Tin whisker formation in thermal cycling conditions

Whisker growth on electroplated tin finishes may cause failures in electronic equipment. Although the mechanism for whisker growth is not understood in all details, different environmental conditions promote whisker growth in tin plated on Cu-based substrates and tin plated on FeNi42. In FeNi42 leadframes the thermal mismatch of tin and FeNi42 most likely promotes whisker formation and growth. This is the first systematic investigation of various temperature cycling conditions on whisker growth rates in Sn on FeNi42. The results indicate a decay of the growth rate with the number of cycles and/or whisker length and a linear relationship between whisker length and /spl Delta/T. In addition, second level assembly appears to reduce the maximum whisker length for a given environmental condition.