Plasma treatment for cleaning of metal parts

Dry plasma etching with 13.56 MHz r.f. or 2.45 GHz microwave frequency was used to clean organic oil layers from metal parts. The etch rate depends on the physical and chemical properties of the oil and the substrate (e.g. copper and aluminum) and on the plasma process parameters. Rapid removal of the organic layer is facilitated by a high vapor pressure and low viscosity of the oil. Preferentially, the oil should contain oxygen-rich hydroxy- and ester groups and be free from additives based on heavy metal ions. The etch rate depends on the different plasma process parameters, e.g. pressure, radiation power, duration. As is shown, all these parameters affect the substrate temperature which is an important factor in plasma etching. As an industrial application, the cleaning of electronic silver contacts from print relays was investigated in more detail. Nine different cleaning methods, including fluorocarbon, halogen-free, or aqueous solvent cleaning as well as dry plasma etching were compared. As a result, environmentally hazardous fluorocarbon cleaning can be replaced by halogen-free solvents and/or dry plasma etching without loss of cleaning quality. The results were obtained using a newly developed plasma gas mixture consisting of oxidizing as well as reducing components.