Microstructures and shear properties of Sb and In strengthened Sn5Bi/Cu joints

Abstract

Abstract The effects of x(Sb/In) (x = 1, 2, 3 wt.%) added to Sn5Bi solder alloy on the melting properties, microstructures and the shear behavior of solder/Cu joints were investigated combined with the corresponding phase diagram. It is found that the addition of Sb reduces the melting range and supercooling with the increase of Sb content caused by SnSb formation, while the In addition can reduce the melting point resulted by In solid solution. Both Sn5BixIn/Cu and Sn5BixSb/Cu are mainly composed of β-Sn and two types precipitates, i.e. Bi particles and Cu6Sn5 compound. The difference lies in that In doping only can dissolve into β-Sn and Cu6Sn5 while Sb doping mainly form tiny SnSb. Increase In content also inhibit precipitation of Bi particles and reduce the phase fraction Cu6(SnIn)5, resulting in that precipitation strengthening becomes weaker and solid solution strengthening becomes stronger. In contrast, the phase fraction of Bi particles and Cu6Sn5 increases with increasing Sb content, leading to that precipitation strengthening becomes stronger. These strengthening mechanism causes that their ultimate shear force monotonically increases with increasing Sb and In content, and the strengthening effect of the Sb element is better. Sb and In addition also can improve the ductility of Sn5Bi/Cu solder joints and both 2 wt.% In/Sb addition present the best shear fracture work. Thus, the optimal mechanical property was achieved by 2 wt.% Sb addition.