Coating

In vacuum it is possible to produce thin metal films by evaporation of metal with its subsequent condensation on the surface to which the coating is applied (so called base coat). For example, silvering in mirror glass production almost everywhere is replaced with vacuum condensation of the thinnest aluminum film. Process units for vacuum metallization of foil from plastic and woven fabric are currently developed. Protective-decorating, heat-reflective and other types of coatings are produced.

Vacuum evaporation technology is used in production of optical filters, coated optics, astronomical glasses, high-reflectivity coatings for lasers and interferometers. In electrical industry and electronic engineering vacuum evaporation is used for manufacturing semi-conductor flow straighteners, condenser tissue metallization, applying conductive layer during printing circuits production and for manufacturing radio-microschemes and storage elements of electronic computer circuits.

In automobile industry signal buttons, levers, head lamps, mirrors, etc. are metallized in vacuum. This method is used for producing anti-corrosive coatings of metals and steel plates. For example, a method of applying two-layer zinc-aluminum coatings by stage evaporation of these metals in a vacuum chamber. To protect high-resistance steel from corrosion in marine environment it is reasonable to use vacuum tinned cadmium coatings. Zinc and cadmium coatings are applied by thermal evaporation under pressure 10-3 - 10-4 Torr.

In some cases vacuum deposition is the only way of obtaining thin films. This method is significantly more cost-effective than other known methods of mass production of metallized products. With its implication mechanical treatment of the surface of the coating is minimized. The method of metallization in high vacuum provides coating of plastics, foil, paper, fabric with a thin metallic layer and its firm adhesion with the basic material.  

In process of metallization the workpiece is spinned around an evaporator and covered with a layer of a metal. Special holding devices must provide simple and reliable fixation of workpieces; the devices must not darken the surface being metallized. Spring type magnetic devices are distinguished due to their high quality. Non-metallic materials, such as quartz, calcium fluoride, can also deposited in thin films. Physical properties of salts and metals can drastically change after their evaporation in vacuum and formation of thin films; their crystalline structure is changed or destroyed.

Most of the plastics and special sorts of paper are metallized under vapor pressure below 10-4 Torr. To reduce the duration of the pumping process baffles, cooled with two- or three-stage cooling units, are installed between the vacuum chamber and a diffusion pump. The presence of the baffle shortens the time of pumping out units, filled with parts made of plastics, containing high-melting elastomers and water.

If metallization occurs on parts, not producing large amounts of gas, it is possible to go without a baffle, but it is necessary to have at your disposal a gas-ballasted pump. For metallization of plastics, releasing large amounts of gases (polyvinylchloride, cellidor, plexigum) and containing elastomers or solvents, another method is successfully used. Its essence lies in varnishing the workpiece (by spraying or submerging into liquid) before metallization. After drying out plastic or metal products release only small amount of gases and fully compact. The varnish fills all the pores of the surface, and the metal layer applied to the varnish comes out glassy smooth and shiny. It adheres to varnished surface better than to the workpiece itself. Multiple layering of high quality varnishes by spraying or submerging into liquid makes it possible to obtain very smooth surface of metal products, comparable with mechanically treated or electropolished surface.

Particularly high efforts are directed on development of technology of coating of thin ferromagnetic films several dozens to several thousand angstrom in thickness. Magnetic properties of such films have a set of distinguishing characteristics in comparison with the magnetic properties of bulky products made of the same materials. They are used as memory or logic elements of computing systems and for high frequency magnetic amplifiers, parametrons, microwave devices. In comparison with other magnetic elements, used for these purposes, advantages of films lie in higher response rate, lower energy consumption and lower occupied volume. Their field of application got a name of microelectronics.

When manufacturing complex electronic schemes by vacuum evaporation semi-conductor elements are used along with passive elements (resistors, capacitors). Thin films of semi-conductor devices have very high electron mobility; therefore when carrying out vacuum evaporation a high degree of purity of semi-conductor devices must be provided, what requires increasing the vacuum. While a certain portion of an inactive gas does not play a significant role, presence of such gas as oxygen, may drastically change the resistance of the film. Therefore, primarily it is necessary to achieve high vacuum with the gas, which negatively influences the process and to reduce its partial pressure up to the necessary minimum.