Grain Refinements of Cu6Sn5 in Sn-3wt%Ag-5wt%Cu High Temperature Solder Alloys

This paper investigated the effect of trace addition of Al and Mg on the grain refinements of Cu6Sn5in Sn-3wt%Ag-5wt%Cu high temperature solder alloys. Furthermore, the effect of Al and Mg addition on the Sn/Ag3Sn eutectic were also investigated. It was found that the addition of both Al and Mg successfully refined the Cu6Sn5in Sn-3wt%Ag-5wt%Cu solder alloy. In addition, Al suppresses the formation of Ag3Sn in the Sn/Ag3Sn eutectic; while Mg promotes the formation of fine Sn/Ag3Sn eutectic microstructure. The refinement of Cu6Sn5is believed to be due to heterogeneous nucleation by Al and Mg rich intermetallic particles respectively. Effect of Al and Mg addition on the undercooling of the Sn/Ag3Sn eutectic was found to be similar, both reducing undercooling effectively at a low addition rate of 0.025wt%. The addition of Al and Mg have mixed effect on the nucleation temperature of Cu6Sn5. It is found that the nucleation temperature of Cu6Sn5is increased with 0.025wt% Al and 0.1wt% Mg addition to the unmodified alloy, while the nucleation temperature slowly decreases again as the trace element addition rate increases.