When to conformal coat - Page 1
Forum section: electronics / projects

author: Fratink
author_rank: Contributor
timestamp: November 02, 2022, 04:43:30 pm
content: Hello,I've been looking for a guide on this but really haven't been able to find much. Took a look around the Forum as well and didn't see anyone asking this question.I'm manufacturing a product and we made the decision to conformal coat because the customer was concerned about what might happen if they didn't. However I'm fairly confident that conformal coating isn't particularly useful in our use case. These devices to live outdoors and have an expected lifetime of 5+ years inside a sealed enclosure (+breather filter for pressure balancing). Voltage is max 8VDC. Because some components can't be coated (buttons, modem) there's also a decent cost to coating, not to mention the effect it has on repairability.I haven't found any real literature about it myself so far.Does anyone have experience with conformal coating and when it should be used, such as when you can predict failure rates could be increased without the use of the coating?Thanks!

author: jkostb
author_rank: Regular Contributor
timestamp: November 02, 2022, 07:30:25 pm
content: I have designed electronics for hazardous environments. There conformal coatings certainly have a function. For example on chemical plants a PCB can completely corrode within couple of yours if you don't apply conformal coatings. Another application is when you apply conformal coating you can decrease the creepage distance conform some safety standards. So conformal coatings certainly can have a use case. However if a product is in a outdoor environment, without chemical pollution and in a IP67 housing, you normally don't require conformal coatings. You need to look at the use case

author: m98
author_rank: Frequent Contributor
timestamp: November 02, 2022, 08:12:11 pm
content: Even in an IP67-Enclosure, you're not safe from condensation. So without a conformal coating, the question isn't if your PCB will fail from corrosion, but when. And you can't answer that with >5 Years without some serious testing.

author: thm_w
author_rank: Super Contributor
timestamp: November 02, 2022, 10:00:26 pm
content: Any idea what climate and locations these will be in? I agree with jkostb, usually its not needed in this case, assuming the layout of the enclosure is reasonable.You might consider a nano type coat that is cheaper to apply, and does not need to be removed before soldering:https://www.techspray.com/the-essential-guide-to-conformal-coatingThere is also this cool device:

author: Fratink
author_rank: Contributor
timestamp: November 02, 2022, 10:02:49 pm
content: That's very true, everything does corrode eventually. And I'm going off my very subjective experience of maintaing lightning detectors around my province that had cracked and flaking conformal coating but worked fine for decades. But I also have some experience with military electronics and I rarely see conformal coating applied there and those things have long service lives where uptime is the main concern.I would just expect there to be a book on it or something.

author: Fratink
author_rank: Contributor
timestamp: November 02, 2022, 10:09:41 pm
content: I'm actually not sure what coating we use, our manufacturing team just specified our standard product.We're going to be deploying all over Canada outdoors in agricultural areas, so conditions can be quite varied. The enclosure itself is fully sealed and waterproof so theoretically well protected against water ingress. The CCA itself is also upside down so any direct water dripping on it would roll off the sides and not sit on components. However condensation could still form on the surface of components.We could do an accelerated test where we cycle the temperature rapidly in high humidity, to attempt and pull humid air into the interior. But probably the most dangerous part for the CCA is the 4 AA l91 cells sitting on top of it. If those begin to leak the conformal coating might be the only thing that would save the device. Otherwise it would just be salts entering the enclosure through the vent that would be a source for corrosion I expect. But I'm just guessing haha.

author: thm_w
author_rank: Super Contributor
timestamp: November 03, 2022, 10:02:01 pm
content: Yeah salt is a concern if you are within ~200m of the ocean or so, which is why I ask location, corrosion will occur much faster. But as you noted, it will affect everything, even the things you can't coat.Conformal could save small QFN packages, those tend to fail first. Large SOIC or DIP will take longer to be affected.There is a book here, no idea if its any goodhttps://www.peters.de/cn/blog/info/reference-book-conformal-coatings-for-electronics-applicationsAs for the cells, if you are worried make a plastic cover. But I don't think those lithium cells leak often.