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I'm looking for suggestions for fully removing no-clean, non-water soluble, liquid flux after reflow. Isopropanol alone is not doing the trick.

What I've found from my research:

  • Aggressive Flux Removers. The products marketed as "aggressive flux removers" (like Techspray 1631-16S G3 Flux Remover) all seem to contain dichloroethylene, trichloroethylene or some similar halogenated hydrocarbon. I consider these chemicals too toxic to keep around the house (I'm a hobbyist), so I've ruled them out.

  • De-greasers. There's another category of aggressive flux removers (like Axarel 2200) that are basically just petroleum de-greasers. I think the toxicity would be ok in a well-ventilated area, but I'm concerned about how flammable this type of mixture is going to be. So, again, ruled it out for safety reasons.

  • Standard Flux Remover. The common flux removers (like MG Chemicals 4140A) are really just isopropanol + ethanol, sometimes combined with a few other nontoxic chemical (e.g., organosiloxanes, which are used in cosmetics, or ethyl acetate, which is also not dangerous). However, I'm struggling to see why this type of product would be any more effective than just using 99% isopropanol (or 99% ethanol) alone, both of which are a lot cheaper.

  • Saponifiers. I've also come across "saponifier" flux removers, i.e., soap. Toxicity and flammability are not an issue here, but I'm unsure about what effect soapy water is going to have on the board, especially if you can't fully remove the soap and it leaves some kind of residue. Have not found a lot of information about this online.

Any suggestions for how best to fully remove no-clean, non-water soluble, liquid flux after reflow?

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    \$\begingroup\$ In my experience a mix of sticky stuff remover (the limonene based stuff) and isopropanol usually does the job of cleaning up pretty much anything less tough than epoxy or carbonised tar. I'm also a fan of ultrasonic PCB cleaner fluid, which seems to be a mix of mild solvents and citric acid - wipe a bit on, scrub with a static safe toothbrush, wipe off with isopropyl wipes. \$\endgroup\$
    – Polynomial
    Jan 19 at 11:49
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    \$\begingroup\$ Why are you using no-clean flux at home? Why do you need to remove the no-clean flux? The idea of no-clean is that you don't have to remove it. While there are cases where you need to, if you are working on your own home projects couldn't you choose a flux that is easier to deal with? \$\endgroup\$
    – JRE
    Jan 19 at 11:52
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    \$\begingroup\$ Have a look here. \$\endgroup\$
    – JRE
    Jan 19 at 12:09
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    \$\begingroup\$ @JRE Rather, the no-clean one is the only form you should be using at home so that you don't have to deal with extra chemicals. \$\endgroup\$
    – Lundin
    Jan 19 at 12:13
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    \$\begingroup\$ For a board here-and-there, I use lacquer thinner and a toothbrush, done in a large shop (over a million cubic feet of air.) Avoid getting liquids near transformers, relays, and other components which can "wick" - can cause failure. \$\endgroup\$
    – rdtsc
    Jan 19 at 12:47

2 Answers 2

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Speaking of my experience, I use Amtech NC-559-ASM-UV No clean flux.

When making a reflow that requires high temperature for example and sometimes is not easy to remove the flux using only isopropilic alcohol, the method I use is using a cotton q-tip with a little of acetone and spread in the surface using good quality absorvent paper.

After that I repeat the same process but now using ispropilic alcohol.

Finally if needed I clean the rest of the surface using compressed air.

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I had to do this at work a few years ago when a batch of boards got made with no-clean instead of water-soluble, also for aesthetic reasons. It was a bit of a challenge to get them clean enough.

Here was the process:

  • Denatured alcohol

  • WD-40

  • Hot Soapy Water (dish soap)

  • Denatured alcohol rinse

  • De-ionized water rinse

  • Warm air dry

The first 3 steps used a nylon brush (toothbrush) to scrub.

They came out beautiful, and worked just fine. Anything less than the above left some amount of residue (white haze, mostly).

We would never attempt this on boards with high frequency, high gain, or controlled impedance.

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