...................................................... 64 5.4.3 Surface Mount - Leaded Components ............... 47 7.3.1 Choosing the Proper Flux .................................. 64 5.5 ElectronicAssemblies ........................................ 47 7.3.2 Flux Types .......................................................... 64 5.6 Packaging of Component ................................... 47 7.3.3 Rosin/Resin Fluxes (RO or RE Classification) ..................................................... 65 5.7 Printed Circuit Board Connectors ..................... 47 7.3.4 ‘‘No Clean’’Fluxes ............................................ 66 5.7.1 Printed Circuit Board Connector Selection ....... 47 7.3.5 Organic Fluxes (OR Classification) ................... 66 5.8 Sockets ................................................................ 48 7.3.6 Inorganic Fluxes (IN Classification) ................. 67 5.9 Test Points and Test Jacks ................................. 49 7.3.7 Topping Oils ....................................................... 67 5.10 Design andAssembly Process Implementation for BGAs (IPC-7095) .............. 50 7.4 Solder .................................................................. 67 5.10.1 Scope .................................................................. 50 7.4.1 SolderAlloy Selection ....................................... 67 5.10.2 Purpose ............................................................... 50 7.4.2 Economics .......................................................... 68 5.11 Design andAssembly Process 7.4.3 Processing andApplication ................................ 69 Implementation for Bottom Termination 7.4.4 Solder Specifications .......................................... 69 Components (BTC) (IPC-7093) ........................ 50 7.5 Low Temperature SolderAlloys ........................ 70 5.12 Design andAssembly Process 7.5.1 Applications ........................................................ 70 Implementation for Flip Chips (IPC-7094) ....... 50 7.5.2 Forms and Techniques ....................................... 72 5.13 Counterfeit Electronic Components and/or Counterfeit Mechanical Fasteners ..................... 50 7.5.3 Wave Soldering .................................................. 72 5.13.1 Counterfeit Mechanical Fasteners ..................... 50 7.5.4 Special Considerations ....................................... 73 5.13.2 Counterfeit Electronic Components .................. 51 7.6 Traditional SolderAlloys ................................... 73 7.6.1 High Temperature Soldering Flux ..................... 74 6 SOLDERABILITY .................................................... 52 7.6.2 High Temperature Stripping and Tinning .......... 74 6.1 Introduction ........................................................ 52 7.7 Lead-Free SolderAlloys .................................... 75 6.2 Inherent Solderability ......................................... 53 7.8 Solder Paste ........................................................ 88 6.3 Surface Finishes ................................................. 54 7.8.1 Solder PasteAlloys ............................................ 88 6.3.1 Organic Surface Finishes ................................... 54 7.8.2 Test Methods to Evaluate Solder 6.3.2 Soluble Finishes ................................................. 54 Paste Properties .................................................. 89 6.3.3 Fusible Finishes .................................................. 54 7.8.3 Solder PasteApplication .................................... 89 6.3.4 Barrier Underplate .............................................. 54 7.9 Solder Preforms .................................................. 89 6.4 Degradation of Solderability .............................. 54 7.9.1 Solder PreformAlloys ....................................... 90 6.5 Accelerated Conditioning .................................. 56 7.9.2 Designing Solder Preforms ................................ 90 vi February2012 IPC-AJ-820A 7.9.3 Preform Heating ............................................. 91 8.6 Component Characteristics, Through-Hole ............................................... 116 7.10 Adhesive Materials ........................................ 91 8.6.1 Axial-Leaded Discrete Components ............ 116 7.10.1 EpoxyAdhesives ............................................ 91 8.6.2 Radial-Leaded Discrete Components .......... 116 7.10.2 SiliconeAdhesives ......................................... 92 8.6.3 Dual-Inline Packages .................................... 117 7.10.3 Polyurethane ................................................... 92 8.6.4 Single-Inline Packages ................................. 117 7.10.4 AcrylicAdhesives .......................................... 92 8.6.5 Ribbon-Lead Components ............................ 117 7.10.5 Cyanoacrylates ............................................... 93 8.6.6 Pin GridArrays ............................................ 118 7.10.6 Electrically ConductiveAdhesives ................ 93 8.6.7 Through-Hole Connectors ............................ 119 7.10.7 Surface MountAdhesives .............................. 94 8.6.8 Through-Hole Sockets ................................. 120 7.10.8 Thermally ConductiveAdhesives .................. 94 8.7 Assembly Sequence, Through-Hole ............ 121 7.10.9 Cure Verification ............................................ 94 8.7.1 Process Steps ................................................ 121 7.10.10 Workmanship Verification .............................. 94 8.7.2 Component Placement ................................. 131 7.11 Tin Whiskers .................................................. 94 8.7.3 Vertical Mounting ........................................ 132 7.11.1 Executive Summary ....................................... 94 8.7.4 Mixed Technology ........................................ 135 7.11.2 General Guidelines for Migrating to RoHS Compliant Finishes ............................. 95 8.7.5 Manual Techniques ...................................... 135 7.11.3 Electronic Component Lead and 8.7.6 Automated Techniques ................................. 135 Terminal Finishes ........................................... 99 8.8 Temporary Masking Guidelines ................... 138 7.11.4 Separable Connectors ................................... 101 8.9 Surface Mount .............................................. 138 7.11.5 Bus Bars ....................................................... 102 8.9.1 Assembly Hierarchy ..................................... 138 7.11.6 Heat Sinks .................................................... 103 8.9.2 ManualAssembly Techniques ..................... 145 7.11.7 Printed Circuit Boards (PCB) ...................... 103 8.9.3 AutomatedAssembly Techniques ................ 145 7.11.8 How Can I Tell IfAComponent 9 SOLDERING .......................................................... 147 ContainsATin-Finish? ................................ 104 9.1 Introduction .................................................. 147 7.11.9 Testing to Detect the Presence of 9.1.1 The Process of Wetting ................................ 147 Various Metals that may, or may not be Present in a Component Lead/ 9.1.2 Wetting and Solderability ............................ 147 Termination Finish ....................................... 104 9.1.3 Solder ............................................................ 148 7.11.10 Energy Dispersive Spectroscopy ................. 104 9.2 SolderAlloys ................................................ 148 8 COMPONENT MOUNTING ................................... 107 9.2.1 Structure of the Solder Bond ....................... 148 8.1 Assembly Classifications ............................. 107 9.2.2 Intermetallic Growth Rates .......................... 149 8.1.1 Producibility Levels ..................................... 107 9.2.3 FactorsAffecting Physical Properties of SolderAlloys ........................................... 149 8.1.2 Printed Circuit BoardAssembly Types ....... 107 9.2.4 Strain Rate Effects ....................................... 150 8.2 General Guidelines ....................................... 108 9.2.5 ‘‘Grain Size’’Effects .................................... 152 8.2.1 Design Options and Considerations ............ 108 9.2.6 Lead-Free Soldering: Process 8.2.2 Assembly Considerations ............................. 109 Considerations: ............................................. 154 8.3 Other Mounting Structure Materials 9.3 Gold Removal .............................................. 156 and Considerations ....................................... 112 9.3.1 Reason for Gold Removal ........................... 156 8.3.1 Heat Sinks .................................................... 112 9.4 Solder Purity ................................................ 157 8.3.2 Spacers .......................................................... 112 9.4.1 Reasons for Testing ...................................... 157 8.3.3 Component-Lead Spreaders ......................... 113 9.4.2 Testing Frequency ........................................ 157 8.3.4 Thermally Conductive Insulators ................. 113 9.4.3 Copper .......................................................... 157 8.4 Assembly Design Cycle ............................... 113 9.4.4 Gold .............................................................. 157 8.5 Placement Guidelines ................................... 114 9.4.5 Cadmium ...................................................... 157 8.5.1 Construction Formats and Process Sequences ..................................................... 114 9.4.6 Zinc ............................................................... 158 8.5.2 AutomatedAssembly ................................... 115 9.4.7 Aluminum ..................................................... 158 vii IPC-AJ-820A February2012 9.4.8 Antimony ...................................................... 158 9.18.2 Meniscus in Solder ...................................... 168 9.4.9 Iron ............................................................... 158 9.18.3 Interfacial Connection Without Lead - Vias ................................................... 168 9.4.10 Arsenic .......................................................... 158 9.18.4 Hole Obstruction .......................................... 168 9.4.11 Bismuth ........................................................ 158 9.4.12 Silver ............................................................ 158 9.19 Machine Soldering ....................................... 169 9.4.13 Nickel ........................................................... 159 9.19.1 Wave Soldering ............................................ 169 9.4.14 Solder Pot Contamination ............................ 159 9.19.2 Machine Controls ......................................... 169 9.4.15 Effect of Contamination on Solder 9.19.3 Fluxing .......................................................... 169 Process .......................................................... 159 9.19.4 Foam Fluxing ............................................... 169 9.4.16 Resolving Contamination Problems ............ 159 9.19.5 Wave Fluxing ............................................... 169 9.5 Tin Depletion ................................................ 159 9.19.6 Brush Fluxing ............................................... 170 9.6 Soldering Processes ...................................... 159 9.19.7 Spray Fluxing ............................................... 170 9.7 Manual/Hand Soldering ............................... 159 9.19.8 Preheating ..................................................... 170 9.7.1 FluxApplication ........................................... 159 9.19.9 The Solder Wave .......................................... 170 9.8 SolderApplication ........................................ 160 9.19.10 Parabolic Wave ............................................. 170 9.9 Hand Soldering ............................................ 160 9.19.11 Bi-Directional Wide Wave ........................... 170 9.9.1 Heat Transfer Considerations ...................... 161 9.19.12 Asymmetrical (Supported) Wave ................. 171 9.10 Temperature Control - Thermal 9.19.13 Special Provisions ........................................ 171 Considerations for Components and Boards .................................................... 162 9.19.14 Printed Board Conveyors ............................. 171 9.10.1 Heat Sinks .................................................... 162 9.19.15 Pallet Conveyors .......................................... 171 9.11 Tip Selection ................................................ 162 9.19.16 Finger Conveyors ......................................... 171 9.11.1 Tip Materials ................................................ 162 9.19.17 Other Conveyors .......................................... 171 9.11.2 Soldering Iron Tip Selection ........................ 162 9.19.18 Conveyor Control ......................................... 171 9.11.3 Shape/Physical Configuration ...................... 162 9.19.19 InertAtmospheres ........................................ 171 9.11.4 Tip Maintenance ........................................... 163 9.19.20 Preparation Fluids ........................................ 172 9.11.5 Soldering Iron Station Maintenance ............ 163 9.19.21 System Considerations ................................. 173 9.11.6 Extending Tip Life ....................................... 163 9.19.22 Design Considerations ................................. 173 9.12 Hand Soldering-Soldering Tools 9.19.23 Process Control ............................................ 173 and Equipment ............................................. 164 9.19.24 Maintenance ................................................. 173 9.13 Terminal Soldering ....................................... 165 9.19.25 Solder Dross Reclamation and Recovery .... 175 9.13.1 Flared Flange Hardware ............................... 165 9.19.26 Training ........................................................ 175 9.13.2 Shank Discontinuities .................................. 165 9.19.27 Safety ............................................................ 175 9.13.3 Flared FlangeAngles ................................... 165 9.13.4 Terminal Mounting ....................................... 165 9.20 Flow-Well/Minipot ....................................... 175 9.13.5 General Requirements .................................. 166 9.21 Static Solder Pots ......................................... 176 9.14 Soldering To Terminals ................................ 166 9.22 Selective Soldering ...................................... 176 9.14.1 Turret and Hook Terminals .......................... 166 9.22.1 Key Process Elements .................................. 176 9.14.2 Bifurcated, Pierced or Perforated 9.22.2 Process Expectations .................................... 176 Terminals ...................................................... 166 9.22.3 Process Optimization and Control ............... 176 9.14.3 Cup and Hollow Cylindrical 9.23 Reflow Soldering .......................................... 176 Terminal Soldering ....................................... 167 9.23.1 The TestAssembly ....................................... 177 9.15 Unsupported Holes ....................................... 167 9.23.2 Attachment of Thermocouples ..................... 177 9.16 Supported Holes (PTH) ............................... 167 9.23.3 Baseline Profile ............................................ 178 9.17 Vertical Fill of Hole ..................................... 167 9.23.4 PIN-In-PASTE .............................................. 183 9.18 PTH Mounted Components - Solder Conditions ......................................... 168 9.23.5 Hold Down of Surface Mount Leads .......... 183 9.18.1 Solder in Lead Bend .................................... 168 9.24 Other Reflow Soldering Methods ................ 183 viii February2012 IPC-AJ-820A 9.24.1 Hot Bar Reflow Soldering-Resistance 10.3.1 Component Mounting withAdhesives ........ 205 ‘‘Hot Bar’’/Pulse soldering .......................... 183 10.3.2 Outer Lead Bonding withAnisotropic 9.24.2 Laser Reflow Soldering ............................... 184 Adhesives ..................................................... 205 9.24.3 Vapor Phase Soldering ................................. 186 10.3.3 Thermally-ConductiveAdhesive Bonding .. 205 9.24.4 IR Soldering ................................................. 188 10.3.4 AdhesiveApplication ................................... 206 9.24.5 The IR Reflow Process ................................ 188 10.3.5 Curing ........................................................... 207 9.24.6 MVC Temperature Determination ............... 193 10.3.6 Heat Sink Materials and Processing ............ 207 9.24.7 Air/Atmosphere Quality ............................... 194 10.3.7 Adhesive Testing and Evaluation ................ 210 9.24.8 Monitoring and Control ............................... 194 10.4 Mechanical Pressure Connections ............... 212 9.24.9 Profiling Devices .......................................... 194 10.4.1 Solderless Backplane Contact Terminations ................................................. 212 9.24.10 Temperature Control .................................... 194 10.4.2 Solderless (Wire) Wrapping ......................... 213 9.24.11 InertAtmosphere Operation ........................ 194 10.4.3 Conductive-Elastomer Pressure 9.24.12 No-Clean Processing .................................... 194 Connections .................................................. 217 9.24.13 Processing Bare Copper ............................... 195 9.24.14 InertAtmosphere Control ............................ 195 11 CLEANLINESS REQUIREMENTS ...................... 219 9.24.15 Machine Selection ........................................ 195 11.1 Definitions .................................................... 220 9.24.16 Conveyor Type ............................................. 195 11.1.1 Solvency ....................................................... 220 9.24.17 Wavelength ................................................... 196 11.1.2 Solvent Stability ........................................... 220 9.24.18 Longitudinal Process Temperature 11.1.3 Film Drying Characteristics ......................... 220 Profiles .......................................................... 196 11.1.4 Soil Capacity ................................................ 220 9.24.19 Lateral Temperature Profiles ........................ 196 11.1.5 Surface Tension or Solvent Wetting ............ 220 9.24.20 Other Concerns ............................................ 197 11.2 Historical Perspective on Cleaning ............. 221 9.24.21 Can the Equipment Do the Job? ................. 197 11.3 Toxicity ......................................................... 221 9.24.22 Critical Parameters for IR Process 11.4 Ultrasonic Cleaning ...................................... 222 Control .......................................................... 197 11.5 Forms of Cleaning ....................................... 222 9.25 SMT .............................................................. 197 11.5.1 Aqueous Cleaning ........................................ 222 9.25.1 Surface MountAssembliesAcceptance Requirements ................................................ 197 11.5.2 Semi-Aqueous Cleaning .............................. 223 9.25.2 High Voltage or High PowerApplications .. 197 11.5.3 Solvent Cleaning .......................................... 223 9.25.3 QualityAssurance (Visual Inspection) ........ 197 11.6 CleaningAgent Considerations ................... 223 9.26 Process Verification Inspection .................... 198 11.6.1 Types of Solvents ......................................... 223 9.26.1 MagnificationAids and Lighting ................. 198 11.6.2 CleaningAgent Compatibility ..................... 224 9.26.2 Sampling Inspection - Process Control ....... 198 11.6.3 Vented Components ..................................... 224 9.26.3 Statistical Process Control (SPC) - 11.7 CleaningAgent Delivery Considerations .... 224 Refer to IPC-9191. ....................................... 198 11.7.1 In-Line Cleaning .......................................... 224 9.3 References .................................................... 198 11.7.2 Batch Cleaning ............................................. 224 10 OTHERASSEMBLYANDJOINING 11.7.3 Interim or Spot Cleaning ............................. 224 METHODS ........................................................... 199 11.7.4 Vapor Degreasing ......................................... 224 10.1 Wire Bonding (Chip and Wire) ................... 199 11.7.5 Ultrasonic Cleaning ...................................... 224 10.1.1 Thermocompression (TC) Bonding ............. 199 11.7.6 Cleaning Process Development ................... 225 10.1.2 Ultrasonic Bonding ...................................... 200 11.7.7 Removal of Contaminants from 10.1.3 Thermosonic (TS) Bonding ......................... 202 Underneath Parts .......................................... 225 10.1.4 Choice of Wire Bonding Method ................ 202 11.8 Cleaning requirements ................................. 225 10.2 TapeAutomated Bonding (TAB) ................. 203 11.8.1 Pre-Soldering Cleanliness Requirements ..... 225 10.2.1 Inner Lead Bonding (ILB) ........................... 204 11.8.2 Post-Soldering Cleaning .............................. 225 10.2.2 Outer Lead Bonding (OLB) ........................ 204 11.8.3 Particulate Matter ......................................... 225 10.3 Polymer Bonding ......................................... 205 11.9 Cleanliness Verification ................................ 226 ix IPC-AJ-820A February2012 11.9.1 Visual Inspection .......................................... 226 13.4.13 Hybrid ........................................................... 241 11.10 Post-Soldering Cleanliness Designator ........ 226 13.4.14 Hydrophopic-Oleophobic Encapsulations ... 241 11.11 Tests for Cleanliness .................................... 227 13.4.15 Inhibition ...................................................... 241 11.11.1 Residual Rosin ............................................. 227 13.4.16 Mealing ......................................................... 241 11.11.2 Ionic Cleanliness (ROSE) ............................ 227 13.4.17 Monomer ...................................................... 241 11.11.3 SIR Testing ................................................... 230 13.4.18 Multi-Layering ............................................. 241 11.11.4 Surface Organic Contaminants .................... 230 13.4.19 Oligomer ....................................................... 241 11.11.5 Other Residue Tests ..................................... 230 13.4.20 Photoresist .................................................... 241 11.11.6 UV-Vis Spectroscopy ................................... 230 13.4.21 Polymer ........................................................ 241 11.11.7 AGeneral Caution on Extraction- 13.4.22 Polymerization .............................................. 241 Based Tests ................................................... 231 13.4.23 Polysiloxane ................................................. 241 11.11.8 Other Contamination .................................... 231 13.4.24 Pot Life ......................................................... 241 11.11.9 OtherAnalytical Tests .................................. 231 13.4.25 Priming ......................................................... 242 11.11.10 Cleanliness Testing for No Clean 13.4.26 Shadowing .................................................... 242 Assemblies .................................................... 233 13.4.27 Shrinkage ...................................................... 242 11.12 Other Guidance on Cleaning ....................... 234 13.4.28 Spectroscopy ................................................ 242 12 CONFORMALCOATING .................................... 234 13.4.29 Stripping ....................................................... 242 12.1 Function of Conformal Coating .................. 234 13.4.30 Surface Tension ............................................ 242 12.2 Conformal Coating Specifications ............... 234 13.4.31 Transfer Efficiency ....................................... 242 12.3 Kinds of Conformal Coating ....................... 235 13.4.32 Wetting ......................................................... 242 12.4 Finding a Qualified Conformal Coating ...... 235 13.4.33 Young’s Modulus ......................................... 242 12.5 Advantage and Disadvantages ..................... 235 13.5 Environmental, Health and Safety 12.6 Storage and Shelf Life ................................. 236 Considerations .............................................. 242 12.7 Surface Preparation ...................................... 236 13.5.1 Emissions ...................................................... 242 12.8 Application Methods .................................... 237 13.5.2 Disposal of Hazardous Waste ...................... 242 12.9 Curing Methods ............................................ 237 13.5.3 Governmental Regulations ........................... 242 12.10 Process Control ............................................ 238 13.6 Types of Encapsulation ................................ 242 12.11 Coating Defects ............................................ 239 13.6.1 Acrylic .......................................................... 243 12.12 Coating Rework ........................................... 239 13.6.2 Epoxy ............................................................ 243 13.6.3 Silicone ......................................................... 243 13 POTTINGAND ENCAPSULATION .................... 240 13.6.4 Polyurethane & Polysulfide ......................... 243 13.1 Introduction .................................................. 240 13.6.5 UV and Solvent Cure ................................... 243 13.2 Purpose ......................................................... 240 13.7 Design for EncapsulationApplication ......... 244 13.3 Scope ............................................................ 240 13.7.1 Design Philosophy ....................................... 244 13.4 Terms and Definitions .................................. 240 13.7.2 PCBs ............................................................. 244 13.4.1 Adhesion Promotion .................................... 240 13.7.3 Component ................................................... 245 13.4.2 Adhesion Failure .......................................... 240 13.7.4 Electrical ....................................................... 246 13.4.3 Anisotropic ................................................... 240 13.7.5 Encapsulation Coverage ............................... 247 13.4.4 ARUR ........................................................... 241 13.7.6 Masking ........................................................ 247 13.4.5 Cross-Linking ............................................... 241 13.4.6 Cure .............................................................. 241 13.7.7 Drawings & Design Guidelines ................... 247 13.4.7 Delamination ................................................ 241 13.7.8 Reworkability/Repairability ......................... 248 13.4.8 Durometer ..................................................... 241 13.8 Raw Materials Characteristics ..................... 248 13.4.9 EMC ............................................................. 241 13.8.1 Viscosity ....................................................... 248 13.4.10 Filler ............................................................. 241 13.8.2 Viscosity vs. Rheology ................................ 248 13.4.11 Gel Time ....................................................... 241 13.8.3 Effect of Temperature on Viscosity ............. 248 13.4.12 Glass Transition Temperature T ................. 241 13.8.4 Surface Properties ........................................ 248 g x February2012 IPC-AJ-820A 13.9 Compatibility ................................................ 248 13.15.4 Environmental, Health and Safety Rework and Repair Considerations ............. 266 13.9.1 Compatibility with Process .......................... 248 13.16 End Use Environment .................................. 267 13.9.2 Inhibition ...................................................... 250 13.16.1 Outdoor Environment .................................. 267 13.10 Adhesion ....................................................... 251 13.16.2 Automotive ................................................... 268 13.10.1 Solder Mask/Substrate ................................. 251 13.16.3 Avionics Environment .................................. 268 13.10.2 Components .................................................. 251 13.16.4 Space Environment ...................................... 269 13.10.3 Surface Finishes ........................................... 252 13.16.5 Medical Environment ................................... 269 13.10.4 Cleanliness .................................................... 252 13.16.6 Geothermal Environment ............................. 269 13.10.5 InterlayerAdhesion ...................................... 252 13.16.7 Nuclear Biological Chemical Warfare 13.11 Methods ofAssessing Compatibility Environment ................................................. 269 and Performance .......................................... 252 13.17 Long Term Reliability and Testing .............. 269 13.12 Processing ..................................................... 253 13.17.1 Failure Mechanism ....................................... 269 13.12.1 Cleanliness .................................................... 253 13.17.2 Accelerated Testing ...................................... 271 13.13 Processing Environment .............................. 254 13.18 Bibliography ................................................. 271 13.13.1 Substrate Preparation ................................... 254 13.13.2 Priming ......................................................... 254 14 REWORKAND REPAIR ..................................... 272 13.13.3 Plasma Treatment ......................................... 255 14.1 General Information and Common Procedures .................................................... 272 13.13.4 Mechanical Etching ...................................... 255 14.1.1 Scope ............................................................ 272 13.13.5 Masking ........................................................ 255 14.1.2 Purpose ......................................................... 272 13.13.6 Manual vs.Automated Masking .................. 256 14.1.3 Background .................................................. 272 13.13.7 Recommended Coverage ............................. 257 14.1.4 Terms and Definitions .................................. 272 13.13.8 Application Methods .................................... 257 14.1.5 Applicability, Controls andAcceptability ... 274 13.13.9 Cure Mechanisms ......................................... 257 14.1.6 Basic Considerations .................................... 274 13.13.10 Cure Process Considerations ....................... 258 14.1.7 Workstations, Tools, Materials 13.13.11 Application Process Monitoring .................. 258 and Processes ............................................... 274 13.13.12 Inspection Guidelines ................................... 259 14.1.9 Lead Free ...................................................... 279 13.13.13 Environmental, Health and Safety 14.2 Handling ElectronicAssemblies - Processing Considerations ........................... 259 See Chapter 2 of this document. ................. 280 13.14 Encapsulation Properties .............................. 259 14.3 Cleaning - See Chapter 11 of 13.14.1 Appearance/Color ......................................... 260 this document. .............................................. 280 13.14.2 Dielectric Properties ..................................... 260 14.4 Coating Removal .......................................... 280 13.14.3 Thermal Properties ....................................... 260 14.4.1 Coating Removal, Identification of Conformal Coating........................................ 280 13.14.4 Flammability ................................................ 261 14.4.2 Coating Removal, Solvent Method............... 281 13.14.5 Flexibility ..................................................... 261 14.4.3 Coating Removal, Peeling Method............... 282 13.14.6 Abrasion Resistance ..................................... 262 14.4.4 Coating Removal, Thermal Method............. 282 13.14.7 Hydrolytic Stability ...................................... 262 14.4.5 Coating Removal, Grinding/ 13.14.8 Permeability .................................................. 262 Scraping Method........................................... 283 13.14.9 Chemical Compatibility and Chemical 14.4.6 Coating Removal, Micro Resistance ..................................................... 262 Blasting Method............................................ 283 13.14.10 UV Stability ................................................. 263 14.5 Replacment of Conformal Coating .............. 283 13.14.11 Radiation Resistance .................................... 263 14.5.1 Coating Replacement, Solder Resist............. 283 13.14.12 Outgassing .................................................... 264 14.5.2 Coating Replacement, Conformal 13.15 Rework and Repair ...................................... 264 Coatings/Encapsulants................................... 284 13.15.1 Removal Methods ........................................ 264 14.6 Conditioning – Baking and Preheating........ 284 13.15.2 Cleaning after Stripping ............................... 266 14.7 Epoxy Mixing and Handling........................ 284 13.15.3 Re-Encapsulation .......................................... 266 14.8 Legends/Markings......................................... 285 xi IPC-AJ-820A February2012 14.8.1 Stamping Method ......................................... 285 Figure7-2 Tinallotropiccrystallographicstructure; (left)tetragonalβ-tin,(right)cubicα-tin ..........69 14.8.2 Hand Lettering............................................... 285 Figure7-3 TinPestTransformationfromSweatman 14.8.3 Stencil Method.............................................. 285 etalInvestigation ...........................................70 14.9 Tip Care and Maintenance............................ 285 Figure7-4 SolderWireCoreFluxComparison ...............76 14.10 IPC-7711 Rework Procedures....................... 286 Figure7-5 SolderAlloySolidificationExample:Blue 14.11 IPC-7721 Modification and Repair............... 288 line-Eutectic,Redline-Non-Eutectic ..........76 Figure7-6 SolderAlloyFractureToughness TestingResults ...............................................77 Figures Figure7-7 SolderAlloyDropShockTestingResults .......77 Figure2-1 J-STD-075ProcessFlowDiagram .................17 Figure7-8 NASATin-WhiskerPhotograph ....................105 Figure3-1 ComponentOrientationwithRespectto Figure7-9 TinWhiskers-ObservedProblems BoundariesandMountingAccessibility ..........22 CausedbyWhiskers ....................................105 Figure3-2 UncoatedPrintedBoardClearance ...............23 Figure7-10 AdditionalTinWhiskerProblems .................106 Figure3-3 LeadTerminations ..........................................24 Figure8-1 Type1PrintedBoardAssembly ...................107 Figure3-4 ClinchedThroughHoleLeads ........................26 Figure8-2 Type2PrintedBoardAssemblies ................108 Figure3-5 Dual-InlinePackage(DIP)LeadBends .........26 Figure8-3 StaggeredHolePatternMounting‘‘MO’’ FlatpackOutlineDrawing(OnlyInches Figure3-6 LeadFormingandStressRelief Shown) ..........................................................110 LeadBends ....................................................27 Figure8-4 ComponentModificationsforSurface Figure3-7 ComponentMountingConfigurations .............27 MountingApplications ...................................110 Figure3-8 ThroughHoleFlat-PackMountingwith Figure8-5 ModifyingDIPforSurfaceMounting .............110 StaggeredPlatedThroughHoles ...................29 Figure8-6 MixedAssemblies .........................................111 Figure3-9 ModifiedFan-OutLands,mm[in] ...................30 Figure8-7 Clip-MountedComponent .............................112 Figure3-10 Custom-GridFan-outLandPattern ................30 Figure8-8 StrapSecuring ..............................................112 Figure3-11 GullWingFlatPackSurfaceMounting ..........31 Figure8-9 TypicalSpacers ............................................113 Figure3-12 Flat-PackLeadFormingfor(Planar) Figure8-10 TransistorMountingwithSpacer ..................113 SurfaceMounting ...........................................31 Figure8-11 MultipleLeadSpreader.................................113 Figure3-13 Surface-MountFlatRibbonLeadFeatures ....31 Figure8-12 ThermallyConductiveInsulator ....................113 Figure3-14 CoinedRoundLeads ......................................32 Figure8-13 Single-SidedSurfaceMountAssembly, Figure4-1 HASLSurfaceTopologyComparison .............45 ReflowOnly ..................................................114 Figure5-1 One-PartPrintedCircuitBoardConnector .....48 Figure8-14 Single-SidedSurfaceMountAssembly, Figure5-2 PrintedCircuitBoardwithEdge-Board ImmersionOnly .............................................114 Contacts ..........................................................48 Figure8-15 MixedTechnologyAssembly,Double- Figure5-3 TypicalOne-PartConnectorwithBellows Sided,ReflowOnly .......................................114 Contacts ..........................................................48 Figure8-16 MixedTechnologyAssembly,Double- Figure5-4 TypicalOne-PartConnectorTuning-Fork Sided:ReflowandImmersion.......................115 Contacts ..........................................................48 Figure8-17 MixedTechnologyAssembly,Double- Figure5-5 TypicalOne-PartConnectorCantilever SidedReflowandManual.............................115 Contacts ..........................................................48 Figure8-18 MixedTechnologyAssembly,Double- Sided,ImmersionOnly .................................115 Figure5-6 TypicalOne-PartConnectorReadout Configuration ..................................................49 Figure8-19 PanelAssemblyToolingHoles .....................116 Figure5-7 TypicalTwo-PartBlade-and-ForkContacts ....49 Figure8-20 PanelAssemblyToolingHoles .....................116 Figure5-8 TypicalZero-insertion-Force(ZIF)Pin- Figure8-21 TapedAxial-LeadedComponents .................116 GridArraySocket ...........................................49 Figure8-22 PolarizedAxialLeadComponent Figure5-9 TypicalPrintedBoardTestPoints ..................49 (TypicalPolarityMarkings)............................116 Figure6-1 DissolutionofSelectedElementsin Figure8-23 16-LeadDip ..................................................117 Sn/PbSolder ..................................................55 Figure8-24 FlatpackOutlineDrawing..............................118 Figure6-2 IntermetallicGrowthRates .............................55 Figure8-25 TypicalRibbonLeadedDiscrete Figure6-3 ComparisonofOxidizedandNon-oxidized DeviceOutlineDrawing(FlatLeads)............118 Sn/PbSurfaceFinish ......................................56 Figure8-26 PinGridArray ...............................................119 Figure6-4 SchematicoftheWettingBalanceTest .........58 Figure8-27 I/ODensityVersusLeadCount Figure6-5 IdealizedWettingBalanceCurve ...................59 (AllDimensionsinInches) ............................119 Figure7-1 TinLeadPhaseDiagram ................................68 Figure8-28 ConnectorwithPressFitContacts ...............119 xii February2012 IPC-AJ-820A Figure8-29 SurfaceMountClipCarrierSocket ..............120 Figure8-71 DIPClearances ............................................137 Figure8-30 SectionThroughSocketSolderContact ......120 Figure8-73 DIPSlideMagazines ....................................138 Figure8-31 ComponentMountingSequence ..................122 Figure8-74 NoBridging ...................................................139 Figure8-32 ThermalShunt ..............................................123 Figure8-75 LeadFormingforSurfaceMounting ............139 Figure8-33 TerminationExamples ..................................123 Figure8-76 CriteriaforLeadAttachmenttoLeadless Figure8-34 ClinchPatterns .............................................125 TypeA(LeadedTypeB) ...............................140 Figure8-35 SemiclinchedLead .......................................125 Figure8-77 SO-16PackageDrawingsTypical Dimension .....................................................140 Figure8-36 LeadDiameterVersusBendRadius ............126 Figure8-78 TypicalSOTPackages .................................141 Figure8-37 BendConfiguration .......................................127 Figure8-79 ModifyingDIPforSurfaceMounting ............141 Figure8-38 Simple-OffsetPreformedLead .....................127 Figure8-80 Gull-WingLeadforSIP-TypeComponent ....141 Figure8-39 DimplePreformedLeads ..............................127 Figure8-81 SurfaceMountReceptacle ...........................142 Figure8-40 CompoundLeadFormExamples ................127 Figure8-41 StressReliefLeads ......................................128 Figure8-82 SurfaceMountConnector ............................142 Figure8-42 TOCanLeadForming..................................128 Figure8-83 D-SubminiatureSurfaceMountConnector ..142 Figure8-43 DimplePreformedLeads ..............................128 Figure8-84 Box-ContactSurfaceMountConnector .......142 Figure8-44 TypicalMountingPatternfor12-Lead Figure8-85 LeadlessGridArraySocket ..........................142 CanswithClinchedLeadsMounting ............128 Figure8-86 SurfaceMountChipCarrierSocket .............142 Figure8-45 MechanicalMounting-LeadForming ..........128 Figure8-87 HighSpeedCircuitSocket ...........................143 Figure8-46 Single-InlineComponent ..............................129 Figure8-88 ScrewDownCover .......................................143 Figure8-47 LeadConfiguration(AfterAssembly) ...........129 Figure8-89 PressureMountedSocket ............................143 Figure8-48 ResilientSpacertoHeatSinkFrame ...........129 Figure8-90 PreferredMountingOrientations ..................146 Figure8-49 StaggeredHolePatternMounting Figure9-1 StructureofaSolderBond ...........................148 (FlatpackOutlineDrawing) ...........................130 Figure9-2 PropertyChangesasaFunction Figure8-50 ComponentMounting-LeadForming .........130 ofTemperature .............................................150 Figure8-51 Through-HoleBoardMountingwith Figure9-3 StressRelaxationwithTimeand UnclinchedLeads .........................................130 Temperature ..................................................151 Figure8-52 Through-HoleMountingwithClinched LeadsandCircumscribingLand ...................130 Figure9-4 CylindricalDeformationLeadingto JointFailure ..................................................151 Figure8-53 Through-HoleMountingwithOffsetLand ....130 Figure9-5 PropertyChangewithStrainRate ...............151 Figure8-54 ComponentsMountedOverConductors ......131 Figure9-6 CyclicShearStrainRange(Figure Figure8-55 HardwareClearance .....................................132 CourtesyofJ.P.Clech) .................................151 Figure8-56 ComponentAlignment ..................................132 Figure9-7 SolderJointGrainSizeStructure Figure8-57 ComponentAlignment ..................................132 (AsSoldered) ................................................152 Figure8-58 HorizontalMountingofRadial Figure9-8 SolderJointGrainSizeStructure LeadedComponent ......................................133 (AfteracceleratedCycling) ...........................152 Figure8-59 HorizontalMountingofRadialLeaded Figure9-9 SolderJointGrainSizeStructure ComponentwithHeatSink ...........................133 (AfterFieldFailure) .......................................152 Figure8-60 HorizontalTOMounting................................133 Figure9-10 SchematicDiagramsofTheMicrostructure Figure8-61 VerticalMountedAxialLeadComponents ...133 FormationinLead-FreePaste-Lead-Free SolderBallsUnderReflow ...........................153 Figure8-62 VerticalMountedRadial-LeadComponents .134 Figure9-11 ALead-freeBGAMicrostructure;Left-As Figure8-63 VerticalMountedComponentsCoating Meniscus .......................................................134 Reflowed,Right-AfterThermalCycling ......153 Figure8-64 RadialComponentsMounting Figure9-12 SolderAlloyMicrostructureDifferences: (UnsupportedHoles) ....................................134 Left-Tin/leadSolderAlloy,Right:SAC305 SolderAlloy ...................................................153 Figure8-65 OffsetLeadCanMounting ...........................134 Figure9-13 Lead-freeSolderAlloy/ComponentSurface Figure8-66 OffsetLeadCanMounting ...........................134 FinishIncompatibilityExample(Reference: Figure8-67 MetalPower-PackageTransistor D.HillmanandR.Wilcoxon,‘‘JCAA/JG-PP MountedonResilientStandoffs ...................134 Lead-freeSolderTestingforHighReliability Applications:-55°Cto+125°CThermal Figure8-68 Dual-InlinePackageGrippingTools .............136 CycleTesting,’’SMTAIConference,2006) ...154 Figure8-69 TransistorAssemblyTools ............................136 Figure9-14 left:Non-uniformSolderJointMicrostructure, Figure8-70 TapingSpecifications(onlyinchesshown) ..137 right:IncompleteSolderJointReflow Figure8-72 DIPLayoutinRowsandColumns ...............137 (Head-on-Pillow) ...........................................155 xiii