Comparison of Sn/Cu solder joints enhanced with Bi, In, and Sb

Abstract 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 Cu 6 Sn 5 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 Cu 6 Sn 5 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.