Influence of Zn addition on the microstructure, melt properties and creep behavior of low Ag-content Sn-Ag-Cu lead-free solders

The effects of Zn addition on the microstructure, thermal behavior and tensile creep properties of Sn-1.0Ag-0.3Cu (SAC103) alloy were systematically investigated. Differential scanning calorimetry (DSC) reveals that the reductions of undercooling and pasty range are more significant for Zn-containing solders, although the solidus temperature remains the same or slightly changed. The creep life time of plain SAC103 alloy was remarkably enhanced two times with the addition of 3 wt% Zn. Moreover, significant improvement in creep resistance of 145% and 360% is realized with the addition of 2 wt% and 3 wt% Zn into SAC(103) solder, respectively. The improvement of creep behavior is due to the microstructural change of Zn-containing solders, since the formation of new (Cu,Ag)5Zn8 intermetallic compound (IMC) phase and fine fiber-like Ag3Sn precipitates at the surface of β-Sn matrix could provide more obstacles for dislocation pile-up, which enhanced the stress exponent values and improved the creep resistance and creep life time. These results show that the Garofalo model is suitable for describing the steady-state creep behavior of SAC(103) solders over the tested stress and temperature ranges.