Influence of oxygen on the joining between copper and aluminium nitride

Aluminium nitride has been developed for electronic ceramic packaging applications because of its high thermal conductivity and high electrical resistivity. To improve the heat dissipation at the metal/ceramic interface, a high quality bonding between the substrate and the copper conductor is needed. This process requires a previous step of AIN pre-oxidation of the substrates by oxygen gas at 1200 °C, in order to form a thin layer of Al2O3 at the surface of AlN. The junction between Cu and the substrate is carried out at 1075 °C in controlled oxygen atmosphere which promote the oxidation of the copper and the formation of an eutectic phase which can form a strong junction with AlN via the layer of Al2O3. The goal of the current work is to study the influence of oxygen supplied by gaseous phase to form the exact amount of the eutectic phase needed to get a strong junction. First, in order to fix conditions for joining, the wetting behaviour of copper has been studied using the sessile drop method. The influence of oxygen brought by surrounding gas is given in terms of wettability of the liquid, interfacial tension and chemical reactions. According to previous results, copper foils and copper cylinders have been directly joined to AIN substrates. Interfacial reactions, mechanical and thermal properties have been investigated.