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…
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.
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.
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.
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.
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.
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….
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.
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.
“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.
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.