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1、Application Report SZZA037A - February 2003 1 Whisker Evaluation of Tin-Plated Logic Component Leads Douglas W. Romm, Donald C. Abbott, Stu Grenney, and Muhammad Khan Logic Packaging ABSTRACT Integrated circuits (ICs) with matte tin (Sn) finished leads for logic products were tested for Sn-whisker-g
2、rowth susceptibility. The ICs were obtained from several assembly-test subcontractors (subcons). The conditions used to promote Sn-whisker growth are typical for the industry: 51C and 51C + 85% RH. In addition, the same conditions were imposed on board-mounted ICs that had a 5-V bias applied to adja
3、cent leads. Biasing of leads in a Sn-whisker test is not typical in the industry, but we believe it represents an in-use condition. The results of these tests were not as expected. Conventionally, the matte Sn finish is thought to be less prone to whiskers. We found whiskers on some matte-Sn-finishe
4、d components and no whiskers on other matte-Sn-finished components. We found whiskers on some larger Sn-grain deposits and no whiskers on some finer Sn-grain deposits. This is contrary to much of the literature. Also, we found whiskers quite consistently on the biased samples, but not on the paralle
5、l run of parts with no bias. Also, we saw whiskers grow on some units that were in shelf storage for several months, with no exposure to the whisker-test conditions. This paper highlights the risks associated with Sn-plated leads and the potential for Sn whiskers. The propensity of a Sn finish to de
6、velop Sn whiskers is not easy to predict. Results lend credence to the notion that there are likely a multiplicity of mechanisms for Sn-whisker growth. Contents Introduction5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7、. . . . . . . . . . . . . . Components Evaluated6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain-Size Measurements7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8、 . . . . . . . . . . . . . . . . . . Test Method9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample-Mounting Procedure10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9、. . . . . . . . . . . . . . . . . . . . . . . . . . Inspection Locations and Procedure11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection Results for Sn-Finished Units13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10、. . . . . . . . . . . . . . . . . Inspection Results for Subcon A, Sn-Finished Units13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection Results for Subcons BD, Sn-Finished Units17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection Res
11、ults for SnBi-Finished Units23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of Results for Subcons BF24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observations25. . . . . . . . . . . . . .
12、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of Results25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions26. . . . . . . . . . . . . . . . . . .
13、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trademarks are the property of their respective owners. SZZA037A 2Whisker Evaluation of Tin-Plated Logic Component Leads References27. . . . . . . . . . . . . . . . . . . . . . . . . . .
14、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . List of Figures 1. Isometric View of SOIC Gull-Wing Package7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Isometric View of SOT Gull-Wing Package7.
15、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Isometric View of TO-220 Through-Hole Package7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Isometric View of QFN Surface-Mount Package7. . . . . . . . . . . . . .
16、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Grain Structure on Subcon A Tin-Plated SOIC Units, 2000X Magnification8. . . . . . . . . . . . . . . . . . . . 6. Grain Structure on Subcon B Tin-Plated SOT Units, 2000X Magnification8. . . . . . . . . . . . . . . . . . . . . 7. Grain Stru
17、cture on Subcon C Tin-Plated TO-22 Units, 2000X Magnification8. . . . . . . . . . . . . . . . . . . 8. Grain Structure on Subcon D Tin-Plated SOT Units, 2000X Magnification8. . . . . . . . . . . . . . . . . . . . . 9. Grain Structure on Subcon E Tin-Plated QFN Units, 2000X Magnification9. . . . . .
18、. . . . . . . . . . . . . . . 10. Grain Structure on Subcon F Tin-Bismuth SOT Units, 2000X Magnification9. . . . . . . . . . . . . . . . . . . 11. SOIC Unit From Subcon A Soldered to PWB11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. SOIC Units Glued t
19、o SEM Inspection Pedestal Prior to Test-Condition Exposure11. . . . . . . . . . . . . . 13. Inspection Locations For Live-Bug Gull-Wing Units12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14. Inspection Locations For Dead-Bug Gull-Wing Units12. . . . . . . . . . . .
20、. . . . . . . . . . . . . . . . . . . . . . . . . . 15. Inspection Locations For TO-220 Units12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16. Inspection Locations For QFN Units12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21、 . . . . . . . . . . . . . . . . . . . 17. Subcon A SOIC Unit at 450X, 1000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4 From Figure 13. No Whiskers Noted.14. . . . . . . . . . . . 18. Subcon A SOIC Unit at 450X, 1000-Hours Exposure to Run-4 Conditio
22、ns (No Precondition, Bias + 51C/85% RH). Inspection Location 1. No Whiskers Noted.14. . . . . . . . . . . . . . . . . . . . . . . . . . 19. Subcon A SOIC Unit at 3000X, 2000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Whisker Length = 12.4 ?m.14. .
23、 . . . . . . . . . . . . . . . . . . 20. Subcon A SOIC Unit at 3000X, 2000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Multiple Whiskers Noted, With Length = 7.99.5 ?m . .14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24、 . . . . . . . . . . . . . . . . . . . . . 21. Subcon A SOIC Unit at 3000X, 2000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Multiple Whiskers Noted, Length of Measured Whisker = 1.6 ?m.15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22. Subcon A SOIC Unit at 3000X, 2000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Whisker Length = 13.916.2 ?m.15. . . . . . . . . . . . . . . 23. Subcon A SOIC Unit at 450
26、X, 3000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Multiple Whiskers Noted, With Length = 8.017.7 ?m.16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27、. 24. Subcon A SOIC Unit at 1400X, 3000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Multiple Whiskers Noted, With Length = 8.017.7 ?m.16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28、. . . . . . . . . . . . . . . . . 25. Subcon A SOIC Unit at 1500X, 3000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 4. Multiple Whiskers Noted, With Length = 1314 ?m.16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29、 . . . . . . . . . . . . . . . . . . . . 26. Subcon A SOIC Unit at 1500X, 3000-Hours Exposure to Run-4 Conditions (No Precondition, Bias + 51C/85% RH). Inspection Location 3, Scratched Surface. Multiple Whiskers Noted, With Length = 1534 ?m.16. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SZZA037A 3 Whisker Evaluation of Tin-Plated Logic Component Leads 27. Subcon B SOT Unit at 450X, 3634-Hours Exposure to Precondition + 51C/85% RH, Unbiased. Inspection Location 1, Right Side. No Whiskers Noted.17. . . . . . . . . . .
31、 . . . . . . . . . . . . . . . 28. Subcon B SOT Unit at 450X, 3634-Hours Exposure to 51C/85% RH, No Precondition, Unbiased. Inspection Location 1, Right Side. No Whiskers Noted.17. . . . . . . . . . . . . . . . . . . . . . . . . . 29. Subcon C TO-220 Unit at 4000X, 3634-Hours Exposure to Preconditio
32、n + 51C/85% RH, Unbiased. Inspection Location 8, Figure 15. Whisker Length = 5.1 ?m.18. . . . . . . . . . . . . . . . . . . . . . 30. Subcon C TO-220 Unit at 7500X, 3634-Hours Exposure to Precondition + 51C/85% RH, Unbiased. Inspection Location 7, Right Side. Whisker Length = 9.3 ?m.18. . . . . . .
33、. . . . . . . . . . . . . . 31. Subcon C TO-220 Unit at 1600X, 3634-Hours Exposure to 51C/85% RH, No Precondition, Unbiased. Inspection Location 9. Multiple Whiskers Noted, With Length = 4.66.2 ?m.19. . . . . . . . 32. Close-Up of Whisker Noted on Subcon C TO-220 Unit at 1600X, 3634-Hours Exposure t
34、o 51C/85% RH, No Precondition, Unbiased. Inspection Location 9. Whisker Length = 6.2 ?m.19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33. Subcon C TO-220 Unit at 7500X, 3634-Hours Exposure to Precondition + 51C/85% RH, Unb
35、iased. Inspection Location 9. Whisker Length = 7.7 ?m.19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34. Subcon C TO-220 Unit at 950X, 3634-Hours Exposure to Precondition + 51C/85% RH, Unbiased. Inspection Location 7. Multiple Whiskers Noted, With Length 6.132 ?m.19. . . . . . . .
36、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35. Subcon C TO-220 Unit at 7500X, After 9-Months Shelf Storage, No Exposure to Whisker-Test Conditions. Inspection Location 8. Whiskers Are 8.8 ?m Wide 6.9 ?m Long.20
37、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36. Subcon C TO-220 Unit at 3000X, After 9-Months Shelf Storage, No Exposure to Whisker-Test Conditions. Inspection Location 8. Whiskers Are 14.6 ?m Wide 9.4 ?m Long.20
38、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37. Subcon C TO-220 Unit at 3700X, After 9-Months Shelf Storage, No Exposure to Whisker-Test Conditions. Inspection Location 9. Whiskers Are 14.2 ?m Wide 14.5 ?m Long.21. . . . . . . .
39、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38. Subcon C TO-220 Unit at 3300X, After 9-Months Shelf Storage, No Exposure to Whisker-Test Conditions. Inspection Location 10. Whiskers Are 20.3 ?m Wide 10.1 ?m Long.21. . . . . . . . . . . . . . . .
40、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39. Subcon D SOT Unit at 600X, 3634-Hours Exposure to 51C/85% RH, Unbiased. Inspection Location 4. No Whiskers Noted.22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41、. . . . . 40. Subcon D SOT Unit at 450X, 3634-Hours Exposure to 51C/85% RH, Unbiased. Inspection Location 1. No Whiskers Noted.22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41. Subcon E QFN Unit at 1000X, 4000-Hours Exposure to 51C
42、Bake, Unbiased. Inspection Location 13. No Whiskers Noted.22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42. Subcon E QFN Unit at 1000X, 4000-Hours Exposure to 51C Bake, Unbiased. Inspection Location 12. No Whiskers Noted.22. . . . . .
43、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43. Subcon F SnBi-Finished SOT Package After 3634-Hours Exposure to 51C/85% RH. Inspection Location 1, Right Side. Whisker Length = 0.40.6 ?m.23. . . . . . . . . . . . . . . . . . . . . . . . . . . 44.
44、 Subcon F SnBi-Finished SOT Package After 3634-Hours Exposure to 51C/85% RH. Inspection Location 1, Left Side. Whisker Length = 1.1 ?m.23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45. Subcon F SnBi-Finished SOT Package After 3634-Hours Exposure to 51C/85% RH. Inspection Location
45、 Left Edge, Foot Area. Multiple Whiskers Noted, Length = 5.76.5 ?m.24. . . . . 46. Subcon F SnBi-Finished SOT Package After 3634-Hours Exposure to 51C/85% RH. Inspection Location Left Edge, Foot Area. Closeup of Whisker, Length = 6.5 ?m.24. . . . . . . . . . . . . SZZA037A 4Whisker Evaluation of Tin
46、-Plated Logic Component Leads List of Tables 1. Source and Plating Details for Each Package Evaluated6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. NEMI Definitions of Matte and Bright Sn Finishes6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47、. . . . . . . 3. Whisker-Test Matrix for Subcon A9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Whisker-Test Matrix for Subcons BD and Subcon F10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. SEM I
48、nspection Summary for Sn-Finished SOICs, Subcon A13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. SEM Inspection Summary for Units from Subcons BF25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SZZA037A 5 Whisker Evaluation of Tin-Plated Logic Componen
49、t Leads Introduction Many integrated circuit (IC) manufacturers are qualifying, or planning to qualify, matte tin (Sn) finish as a lead (Pb)-free replacement for tin-lead (SnPb) on component leads.1,2 The target packages for a Sn finish are peripherally leaded surface-mount packages, exclusive of ball grid arrays. Sn-whisker growth is a concern with Sn-plated components. Whiskers are spontaneous filamentous or needlelike growths from the Sn surface.36 The whiskers have the potential to short adjacent leads or break off and short or cause m