Effect of Au addition on Microstructural and Mechanical Properties of Sn-Cu Eutectic Solder

摘要

The effect of Au addition on the microstructural and the tensile properties of Sn-0.7 mass percent Cu alloy was examined. Tensile strength and 0.2 percent proof stress remarkably increase up to 0.3 mass percent Au primarily due to solid solution hardening. Beyond 0.3 mass percent Au, due to precipitation of large intermetallic compounds, elongation decreases while tensile strength and 0.2 percent proof stress increase slightly. With Au addition to Sn-Cu binary alloy, the eutectic endothermic peak in DSC, i.e., the melting reaction at 227 deg C, becomes broader and shifts to the lower temperature range. With Au beyond 2 mass percent, the broad peak becomes smaller splitting into two peaks and moving towards lower temperature while a new peak appears at about 212 deg C. these thermal reactions can be well explained by the formation of beta-Sn, Cu_6Sn_5 and AuSn_4 with Au more than 1 mass percent. EPMA observation revealed that much amount of Au and Cu dissolve into Cu_6Sn_5 and AuSn_4, respectively.