The effect of iron and bismuth addition on the microstructural, mechanical, and thermal properties of Sn-1Ag-0.5Cu solder alloy

This work investigates the effect of Fe and Bi addition, 0.05 wt.% Fe and 1 wt.% or 2 wt.% BL on the microstructural, mechanical, and thermal properties of the low silver Sn-1Ag-0.5Cu (SAC105) solder alloy. Adding Bland Fe to SAC105 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. While 0.05 wt.% Fe made few FeSn2 in the solder bulk which 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 SAC105-Fe solder alloy, thereby increased beta-Sn and degenerated Cu6Sn5 and Ag3Sn into a chain-like arrangement. Surface fracture of SAC-Fe-Bi solder alloys showed brittle fracture because Bi prevented beta-Sn to deform and therefore Bi decreased its ductility. Finally, Bi significantly reduces the melting point and undercooling. (C) 2015 Elsevier Ltd. All rights reserved.