1. Tin Whiskers and Bono Update Chris Brightwell

2. Tin Whiskers

3. Background Spontaneous growths of single crystal filaments from tin platings

4. Whiskers on SOIC component

5. Lead Free RoHS – moving towards Lead Free Pure tin has tendency to ‘whisker’

6. Tin Whiskers – Driving Force

8. Mitigation Annealing/reflow Can reduce internal stress of plated deposit Nickel undercoat Significantly slower intermetallic growth Other coatings (eg nickel) Put some lead back in? Conformal coating

9. Which industries does this effect? Source: Boeing Source: Defence Update Source: www.ocrwm.doe.gov Source: health.yahoo.com Source: Swatch

10. Collaborations with NPL Source: Defence Update National Physical Laboratory ‘Do Conformal Coatings help prevent whiskers?’

11. Collaborations with NPL Source: Defence Update Copper test vehicle……

12. Collaborations with NPL Source: Defence Update ….Folded over to create parallel Plates, Tin Plated……

13. Collaborations with NPL Source: Defence Update …Interlocked with another set……

14. Collaborations with NPL Source: Defence Update …….Monitored for ‘shorts’ caused by whiskers

15. Humiseal Involvement Coatings reduced shorts by whiskers significantly Silicone and Urethane coatings most effective Whiskers most prevalent on corners and edges

16. Whiskers from Edges Source: Defence Update

17. This whisker penetrates the coating…… Source: Defence Update

18. Silicones are effective deterrents Source: Defence Update

19. Modern Circuit- boards are all corners and edges Source: Defence Update

20. New Collaboration Source: Defence Update Pseudo SOIC Device High Tin Whisker Plating Monitor continuously for shorts over 12 months

21. Whiskers on SOIC component

22. Possibly the most Famous Victim? Source: Defence Update

23. Conformal Coating/Solder Paste Compatibility Testing Using Bono Test Method

24. Background to Bono Test Adoption of ‘no clean’ methods Long term reliability Corrosive residues from paste/flux Manufacturers want to test the corrosion levels, and protection offered by conformal coatings

25. Bono Test Developed in France Assesses the corrosive effect of paste residues and Conformal Coatings Measures change in resistance of copper tracks due to Electrolytic Corrosion

26. How is Test Carried Out? Dedicated Bono Boards are commercially available 9 anode/cathode pairs per board

27. Bono Test Board

28. Solder Paste Stencilled and re-flowed

29. How is Test Carried Out? Boards are heated at 85C/85%RH Moisture promotes corrosion 20 Volt Bias on Cathode Corrosion ‘eats away’ thin anode Corrosion products visible Electrical Resistance increases

30. Corrosion Factor - Daily Measurements Bono Anode resistance R = V  At T=0 days R = approx 4Ω At T=n Days Corrosion Factor: ….F c = (ΔΩ / Ω) x 100%

31. Why the Corrosion? No coating or paste gives no corrosion Corrosion driven by voltage and moisture Corrosive materials (ionic) must help the corrosion

32. Why the Corrosion? Anode is showing evidence of corrosion Black = copper oxide

34. Why the Corrosion? Black = copper oxide Green = copper chloride Reduction in width of Anode can be observed

35. Why the Corrosion? Corrosion is Electrolytic – no volts = no corrosion

36. Corrosion Factor - Daily Measurements Corrosion factor = F c = (ΔΩ / Ω) x 100% No actual good/bad figure 8% is common

37. Fans of Bono Test Very good to differentiate pastes and coatings Real life test – can observe the corrosion of tracks and bi-products Not all combinations of paste and coating are successful, so useful to check combinations

38. Critics of Bono Test “Exaggerates problems” “Too many residues” “Spacings very close” “Standardised conditions not optimal” “Small changes make big differences” “Inconsistent”

39. Humiseal have developed in House Bono testing methods Custom made boards Dedicated Environmental chamber and Racks 16 Boards in Parallel Precision measurements

40. 16 Bono Boards in Parallel

41. What we will achieve……….. On-going tests to check corrosion levels with various paste / existing coating combinations Future products will be checked prior for ‘Bono Score’ before marketing Test can be used to identify problem components and best curing conditions

42. >>Bono Test is becoming increasingly important<< >>Humiseal are at the Forefront of developing the best coatings<<