Development of Cu-Ag pastes for high temperature sustainable bonding

Abstract

The combination of excellent electrical conductivity and low cost makes copper a good selection for interconnect materials. However, rapid oxidation of Cu nanoparticles especially at high temperatures is a fatal demerit. To improve the oxidation resistance and realized mass production, Cu@Ag core-shell submicron particles were prepared using commercial copper oxide particles through a low temperature reduction method and subsequent electroless-plating to form Ag shells. Thermal analytical results suggest that Ag coated Cu particles show improved anti-oxidation ability. Mixed with Ag submicron particles obtained from thermal spray pyrolysis, the electrical resistivity of the sintered Cu-Ag composite pastes reaches 10.4μΩcm under a reductive atmosphere. Under the bonding pressure of 10MPa at 275°C for 30min, robust Cu to Cu bonding can be achieved with the Cu-Ag composite pastes, for which the shear strength of the joints reaches 32.7MPa, and it remains 28.2MPa as the bonding pressure is reduced to 5MPa. It was also demonstrated that the joints thus formed have superior elevated temperature strength, and excellent reliability subjected to high temperature storage at 250°C as well as thermal cycling ranged from −65°C to 150°C.