A Novel Method to Fabricate a Thick-Film Cu Electrode Fired in Air through Printing Al Electrode and Reduction-Oxidation Substitution Reaction

The thick-film conductor pastes that are applied most widely are Ag and Cu due to their high conductivity. Ag paste can be sintered in air to have high conductivity, but its disadvantage is the overly high cost. Contrarily, although Cu thick paste is not expensive in terms of materials, Cu thick-film paste must be sintered in a reducing atmosphere to obtain high conductivity, which leads to high processing costs. A novel method for fabricating the base metal electrode Cu in an air atmosphere for high-temperature firing was successfully developed based on thick-film screen-printing Al pastes utilizing a reduction-oxidation substitution reaction. To make an excellent Cu electrode that can be substituted for a thick-film Al electrode, Al paste with high solid content, a large Al powder particle size, a CuSO4 solution with low pH, high temperature, and proper soaking time are all positive parameters. The first thick-film screen-printing Cu electrode with high conductivity (> 10-6 Ω), which is comparable with a thick-film Ag electrode, was successfully fabricated in air firing instead of reducing atmosphere firing.