Again with flux removal

Well this is a good thread

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$20flux%7Csort:relevance/sci.electronics.design/iYOz2oYarTY/xFZwiD-1izYJ

(Sorry I'm not sure how to rip out the search function.)

Oh and an updated link to Jeff L's White residue pdf

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Anyway I've got a few hand built pcb's Kester 44 solder/ rosin flux. They are not high impedance and I just want them to look nice.

I tried cleaning with IPA only... looked like crap.

So I'm using IPA then detergent and hot water. Well the detergent is this "awesome cleaner"

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(as seen on TV :^)

Any thoughts? George H.

Reply to
George Herold
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Acetone is probably the most aggressive flux cleaner. Brake cleaner is a bit less aggressive.

Reply to
John S

George Herold wrote on 5/25/2017 2:32 PM:

I'm pretty sure I've seen this one before, but all I can think of is India Pale Ale which I don't care for much. All the ones I've tried were too bitter and I'm pretty sure they won't dissolve rosin flux worth a durn. Maybe something a bit stronger like MadDog 20/20?

Oh! I just got it. I was going to suggest methylated ethanol and I realized you are abbreviating isopropyl alcohol. Ethyl or methyl alcohol should work a bit better, but hard to say. I'm pretty sure that's what is in the flux remover products I've bought.

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Rick C
Reply to
rickman

Dry IPA works a lot better than the drugstore stuff.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

AWESOME/dp/B0017KT3IM

We do some boards that need to be VERY clean. We put them in a heated ultrasonic bath of ethanol for 10 minutes, then wash with de-ionized water and air dry. If not clean enough, we repeat with fresh alcohol. Often, we do a hand-wash first with a spritz of alcohol and then scrub with a toothbrush before goign in the ultrasonic cleaner.

We got some solution years ago that was supposed to be better, and I think it was. It was a mix of Isopropyl and ethanol plus ethyl acetate, which I think was supposed to keep the dissolved flux in suspension. I'm guessing you make ethyl acetate by mixing ethyl alcohol with acetic acid, but that reaction could be exothermic, so I have never tried it.

Jon

Reply to
Jon Elson

You need NON-polar solvent to dissolve rosin. The heavier the better.

Try a 50/50 mix of IPA/Xylene, you would be surprised. But IPA should be dry otherwise water would make it a mess. If there is no anhydrous IPA available you can use home improvement store Denaturated Alcohol that is anhydrous

50/50 mix of Methanol with Ethanol.
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Reply to
Sergey Kubushyn

If you want a non-ionic solvent, it is time to break out the WD-40! Where is Phil when you need him? Just be sure to thoroughly clean the board afterward with ethyl alcohol to remove the WD-40.

I wonder if the FR-4 absorbs the WD-40 much?

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Rick C
Reply to
rickman

Find any interesting article (like mine) and click on the down arrow to the right side of the page on the same line as the authors name. Select "Link" or Direct Link". That should get you to the article, like this:

It's not mine, but belongs to Kester. It's a very good article on the topic but misses an obvious source of white residue in the section on "water cleaning".

Tap water is full of lime which is a mix of calcium carbonate (limestone), calcium hydroxide (slacked lime), and calcium oxide (quicklime). In sufficient concentrations, it will look very much like the mess left behind by flux, except that organic solvents like IPA will not touch it. It's also part of the formulation for Roman style concrete, which might explain why it does such a good job of resisting abrasive removal.

I have a guess(tm). Did you wash these PCB's in hot tap water? If so, that might be the source of the white stuff.

Well, if my guess(tm) is correct, and it's a lime problem in the water, then lemon juice, vinegar, or any weak acid is the common solution (literally). Hot water will help, but if you use hot water with more lime dissolved in it, you'll just make it worse. I tried loading white vinegar into a steam cleaner which cleaned the PCB's but also produced a smell similar to very ripe gym socks. Not recommended.

Visitor bearing broken equipment and checkbook just arrived. Gotta go.

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Reply to
Jeff Liebermann

For prototypes I use Recochem lacquer thinner from Crappy Tire and a toothbrush. The boards look great and are easy to inspect.

Not all lacquer thinners are equal- this one is relatively low in acetone, about 10%.

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It's mostly toluene + methanol + xylene. It can take markings off of some parts, but it is nowhere as bad as pure acetone.

--sp

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Best regards,  
Spehro Pefhany
Reply to
Spehro Pefhany

Isopropanol slowly dissolves rosin. So, you want to keep fresh solvent applied for a while (maybe hours). Dissolving tree sap into alcohol solvent, it takes a day or so with no agitation.

Industrial-scale, spray the solvent onto boards, let 'em drip into a still, which freshens the solvent to spray 'em again and again. There are apparatuses for doing this elegantly in the small scale, too. Basically, a heat pump can warm a pan of dirty solvent, chill and condense fresh solvent from vapor, and cycle it through the board wash booth/tank.

Reply to
whit3rd

Spehro Pefhany wrote on 5/25/2017 10:43 PM:

Seems like a bit of overkill. Does ethyl alcohol not work for you? Toluene and xylene have been found to increase the risk of some leukemias. I can't see a reason to use them at all if you can avoid it.

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Rick C
Reply to
rickman

Thanks Jeff.

Right, not your article but just the link.

Right hot tap water. The pcb looks great now. (Well except for a few of my less than ideal (smd) solder joints.)

George h.

Reply to
George Herold

Thanks Spehro, I think you mentioned that before. I'm leery of acetone. (But sniffing a little toluene/ xylene could be a head rush. :^) George H.

Reply to
George Herold

Huh, so what dissolved it then? The hot water and detergent? The IPA alone seemed to dissolve it, but then left film over the entire pcb when dried. With hot water that went away. (I should have just used the water soluble flux and followed SOP.)

George H.

Reply to
George Herold

There is no magic in WD-40. Nada, zero, zilch. And it is _NOT_ very good for flux removal. Xylene is wa-a-ay better.

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Reply to
Sergey Kubushyn

Thanks Sergey I'm using 91% IPA, The 99.x% stuff is more expensive. I've got some denatured alcohol. I'll try that next time.

George H.

Reply to
George Herold

Uh-oh!

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Rick C
Reply to
rickman

Even very hard water won't leave much residue on boards. At worst it would be a very fine powder that should rub off easily. The photos on the web pages Jeff pointed to were from decades of accumulation.

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Rick C
Reply to
rickman

They aren't good chemicals to be sniffing much. When I was a chemist they were just starting to treat safety seriously and we were warned to be careful of any aromatic compounds. BTW, "aromatic" doesn't mean it smells nice. It means it contains a Benzene ring. Benzene is a known carcinogen and is banned from many products.

Chemical safety is a complicated topic partly because not everyone has the same tolerance of various chemicals and partly because chemicals in combinations can be dangerous in ways the separate chemicals aren't. The point is don't take this stuff lightly. I watched a friend of mine die from leukemia and it wasn't nice. Even if exposure raises your risk by only 10%, why do that?

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Rick C
Reply to
rickman

Any solvent will leave residue if not rinsed thoroughly. If the isopropyl alcohol dissolved the flux it did its job. You just need more of it to wash off the dirty alcohol.

I assume when you used the hot water you used a lot more of it? But if the water works, why bother with organic solvents?

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Rick C
Reply to
rickman

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