Diffusion Soldering of Pb-Doped GeTe Thermoelectric Modules with Cu Electrodes Using a Thin-Film Sn Interlayer

Directly coating a GeTe(Pb) thermoelectric device with a Ni barrier layer and an Ag reaction layer and then diffusion soldering with a Cu electrode coated with Ag and Sn leads to breakage at the GeTe(Pb)/Ni interface and low bonding strengths of about 6 MPa. An improved process, precoating with 1 μm Sn film and heating at 250°C for 3 min before electroplating with Ni and Ag layers, results in satisfactory bonding strengths ranging from 12.6 MPa to 19.1 MPa. The precoated Sn film leads to the formation of a (Ni,Ge)3Sn4 layer between the GeTe(Pb) thermoelectric material and Ni barrier layer, reducing the thermal stress at the GeTe(Pb)/Ni interface.