Operation flow of evaporation coating

The basic operation flow of evaporation coating is as follows:

Preparation before plating → vacuumizing → ion bombardment → baking → premelting → evaporation → taking parts → film surface treatment → finished product.

1. Preparation before plating

Include cleaning of plating parts, manufacturing and cleaning of evaporation source, cleaning of vacuum chamber plating fixture, installation of evaporation source and mounting of plating parts, etc.

① Cleaning and treatment of plated parts

The bonding force with the surface of the plated film is an important index of product quality. It is determined by many factors, and the surface treatment before coating is one of the most basic factors. If there are grease, adsorbed water and dust on the surface of the plated parts, the adhesion of the film will be reduced and the surface roughness will be affected.

Chemical degreasing: Various kinds of metal and nonmetal plated parts should adopt corresponding degreasing and degreasing processes. For specific methods, you can search for degreasing in the technical column of this website to view related articles.

Electrostatic removal: The plated parts are prone to static electricity during molding, which may cause pinholes in the film layer or reduce the adhesion of the film. Therefore, the static electricity must be removed before priming.

Priming: The film thickness of evaporation bottom is generally 0.05~0.1um, while the surface roughness of common plated parts is 0.5um, so the film thickness is far from enough to fill the pits. In order to reduce the surface roughness, a special primer of 7~10um is usually applied on the surface of plated parts to eliminate pits and achieve the effect of smoothing the surface.

② Manufacture of evaporation source

According to the use requirements of products and the materials of plated parts, choosing appropriate evaporation materials is the basic condition for obtaining high-quality film.

The basic principles for selecting metal film materials are: good thermal stability and chemical stability, high mechanical strength, low internal stress, certain toughness, good adhesion with primer, high reflectivity and small outgassing in vacuum; Wide source of materials, low price and corresponding evaporation source.

Different evaporation materials need to choose the corresponding evaporation source and evaporation plating method.

③ Cleaning of vacuum chamber and plating fixture

If the vacuum chamber with inner cover is polluted, the cover can be removed for cleaning or renewal. If there is no inner cover, it can be wiped with calcium carbonate, then wiped with water, and finally wiped with absolute ethyl alcohol.

Commonly used aluminum fixtures can be soaked in 20%NaOH solution until the surface is brown, then washed with running water, soaked in HNO3 until brown disappears, and then washed and dried.

④ Install evaporation source.

Pay attention to wearing degreasing gloves, and tools should be degreased beforehand. Pay special attention to the good contact between evaporation source and electrode.

⑤ Place plated parts.

They should be placed stably and firmly on the plated parts and the plated parts clamp to prevent the plated parts from being thrown away from the clamp due to the rotation of the clamp during evaporation. Wear degreasing gloves, do not talk, and keep the plated parts clamp clean.

2. vacuumizing step

Open the cooling water valve, adjust to the required water pressure, turn on the main power supply, close the air valve leading to the vacuum chamber, close the piping valve, start the power supply of the mechanical pump, and open the pre-vacuum valve. At this time, the mechanical pump is sucked into the vacuum chamber, then ion bombardment is carried out, the heating power of the diffusion pump is turned on, and the pre-vacuum valve is closed. When the diffusion pump meets the working requirements, the vacuum valve is closed, the piping valve is opened, and the high vacuum valve is opened. At this time, the diffusion pump and the mechanical pump are sucked into the vacuum chamber, and after the vacuum degree reaches a certain value, baking, pre-melting and evaporation are carried out.

3. Ion bombardment

During glow discharge, ions bombard electrons at a high speed, and rapidly carry negative charges around the plated parts due to the larger mobility of electrons. Under the action of negative charge attraction, positive ions bombard the surface of the plated parts, and there is energy exchange on the surface of the plated parts, and chemical reaction occurs between the adsorption layer of the plated parts and active gas, thus achieving the effect of cleaning the surface.

The conditions of ion bombardment are that the residual gas pressure is stable at 0.13~13Pa, the voltage is 1.5~10kV, and the time is 5~60min.

4. Baking

It can accelerate the rapid escape of the gas adsorbed by the plated parts or fixtures, which is beneficial to improve the vacuum degree and the adhesion of the film layer. When baking, it should be noted that the baking temperature for nonmetal is 20~30℃ lower than the thermal deformation temperature of the plated parts, and the baking temperature for metal is generally not more than 200℃.

5. Pre-melting

It can remove the low melting point impurities in the evaporation material and the gas adsorbed in the evaporation source and the evaporation material, which is conducive to the smooth progress of evaporation. The vacuum degree of premelting is generally 6.6×10-3Pa, and the time is until it is completely melted. The material with high hygroscopicity should be premelted repeatedly. The general requirement is that when the evaporation material is heated to the evaporation temperature, the vacuum degree will not decrease.

6. Evaporation

Evaporation technology has great influence on coating quality, and has different requirements for general metals, special metals and compounds. For example, some metals need to evaporate quickly, while others are not suitable. The heating method and the shape of the evaporation source should depend on the different evaporation materials.