Matte tin (Sn) plating: whisker growth study

In the industry's drive towards becoming lead-free (Pb-free) by July 1, 2006, as dictated by the WEEE Directive, several Pb-free terminal finishes have been proposed and evaluated. Some of them were rejected as soon as evaluations began. Others have been dropped along the way due to problems with either manufacturability or reliability. However, a few alternatives are becoming increasingly popular and seem to be the "chosen ones". SnAgCu alloys, for example, have emerged as the clear, choice for Pb-free solder. In contrast, there is no clear winner yet in the area of Pb-free plating alternatives. Electroplated matte tin (Sn) can be considered as a drop-in replacement for SnPb terminal finishes. However the tin whisker is often considered for pure tin plating. This paper presents the findings of a series of whisker growth studies performed on 100% matte Sn plating on Copper (Cu) leadframes. Studies were done on different package types, assembled at different locations at different times, with and without mitigation techniques and on samples at a component level (such as annealing etc.) and as mounted on PWBs. And also included study on plating additive and plating temperature effect on whisker growth on matte tin.. Since these studies started when no Pb-free or whisker definitions or standards were available, best known methods were employed in the studies. However, results from a new study done using NEMI's recommended Sn whisker test methods and failure criteria are also included.