Effect of Cu Addition on the Microstructure and Mechanical Properties of Sn-58Bi-0.5Ag Solder Alloys

In this study, the effects of Cu addition to Sn-58Bi-0.5Ag solder were investigated with respect to the alloy properties and fracture behavior of solder joints. The results show that adding Cu to the solder did not cause a significant change in the melting temperature. The melting temperature of all samples was 153.3–155.4°C. With the addition of Cu, the wettability of the solder first increased and subsequently decreased. When the Cu content was 0.5 wt.%, the area of spread was greatest (28.32 mm2), the wettability angle was lowest (12.9°), and the tensile strength of the solder joint was the highest (35.73 MPa). In addition, the proper amount of Cu content helped to refine the microstructure of eutectic solder and reduce the brittleness of joints. With increasing Cu content, the fracture mechanism of solder joints changed from a mixed fracture of toughness and brittleness to a brittle fracture.