ICT2014 Abstracts

Soldering is a widely-used method to connect metallic conductor such as Cu with thermoelectric (TE) materials. The intermetallic compounds (IMCs) formed between solder and TE materials may deteriorate the thermoelectric and mechanical properties of TE modules. In this paper, electroplated Co-P film was used as a diffusion barrier between bulk SiC-dispersed Bi₂Te₃ and In-48Sn solder. SiC-dispersed Bi₂Te₃ coated with 6 µm thick Co-P film was used as substrate, which was joined with In-48Sn solder by reflow process. The IMCs formed at the interface between In-48Sn and substrate were examined using SEM and EDS. Samples annealed at 375 K up to 625 h were used to study the evolution and growth kinetics of IMCs. The results showed that at the interface Co(In,Sn)₃ formed as an irregular layer adjacent to the side of solder due to the diffusion of Co towards solder, and a small amount of Co-In-Sn-P formed at the side of Co-P because of the diffusion of In and Sn into Co-P. The growth rates of the two IMCs were small and controlled by interfacial reaction. For comparison, In-48Sn/Bi₂Te₃ joints were also prepared and the formation of IMCs was analyzed. Without diffusion barrier, In penetrated rapidly into the substrate and led to the formation of Bi-rich and In-rich phases. These IMCs grew fast with increasing annealing time, and their growth rates were limited by volume diffusion of elements. The experimental data clearly demonstrate that Co-P film can be an effective diffusion barrier used in TE modules.