Plasma is a gas in an ionized state, which is a collection of particles such as electrons, ions, atoms (ground state or excited state), molecules (excited state or ground state), and free radicals formed by the dissociation and ionization of gas molecules excited by heat, external electric fields, or radiation. Due to both partial and complete ionization in plasma, the total number of positive and negative charges is numerically equal and macroscopically exhibits electrical neutrality, hence it is called plasma.

Plasma, due to its strong chemical activity, is prone to react with solid surfaces, and this property is often used in industry to remove surface stains from objects.

Principle of low-temperature plasma cleaning

Plasma cleaning often uses low-temperature plasma cleaning. The energy of low-temperature plasma is about tens of electron volts. Plasma can achieve the cleaning effect because the charged particles (ions and electrons), active neutral atoms and other active particles, and even ultraviolet radiation contained in it are easily reacted with impurities and pollutants attached to the material surface and removed, thus achieving the effect of cleaning the material surface. Low temperature plasma cleaning technology is usually divided into two cleaning methods due to the chemical properties of plasma (active/inactive waves): physical cleaning method and chemical cleaning method. The physical cleaning method mainly uses the neutral particle groups in the plasma generated by inert gas discharge to bombard the material surface (without chemical reaction with the material surface), and the neutral particles sputter pollutants to complete the cleaning. The principle of chemical cleaning mainly involves the reaction between active particles (ions, electrons, neutral particles, etc.) and the surface of the material, and these reactions are usually chemical reactions with the molecules on the surface of the material, triggering chemical reactions of substances on the surface of the material to remove impurities. As shown in Figure 1.1, the interaction between electrons and the surface of an object, where electrons collide and bombard the surface of the object, can cause the gas molecules originally adsorbed on the surface of the object to decompose; The interaction between ions and object surfaces: Positively charged cations in plasma are accelerated by Coulomb force towards negatively charged surfaces, colliding with particulate matter attached to the surface and causing it to detach from the material surface. This behavior is called sputtering. Compared to lasers and high-energy rays, the energy of low-temperature plasma is very small, so it will not damage the material itself during low-temperature plasma cleaning.

The main advantages of low-temperature plasma cleaning compared to traditional physical cleaning and chemical cleaning are:

(1) After being cleaned by low-temperature plasma, the material becomes even drier and can proceed to the next preparation process without further drying treatment.

(2) Compared to chemical cleaning methods, traditional chemical cleaning methods may use harmful and toxic solvents for cleaning, or produce harmful substances after cleaning. If these cleaning waste liquids are not completely cleaned, they will cause harm to the environment and nature when discharged later, which is not conducive to environmental protection and sustainable green development.

(3) The directionality of low-temperature plasma cleaning is not strong, and the requirements for cleaning are not high. It can achieve partial or overall cleaning of metals, semiconductors, oxides, and most polymer chemical materials or more complex structures, without causing any damage to the material surface.

Low temperature plasma cleaning is a green and environmentally friendly surface cleaning method. Currently, low-temperature plasma cleaning technology is widely used in electronic component manufacturing, multi ceramic shell processing, microwave tube manufacturing, LED packaging, and engine oil seal bonding treatment.