The criteria for the formation of a CuAlO2 reaction phase at the Cu/Al2O3 interface are explored. Oxygen solutes up to 2 wt% were introduced into the copper first. The bonding was carried out at 1075°C. The reaction phase was observed only when the oxygen solute in copper before bonding was higher than 1.3 wt%. The CuAlO2 phase is polycrystalline and covers only part of the interface. The CuAlO2 grains interact with the crack, which improves the interface strength. As CuAlO2 is not continuous at the interface, the thermal conductivity of the Al2O3/Cu/Al2O3 laminate is affected little.