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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 04:42:17 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <email@example.com>,
>On Wed, 20 Nov 2002 20:04:54 +0100, "PCS Electronics"
>>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?
> I have very good results with an alcohol wash followed by a soap
>water bath. The alcohol removes the non-ionic residue and the water gets
>ionic white stuff left over. Electric dishwasher detergent maked a useful
>non-foaming solution with good cleaning properties and rinses away cleanly.
Nonsense. Alcohol is an excellent polar solvent, so washing with water later
is pointless. Alcohol readily dissolves the ionic activator salts. But it is
a poor nonpolar solvent, and it dissolves the resin only relatively slowly.
For years, one of the most popular flux solvents was a mix of
trichloroethane (a nonpolar solvent that rapidly dissolves the resin), and
isopropanol (used for its POLAR solvency to get rid of the activator salts).
Another popular one was a type of Freon mixed with isopropanol, where (once
agaon) the freon took care of the resin, and the alcohol handled the salts.
In both cases, an azeotropic mix was used which was around 30% isopropanol
and the remainder being TCE or Freon.
Isopropanol alone has also been used, but althoug it handles the ionic stuff
nicely, it only slowly dissolved the resin. Thus the addition of an agresive
nonppolar solvent to the mix is what is normally used to solve this. See my
parallel post on this.
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