Can you use brake cleaner for flux removal on PCBs? According to [Half Burnt Toast], yes you can. But should you? Well, that’s another matter.
In our experience, flux removal seems to be far more difficult than it should be. We’ve seen plenty of examples of a tiny drop of isopropyl alcohol and a bit of light agitation with a cotton swab being more than enough to loosen up even the nastiest baked-on flux. If we do the same thing, all we get is a gummy mess embedded with cotton fibers smeared all over the board. We might be doing something wrong, or perhaps using the wrong flux, but every time we get those results, we have to admit toying with the idea of more extreme measures.
[Toast] went there, busting out a fresh can of brake cleaner and hosing down some of the crustier examples in his collection. The heady dry-cleaner aroma of perchloroethylene was soon in the air, and the powerful solvent along with the high-pressure aerosol blast seemed to work wonders on flux. The board substrate, the resist layer, and the silkscreen all seemed unaffected by the solvent, and the components were left mostly intact; one LED bar graph display did a little melty, though.
So it works, but you might want to think twice about it. The chlorinated formula he used for these tests is pretty strong stuff, and isn’t even available in a lot of places. Ironically, the more environmentally friendly stuff seems like it would be even worse, loaded as it is with acetone and toluene. Whichever formula you choose, proceed with caution and use the appropriate PPE.
What even is flux, and what makes it so hard to clean? Making your own might provide some answers.
I’ve seen water soluble flux used 100% successfully in a large production environment. Chlorinated solvent stuff was only good for nasty accidents involving unwary workers.
Water soluble flux is very corrosive. It must be cleaned off quickly and thoroughly.
I tried using some and ruined several boards with it. Running water and a brush is not enough to get it out from under components. It needs an ultrasonic cleaner.
Is water soluble flux what results in that crusty white residue on cheap Chinese electronics?
Water soluble flux is used for plumbing. It is readily washed off while the joint is still hot. It is corrosive if not washed off.
I use sometimes break cleaner to remove flux. Just be sure to pick a break cleaner without acetone…
Is it good for broken parts or for intentionally breaking parts?
Why no acetone? I used to clean my board with acetone. Worked like a charm, however depending on the temperature it tends to evaporate rather quickly, which isopropanol does considderable less.
I once soaked a computer power switch in a jar of industrial degreaser overnight. Came back to a bunch of loose parts in the jar. Apparently the cap part of the switch that held everything together just dissolved away…
Acetone dissolves a lot of stuff that you don’t want dissolved.
What’s worse it may also weaken or soften things that you would not notice until they failed sometime later.
The best way to remove flux is using isopropanol and an old toothbrush. Isopropanol does not attack the silkscreen or the components. Cleaning the PCB from flux after assembly is essential to avoid corrosion.
I print a special machine! Works well.
View the movie at bottom of the thread:
https://www.mikrocontroller.net/topic/564508
Another vote for isopropanol. Mostly, though, I just leave the flux on. It doesn’t seem to hurt anything.
Leaving the flux on doesn’t hurt anyhing until you need to repair the board and then have to deal with fossilized flux residue.
My experience is the same. 75% or better 90% isopropanol will get rid of the flux. I go further and rinse with DI or distilled water, blow dry with compressed air and finish with a hair dryer on high setting to make sure all is completely dry. Vodka or Everclear also work in place of the alcohol.
I second the alcohol recommendation, though I like ethanol (usually sold as ‘denatured alcohol’ for camp stove fuel) over isopropanol.
Regardless, any alcohol works way better if you cut it with 1/3 Windex. I am not a chemist, but I suspect that there’s some detergent or surficant in the Windex that helps keep the flux from coming back out of solution and leaving a smeary mess as the alcohol evaporates.
I suppose there could be ammonia in some window cleaners that could react badly with copper, but I’ve been using the alcohol/Windex thing since someone tipped me to it decades ago, and haven’t had any problems.
Residue will always be left behind if you let your cleaning solution (alcohol) evaporate.
My current method is:
Scrub with alcohol and a brush.
Rinse with tap water. (Alcohol dissolves in water) I often add some dish washer soap too.
Rinse with tap water (no additions).
Tie a cord to the PCB and fling it around. Centrifugal force will fling off nearly all liquid.
Let it dry for a day or so before applying power.
Compressed air as [Gene M] mentions also works. It blows away the liquid under force.
If you don’t want to wait long for the final drying, you can do the final rinse (Step 3) with IPA too. The last remnants evaporate a lot quicker. Heating a bit in an oven also helps of course.
Do not use ‘denatured alcohol’ without testing it for each new batch you get. Don’t. Trust me. Even if it worked once, twice, or a thousand times – don’t.
Denatured alcohol is ethanol that has “something” (the denaturant) added to it to prevent human consumption. But there isn’t just one thing that’s added as a denaturant – there are different denaturants you can add, and some of them are Extremely Bad to use with circuit boards.
Upvote. I always toothbrush and isopropyl / ethyl alcohol. Just make sure to blast/alcohol rinse off the flux saturated alcohol so it doesn’t just cost your entire board in a much thinner layer of schmoo as it dries. The air compressor treatment leaves a terrible mist, unfortunately, so while it works, I’m not sure I ought to recommend it.
Brake cleaner in EU is becoming mostly IPA and fragrance these days.
Or 80% 2-methylpentane.
Don’t know if this could be useful but scale modelers use brake fluid (which is, I suppose, different from brake cleaner) to strip paint off of plastic scale models. I believe this works with enamel and acrylic paints, and leaves the plastic bits (polystyrene) unerneath intact. Another way to do it is with oven cleaner, which was what I tried on my models and it did require soaking for some time in the cleaner and some scrubbing with a toothbrush afterwards but removed most of the (in my case enamel) paint. PCBs should be more durable than polystyrene and flux would seem easier to remove than enamel, but how oven cleaner would react with flux I can’t even guess.
The oven cleaners I’ve seen are pretty corrosive, think of Lye/Alkaline based drain cleaners.
Even some of the “purple” or green colored spray cleaners will etch or turn aluminum dark gray.
I’d be very concerned with oven cleaner attacking the copper and/or other metals.
I’d say to let a test board sit for a few weeks after contact and see if it eats something.
Try it on a scrap or some other test item that you can stand to loose in case it goes badly.
Another issue to consider with some of the brake cleaners, before you gear up around using them.. the EPA banning Chlorinated solvents.
https://www.cnn.com/2024/12/09/health/epa-tce-pce-cancer-causing-contaminants/index.html
Hollywood has given acetone a bad name, but the truth is the opposite (again).
Every cell in the human body produces acetone so the body is very OK with low levels of it. Too much of anything is always too much, but check the LD50: Ethanol is just as ‘toxic’. Try a low carb diet: you body boosts acetone production so much that people around you will complain about it.
It sure will dry out your hands and make them crack, that’s the only reason I try to keep it off my skin. Other than that it’s really not a big deal. Keep a tin of Working Hands around in case it gets bad.
No thank you on the low-carb diet
The biggest fears I have with acetone are the flammability and the fact that it attacks certain thermoplastics.
Acetone vapor smoothing is used in the 3D printing hobby to make smooth. glossy models.
I dont think the flammability issue with Acetone is significantly worse than with IPA, both readily vaporize and burn with sooty flames.
Acetone isn’t the worst, but there’s a difference in soot and vapors from isopropanol, at reasonable quantities.
Acetone is neurotoxic, the dose makes the poison. You can certainly inhale a goodly quantity evaporating from a big pcb in a poorly ventilated space. https://www.sciencedirect.com/science/article/abs/pii/S0013935197937038
Isopropyl alcohol and a stuff brush, cotton buds for smaller areas and lint free wipes are all useful, I suspect one reason for isopropyl not working well is that it’s absorbed a load ofoisture from the air or perhaps was only rubbing alcohol to begin with.
You’ll also get the sticky mess if you don’t use enough.
All fluxes I ever met, including rosin could be perfectly washed out with gasoline, diesel, kerosene and in between including zippo lighter fluid. Basically any mix of alkanes works. Cheap, easy to buy, do no harm to any common components or PCB. Combined with ultrasonic bath it is the best of best for PCB cleaning.
Alkanes usually could dissolve rubber, but it take time, so even if there are some components with rubber, gasoline will evapourate much earlier than it could begin to dissolve rubber.
I don’t know why kerosene or gasoline is not popular for that in DIY, with isopropyl alcohol as the top choice. Isopropyl often leave white residue after washing, making PCB look dirty. Gasoline from regular gas station (normal one, not that thing with alcohol) do much better job.
Acetone is a good solvent for the flux too, but unfortunately it is not friendly to ABS, PS and acrylic compounds sometimes used in PCB-mounted parts, so if you have such components you can’t dip your PCB in it and have to be very careful washing PCB with brush, because acetone is very fluidic and easily could wet parts you want to keep from acetone.
Gasoline is a Very Bad Idea. One spark could ruin your whole day. Diesel (kerosene) is a far better choice, if you need something that strong, but isopropanol will do the job.
Isn’t the same true for any form of high grade alcohol, acetone and many other solvents?
I only have anecdotal experience, but I’ve found acetone to be way less flammable than I expected. Gas burns hard, but acetone burns fairly mildly, closer to how rubbing alcohol does
Acetone and isopropanol have octane numbers well over 100 (110 for acetone and 112 for IPA) which means there is a higher threshold for ignition than standard pump gasoline.
Isopropanol is not nearly as bad as gasoline, which is designed to explode. And the gasoline vapors hang around longer. They sink and accumulate, then a spark and BANG
There goes your day. Kids, don’t use gasoline for cleaning, or starting campfires.
Use white gasoline or alkylate gasoline, the stuff vaporizes much less than pump gas. The pump gas also has all kinds of volatile additives that are both flammable and unhealthy. Bentzene comes to mind.
Safety trolling is a disgusting thing, if you are not aware, especially in places with “hack” in name.
You probably pour gasoline in your car daily and may be use gas stove like billions of people but somehow this is not a Bad Idea, despite not being much different from washing PCBs with gasoline in terms of that pesky sparks ruining your whole day.
Just don’t do stupid things, use common sense and everything will be perfectly OK.
If you are not smart enough to not use open fire or run tesla coil near ultrasound bath with gasoline, you obviously don’t have a problem with washing away flux from PCBs you just soldered.
IPA you could buy, with high probability, will have denaturing agent dissolved in it (Bitrex?). This white residue from IPA is denaturing agent and/or impurities. IPA, clean enough to dry without white residue (chemical lab grade for analysis f.e.) is much more expensive than gasoline/diesel/kerosene. It is just a wasting of money for nothing.
Interesting, that methanol, ethanol and isopropyl are really cheaper than gasoline, but legislations make them more expensive and sometimes unuseable.
If you prefer alcohol solvents for some real reason (IDK, say, because of severe allergy to alkanes), then moonshine is much better than IPA for PCB cleaning. And it could be produced in quantities at home easily. However, it took more time than visiting nearby gas station for gasoline.
Ancient bench tech here, The way I was taught many years ago and still use it today. An acid brush with the bristles cut to 1/2 inch or less and MEK. Both are available at a very reasonable price at any hardware store. MEK needs to be kept away from plastic parts but can be with minimum care. I now use one of the cheap “glue dispenser” bottles with a blunt 20ga needle to apply and the brush to loosen and clear the flux.
MEK isn’t very kind to human bodies. I believe it’s difficult to source for just that reason. Isopropanol is much more available.
Interesting, maybe why my 70 year old body feels so old after 50 years of use.. quart cans are on every hardware store and paint store shelf in my area with no restrictions on purchase.
Cuts new and old (as in tube type chassis equipment) flux with minimum fuss.
To each their own as this thread proves.
Adding MEK into paints/wood varnishes is banned in EU, because lot of woodworker used to apply it while windows and doors were closed to avoid dust contamination of the finish and ofc no PPE. They become <70 IQ after 5-10 years of work, and some dead too.
I using brake cleaner on PCBs for a long time now. My first choice is a ultrasonic bath with isopropanol but for the hard cases, break cleaner.
I had success with the 4th recipe of this post https://electronics.stackexchange.com/a/424392
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.
It is a similar recipe (not the same) than “MG Chemicals 4140 Liquid” flux remover.
I find it useful when the usual Isopropyl Alcohol is just not strong enough to remove “burnt” dried flux.
I think this kind of brake cleaner is too harmful to be used as flux cleaner.
Many other brake cleaners are based on a mixture of light petochemicals (n-alkane, cyclohexane, n-hexan and similar). If you mix one of these break cleaners half/half with isopropyl alcohol it works quite well as flux cleaner, even for non water-soluble flux. For an even better result you can mix in like 5% of orange terpene.
I worked with a guy who swore a dishwasher was the tool of choice. Seriously: load up a dishwasher with your batch of boards and run the load like it was a bunch of dirty dishes.
Seems like a pretty harsh way to treat your boards, but he swore it worked well. Never had the guts to try it myself, nor enough boards at once to justify the bother of it.
A chip brush and acetone/water/propanol/methanol (equal parts) mix works great for me.
I built a “board wash” from a used Bosch dishwasher (metal tub), water/DI filters, pumps, couple costco tubs and an inline water heater.
After the wash use DI compressed air to blow off the boards.
DI water filters are sold as “spotless car wash” filters. I use a standard charcoal/mesh filter before the DI filter. The whole thing recycles the water (start with distilled).
Haven’t done a side by side comparison between an industrial inline wash and the dishwasher but there is little difference in operation except the industrial ones have a higher pressure.
I have been meaning to do a blog post about it….
Can confirm: a dishwasher works just fine.
I used to send work to a local mom & pop board house that had a roomfull of them, all with special home-built racking. It worked so well that I occasionally use the method at home when my wife wasn’t looking (tip: you can use the little baskets designed for baby bottles to restrain the boards)
Of course, as with any immersion cleaning, save things like switches, piezo buzzers and other similar items that aren’t happy having water forced inside them for final installation after overall cleaning.
Can confirm the dishwasher. First stop for any dirty pcbs or power modules at many industrial board repair shops was the dishwasher. Usually sprayed them down with a degreaser first (usually 409 or similar) then ran the dishwasher with no detergent. Blow them off after the cycle and put them on a rack with fans to finish air drying for a few days until you get to them. If they had unsealed relays you either removed them if socketed or manually cleaned the boards. Thousands of boards done this way back in the day.
Be happy, be safe and stick to the old standby 90% isopropyl alcohol. Tried and true.
Electrical contact cleaner is your friend. All the fun of brake kleen, with fewer damaged plastics n rubber
CRC QD electronic cleaner. This is the stuff! Works great and I’ve never had it damage anything. Every kit or repair I’ve done has been cleaned and it works!!! Dries quickly with no residue. Available at most auto parts stores and online.
I was going to suggest/ask about using this. I usually have some on hand, as the go-to guy for car repairs in my family, and while I’ve used this to clean contacts in game controllers and TV remotes, I never considered trying it for flux until tonight.
I really wonder why this isn’t high on the list. Same brand that makes brake cleaner makes electronic contact cleaner. It specifically lists being used for flux removal. And depending on the brand you pick, safe on plastic, etc.
Alcohol for fresh flux or pre-cleaning where you need a lot of rinsing, but for serious cleaning, I’ve found nothing that is as effective and fast as 3M Novec. It’s pricey and not all that easy to find, but if you preclean with alcohol, it (with very little brushing) will remove the hardest, nastiest, baked on for years gunk off of your boards and you’ll only need a tiny bit. Works great for fine pitch parts and bgas. The only things that works better in my 40+ years of experience are Freon TF and trichlorethylene which are both banned. Novec is comparatively harmless to people and the environment.
I usually use isopropyl alcohol in most cases, but the best performer so far has been Denatured alcohol (methylated spirits). I haven’t really had the need to use harsher solvents as it works even clearing the hard cooked flux.
This appears to be one of those cases where it’s like asking a mechanic forum which motor oil you should use: ask sixty mechanics, get sixty-five different brands and grades of oil. Each one swore up and down to be the one and only true and essential product to use, or else your engine will immediately explode!
Warning: Brakleen formula varies by country, according to environmental regulations. It is generally nasty stuff that cleans automotive well but contains the usual carcinogens. Also over the many years the formula has changed. It was terrible around 2000, tradespeople got sick working with the stuff.
For dirty boards, a soak in a tray of 90%+ IPA for many minutes really works well.
In my part of the world, they sell two formulations: a newer, safer one and the old one on a higher shelf at a markup. The old stuff definitely works real good, but don’t do it in a garage… Even with the doors open. Similar to Sea Foam. I’ve gotten sick from foaming an engine and breathing too many fumes before.
“Flux-Off” if it has to be ‘spotless’. Isopropyl is ok, sometimes it leaves a chalky (or something) residue. Or use ‘no clean’ solder / flux.
“Flux Off” is a wonderful name.
Brake Cleaner comes in a couple of different formulas, and at least one of them will turn some plastics brittle and others into mush. I only use it where absolutely necessary after testing carefully to make sure it won’t ruin something.
Instead, I usually start by trying 90% rubbing alcohol. If that doesn’t do what I need, I move on to Automotive Starter Fluid as my next choice solvent. I have yet to find a plastic that it damages.
After >35 years in the trade I still use trichlor degreaser as I mix my own parabene grease based rosin & ammonium chloride flux. No cancer nor nerve damage so far.
After >35 years in the trade I still use trichlor degreaser as I mix my own parabene grease based rosin & ammonium chloride flux. No cancer nor nerve damage so far.
In a more general sense, you may work your way up or down the aggressiveness chain depending what you’re doing. Isopropanol is a pretty good one for a lot of things, and if you have to get more aggressive then acetone is still fairly minor to be exposed to in small amounts. I think sometimes something a little weaker than brake cleaner that evaporates faster can be useful, such as the non-lubricated version of starting fluid, aka ether. On the other end of the scale, something like diesel can get black grease off your hands without being so volatile, but in my opinion if you don’t like the orange goop you might try lanolin hand cream or baby wipes for that sort of thing. People have thrown diesel and gasoline around too much just because they’re cheap. They’re still not friendly chemicals.
Personally, I use an ultrasonic bath with Tikopur, followed by a wash in deionized water. If I want it to be quick, I then have a second wash in IPA to push out the water and have the PCB dry quicker.
Gets me nice a professionally clean PCBs.
Personally, I use an ultrasonic bath with Tikopur, followed by a wash in deionized water. If I want it to be quick, I then have a second wash in IPA to push out the water and have the PCB dry quicker.
Gets me nice a professionally clean PCBs.
I have good luck with No-Clean Flux pens.
Naptha and a reasonably soft 5cm paintbrush.
100% guaranteed.
Strangest article I have read in a while with some over-the-top suggestions.
90% IPA == 10% water
Use of IPA should be at the 99.9% quality, tech grade, easily purchased in US from Amazon by the gallons at a cost of approx $17/gal.
Flux on circuit boards only is an issue when sensitive analog IC/OpAmps are used as flux can be hydroscopic with ambient humidity thus creating resistive bridges. Even a partially cleaned board is subject to humidity which is one reason that many Mil boards use conformal coatings.
I prefer commercial flux removers, but have used 99.9% IPA, but be aware that as the IPA evaporates, the board is likely to have moisture condensation due to cooling. Therefore, hot air should be considered or a bake in an oven for a few hours – especially if a conformal coating is to be applied to non-epoxy composite boards.
The board should be vertical with the IPA dispensed from the top and the brushing from top to bottom. DO NOT use a hair dryer to dry as not all dryers are brushless! Sparks are not good around IPA fumes, so best practice would be to do the cleaning in a very well ventilated area … outside.
Two-sided boards should be cleaned without parts like displays and potentiometers affixed as dissolved flux can get trapped… even slight resistance between LCD contacts can cause phantom segments. If a pot is ‘open’ for spraying, you may consider applying a volume-control cleaning product as they typically have a residual silicone lubricant that will help keep stray IPA and dissolved contaminants at bay.
Hacking and ‘cheap’ do not necessarily have to be mutually inclusive; good quality electronic specialty cleaners and lubricants are expensive, but normal usage is typically minimal, so the investment is amortized over time.
My ill advised strategy: Place completed boards in a sealed plastic container of >99% isopropyl (well, it was before being contaminated with flux!). Submerge the container 1/2 way into a heated (30’C) ultrasonic cleaning bath for 90 seconds. Let sit for a few minutes for the alcohol vapor to settle back down. Remove the boards and rinse with water (distilled preferred, especially if you have a high dissolved solids count in your tap water). Dry at 70’C in reflow oven for several minutes. Be sure to keep the alcohol bath sealed between and during use. Observe safety precautions regarding (individually) the reflow oven and alcohol vapors. 70’C is within the safe temperature range for most components to be exposed to long enough to dry out residual moisture, while being high enough to accelerate evaporation, and low enough to not cause steam & violent release of such from hygroscopic components.
You only need to clean if repairing an old board, have super low current or have very high voltage. If soldering new components to new boards with typical circuits and the using the correct solder, cleaning isn’t needed.
Just use a no-clean/low-activity/low-rosin solder. You wont even see the solder flux without magnification. There are water soluble versions that clean up nice in just warm water with a little soap.
When I want to clean the board, I clean the entire board after reflow, then spot clean after through-hole.
“Brake Cleaner” covers a wide array of chemicals, I wish HaD would specify – there appears to be a difference in the commonly sold version in the US vs Europe as I’ve seen warnings from (American) welding channels about cleaning items with brake cleaner as it can release toxic fumes when heated up, while it’s common here in the UK to use brake cleaner for exactly that.
I’ve used the non-chlorinated version off and on for years without any issues; but allways outdoors
https://www.walmart.com/ip/Super-Tech-Non-Chlorinated-Brake-Parts-Cleaner-14-5-oz/35056305