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Re: [OM] Use of acid flux in soldering - a heresy; CAIG; plumbers flux

Subject: Re: [OM] Use of acid flux in soldering - a heresy; CAIG; plumbers flux
From: Joe Gwinn <joegwinn@xxxxxxxxx>
Date: Sun, 19 May 2002 16:59:18 -0400
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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