Cleaning a vintage PCB - Page 1
Forum section: electronics / repair

author: PotatoBox
author_rank: Regular Contributor
timestamp: June 18, 2025, 06:22:59 pm
content: Hello,I have a vintage arcade PCB from the 90s (QFP SMD technology as well as some through-hole EPROMs) that has some sort of odor-less residue on the surface of most of the board, including the EPROMs. It makes the board look a little bit shiny.These have those 1/2 AA Maxell batteries that had axial leads on them that are infamous for exploding and/or leaking. But I don't believe a battery leak is what caused this since those usually explode in a spectacular fashion. Maybe it was stored in not so nice conditions? I am not so sure.But regardless, I am trying to clean this board and get it going again. My idea to clean this is to use a soap/water bath with a painters brush to clean, followed by a rinse water bath, and then a final, alcohol bath to evaporate all the water.Just wondering to hear your thoughts.

author: benj38
author_rank: Frequent Contributor
timestamp: June 18, 2025, 06:50:26 pm
content: Sounds fine except for the last step. The problem with water is not the water itself, but minerals in the water which remain on the board after it evaporates, regardless of your proposed alcohol bath.The solution is to rinse off the tap water you use for the soap cleaning process with de-ionized water. In other words, once you finished thoroughly rinsing off the soap with tap water, use de-ionized water to rinse off the tap water (doing everything with de-ionized water is obviously possible, but it will use more of it, and saves little time). I usually use a spray bottle (set to emit something between mist and a laser-beam jet) and spray everything liberally, getting into all the nooks and crannies under ICs etc., displacing the tap water and pushing it over the edges of the board by the stream of de-ionized water.The de-ionized water will then evaporate without leaving any residue, and you do not need to use alcohol at all. Gentle heat --- I use a convention oven set to 100 F (bread rise setting) --- will accelerate the process, but is not strictly necessary if you do not have the option and you are patient.

author: edpalmer42
author_rank: Super Contributor
timestamp: June 18, 2025, 07:34:29 pm
content: Are you sure it's a 'residue'? Could it be a conformal coating that's starting to flake off?

author: tooki
author_rank: Super Contributor
timestamp: June 18, 2025, 07:48:42 pm
content: The shiny coating could also be nothing more than rosin flux. I have seen old boards that were literally coated in it.benj38, what’s wrong with doing a final rinse with alcohol instead of DI water?

author: jpanhalt
author_rank: Super Contributor
timestamp: June 18, 2025, 07:49:51 pm
content: Many/most soaps leave residues. You probably mean detergent, anyway. Try a less ionic solution like aqueous flux cleaner that is better on resins and such.

author: PotatoBox
author_rank: Regular Contributor
timestamp: June 18, 2025, 09:01:37 pm
content: Quote from: tooki on June 18, 2025, 07:48:42 pmI believe it is from after it was manufactured. The residue is also ontop of the EPROMs too and of all the photos of the same board I see online, none of them have a residue or anything left over from manufacturing.Quote from: jpanhalt on June 18, 2025, 07:49:51 pmI mean dish-soap, sorry.Quote from: edpalmer42 on June 18, 2025, 07:34:29 pmIt really feels like something that occurred way after it was manufactured.I will get a photo to help describe my situation.

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2025, 09:23:57 pm
content: Do a test with a Q-tip swab and isopropyl alcohol, at the edge of the board, to see if the coating is soluble in that. Soapy water as well.Some PCB contamination is water soluble, so dish soap works- but oily residues need IPA or stronger.PCB's from bars and lounges where there were smokers were really the worst.If it's a silicone conformal coating, then not much will happen. Acrylic conformal coatings usually crack with age more so you can have an idea if that's the coating.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 18, 2025, 10:22:03 pm
content: Quote from: floobydust on June 18, 2025, 09:23:57 pmI disagree with that statement that IPA is stronger than water-based removers/cleaners. It is quite the opposite.QuoteAcrylic will be soluble in acetone/lacquer thinner, but not very soluble in IPA. It may become sticky in IPA depending on the water content.

author: floobydust
author_rank: Super Contributor
timestamp: June 19, 2025, 12:16:33 am
content: Quote from: jpanhalt on June 18, 2025, 10:22:03 pmI was trying to say there is a difference between IPA and soapy water - some substances dissolve in one but not the other.For contaminated boards, I have seen tar/smoke, dust and coal dust, glycol (CNC lathe coolant mist), liquor/booze, as the uglier ones. A toothbrush scrub or ultrasonic cleaning worked.So for OP's video game board, it sorta sounds like a conformal coating

author: jpanhalt
author_rank: Super Contributor
timestamp: June 19, 2025, 11:48:08 am
content: @floobydustI was responding the the "water soluble" part. Fats and oily residues clearly are not very soluble in water alone, but detergents in water and mixed solvents like Kester water-based flux removers are more effective at removing them than IPA alone. That applies particularly if some of the gunk on the board is flux residue as suggested by others.Except for spot cleaning, I stopped using alcohols (my favorite being absolute ethanol with or without acetone) a few years ago. The difference was startling.

author: Jeroen3
author_rank: Super Contributor
timestamp: June 19, 2025, 11:58:43 am
content: You shouldn't be using pure IPA anyways, dilute it to 70% first with de-ionized water.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 19, 2025, 01:01:07 pm
content: Quote from: Jeroen3 on June 19, 2025, 11:58:43 amWhy? If worried about residues such as from flux, smoke, etc. (i.e. resins and oily stuff) water decrease the ability of ethanol and IPA to remove them.

author: PotatoBox
author_rank: Regular Contributor
timestamp: June 19, 2025, 05:45:17 pm
content: Here are the following boards:

author: jpanhalt
author_rank: Super Contributor
timestamp: June 19, 2025, 06:05:02 pm
content: Are those before or after cleaning? If before, it looks like only a little spot cleaning might be used for appearance.

author: PotatoBox
author_rank: Regular Contributor
timestamp: June 19, 2025, 07:07:22 pm
content: Quote from: jpanhalt on June 19, 2025, 06:05:02 pmNo I have not cleaned it yet. There is a very light glaze of residue, especially visible on the black plastic on the ICs.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 19, 2025, 10:36:42 pm
content: I hope your house is as clean as those boards are before cleaning.

author: benj38
author_rank: Frequent Contributor
timestamp: June 21, 2025, 06:08:32 pm
content: Quote from: tooki on June 18, 2025, 07:48:42 pmAssuming that the board isalready cleanof all the dirt that was on it to begin with: mostly price.The purpose of the last rinse is to get rid of all the tap water used earlier, and thus removing the minerals dissolved in it.This is done by diluting and mechanically pushing or flushing the tap water and residual minerals with relatively large amounts of a liquid that has no dissolved solids in it. DI water is by far cheaper than alcohol, so one is not tempted to be skimpy, and correct thorough flushing can be easily achieved. In addition, the minerals dissolve in it better (but I guess this will not make much of a difference if the board is already completely wet with tap water in which the minerals are dissolved).

author: KrudyZ
author_rank: Frequent Contributor
timestamp: June 21, 2025, 06:18:57 pm
content: Quote from: PotatoBox on June 19, 2025, 05:45:17 pmThese boards are already quite clean.I would only clean the area around the removed battery and leave the rest alone.This is not an electrometer front end and a tiny amount of leakage current will do no harm at all.