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.