[volt-nuts] low emf solder

Attila Kinali attila at kinali.ch
Sat Oct 29 14:41:48 EDT 2016

On Sat, 29 Oct 2016 15:27:49 +0100
"Dr. David Kirkby (Kirkby Microwave Ltd)" <drkirkby at kirkbymicrowave.co.uk> wrote:

> 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

Copper is more and more used for bonding wires.

But be aware, that the bond pad on the chip is still aluminium in most cases
I don't know whether there is any process that uses copper bond pads at all.
As far as I know, all of the relevant processes for analog designs (ie those with node sizes over 130nm) still use aluminium interconnect only. IIRC the
first node size that got copper interconnect was 65nm and about 10 years ago.

> 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.

The normal copper wires you get are usually 99.9%. If you go for the
oxygen-free variant you can get to 99.99% (don't ask me whether the
audiophool grade is really that pure). I have no idea how much the EMF
of the impurities is.

			Attila Kinali

Malek's Law:
        Any simple idea will be worded in the most complicated way.

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