Electronics > Manufacturing & Assembly

Cleaning dirty PCB

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gaminn:
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 this https://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.

eleguy:
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.

gaminn:
Can you please recommend a good ultrasonic cleaner and good cleaning liquid that will actually work? I have this one https://www.ebay.com/itm/143779950610 with 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.

SMTech:
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.

jpanhalt:
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-Butoxyethanol
https://en.wikipedia.org/wiki/Glycol_ethers
Don't let the name confuse you.

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