Rapid pressureless and low-temperature bonding of large-area power chips by sintering two-step activated Ag paste

Pressureless and low-temperature sintering of Ag paste has been mentioned as a promising strategy to solve the poor performance of large-area chips. In this paper, we develop a two-step surface activation process to achieve rapid pressureless and low-temperature bonding of Cu in air using a micron-scale Ag paste for large-area chips. The organics that adsorb on the Ag particles are initially removed by oxygen plasma cleaning, and the silver oxide byproducts are subsequently deoxidized by a methanol/hydroxide mixed vapor treatment. The two-step activation significantly improves the sinterability of the micron-scale Ag paste, leading to excellent interfacial properties after rapid sintering at 200 degrees C for only 10 min in air. Robust-bonded joints are achieved with a shear strength and thermal conductivity that are four times higher than those of the non-activated bonded joints. The bonding strength and thermal conductivity of the Cu joint structure are approximately 25 MPa and 96 W/mK, respectively, which are superior to those of traditional Sn-Pb solders. Void-free bonding interfaces are confirmed by large-area chips even without pressure in air; this method shows great potential for the cost-effective commercial packaging of power electronics.