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PCB Surface Finishes
- 1. PCB Surface Finishes In A Lead-Free World
- 2. The Choices • HASL - Hot Air Solder Level • ENIG - Electroless Nickel Immersion Gold • Immersion Tin • Immersion Silver • OSP - Organic Solderability Preservative • Others - ENEPIG, Electroless Pd, Plasma
- 3. Decision Factors • Cost Sensitivity • Volume of Product • SnPb, Pb-Free or Both • Shock/Drop Testing • Cosmetics • Product Environment • Fine Pitch Components (≤0.5mm Pitch) • Design for Testability • Shelf Life
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- 5. Cost Comparison *NOTE: Priorto drastic gold price rise in 2011! - Now ~$7/panel in just metals!
- 6. HASL (Hot Air SolderLevel) Horizontal Vertical
- 7. HASL Process Cool Down Post Clean Pre-Clean Pre-Heat Air Knife Solder Flux 240°C 265°C 280°C 42psi Variables: Solder Temp, Dip Time, Air Temp, Air Pressure, Knife Angles
- 8. HASL Standards • IPC Standard - 100% Copper Coverage • Optimum Thickness - 1.5um - 30.5um • Based on Solder Paste Man. & Lessons Learned
- 9. HASL Issues • Coplanarity • HASL: 28um • QFP: 101um • Stencil: 100-127um • Copper Dissolution (per Pass) • SnPb HASL: 1.5um AVG • Pb-Free HASL: 3.5um AVG • PTH Barrel: 20um MIN • Bare Board Cleanliness • Process Control & Verification
- 10. HASL Summary Advantages Disadvantages • Low Cost • Coplanarity • Solder Wetting • Thermal Shock • Re-Workable • Copper Dissolution • Shelf Life • Cleanliness • Availability • Process Control
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- 12. DI Rinse Rinse 90°C Au Rinse Rinse ~One Hour Total Process Time Nickel 90°C Nickel Rinse Rinse Acid Dip Rinse Rinse ENIG Process Activator Pre-Dip Rinse Rinse Micro-Etch Rinse Rinse 50°C Cleaner
- 13. ENIG Process Au Ni Pd Cu
- 14. ENIG Standards • IPC-4552
- 15. ENIG Issues • Skip Plating • Tin Residues • Broken Soldermask Tent • Nickel Foot • Under-etching • Palladium Issues • Brittle IMC • SnNi vs. NiSnCu
- 16. ENIG Issues (con’t) • Black Pad • Nickel Hypercorrosion • Poor Mechanical Bond • Gold Porosity • Exposure to N2O
- 17. ENIG Summary Advantages Disadvantages • Planarity • Expensive • Shelf Life • Black Pad • Good for PTH • Process Control • Damage by ET • Signal Loss (RF)
- 18.
- 19. Dry DI Rinse ~30 Minutes Total Process Time Rinse Rinse 65°C ImSn Pre-Tin ImSn Process Rinse Micro-Etch Rinse Cleaner
- 20. ImSn Standards • IPC-4554
- 21. ImSn Issues • Tin Whiskers • Inhibitors (Ag) • IMC Aging
- 22. ImSn Summary Advantages Disadvantages • Planarity • Tin Whiskers • Re-workable • Corrosion • Shelf Life • Non Multiple Reflows • Carcinogen (Thiourea) • Availability
- 23.
- 24. Dry DI Rinse ~30 Minutes Total Process Time Rinse Rinse 55°C ImAg Pre-Silver ImAg Process Rinse Micro-Etch Rinse Cleaner
- 25. ImAg Standards • IPC-4553
- 26. ImAg Issues • Silver Dendrites • Inhibitors (Organic) • Creep Corrosion • Sulfides & Chlorides
- 27. ImAg Issues • Microvoiding • Ag Plates Void • Galvanic Cave • Soldermask Interface Etching • Poor LPI Adhesion • Galvanic Corrosion
- 28. ImAg Summary Advantages Disadvantages • Planarity • Silver Dendrites • Re-workable • Corrosion • Tarnishing • Shelf Life • Handling Issues
- 29.
- 30. Dry DI Rinse ~15 Minutes Total Process Time Warm Rinse 35°C OSP Rinse OSP Process Micro-Etch Rinse Cleaner
- 31. What is OSP? • Benzotriazole • Benzimidazole • Phenylimidazole
- 32. OSP Standards • IPC-4555 - Announced in 2008 • 2011: IPC Announces “No Standard” • Too Many Variations Based on Chemistry • Chairman of IPC Committee • Round Robin Testing Underway • Suppliers Not Ready to Release Thickness Data • Will Require Internal Standards • Lessons Learned From Companies Using OSP • J-STD-003A - Solderability Tests
- 33. OSP Issues • Poor Solder Wetting • No Clean Fluxes (Ask!) • 1:1 Solder Stencil • Exposed Copper • Cupric Oxide • Statue of Liberty (1886) • ICT First Pass Yields • Soldering Increases Yield • Thinner Coatings
- 34. OSP Summary Advantages Disadvantages • Planarity • Shelf Life • Re-workable • ICT Yields • Lowest Cost • Handling Issues • Simple Process • No Thermal Stress
- 35. Others ENEPIG Plasma Palladium Over Bare Copper
- 36. ENEPIG • The “Universal Finish” • Wire-bondable • Palladium Barrier • Black Pad • Nickel Diffusion In Gold • Highest Cost • ENIG + Palladium
- 37. Plasma • Cleaning & Application - 1 Step • Outlasts Noble Metals • Re-workable • Excellent Solderability • Wire-bondable • Less than Noble Metals • Lot Limitations • Poor Availability
- 38. Electroless Pd • 15-Minute Process • Electroless Deposition • 25.4 Angstroms • Cheaper than ENIG • No Black Pad • Extensive Shelf Life • Poor Availability
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- 40.
- 41. Testing • Solderability Testing • ENIG, ImSn, ImAg, OSP - All OK • Reliability Testing • ENIG, ImSn, ImAg, OSP - All OK • ImAg - Corrosive Gas Issues • ImSn - Losing Favor • ENIG - 10-30% Cost-up • OSP - Best “Compromise”
- 42. Quantify OSP • For example: EAU $40M PCB’s • Assuming 1.0x HASL Cost Factor • OSP at 0.7x is a $12M Savings! • ROI as a System Price • Not “Plug-and-Play” • Choose Best Compromise • Ensure <$12M Annual • Market Trend vs. Availability vs. Cost
- 43. Next Steps • Single Finish = Less Variation in EA • Solder Profiles • Solder Stencil Geometries • Solder Paste Recipes • Evaluate OSP ICT Yield Concerns • OSP-Specific Test Probes • Reduced Thickness OSP (1500-2000Å) • Run-At-Rate - Low Risk Volunteers ...