Co-P Diffusion Barrier for p-Bi₂Te₃ Thermoelectric Material

(Bi_0.25Te_0.75)₂Te₃ (p-Bi₂Te₃) is thermoelectric material that can harvest waste heat into useful electric power. A severe reaction between p-Bi₂Te₃ and Sn-based solder decreases the reliability of thermoelectric modules. Sn/p-Bi₂Te₃ and Sn3.0Ag0.5Cu (SAC305)/p-Bi₂Te₃ with and without electroless Co-P at the interfaces were investigated in this study. Without a Co-P layer, brittle SnTe, Sn₃Sb₂, and Bi precipitates formed at the interface. A thin layer of SnTe after reflow results in growth of a layer-type Sn₃Sb₂ instead of a strip-like Sn₃Sb₂. The addition of a Co-P layer to both systems successfully inhibited the formation of brittle intermetallic compounds. Shear test results confirmed that the Co-P diffusion barrier also effectively increased the joint strength.