Correlation between microstructure and mechanical properties of Sn-Bi-X solders

A comparative analysis between the microstructure and the tensile properties of eutectic Sn-Bi, (Sn-Bi)-0.5In, and (Sn-Bi)-0.5Ni solder alloys was conducted, and the shear strengths of the alloys as Cu/solder/Cu joints were evaluated. Tensile tests were performed on bulk solder alloys, followed by post-test fracture surface analysis. The cross-sectional microstructure and shear strength of the Cu/solder/Cu joints were investigated, and the fracture surface of the joints was examined after shear tests. The results of the tensile tests indicated that the In-bearing solder alloys had the highest elongation property and the lowest ultimate tensile strength among all the solder alloys tested in this study. The shear-test results also indicated the advantage of In addition for the suppression of both the excessive growth of solder/substrate interfacial intermetallic compounds and Bi coarsening within the solder bulk, which resulted in superior shear strength in both as-reflowed and thermally aged solder joints. In addition, the dimple-like structure on the fracture surfaces of the tensile- and shear-tested In-bearing solder alloys and joints indicated the ductile property of the alloys.