Coupled effect of Ag and In addition on the microstructure and mechanical properties of Sn–Bi lead-free solder alloy

Abstract

The microstructure and mechanical properties of Sn–Bi solder alloys with various Ag and In addition are comparatively investigated. The results illustrate that the tensile strength and ductility of the solder alloy could be dramatically enhanced with negligible loss of the plasticity. Especially, the Sn–Bi solder alloy with 0.4 wt. % Ag and 1.5 wt. % In exhibits the maximum tensile strength and elongation of 79.7 MPa and 45.9%, respectively. The microstructure of the Sn–Bi solder alloys is mainly composed of Bi-rich and β-Sn phases. With the addition of elements Ag and In, the microstructure is significantly refined, and the lamellar eutectic structure with thinner interlayer spacing could be detected. Element Ag tends to form Ag3Sn phase while element In solutes in the Sn matrix. The mechanical properties of the as-prepared Sn–Bi solder alloy are improved attributed to the precipitated-phase strengthening of the fined Ag3Sn phase and the refinement effect of In on coarse Bi-rich phase.