Vacuum coating is an important aspect of vacuum applications. 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 magnetron, to provide a new technology for film preparation for scientific research and practical production. Simply put, the method of evaporating or sputtering metals, alloys or compounds in vacuum to solidify and deposit them on the coated objects (called substrates, substrates or substrates) is called vacuum coating.

It is well known that, as long as a thin film is coated on the surface of some materials, many new and good physical and chemical properties can be obtained. In the 1970s, electroplating and electroless plating were the main methods of coating on the surface of objects. The former is electrolyzed by electrifying the electrolyte, and electrolytic ions are plated on the surface of the substrate as another electrode. Therefore, the condition of this coating is that the substrate must be a good conductor of electricity, and the thickness of the film is difficult to control. The latter is the chemical reduction method. The film must be prepared into a solution and can take part in the reduction reaction quickly. This coating method not only has poor bonding strength, but also is not uniform and easy to control. At the same time, it also produces a large number of waste liquids, causing serious pollution.Therefore, these two plating processes, which are called wet plating, are greatly limited.

Vacuum coating is a new kind of coating technology developed in comparison with the wet coating method mentioned above. It is usually called dry coating technology.

Compared with wet coating technology, vacuum coating technology has the following advantages:

(1) Thin films and substrates are widely selected. The thickness of thin films can be controlled to prepare functional films with various functions.

(2) Thin films are prepared in vacuum. The environment is clean and the films are not easily polluted. Therefore, thin films with good compactness, high purity and uniform coating can be obtained.

(3) The bonding strength between the film and the matrix is good and the film is firm.

(4) Dry coating produces neither waste liquor nor environmental pollution.

Vacuum plating technology mainly includes vacuum evaporation plating, vacuum sputtering plating, vacuum ion plating, vacuum beam deposition, chemical vapor deposition and other methods. In addition to chemical vapor deposition, other methods have the following common characteristics:

(1) All kinds of coating technologies need a specific vacuum environment to ensure the movement of vapor molecules formed in the process of heating, evaporation or sputtering, not to be impacted, blocked and interfered by a large number of gas molecules in the atmosphere, and to eliminate the adverse effects of impurities in the atmosphere.

(2) All kinds of coating technologies need to have an evaporation source or target in order to convert evaporating materials into gases. With the continuous improvement of source or target, the selection range of film-making materials has been greatly expanded. Whether metal, metal alloy, intermetallic compound, ceramics or organic substances, all kinds of metal and dielectric films can be evaporated, and multi-layer films can be obtained by evaporating different materials at the same time.

(3) Evaporated or sputtered film-making materials can measure and control the film thickness accurately in the process of forming film with the workpiece to be plated, so as to ensure the uniformity of film thickness.

(4) Each film can precisely control the composition and mass fraction of residual gases in the coating chamber through a fine-tuning valve, thus preventing the oxidation of evaporating materials, reducing the mass fraction of oxygen to a minimum, and filling inert gases, which is impossible for wet coating.

(5) Because of the continuous improvement of the coating equipment, the continuous coating process can be realized, thus greatly improving the output of products, and in the production process, no pollution to the environment.

(6) Because of the high purity, good compactness and bright surface of the film, the mechanical and chemical properties of the film are better than those of the electroplated film and the chemical film.