Mechanical property optimization of Sn-1.5Ag-0.5Cu solder alloys with additions of Bi, In, and Te

Abstract

The mechanical characteristics of Sn-1.5Ag-0.5Cu (SAC155) alloy modified with In, Bi, and Te microalloying are investigated in relation to three strengthening mechanisms that withstand coarsening: i) micron-scale Ag3Sn, Cu6Sn5, SnTe, Ag2In and InSn4 IMC precipitated phases, ii) Bi in solid solution and iii) Bi precipitated particles formed upon eutectic solidification. Compared to SAC155 alloy with a single strengthening mechanism, the combined effect of threedeformation processes operating in SAC(155)-3Bi-2In with high In content and SAC(155)-3Bi-0.2Te (wt%) with low Te content alloys greatly improved the mechanical properties at high temperatures. It was found that, despite a discernible reduction in ductility, the high In content could refine the microstructure,enrich the elastic modulus (E), yield stress (YS), and ultimate tensile strength (UTS) of SAC(155)-3Bi-2In to almost 2.3 times that of SAC155 solder. On the other hand, a low Te content greatly increased SAC(155)-3Bi-0.2Te's mechanical strength ⁓2.3 times, while a large atomic size difference between Te and Sn atoms caused excessive misfit strain, which in turn increased Bi's solubility in β-Sn grains, and improved ductility by approximately twice that of SAC(155)-3Bi-2In solder.