Influence of Hydrogen-Enhanced Annealing on the Morphology of Atmospheric Plasma Sprayed Copper

Plasma spray under atmospheric conditions leads to oxidation of the copper during the coating process, especially when the workpiece is preheated. To successfully coat sensitive materials such as semiconductor chips with an electrically and mechanically functional copper coating, alternative spraying technologies that are less prone to oxidation, such as cold spraying, cannot be used due to their inherent shot peening effect on sensitive materials. Therefore, an annealing process under hydrogen-containing atmosphere has been developed to not only adjust material hardness but reduce Cu-oxides for higher electrical conductivity. The influence on the coating properties is analyzed before and after annealing with N2 or N2-H2. While the electrical conductivity is significantly improved with H2-containging annealing, the tensile strength is reduced due to hydrogen embrittlement. However, N2 alone is not sufficient enough for improving electrical conductivity. Metallographic cross sections and EDX analysis determine the oxide content and porosity from various parameters. The sweet spot between spray and annealing parameters determines the ideal electric conductive and cohesive coating parameters.