Microstructure evolution during reflow and thermal aging in a Ag@Sn TLP bondline for high-temperature power devices

摘要

AbstractIn this paper, we investigated the microstructure evolution and the resulting change in mechanical properties in a Ag@Sn TLP bondline during reflow and thermal aging. A Ag@Sn high-remelting-point bondline was rapidly achieved with thermocompression bonding of Ag@Sn powder in only 5 min at 250 °C. After reducing the thickness of the Sn coating on the Ag particles, the main phases in the resulting bondlines changed from Ag/Ag3Sn to Ag/ζ-Ag, increasing the remelting temperatures to 480 °C and above. The voids were effectively controlled by reducing the thickness of the Sn coating, thereby increasing the shear strength by 38%. The large surface area of the Ag/Sn interface, provided by a high density of core–shell Ag@Sn particles, enabled the rapid formation of an interconnection that is entirely composed of Ag and ζ-Ag. After thermal aging, the main phases transformed from Ag/ζ-Ag to Ag/Ag (Sn) solid solution/ζ-Ag, which causes an increase in the remelting temperature of aged interconnections up to 724 °C. The thermal aged samples showed slight decreases in shear strength, but the morphology of the fracture surfaces indicated better ductility.