Analysis of common defects in coating(2)

Summary:Membrane white fog Phenomenon: After the coating is completed, there is some light white mist on th...
Membrane white fog
Phenomenon: After the coating is completed, there is some light white mist on the surface. If you wipe it with acetone or a mixed solution, the phenomenon will become more and more serious. Wipe with cerium oxide powder, which can be wiped off or lightened, (also: wipeable gram)
Analysis: The causes of white fog outside the membrane are more complicated, and the possible causes are:
①, film structure problem: the columnar structure of the outer film is loose, and the outer film is too rough;
②, the evaporation angle is too large, the film structure is rough.
③, temperature difference: when the lens is out of the cover, the temperature difference between inside and outside is too large
④, moisture; the moisture of the environment after the lens is out of the cover
⑤. The water vapor is too heavy when the Polycold is thawed in the vacuum chamber
⑥. Incomplete oxygenation during evaporation and uneven film structure
⑦, the stress between the film and the film
Improvement ideas: There are many causes of white fog outside the membrane, but each has its own characteristics. Try to prescribe the right medicine. The main idea is to make the membrane denser and smoother, which is not easy to adsorb, and the second is to improve the environment and reduce the objects of adsorption.
Improve strategy:
1. Improve the film system and add silica to the outer layer to make the surface of the film smooth and not easy to adsorb. Improve the environment when the lens comes out (dry, clean)
2. Reduce the temperature of the lens when it is out of the cover (extend the cooling time in the vacuum chamber) to reduce the temperature difference and reduce the stress.
3. Improve oxygenation (increase) and improve membrane structure.
4. Appropriately reduce the evaporation rate and improve the columnar structure
5. Ion-assisted coating to improve the film structure
6. Add a small inflation valve when the polycold is thawed (its function is to take away the 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.
9. Pay attention to the vacuum degree when the polycold is thawed.

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