Vacuum coating is a method of heating metal or non-metallic materials under high vacuum conditions to evaporate and condense on the surface of plated parts (metal, semiconductor or insulator). For example, vacuum aluminum plating, vacuum chromium plating, etc.
Vacuum coating is an important aspect in the field of vacuum application. It is based on vacuum technology, using physical or chemical methods, and absorbing a series of new technologies such as electron beam, molecular beam, ion beam, plasma beam, radio frequency and magnetic control, which provides a new technology for film preparation for scientific research and practical production. In short, the method of evaporating or sputtering metals, alloys or compounds in vacuum to solidify and deposit on the coated object (called substrate, substrate or substrate) is called vacuum coating.
It is well known that as long as a thin film is deposited on the surface of some materials, the materials will have many new and good physical and chemical properties. In the 1970s, the main methods of coating on the surface of objects are electroplating and electroless plating. The former is to electrolyze the electrolyte by electrifying. The electrolyzed ions are plated on the surface of the substrate as another electrode. Therefore, the substrate must be a good conductor of electricity and the thickness of the film is difficult to control. The latter is chemical reduction method. The film material must be prepared into solution and can participate in the reduction reaction quickly. This coating method not only has poor adhesion strength, but also is uneven and difficult to control. At the same time, a large amount of waste liquid will be produced, causing serious pollution. Therefore, these two kinds of coating process, which are called wet coating method, are greatly limited.
Vacuum coating is a new type of coating technology, which is usually called dry coating technology.
Compared with wet coating technology, vacuum coating technology has the following advantages:
(1) The thickness of films can be controlled to prepare functional films with various functions.
(2) The film prepared under vacuum condition is clean, and the film is not easy to be polluted. Therefore, the film with good compactness, high purity and uniform coating can be obtained.
(3) The bonding strength between the film and the substrate is good and the film is firm.
(4) There is no waste liquid and no environmental pollution.
Vacuum coating technology mainly includes vacuum evaporation plating, vacuum sputtering plating, vacuum ion plating, vacuum beam deposition, chemical vapor deposition and so on. Except chemical vapor deposition, other methods have the following common characteristics
(1) All kinds of coating technologies need a specific vacuum environment to ensure that the movement of vapor molecules formed in the process of heating evaporation or sputtering will not be impacted, blocked and interfered by a large number of gas molecules in the atmosphere, and the adverse effects of impurities in the atmosphere can be eliminated.
(2) All kinds of coating technologies need a evaporation source or target in order to convert the evaporation film material into gas. Due to the continuous improvement of source or target, the selection range of film-making materials has been greatly expanded. Whether it is metal, metal alloy, intermetallic compound, ceramic or organic matter, all kinds of metal film and dielectric film can be evaporated, and different materials can be evaporated at the same time to obtain multilayer film.
(3) The film thickness of evaporated or sputtered material can be accurately measured and controlled in the process of forming film with the workpiece to be plated, so as to ensure the uniformity of film thickness.
(4) The composition and mass fraction of the residual gas in the coating chamber can be precisely controlled by the fine tuning valve for each film, so as to prevent the oxidation of the evaporation material, reduce the mass fraction of oxygen to the minimum degree, and can also be filled with inert gas, which is impossible for wet coating.
(5) Due to the continuous improvement of coating equipment, the continuous coating process can be realized, thus greatly increasing the output of products, and there is no pollution to the environment in the production process.
(6) Because the film is made under vacuum condition, the film has high purity, good compactness, bright surface and no need to be reprocessed, which makes the mechanical and chemical properties of the film better than that of Electrodeposited film and chemical film