The application of direct bonding method for Cu to silicon nitride bonding was investigated. Silicon nitride was sintered with 5 wt.% MgO at 1700$^\circ{C}$ for 30min in nitrogen atmosphere, and oxidized at various temperature. The bonding was performed at 1075$^\circ{C}$ in nitrogen atmosphere with low oxygen partial pressure.
In this experiment the direct bonding was not achieved for the silicon nitride oxidized below 1200$^\circ{C}$. During oxidation, Mg added as sintering aid, diffused out to the surface and formed $MgSiO_3$, which seemed to have an important role in the bonding.
Fracture of bonded specimen under tensile stress took place at the oxide layer of silicon nitride. The bond strength was decreased with oxidation temperature and time. Maximum strength was 106Kg/$cm^2$ for the silicon nitride oxidized at 1200$^\circ{C}$ for 1hr.
Diffusion layer could not be found at the metal-ceramic interface and then the bonding seems to take place through a very thin layer.
