Influence of intermetallic compounds on tensile strength of lead-free solder

The purpose of this study was to investigate the influence of size of specimens on tensile strength. Pure Sn, Sn-Ag-Cu, Sn-Cu and Sn-Ag solder alloys were used in this study in order to investigate the effect of intermetallic compound, such as Ag₃Sn and Cu₆Sn₅, on tensile strength. Three types of specimens, aspect ratio of 2:5, 6:15, 8:20, were used. The tensile test was performed at a strain rate of 2.5×10^-4 s^-1 at room temperature. Microstructure of solders was observed by OM and SEM. Pure Sn and Sn-Cu showed the size effect on the tensile strength. Moreover, tensile strength decreased as specimen size is small because small test piece have more grain boundaries. On the other hand, Sn-Ag-Cu and Sn-Ag did not show the size effect. From these results, it can be suggested that intermetallic compounds suppress the size effect on tensile strength and Ag₃Sn has a strong effect on tensile strength comparing with Cu₆Sn₅. This means that the obstruction of slip deformation by Ag₃Sn can enhance the mechanical property.