A plasma is a mixture of positive ions, negative ions, and electrons produced by an electrostatic or electromagnetic field. The ions or charged molecules (excited radicals) remove contaminants by physically sputtering them from the surface or reacting with them chemically. In chemical removal, the plasma breaks the contaminant molecules into water vapour, carbon dioxide gas, and small, volatile organic molecules. These are then exhausted from the area. Most plasma cleaning processes are done in vacuum chambers with argon or oxygen plasmas.
Plasmas are effective for removal of very thin organic layers. Plasma cleaning is common in the semiconductor industry. It often improves wire bonding on hybrid microcircuits. Plasma cleaning can strip wire insulation from coils and magnetic assemblies. It is also used to prepare surfaces before plating on plastics.
Plasmas are best suited for line-of-sight cleaning. Some work has been done to develop atmospheric pressure plasmas, which may expand the applications for this technique.
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