Abstract: Ag-Cu bimetallic nanoalloy, integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu, is a prospective bonding material for power electronic packaging. The Ag-coated Cu nanoparticles (Cu@Ag NPs) paste can execute bonding with high quality at 250 °C, and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength (152 MPa) dramatically exceeds most nano-paste joints. The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength. Besides, the numerous ultrafine nanograin, high proportion of low angle grain boundaries (7.44%) without deformation, and the Cu nanoprecipitates in the joint would improve subordinately. Furthermore, the high content (16.8%) of Σ3 twin boundaries would contribute to the electrical and thermal conductivity. Thus, the multiple strengthening mechanisms with the solid solution, the second precipitated phase, and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.

Key words: Supersaturated Ag-Cu solid solution, Cu nanoparticle precipitates, Ultrafine nanograin, Strengthening mechanism, Electronic packaging