Effects of small addition of In on the structure of the rapidly cooled Sn–Ag–Zn solder

The effect of small additions of In, up to 1 wt.%, on the microstructure of the eutectic Sn–3.7 wt.%Ag–0.9 wt.%Zn solder was investigated. As observed by microstructural analysis, the increase of In content made β-Sn easy to form but suppressed the formation of the AgZn phase in the Sn–3.7Ag–0.9Zn solder. After annealing at 473 K for 20 and 50 h, the microstructure varied a lot in the morphology of the investigated Sn–Ag–Zn–In solder. The β-Sn dendrites grew coarser but dimmer accompanied with the segregation of the intermetallic compounds (IMCs) along their boundaries. Furthermore, the suppressed Ag–Zn IMCs formed in the Sn–3.7Ag–0.9Zn–1In solder. And the coarsening of the β-Sn dendrites and the growth of IMCs particles in the microstructure of the samples brought a significant softening during annealing of the investigated Sn–Ag–Zn–In alloys.