Effects of Thermal Aging on Microstructure and Microhardness of Sn-3.7Ag-0.9Zn-1In Solder

摘要

The structural stability of Sn-3.7wt.(percent)Ag-0.9wt.(percent)Zn-1wt.(percent)In solder was explored by thermal aging at 473 K. According to the microstructural observations, the high cooling rate (about 10~(2) K/s) applied to the water-cooled specimens prompted the formation of beta-Sn dendrites and inhibited the formation of the AgZn phase. After annealing for 20 h and 50 h, the corresponding microstructure changed significantly, especially the morphology of the intermetallic compounds (IMCs) in the slowly cooled solder. IMC particles grew in order to minimize the system energy. In addition, beta-Sn dendrites grew coarser as the IMCs segregated along their grain boundaries in the water-cooled solder. Furthermore, the Ag-Zn IMCs were suppressed in the water-cooled Sn-Ag-Zn-In solder. It is suggested that coarsening of the microstructure led to significant softening during annealing of the investigated Sn-Ag-Zn-In alloys.