A novel lead-free solder alloy with high strength-ductility by doping rare Bi and Zr into SnAgCu solder alloy

The rapid development of electronic information technology drives the miniaturization, high density and multifunctionality of electronic products, imposing intense demands for lead-free solder with high performance. At the present study, a lead-free solder alloy with high strength-ductility synergy is achieved by doping rare Bi and Zr into Sn-3.0Ag-0.5Cu (SAC305) solder alloy. First-principles calculation and electron back-scattered diffraction are used to analysis the effects of Bi and Zr doping on the mechanical properties. Doping 2wt.% Bi into SAC305 increases the ultimate tensile strength (UTS) due to the solid solution strengthening effect of Bi, but reduces the elongation to failure. While the UTS and elongation to failure are both enhanced by the further addition of 0.2wt.% Zr, since the strong interaction between Sn and Zr promotes the nucleation of Sn and refines Sn grains, which plays grain refinement strengthening effect on the solder alloy. The UTS of SAC305-2Bi-0.2Zr solder alloy reaches up to 71.27 MPa and the elongation to failure is 48.42%. Additionally, the melting point of the SAC305-2Bi-0.2Zr is lower than that of SAC305, while the contact angle shows no apparently difference.