Effect of Crystal Orientation on Sn Whisker-Free Sn–Ag–Cu Plating

Abstract

Mechanically induced Sn whiskers are a serious problem in the electronics industry because they can cause electrical short circuits in narrow gaps between electrodes such as fine pitch connector pins. The authors tried to prevent the formation of them by using one of the typical Pb-free solder materials, Sn–Ag–Cu alloy, as a plating material on connector pins. It was found that reflowed Sn–Ag–Cu plating was whisker-free even under mechanical stress. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses revealed that Sn grains of reflowed Sn–Ag–Cu plating were extremely larger than those of whisker-prone pure Sn or Sn–Cu platings that have columnar structures. The notable feature was no obvious microstructural changes in reflowed Sn–Ag–Cu plating even after applying mechanical stress for 38 days. The present study demonstrates that reflowed Sn–Ag–Cu plating is one of the best candidates as whisker-free plating.