Controlling Ag3Sn plate formation in near-ternary-eutectic Sn-Ag-Cu solder by minor Zn alloying

As a result of extensive studies, nearternary-eutectic Sn-Ag-Cu (SAC) alloys have been identified as the leading lead-free solder candidates to replace lead-bearing solders for ball-grid array module assembly. However, recent studies revealed several potential reliability risk factors associated with the alloy system. The formation of large Ag3Sn plates in solder joints, especially when solidified at a relatively slow cooling rate, poses a reliability concern. In this study, the effect of adding a minor amount of zinc in SAC alloy was investigated. The minor zinc addition was shown to reduce the amount of undercooling during solidification and thereby suppress the formation of large Ag3Sn plates. In addition, the zinc was found to cause changes in both the microstructure and interfacial reaction of the solder joint. The interaction of zinc with other alloying elements in the solder was also investigated for a better understanding of the role of zinc during solidification of the nearternary-eutectic alloys.