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1. Characteristics and effects of pitting defects
Pitting appears as tiny bumps or depressions on the surface of the UV conformal coating, which vary in size and shape, and may be single or densely distributed. These pitting spots make the surface of the coating rough and uneven, losing its original smooth texture. When exposed to light, pitting creates shadows that further accentuate imperfections in the surface of the coating.
Although the pitting itself may not directly lead to a significant decrease in the protective performance of the coating, the coating structure at the pitting may have weak links and can easily become a channel for the invasion of harmful substances such as moisture and salt spray. In the long run, this can affect the longevity and reliability of electronic components.
2. Exploration of the causes of pitting defects
1. Interference from external factors
Dust impurities: Dust in the coating environment is one of the important causes of pitting. Dust particles may adhere to the surface of the substrate or be suspended in the varnish, where they can be encapsulated or embedded in the varnish during the coating process, curing and forming pits
Oil contamination of the substrate: The oil stain on the surface of the substrate will affect the adhesion between the paint liquid and the substrate, resulting in the uneven spread of the paint during the coating process. Some of the paint may accumulate or shrink in the oily area, forming pitting after curing. In addition, oil stains may also react chemically with components in the paint liquid, producing insoluble substances that further exacerbate the formation of pitting.
Electrostatic adsorption of foreign matter: During the coating process, the friction between the paint liquid and the substrate generates static electricity. Static electricity adsorbs foreign substances such as dust and fibers in the air, which adhere to the surface of the coating and form pitting after curing. The electrostatically adsorbed foreign matter is of different sizes and unevenly distributed, which makes it difficult to control the shape and number of pittings.
2. Influence of coating factors
Incomplete filtration of the formulation: UV conformal coating formulations may contain some tiny particles or insoluble impurities, if not sufficiently filtered during the production process, these impurities will be coated with the paint liquid to the surface of the substrate, and form pitting after curing.
Unreasonable formula matching: The proportion and matching relationship between each component in the formula have an important impact on the coating quality. If the ratio of resin to hardener is incorrect, or if incompatible additives are added, it may cause the leveling of the paint to deteriorate and pitting may occur after curing. In addition, improper solvent selection in the formulation may also affect the evaporation rate and leveling of the paint liquid, which can lead to pitting defects.
Improper coating process: Unreasonable setting of process parameters in the coating process, such as unstable spraying pressure, uneven spraying speed, inconsistent coating thickness, etc., may lead to uneven distribution of paint liquid on the surface of the substrate and the formation of pitting. In addition, the cleanliness of the coating equipment can also affect the quality of the coating, and if impurities or varnish solids remain inside the equipment, new varnish may be mixed into the paint during the painting process, resulting in pitting.
3. Strategies for solving pitting defects
1. Purify the coating environment
Enhanced air purification: Install an efficient air filtration system in the paint shop to remove dust particles from the air. Regularly maintain and replace the air filtration system to ensure its effectiveness. At the same time, keep the paint shop clean and hygienic to reduce the generation and accumulation of dust.
Strict degreasing treatment: Carry out thorough degreasing treatment on the coated substrate, in the degreasing process, to ensure that there is no oil residue on the surface of the substrate, and to avoid corrosion of the substrate caused by degreasing agent.
Eliminate the influence of static electricity: Install static elimination devices on the coating equipment and substrate to eliminate static electricity in time. During the painting process, it is necessary to maintain a good grounding of the equipment and substrate to avoid the accumulation of static electricity. In addition, it is possible to reduce the generation of static electricity by controlling the humidity of the coating environment.
2. Optimize the coating assembly
Fine filter varnish: In the production process of UV conformal coating, a multi-stage filtration process is adopted, and high-precision filters, such as microporous membrane filters, are used to remove tiny particles and insoluble impurities in the varnish. According to the viscosity of the paint liquid and the size of impurities, select the filter with the appropriate pore size, and check and replace the filter regularly to ensure the purity of the paint liquid.
Reasonable matching formula: Through a large number of experiments and research, determine the optimal proportion and matching relationship of each component in the formula. During the formulation design process, the compatibility between the components, the reactivity and the influence on the coating properties should be considered. Small-scale, pilot and mass production tests can be carried out to continuously optimize the formula and improve the leveling and curing quality of the paint liquid.
3. Standardize the coating process
Precise control of process parameters: according to different substrates and coating requirements, accurately set the process parameters such as spraying pressure, spraying speed, coating thickness, etc. During the coating process, professional measuring instruments are used to monitor and adjust the process parameters in real time to ensure that the paint liquid can be evenly coated on the surface of the substrate.
Regular maintenance of coating equipment: Establish a complete maintenance system for coating equipment, and regularly clean, inspect and repair coating equipment. Ensure the normal operation of spray guns, pipelines, pumps and other equipment, and avoid unstable paint supply or impurities due to equipment failure. At the same time, it is necessary to clean up the residual paint and solidified materials inside the equipment in time to prevent them from affecting the new painting task.
