Electrochemically induced degradation of screen-printed gold thick films

Gold thick films have been characterized by means of cyclic voltammetry in nitric acid and are compared with a pure gold electrode. Surface reconstruction and roughening is found for all electrodes, whereby the pure gold reference sample rapidly exhibits stationary behavior. In contrast, the screen-printed electrodes show a permanent linear increase of the gold surface area as measured by the charge densities for gold oxidation, which is connected with the dissolution of glass-ceramic compounds. Oxides of bismuth and copper and their aluminates are regularly used to adjust the morphology of thick films and to enhance the adhesion of screen-printed layers. Electrochemical reactions of both elements (Bi, Cu) are detected. An in-house produced gold paste free of these oxides was used for comparison and shows a linear increase in oxidation charge density as well. Cu and Bi compounds take part in the electrochemical reaction and accelerate the surface increase. The dissolution of glass-ceramic components from the surface and at the interface between thick film and substrate is revealed in FESEM images of the electrodes and at cross-sections. A model is set up for the electrochemically induced localized degradation of the thick films, which are attacked at the boundary layer to the electrolyte and the glass-ceramic interface between the LTCC substrate and gold layers.