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Plasma, which consists of ionized gas atoms, is the fourth state of matter. On Earth, plasma does not occur naturally, but it is sometimes visible at high altitudes as auroras. But off-planet, elsewhere in the universe, almost all visible matter is plasma. Plasma is a mixture of positively charged atomic hulls, free electrons, free radicals, and neutral particles; the total electrical charge is neutral, conductive, and highly reactive. Due to permanent recombination, plasma lights can come in different colors. The colors depend on the nature of the gas.
The plasma particles have great speed, and thus, high energy content. Irving Langmuir was the first who called ionized gas “plasma.” Although there are several methods known to produce plasma, only one method is widely used in manufacturing PCBs: RF discharge at 40 kHz or 13.56 MHz or microwave discharge at 2.45 GHz at low pressure 0.1–1.0 mbar. This method produces what is commonly known as “cold plasma.” There is also plasma at atmospheric pressure, with technical applications. This article deals only with low-pressure plasma.
Equipment Available to Produce Plasma
Most plasma equipment is comprised of discontinuous (batch) systems, although there are also continuous systems available. The batch systems have some volume of l.0 to 10 m³ and more. The common units in the PCB industry have volumes of approximately 0.2 to 3 m³. Continuous systems are available for flexible circuits, reel to reel, and rigid products as well.
To read this entire article, which appeared in the May 2020 issue of PCB007 Magazine, click here.
