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106 SMT Magazine • September 2015 by sean Horn DiaMonD MT Conformal coatings are protective substrate coverings applied to circuit board technology, moving parts of strategically located compo- nents, or similar electro-mechanical assem- blies; they are composed of selected chemicals or polymer films. Acrylic, epoxy, paralyne (po- ly-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 secur- ing the component from exposure to corrosive elements. The substances acrylic, epoxy, sili- cone and urethane benefit from simple appli- cation—by dipping, flow-coating or spraying the material to the selected substrate—and rel- atively 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, be- cause 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 auto- motive purposes. Selection of coating type depends upon its function and degree of need for surface protec- tion. expanded Automotive use of Conformal Coatings Electrically insulating, conformal coatings maintain levels of long-term surface insulation resistance (SIR) appropriate to the optimal func- tion of the protected system. Thus, electronic circuits and operational equipment receive pro- tection sufficiently reliable to ensure their op- erational integrity despite the situation within an engine, generating harsh environments that may contain moisture, humidity, electric cur- rent, 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 con- ditions exemplified by persistent mechanical vibration in the presence of various combina- tions of aggressive chemicals, harsh liquids and vapors. For automotive purposes, the security generated by conformal coatings simultaneous- ly protects the products and systems within the engine, while adding to the functional perfor- mance, better assuring the vehicle operates as intended. Benefits of Paralyne Conformal Coatings in Automotive Applications FeAture