Interface evolution analysis of graded thermoelectric materials joined by low temperature sintering of nano-silver paste

Lead free solder Sn96.5Ag3.0Cu0.5 (SAC305) and nano-silver paste were used to connect graded thermoelectric (TE) arms, respectively. A series of harsh aging tests were carried out on joints of both p-type and n-type graded TE arms. The results showed that nano-silver paste printed by low-temperature joining technique was much more suitable for the stable connection of TE materials working in medium temperature range. 316 stainless steel and nickel were proved effectively as diffusion barrier layers in p-type junctions. While for n-type TE junctions, when aging at 300 °C, (Fe, Cr, Te) ternary alloy could be detected at Bi2Te2.7Se0.3/316 stainless steel interface. The formation of ternary compound realized fine metallurgical interconnection which was benefit for the improvement of joint strength. The average joint strength for p-type and n-type junctions in graded TE arms were above 20 MPa and 30 MPa, respectively.