A method is provided for the removal of tin or tin alloys from substrates such as the removal of residual tin solder from the molds used in the making of interconnect solder bumps on a wafer or other electronic device. The method is particularly useful for the well-known C4NP interconnect technology and uses an etchant composition comprising cupric ions and HCl. Cupric chloride and cupric sulfate are preferred. A preferred method regenerates cupric ions by bubbling air or oxygen through the etchant solution during the cleaning process.