Enhanced pressure-free bonding using mixture of Cu and NiO nanoparticles

Pressure-free bonding using mixed Cu-NiO nanoparticles was examined. The effect of mixing NiO nanoparticles with Cu nanoparticles on bonding strength was identified for a NiO content between 0.005 and 2 wt%. The bonding layer, which presented a high bonding strength, was thin and dense. The Ni in the bonding layer was segregated at the surface and at grain boundaries of crystalline Cu grains as a metallic Cu-Ni alloy. These results suggest that the effect of the NiO addition is caused by the enhancement of sintering by surface diffusion in the bonding layer, resulting from sufficient removal of surface oxides on the Cu nanoparticles through their reaction with the NiO nanoparticles.