Intermetallic Reactions during the Solid-Liquid Interdiffusion Bonding of Bi₂Te_2.55Se_0.45 Thermoelectric Material with Cu Electrodes Using a Sn Interlayer

Author： Chuang Chien-Hsun Lin Yan-Cheng Lin Che-Wei

Publisher： MDPI

E-ISSN： 2075-4701|6|4|92-92

ISSN： 2075-4701

Source： Metals, Vol.6, Iss.4, 2016-04, pp. : 92-92

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Abstract

The intermetallic compounds formed during the diffusion soldering of a Bi₂Te_2.55Se_0.45 thermoelectric material with a Cu electrode are investigated. For this bonding process, Bi₂Te_2.55Se_0.45 was pre-coated with a 1 μm Sn thin film on the thermoelectric element and pre-heated at 250 °C for 3 min before being electroplated with a Ni barrier layer and a Ag reaction layer. The pre-treated thermoelectric element was bonded with a Ag-coated Cu electrode using a 4 μm Sn interlayer at temperatures between 250 and 325 °C. The results indicated that a multi-layer of Bi–Te–Se/Sn–Te–Se–Bi/Ni₃Sn₄ phases formed at the Bi₂Te_2.55Se_0.45/Ni interface, ensuring sound cohesion between the Bi₂Te_2.55Se_0.45 thermoelectric material and Ni barrier. The molten Sn interlayer reacted rapidly with both Ag reaction layers to form an Ag₃Sn intermetallic layer until it was completely exhausted and the Ag/Sn/Ag sandwich transformed into a Ag/Ag₃Sn/Ag joint. Satisfactory shear strengths ranging from 19.3 and 21.8 MPa were achieved in Bi₂Te_2.55Se_0.45/Cu joints bonded at 250 to 300 °C for 5 to 30 min, dropping to values of about 11 MPa for 60 min, bonding at 275 and 300 °C. In addition, poor strengths of about 7 MPa resulted from bonding at a higher temperature of 325 °C for 5 to 60 min.