![]() ![]() ![]() Paul over at Hackaday reports success using clear acrylic spray paint as a kind of poor man’s Parylene after “comparing the MSDS sheets for ‘real’ acrylic conformal spray coatings, and acrylic paint. ![]() The delicacy of application required when working with IC sensors means that spray-on coatings are usually a bad idea, but there are exceptions. (If you are using cheap sensors from eBay, expect ~20% infant mortality) Be careful not to let coatings wick onto metal contacts like those inside an SD card module or USB connector and remember to seal the cut edges of that PCB so water can’t creep between the layers. Even when we intend to pot a circuit completely, I still give it a thin coat of conformal to protect it during the week long burn-in test before encapsulation. But coatings really shine as a second line of defence that keeps your logger going when the primary housing suffers minor condensation or makes the unit recoverable after a battery leak. You never get 100% coverage so the areas underneath components usually remain unprotected. Both of these two failures pre-date our use of conformal on everything. Like the white example above, this potting was still OK at the surface. ![]() Some epoxies permit slow water vapour migration leading to corrosion at points with leftover flux. Conformals can be made from other compounds like acrylic or urethane, and at the top of the market you have vacuum-deposited coatings like Parylene. You can also just burn the stuff off with a soldering iron if you need to go back for quick modification after its been applied. I like the flow characteristics of 422 for our small scale application, though the vapours are nasty enough to make you wonder how much brain damage your project is really worth. I’ve never seen a head-to-head test of how well the different conformals stand up over time, but the loggers we’ve retired after 5-6 years in service look pretty clean. The RC/Drone crowd regularly report on many of the other options on the market like Corrosion-X, Neverwet, KotKing, etc. Like most conformals, 422-B fluoresces under UV-A so a hand-held blacklight lets you check if it’s thin at some corner, or if you simply missed a spot. Even with a clean board, adhesion to raised ICs can be tricky as surface tension pulls it away from sharp edges. MG Chemicals 422-B Silicone Modified Conformal Coating is the one we’ve used most over the years. ![]()
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