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September 2015 • SMT Magazine 109 urethane conformal coatings have a Tg of about 40–90°C. These levels are insufficient for prolonged automotive purposes, as they tend to stimulate additional undue stress during opera- tion, generating poor performance and failure when thickness of the coating material is not carefully managed. Despite their reputation, these coatings also are moderately hygroscop- ic, displaying a marked tendency for moisture penetration and retention (between 0.3–1.0% of moisture left in the material). In these cir- cumstances, they are particularly susceptible to wet weather conditions, winter road-salt, and the intrusion of corrosive indus- trial liquids or gases typical of automotive engines active in heavy traffic environments. silicone Silicone is a better choice for automotive conformal coating. With a usable oper- ating temperature range be- tween -55°C to +200°C, sili- cone possesses the capacity to withstand prolonged expo- sure to higher temperatures than most other available conformal coatings. Thus, it has sufficient resistance for high humidity auto-engine en- vironments. At the same time, silicone also dis- plays a very low contact angle when exposed to water and thus is very hydrophobic. Because it displays 10–20 times higher moisture perme- ability than acrylic, epoxy or urethane confor- mal coating, it cannot prevent printed circuit boards (PCBs) or other electronic components from retaining excess moisture and water. This eventuality potentially leads to corrosion and metallization of the component. In all cases, the method of coating ap- plication represents an important consider- ation when factoring its use as an automotive coating. For instance, a silicone coating that has been UV-cured may lack sufficient utility for high-profile, consistently active automo- tive electronic components. If shadowing oc- curs during the application process, some of the coating may be left uncured, a factor that will necessarily compromises the reliability of the assembly. paralyne's uses as Automotive Conformal Coating Paralyne conformal coatings, one example of which is paralyne, provide dependable pro- tection for electrical contacts, PCBs, battery ter- minals and all variety of automotive electronics. In this respect, paralyne also generates stress- free protection against moisture penetration, corrosive elements, winter road-salts, water im- mersion, and changes in temperature. More than this, paralyne's vapor deposition process allows for both deep penetration of the substrate and the thinnest possible effective layers of pinhole-free conformal coat- ing, supporting its use in even the most spatially-confined segments of any automotive engine. Parylene, in particular, of- fers exceptional qualities as a conformal coating for the automotive digital sensors frequently used under condi- tions of duress, and often at risk for diminished performance or product failure. Parylene gener- ates chemical, dielectric, moisture and thermal protection that far surpass competitive coatings for automotive purposes. It is the con- formal coating of choice for the following auto- motive applications: Automotive microelectricalmechanical systems (mems) Uniting signal processing and communica- tion functions, MEMS automotive sensors are instrumental in the function of such electronic vehicular systems as: • manifold air pressure (MAP) • manifold air temperature (MAT) • power train/chassis control • provision and maintenance of passenger comfort/convenience if shadowing occurs during the application process, some of the coating may be left uncured, a factor that will necessarily compromise the reliability of the assembly. " " FeAture beNeFIts OF pArALyNe CONFOrmAL COAtINGs IN AutOmOtIve AppLICAtIONs continues