The bulk alloy microstructure and mechanical properties of Sn-1Ag-0.5Cu-xAl solders (x=0, 0.1 and 0.2 wt. %)

This work investigates the effects of 0.1 and 0.2 wt. % Al additions on bulk alloy microstructure and tensile properties as well as on the thermal behavior of Sn-1Ag-0.5Cu (SAC105) lead-free solder alloy. The addition of Al reduces the amount of Ag3Sn intermetallic compound (IMC) particles and leads to the formation of larger Al-Ag IMC particles. Moreover, the addition of Al suppresses the formation of Cu6Sn5 IMC particles and leads to the formation of larger Al-Cu IMC particles. The Al added solders show a microstructure with large primary beta-Sn grains. The tensile tests show that the 0.1 wt. % Al addition reduces the elastic modulus, yield strength and ultimate tensile strength (UTS). However, the 0.2 wt. % Al addition brings the yield strength up to SAC105 level and the UTS up to level slightly higher than that of SAC105, while its effect on reducing the elastic modulus becomes less dependent compared with the 0.1 wt. % Al addition. Moreover, both 0.1 and 0.2 wt. % Al additions deteriorate the total elongation. The two additions of Al slightly increase the solidus and liquids temperatures, while slightly reduce the pasty range, hence allowing the use of the Al-containing Sn-1Ag-0.5Cu alloys, to be consistent with the conditions of usage for conventional Sn-Ag-Cu solder alloys.