Influence of Cu addition on intermetallic compound formation and microstructure of Sn–3Ag–1˙5Sb–xCu solder joints

This study investigates the influence of 0–1˙5 wt-%Cu addition on the microstructure and the intermetallic compound (IMC) formation of the as soldered Sn–3Ag–1˙5Sb– xCu (wt-%) solders and following thermal storage at 150°C for 0, 25, 200 and 600 h, with the intention of identifying the optimum Cu addition for industrial applications. The experimental results show that the melting point of Sn–3Ag–1˙5Sb– xCu solder decreases with Cu addition. For Cu additions of 1˙0 wt-% or higher, an IMC of Cu₆Sn₅ particles is dispersed throughout the matrix, resulting in a dispersion strengthening effect, and its size increases with the levels of Cu addition increasing. The coarsened long strip like Cu₆Sn₅ with a length of more than 100 μm growing from the upper interface of IMC layer into the solder matrix is observed in the solder with 1˙5 wt-%Cu addition after thermal storage. Cu₆Sn₅ grains in the IMC layer develop the ripening grains with a more hexagonal or polygonal shape and smooth edged flat surfaces instead of scallop shape. Additionally, the microhardness of each solder increases with Cu addition and decreases with increasing time of thermal storage at 150°C.