Influence of Ni and Cu electrodeposits on the interfacial reaction between SAC305 solder and the Bi2(Te,Se)3 thermoelectric material

Abstract

This research systematically investigated three joint systems (SAC305/Bi2(Te,Se)3, SAC305/Ni/Bi2(Te,Se)3 and SAC305/Cu/Bi2(Te,Se)3) and compared the influence of Ni and Cu electrodeposits on the interfacial reaction. The thermoelectric material possessed an isotropic microstructure, and hence its surface had no significantly effects on deposited direction of Ni or Cu atoms. The crystal orientations of Ni and Cu grains were indexed to be (111) and (200), and no noticeable impure products were formed in these two electrodeposits. Compared with the defective Cu plating, fully crystallization of the Ni plating was more beneficial to the spreadability of solder, and this advantage could dramatically promote the reliability of solder joints. Under aging treatment at 160 °C for various hours to 360 h, heterogenetic compounds grew excessively in the SAC305/Bi2(Te,Se)3 couple, which could result in brittle failure. This reliability of this joint system was improved by depositing Ni or Cu on the substrate. However, the poor interfacial contact between the Cu coating and TE substrates severely resulted in the deterioration of mechanical properties of solder joints. In contrast, the SAC305/Ni/Bi2(Te,Se)3 system were more reliable during the whole aging period.