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64 DESIGN007 MAGAZINE I MAY 2020 Conformal Coating Enemies: Challenges Sabotaging Your Process Coatings fail for any number of reasons— some common, and some not so common. I have more than 20 years' experience and knowledge of the conformal coating business, and I'm still learning, but there are certain production-related issues that cause problems time and time again—some of which could have been easily resolved. In my previous col- umns, I have examined a number of coating failure issues, but this month, I'm going to talk about some of the arch enemies of conformal coatings, the challenges posed by sensitive ar- eas and higher profile parts, and the best ways to avoid wicking to help you achieve a uni- form and defect-free finish. Hopefully, it will provide useful background information to help you with your coating-related activities. 1. Why do taller/vertical pins on PCBs represent more of a challenge to coat, and can you suggest some key pointers for success? Tall and vertical surfaces present challeng- es to achieving coverage with liquid conformal coatings, predominantly due to gravity and the application method, to a certain degree. Tra- ditionally, liquid conformal coatings rely on solvent evaporation to increase their viscosity and prevent the material from flowing away from sharp corners and vertical surfaces by the combination of gravity or capillary forces. This process is relatively slow, and some degree of coverage issues is always likely to be present. UV-curable materials solidify very rapidly un- der UV radiation of the correct wavelength and intensity; however, there is nearly al- Sensible Design by Phil Kinner, ELECTROLUBE

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