Effect of bismuth–tin composition on bonding strength of zinc particle–mixed copper nanoparticle/bismuth–tin solder hybrid joint

Abstract

In this study, the effect of Bi–Sn composition on the bonding strength of Zn-mixed hybrid joints composed of SiC/Cu and SiC/direct bonded copper (DBC) was examined. For both joints, the bonding strength exhibited a similar dependence on Bi–Sn composition, and the maximum strength obtained for the average Bi fraction in the Bi–Sn alloy particles was 38.2 wt%. This composition is more Sn-rich than the eutectic composition of the Bi–Sn alloy. The bonding strength of the SiC/Cu joints was lower than that of the SiC/DBC joints throughout the entire Bi–Sn alloy composition range. The degree of Bi segregation at the interfacial region decreased with a decreasing Bi fraction in the Bi–Sn particles and was correlated with the bonding strength for the Bi fraction below 38.2 wt%. Defects such as voids and cracks were also observed in the bonding layer, which were likely a result of the difference in the bonding strengths between the SiC/Cu and SiC/DBC joints. Furthermore, delamination of the bonding layer at the interface was observed in the joint that had Sn particles as the starting material. These results indicate that Zn mixing in the hybrid joint enables the reduction of the Bi fraction of the Bi–Sn alloy, leading to improved bonding strength.