Interfacial reactions between diffusion barriers and thermoelectric materials under current stressing

This study investigates the stability of the interfaces between an n-type thermoelectric material, Bi₂Te₃, and pure tin solders in a thermoelectric module. The module was stressed by a current at elevated temperatures. A map of the failure criteria of the module was constructed. Ni was used as the diffusion barrier between the solder and the thermoelectric materials, but it reacted with these materials and formed intermetallic compound (IMC) layers. The phase transformation of the IMC layers formed voids at the interfaces and reduced the strength of the joints. Current stressing promoted the formation of IMC. The kinetics of the compound growth was studied. The results suggested that the formation of NiTe IMC was successfully inhibited, but the Bi₄Te₅ compound grew from an infinitely adaptive series of (Bi₂)_m(Bi₂Te₃)_n because of the depletion of Te.