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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.