Cleaning flux from PCBs the easy way

While we’re all for building circuits on protoboard or constructing a deadbug circuit for a last minute project, it’s always nice to see a proper PCB now and again. We think that leftover flux can sometimes make even the nicest of circuit boards look a bit dingy, and Hackaday reader [RandomTask] wholeheartedly agrees. He wrote in to share a method he found online that he uses to get his PCBs squeaky clean after soldering.

The secret to his clean PCBs is a product called Poly Clens. It’s essentially a paint brush cleaner that does a great job at removing flux without having to resort to using a brush to scrub it off the board. [RandomTask] simply submerges his newly assembled board in a small container filled with Poly Clens, agitating it for about half a minute or so. After the flux has been removed he rinses it with water, pats it dry, then ensures the board is moisture-free with a few passes of his heat gun.

He says that the entire process takes him less than 5 minutes per board, which is far better than the old alcohol and stiff brush method he used in the past.

What tips or tricks do you have for getting your new projects cleaned up? Be sure to share them with us in the comments.

68 thoughts on “Cleaning flux from PCBs the easy way

  1. Good solution for regular resin flux is to submerge the board in 10% ammonia solution – resin turns into a kind of soap, so a warm water and toothbrush is enough to clean it later. Hairdrier until dry and you are done. This is quite smelly method, but nothing cleans my nose like small bathroom with filled with ammonia ;P

  2. Sorry to bump I’m surprised nobody blots the flux with tissue. I use an uncut acid brush and douse the flux and leave it for a few seconds. Then I use a tissue to soak up the flux and alcohol. I do it a few times and the flux is almost gone. A lot better than leave leave the flux as-is. Cheaper tissues and 90+% isopropyl work great. Like I said, douse the flux, and blot several times.

  3. Apparently most of us do think along similar lines.

    91% iso alcohol and an uncut acid brush user here, with appearances by an old toothbrush for the tougher stuff. I’ve never had any trouble finding 91% iso, it’s available at any drug store and most grocery stores around here. Under extreme circumstances, I’ll pull out the can of cleaner/degreaser commercially sold for the task, but it’s rare that I need it.

    To the earlier comments about acetone no longer being in nail polish remover: I regularly buy 100% acetone in plastic bottles at the drug store, in the nailpolish/makeup section. Never get a question or a raised-eyebrow “you’re a huffer” look, but I’m not a teenager anymore, either.

  4. I see everyone has answered about regular flux, but what about no clean solder flux, I have cleaned boards for 3 days with alcohol, blue shower and di water, non of this cleans, we are picking with probes and keep going thru blue shower, alcohol and di water, it took me all day to clean 4, 4×4 boards, alot of manual labor.

  5. another issue with flux is a no brainer it is a heat conductor so not a good idea to have just stuck on a board near high heat or super tight enclosed areas of high heat emitting components. As stated before flux also has corrosive qualities.

    best cleaning agent 99-100% isopro alchy and toothbrush/paintbrush something soft bristle to not scratch your solder connection (expose copper) and the conformal coating or CCA laminate.

  6. I use a fibreglass pencil brush (RS sell them) does a great job and is not messy. Also if you want small amounts of isopropyl alcohol which works well too, get some earlobe cleanser at a local ear piercing place…it’s isopropyl alcohol!
    From Chris in Somerset, England.

  7. Hello. ☺

    If this poly-cleanse is the same poly-cleanse that is represented on this webpage:


    This shouldn’t substitute a flux remover. It is a really BAD idea to try this out as a substitute. The micro-organisms will eventually make the environment humid enough to solubilize charged particles from activated flux in respired water and will likely cause problems with the board. Remember that, what is invisible to the eye may be visible under a microscope.

    In response to comments that I happened to read:

    IF your using water, it should be distilled. Theoretically, this is still bad in comparison to an organic solvent like IPA (isopropyl alcohol; due to auto-ionization of water and resultant potential for oxidation). Acetone is also slightly more reactive than IPA. At this moment, I am not sure how relevant that is in the case of cleaning computers. IF memory serves, terpentine and trichloroethylene are quite toxic. Xylene is very toxic. And, I would avoid the use of Windex if I have not given thought to the consequences, but I can see how it may work. I am probably going to read up on that to determine if I would deem it safe for me to use on PCBAs. Nonetheless, that’s an interesting idea!

    I thought that the eyelash brush for scrubbing is a great idea.

    I myself am looking for a cost-efficient way of cleaning flux from my experimental projects. If anyone can chime in on this, I would appreciate that.


    knowledge in physiology/molecular biology, chemistry, and computer engineering.

  8. Like in earlier comments, i use a windex/IPA mix for boards that are soiled by use. (Like in synth repairs i do) The windex part will take off clogged up dust and spilled drinks residue (sugar); IPA won’t. Takes a while for boards to get really dry though. Compressed air helps and a couple of hours in a 50 deg C (120 deg F) oven.

    Just IPA for flux cleaning on new boards; used to use 50/50 IPA/Xylene, but Xylene i believe is a carcinogenic so i don’t use it anymore. IPA alone is slower, but with stiff brush and cleaning with absorbing paper does a good job.

    Boards with high impedance circuitry (CMOS/FET), high frequency or connector systems (IC sockets and header connectors!) are most likely to benefit from a clean. Mostly i stick to cleaning those parts only.

    1. You’re right–Xylene is extremely toxic as it is carcinogenic. Regarding slow drying times, if its more economical, you could always wash with isopropyl alcohol after using an isopropyl/ammonia-based solution mix. I could guess 2 small rinses would speed up the process.

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