What to remove solder flux

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I just started soldering my first ATmega128 circuit board. All those little surface mount thingies are tought to do!

Now I have solder flux residue all over the place. What do I use to remove it. A household substance would be most convenient. What should I not use?

-Tony

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Tony,
This depends greatly on what kind of solder and flux you used. Check with the manufacturer for recommended solvents. Usually no-clean flux cleans up nicely with isopropyl alcohol or distilled water. There are also several brands of chemical cleaners specifically designed to clean flux goop. They come in aerosol cans like hair spray or shaving cream. I'd also recommend a good stiff brush and a set of dental picks for getting the residue out of cracks and crevices. At my work, the usual rule of thumb we follow is:
1) cover the area with flux cleaner (we use one of the cans)
2) scrub with the brush to loosen what you can
3) use the picks for really small places like crystal leads or fine pitch surface mount
4) rub away what you can with a cotton tipped swab (Q-tip, etc.)
5) blast away the remaining sludge and liquid with compressed air
6) repeat until satisfied

I've had some problems at work with the crystals going goofy and turned out the flux gunk was getting caught in the leads of the Atmega128 and messing with either the capacitance or resistance or both. Since then we've implemented the above protocol and been very happy.
-Will

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Well, it might be a little hard to figure out WHICH manufacturer. I got the stuff at radioshack. It is probably the most primitive and cheap stuff round. It works ok.

I will try isopropyl alcohol and a tiny stiff brush.

Thanks!

-Tony

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GC Electronics sells cleaning chemicals in the spray can that are specifically for PCB's and their delicate components. I've used the CG line and many other brands that were specifically taylored to electronic components and not had any problems, and not ever dit they affect crystal operation.

Of course, if you're on the cheap and use some other chemicals that aren't specifically designed for this purpose, your at risk of not only issues with crystals but, other component failure, such as plastic parts crystalizing and shattering, and even corrosion...

Because I do a lot of controls systems for work, they don't seem to mind providing me with the chemicals that I need so, cost isn't as important to me right now.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Someone will probably call me "nuts", but I've been using "Goof Off" to remove flux from my PCB boards. I originally got it from Home Depot to take crayon off a wall after one of my kids decided to be artistic one day. I use a small paint brush to put it where I need it on the PCB and then quickly wipe up with a cloth or ear swab. It evaporates very quickly and doesn't seem to leave a residue. Hasn't seemed to kill an AVR yet.

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I use mostly water soluble fluxes, but sometimes I'll use rosin on a pcb and clean
it with toluene. Might be bad news for certain plastics, but I have not seen it
harm anything yet. Freon TF used to be really great until the tree huggers
got it banned 8-)

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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I use regular colophony (rosin?), sometimes alcohol-based solvent of colophony. Guess that's the same stuff you get in RadioShack. It's not conductive but for aesthetics I wash it with regular clean alcohol, works like a charm. Isopropyl alcohol or acetone would wash off most everything just as nicely, just don't breathe it too much or you'll be hearing funny things.

The Dark Boxes are coming.

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microcarl wrote:
I've used the CG line and many other brands that were specifically taylored to electronic components and not had any problems, and not ever dit they affect crystal operation.

My bad, I wasn't clear enough. The gunk was from the flux and solder, not the cleaner. Starts out clear so you don't even know it's there and then over time turns white translucent/opaque and finally a brown color like old bananas... You couldn't even tell with the naked eye, we have a sweet magnifying inspection station. This was screwing with the crystals and a few other parts of the circuit. The flux cleaner was what solved this problem so the moral of the story boys and girls is always clean up your flux residue, even the ones that claim to be "no-clean".
-Will

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svofski wrote:
I use regular colophony (rosin?), sometimes alcohol-based solvent of colophony. Guess that's the same stuff you get in RadioShack. It's not conductive but for aesthetics I wash it with regular clean alcohol, works like a charm. Isopropyl alcohol or acetone would wash off most everything just as nicely, just don't breathe it too much or you'll be hearing funny things.

I was afraid to try acetone because of the solder resist coating. I thought it might disolve important plastics.

I was not thrilled with the isopropyl alcohol's cleaning ability, but it seemed to do a decent job, and the residual water did not seem to corrode anything.

I would not mind trying methanol. I believe that is 100% (i.e. no water added) compared to the 70% isopropyl. That will be the next thing to try. I would rather not have to special order asnything right now, but I can get the proper GC-brand cleaner in my next order from Digikey.

-Tony

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Dishwashing detergent works fine on the "no-clean" stuff. Just put a some on an acid brush and hold your board under the faucet and go to town!

Isoprop works ok for everything. That's what we use at work.

Genasolve is the real deal but the environmentalists had that stuff banned too. Probably a good thing though since it disolved ANYTHING. Just had to dip your board in it and it came out clean!

Go electric!
Happy electric car owner / builder

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Funny, here isopropyl alcohol is much harder to find than 98% ethyl alcohol. On a second thought, this is Russia or where..

For PCB's both work equally fine though. What's not recommended is various mixed solvents, they tend to contain hell knows what and it might be greasy and/or conductive.

The Dark Boxes are coming.

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Quote:

...and/or conductive

Just a note on the "dishwashing" solution for no-clean fluxes. It does, in fact, work quite well. But you need to be VERY concerned about the residue OF THE DISHWASHING SOLUTION left behind. Real life experience; trust me. An entire product line in a past life had problems in the field where the residue became very slightly conductive over time, and affected high-impedance paths on the circuit board. It was a very costly situation.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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svofski wrote:
Funny, here isopropyl alcohol is much harder to find than 98% ethyl alcohol. On a second thought, this is Russia or where..

For PCB's both work equally fine though. What's not recommended is various mixed solvents, they tend to contain hell knows what and it might be greasy and/or conductive.

Well, Alcohol of all sorts is reasonably available here in the US.

The hardest is pure ethyl alcohol because it can be ingested and the government wants us to pay TAXES on alcohol for human consumption. And they think that 98+% pure EtOH is too dangerous to people to drink. So, it is hard to get good pure reagent-grade ethanol.

In the US the names of alcohol are also confusing.

"Wood Alcohol" is relatively pure methanol and is a good solvent.

"Rubbing Alcohol" is 70% isopropyl alcohol, and is, in my opinion, not good for much other than a rub down.

"Denatured Alcohol" is reasonably pure Ethanol with something added to make it poisonous (to denature it). I think it used to be benzene that was added, but now I do not know what it is that is added (Toluene?). I am afraid that the additive will be too good a solvent for plastics, and might harm my PCB and devices.

BTW, I hope to visit St. Petersburg some time as a tourist, it seems like a very nice city.

-Tony

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Spamiam wrote:

BTW, I hope to visit St. Petersburg some time as a tourist, it seems like a very nice city.

Nice city with terrible weather! :) I think it's better to chose mid-summer or mid-winter, when weather is more[edit:LEAST] likely to be funny.

Here's a historical propaganda poster. It says:
DO NOT DRINK METHANOL!
Methyl (Wood) Alcohol is a Dangerous Poison. Wood alcohol can't be naturalized, it is only to be used for technical purposes. Warn your comrade!

Attachment(s): 

The Dark Boxes are coming.

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Hey,

Methal Hydrate (aka Wood Alcohol) works well if you let the boards soak a bit in it, and brush it off after. Make sure you have a tight fitting cover for the tub you sock the boards in so you don't have to breath the fumes a smuch.

-Colin

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GC Electronics has an Anhydrous-Pure (no water) Isopropyl Alcohol. Catalog number 10-1507.

BTW, it is poisonous, so do not confuse it with real "pure" alcohol.

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Quote:

Now I have solder flux residue all over the place. What do I use to remove it.

Mineral spirits and a soft toothbrush preferably children size. Brush lightly. Do not use Acetone or any other powerful solvent.

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Isopropyl Alcohol is my favorite. If you have trouble getting it legitimately in your country, your local homebake dudes always have a 200 ltr drum out back.

JimK

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HMm, I wonder why a government would want to limit access to isopropyl alcohol. From my organic chemistry classes eons ago, I remember no fun or interesting things it can be used for. Now reagent grade ethanol has many uses, as does... what was it? Anhydrous something or other. It was a great thing for concocting fun stuff.

I did use the Denatured EtOH to remove the flux with good results. It was a great success.

-Tony

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From what I remember from some old book, isopropyl alcohol doesn't have any special toxic abilities like methanol, it was said that its effect on humans is about 5 times fold that of ethanol. Not that anyone in his right mind would try anyway, but restricting access to such a powerful substance makes some sense :)

Here we have a lot of ugly restrictions. Strangely enough, glycerine still can be bought, but potassium permanganate is not in drug stores anymore: poor kids of today can't study chemistry by making their magnesium bombs anymore :( Same for acetone, no clean acetone in stores, only weird mixes that are not suitable for anything useful. Sale of that stuff is not prohibited, but is subject to some overly complex bureaucracy which noone wants to deal with. Probably it's all the same with isopropynol: never seen a bottle in a store, yet everybody who needs it has some.

The Dark Boxes are coming.

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Quote:
your local homebake dudes

What!

Keep it simple it will not bite as hard

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Most "rubbing alcohol" sold here in the USA is 70% Isopropanol (2-propanol) and the rest water, sometimes with a trace of glycerine and/or perfume. I've never heard of it being abused, one source says 4 oz will blind you and twice as much will kill. Here you can get acetone by the gallon in paint stores, but I don't know how pure it is. Muriatic (Hydrochloric) acid is in pool supply departments for correcting the pH of swimming pools.

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mpthompson wrote:
Someone will probably call me "nuts", but I've been using "Goof Off" to remove flux from my PCB boards. I originally got it from Home Depot to take crayon off a wall after one of my kids decided to be artistic one day. I use a small paint brush to put it where I need it on the PCB and then quickly wipe up with a cloth or ear swab. It evaporates very quickly and doesn't seem to leave a residue. Hasn't seemed to kill an AVR yet.
 

 

Thanks!  That works!  ...after YEARS of putting up with that sticking jar.

Last Edited: Sun. Feb 4, 2018 - 07:18 PM