Résumé
Conformal coating is a protective, breathable coating of thin polymeric film applied to printed circuit boards (PCB), so named because it conforms to the contours of the PCB. Conformal coatings are typically applied at 25–250 μm to the electronic circuitry and provide protection against moisture, dust, chemicals, and temperature extremities. More recently, conformal coatings are being used to reduce the formation of whiskers, and can also prevent current bleed between closely positioned components. Coatings can be applied in a number of ways including brushing, spraying, dispensing, and dip coating. A number of materials can be used as a conformal coating such as acrylics, silicones, urethanes and parylene. Each has its own characteristics, making them preferred for certain environments and manufacturing scenarios. Many circuit board assembly firms can coat assemblies with a layer of transparent conformal coating, which is lighter and easier to inspect than potting. Conformal coatings are used to protect electronic components from the environmental factors they are exposed to. Examples of these factors include moisture, dust, salt, chemicals, temperature changes and mechanical abrasion. Successful conformal coating will prevent the board from corroding. More recently, conformal coatings are being used to reduce the formation of whiskers, and can also prevent current bleed between closely positioned components. Conformal coatings are breathable, allowing trapped moisture in electronic boards to escape while maintaining protection from contamination. These coatings are not sealants, and prolonged exposure to vapours will cause transmission and degradation to occur. There are typically four classes of conformal coatings: Acrylic, Urethane, Silicone, and Varnish.
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