Ni–W–P layer-induced strength improvement of solder joint in Bi₂Te₃ thermoelectric module

In this study, we examined the thermal stability, bonding strength, and interfacial characteristic of a Ni–W–P coating applied for solder joint of Bi₂Te₃ thermoelectric modules. This layer had uniform thickness and was confirmed to be amorphous even after annealing at 200°C for 150 h, demonstrating its thermal stability. Moreover, the barrier layer hindered the interdiffusion between Sn and Te, eliminating the formation of brittle intermetallic at the solder joint. Thus, the bonding strengths of p- and n-type thermoelectric units were improved approximately 1.3- and 2.8-fold, respectively, compared to the bonding strengths obtained without a Ni–W–P layer. In addition, the bonding strength was not affected by heating at 200°C for 150 h. The reliability of bonding strength was caused by the excellent thermal stability, and solder wettability of the barrier layer, which resulted in a bonding interface without brittle intermetallic and defects.