Properties and Whisker Formation Behavior of Tin‐Based Alloy Finishes

This chapter reviews the basic properties of tin‐based alloy finishes and the effect of various alloying elements on whisker formation. The focus is on whisker test data and potential mechanisms for whisker suppression or enhancement for each element. A close look based on experimental data at the mechanisms of spontaneous whisker formation or suppression in matte Sn‐Cu alloy finishes reveals how adding minor elements to the copper base material (lead frame) can significantly change the whisker formation propensity of the alloy finish. Significantly different tendencies of whisker formation from the same matte Sn‐Cu coating electrodeposited on two different copper lead frames, namely, copper‐iron and copper‐chromium, were found. The results of these examinations clarified the mechanisms of formation and suppression of whiskers grown from the Sn‐Cu coating, and they established a countermeasure against the spontaneous whisker formation through the selection of the copper lead‐frame material.