Viscoplastic characterization and mechanical strength of novel Sn–1.7Ag–0.7Cu lead-free solder alloys with microalloying of Te and Co

A persistent dream in lead-free Sn–Ag–Cu solder community is to attain both high strength and ductility for the design and reliability of soldered joints. Microalloying Te or Co has been anticipated to modify the low Ag-content Sn–1.7Ag–0.7Cu solders in different aspects. This research investigates the effect of minor additions of Te and Co on the development of solidified microstructure, thermal and tensile properties of Sn–1.7Ag–0.7Cu solders alloys. It is seen that trace amount of Te addition (0.2 wt%) results in the formation of SnTe intermetallic (IMC) and increasing eutectic microstructure, whereas a minor amount of Co (0.5 wt%) is completely changed the solidification mode. Microalloying Co refines the Cu₆Sn₅ and Ag₃Sn particles and leads to formation of more stripe-like (Cu, Co)₆Sn₅ morphology together with Co₃Sn. These effects were significantly enhanced both the high strength by ~ 16% and ductility by ~ 72% at 110 °C, respectively, which play a vital role in drop impact implementation development. Moreover, Te or Co-microalloying could severely modify the growth restriction factor of SAC177 solder and markedly reduce the degree of undercooling of SAC177 from 17.8 to 11.6 and 2.6 °C, respectively. The utility of this research was demonstrated by design of lead-free micro-joints that simultaneously exhibit high-reliability with low cost.