[volt-nuts] low emf solder

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Sat Oct 29 10:27:49 EDT 2016

On 29 October 2016 at 14:51, NeonJohn <jgd at neon-john.com> wrote:

> On 10/28/2016 08:39 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> > I wonder how practical it is to weld test leads, so there's no solder or
> > thermal EMF.
> >
> > I know that this will sound crazy, and probably is, but could one weld
> > components to a PCB?
> Yes indeed.  About 20 years ago I had a machine that made circuit board
> by routing tiny wires and spot welding them to the connection.  I can't
> for the life of me remember that process name.
> Only problem is, if you weld two different metals together, even copper
> with different compositions, you've still made a very rugged and durable
> thermocouple.
> John

But if one could use copper as the bond wire, rather than gold which is
quite common, then it would give you very little thermal EMF

I would have thought any impurities in copper wire, would be quite small,
as it would reduce the electrical conductivity. Whilst I accept one is not
going to get 100.0000000000000000000000 % pure copper, I would have thought
the effect of any impurities at least an order of magnitude less than using
solder. I'm only postulating this - I have no evidence to back it up, and
have never studied the subject.

Perhaps the person who was making the measurements on the solder, could try
making a thermocouple by welding two bits of wire taken from different
sources. I guess the problem would be preventing any impurities entering
the weld. A quick Google suggests one needs argon gas when welding copper.


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