Discoloration resistance of electrolytic copper foil following 1,2,3-benzotriazole surface treatment with sodium molybdate

The copper which an important component in the electronics industry, can suffer from discoloration and corrosion. The electrolytic copper foil was treated by 1,2,3-benzo-triazole (BTA) for an environmentally friendly non-chromate surface treatment. It was designed to prevent discoloration and improve corrosion resistance, consisted of BTA and inorganic sodium molybdate (Na₂MoO₄). Also the ratio of the constituent compounds and the deposition time were varied. Electrochemical corrosion of the Cu-BTA was evaluated using potentiodynamic polarization. Discoloration was analyzed after humidity and heat resistance conditioning. Surface characteristics were evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Increasing corrosion potential and decreasing current density were observed with increasing Na₂MoO₄ content. A denser protective coating formed as the deposition time increased. Although chromate treatment under severe humidity (80% humidity, 80 °C, 100 h) provided the highest humidity resistance, surface treatment with Na₂MoO₄ had better heat discoloration inhibition under severe heat-resistant conditions (180 °C, 10 min). When BTA reacts with Cu to form the Cu-BTA-type insoluble protective film, Na₂MoO₄ accelerates the film formation without being itself adsorbed onto the film. Therefore, the addition of Na₂MoO₄ increased anticorrosive efficiency through direct/indirect action.