What are the methods of surface treatment of PVD vacuum coating machine？
The cleanliness of the PVD coating process is a major indicator that affects the adhesion of the vacuum coating film. Therefore, in order to avoid vacuum pollution, the surface cleaning of equipment parts is very important. There are four basic methods for surface treatment of vacuum coating machines:
1. Solvent degreasing
The grease adhered to the parts of the vacuum equipment can be divided into two types: animal and vegetable oil and mineral oil. Alkaline solutions can be used to chemically remove animal and vegetable oils; organic solvents can be used to remove mineral oils.
However, in practical applications, these two kinds of grease are often present at the same time, so it is often necessary to use multiple different solvents to clean equipment parts.
2. Erosion treatment of acid or alkali
After the equipment is degreasing, it can be treated with acid or alkaline etching to remove oxides on the metal surface. After the heat treatment, the equipment parts are no longer oily, and can be directly treated with acid/alkali etching to remove the oxide layer pollution left after vacuum annealing.
3. Electrochemical cleaning and electropolishing
In the previous article, we have introduced the principle and formula of electrochemical cleaning, and the electrolyte for electropolishing is different from the electrolytic etching solution. The electrolyte formula and polishing specifications for electrochemical polishing are:
1.） Orthophosphoric acid (H₃PO₄): 65% (mass percentage);
2. Sulfuric acid (H₂SO₄): 15%;
3.） Chromic acid (CrO₃): 6%;
4.） Deionized water: 14%;
5. ）Current density: 0.2~0.5A/cm²;
6. ）Voltage: 6~12V;
7. ）Working temperature: around 75°C;
8. ）Time: 5~10min.
After electropolishing, the parts are neutralized in 2%-5% ammonia water for 15s-20s, then washed with water, dehydrated with absolute ethanol, and dried.
4. ultrasonic cleaning
The principle of ultrasonic cleaning: the principle of "void phenomenon" caused by ultrasonic waves (that is, the density of the cleaning medium is changed by ultrasonic vibration), so as to achieve the cleaning effect of the PVD vacuum coating machine. Ultrasonic vibration causes the medium to form an instantaneous gap when it is sparse, and the instantaneous impact pressure generated when it is closed can be as large as the impact force of several atmospheres. This pressure is strong enough to destroy the oil film attached to the surface of the object, causing the oil film and pollutants Fall off into the solution together.
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