Microstructure, mechanical properties, and interfacial reaction with Cu substrate of Zr-modified SAC305 solder alloy

Abstract

Four component solder alloys (Sn-3.0Ag-0.5Cu-xZr; x = 0, 0.05, 0.2, and 0.5 wt%) were obtained using vacuum induction melting. The microstructure of the solder alloys and solder joints was characterized via OM, SEM, XRD and EPMA. Tensile and shear tests were performed to evaluate the mechanical properties. The results showed that with the increase of the Zr content, the size of the primary β-Sn phases decreased gradually, and Ag3Sn decreased first and then increased. The SAC305-0.2Zr solder exhibited the finest microstructure. The size of the primary β-Sn phase decreased by 59%, and the Ag3Sn resembled a dot 1 μm in size. Tensile tests indicated that as the Zr content increased, the strength of the solder increased, and the elongation first increased and then decreased. Compared to the original joints, the joints fabricated with Zr-modified solders had thinner intermetallic compound (IMC) layers and exhibited higher shear strength. The SAC305-0.2Zr/Cu joints had a 17% reduction in the interfacial reaction layer thickness and a 20% increase in the maximum shear force. Moreover, the Zr-modified solders showed a significant decline in undercooling. The melting range and melting point was slightly reduced. In this study, 0.2 wt% was determined to be the optimum amount of Zr in the SAC305 solder.