EFFECT OF AGING ON MECHANICAL PROPERTIES OF Sn-Cu-Fe-Bi SOLDER ALLOY

Abstract

The current work study the effect of Fe and Bi addition, 0.05wt% Fe and 1wt% or 2wt% Bi, on the microstructural and mechanical properties of the Sn-0.7Cu (SC07) solder alloy. The addition of Fe and Bi to SC07 increased ultimate tensile strength (UTS) and yield strength and decreased the total elongation which is related to solid-solution and precipitation strengthening effects by Bi in the Sn-rich phase. Minor addition of Fe does not have considerable effect on mechanical properties. Scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) showed that Bi strengthen solder by scattering in the bulk of SC07-Fe solder alloy, thereby increased β-Sn and degenerated Cu6Sn5 into a chain-like arrangement. After aging due to IMCs coarsening UTS and yield strength decreased for SC07 and SC07-Fe. Total elongation for SC07 and SC07 Fe increased. However, for sample with Bi, UTS, Yield strength and total elongation are approximately constant, because Bi prevent the Cu and Sn to interact with each other, therefore spheroidization and growth of IMCs slowed down and decreased the rate of IMCs coarsening.