No Clean Flux?

what is meant by the phrase no-clean flux as it pertains to soldering?

is the opposite of "no clean flux" considered bad?

is no-clean flux a relatively new thing?

I 'presume' it means you don't have to clean the PCB before soldering?, and that the flux will penetrate the oxide layer.

I think the more common use of the term in electronics is a flux that does not need to be removed after soldering.

Some actually are said to provide a protective coating, like a conformal coating. The need for removal of ordinary rosin flux applies more to a commercial setting than a DIY'er, but I always remove rosin flux anyway.

https://en.wikipedia.org/wiki/Soldering

John

I also recommend cleaaning the flux off. You can use brake cleaner spray which has acetone in it. Just be careful not to spray painted surfaces it may strip it off/

Flux strippers got bad rap because they release CFCs into the air. The new "flux cleaner" sprays that are legal here don't work at all.

Alcohol will clean most fluxes with no problems, with a little scrubbing, or alcohol in an ultrasonic cleaner if time is an issue. No need for special cleaning solutions that might be bad for your health or the environment.

Alcohol is basically useless for typical flux. It just makes a mess. Acetone removes it in five seconds. If you don't like the smell, use it outdoors.

No-clean-flux means the PCB won't require clean off flux remainders after soldering.

Used sparingly it does a good job and won't require treatment with a solvent normally consisting of acetone and alcohol.

Boncuk

We switched to no-clean flux at my last employer. Certain lackadaisical maintenance personnel and impatient supervisors had a habit of leaving too much of the old rosin core stuff behind on some probe assemblies in spite of ultrasonic cleaning. It would shift ultra-precise resistance measurements by about 0.1% (even more when they refused to let them dry) and hammer yields. The sloppier work would also lead to arcing in some YAG laser and other triggering circuits. The lackadaisical and impatient maintenace still led to flux being left behind but switching eliminated some of the problems.

bountyhunter said:

Alcohol is basically useless for typical flux. It just makes a mess. Acetone removes it in five seconds. If you don't like the smell, use it outdoors.

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I don't have problems with smell, I make decisions logically based on the best choice for the job. Alcohol does the job fine, and is better than acetone as it is less toxic on the hands and lungs, less damaging to other components like glues and paints and plastic equipment.

Maybe you had a bad experience with alcohol as a flux cleaner but that's your problem, not mine. Your statement; "Alcohol is basically useless for typical flux" is just plain wrong, sorry.

been using alcohol as a flux remover for years. for a while a lot of far east manufacturers were using water soluble flux to cut costs, but it was hygroscopic and caused a lot of failures in humid environments. maybe some manufacturers still use it..... i used to use the more harsh solvents before all the hoo-hah about CFC's. one manufacturing plant i worked at had a soldering machine that used trichlorethylene by the gallon, but it had an ingenious "vapor barrier" that used supercooled air to precipitate all of the TCE vapor back to it's liquid state with hardly any vapor leakage into the atmosphere. the boards came out exceptionally clean.

Mr RB said:

Maybe you had a bad experience with alcohol as a flux cleaner but that's your problem, not mine. Your statement; "Alcohol is basically useless for typical flux" is just plain wrong, sorry.

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OK, well I've only been doing this for about 45 years and I can tell you acetone works better than anything else. And I have wasted my time using the other junk (when my company made us switch) which is why never use them anymore. I went out and bought cans of brake cleaner for me and my techs so we could clean boards.

If you don't believe me go to Pep Boys and plunk down $2 and buy a big can of brake parts cleaner spray. It is not only the best flux stripper it's also the cheapest. Or waste your time and money using something else. This will clean a board in about ten seconds and leaves no gunk or sticky residue.

Bountyhunter I respect your experience and never argued whether or not acetone worked better, as it probably would be better than alcohol at dissolving the flux as it is a much harsher solvent. And the same probably goes for many harsh toxic solvents.

The only point I argued with was your blanket statement "Alcohol is basically useless for typical flux" as I too have a lot of years experience and use alcohol, and it is NOT basically useless, it works well enough and has the benefits of being less damaging and less toxic etc.

Thanks for the tip on the brake cleaner working well, I will check that out and see what is in it and if it might damage paints or plastics etc.

Mr RB said:

. And the same probably goes for many harsh toxic solvents.

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The specter of toxicity is often raised and far less often documented on ETO and other forums. Here are some data for acetone, ethanol, and isopropyl alcohol. Isopropyl alcohol (IPA), as you know is also called rubbing alcohol. People rub it generously on their skin.

View attachment 62475

As you can see, there is not a lot of difference in toxicity at the levels one is likely to encounter, and of the three, IPA has the lowest OSHA TWA.

The real difference is in their solvent properties. In general, like dissolves like. Acetone is less polar and does not hydrogen bond. It lacks a hydroxyl group. It is a better solvent for non-polar things like plastics such as polystyrenes. The principle component in rosin flux is abietic acid. It is a terpene (https://en.wikipedia.org/wiki/Terpene) and is soluble in all three of the solvents mentioned, but not very soluble in water. It has a single carboxyl group which makes it an acid, but it also has 19 more carbons, which make that portion of the molecule non-polar. Hence, acetone is an excellent solvent for it. Ethanol and IPA are also good solvents for it. Adding water to any of those solvents will reduce the solubility of rosin in them.

Acetone is the name of a single chemical, and unless stated otherwise, it is assumed to be undiluted with water. On the other hand "alcohol" is a class of chemicals; although, in common use it usually refers to ethanol or isopropyl alcohol. What some people call pure ethanol is really the azeotrope containing 95% ethanol and 5% water obtained by distillation. Its solvent strength for non-polar compound is vastly different from absolute ethanol (i.e., ethanol without water). Similarly, isopropyl alcohol may be the azeotrope (91% as I recall) and water. Both ethanol and IPA can be obtained that are anhydrous or almost so.

Neither Mr RB nor Bountyhunter have said which alcohol they use/used, and most important, neither has said how much water that alcohol contains. Perhaps the difference in their experiences is related simply to which alcohol was used and the water content of that alcohol. Note: There are many formulations for "denatured alcohol." Some have considerably increased solvent potency compared to pure (>99%) ethanol alone.

John

jpanhalt said:

Isopropyl alcohol (IPA), as you know is also called rubbing alcohol. People rub it generously on their skin.

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Yes, and the rubbing alcohol available for consumer purchase is about 30% water. If you use that to try to strip flux, it will leave your board covered with water.

If you use non-chlorinated brake cleaner spray, it is specifically designed to leave zero residue of any kind which is why you can use it to clean brake rotors. It's main ingredients are acetone, methanol and toluene.

Most surface mount PCB assemblies use no clean flux. Much of the solvent contained in no clean flux within solder paste evaporates away during reflow temp. Some small amount of residue remains. The flux is not as active as old cleaning required flux. PCB and parts need to be kept sealed until just before assembly to avoid oxidation that reduces solderablity.

For a commercial PCB assembly, cleaning produces a hazardous waste disposal problem that most companies want to avoid.

jpanhalt said:

...
Neither Mr RB nor Bountyhunter have said which alcohol they use/used, and most important, neither has said how much water that alcohol contains. Perhaps the difference in their experiences is related simply to which alcohol was used and the water content of that alcohol. Note: There are many formulations for "denatured alcohol." Some have considerably increased solvent potency compared to pure (>99%) ethanol alone.
...

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Thanks for the info Jpanhalt that was a good read. I use methylated spirits and get a good brand that is 95% alcohol, and much prefer to get alcohol on my hands than acetone, especially when they are carrying dissolved impurities. I've heard acetone gets through the skin faster better (worse?) than alcohol, plus I still have a workshop full of paint and plastic and save acetone for when it is really necessary, not using it on jobs where alcohol works fine.

I have seen examples of watered-down metho becoming more common here in Australia, which is just a consumer ripoff as far as I'm concerned. If I wanted to have 30+% water in my metho I would mix it in! If I pay for cleaning alcohol I want 100% alcohol (but I understand there's a few percent water in it due to being hydroscopic).

Can you explain more about the allowable "1000 parts per million" in your data? Is that for drinking or inhalation? How does that apply to the health risks of getting pure alcohol or pure acetone directly on the skin, especially if that undiluted solvent is carrying dissolved nasty toxins?

I Recommend using a Solder like "Kester 331" .
It has a Flux that is Easily Washed off with just "Warm TAP WATER".
Making it very easy to remove the solder flux from Both Sides of the board.

And there will be about as much flux on the Parts site as there is on the Solder Side.

deleted

@Mr RB:

As you may have guessed, I like chemistry. I looked up "methylated spirits," and according to Wikipedia, it is synonymous with denatured alcohol. Moreover, Wikipedia gives the following formulation for it:

There are several grades of denatured alcohol, but in general the denaturants used are similar. As an example, the formulation for completely denatured alcohol, according to British regulations must be:[2]

Completely denatured alcohol must be made in accordance with the following formulation: with every 90 parts by volume of alcohol mix 9.5 parts by volume of wood naphtha [ed: wood naphtha = methanol = methyl alcohol] or a substitute and 0.5 parts by volume of crude pyridine, and to the resulting mixture add mineral naphtha (petroleum oil) in the proportion of 3.75 litres to every 1000 litres of the mixture and synthetic organic dyestuff (methyl violet) in the proportion of 1.5 grams to every 1000 litres of the mixture.

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Just so no one feels I am picking on the UK, let me add that many US formulations also contain pyridine and methanol. I am a little surprised at the inclusion of both ingredients in a product sold to the general public. Pyridine does have a terrible taste. It is also considerably more toxic than ethanol or acetone. Its OSHA TWA is just 5 ppm compared to 1000 ppm for ethanol/acetone. It is also classed as a known carcinogen -- not only to the State of California. Here's its MSDS: https://fscimage.fishersci.com/msds/19990.htm

Methanol, as you know, can cause permanent blindness. I had thought that most consumer formulations had removed methanol because consideration of the risk to abusers and accidental users outweighed the risk of lost revenue from alcohol taxes. That appears not to be the case.

If you are interested in what formulations exist in the USA, they are described in what we call our Code of Federal Regulations (CFR) (https://www.electro-tech-online.com/custompdfs/2012/03/CFR-2007-title27-vol1-1.pdf ) The approved formulations are given on pages 532-546.

If you want something that is less toxic, you may want to find a denatured formulation that contains various ketones and petroleum products, but no methanol or pyridine. Even one containing methanol and ketones would be less toxic, so long as it was not drank.

Isopropyl alcohol will also work and is available at 99% purity without any license. I have no experience removing flux with the more common 91%, but it is said by others to work well. Adding a little acetone might help.

John

Added: Time-weighted average (TWA) is for inhalation. Each agency has its own definitions and procedures, but for volatile substances, the permissible limits generally relate to inhalation.

I think you want to stay away from denatured alcohol. Naphtha can soften up some types of resist solder masks.

For the average user, go for 91% Isoproplyl alcohol (not 70%).

I personnally have a coveted stash of carbon-trichlor which is excellent that I bought several years back.