Indentation Creep of Lead-Free Sn-5Sb Solder Alloy with 1.5 wt% Ag and Bi Additions

Creep behavior of the ternary Sn-5Sb-1.5Ag and Sn-5Sb-1.5Bi alloys was studied by indentation testing at 298 and 370 K, and compared to that of the binary Sn-5Sb base alloy. Among all tested materials, as indicated by their minimum creep rates, Sn-5Sb-1.5Bi showed the highest creep resistance followed by Sn-5Sb-1.5Ag and Sn-5Sb. The superiority of the Bi-containing alloy is mainly due to the microstructural refinement and solid solution hardening effects of Bi in the Sn matrix, while the improvement in the creep resistance of the Ag-containing alloy is caused by the formation of spherical and rod-shaped Ag3Sn particles. The stress exponent values in the range 11.0-12.2 are close to those determined by tensile and impression creep testing of the same alloys reported in the literature. These high stress exponents together with the activation energies of 58-70 kJ/mol may suggest that the dominant creep mechanism is dislocation creep.