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Conformal coatings are protective substrate coverings applied to circuit board technology, moving parts of strategically located components, or similar electro-mechanical assemblies; they are composed of selected chemicals or polymer films. Acrylic, epoxy, paralyne (poly- paraxylene), silicone and urethane are the major substances comprising most conformal coating used today. Although each has different properties and applications, the coatings they provide are generally between 25–75 μm thick, with coverage that accurately conforms to the contours of the substrate.
All conformal coatings exhibit some degree of physical flexibility, and protection against mechanical and thermal shock, while securing the component from exposure to corrosive elements. The substances acrylic, epoxy, silicone and urethane benefit from simple application— by dipping, flow-coating or spraying the material to the selected substrate—and relatively easy removal, repair and replacement, if necessary. In contrast, paralyne requires a specialized vapor deposition process, which is slower to enact and more costly. However, because the vapor deposition process causes the paralyne to penetrate far more completely into the substrate surface, it produces the highest levels of protection available for many automotive purposes.
Selection of coating type depends upon its function and degree of need for surface protection.
Expanded Automotive Use of Conformal Coatings
Electrically insulating, conformal coatings maintain levels of long-term surface insulation resistance (SIR) appropriate to the optimal function of the protected system. Thus, electronic circuits and operational equipment receive protection sufficiently reliable to ensure their operational integrity despite the situation within an engine, generating harsh environments that may contain moisture, humidity, electric current, chemical contaminants, or a mixture of them.
These features are particularly necessary where the protected equipment is expected to operate at high levels of reliability under conditions exemplified by persistent mechanical vibration in the presence of various combinations of aggressive chemicals, harsh liquids and vapors. For automotive purposes, the security generated by conformal coatings simultaneously protects the products and systems within the engine, while adding to the functional performance, better assuring the vehicle operates as intended.
Editor's Note: This article originally appeared in the September 2015 issue of SMT Magazine.