Joining of copper at low temperatures using silver(I) carboxylates

The synthesis of three different Ag(I) carboxylates [(AgO2CCH2)3N] 1, [(AgO2C)2C5H8] 2, and [AgO2CC19H29] 3 and their suitability for joining of pure copper at low temperatures is reported. Upon heating silver(I) species 1–3, Ag nanoparticles are formed. Since nanoparticles exhibit a decreased melting and sintering temperature, low joining temperatures are possible. Major advantages of the Ag(I) carboxylates in comparison to conventional nanopastes are a low-cost synthesis, long-term stability, and simplified handling of the material. Besides description of the synthesis, the thermal behavior of 1–3 is discussed. Moreover, results of joining experiments, whereby the joints were characterized regarding to strength properties and microstructure, are discussed. The results show that with 1–3, partly equivalent strength properties, compared to a commercial Ag nanopaste, can be achieved. For pressureless joining, 1 and 2 represent a promising alternative to a conventional Ag nanopaste, since equivalent strengths can be reached. In particular, with 1, higher strengths can be achieved compared to the Ag nanopaste at a temperature of 250 °C and without pressure. However, at a higher temperature of 400 °C and a pressure of 40 MPa, strengths of the Ag nanopaste can be reached with 2 (with additives) and 3.