Copper is widely used as a material for electronic components because of its excellent electrical properties and thermal conductivity, and because it is easy to plate and process. However, it is a metal that oxidizes easily when heated in an oxygen atmosphere, etc., and when wiring is done on the surface of copper oxide, it becomes resistance, causing problems such as changes in electrical resistance and poor contact. Aqua Plasma® is a reductive plasma cleaning process that can be used to clean copper without oxidizing it. The result of treating the copper oxide medallion with Aqua Plasma® is that the area that was oxidized and discolored red is reduced and returned to its original copper color.