Low-temperature soldering using Sn/Bi electrodeposited bilayer

Low-temperature soldering is a joining technology that attracts considerable attention in recent years due to its potential in energy saving and carbon reduction. Eutectic SnBi alloy is a common low-temperature solder. The material manufacturing using cost-effective electrodeposition suffers from composition control problem caused by very different reduction potentials between Sn and Bi. In this study, a Sn/Bi bilayer structure is constructed using electrodeposition and the microstructural evolution under thermal annealing is investigated in detail to evaluate its potential in replacement of eutectic SnBi alloy. Results show that interfacial liquation occurs rapidly in the Sn/Bi bilayer structure heated at 180 °C for only 5 s, and the bilayer structure completely transforms into a eutectic-like structure after 30 s. The microstructural evolution history is established with the help of phase diagram and electron microscopy examination. Shear test results indicate that the eutectic-like structure exhibits good mechanical property comparable to commercial eutectic SnBi solder paste. The rapid phase transformation feature and high shear strength make the Sn/Bi bilayer structure a promising candidate for low-temperature joining applications.