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For removing rosin flux from my board, should I use Acetone or Isopropyl Alcohol? I need an easily available solvent.

Voltage Spike
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MetricSystemAdvocate
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    IPA is widely used for removing flux, I'd say go with that. Acetone can dissolve certain plastics, it may be too aggressive for cleaning a PCB (but I haven't tried). – marcelm Jul 17 '17 at 11:03
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    @marcelm If you want to answer the question, please do so in the appropriate place. Comments are for requesting clarification or pointing out problems. – pipe Jul 17 '17 at 11:08
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    I do love a good pint of it: http://www.anchorbrewing.com/blog/wp-content/uploads/2014/02/Anchor-IPA-bottle-and-pint-3.png – Andy aka Jul 17 '17 at 13:13
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    Weigh in the toxicity. IPA is quite harmless unless you drink a lot of it. Acetone has noxious fumes and is hard on your skin. – winny Jul 17 '17 at 14:32
  • did anyone define "better" before the answer was accepted? I like Andy's IPA better. – Tony Stewart EE75 Jul 24 '17 at 22:00

9 Answers9

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Acetone being used to clean circuit boards can be problematic. The biggest issue that I found was that it leaves a residue in the board that still requires several other cleaning steps to get rid of including IPA and hot water.

Even IPA can leave a residue as it dries.

There is also the problem mentioned in the comments that the acetone can dissolve certain plastics to the great detriment of your electronics assembly. I've seen it eat away the plastic winding wraps on small transformers as an example.

curious_cat
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Michael Karas
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    I've also seen acetone eat away at the casigns of connectors and trimmer pots – Joren Vaes Jul 17 '17 at 13:28
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    Acetone is a definite no-no when cleaning PCB. It eats half your components and who knows what it does with the rest. Stay away from it at all times. – Mast Jul 18 '17 at 09:06
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If you want real results to clean PCBs after rosin-based fluxes, you should use a specially-formulated solvent. Typically the solvents are based on IPA, but contain Toluene, Heptane, and Difluoroethane. Note - no acetone there.

Ale..chenski
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  • I need a more environmentally friendly option, and these solvents are not easily available in India. – MetricSystemAdvocate Jul 17 '17 at 22:46
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    @NullCoderExists rubbing alcohol (IPA) works fine, especially the 99% type (faster dry, doesn't leave water behind.) – wbeaty Jul 17 '17 at 23:18
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    @NullCoderExists, special chemicals are always hard to find for household use. You need to find a manufacturer for the flux-removing mixture. Some producers (like the Chemtronics) charge too much ($12-$25 per can). I took the cheapest one ($6.99) from Fry's (Puretronics #6000 from T.E. Emerald), it works extremely well. – Ale..chenski Jul 18 '17 at 18:57
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For rosin based flux I clean with IPA (93%) and then hot water with a detergent. Then dry. That is for one-of's or a small number of pcbs.

George Herold
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Just adding to the answers because nobody's mentioned it yet - as well as melting plastic, acetone can strip the insulation off enameled (magnet) wires. So if you decide to use it be super careful not to spill any on motors or transformers!

Flyingfirepig
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I can't give you a definitive answer, but see below for a small compilation of DIY flux removers that people have proposed. Additionally, you should consider rinsing the circuit in deionised water and air-drying it. (As a final step, a urethane-based conformal coating ≥2.0 mil thick may be advisable to mitigate against tin whiskers and other contaminants.)

N.B. Observe the safety warnings on the packaging or MSDS of any artificial solvent that you use. Also consider making at least two copies of your circuit: one on which to test your candidate solvent(s) for compatibility, and one for the finished product.

0. Acetone

Reportedly decent at removing some fluxes, probably including rosin-based ones, but may damage plastics.

1. Isopropyl alcohol (IPA)

Perhaps not quite as effective at removing flux as acetone, but close, and less likely to damage plastics. Recommended by Maker.io/DigiKey.

2. Mixture of IPA and acetone

Jeri Ellsworth uses, as a flux remover for rosin flux, a DIY mixture of IPA and acetone "in no exact proportions". At least one other person reports success with this recipe, using a 50/50 mixture (by volume, I guess).

3. Methylated spirits

Burton Lang suggests methylated spirits as a readily available flux cleaner.

4. Mixture of methylated spirits, IPA and ethyl acetate

The Get GUI website suggests a different DIY mixture that they claim is suitable for rosin fluxes and also suitable for non-rosin and no-clean fluxes:

  • 85% by volume ≥95% pure denatured ethanol (ethyl alcohol), aka methylated spirits.
  • 10% by volume ≥95% pure isopropyl alcohol, AKA isopropanol, 2-propanol, IPA.
  • 5% by volume ethyl acetate, AKA ethyl ethanoate, EtOAc, EA.

These are apparently the same three chemicals used in a commercial flux cleaner made by MG Chemicals.

5. Poly-Clens

Burton Lang (mentioned above) also suggests, as a flux cleaner, the Poly-Clens product, though this may not be available globally, and can damage some plastics. There is a discussion of the Poly-Clens suggestion at Hackaday.

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You can use certain dish detergents provided that A: they are not overly acidic/corrosive (rosin/flux itself is fairly acidic) and B: they don't leave any residue/salts. I have had good luck with "hand-safe" detergents. Some people "might" object to it, but I have had far better success with detergents over alcohol or anything else. In truth, there is really no reason to not use a detergent, it's really just a gel consisting of hydrocarbon chains with hydrophillic and hydrophobic components, historically manufactured from some kind of fat and lye. As long as it leaves no residue, or as long as you rinse it off well with distilled water, and you allow it to dry/bake at a low temperature (or blast it with compressed air), you shouldn't have any issues with it, I never have had any issues myself. A lot of the solvents used for flux certainly are not safe to handle, alcohol and detergent are really the only things that won't give you cancer or liquefy your brain. Its simple, cheap, and effective. It's also environmentally safe to use alcohol and dish detergents.

I usually scrub my PCBs with a cotton swab doused in alcohol to get rid of the large blobs of flux, unfortunately even 90-99% IPA seems to always leave a sticky, foul residue, (especially with "no-clean" fluxes) even with mechanical brushing. Dish detergent and hot distilled water, on the other hand, almost always get all of the residue off, especially if you leave it to soak for five or ten minutes. I have heard that manufacturers use a similar process that uses detergents, mechanical scrubbers, and water jets to remove flux, then they either bake them in a low temperature oven (say 60C) or they spray it with compressed air to evaporate all of the water off of the board. Alternately, you can use a water soluble flux and just wash it off with distilled water which is far easier than using traditional or no-clean fluxes. The only reason to use no-clean flux is if you are worried about some residue still remaining after the cleaning process, such as under SMD packages.

If you do rinse your board off with water, regardless of how you clean them, don't use tap water. Distilled water won't have anything in it but water, so you don't have to worry about any minerals, metals, etc that may be in tap water. Distilled water won't leave any residue, and as long as you wash your detergent off, your boards will be residue free.

RedRyder
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  • For rinsing, do you mean carefully applying sparingly to the board and not the components? Surely you can't get the whole board and its components soaked with water... (rust? ingress into caps etc?) – BCA Jan 16 '21 at 03:45
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Use methal spirit, it’s similar with IPA, the difference is methal spirit dry a bit slow. Sometimes people use it to clean windows

Klng Lim
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Easily available solvent: I have used for years trichloroethane, cheap, effective, and not visible residue.

andrea
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  • Hi - Is it *still* easily available? Its use as a solvent was banned in the EU from 1 Oct 2000 by EU Ozone Regulation 2037/2000 (later superseded by EU Regulation 1005/2009, I think) due to it being an ozone depleter. (Other dates apply to counties outside the EU.) I agree it was a very good cleaner when we *could* use it, but unless you have a legitimate source now, and have found some rules that allow its use, then I don't see it being easily available now. :-( – SamGibson Sep 23 '17 at 21:54
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    Hi Sam, I didn't pay attention and didn't know. Honestly the last time I bought is 4-5 years ago, at supermarket; I resumed doing pcbs only in the last year so 2 bottles are still there... I will keep an eye if I can find it. If not available any longer: IPA is expensive, why not using simple ethyl alcohol (C2H5OH)? the coloring agent maybe leaves residual, but then one can always buy that for food use, pure (and good taste :) ); I think it is easier to find than IPA, and - guessing - less expensive. – andrea Sep 24 '17 at 08:03
  • Expensive? A couple of bucks for the good stuff (90%). – Robert Endl Nov 10 '17 at 15:30
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Acid based would be Acetone.

ISO is more than enough for what I'd assume 99.99% of Engineering@Home Apps. to need. However that being said, they both work wonders on hardened, nasty, PCB, with flux everywhere. So if you want to rejuvenate your board, get acetone, less aqueous the better. Flammable, be careful like you would with a grenade. Use a gritted cloth and rubber gloves to slowly wipe away and immediately let dry your PCB. Circuitry should be ready for Re-Flux within 3-4 hrs if done properly. (Full-ATX Motherboard sized, etc.)

clabacchio
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Cam
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