Effects of Minor Cu, Ni and Ag Additions on the Reactions Between Sn-Based Solders and Co Substrate

Abstract

This study investigated the effects of minor Cu, Ni, and Ag additions in the interfacial reactions between Sn-based solders and Co. In the liquid-state reactions, the Cu contents greatly affected the formed intermetallic compounds and their growth rate. In the Sn-0.7 wt.%Cu/Co at 250°C, the CoSn₃ growth was significantly inhibited by ~ 35%, in comparison with the Sn/Co reaction. With increasing to 0.9–2 wt.%Cu contents, both the (Cu,Co)₆Sn₅ and CoSn₃ phases were simultaneously formed, and the interfacial evolutions were examined. With 0.7 wt.%Ni addition, the CoSn₃ growth was slightly retarded by ~ 20%. In contrast, the 3.5 wt.%Ag addition showed no obvious difference. The inhibiting effects of adding these elements were Cu > Ni > Ag (= pure Sn). In the solid-state reactions with 0.7 wt.%Cu addition at 200°C, the CoSn₃ growth was strongly retarded by ~ 55%. Minor additions of 0.7 wt.%Ni or 3.5 wt.%Ag exhibited a weak inhibiting effect on the CoSn₃ growth.