Liquidus Temperature Design of Lead-Free Solder

A method for designing lead-free solder was studied using the liquidus temperature of a 2-component eutectic solder in order to develop a high temperature lead-free solder. In this work, tests were done to obtain a targeted liquidus temperature of a 4-component lead-free solder based on the weight percentage of two sets of 2component eutectic solders. This 2-component eutectic solder was assumed to be thermodynamically stable in itself. The weight percentages of five respective types of Bi–Cu, Ag–Cu etc. eutectic solders were varied and the design temperature was predicted and compared against the measured liquidus temperature. In doing this, it was learned that the measured apparent liquidus temperatures were liniear with respect to the design temperatures. Similar studies were conducted into a medium temperature material of Sn–Ag–Cu and a low temperature material of Sn–Bi–Ag. The measured temperatures of these solders also corresponded to the design temperatures.