Thermal Stability of Electroless NiP Diffusion Barrier on BiTe-Based Thermoelectric Materials

Abstract

To produce BiTe-based thermoelectric modules, BiTe-based species with an electroless NiP (EN) coating layer acting as a diffusion barrier were connected to Cu electrodes by a soldering process. In order to investigate the thermal stability of the EN diffusion barrier on BiTe-based thermoelectric materials, Ni-coated BiTe-based modules were annealed at 200 °C for 200, 500, and 1000 h. The bonding strength of the BiTe species was >8 MPa, and it remained stable after 200, 500, and 1000 heating hours. The interfacial structure indicated the formation of a Sn–Cu intermetallic compound (IMC) below the EN-plated region. The morphology of Sn–Cu IMC before and after heating was observed. As the current flow was applied through the BiTe-based thermoelectric module, the temperatures on the hot and cold side of the modules were recorded. Owing to the thermal stability of the EN layer, the 200 h heated modules presented heating and cooling efficiencies similar to those of non-heated modules.