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From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: Washing PCB's after soldering...with what?
Date: Thu, 21 Nov 2002 04:53:46 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <email@example.com>,
>"PCS Electronics" wrote in
>> We're hand-soldering (small series) our PCBs and are
>> wondering what would be the best chemical for washing
>> the boards afterwards.
>> We've tried Acetone and Ethanol, the first is way too strong as
>> it melts the caps and other plastic, the second (Ethanol - alcohol)
>> leaves the PCB looking very dry and ugly with white powder
>> where the soldering paste used to be.
>> Does anyone here have experience with this kind of stuff?
>> Best regards,
>> Marko - PCS Electronics
>Denatured alcohol, although isopropanol is safer. What's needed
>is an old-school thing called "elbow grease." Get some brushes
>called "acid brush(es)" - McMaster-Carr has them at about three
>times the hardware store price - and cut back the bristles to
>about half the length of toothbrush bristles.
>This comes under the umbrella of 'TANSTAAFL' - There Ain't No
>Such Thing As A Free Lunch. Ordinary soap and water will clean
>the board. Try liquid Windex. (I haven't tried that myself, but
>have always had good luck with isopropyl or denatured ethyl
>alcohol - straight ethyl alcohol is MUCH too valuable as a
>IOW, just about any cleaning solution should work, but you
>do need to use a stiff brush. Actually, the stiffest toothbrush
>you can get at the store should be fairly effective, with
>soapy water and/or alcohol (they needn't be mixed - just one
>or the other), and elbow grease.
>Stay away from aggressive solvents, because, as you've
>observed, they attack plastic components. If you're using
>real live electronic-type solder, the flux should be washable
>with ordinary washing stuff. If your flux is so tenacious that
>you need solvents, then you need to find a different solder
>The white crud that you mention is just the residue left when
>the volatiles in the rosin get carried away - For a comparison,
>would you wash your back in the shower by just letting the
>water out of the showerhead just splash off your back and
>run down the drain? Of course not! So maybe your answer is
>to use a brush and whatever you're using now. Last Millennium,
>I worked at a game repair place, and one of the substances
>we used on PCBs that had had beer and coke and gawdknowswhat
>spilled on them was [drumroll please] club soda! (which in
>Minnesota is referred to as "charged water.") Carbonic acid.
>NaHCO3 + H2O.
Sorry, that is totally wrong! That "white crud" is the corrosive activator
salts added to the resin to make it dissolve the metal oxides faster when
soldering! It is hygroscopic, corrosive, and conductive. Before it was
exposed by incorrect cleaning, it was trapped in a matric of solid resin,
and could cause no harm.
Cleaning the board incorrectly (by dissolving the resin only) exposes the
stuff and causes far more harm than just leaving the resin alone.
Using a proper polar/non-polar solvent mix (as I pointed out in a parallel
post) requires no brushing of the PCB; all you need is the correct solvents
to dissolve the stuff. The requirement to aggressively brush the PCB to
clean it means that you are doing it wrong. Flux removal is a very well
documented subject; the information is out there!
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