Solid-state and liquid-state interfacial reactions between Sn-based solders and single crystal Ag substrate

Growth kinetics and interfacial morphologies of the intermetallic compounds (IMCs) between single crystal Ag and Sn–4Ag, Sn–3Cu and Sn–37Pb solders were investigated by solid-state aging at 160 °C and liquid-state aging at 260 °C. Isothermal equation of chemical reaction and phase diagrams were used to explain the effects of Ag, Cu and Pb on the growth kinetics of IMCs under solid-state and liquid-state aging conditions. The diffusion coefficients for the three solder joints of Sn–4Ag/Ag, Sn–3Cu/Ag and Sn–37Pb/Ag were calculated after solid-state and liquid-state aging. It is found that Pb can effectively retard the growth of IMCs during liquid-state aging but has little influence on the growth rate of IMCs during the solid-state aging. Some local small cracks were frequently observed in the Cu6Sn5 particles near interfaces of the Sn–3Cu/Ag solder joints after solid-state aging for several days. However, there were no such local small cracks when solders or interfaces did not contain the Cu6Sn5 particles after the same aging time.