Help removing rosin from PCB

[lazarusr]

I know that this is a subject on which there are loads of posts, both here and elsewhere. But I really haven't had found a solution that works for me.

I am working on a project where it is not only import that it functions correctly, but that the finished PCB looks pristine as well. I do not want to have spatters of flux all over the place. The general advice seems to be that the flux can be removed with 100% IPA. However, that doesn't work properly for me. What seems to happen is that the flux dissolves in the IPA so it seems to be removed. However, the rosin is still there, dissolved in the IPA. As the IPA evaporates, the rosin comes out of solution. I then no longer have splatters of rosin on the PCB, instead I now have a more widely distributed sticky layer on the PCB which then acts as a dust and fluff magnet.

I have tried repeated cleaning with IPA. This tends to reduce the sticky layer, but not remove it entirely. I have seen references to people using cotton buds, but I am not really sure what to do with them. They just get caught on all the little spikes of solder and leave little bits of cotton everywhere. I have also seen suggestion of wiping the PCB with a cloth. Again, I don't understand how this is done without the cloth catching on the solder. I have also seen reference to absorbing the IPA with kitchen towel. That works to an extent, but again, it is very difficult to get the towel in between all the solder with a very densely packed board.

Despite spending more time cleaning the PCB than I did actually soldering the components, I am still left with a sticky residue and also a slightly blotchy pattern.

All this is driving me (and my OCD) nuts. I am sure there must be an easier way to clean a PCB.

Any suggestions massively appreciated.

[suicidaleggroll]

I bathe the board in IPA for a few minutes, let all of the rosin dissolve, brush it with a clean paint brush to get it all off of the board, and then pull the board out of the bath and rinse it with fresh IPA from a squirt bottle.

[orbiter]

I use Electrolube Flux-clean.. for removing Multicore/Loctite PC21A flux which is very like the flux you describe, in that it's very sticky stuff. 100% IPA alone
will not remove PC21A either. Not properly anyway

It's rather expensive for 1L tins, but it's good stuff.

http://uk.farnell.com/electrolube/flu01l/fluxclene-tin-1l/dp/298189

[kolonelkadat]

have you tried the dishwasher?

[apelly]

When IPA fails, I use an ultrasonic bath with dishwasher powder followed by a rinse.

[Howardlong]

Another vote for Fluxclene, but I use it in an aerosol with a semi stiff brush attachment. The boards I do are pretty small, maybe 1 or 2 sq ins., so it lasts quite a while.

If you look at it under the microscope, there's a whole lot of Brownian motion and evaporation action going on.

[mos6502]

I'm sure IPA works, but I use denatured alcohol, it's cheaper. Pour some on a toothbrush, brush, rinse, repeat until clean.

[alank2]

This is why I don't use rosin.  I use water soluble from Kester, it rinses clean with a simple water rinse and then I blast it with compressed air.

[matseng]

How sensitive are those standard tactile buttons? Can they be soldered onto the board before it's cleaned with IPA (possibly in an ultrasonic bath)?  Will flux residue setup into the switch and stay there?

I've always cleaned the pcb before soldering switches and connectors to it. Am I just overly cautious?

[IconicPCB]

Try mineral terps

[alank2]

I've always cleaned the pcb before soldering switches and connectors to it. Am I just overly cautious?

Out of 4 or 5 tactile and pushbutton switches I've cleaned which involves running under water and blasting with compressed air, only 1 tactile switch was sensitive.  A quick bake for 10 minutes at 105 deg C fixed it up though.  I don't normally have a problem water cleaning switches though.

[dave_k]

I am in a similar position to the OP where I am producing a run of boards that need to be clean.

I plan to firstly scrub the boards in a bath of Electrolube Safewash SWAS (they're too big for the ultrasonic bath  ), then rinse with tap water and finally rinse with de-ionised water.

SWAS claims that it is able to absorb up to 15% of it's weight in flux while still being able to clean to military standards. It is biodegradable and safer to work with than IPA too.

More info is here:
http://www.electrolube.com/core/components/products/tds/044/SWAS.pdf

[fivefish]

I use 99.9% IPA and a brush.  First I squirt IPA to the board, brush in circular motion with brush to dislodge  the rosin, then continuing to keep it wet, squirt more IPA, and brush off the board the "dirty IPA". I brush it off to the nearest side so I don't drag any rosin and spread it to  other places. . And then do another squirt of IPA, and while still wet pat dry it. 

[tautech]

Try mineral terps

Thanks for that.
Did some rework yesterday and IPA was useless on the Multicore solder used.

Note to self...try Turps next time.

[helius]

I noticed that most people don't clean correctly, they just spray on IPA or try to brush it around. This can't clean anything as there is nowhere for the dissolved residue to go. You need to use non-lint paper towels and brush them against the board to transfer residues from the board onto something you throw away. For very burned flux you can try acetone or ethyl acetate, but they eat plastic.

[IconicPCB]

Carbon tetrachloride used to be all the rage in seventies.. and then..

[Psi]

I clean boards often with IPA,  visually it's more of an issue with black solder mask because it shows up all the streaks more.

My standard approach is a 2L icecream container on a 45deg angle with maybe 100ml of iso in it.
While holding the PCB 20% submerged I use a semi-stiff brush to scrub the board. Moving ipa up onto the board so it runs down while i scrub.

After 30sec of scrubbing on each side i move to my 2nd ice cream container and use 100ml of fresh solution to rinse the board. No more scrubbing, just letter than iso run over the pcb.

I then take the PCB and instantly blasted with compressed air. This blows off all the iso before it can evaporate and leave anything behind.

However, Electrolube Flux-clean works much better than iso. flux clean can absorb much more flux before you have to replace it.
My two tubs with 100ml of iso do three 80x80mm PCBs before it needs replacing.
Flux clean is quite expensive though, which is why i dont use it

[tautech]

I clean boards often with IPA,  visually it's more of an issue with black solder mask because it shows up all the streaks more.

My standard approach is a 2L icecream container on a 45deg angle with maybe 100ml of iso in it.
While holding the PCB 20% submerged I use a semi-stiff brush to scrub the board. Moving ipa up onto the board so it runs down while i scrub.

After 30sec of scrubbing on each side i move to my 2nd ice cream container and use 100ml of fresh solution to rinse the board. No more scrubbing, just letter than iso run over the pcb.

I then take the PCB and instantly blasted with compressed air. This blows off all the iso before it can evaporate and leave anything behind.

However, Electrolube Flux-clean works much better than iso. flux clean can absorb much more flux before you have to replace it.
My two tubs of 100ml of iso do maybe 3x 80x80mm PCBs before it needs replacing.

Have you ever had problems with ESD and compressed air?

[Psi]

Na, not that i'm aware of.
I test all my products after being cleaned and assembled, out of ~250 units i've never found any dead chips. Just bad solder joints.

[mauroh]

I noticed that most people don't clean correctly, they just spray on IPA or try to brush it around. This can't clean anything as there is nowhere for the dissolved residue to go. You need to use non-lint paper towels and brush them against the board to transfer residues from the board onto something you throw away. For very burned flux you can try acetone or ethyl acetate, but they eat plastic.

+1 

Mauro

[MarkF]

I've seen a few videos where a Kimwipe was placed over the board and the IPA is brushed through the wipe.  I could never figure out why.  Now I can see that the wipe would absorb the residue and flux.

[Fat]

I spray on some 91% IPA then use my wife's toothbrush to work the flux into solution. Then I place a Kemwipe over the board while the alcohol is still in solution and dab the Kemwipe with a clean flux brush with the bristle cut short. This pulls off the major crud.  I repeat the process and use the short bristled flux brush on the bare board, then repeat the Kimwipe routine.  They are not perfect, but are pretty clean.

Fat

[lazarusr]

So many useful ideas. Thanks so much! A lot for me to try out. And confirmation of what I expected, that I was probably doing it wrong.

[stevenhoneyman]

+1 for IPA and a brush, followed by clean IPA and a wipe/compressed air

I bought a couple of these, which weren't much more expensive than a toothbrush and say "esd safe" on them which I know everyone loves
The little one is good for around QFNs.

http://www.ebay.co.uk/itm/Nylon-Soft-Bristle-Toothbrush-Shape-ESD-Anti-Static-Dust-Dirt-Brush-/191646037260
http://www.ebay.co.uk/itm/1-5-x-0-5cm-Black-Plastic-Round-Handle-Anti-Static-ESD-Brush-/191677891868

P.S. "Ultra Sonic cleaners" (note the space after ultra) are complete crap/chinese scam. I bought one for a few quid and it was just a plastic tub with a vibrator motor stuck to it! I got a refund very quickly...

[Gyro]

Another vote for Fluxclene, but I use it in an aerosol with a semi stiff brush attachment. The boards I do are pretty small, maybe 1 or 2 sq ins., so it lasts quite a while.

If you look at it under the microscope, there's a whole lot of Brownian motion and evaporation action going on.

I just wanted to add a word of caution based on personal experience, I've used Fluxclene (and I'd probably better add 'similar products') fairly frequently during my career and during certain project phases a bit too often, and it is really effective on fluxes compared to IPA.

I know that it's easy to become careless and maybe not be as careful as you might in terms of skin contact (which tends to turn your finger tips temporary white as it leaches oils) and inhalation of the (quite orangy) vapors, especially when you're peering at the board and mopping the excess off with paper towel.

It really is important to read those directions on the side of the can, avoid direct skin contact and only use in a very well ventilated area, Minimize leaning over too close to the board too (microscope reference caught my attention).

IPA must be pretty safe because it's used for medical swabs etc. however with more effective action comes a stronger cocktail of solvents which may or may not be as 'benign' over long term exposure if you let your guard drop.

'nuff said