Investigation of the Interfacial Reactions between the CoCuFeNi High Entropy Alloy and Sn Solder

Abstract

The CoCuFeNi high entropy alloy (HEA) has excellent electrical, thermal, and mechanical properties. In electronic packaging technology, Sn is the major element of lead-free solders. In this study, we used the CoCuFeNi HEA as the substrate and Sn as the solder and investigated the liquid/solid interfacial reactions of the Sn/CoCuFeNi system at 300, 375, and 450 °C for 30, 60, 100, 150, 360, and 480 min. The results indicated that the (Fe, Co)Sn2 phase was formed in the Sn/CoCuFeNi couples for all various reaction temperatures and at different durations. Additionally, the (Co, Ni)Sn2 phase was precipitated at the solder side and near the (Fe, Co)Sn2 phase when the reaction time increased. The thickness of the (Fe, Co)Sn2 phase increased with the increase in reaction temperature and time, and it was proportional to the square root of the reaction time. Overall, our results showed that the growth mechanism of the (Fe, Co)Sn2 phase was diffusion-controlled in the Sn/CoCuFeNi couples.