Effect of different sizes of Cu nanoparticles on the shear strength of Cu-Cu joints

•A novel mixed Cu nanoparticles of 20nm and 100nm paste was investigated.•The optimized mass ratio of (20nm : 100nm) was proposed.•The joints showed a high bonding strength of over 15MPa at 250°C and 4MPa. In order to enhance the bonding strength of joints by using Cu nanoparticles paste at a relative low bonding temperature and a suitable pressure, a novel mixed Cu nanoparticles of 20nm and 100nm (in diameter) paste for Cu-Cu joints was investigated in this study based on the density increment of packing two different sizes of spheres. The optimized mass ratio of 20–100nm nanoparticles for maximum sintering density was proposed (9/1) by simulation and experiments. The bonding strength of joints over 15MPa was achieved even at a lower bonding temperature of 250°C and pressure of 4MPa.