Phase equilibria studies of Sn-Ag-Cu eutectic solder using differential cooling of Sn-3.8Ag-0.7Cu alloys

This paper is a study of the phase equilibria of the Sn-3.8Ag-0.7Cu alloy investigated by a differential cooling method. The difficulty in assessing phase equilibria of the Sn-Ag-Cu (SAC) system because of the insufficient resolution of conventional characterization techniques is solved by inducing preferential growth of a solid phase in a melt by holding the alloy at the solid-liquid phase-equilibrium field. Application of the technique to Sn-3.8Ag-0.7Cu with varying holding temperatures yielded results that the alloy is slightly off eutectic composition. The phase-formation sequence of the alloy during solidification was found to be Ag3Sn, β-Sn, and finally the ternary eutectic microstructure.