SMT007 Magazine

SMT-Sept2015

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108 SMT Magazine • September 2015 Automotive systems have been subjected to increasing computerization, applied to virtually all of the vehicle's operational technology. Elec- tronic sensors throughout the engine control the signal processing required to connect sys- tems' functions for such essential vehicular sys- tems such as: • analytical performance measurement of automotive systems' functioning • anti-lock brakes control • emissions' management • engine control unit (ECU) • instrument pods' circuitry (IPC) • power controls/modules for doors, mirrors, seats, sunroof, and windows • power train/chassis operations • passenger comfort/convenience • tire-pressure gaskets/seals Many additional uses of automotive elec- tronics currently exist, and their uses will grow more numerous in the future. Since these as- semblies are increasingly situated in demand- ing end-use environments, selection of ap- propriate conformal coatings for automotive applications is essential to assure efficient per- formance. Coatings protect circuits and sensors from aggressive automotive environments con- taining fluctuating mixtures of brake/transmis- sion fluid, ethylene, engine humidity, noxious exhaust gases, fuel/oil, salt-spray, or other sub- stances that add to the risk of degradation in performance. selecting the Conformal Coating best-suited to Automotive Applications While several choices of conformal coat- ing materials exist for auto applications, un- derstanding the specified end use is essential to making the appropriate selection. In the case of automotive electronics, exception- ally high-performance conformal coatings are necessary to provide adequate operational safe- guards against condensation, corrosive liquids, high temperatures, humidity, and water spray. While enacting effective masking material solu- tions to ensure cost effectiveness with easy ap- plication and removal is a desirable objective, more expensive solutions may be necessary to generate the protection and functionality re- quired to sustain the vehicle's systems and op- eration. Thus, care must be made in selecting the coating material most appropriate to the job. Acrylic, epoxy, and urethane Fast drying acrylic conformal coatings have many product uses. Highly dielectric, acrylic conformal coatings work generally well in limited high moisture environments. They can adequately protect many types of elec- tric circuit assemblies against moisture, dirt, dust, thermal shocks, or similar conditions that might corrode, short circuit, or otherwise damage the electric component. Acrylic is also highly flexible and provides insulation against high-voltage arcing and static discharges. However, despite these advantages for many product uses, acrylic conformal coat- ings are not recommended for most automo- tive applications. While acrylics provide good moisture and thermal resistance in many op- erational environments, they are poorly suited for extensive use within the high temperatures common to automotive applications and they don't respond well to exposure to higher tem- perature, corrosive moisture, chemicals or pe- troleum residues. Similarly, both epoxy and urethane are use- ful conformal coatings for many products. Ep- oxy possesses excellent chemical and abrasion resistance—its coatings are generally very du- rable, and resist the effects of moisture and sol- vents exceptionally well. However, epoxy con- formal coatings can cause stress on components during thermal extremes. In contrast, urethane generates far greater chemical resistance than acrylic coatings, and dependable humidity re- sistance, as well. Although highly resistant to solvents, urethane's automotive uses are never- theless limited by its properties. In this respect, evidence has shown that acrylic and epoxy conformal coatings exhib- it transition temperatures between 10–20°C, in- ducing further and excessive surface stresses during usages. Performance of automotive elec- tronics conformally coated with these materials is frequently compromised. Furthermore, acrylic, epoxy and poly- FeAture beNeFIts OF pArALyNe CONFOrmAL COAtINGs IN AutOmOtIve AppLICAtIONs continues

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