Wetting and IMC Growth Behavior Between Cu Substrate and Zn-25Sn-xCu-yTi High-Temperature Solder Alloys

One of the suitable candidates to replace conventional high-temperature Pb-containing solders is Zn-xSn solder alloy. However, its high Zn content may cause poor wettability. Addition of Cu and Ti has been proposed to improve the wettability of Zn-25Sn solder alloy. This study investigated the wetting and intermetallic compound (IMC) formation behavior between Zn-25Sn-xCu-yTi solder alloys (x = 0.1 wt.% to 0.3 wt.%, y = 0.01 wt.% to 0.03 wt.%) and Cu substrate. The wetting behavior was investigated using a wetting balance with flux at a temperature ∼ 40°C above the liquidus temperature of Zn-25Sn solder. The results indicated that combined addition of 0.3 wt.% Cu and 0.03 wt.% Ti gave rise to the best performance in terms of wetting time and wetting force. CuZn₅ and Cu₅Zn₈ IMCs formed at the solder–Cu interface, with Cu₅Zn₈ being the predominant layer. Cu₅Zn₈ also grew much faster than CuZn₅ with respect to dipping time. Combined addition of Cu and Ti also decreased the activation energy for Cu₅Zn₈ IMC formation in the Zn-25Sn system.