Electronics > Repair

Flux, "No Clean" Flux, Cleaning, and Re-Coating?

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Fried Chicken:
I'm getting deeper into soldering work, and I'm having trouble understanding, using, applying, cleaning, flux, etc.

It sounds obvious but it's not.  I have some Chip-Quik "no clean" flux I got from mouser that comes in a syringe.  It takes quite a bit of effort to get out of the tube, and doesn't apply well in small amounts.  As a result I end up with flux everywhere I don't want it, and then cleaning becomes a mess.

I have a chip-quik marker applicator that applies very little flux, which I like, only onto the parts I need fluxed, but the marker tip got all destroyed, and it's quite fat so hard to reach onto some solder points.

But then it comes to cleaning, right now I'm using 91% IPA b/c it's cheap and plentiful.  I have a special flux remover spray that claims all sorts of good things, but while it might be healthy for the board, I'm not sure it's healthy for the user.

I noticed now too, after having done some work on a pretty mission critical board that the board looks very "dry", like the coating might have been removed.  Should I recoat these boards?  Lacquer?  Polyurethane?

Does someone have a recommendation for a flux that's easy to deal with?  Do I not have to clean "no clean" fluxes?

I've done research in this area, but specific recommendations and advice would be highly appreciated!

Smokey:
https://www.eevblog.com/forum/chat/good-soldering-flux/msg5237004/#msg5237004
https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784

IPA and a tooth brush for the first scrubbing.  Then another IPA rinse until clean.

(no-clean just means that if properly used it won't eat holes in the board after use)

NE666:

--- Quote from: Fried Chicken on January 09, 2025, 07:24:10 am ---comes in a syringe.  It takes quite a bit of effort to get out of the tube, and doesn't apply well in small amounts.

--- End quote ---

Not wanting to hijack the OP's thread but I'm having a very similar experience. I just recently started trying to use gel/paste flux, as opposed to pens and liquids, and purchased MG Chemical's 8341 "No Clean Flux Paste".

I had expectations, based on what I've seen used in various YT reworking videos, of something akin to toothpaste viscosity and slump, whereas what I have is much more like a stiff Vaseline jelly. On dispensing, it seems to prefer adhering to itself and the syringe tip rather than the PCB. It's wasteful and annoying to work with.

Can anyone recommend something easier to work with, in terms of fluidity, adhesion and ease of dispensing manually from a syringe?

coromonadalix:
for the syringe paste  you have many  with different use and densities,   i use the ones for smd,  softer smoother easier to apply  and dont run     

from QuickChip, i dont have the part on hand   but smd use  everywhere loll


and the no "flux clean",  tried them   but it leave a sticky hard residue,  very hard to remove if you really need a clean borad from  Aim brand (dont know the others),   

and we did saw some problems in hf uhf equipment,   reverted to the ol 63/37  60/40    ROHS ones are a pain in the @,   you need to flux many times   and the flux sip everywhere

we use aqueous cleaners lie Atron and Vigon

tooki:

--- Quote from: Fried Chicken on January 09, 2025, 07:24:10 am ---I have some Chip-Quik "no clean" flux I got from mouser that comes in a syringe.  It takes quite a bit of effort to get out of the tube, and doesn't apply well in small amounts.  As a result I end up with flux everywhere I don't want it, and then cleaning becomes a mess.

--- End quote ---
What kind of nozzle are you using? For thick products like flux gel, I recommend using a conical tip. This requires far less force than a straight tip like a needle. A very fine conical tip will give you good control without undue force.

Which flux did you get? ChipQuik makes many no-clean fluxes, some of which are much lower viscosity than others. Please give a complete model number (in particular, don’t truncate letters: for example, SMD291 and SMD291NL are not the same product!).


--- Quote from: Fried Chicken on January 09, 2025, 07:24:10 am ---I have a chip-quik marker applicator that applies very little flux, which I like, only onto the parts I need fluxed, but the marker tip got all destroyed, and it's quite fat so hard to reach onto some solder points.

--- End quote ---
You can buy replacement pen nibs.

But if you really want careful control of a liquid flux, look at the Bon-Kote series of flux pens. They come in various brush tips. They’re sold empty and you fill them with your flux of choice. Buy only from an authorized dealer (expect to pay $30 for it), as the ones found on AliExpress, etc. are invariably fakes, and those have a reputation for performing poorly.


--- Quote from: Fried Chicken on January 09, 2025, 07:24:10 am ---But then it comes to cleaning, right now I'm using 91% IPA b/c it's cheap and plentiful.  I have a special flux remover spray that claims all sorts of good things, but while it might be healthy for the board, I'm not sure it's healthy for the user.

--- End quote ---
IPA is not the best flux cleaner, no matter how many people claim that it is. <99%, even worse. IPA will get off most of it, but the problem is that “most” isn’t good enough. What gets left behind are any bits of really burnt flux (usually harmless, but ugly) and ionic contaminants, which are now no longer entombed in flux residue.

Commercial flux cleaners do better, by using blends of solvents that together keep everything dissolved. But you still need proper technique.

If you have access to an ultrasonic cleaner that your boards fit in, this is my favorite way to clean them. You can either use small amounts of solvent in a small container or baggie floating in a bath of water (do not fill an ultrasonic bath with flammable solvent!!!!), or you can use water-soluble no-clean flux, or you can use a water-based (aqueous) flux cleaner like Electrolube Safewash Super (SWAS), which does a perfect job.


--- Quote from: Fried Chicken on January 09, 2025, 07:24:10 am ---Does someone have a recommendation for a flux that's easy to deal with?  Do I not have to clean "no clean" fluxes?

--- End quote ---
I like ChipQuik SMD291NL.

SMD191 is their “smooth flow” flux, and it really is much “looser” in consistency, but it is a more delicate flux, in that it is “spent” after being heated once. So it’s fine for assembly, but not great for rework or drag soldering, where you may go over a joint a few times before you’re done. SMD291NL is better at that, and has the unusual characteristic of being crystal clear (amber, but not opaque at all) even at room temperature, so it doesn’t totally occlude things as you apply the flux. Really handy under the microscope.

No-clean residues are safe to leave on, but only if the flux has been fully heated to soldering temperature to neutralize it. Many no-clean fluxes are corrosive if they haven’t been heated. When hand soldering with an iron or hot air, some of it will get warmed enough to get runny and flow away, but not get heated enough. The only way to guarantee it gets hot enough to neutralize is when reflowing in an oven. Upshot is, when I hand solder, I always clean the flux.

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