Ni and Sb improve the microstructure, mechanical properties, and solder joint reliability of Sn-3.0Ag-0.5Cu alloy

In this study, SAC305-0.1Ni and SAC305-0.1Ni-xSb (x = 1.5 wt %, 2.0 wt %, 2.5 wt %) composite solders were fabricated by incorporating Ni and Sb alloying elements into Sn3.0Ag0.5Cu (SAC305) solder. A comprehensive investigation was carried by utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), microhardness tests, nanoindentation, transmission electron microscopy (TEM), and a universal mechanical testing machine. The effects of Ni and Sb additions on microstructures, thermal properties, wettability, mechanical characteristics, as well as thermal aging, interfacial growth, and mechanical properties of welded joints were systematically explored, and these results were compared with SAC305 solder. The results indicated that the incorporation of Sb and Ni enhanced the microstructure of the solder alloy through the formation of (Cu, Ni)₆Sn₅ and SnSb phases, leading to a 23.90 % increase in the solder wetted area. Additionally, the formation of (Cu, Ni)₆Sn₅ and SnSb intermetallic compounds (IMC) increased resistance to dislocation motion, thereby enhancing the mechanical properties of the solder alloys in comparison to SAC305 solder. The creep resistance of the solder alloys was significantly improved, with a corresponding 49.19 % increase in Vickers hardness. During the thermal aging of solder joints, the interfacial growth coefficient decreased, with the SAC305-0.1Ni-2.0Sb joints exhibiting the lowest value at 0.0185. Furthermore, the co-addition of Ni and Sb consistently enhanced the mechanical properties of the welded joints. The average tensile strength of SAC305-0.1Ni-2.0Sb joints reached 77.87 MPa, which represents a 28.45 % increase compared to SAC305 joints. As the Sb content increased, the fracture mode transitioned from brittle fracture to ductile fracture, and eventually to a mixed ductile-brittle fracture.