Removing conformal coating - Page 1
Forum section: electronics / projects

author: HwAoRrDk
author_rank: Super Contributor
timestamp: September 08, 2018, 05:00:48 pm
content: I have this blower fan from a heating system that I am trying to diagnose a possible fault on, and I'm finding it difficult to trace any of the circuitry because the entire control board is covered with a lacquer-type conformal coating. Are there any easy ways to remove this stuff, perhaps chemically?I have been scraping some of it by hand to read chip part numbers, but that gets tedious really quickly.I have available some white spirit (aka mineral spirits), meths (aka denatured alcohol) and acetone - will any of these help?(By the way, the suspect area of the fan controller that I think is at fault is the PWM speed input. I'm trying to determine what kind of signal it's expecting so I can feed it something to test it. I tried a 5V 390Hz signal from an Arduino I had at hand, but no dice.)

author: duak
author_rank: Super Contributor
timestamp: September 09, 2018, 05:18:27 pm
content: There are two general purpose products you could try. If the coating you're working with is like what I used many years ago, lacquer thinner is the stuff as it contains toluene.The second is paint stripper. The more common type has methylene chloride that dissolves most common polymers. Another type, introduced by 3M, uses lye (sodium hydroxide) that might work but would probably attack any exposed metal too. Paint stripper uses a thick carrier that holds the solvent in place to reduce evaporation.Please note that conformal coating is fairly tough and that anything that dissolves it will also attack most every other polymer on the board.Cheers,

author: coppercone2
author_rank: Super Contributor
timestamp: September 09, 2018, 05:23:20 pm
content: sodium hydroxide will make the leads of various components turn into this blue slimy shit.. I once used broke DIP chips as spacers in a hydrogen generator that used lye as a electrolyte

author: Terry01
author_rank: Frequent Contributor
timestamp: September 09, 2018, 05:25:32 pm
content: It's a PITA buddy!I haven't found anything that gets it off without loads of elbow! I am no expert nor have I loads of experience or anything like that so maybe someone with more to offer than me will be along soon!Good luck!

author: HwAoRrDk
author_rank: Super Contributor
timestamp: September 10, 2018, 01:13:32 am
content: I actually managed to find some notes and example schematic of a driving circuit in an old catalogue PDF from the manufacturer of the fan (Papst). I now know that I need to feed it a 1-6kHz PWM signal using an open-collector output, so no need right now to bother stripping any of the conformal coating in order to go poking at the PCB.I don't have any of the suggested stuff on hand, but as acetone is the nearest thing to lacquer thinner, I still might try out using some on a non-important area of the board, just for an experiment.Regarding fault-finding on the fan, even though I can now operate it on the bench at variable speeds, I think something is indeed faulty in the fan's circuitry, because it won'tstayrunning. It cuts off after a random period of time - anywhere from a few seconds to a minute. Don't think it's an overheating problem, as none of the ICs get anywhere near warm. Cycling the power always gets it going again immediately, which is odd. If I can be bothered, further troubleshooting will be dependent on my success with experimenting with some acetone to strip the lacquer.