| Thermoelectric (TE) device has attracted much attention in solid-state cooling andpower generation due to its unique features such as friendliness to the environment,highly reliability with no moving parts, and noiseless operation. The efficiency andreliability of TE device are determined basically not only by the materials with highfgure of merit, but also by the fabrication factors. And the most popular failure part inTE device was found to be the solder joint between the thermoelectric element andelectrode.During aging period (180℃), the diffusion barrier layer Ni was consumed by boththermoelectric material P-type Bi0.5Sb1.5Te3and N-type Bi1.8Sb0.2Se0.15Te2.85. Nireacted with Bi0.5Sb1.5Te3and Bi1.8Sb0.2Se0.15Te2.85to produce NiTe and Ni (Bi,Te).The consumption rates were0.029μm/h and0.026μm/h, respectively. Besides,microstructure of the thermoelectric device interface changed greatly. Many voids thatreached about4-5μm appeared at the interface of IMC NiTe and thermoelectricmaterial Bi0.5Sb1.5Te3. In addition, shear stress of P-type thermoelectric material jointschanged significantly. When the aging time reached800h, the strength reduced to7.59MPa. The N-type thermoelectric joints followed the similar trends. What is more,the fracture modes of the both thermoelectric joints have changed.At260℃, the major products in SAC305/Bi0.5Sb1.5Te3couple reaction wereinitially SnTe and SbSn. With the reaction time increasing, a two-phase layer, whichwas SnTe-SbSn mixture with pores with200-500nm size，appeared next to the denselayer. However, the reaction products did not change significantly; the growth ratewas about4.05μm/min. As for the SAC305/Bi1.8Sb0.2Se0.15Te2.85couple reaction,besides SnTe phase, Bi-Te phase was also formed at the solder/Bi1.8Sb0.2Se0.15Te2.85interface. As the reaction time increased, the morphology of IMC layer became rough,and then a stable scallop-type IMC appeared; the growth rate was about0.39μm/min. |
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