Growth kinetics of the solid-state interfacial reactions in the Sn–Cu/Co and Sn/Co–Cu couples

Two different Sn–Cu/Co and Sn/Co–Cu reaction couples were examined at temperatures ranging from 150 °C to 200 °C to examine the Cu alloying effect by varying Cu contents. Two reaction phases, CoSn3 and (Cu,Co)6Sn5, were observed simultaneously at the interfaces of the Sn–Cu/Co couples (0.1 wt%–3 wt%Cu). The CoSn3 layer was much thicker than (Cu,Co)6Sn5, and CoSn3 exhibited a linear growth rate at the initial reaction stage. Remarkably, minor Cu addition into the solders resulted in strongly suppressing the layer growth. On the other hand, the potential Co–Cu alloy substrate was also considered because of its impact on decreasing the growth rate. Sn/Co–Cu (less than 10 wt%Cu) interfacial reactions were carried out. Only one CoSn3 phase layer was produced. In addition, the temperature dependence of the reaction layer growth was also examined. Compared with the binary Sn/Co couple, the layer growth rates in the Sn–Cu/Co and Sn/Co–Cu couples are relatively lower and more temperature-sensitive.