Effect of silver content and nickel dopant on mechanical properties of Sn-Ag-based solders

In this work, five solder materials of Sn-3.0Ag-0.5Cu (SAC305), Sn-2.0Ag-0.5Cu (SAC205), Sn-1.0Ag-0.5Cu (SAC105), Sn-1.0Ag-0.5Cu-0.05Ni (SAC105Ni0.05) and Sn-1.0Ag-0.5Cu-0.02Ni (SAC105M0.02) were tested using tensile loading at room temperature to investigate the Ag content and Ni dopant effect on solder mechanical properties, respectively. In addition, different testing temperature conditions including -35 deg.C, 25 deg.C, 75 deg.C and 125 deg.C were used for SAC105M0.02 solder to investigate the temperature effect on mechanical properties. Tensile test under different strain rates from 0.000011/s to 0.11/s was conducted to study the strain rate effect on material properties. Test results show that the material properties of modulus, UTS and yield stress increase with strain rate and Ag content, but decrease with temperature. The 500 ppm Ni dopant has the significant effect on material properties of Sn-Ag-based solder than 200 ppm Ni dopant. Lower modulus, yield stress and UTS, higher elongation can be achieved for SAC105M0.05 solder compared to SAC105M0.02 solder. The rate dependent and Ag content dependent material models were developed for Sn-Ag-Cu lead free solders. In addition, the temperature and rate dependent models were developed for SAC105M0.02 solder. The microstructures of different solder alloys were analyzed based on SEM images. It was found that Ag content affects the Ag₃Sn intermetallic compound dispersion and Sn grain size. The microstructure of solder alloy has finely dispersed IMC and fine Sn grain size for the high Ag content solder, which make the solder exhibit high strength.