Author Topic: Removing excess flux from soldered PCB  (Read 8996 times)

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Offline RogerMc

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Removing excess flux from soldered PCB
« on: January 17, 2014, 06:06:46 pm »
Finished a project and wanted to remove the flux from the solder side of the PCB.  I used MG Chemicals Flux Remover - Cat 4140-400G.  I sprayed it on and brushed entire board with an anti-static brush.  Clumps of flux disappeared.  Disappointed that the flux was simply spread in a thin coat rather than actually removed.

The ingredients of the MG product are: ethanol, tetrafluoroethane, isopropanol, ethyl acetate.

Any suggestions on a better product or technique?

Thanks!
 

Offline godfrey

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Re: Removing excess flux from soldered PCB
« Reply #1 on: January 17, 2014, 06:29:09 pm »
I've always used denatured alcohol.  I'm not sure if this will yield results any differently than what you've tried…your milage may vary.  20 or so years ago, we'd use this method (it was probably cheaper than most chemicals), and we'd follow the process with a rinse with very hot water and soap…then dry with an air compressor.

I've always bought it in the tin containers available in the paint section of nearly every major hardware store.
 

Offline Kohanbash

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Re: Removing excess flux from soldered PCB
« Reply #2 on: January 17, 2014, 06:37:55 pm »
Hi
I have used flux remover from Techspray with success as well as ultrasonic bath cleaners.
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Offline rdl

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Re: Removing excess flux from soldered PCB
« Reply #3 on: January 17, 2014, 07:36:55 pm »
You probably just need to follow your spraying and scrubbing with a final rinse of clean solvent. Like godfrey said, you should be able to find something at the hardware store in the paint dept. Denatured alcohol is just ethanol with a bit of other solvent(s) mixed in to make it undrinkable. That way they don't have to add liquor taxes :) Some of the the cheaper grades will contain up to 15% water. A second rinse with distilled water may be needed to get it really clean.
 

Offline IanB

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Re: Removing excess flux from soldered PCB
« Reply #4 on: January 17, 2014, 07:44:34 pm »
Finished a project and wanted to remove the flux from the solder side of the PCB.  I used MG Chemicals Flux Remover - Cat 4140-400G.  I sprayed it on and brushed entire board with an anti-static brush.  Clumps of flux disappeared.  Disappointed that the flux was simply spread in a thin coat rather than actually removed.

When you clean things you need to remove the dirt rather than just spread it around.

After you applied the flux remover, where did you expect the flux to go? It should have evaporated into thin air?

As mentioned above, a clean rinse is required, just as when washing dishes or clothes... ;-)
I'm not an EE--what am I doing here?
 

Offline alank2

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Re: Removing excess flux from soldered PCB
« Reply #5 on: January 17, 2014, 09:18:20 pm »
Some fluxes are just hard to remove.  I find that water soluble flux'd solder is much easier to work with.  Hot rinse and compressor air dry and it looks beautiful.
 

Offline RogerMc

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Re: Removing excess flux from soldered PCB
« Reply #6 on: January 17, 2014, 10:32:22 pm »
Thanks

I'm glad I asked.  I *never* would have considered getting water anywhere near an electronic project.  I'll give it a try.

Guess my expectations for flux REMOVER were high.  I actually expected REMOVAL.  Better name might be Flux Solvent.
 

Offline jmole

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Re: Removing excess flux from soldered PCB
« Reply #7 on: January 17, 2014, 10:37:03 pm »
I use a bath of 90% denatured alcohol along with a toothbrush. Electronic toothbrushes (esp the ultrasonic kind) work really really well for this.
 

Offline IanB

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Re: Removing excess flux from soldered PCB
« Reply #8 on: January 17, 2014, 10:52:02 pm »
Guess my expectations for flux REMOVER were high.  I actually expected REMOVAL.  Better name might be Flux Solvent.

Not to belabor the point, but I'm still confused. Where did you expect the flux to be removed to? A basic law of physics says you can neither create nor destroy matter. Flux is matter. It cannot vanish into thin air just because you pour flux remover on it. You have to remove it yourself by transporting the flux from the board to another place.

Washing consists of two steps. The first step is you use some kind of solvent, detergent or soap with agitation to loosen the dirt. In the second step you use a clean rinse to remove the loosened dirt and carry it away from the thing being cleaned.

Choices for your rinse agent may include isopropyl alcohol, clean flux remover, or possibly deionized water. You may put the rinse in a bath and immerse the board in it, or if the board contains components that should not be immersed you may spray the board with clean rinse liquid and allow it to drain off.
I'm not an EE--what am I doing here?
 

Offline RogerMc

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Re: Removing excess flux from soldered PCB
« Reply #9 on: January 17, 2014, 11:06:17 pm »
Not to belabor the point, but I'm still confused.

You've made your point.  Thank you very much.
 

Offline nanofrog

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Re: Removing excess flux from soldered PCB
« Reply #10 on: January 17, 2014, 11:52:04 pm »
I *never* would have considered getting water anywhere near an electronic project.
If you use water, used deionized/distilled water, not tap water.  ;) Tap water can have dissolved substances that can cause problems.
 

Offline con-f-use

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Re: Removing excess flux from soldered PCB
« Reply #11 on: January 18, 2014, 12:36:58 am »
Ian, before you imply someone is being stupid, think hard.

A basic law of physics says you can neither create nor destroy matter.
Energy. You can destroy or create matter (e.g. in nuclear power plants), but not energy as far as we know.

Flux is matter. It cannot vanish into thin air just because you pour flux remover on it.
It could vanish into thin air and it does. E.g. if you chemically dissolve it into gasses or if you heat it. See your soldering iron for the latter.

It was a perfectly good assumption for a non-expert that a flux remover would actually remove flux.
« Last Edit: January 18, 2014, 12:40:41 am by con-f-use »
 

Offline nicknails

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Re: Removing excess flux from soldered PCB
« Reply #12 on: January 18, 2014, 02:56:21 am »
I usually use acetone with a rag, works pretty well, just use a fan!
 

Offline RogerMc

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Re: Removing excess flux from soldered PCB
« Reply #13 on: January 18, 2014, 03:09:16 am »
Thanks Nick, acetone is next ...
 

Offline zapta

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Re: Removing excess flux from soldered PCB
« Reply #14 on: January 18, 2014, 04:40:45 am »
After you applied the flux remover, where did you expect the flux to go? It should have evaporated into thin air?

No, drip down with the excess cleaner, just like car wash. The problem is that it stays on the board as a thin film.
Drain the swamp.
 

Offline IanB

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Re: Removing excess flux from soldered PCB
« Reply #15 on: January 18, 2014, 05:53:53 am »
Right, but when you wash your car you always rinse off last with clean water or you end up with an ugly film smeared over the windows and paintwork.
I'm not an EE--what am I doing here?
 

Offline RogerMc

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Re: Removing excess flux from soldered PCB
« Reply #16 on: January 18, 2014, 06:07:10 am »
Right, but ...

Now I wish I'd never asked ... Thanks for helping
« Last Edit: January 18, 2014, 06:14:23 am by RogerMc »
 

Offline zapta

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Re: Removing excess flux from soldered PCB
« Reply #17 on: January 18, 2014, 08:59:08 am »
Now I wish I'd never asked ... Thanks for helping

I am having same problem with same product. I got out to the yard, spray the board generously, everything looks nice, but when it dries it has an ugly white film from left over flux. If you find a combination that works, please post it here.
Drain the swamp.
 

Offline mrflibble

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Re: Removing excess flux from soldered PCB
« Reply #18 on: January 18, 2014, 11:00:28 am »
IPA + toothbrush to loosen the gunk. Sometimes a rough paper towel over a particular dirty spot + IPA + toothbrush. Demineralized water to flush the gunk.

Or use an ultrasonic cleaner...
 

Offline rdl

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Re: Removing excess flux from soldered PCB
« Reply #19 on: January 18, 2014, 12:19:00 pm »
Please read the MG Chemicals "Flux Removal Guide". It is available at this link:

http://www.mgchemicals.com/tech-support/instructional-guides/flux-removal/


Quote
Q. How do I remove flux?

A. Removing flux is a two-step process. The first step is dissolving the flux. The second step is rinsing the dissolved flux off of the PC board. The rinsing step is very important because after dissolving the flux it may appear that the solids in the flux have disappeared, but once the flux remover has evaporated away, the solids will re-deposit on the board as white residue.
 

Offline zapta

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Re: Removing excess flux from soldered PCB
« Reply #20 on: January 18, 2014, 04:59:00 pm »
Please read the MG Chemicals "Flux Removal Guide". It is available at this link:

http://www.mgchemicals.com/tech-support/instructional-guides/flux-removal/


Quote
Q. How do I remove flux?

A. Removing flux is a two-step process. The first step is dissolving the flux. The second step is rinsing the dissolved flux off of the PC board. The rinsing step is very important because after dissolving the flux it may appear that the solids in the flux have disappeared, but once the flux remover has evaporated away, the solids will re-deposit on the board as white residue.

What is a simple and effective way to rinse?  I just kept spraying, letting the excess to drip but it does not work.

I have an ultra sound cleaner that I use for bike chains, is it useful for PCBs? What solution?    (I occasionally need to clean one off boards, no large quantities).
Drain the swamp.
 

Offline nanofrog

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Re: Removing excess flux from soldered PCB
« Reply #21 on: January 18, 2014, 06:12:01 pm »
What is a simple and effective way to rinse?  I just kept spraying, letting the excess to drip but it does not work.

I have an ultra sound cleaner that I use for bike chains, is it useful for PCBs? What solution?    (I occasionally need to clean one off boards, no large quantities).

From the MG Chemical page...
Quote
Step 2 :

Rinsing the board You must ensure that you push the dissolved flux solids off of the board, before the flux remover evaporates and the solids re-deposit. If you are using flux remover in aerosol form, the easiest way to do this is to hold the board vertically and liberally apply more flux remover until you see the flux remover running off of the board. If you have dissolved the flux by submerging the board in liquid flux remover, just dip the board into the tray and swish the flux remover and you should be ok. If you have been using the particular tray to dissolve flux on a number of boards, dissolved flux may accumulate in the tray and dipping the board may actually deposit flux solids onto the board. In this case you will want to either set up a separate tray for rinsing, or have an aerosol can handy for rinsing. A particularly good option for rinsing dissolved flux off of a board is to use our 406B Super Wash. Super Wash comes in a large aerosol can, allowing for liberal use, and it dries very rapidly. Super Wash will rinse off un-evaporated flux remover as well as flux solids, and almost immediately after rinsing your board with it the board will be dry and ready for service. - See more at: http://www.mgchemicals.com/tech-support/instructional-guides/flux-removal/#sthash.m1tcpgq1.dpuf

That said, what you tried does work, but you may not have used enough of it (bold text).  :-// They're in business to sell you chemicals of course, and they're not exactly inexpensive products when you find yourself going through a can on one or two boards, depending on size and how much crap has to be cleaned off.

IPA in the highest concentration you can get is a much less expensive solvent for removing flux, so something you might want to give a try and see how it works for you. Some ESD brushes will help too to break up heavy, stubborn deposits (cheap on eBay, aliexpress, or deal xtreme <dx.com>). Cheap dental picks/scrapers can be useful for this too.

You'd be able to use an ultrasonic cleaner, either with IPA or distilled water. Heated works even better, but don't leave the boards in there too long, as it can cause problems (heated or not). Experimentation would probably be the best way to go about it, no knowing anything about the unit you have.

Also make sure you're components can be immersed, as not all can be (check the datasheets).
 

Online BravoV

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Re: Removing excess flux from soldered PCB
« Reply #22 on: January 18, 2014, 06:18:26 pm »
Since cleaning flux basically dissolving the flux with the solvent, even with fresh solvent, it will never gone completely right ? The flux is just getting lesser until you just can't see it anymore, but still there at very tiny amount, maybe like ppm or ppb quantity ?

Just curious on how volt nuts clean their ultra precision circuits like say voltage reference board ? Clean, dry, measure ... if not in spec, then repeat until in spec ?  >:D

Offline rdl

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Re: Removing excess flux from soldered PCB
« Reply #23 on: January 18, 2014, 06:42:31 pm »
I spent nearly 25 years formulating industrial coatings, and not the water based stuff. We dissolved polymers in organic solvents. I will give you a little hint, rosin is not actually all that soluble in the solvents contained in those commercial "flux removers", or in alcohols such as IPA and ethanol. There are solvents you can get which would work much better for rosin based flux, but I would guess their use in "flux removers" is overly regulated. You might want to try some of the newer type solders with water removable flux.
 

Offline nanofrog

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Re: Removing excess flux from soldered PCB
« Reply #24 on: January 18, 2014, 11:25:00 pm »
You might want to try some of the newer type solders with water removable flux.
To much of an issue with corrosion for a hobbyist user (too easy to leave it on too long w/ hand soldering IMHO), so I wouldn't. Don't see many others that recommend using it either.

BTW, what where you using? TCE, Benzene, and/or CFC's?
 


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