Cleaning dirty PCB - Page 1
Forum section: electronics / general

author: gaminn
author_rank: Frequent Contributor
timestamp: November 23, 2023, 10:29:13 am
content: Hi,I have some PCBs, after many years of operation in dusty environment, they are very dirty - mainly dust from red bricks. The dusty boards fail often, probably humidity is catched by the dust creating unwanted conductive paths. I tried to clean it with compressed air, still there is a dust that solidified due to the humidity. Then I desoldered vulnerable parts like pushbuttons, transformers, etc., immersed the PCB into isopropylalcohol and with brush I got rid off some additional dirt. But still, there is some remaining, it is impossible to reach all with the brush.How would you clean the dirt? I can see only one option and that is ultrasonic cleaner, but I think I should first desolder all aluminium capacitors, as I already saw what ultrasonic waves cause to aluminium foil... Desoldering all capacitors will be pain...Isn't there any other option. Maybe some pressure washing?EDIT: I desoldered all caps from one board and tried to clean it in the ultrasonic cleaner (15l version of thishttps://www.ebay.com/itm/143779950610) with isopropylalcohol. After 5 mins, nothing happened, the dirt is not dissolved at all. Maybe I should use a better agent than isopropylalcohol, but anything water based seems to be quite risky, as there are many connectors etc where the water will have real difficulties to evaporate from.

author: eleguy
author_rank: Regular Contributor
timestamp: November 23, 2023, 10:58:25 am
content: Been there. Sweeping ultrasonic cleaner with proper PCB cleaning liquid works usually best. IPA works also great but as we all know mechanical work is required. Sometimes I have had luck(?) with PCB cleaning solvents. It does not work in all cases but you could give a try.

author: gaminn
author_rank: Frequent Contributor
timestamp: November 23, 2023, 11:08:27 am
content: Can you please recommend a good ultrasonic cleaner and good cleaning liquid that will actually work? I have this onehttps://www.ebay.com/itm/143779950610with IPA and to be honest, at least for PCBs contaminated with soldering flux (and now with solidified dust), it doesn't work at all. The brush is a must.

author: SMTech
author_rank: Frequent Contributor
timestamp: November 23, 2023, 11:58:46 am
content: non-volatile, non flammable cleaners are the only thing you should be putting in an ultrasonic bath. There's lots of them out there specifically for this purpose.Cheap ultrasonic baths may or may not actually have an ultrasonic transducer, some might have a buzzy speaker glued to the chassis to sound the part. Cheap electricals exist on Bay to kill cheapskates and entertain us with Bigclive videos.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 23, 2023, 12:24:30 pm
content: One could use Kester water based flux removers. Their active ingredients are principally a cellosolve (e.g., butyl cellosolve) and ethanol amine (keeps pH high and is also a solvent). A virtually identical composition is in many household floor cleaners/strippers. I use ZEP brand heavy duty floor stripper. Whatever one chooses, the final concentration of cellosolve is about 10%. Hence, they are nonflammable. In my ultrasonic, it takes about 2 minutes.Rinse with water and let dry. I use DI water.Cellosolves are sometimes described using a chemical name like butoxyethanol or mono-butyl ethylene glycol.https://en.wikipedia.org/wiki/2-Butoxyethanolhttps://en.wikipedia.org/wiki/Glycol_ethersDon't let the name confuse you.

author: eleguy
author_rank: Regular Contributor
timestamp: November 23, 2023, 12:58:43 pm
content: Quote from: SMTech on November 23, 2023, 11:58:46 amThat is exactly so! I did not mean that IPA should be put into ultrasonic, no no... I was just referring to other way to clean boards.

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 23, 2023, 04:00:00 pm
content: Hot soapy water and brush my the usual first try for caked on dirt.

author: gaminn
author_rank: Frequent Contributor
timestamp: November 23, 2023, 04:14:36 pm
content: OK, thanks. I never put IPA directly into the ultrasonic cleaner. My ultrasonic cleaner is filled with water, then I put a plastic container filled with IPA into the bath. This might be also the reason it doesn't work clean very well.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 23, 2023, 06:16:37 pm
content: Your original picture looks like accumulated environmental dust/dirt, not solder flux residue. IPA is not great for removing dirt. Hot water and surfactant is effective There are stories about how Tektronix used a household dishwasher with detergent to clean old boards sent for repair.That would probably still work. The water-based flux removers I mentioned are much the same. They use the same chemicals in water that are used to clean tracked on dirt from floors. The difference is that household detergents are often ionic; whereas, the mixtures I mention are less so. The pH is high enough (about 10 or more) that the ethanolamine is mostly non-ionic. (I haven't done that calculation. Its pKa is 9.5 according to Wikipedia.) In any event, it is easily washed off.

author: gaminn
author_rank: Frequent Contributor
timestamp: November 23, 2023, 07:37:59 pm
content: Yes, the dirt comes mainly from brick dust present in the environment, as mentioned in my first message.Any water based solution means I have to dry the PCB very well, which will be problematic as there are many components with cavities very hard to dry. There is e.g. an IGBT module which is definitely not water proof, many female connectors. I will have to remove them before cleaning probably.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 23, 2023, 08:02:52 pm
content: Well, you have a problem. IPA and pure organic solvents that you might consider are not very good for dirt. However, there is an easy way to get rid of water. Just get the board clean, then use any organic solvent that is miscible (soluble in all proportions) with water. Do that a couple times, and the water will be gone.In an extreme case, you can finish with diethyl ether, which is not miscible with water but can dissolve a fair bit. Or, finishing with 99% IPA will get rid of a lot of water too, as the azeotrope is 9% water.

author: CaptainBucko
author_rank: Regular Contributor
timestamp: November 24, 2023, 12:05:27 am
content: Quote from: gaminn on November 23, 2023, 04:14:36 pmHave you tried putting the IPA into a zip lock bag with the PCB inside that? You might getter better transfer of the ultrasonic energy that putting the IPA into a plastic box

author: CaptainBucko
author_rank: Regular Contributor
timestamp: November 24, 2023, 12:08:39 am
content: MendItMark on YT uses a spray on foam type of product on many of the old dirty PCBs, then a tooth brush and it seems to do a decent job.https://www.youtube.com/@MendItMark/videosI don't know what the product is tho.

author: Matt-Brown
author_rank: Regular Contributor
timestamp: November 27, 2023, 02:50:17 pm
content: As long as you dont have parts that cannot be washed (you mentioned female connectors, which can be washed and we do wash here). You just wash in di water, and shake off the excess and bake the boards for a few hours

author: coppercone2
author_rank: Super Contributor
timestamp: November 27, 2023, 10:31:24 pm
content: Quote from: jpanhalt on November 23, 2023, 08:02:52 pmoh boy I can see some problems if someone puts ether in the ultrasonic! boom baaybeeeAlso, with ether, you want to bake your PCB after its dry. Same with spray flux cleaners. I see condensation forming on the boards after cleaning them.stuff in ether, anhydrous IPA, freon... gets really cold. Well maybe not if you pour it on, but from a compressed can it sure does. Ether might get cold enough from the bottle on a humid day to condense on the PCB. But you need to keep your ether dry, if you really want it dry. I would call it advanced as far as solvents go.if you heat the solvent, the problem goes away, but hot ether is lol waiting to happenfor those that don't know what i mean, its basically as safe as fresh gasoline, well a little worse (it is less toxic then gasoline though, I mean flammability, plume, etc). but it also sucks up water from the air

author: jpanhalt
author_rank: Super Contributor
timestamp: November 27, 2023, 11:29:34 pm
content: @coppercone2Rubbish. I did not say to put ether in an ultrasonic. How hot is "hot ether." It's boiling point is below my body temperature. Ether was an option for drying. Is it needed? No. Water +detergentsurfactant (preferably non-ionic) followed by a thorough water rinse and an alcohol if the TS is that concerned about getting rid of water.

author: coppercone2
author_rank: Super Contributor
timestamp: November 27, 2023, 11:35:05 pm
content: just because you ain't say it does not mean someone might just try ithot ether is boiling a measure of ether and then immediately pouring it on or in somethingnot recommended without a good fume hood with a tray. can be used as a final rinse for science things

author: CaptainBucko
author_rank: Regular Contributor
timestamp: November 28, 2023, 06:49:10 am
content: You can put IPA or other plastic compatible flammable solvents into a plastic bag (like a zip lock) with the object to be cleaned, and then place that it the water bath in the cleaner.

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 28, 2023, 08:26:02 am
content: I put my dirty PCB's in the dishwasher (except when there are water sensitive parts like DIP switches, piezo buzzers etc that I can't cover with some kapton tape).Otherwise it's dish soap and an ESD brush.Works well. Have cleaned many greasy welder control boards and test gear/scope PCB's and have yet to kill one.