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66 DESIGN007 MAGAZINE I DECEMBER 2019 Over the past few months, I have covered the topic of conformal coatings in as much depth as possible. In this column, I'm going to explore some of the essential factors for de- signers in coating selection. As we have all ex- perienced, sometimes, things are not always as simple or straightforward as we would like them to be, and in any engineering discipline, there is always the slightest chance that some- thing might go wrong. Thankfully, the key to kicking that possibility is to be as fully pre- pared as possible. Thus, I'm going to concen- trate on helping you avoid coating pitfalls in my five-point guide. Understanding Coating Values When choosing a conformal coating, con- sider critical material parameters like CTE, Young's modulus, Tg, and gas permeability, as coatings can vary widely in these respects. Designers should also be aware that the val- ues listed in a vendor datasheet are general- ly measured at ambient conditions for newly cured coatings. It is important for designers to understand how the behaviour of materials will vary with temperature and time, especial- ly ageing at higher temperatures. The coating vendor may have information regarding how materials will vary with temperature and time; however, it is imperative to bear in mind that materials will have to be tested by the OEM to make certain the material is fit for use on their assemblies. Temperature excursions must be factored in. For instance, if thermal shock or thermal cycling is overlooked, it could lead to the coating cracking, which will severely com- promise its protective capabilities. Getting Coating Thickness Right Achieving the correct coating thickness is es- sential; bear in mind that if the coating is too thick, it can lead to entrapment of solvents in Top Tips for Conformal Coating Selection Sensible Design by Phil Kinner, ELECTROLUBE

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