Plasma Cleaning

Low pressure vs. high pressure plasma cleaning

While in former times the most common plasma cleaning technologies were based on low pressure plasma with high frequency plasma sources (mostly in the kHz to MHz range). The advantage of low pressure plasma cleaning is that it is very precise and can be administered over large areas. It also offers the benefit that the desorbed contaminants from the cleaned surface can be readily pumped out of the process chamber, which makes the whole process very clean. However, this comes at the cost that vacuum equipment is needed and the integration into existing processes is not that easy. The good news is that in recent years there have been a lot of advances in the field of atmospheric pressure plasma cleaning, which complements low pressure processes. Plasma at ambient pressure is commonly created from argon or helium with admixtures of oxygen or hydrogen. Such gas mixtures allow a very rapid cleaning process but at relatively low surface areas (compared to low pressure plasma). Nevertheless, there is no need for vacuum equipment and, thus, plasma cleaning systems at atmospheric pressure can be integrated easily in existing production lines. Since most of these plasma sources are plasma jets, it is possible to combine several of those jets to treat a larger surface at the same time. This, eliminates the aforementioned disadvantage to some extend.

Plasma cleaning systems are used in many industries and applications:

• Automotive: Plasma cleaning is applied to the application of surface preparation prior to the application of a sealant, adhesive or coating. The ability to do this in an environmentally friendly, high volume, low takt time process.
• Aerospace: Plasma cleaning is used to produce ultra-clean surfaces in propellant and oxidizer valving, pumping and other hardware prior to assembly. The ultra-clean process capability is used extensively in Aerospace applications.
• Archeology and Restoration: These are very new fields in which plasma cleaning is employed. Plasma cleaning is hereby used to remove incrustations or unwanted patina layers from antiques or archaeological findings. This is mostly done with mixtures of argon and hydrogen that can achieve relatively low temperatures and, thus, doesn’t damage the fragile surfaces.
• Consumer Goods: Plasma cleaning and activation is applied to the preparation of polymer and composite components prior to adhesive application to improve bond strength. It is also used for obtaining decorative surfaces since plasma can polish surfaces down to the atomic or molecular level.
• Electronics: Plasma cleaning is employed to reduce oxides, clean and degrease metal surfaces prior to bonding, soldering, circuit printing, or conformal coating. This surface treatment is especially advantageous because the structures on microchips are getting smaller and smaller – down to the nanometre size. Such fragile surface morphologies can get easily damaged by conventional cleaning methods but plasma treats them gently.
• Medical Devices: Medical product manufacturing requires the highest levels of surface cleaning and activation. Plasma processing provides the ability to produce an ultra-clean surface. This ability to create an ultra-clean surface can clean materials on a molecular level, removing contamination; other cleaning methods have no chance of removing. Trace level contaminants in the micro-structures or fine cracks of a surface are removed, providing a clean surface free of foreign material, contamination and pyrogens.
• Optics: When it comes to high-tech optical components plasma cleaning is a powerful tool. It is often used for cleaning mirrors, lenses or other optical components, especially in the field of high power laser applications or telescopes.
• Semiconductor: Plasma cleaning and activation is applied to wafers, bond pads and lead frames to promote adhesion and improve reliability of secondary processes.
• Solar: Plasma cleaning is used to clean bond pads and conductive materials for improved conductivity and reliability of device and package electrical connections.
• Textiles: Plasma cleaning and activation is used to remove manufacturing contamination from textiles to improve coating durability and performance life.
• Rubber Processors: Removal of mold release and lubricants prior to glueing or bonding.