The Sn-Ag-Cu (SAC) solder alloys with a low Ag (Ag < 3 wt.%) content have attracted great attention owing to their low cost, increased ability in bulk compliance, and plastic energy dissipation. However, some of their mechanical properties are generally lower than the SAC alloys with a higher Ag content. Adding alloying elements is an effective approach for improving the mechanical properties of the SAC alloys. In this study, the effect of Bi, Sb, and Ti on Sn-1 wt.%Ag-0.5 wt.%Cu (SAC105) solder alloys was investigated. The SAC solders with four compositions: SAC105-1 wt.%Bi, SAC105-1 wt.%Sb, SAC105-1 wt.%Bi-1 wt.%Sb, SAC105-1 wt.%Bi-1 wt.%Sb-0.4 wt.%Ti were prepared. The microstructure and phase compositions were characterized using electron scanning microscopy, and X-ray diffraction. The thermal properties and wettability were also examined. Uniaxial tensile tests and nano-indentation tests were conducted to evaluate the mechanical properties. The results show that adding Bi or Sb could increase the strength of SAC105 alloys mainly due to the solid solution strengthening effect. The creep resistance of SAC105 alloys was also improved with the additions of Bi and Sb. The co-additions of Bi and Sb into SAC105 alloys exhibit an enhanced creep resistance than that calculated by the theoretical calculation. The further addition of Ti into SAC105-1Bi-1Sb alloys demonstrated a much-improved creep resistance, which could be attributed to the synergistic effects of both solid solution strengthening and the precipitation hardening effects.

The effects of elements In, Bi and Sb with 1, 2, 3, 4 and 5 wt% added to pure Sn metal were investigated, in order to study their influence on their melting behavior, microstructure and mechanical properties. The findings indicate that the addition of In, Bi and Sb reduces the undercooling of pure Sn. After adding the three elements to the Sn/Cu solder joints, the microstructure remains predominantly composed of the β-Sn phase and the Cu₆Sn₅ phase, aligning with the microstructures of the corresponding Sn based bulk alloys. The difference arises when Bi is added up to 5 wt%, leading to the precipitation of Bi particles. The element In, however, only dissolves in the β-Sn and Cu₆Sn₅ phases. When the mass fraction of Sb reaches 5%, a dark gray square SbSn phase precipitates. Among the elements, Bi and In play the role of solid solution strengthening, due to the precipitation phase of Bi and the presence of SbSn phase. Additionally, Bi and Sb exhibit precipitation strengthening effect. These strengthening effects make the maximum shear force and microhardness of the joints with the increase in the amount of alloying elements added to show a monotonous upward trend. The results show that the strengthening effect of Bi is superior to that of Sb,In when the doping amount of alloying elements is the same. The research results have guiding significance for alloy design, especially in the field where the reliability of electronic equipment is required at high temperature.