Cleaning PCB soldering paste residues

[tooki]

I would add that if your intent is to clean the boards, then avoid no-clean flux, because many of them are hard to remove. Rosin flux is easier, and of course water-soluble is designed such that it must be cleaned. (Do not use water-soluble for any connections that flux can wick into and become difficult or impossible to clean, like stranded wire or many unsealed switches.)

Water-soluble no-clean fluxes are now available, but I haven’t had a chance to test them yet.

[LinuxHata]

IPA works well with old style fluxes, but it does nothing to modern fluxes.
Even if you help with brush, all your actions will just smear the flux over the PCB.
Acetone works far better, and it is the main component of "flux off" and other things (just look up their MSDS)
However, acetone also requires mechanical interaction (brush), which I found non-practical in case of a lot of PCBs with a lot of fine components.
One that works reasonably well without brush, is Sodium hydroxide (caustic soda), but it also will hurt plastic of electronic components and might mess with enamel in inductor wires, too.

I was able to get information of what do they use in big PCB factories for flux removal and while these substances are available in US only, they're industrial use, have very bad fumes and some of them are even regulated substances (Hint - name of most common used one starts with "per" (No it is not ammonium perchlorate) and it is also used in industrial clothing cleaning systems)

[tooki]

IPA works well with old style fluxes, but it does nothing to modern fluxes.
Even if you help with brush, all your actions will just smear the flux over the PCB.
Acetone works far better, and it is the main component of "flux off" and other things (just look up their MSDS)
However, acetone also requires mechanical interaction (brush), which I found non-practical in case of a lot of PCBs with a lot of fine components.

I’ve looked at the MSDSs of a bunch of (non-water-based) commercial flux removers, and almost all of them avoid acetone entirely because it’s so harsh on plastics.

They are mostly blends of alcohols and hydrocarbons. Using multiple solvent types has synergistic effects that make them far more effective than any of the ingredients alone.

The best way to use them is basically the same way we use Windex when cleaning glass: mop it up with wipes or swabs. A brush will only help dissolve the flux, but you must remove the flux-laden solvent.

[LinuxHata]

I don't know where you were looking, but I just opened the "flux off" MSDS and it clearly says acetone:

https://docs.rs-online.com/95f7/0900766b803e8dfd.pdf

[tooki]

I don't know where you were looking, but I just opened the "flux off" MSDS and it clearly says acetone:

https://docs.rs-online.com/95f7/0900766b803e8dfd.pdf

So what?

I said that almost none contain acetone, which is true. I did NOT say that NONE of them do.


Looking at solvent-based flux cleaner sprays for hand use (I just checked the MSDSes of all of these), not the stuff sold in canisters for machine use, and excluding aqueous cleaners:

Chemtronics alone has 8 different solvent-based flux cleaners, and of those, only 3 contain acetone, and it’s not the main ingredient in all of them. The 3 that do are the ones sold for lead-free or no-clean fluxes.

Kontakt Chemie has only one flux cleaner, and it contains no acetone.

Electrolube has three solvent-based flux cleaners and none contains acetone.

Techspray has four solvent-based flux cleaners for manual use, and none contains acetone.

3M makes one flux cleaner and it contains no acetone.

MicroCare makes 9 flux cleaners and only one contains acetone.


So… that’s 4 with acetone out of 26 cleaners. I think that at minimum, one can say that the vast majority are acetone-free.

[Solder_Junkie]

Some items are best not cleaned, such as this GPS module, which is copied from the U-Blox Neo 8 hardware integration manual:
---------------
Cleaning
In general, cleaning the populated modules is strongly discouraged. Residues underneath the
modules cannot be easily removed with a washing process.
• Cleaning with water will lead to capillary effects where water is absorbed into the gap between the
baseboard and the module. The combination of residues of soldering flux and encapsulated water
leads to short circuits or resistor-like interconnections between neighboring pads.
• Cleaning with alcohol or other organic solvents can result in soldering flux residues flooding into
the two housings, areas that are not accessible for post-wash inspections. The solvent will also
damage the sticker and the ink-jet printed text.
• Ultrasonic cleaning will permanently damage the module, in particular the quartz oscillators.
The best approach is to use a “no clean” soldering paste and eliminate the cleaning step after the soldering
------------------------
SJ

[LinuxHata]

So we have 4 out of 26, this is rougly saying, 15%, quite different from "close to none", right?
And by the way, as you've observed by yourself, acetone is present in a flux removers for the modern solder paste/fluxes - where we all are going to.
So as I said above, if you're old tech, stick with IPA and will be fine, but if you're into newer solder pastes and fluxes, you need to go serious.

[Solder_Junkie]

For those in the UK, this cleaner from Farnell is very effective and cheap too. Order code 1736213.

SJ

[PlainName]

this cleaner from Farnell is very effective and cheap too

Quality, this - even has CAD models!

[tooki]

So we have 4 out of 26, this is rougly saying, 15%, quite different from "close to none", right?
And by the way, as you've observed by yourself, acetone is present in a flux removers for the modern solder paste/fluxes - where we all are going to.
So as I said above, if you're old tech, stick with IPA and will be fine, but if you're into newer solder pastes and fluxes, you need to go serious.

All the ones that contain acetone are for lead-free/no-clean, but not all flux cleaners that are for lead-free/no-clean use acetone. Most brands do them without.

Anyhow, even for classic rosin fluxes, while IPA gets it all off, blended-solvent flux removers do a better job, in that they dissolve it much faster, and without needing as much solvent. IMHO the reduced time and effort make it worthwhile.

[JustMeHere]

I use a toothbrush and flux cleaner.  Don't just spray it on, rinse the board with it.  Spraying on doesn't rinse the rosen away.  Those toothbrushes the dentist give you are perfect. (Yes, maybe, it should be an ESD, but there's no way you need to worry about ESD if the board is wet with flux cleaner.)

I’ve mostly switched from rinsing away with solvent to instead mopping it clean with wipes (like kimwipes) or cotton swabs. You use up far, far less solvent that way.

I started this way, butI found I was spending more on cotton swabs than flux cleaner and getting poorer results. 

[LinuxHata]

I talked to my grandpa, and as he says, in the "good ol days" they used a boiling acetone(!) to remove all flux and greasy residues from the PCB, but only if it contained no plastic parts. Since process was quite dangerous, they later shifted to "less dangerous" mixture, which contained equal portions of acetone, methyl ethyl ketone, tetrahydrofuran and cyclohexanone. Still, can't be used on most of plastics. However, I think I'll give a try to it, since it is currently commercially available in US in almost any brick and mortar store and is called PVC pipe primer.

[jpanhalt]

Those solvents will do it, but a bit safer is alkaline (for "saponification") plus  butyl cellosolve (10%) with water in an ultrasonic.  I am an 80 yo grandpa myself, and I had to do it to believe it.

[MathWizard]

Put it in the dish washer... 

Tried a water-soluble flux remover one time. Foam in a can - spray on, scrub, rinse off with water. It was a very strange feeling running a PCB under the kitchen faucet!

These days I like to use Fluxclene, made by Electrolube. Its a mixture primarily of hexane (white gas / white spririt), isopropyl alcohol and orange terpenes. That stuff will dissolve all sorts of resinous or oily crap - I don't just use it on PCBs.

These days I use a toothbrush and hot soapy water. Cheap and easy, I try not to use the kitchen sink, but I do sometimes with little proto-boards. Then I rinse them in hot water, dry them off, sometimes with the vacuum, then leave them on a radiator to dry.

But sometimes I still need to use IPA before, or after, 1 of my fluxes leaves a conductive residue, ans soap doesn't always get it.