At 12:49 PM +0000 5/19/02, olympus-digest wrote:
>Date: Sat, 18 May 2002 23:14:18 -0400
>From: ll.clark@xxxxxxxxxxx
>Subject: Re: [OM] Use of acid flux in soldering - a heresy
>
>In <v04220800b90c321bc0b7@[192.168.1.100]>, on 05/18/02 at 01:01 PM,
> Joe Gwinn <joegwinn@xxxxxxxxx> said:
>
> >When done, wash the battery holder with very hot water. Later, install
> >the battery holder in the circuit. If this [soldering] step is omitted, the
> >battery holders develop intermittant connections as the atmosphere
> >causes corrosion betweem rivet and tab.
>
>Joe, do the various concoctions from CAIG offer any help for this sort
>of thing? [http://www.caig.com/]
Not that I can see. They have no fluxes, but do have some cleaners, but talk
mostly about how green their formulas are, which is generally a tipoff that it
won't be that effective. Anyway, for surface corrosion that prevents
soldering, gentle methods aren't going to work.
One can also use a dilute solution of ammonia to neutralize the acids in the
tinners flux, but hot water is pretty effective all by itself. The basic issue
is to arrange things so that being washed in hot water won't damage anything
else. Likewise, ammonia.
This may seem strange, but Hydrochloric acid (the principal ingredient of
tinners flux) is not a poison. How can I be so sure? Because our own bodies
make it, in the stomach. Likewise, ammonia is not a poison, it's a normal
byproduct of our protein metabolism. These are corrosive if concentrated
enough, but although unpleasant they pose exactly zero threat when dilute.
I've also used plumbers grease flux, intended for soldering copper pipes and
fittings and available in hardware stores everywhere, to solder cadmium-plated
steel, which leads me to a story from the 1970s:
A friend of mine was working for a NASA contractor in the Baltimore, MD, area,
and they were having great difficulty soldering copper heat-exchanger tubing to
a cadmium-plated brass (?) vessel. This assembly was to fly in some space
mission. They were not allowed to use acid flux, for fear of unreliability
induced by trapped corrosive residues, and they had been trying everything
under the sun, with increasing desparation, so far without success. When she
told me this story, I was amazed, as I had been soldering Belden test-prod wire
to Mueller cadmium-plated steel alligator clips for years, without difficulty.
The trick was to mechanically clean the cadmium surface with a typewriter ink
eraser, pre-tin the wire with radio solder, assemble, solder with plumbers flux
and more radio solder, and clean the flux off with acetone after the joint
cools. Next day, she went to the hardware store across the street from work
and got a tin of plumbers flux, and it worked, causing an !
odd mixture of relief and embarrassment.
Why did this work? Because plumbers flux is a bit more aggressive than the
rosin flux used in radio solder, but far less aggressive than tinners flux.
Plumbers flux can be left in place without undue corrosion, at least on copper
pipes. Most houses have ample evidence of this.
Before I knew any better, in the 1950s I assembled a Heathkit vacuum-tube
voltmeter kit using plumbers solder and plumbers flux (rather than radio
solder), and it worked fine and never failed. I probably still have it, though
it became obsolete and fell into disuse years ago. Probably the electrolytic
capacitors have failed by now.
Joe Gwinn
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