Analysis of Common Defects and Improvement Countermeasures in Optical Coating

Common problems of coated products are partly caused by the coating process itself, and partly left over from the previous project. The final quality of the coating is a comprehensive reflection of the processing of the entire optical parts (especially polishing and cleaning). Only by comprehensive consideration can the cause of the defect be found, and the improvement of countermeasures can be effective.

Dirty membrane (also called white pressure)

As the name suggests, the membrane is dirty. The general membrane viscera occurs inside or outside the membrane. Dirty can include: dust spots, white fog, oil spots, fingerprints, saliva spots, etc. (Single row of dust spots and white fog)

01 dirty spots

Phenomenon: There are some points on the surface or inside of the lens film (not the film material points), some can be erased, and some cannot be erased. And there will be a bit of peeling.

cause:

1. The vacuum chamber is dirty. The air vortex at the beginning of vacuuming will bring the dirty dust from the bottom plate and guard plate of the vacuum chamber to the lens to form a gray dot layer. (Inside the film, it cannot be wiped off, it will peel off a bit)

2. The lens ring or disc is dirty, with floating dust, which adheres to the lens under the action of the ion beam to form a gray dot layer. (Inside the film, it cannot be wiped off, it will peel off a bit)

3. There are dust spots when the lens is put on the umbrella, and there is no inspection and selection when putting on the umbrella. (Inside the film, it cannot be wiped off, it will peel off a bit)

4. Environmental pollution after plating is the main cause of dust spots outside the film, especially when the lens is hot, it is easier to absorb dust and it is difficult to erase. (Outside the membrane)

5. Dirty air inlet of the vacuum chamber, too much initial inflation, dirty air filter, and high temperature of the lens during inflation are also the reasons for the bad dust spots on the outside of the lens film. (Outside the membrane)

6. Dust pollution caused by operators (inner and outer membrane)

7. Excessive dust in the working environment

Improvement ideas: eliminate dust sources

Improve strategy:

1. The working environment is transformed into a clean workshop and implemented in strict accordance with the clean workshop specifications.

2. Do the best possible environmental sanitation. Try to use clean workbenches.

3. Clean the vacuum chamber periodically to keep it clean.

02 White fog outside the membrane

Phenomenon: After the coating is completed, there is some faint white mist on the surface. Wipe it with acetone or mixed liquid, and the phenomenon will become more serious. Wipe with cerium oxide powder, it can be wiped off or lightened, (also known as: wipeable acrylic)

Analysis: The causes of white fog outside the membrane are more complicated, and the possible causes are:

①. Membrane 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 and the membrane structure is rough.

③Temperature difference: The temperature difference between the inside and outside of the lens is too large when the lens is out of the cover

④ Moisture; moisture in the environment where the lens is placed after the lens is out of the cover

⑤, Polycold in the vacuum chamber is too heavy when thawing

⑥ Incomplete oxygenation during evaporation and uneven film structure

⑦, the stress between the membrane and the membrane

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 dense and smooth and not easy to adsorb, and the other is to improve the environment and reduce the objects to be adsorbed.

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 absorb. Improve the environment when the lens is out of the cover (dry, clean)

2. Reduce the temperature of the lens when the lens 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 polycold is thawed (its function is to take away water vapor in time)

7. Think of 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 degree of vacuum when the polycold is thawed.

03 White fog in the film

White mist is formed in the film and cannot be removed by wiping.

Possible causes:

① Dirty substrates, residues from the previous work

② Corrosion pollution on the lens surface

③ Mismatch between the film material and the film material, between the film material and the substrate.

④ Insufficient oxygenation of oxides.

⑤ A layer of zirconia film material may cause white halo on some substrates

⑥. The substrate is contaminated by moisture before entering the cover (after washing)

⑦, poor washing or wiping, washing marks, wiping marks

⑧, the vacuum chamber is dirty and the moisture is too heavy

⑨, the environment humidity is large

Improvement ideas: The problem of the substrate itself may be the main one, the coating is to make up as much as possible, and the coating itself may be the problem of film material matching.

Improve strategy:

1. Improve the film system, the layer does not use zirconia.

2. Minimize the opening time of the vacuum chamber, and make preparations for cleaning and coating the vacuum chamber in a short time between the cover and the cover.

3. After the guard plate is replaced and cleaned in the vacuum chamber, the hood can be vacuumed and baked. The parts of the vacuum chamber such as the replaced guard plate must be dry and clean.

4. Improve the environment

5. Properly protect the lens on the umbrella before entering the hood from pollution.

6. Improve the cleaning and wiping effect.

7. Improve film matching (consider using Al2O3 for the layer)

8. Improve membrane oxygenation and evaporation rate (decrease)

9. Speed ​​up the process of the previous project. The protection of the processed smooth surface has been strengthened by the previous project.

10. The polished surface must be cleaned immediately without polishing powder or other impurities adhering to it.

(The source of the article: This article is reproduced on the network platform. If there is anything inappropriate, please feel free to contact us, and we will make changes in time.)

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