Low-pressure plasma offers a wide range of options for surface modification, for example fine-cleaning of contaminated components, plasma activation of plastic parts, etching of PTFE or silicon, and coating of plastic parts with PTFE-like layers. This means that low-pressure plasma is used in a great variety of industries when it comes to combining materials or changing the surface characteristics in a directly targeted manner.
In the low-pressure plasma technology, gas is excited in a vacuum by supply of energy. This results in energetic ions and electrons, as well as other reactive particles which constitute the plasma. It can be used to effectively alter surfaces. Three plasma effects are differentiated:
The mode of operation of the plasma is changed by varying the process parameters such as pressure, power, process time, gas flow and gas composition. Thus, several effects can be achieved in a single process step.
Plasma removes release agents (also silicones and oils) from the surface. They are chemically attacked for example by oxygen and converted into volatile compounds. Under-pressure and surface heating cause the release agents or their residues to evaporate in part. The high-energy particles in the plasma disintegrate the molecules of the release agent into smaller molecule fragments which can now be extracted. Furthermore, a "micro-blasting effect" is generated on the atomic level. UV radiation can disintegrate release agents.
Usually, invisible deposits such as greases, oils, silicones, moisture or oxidation layers are found on freshly produced as well as stored products. To ensure perfect coating of these surfaces, they must be PWIS-free (PWIS = contaminated with Paint Wetting Impairment Substances), which can be achieved with plasma cleaning.
Flow rate: 500 Watt, process chamber volume: 100 litre, process gas: air or oxygen, pressure: 0.2 - 0.6 mbar, duration: 1 – 5 minutes
A wide range of process gases (e.g. air, oxygen, argon, argon-hydrogen, tetrafluormethane-oxygen) and chemicals (e.g. hexamethydisiloxane, vinyl acetate, acetone, fluorinated chemicals) are available.
However, there is the following basic rule: The process know-how is the decisive factor. The plasma must match the material so that all desired effects can be achieved in a directly targeted manner.