Impact test performance of Zn-based die-attach joints for power devices

Fracture behavior under high speed deformation of the high temperature solder joints with Pb-free Zn-Sn and commercial Pb-Sn alloys bonded on different surface finishes was studied by ball impact test (BIT) method. All in all, Zn-Sn joints exhibited greater impact strength but inferior impact toughness than Pb-Sn joints. This can be ascribed to the high hardness of Zn-Sn solders resulting in partial or overall interfacial fracturing. In contrast, the joints with soft Pb-Sn solders all showed a ductile fracture feature. It can be suggested that for the joints revealing brittle fracturing the impact toughness increased with the plastic ability of interfacial intermetallic compounds (IMCs), while those showing ductile fracture mode, the impact energy deteriorated with a hardened solder matrix resulting from substrate dissolution.