Effect of Zn and Sb Additions on the Impression Creep Behavior of Lead-Free Sn-3.5Ag Solder Alloy

Abstract

The effect of separate additions of 1.5 wt.% Zn and 1.5 wt.% Sb on the creep behavior of Sn-3.5 wt.% Ag lead-free solder alloy was investigated by impression testing. The tests were carried out under constant punching stresses in the range of 60–120 MPa and at temperatures in the range of 298–370 K. Both of the ternary alloys showed creep resistances higher than that of the eutectic binary Sn-3.5Ag alloy. The superior creep resistance of the ternary Sn-3.5Ag-1.5Sb alloy is attributed to the strong solid solutioning effect of antimony in the tin matrix, while the formation of AgZn particles and refinement of the Ag3Sn precipitates account for the higher creep resistance of the Sn-3.5Ag-1.5Zn alloy. The average stress exponents of 8.2, 8.5, and 8.6 and activation energies of 47.4 kJ mol−1, 45.3 kJ mol−1, , and 43.3 kJ mol−1 were obtained for Sn-3.5Ag, Sn-3.5Ag-1.5Zn, and Sn-3.5Ag-1.5Sb, respectively. These activation energies are close to 46 kJ mol−1 for dislocation pipe diffusion of tin. This, together with the stress exponents of 8.2–8.6, suggests that dislocation climb controlled by dislocation pipe diffusion is the predominant creep mechanism in these alloys.