Surface tension of the 60%Bi–24%Cu–16%Sn alloy and the critical temperature of the immiscible liquid phase separation

In order to control the core-shell structure of bimetallic lead-free solder balls, the surface tension and the critical temperature for the phase separation of two immiscible liquid phases are required. In this study, the temperature dependence of the surface tension of the 60%Bi–24%Cu–16%Sn alloy was measured using the constrained drop method. The temperature dependence of the surface tension was changed at the critical temperature due to phase separation and corresponding modification of the atomic structure of the surface layer. This simple and new procedure enables us to determine the surface tension and the critical temperature for the separation of two immiscible liquid phases simultaneously.