Conformal coating is a specially formulated coating used to protect circuit boards and their associated equipment from corrosion, thereby improving and extending their service life and ensuring safety and reliability.
Basic introduction Chinese name ：Protective coating Foreign name ：Conformal coating Usage ：Coating Benefits ：Protect circuits from chemicals Advantages, Types, Application field, Usage method, Usage process, Advantages Under real conditions, such as chemical, vibration, high dust, salt spray, humidity and high temperature, circuit boards may corrode, soften, deform, and mildew, causing circuit boards to fail. This can lead to malfunction of the circuit board. Three-proof paint coated on the surface of the circuit board to form a layer of three-proof protective film (three-proof refers to moisture-proof, anti-salt spray, anti-mold). It can effectively isolate the circuit board, and can protect the circuit from the erosion of harsh environments, damage, thus improving the reliability of the circuit board, increase its safety factor, and ensure its service life. Because the three-proof paint can prevent leakage of electricity, it allows higher power and closer spacing of printed boards. Thus, the purpose of component miniaturization can be met. Whether transparent or colored, triple-proof lacquer improves the appearance of the printed circuit board, while the latter also ensures a higher degree of confidentiality by covering components and design layouts. Types *** Sex lamination from the chemical composition can be divided into acrylate, silicone, polyurethane, epoxy resin four categories. And from the curing method, there are solvent curing, room temperature curing, heat curing and UV curing and other processes to choose from. The following are about their advantages and disadvantages: solvent-containing acrylic ester (the current market set of the most used) has a surface drying, fast curing time, better moisture resistance, inexpensive, transparent color, flexible texture, with easy to repair the characteristics. But high temperature characteristics are limited. solvent-free acrylic ester UV curing can be in a few seconds to a dozen seconds table dry, transparent color, hard texture, chemical corrosion and abrasion resistance is also very good. However, the high temperature resistance characteristics have limitations, the need for UV curing, repair difficulties. Epoxy resin epoxy resin as the substrate of the coating material is very hard, usually opaque, can be very good moisture and humidity. In addition epoxy resins are very good at resisting chemical corrosion and abrasion. However, at the temperature limit, it can cause high stress on components due to its high temperature instability. Polyurethane has a brittle texture and excellent solvent resistance. In addition to superior moisture resistance, and stable performance in low temperature environment. However, high temperature resistance is poor, coupled with the difficulty of repair, so that the scope of its application is narrowed. Organic silicon (1) soft elastic coating material, can be a good release of pressure. (2) Solvent-free, heat-cured coating material with rapid curing characteristics. The first two of these are RTVs, and they share the same characteristics of a wide range of application temperatures, good moisture and humidity resistance, easy processing, easy repair, and low toxicity. Applied in the field Initially, the protective varnish was only applied to the printed circuit boards in the high-tech field. As electronic devices are more and more widely used in everyday life, consumers are now more and more concerned about the quality and reliability of their products. The use of ****-based laminates allows manufacturers to effectively improve the quality of their products and reduce the cost of expensive warranty failures. Typical applications include the following: Civil and commercial applications Protective lacquers provide protection for electronic circuits in household appliances against: (1) water and detergents (washing machines, dishwashers, sanitary products, outdoor electronics) (2) unfavorable external environments (burglary, fire alarms, etc.) (3) chemical environments (air-conditioners, dryers) (4) hazardous environments in offices and homes (e.g., air-conditioning). (4) Harmful substances in the office and home (computers, induction cookers) (5) All other circuit boards that require three-proof protection Automotive Industry The automotive industry requires protection paint to protect the circuits from the hazards of the following situations, such as: gasoline evaporates, salt spray/brake fluid, and so on. The use of electronic systems in automobiles continues to grow rapidly, so the use of ****ty laminates has become an essential requirement to ensure the long-term reliability of automotive electronics. Aerospace Due to the special nature of the use of the environment, aviation, aerospace environment on the electronic equipment requirements are stringent, especially in the rapid pressurization, depressurization conditions, but still to maintain good circuit performance. **** The voltage stability of the laminate is therefore widely applied. Maritime Both fresh and salty seawater can be harmful to the electrical circuits of marine equipment. The use of ****-coated films maximizes the protection of equipment on the water surface and even submerged and underwater. Medical ****coat protects electronic equipment from external chemicals and special environments, ensuring its continued stability. Methods of application There are several ways of applying protective coatings, which can be listed as follows: Dipping: Dipping ensures a complete coating without the waste of material caused by overspray. It is the most economical method of coating large equipment, but the quality of the coating, such as thickness, is affected by a number of factors such as equipment temperature, temperature of the dipping vessel, dipping time, extraction rate and droop time. Dip coating provides a thorough and complete sealing coating and represents the lowest production cost in high volume application. Boards are dipped in a liquid form coating, then removed and the excess coating is dripped off before curing, a method that is difficult to mask. Board and reservoir temperatures, speed of removal from the reservoir, curing temperatures, and the amount of time spent dipping the coating all play a role in the thickness of the application. Spray: Using spray can type products can be easily applied for maintenance and small scale production use, spray guns are suitable for large scale production, for medium size equipment is a more economical way to protect the mold layer formation is easier, but the bottom of the component is difficult to apply to, and therefore need to be re-treated. The thickness of the coating is influenced by the relative linear travel speed, the temperature of the material and the pressure of the spraying device. Spray coating is typically used for medium volume production with high production rates and low production costs. Spray coating is difficult to work under parts and requires more maintenance. The type of feed system, line speed, temperature of the material, and atomizing pressure used will affect the applied thickness. Selective Coating: Coating is accurate and does not waste material, and is mainly used on medium to large equipment. Coating equipment is usually very expensive and requires high maintenance. The thickness of the coating is influenced by four factors: the nature of the coating, the temperature, the pressure and the design of the unit. Selective coating can be used for medium to large sets. Closure is usually not required because the coating is applied only to selected areas of the circuit. It uses operating equipment that is more expensive than that normally used in large-scale operations and requires higher maintenance than dip coating and spraying. The viscosity of the material, temperature, pressure and dispersion head configuration all affect the thickness of the coating. Brush (Flow) Coating: Commonly used, it is the least expensive method and produces excellent coating results on smooth surfaces. It is mainly used for the application of small volume products or the repair of coated layers. Flow or brush application is used for low volume production or for patching. Equipment costs are very low. The coating is simply dripped or brushed onto the board and then cured. Application process Before applying the coating, the surface of the object to be coated must be cleaned of dust, water (moisture) and oil. In case of moisture, it is recommended to bake the board at 80°C for 10 minutes and cool it naturally in the oven before removing it for coating. Brush coating process (1) brush coating area should be larger than the area occupied by the device to ensure full coverage of the device and pads; (2) brush coating the circuit board as far as possible flat, brush coating should not drip dew, brush coating should be flat, and there can not be a *** part of the 0.1-0.2mm between the appropriate; (3) brush coating is placed flat on the bracket ready to be cured, you need to use heat to accelerate the curing method is coating. The heating method is needed to accelerate the curing of the coating. If the surface of the coating is uneven or contains air bubbles, it should be left at room temperature for a longer period of time to allow the solvent to flash out before being placed in the oven for curing. Spray coating process (1) **** sex laminating products can be used in the special diluent dilution, the amount of diluent to add a large amount of adhesive viscosity is low, the thickness of the adhesive coating thin; on the contrary, the adhesive viscosity of the adhesive is high, the thickness of the adhesive coating thick. The amount of thinner is recommended to add 1:0.7-1. Ensure that the diluted product is fully stirred, service bubbles after elimination, can be used. (2) Put the diluted glue into a spray bottle and spray. (3) After spraying, use thinner to clean the spray bottle. Dip coating process (1) with 2 (1) (2) the diluted glue into the dip bucket, the circuit board components should be vertically immersed in the paint dregs, the connectors should not be immersed, unless carefully covered, circuit boards or components should not be immersed in the speed of too fast in order to avoid the generation of air bubbles. (3) When using again after dipping, if there is crusting on the surface, remove the skin and continue to use. Note: 1. If a thicker coating is desired, it is best to obtain it by applying two thinner layers, and it is required that the first layer must be completely dried before the second layer is allowed to be applied. 2、 When applying coatings to the PCB, generally connectors, flexible sockets, switches, heat sinks, heat dissipation areas, plug board areas, etc. are not allowed to have coating materials. It is recommended to use a tearable soldermask to cover Repair has been protected device method Repair methods are usually three, cleaning solvents, mechanical erasure and high temperature to dissolve the coating: If the repair has been coated device, simply soldering iron directly in contact with the coating can be removed from the component. Then install the new component, and then the area with a brush or solvent cleaning; can also be solvent cleaning; after drying and re-coating with a good coating.