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Proper Application of Silicone Conformal Coatings will Eliminate Premature Device Failures in Harsh Automotive Environments
Keywords: silicone, coating, protection
A manufacturer of diesel engine management systems has developed an advanced electronic control actuator that operates remotely to improve the dynamic flow control of exhaust gas recirculation and can improve the control, speed, and precision for variable geometry turbocharger vane controls. An enabling material that protects the electronic circuit board from environmental and mechanical stressors within this device is a silicone conformal coating protecting the electronic circuit board. Conformal coatings protect electronic printed circuit boards from moisture and contaminants, preventing short circuits and corrosion of conductors and solder joints. Silicone conformal coatings will do this in severe environments, especially those harsh environments seen in military, industrial, and automotive under-hood environments. The silicone conformal coating will greatly extend the life of the components and circuitry it is protecting; however, if it is misapplied the opposite can occur. Silicone coating’s inherent thermal expansion characteristics as quantified by its coefficient of thermal expansion (CTE) are generally a non-issue. Nonetheless, it was shown that if the silicone conformal coating is over applied and/or completely underfills the under-cavity of a chip or component device failure can occur via lead fracturing. Furthermore, if greases or lubricants are used elsewhere in the application and are not contained, certain greases can swell the coating thus amplifying the expansion forces exerted on the chip leads. It was determined through studies, experiments, and application reviews that implementing an automated coating spray process that controlled the amount and deposition location of coating alleviated the problem. Furthermore, the choice of fluorinated grease is advised so in the event the silicone coating is exposed to the grease, no swell will occur.
Jason D. Clark, Application Engineer & Technical Service Professional
Dow Corning Corporation
Midland, MI

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