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Vacuum deposition technologies have some unique features among the techniques for the coating of surfaces.
 
They allow to deposit a very wide range of materials  which includes, not only all metals, but also oxides and ceramic materials.
 
Vacuum deposition technologies have low environmental impact because they don’t produce fumes or liquids to be disposed.
 
With these technologies is also possible to coat a wide range of substrates, in particular metals, plastics and glasses.
 
The high automation of the Tecno Vacuum equipment  makes their use easy and safe, even for unskilled personnel.

The technologies of vacuum deposition are divided into two large families, named CVD (Chemical Vapour Deposition) and PVD (Physical Vapour Deposition).
The CVD technologies realize the coating dissociating chemically gases or vapours, while in the PVD techniques vapours are obtained by physical means.
Types of PVD technologies are, for example, thermal evaporation, sputtering and arc evaporation.
Among the CVD techniques, the PECVD (Plasma Enhanced CVD) deserves mention, in which the dissociation is obtained by turning on an electric discharge (a plasma) in a suitable mixture of gases at low pressure.


During the thermal evaporation, the material to be deposited is placed in a crucible that is heated by passing a high electric current (Joule effect). The material evaporates and the vapours condense on the parts to be coated. If the material is available in wire, spiral resistances may be used in place of the crucibles, inside which is placed a piece of wire. Thermal evaporation is one of the less expensive PVD technologies and allows to reach very high deposition rates. On the other hand it is not possible to deposit materials that melt at high temperatures (for examples chromium, titanium).
The thicknesses are limited by the capacity of the crucibles (or of the spirals) and typically range  between 0.1 and 0.5 microns.
Thermal evaporation does not cause temperature increase of the pieces to be coated and thus it is very convenient for the deposition on plastic materials.
Most of thermal evaporation applications with spirals regards the deposition of aluminium, in particular in the automotive (for example for the  car lamps), lighting and decorative sectors.


Sputtering technology consists in turning on an electrical glow discharge between a slab of the material to be deposited and the chamber walls. The ions of the discharge erode the material generating the vapours necessary to obtain the coating. The erosion takes place for any conductive material, even if it melts at high temperature, and therefore the range of coatings obtainable is very large. In particular, any metal can be deposited (included chromium, titanium, zirconium, inox steel), metal alloys (for example brass) and also graphite.
 
The erosion of insulating materials requires more complex machinery and is slower. It is still possible to obtain very good deposition rate for many ceramic materials thanks to the reactive deposition, where the metal is eroded in presence of suitable process gases. A typical example is the deposition of titanium nitride (TiN), a ceramic with excellent wear resistance properties, obtained by using a slab of titanium eroded under an atmosphere of Argon and Nitrogen.
With sputtering it is possible to deposit simultaneously many metals, thus obtaining a wide range of colours. The high stability of the sputtering guarantees an excellent reproducibility of the colours obtained.
It is also possible to  deposit high thickness (up to a few  microns) because the material reserve guaranteed by the slab is very large.

Sputtering  also does not cause temperature rise of the pieces to be coated, and therefore allows the deposition on plastic materials.
In arc evaporation also the vapours are obtained by eroding, by an electric discharge at low pressure, a slab of the material to be deposited, but in this case the discharge is precisely the arc type. The arc discharge causes a very energetic evaporation of the material, allowing high deposition rates. By contrast, for this reason, some materials are more critical to deposit. Furthermore, this technique tends to heat in an appreciable way the pieces to be coated and is therefore less suitable than sputtering, for the deposition on plastic materials.
The reactive arc evaporation is very suitable for the deposition of ceramic on metallic materials, for functional uses (moulds, tools) and for decorative uses (handles, taps). The most popular coatings are titanium nitrides (TiN), chromium (CrN) and zirconium (ZrN).
As with the sputtering it is possible to deposit high thicknesses thanks to the quantity of material guaranteed by the slab.


PECVD technology is used for example in the sector of car headlights, to deposit water-repellent layers on the reflective layer of aluminium. The water-repellent layer is indispensable to guarantee the necessary durability to the headlight. The deposition takes place by injecting into the process chamber, in a controlled manner, vapours of compounds such as HMDSO and dissociating the molecules by an electric discharge (plasma). In modern systems, to turn on the discharge, medium frequency generators (MF, generally 40 kHz) are used instead of DC generators, providing a more effective discharge.



 
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