When the pvd coating machine is coating the coating layer, the coating layer often has various abnormalities. Many merchants are helpless because they cannot find the reason for this situation, which affects the coating quality and progress. The most common one is the occurrence of color spots. The following small series will introduce in detail what causes the color spots when the coating layer of the pvd coating machine is coated, and how to improve them later.

Stain (also known as film color lacquer, ablation) refers to the local variation (generally irregular) of film color on the lens. There are two types of intra-membrane stains (including membranous stains) and extra-membrane stains. Sometimes there are regular local areas (such as the center of the concave lens or the annular area, etc.) film color variation. What caused the stains? The color spot is the local refractive index variation of the film color. The so-called film color is the reflection of the spectral characteristics of the film. The design and realization of the spectral spectral characteristics of the film are based on the substrate with a certain refractive index. If the local refractive index of the substrate changes, all the The coated film also has changes in the local spectral characteristics. There will be variations in the color of the film at local points, resulting in the formation of color spots in the film. Due to various reasons during and after the coating, the local refractive index of the film varies, forming a color spot on the film or outside the film. The color spots outside the film are generally shallow and can be wiped off with polishing powder or calcium carbonate. An effective way to distinguish the inner film layer and outer color spot of the film is to wipe with polishing powder or calcium carbonate powder. The countermeasures for the treatment of stains inside the film, film layer and outside the film are different.
Membrane pigmentation causes:
(1) It is brought by the fixture and processing method during the previous processing. This part may be large, small, or large, so there may be stains of varying sizes. This kind of stain has a characteristic, the shape of the stain is regular, the parts are consistent, and the boundaries are clear.
(2) Turnover, transportation and inventory generation. Some substrates have poor chemical properties, such as H-ZK9, which has weak moisture resistance and acid resistance. It will inevitably come into contact with water and humid air during the pre-processing process, resulting in corrosion. If the cycle of pre-processing and coating For a long time (more than 5 hours), it is easy to produce color spots in the film. If it is a reflective film or an infrared cut-off film, such color spots will be very obvious. It may also be a good product just after plating, and there will be color spots after a few days. become defective products.
(3) After the grinding and polishing project is completed, the surface of the lens is not cleaned in time, and the residual polishing powder and liquid are dried on the surface of the lens, causing corrosion or pollution to the lens. This kind of corrosion or pollution cannot be removed by washing or wiping, and stains appear after coating.
(4) The pH value matching of the polishing liquid used for grinding and polishing is not controlled, which affects the chemical stability of the lens between the grinding process and the coating process. 
The reasons for the film layer and outer film stains are as follows:
(1) After the coating, the impurity that is difficult to eliminate is penetrated into the gap of the film layer, which changes the refractive index of the local film layer, so that color spots are formed outside the film.
(2) During the coating process, the temperature of some high-refractive-index substrates is too high, causing the refractive index variation of the local film layer (and possibly the joint of the film layer and the substrate). It can also cause blemishes on the film.
(3) In the film system matching, some film layers are too thin, the crystals are in an unstable state, and film color spots may also occur.
(4) The poor match between the film material selection of the film system and the substrate material is also one of the reasons for the color of the film layer.
(5) A small amount of oil returning from the unit forms a local very thin oil spot in the lens or film layer, which is also the cause of the film layer color spot. The film strength at such a color spot is generally poorer.
Membrane pigmentation improvement countermeasures are as follows:
(1) Speed up the period from grinding (polishing) to coating to reduce the chance of the lens being polluted and corroded. Note: it is the entire polished surface of the lens.
(2) During the polishing process, pay attention to the protection of the other polished surface
(3) Pay attention to the tooling, fixtures and processing methods in the polishing process to avoid local corrosion damage to the lens surface.
(4) The polished surface must be cleaned immediately, and there should be no polishing powder or other impurities adhering to it.
(5) Control the PH value of the grinding and polishing liquid.
(6) Before coating, use polishing powder (cerium oxide, iron oxide) or calcium carbonate powder (mixed with glycerin or water) to renew the polished surface of the lens. and clean as soon as possible.
(7) Strengthen the ion bombardment before plating
(8) For the anti-reflection film in the visible light region, it is designed and made into a single-peak shape under the premise of meeting the technical requirements, and the reflection color is light green, covering the color spots.
(9) For lenses with better chemical properties, soak them with stripping solution or dilute acid solution to remove corrosion spots before cleaning.
(10) Selecting the appropriate film layer matching is also helpful for the improvement of pigmentation.
(11) Increase the temperature of the substrate during plating to speed up the complete volatilization of water vapor. (However, there may be color spots on the film layer, and the countermeasures should be analyzed according to the specific situation.
(12) The first layer plated with Al2O3 film will generally have a good improvement effect.  
Measures to improve the color spots on the film layer and outside the film:
(1) For the anti-reflection film, when the design conditions permit, a SiO2 layer can be added to the outer layer, about 10nm (the general outer layer film is MgF2). The outer layer tends to be smooth and dense, reducing the erosion of harmful substances. (The SiO2 layer will be rough if the ions bombard it after plating.)
(2) Appropriately reduce the evaporation rate (within a certain range) to improve the smoothness of the film and reduce adsorption.
(3) After the lens is out of the cover, it will be cooled and then put under the umbrella and wiped.
(4) After the lens is out of the cover, it should be placed in a clean and dry place for cooling. Reduce the possibility of contamination.
(5) Use calcium carbonate powder to gently wipe off the outer layer attachments.
(6) Improve the humidity and temperature difference of the working environment.
(7) Improve the environment near the inflation port to make the charged atmosphere dry and clean.
(8) The personal hygiene of staff (masks, clothing, gloves, finger cots, etc.) is improved.
(9) Check the oil return condition of the vacuum chamber to prevent oil return.
(10) Appropriately reduce the temperature of the substrate; (cannot affect the strength of the film)
(11) Improve the film system, cancel the too thin film layer, and select the appropriate film layer material according to the characteristics of the nitrate material.
It is actually very common for the coating layer of the pvd coating machine to have a variety of abnormal film layers, but when this happens, we must know the cause of its occurrence, and we must also know how to improve and reduce it. This happens, and it's a skill every coating engineer should master.