Sintered Nano-Ag as Joining Material for Thermoelectric Modules

Abstract

The use of sintered silver particles as an alternative to other types of joining materials for the electrical connection between thermoelectric materials and the substrate in thermoelectric modules (TEM) has been investigated. Sintered silver particles have recently gained attention in the field of power electronics due to the high thermal and electrical conductivity of the material. The nanosilver paste used in this work has originally been developed for use as a die attach material, where these properties are important. The sintering process involved a thermal treatment at 310 °C, under a 15 kg mechanical load, in a nitrogen atmosphere. Sample TEMs with sintered silver connections were tested both mechanically and electrically. Initial results showed that the TEMs performed well during thermal gradient tests with the hot side heated from 50 °C to 550 °C and the cold side kept at 20 °C. This performance also indicates that the nano-Ag joints have good contact resistance. The resistivity of the sintered silver joints were measured at room temperature to ρ = 15 μΩ m (average value of Ti/Au plated thermoelectric legs). Shear force tests of the sintered thermo electrical leg material showed that the joints are brittle when W metallized AlN substrates were used and these have an average shear strength of 3.3 ± 1.9 MPa. On Cu metallized AlN substrates, ductile fracture behavior was observed and an average shear strength of 2.4 ± 1.4 MPa was measured.