Methods and classification of coating
Film forming under vacuum conditions has many advantages: it can reduce the collision of atoms and molecules of evaporation materials with molecules in the process of flying to the substrate, reduce the chemical reaction (such as oxidation) between active molecules in gas and evaporation source materials, and reduce the amount of gas molecules entering the film to become magazines in the process of film forming, so as to provide the density, purity, deposition rate and adhesion with the substrate of the film. In general, vacuum evaporation requires that the film forming chamber is equal to or lower than 10-2P. For situations where the evaporation source is far away from the substrate and the film quality is required to be high, the pressure is required to be lower.
It is mainly divided into several categories:
Evaporative coating and sputtering coating
Evaporative coating: It evaporates some substance by heating to make it deposit on the solid surface, which is called evaporative coating. This method was first proposed by M. Faraday in 1857, and has become one of the commonly used coating technologies.
Evaporated substances such as metals and compounds are placed in the crucible or hung on the hot wire as evaporation source and workpieces to be plated, and substrates such as metals, ceramics and plastics are placed in front of the crucible. After the system is pumped to high vacuum, heat the crucible to evaporate the substances in it. The atoms or molecules of the evaporated substance are deposited on the substrate surface by condensation. The film thickness can vary from hundreds of angstroms to micrometers. The film thickness depends on the evaporation rate and time of the evaporation source and the distance between the source and the substrate. For large area coating, rotating substrate or multiple evaporation sources are often used to ensure the uniformity of coating thickness. The distance from the evaporation source to the substrate should be less than the average free path of the vapor molecules in the residual gas, so as to avoid the chemical reaction caused by the collision between the molecules and the residual gas molecules. The average kinetic energy of vapor molecules is about 0.1~0.2 electron volts.
Evaporative coating can also be applied to many products, such as mobile phone plastic structure, smart home, digital products, cosmetics packaging, handicrafts, toys, alcohol packaging and electronic components.
The application products of sputtering coating include: electronic products hardware, high-end clocks and watches, high-end jewelry, brand leather hardware and other products.
