Removing excess flux from soldered PCB - Page 1
Forum section: electronics / beginners

author: RogerMc
author_rank: Contributor
timestamp: January 17, 2014, 06:06:46 pm
content: Finished a project and wanted to remove the flux from the solder side of the PCB. I used MG Chemicals Flux Remover - Cat 4140-400G. I sprayed it on and brushed entire board with an anti-static brush. Clumps of flux disappeared. Disappointed that the flux was simply spread in a thin coat rather than actually removed.The ingredients of the MG product are: ethanol, tetrafluoroethane, isopropanol, ethyl acetate.Any suggestions on a better product or technique?Thanks!

author: godfrey
author_rank: Contributor
timestamp: January 17, 2014, 06:29:09 pm
content: I've always used denatured alcohol. I'm not sure if this will yield results any differently than what you've tried…your milage may vary. 20 or so years ago, we'd use this method (it was probably cheaper than most chemicals), and we'd follow the process with a rinse with very hot water and soap…then dry with an air compressor.I've always bought it in the tin containers available in the paint section of nearly every major hardware store.

author: Kohanbash
author_rank: Regular Contributor
timestamp: January 17, 2014, 06:37:55 pm
content: HiI have used flux remover from Techspray with success as well as ultrasonic bath cleaners.

author: rdl
author_rank: Super Contributor
timestamp: January 17, 2014, 07:36:55 pm
content: You probably just need to follow your spraying and scrubbing with a final rinse of clean solvent. Like godfrey said, you should be able to find something at the hardware store in the paint dept. Denatured alcohol is just ethanol with a bit of other solvent(s) mixed in to make it undrinkable. That way they don't have to add liquor taxesSome of the the cheaper grades will contain up to 15% water. A second rinse with distilled water may be needed to get it really clean.

author: IanB
author_rank: Super Contributor
timestamp: January 17, 2014, 07:44:34 pm
content: Quote from: RogerMc on January 17, 2014, 06:06:46 pmWhen you clean things you need to remove the dirt rather than just spread it around.After you applied the flux remover, where did you expect the flux to go? It should have evaporated into thin air?As mentioned above, a clean rinse is required, just as when washing dishes or clothes... ;-)

author: alank2
author_rank: Super Contributor
timestamp: January 17, 2014, 09:18:20 pm
content: Some fluxes are just hard to remove. I find that water soluble flux'd solder is much easier to work with. Hot rinse and compressor air dry and it looks beautiful.

author: RogerMc
author_rank: Contributor
timestamp: January 17, 2014, 10:32:22 pm
content: ThanksI'm glad I asked. I *never* would have considered getting water anywhere near an electronic project. I'll give it a try.Guess my expectations for flux REMOVER were high. I actually expected REMOVAL. Better name might be Flux Solvent.

author: jmole
author_rank: Regular Contributor
timestamp: January 17, 2014, 10:37:03 pm
content: I use a bath of 90% denatured alcohol along with a toothbrush. Electronic toothbrushes (esp the ultrasonic kind) work really really well for this.

author: IanB
author_rank: Super Contributor
timestamp: January 17, 2014, 10:52:02 pm
content: Quote from: RogerMc on January 17, 2014, 10:32:22 pmNot to belabor the point, but I'm still confused. Where did you expect the flux to be removed to? A basic law of physics says you can neither create nor destroy matter. Flux is matter. It cannot vanish into thin air just because you pour flux remover on it. You have to remove it yourself by transporting the flux from the board to another place.Washing consists of two steps. The first step is you use some kind of solvent, detergent or soap with agitation to loosen the dirt. In the second step you use a clean rinse to remove the loosened dirt and carry it away from the thing being cleaned.Choices for your rinse agent may include isopropyl alcohol, clean flux remover, or possibly deionized water. You may put the rinse in a bath and immerse the board in it, or if the board contains components that should not be immersed you may spray the board with clean rinse liquid and allow it to drain off.

author: RogerMc
author_rank: Contributor
timestamp: January 17, 2014, 11:06:17 pm
content: Quote from: IanB on January 17, 2014, 10:52:02 pmYou've made your point. Thank you very much.

author: nanofrog
author_rank: Super Contributor
timestamp: January 17, 2014, 11:52:04 pm
content: Quote from: RogerMc on January 17, 2014, 10:32:22 pmIf you use water, used deionized/distilled water, not tap water.Tap water can have dissolved substances that can cause problems.

author: con-f-use
author_rank: Unknown
timestamp: January 18, 2014, 12:36:58 am
content: Ian, before you imply someone is being stupid, think hard.Quote from: IanB on January 17, 2014, 10:52:02 pmEnergy. You can destroy or create matter (e.g. in nuclear power plants), but not energy as far as we know.Quote from: IanB on January 17, 2014, 10:52:02 pmIt could vanish into thin air and it does. E.g. if you chemically dissolve it into gasses or if you heat it. See your soldering iron for the latter.It was a perfectly good assumption for a non-expert that a flux remover would actually remove flux.

author: nicknails
author_rank: Regular Contributor
timestamp: January 18, 2014, 02:56:21 am
content: I usually use acetone with a rag, works pretty well, just use a fan!

author: RogerMc
author_rank: Contributor
timestamp: January 18, 2014, 03:09:16 am
content: Thanks Nick, acetone is next ...

author: zapta
author_rank: Super Contributor
timestamp: January 18, 2014, 04:40:45 am
content: Quote from: IanB on January 17, 2014, 07:44:34 pmNo, drip down with the excess cleaner, just like car wash. The problem is that it stays on the board as a thin film.

author: IanB
author_rank: Super Contributor
timestamp: January 18, 2014, 05:53:53 am
content: Right, but when you wash your car you always rinse off last with clean water or you end up with an ugly film smeared over the windows and paintwork.

author: RogerMc
author_rank: Contributor
timestamp: January 18, 2014, 06:07:10 am
content: Quote from: IanB on January 18, 2014, 05:53:53 amNow I wish I'd never asked ... Thanks for helping

author: zapta
author_rank: Super Contributor
timestamp: January 18, 2014, 08:59:08 am
content: Quote from: RogerMc on January 18, 2014, 06:07:10 amI am having same problem with same product. I got out to the yard, spray the board generously, everything looks nice, but when it dries it has an ugly white film from left over flux. If you find a combination that works, please post it here.

author: mrflibble
author_rank: Super Contributor
timestamp: January 18, 2014, 11:00:28 am
content: IPA + toothbrush to loosen the gunk. Sometimes a rough paper towel over a particular dirty spot + IPA + toothbrush. Demineralized water to flush the gunk.Or use an ultrasonic cleaner...

author: rdl
author_rank: Super Contributor
timestamp: January 18, 2014, 12:19:00 pm
content: Please read the MG Chemicals "Flux Removal Guide". It is available at this link:http://www.mgchemicals.com/tech-support/instructional-guides/flux-removal/Quote

author: zapta
author_rank: Super Contributor
timestamp: January 18, 2014, 04:59:00 pm
content: Quote from: rdl on January 18, 2014, 12:19:00 pmWhat is a simple and effective way to rinse? I just kept spraying, letting the excess to drip but it does not work.I have an ultra sound cleaner that I use for bike chains, is it useful for PCBs? What solution? (I occasionally need to clean one off boards, no large quantities).

author: nanofrog
author_rank: Super Contributor
timestamp: January 18, 2014, 06:12:01 pm
content: Quote from: zapta on January 18, 2014, 04:59:00 pmFrom the MG Chemical page...QuoteThat said, what you tried does work, but you may not have used enough of it (bold text).They're in business to sell you chemicals of course, and they're not exactly inexpensive products when you find yourself going through a can on one or two boards, depending on size and how much crap has to be cleaned off.IPA in the highest concentration you can get is a much less expensive solvent for removing flux, so something you might want to give a try and see how it works for you. Some ESD brushes will help too to break up heavy, stubborn deposits (cheap on eBay, aliexpress, or deal xtreme <dx.com>). Cheap dental picks/scrapers can be useful for this too.You'd be able to use an ultrasonic cleaner, either with IPA or distilled water. Heated works even better, but don't leave the boards in there too long, as it can cause problems (heated or not). Experimentation would probably be the best way to go about it, no knowing anything about the unit you have.Also make sure you're components can be immersed, as not all can be (check the datasheets).

author: BravoV
author_rank: Super Contributor
timestamp: January 18, 2014, 06:18:26 pm
content: Since cleaning flux basically dissolving the flux with the solvent, even with fresh solvent, it will never gone completely right ? The flux is just getting lesser until you just can't see it anymore, but still there at very tiny amount, maybe like ppm or ppb quantity ?Just curious on how volt nuts clean their ultra precision circuits like say voltage reference board ? Clean, dry, measure ... if not in spec, then repeat until in spec ?

author: rdl
author_rank: Super Contributor
timestamp: January 18, 2014, 06:42:31 pm
content: I spent nearly 25 years formulating industrial coatings, and not the water based stuff. We dissolved polymers in organic solvents. I will give you a little hint, rosin is not actually all that soluble in the solvents contained in those commercial "flux removers", or in alcohols such as IPA and ethanol. There are solvents you can get which would work much better for rosin based flux, but I would guess their use in "flux removers" is overly regulated. You might want to try some of the newer type solders with water removable flux.

author: nanofrog
author_rank: Super Contributor
timestamp: January 18, 2014, 11:25:00 pm
content: Quote from: rdl on January 18, 2014, 06:42:31 pmTo much of an issue with corrosion for a hobbyist user (too easy to leave it on too long w/ hand soldering IMHO), so I wouldn't. Don't see many others that recommend using it either.BTW, what where you using? TCE, Benzene, and/or CFC's?