Mechanism for generation of voids bounded on Cu conductors in Cu/glass ceramic co-fired multilayer wiring substrates

Voids of 50-100 μm in size may be generated adjacent to the Cu conductor when a Cu/glass ceramic multilayer wiring substrate is co-fired. Carbon residue derived from the binder (ethyl-cellulose) in the Cu paste is related to the generation of such voids. The main components of the gas that generates a void are H2O and CO. In addition, Cr-Fe-O particles from Cr and Fe impurities in the Cu powder of the Cu paste are present in the void. The mechanism for generation of a void is presumed to be that carbon residue derived from the binder in Cu paste is oxidized by H2O introduced at the binder burnout stage, and as a result, H2 and CO are generated (water gas shift reaction). Cr2O3 and Fe2O3 function as catalysts for a reaction that becomes a trigger for the water gas shift reaction. CuOH can be formed on the surface of the Cu conductor by reaction with the OH generated from this trigger reaction. H2O is generated by the dehydration of CuOH on the surface of the Cu conductor during the sintering stage. When the Cr and Fe content in the Cu powder of the Cu paste, the carbon residue derived from binder in the Cu paste, and the amount of H2O introduced when the binder is burnt out, were decreased according to the derived void generation mechanism, the number of the voids bounded on the Cu conductor was decreased.