Solder Flux Removal

I've been working with circuit boards for a long time and used to be I wouldn't worry about the leftover flux on the boards.  Recently, though, I decided that they'd look better if I "washed" the flux off.  I'e tried alcohol, as well as "flux remover" but the boards are "sticky" after the "wash".  My solution, so far, is multiple washes and letting the alcohol with the dissolved flux run off of the board.  Is there a better solution.  I seem to have to do this 5-6 times to eliminate the "stick".
Thanks!
Best,
Bruno2000

I've used a flux remover spray - but it also sometimes takes many sprays for it to work. The board can even look clean, but some components can still be sticky, requiring yet more sprays until really clean. And the spray is expensive too, so I'm not sure I would recommend it over alcohol.

Flux can be conductive... We had an issue where flux was causing an opamp  to have the audio output go to ground. When flux was removed, said opamp was  fine and no audible issues.

I use flux remover spray and scrub pcb with the attached brush or an old tooth brush, then use iso alcool to clean i further. While cleaning I try to handle the pcb vertically not to let too much flux going to the other side. Often I use cotton swab to do final cleaning with alcool.
Tedious process but pcb is nice and solder pads shine at the end.
Either I clean the PCB thoroughly or I don't clean it as I found half cleaning a PCB looks worst than no cleaning at all

old toothbrush is a good cleaning tool 

I regularly had problems with sticky flux residues after scrubbing  with toothbrush using isopropyl alcohol.
But then I saw a guy on youtube use paper towels and stiff paint brush. Just dip the brush in alcohol, put a paper towel over the board and pinch with brush vertically. That way flux is picked up by paper and after I do it twice it's clean as new.
You just have to keep flux from spreading all over the board. Paper towels do the trick!

I usually use a toothbrush and cellulose thinner (?) or in german: "Nitroverdünnung". This is really aggressive and you have to be careful as it can wipe the paint off of your resistors on the stuffed side of a PCB but it's clean really quick on the solder side.  Final cleaning with a cotton stick and alcohol. Having tried flux remover and isopropyl alcohol besides other stuff with little succes, this has been the best solution for me so far.

Thanks for the trick with the paper towel, need to try this.

Could scratch off big blobs of excessive flux (e.g. using pointed wood tool) before isopropanol etc washing. Tedious though.

shot said:

I regularly had problems with sticky flux residues after scrubbing  with toothbrush using isopropyl alcohol.
But then I saw a guy on youtube use paper towels and stiff paint brush. Just dip the brush in alcohol, put a paper towel over the board and pinch with brush vertically. That way flux is picked up by paper and after I do it twice it's clean as new.
You just have to keep flux from spreading all over the board. Paper towels do the trick!

Click to expand...

Great trick, thanks!  I'll try it.
Best
Bruno2000

Kimwipes and alcohol.

But I clean joints right away, when they're still fresh. Flux hardens and becomes much more difficult to remove after a few minutes.

Most fluxes don't actually break down in iso alcohol,  so it really just spreads it around the board rather than removing it.  You have to keep changing the iso as you brush it, and it takes 5 or 6 rounds before the residue disappears.

Acetone actually breaks down flux, so it works REALLY well. It also removes silkscreen and a lot of other stuff as well, so you have to be really careful with it.  I typically don't put silkscreen on the bottom / solder side of PTH PCB's so it isn't too much of an issue.

Many PCB houses use water-soluble solder flux, and clean ultrasonically in a light solution of water and a wetting agent.

bruno2000 said:

I've been working with circuit boards for a long time and used to be I wouldn't worry about the leftover flux on the boards.  Recently, though, I decided that they'd look better if I "washed" the flux off.  I'e tried alcohol, as well as "flux remover" but the boards are "sticky" after the "wash".  My solution, so far, is multiple washes and letting the alcohol with the dissolved flux run off of the board.  Is there a better solution.  I seem to have to do this 5-6 times to eliminate the "stick".

Click to expand...

Water-soluble fluxes clean well with water, scrub with a toothbrush or a chip (paint) brush with the bristles trimmed to about ⅛" in length.

Other fluxes need an actual surfactant cleaner to remove them, alcohol doesn't work. Again, we use something called Detergent 8 at work. It's a low-foam (foaming cleaner is BAD), no phosphate cleaner. I suspect it's similar to a dishwasher detergent. Dilute and go, and rinse with deionized or distilled (not tap) water.

Anything wrong with using Kester 331? Water soluble but ya gotta wash it very well, which is not hard to do with a good used toothbrush.

Mix alcohol with acetone in a 10:1 ratio and you have a commercial product for removal.

That detergent 8 is wonderful, very expensive stuff.

Am I weird for always using "no clean" solder and just leaving the flux as is? Is there really an advantage to cleaning non conductive flux off a board minus cosmetic reasons?

iampoor1 said:

Am I weird for always using "no clean" solder and just leaving the flux as is? Is there really an advantage to cleaning non conductive flux off a board minus cosmetic reasons?

Click to expand...

That's why no-clean flux was invented ... so boards would not need a cleaning step after stuffing.

This is very helpful when a board has parts which cannot be immersion cleaned (unsealed pots, displays, etc).

Indeed..with a factory fresh PC board, nasty fluxes are not required.

Buuuuuuttttt..  <g>  when working with "antique" gear....all bets are off.


Bri