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80 PCB007 MAGAZINE I MAY 2020 an RF or microwave generator (Figure 1). In the chamber, there are several antennas be- tween which the radio frequency travels. The antennas can be cooled or heated. The boards for plasma treatment are stacked with gaps in the chamber. The pressure in the chamber (vessel) is reduced to 10 -2 to 10 -3 mbar. The gas that is introduced in the chamber is ionized by the high-frequency generator, creating the plasma. A specific characteristic of the plasma is the visible glow discharge in different colors, de- pending on the type of gas. At the same time, invisible UV radiation is generated. The color can be used as an indicator of whether the gas is contaminated. The highly reactive particles react with the surface of the boards with chem- ical and physical modifications of the surface. The Effect of Plasma With low-pressure plasma technology, gas is excited in a vacuum by energy supply. It gen- erates energetic ions and electrons, as well as other reactive particles constituting the plas- ma. These produce effective surface changes. There are three plasma effects: 1. Micro-sandblasting (the surface is removed by ion bombardment). 2. Chemical reaction (the ionized gas chemically reacts with the surface). 3. UV radiation (breaks long-chain carbon compounds). Varying the process parameters—such as gas composition, pressure, power, process time, gas flow, and exhaust—changes the effect of the plasma. The General Use of Plasma In general-purpose industrial applications, plasma is used for: • Cleaning of metal parts before printing, coating, and bonding • Activation of plastics, elastomers, and foils before gluing, printing, casting, painting, and coating • Etching of components, milling • Reducing of metals and chemicals • Polymerization of coatings, protective coatings, hydrophobic coatings, insulating layers • Soldering pretreatment, soldering without flux • Artificial aging of components • Epilamisation, deposition of a PTFE-like layer to prevent creeping away of lubricating oil • Pretreatment before bonding (e.g., gold wire, copper wire, or aluminum wire) • Sterilization • Cleaning, drying, and preserving of archaeological objects • Hydrophilize, hydrophobize, and change of the surface tension • Cleaning of metal powders Figure 1: A simple schematic diagram for generating plasma.

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