LAUSR

Abstract In this study, an electroless nickel (EN), electroless palladium (EP), and immersion gold (IG) (ENEPIG) multilayer coat was developed for application on BiTe-based thermoelectric materials to increase the bonding strength between BiTe-based materials and Cu electrodes in thermoelectric modules. The ENEPIG-plated thermoelectric module exhibited a bonding strength of over 11 MPa, which was approximately 40% higher than those of conventional EN-plated modules. According to the interfacial analysis of the bonding areas via a field emission electron probe micro analyzer (FE-EPMA), the Ni layers in ENEPIG and EN acted as diffusion barriers to inhibit the formation of brittle Sn-Te intermetallic compounds (IMCs). Sn-Cu-Pd and Sn-Cu IMCs were formed below the Ni-plated area at the bonding interface of the ENEPIG and EN-plated modules, respectively. However, Sn-Cu-Pd IMCs in the ENEPIG interface exhibited thicker and more homogeneous IMC layers after heat treatment compared to the Sn-Cu IMCs in the conventional EN interface. The wettability of the ENEPIG-plated BiTe surface was significantly greater than that of the EN-plated surface. This directly induced fewer and smaller pores on the bonding interface of the BiTe-based materials with ENEPIG plating compared to those with EN plating, thereby resulting in the higher bonding strength of ENEPIG-plated modules.