The effect of Bi/Sn ratio of Bi-Sn-Ag solder on the mechanical and electrical properties of interfaces between solder/thermoelectric material and solder/electrode

The properties of solder junction in the thermoelectric (TE) module can significantly affect the electrical and mechanical properties of the whole module. In order to study the mechanical and electrical properties of the Bi-Sn-Ag solder junction of a TE module, the effect of Bi/Sn ratio in the Bi-Sn-Ag solder (at the interfaces of solder/TE materials and solder/electrode) was investigated. Dynamic contact angles were measured by the real-time imaging of droplets to investigate the wettability of the Bi-Sn-Ag solders with different Bi/Sn ratios on the Bi₂Te₃ and Au. The scratch test using a stylus under a constant load was carried out to evaluate adhesion properties of the solders. The contact resistances of the interfaces between the solders and the Bi₂Te₃ were measured to assess the effect of the solder composition on the electrical properties of the interfaces. As the Bi/Sn ratio of the Bi-Sn-Ag solder increased, the wettability and the degree of adhesion were improved. The contact resistances were decreased with the increase of the Bi/Sn ratio. The increase of the amount of Bi in the Bi-Sn-Ag solder was found to improve the mechanical and electrical properties of the solder junction of a thermoelectric module.