Study on Etching Characteristics of Contacting Copper and other Metals by Sulfuric Acid Solution Containing Thiourea

Abstract

Using a sulfuric acid solution containing thiourea was investigated for selective and equivalent etching of copper in contact with dissimilar metals: Sn, Ni, Fe, and Zn. The copper electrode potential was dropped with increasing thiourea concentration. In contrast, the potentials of the other metals （Sn, Ni, Fe, Zn） exhibited upward trends with increasing thiourea concentration. Each metal, except for Zn, showed a potential crossing point with copper at a certain thiourea concentration depending on the metal. Copper was etched selectively at thiourea concentrations higher than the potential crossing point. Copper and the other metals were etched equivalently around the potential crossing point. The thiourea concentration of the potential crossing point was increased concomitantly with increasing metallic ion concentration. Results show that the etching rates of contacting copper and the other metal were controlled arbitrarily by adjusting the thiourea concentration. The thiourea concentration must be strictly controlled to establish a sustainable selective or equivalent etching system.