Many pvd coating machine engineers sometimes find that white fog appears on the surface of the workpiece after the coating is completed. Some appear on the outer surface, and some appear on the inner surface. If they are wiped with acetone or a mixed solution, the phenomenon will become more serious the more they are wiped. If the cause cannot be identified in time, the defective rate will increase. This is a problem that many coating engineers worry about. Below, the editor of Huicheng Vacuum will introduce to you the reasons for the white fog outside the film and the white fog inside the film, as well as the solutions. Hope it helps everyone:

The white fog on the workpiece coated by the pvd coating machine is tested inside. The causes of white fog outside the film are more complicated. The possible causes are:
① Membrane structure problem: The columnar structure of the outer membrane is loose and the outer membrane is too rough;
② The evaporation angle is too large and the membrane structure is rough.
③ Temperature difference: The temperature difference between the inside and outside is too large when the lens comes out of the cover
④ Moisture; moisture in the environment where the lens is placed after taking it out of the cover
⑤ The water vapor in the vacuum chamber is too heavy when POLYCOLD is defrosted.
⑥ Incomplete oxygenation during evaporation and uneven film structure
⑦ Stress between membranes
Improvement ideas: There are many causes of extra-membrane white fog, but each has its own characteristics. Try to prescribe the right medicine. The main ideas are, first, to make the membrane dense and smooth so that it is not easy to adsorb, and second, to improve the environment and reduce the objects of adsorption.

Improve strategy:
(1) Improve the membrane system and add silica to the outer layer to make the membrane surface smooth and difficult to adsorb. Improve the environment when the lens comes out of the cover (dry and clean)
(ii) Reduce the lens temperature when coming out of the cover (extend the cooling time in the vacuum chamber) to reduce temperature differences and reduce stress.
(iii) Improve oxygenation (increase) and improve membrane structure.
(IV) Appropriately reduce the evaporation rate and improve the columnar structure
(5) Ion-assisted coating to improve membrane structure
㈥ Add a small inflation valve when polycold is defrosted (its function is to take away water vapor in time)
(7) Find ways to improve the evaporation angle from the evaporation source and fixture.
(8) Improve the surface roughness of the substrate.
㈨ Pay attention to the degree of vacuum when polycold is thawed.


When the pvd coating machine coats the workpiece, white mist is formed in the film and cannot be removed by wiping.
Possible causes:
① The substrate is dirty and remains of the pre-adhesion process
② Corrosion and contamination on the lens surface
③ Matching between film materials and film materials, and between film materials and substrates.
④ The oxide is not oxygenated enough.
⑤ The first layer of zirconium oxide film material may cause white halo on some substrates
⑥ The substrate is contaminated by moisture before entering the cover (after cleaning)
⑦ Poor washing or wiping, traces of washing and wiping
⑧ The vacuum chamber is dirty and the water vapor is too heavy
⑨ High ambient humidity

Improvement ideas: The problem of the substrate itself may be the main problem, and the coating should try to make up for it. The biggest problem of the coating itself is probably the matching of film materials.
Improve strategy:
(1) Improve the film system, without using zirconium oxide in the first layer.
(ii) Minimize the time it takes to open the vacuum chamber, and prepare the vacuum chamber for cleaning and coating in the shortest possible time between covers.
(iii) After replacing the guard plate and cleaning the vacuum chamber, it is best to vacuum and bake it with an empty cover. The replaced guard plate and other vacuum chamber components must be dry and clean.
(IV) Improve the environment
(5) Properly protect the lens on the umbrella piece before entering the cover to avoid contamination.
(VI) Improve the cleaning and wiping effect.
㈦Improve film matching (consider using Al2O3 for the first layer)
(8) Improve membrane oxygenation and evaporation rate (reduce)
㈨Speed up the process of front engineering. The protection of the processed smooth surface in the previous project is strengthened.
(9) The smooth surface after polishing must be cleaned immediately, and there must be no polishing powder or other impurities attached to it.