[volt-nuts] cadmium solder alloy for low thermal emf?

[Andreas Jahn]

Hello

>I do not imagine cadmium bearing solder being easy to acquire.  The
> Wikipedia entry for solder says Pb90Sn10 can be used as a replacement
> for Cd70Sn30 in low thermal EMF applications:
>
> http://en.wikipedia.org/wiki/Solder
>
> On Thu, 30 May 2013 04:00:19 +0200, Volker Esper <ailer2 at t-online.de>
> wrote:
>
>>
>>By the way: does anyone know, if Agilent uses special solder alloy? I've
>>heard that a cadmium containing solder is used to get extremely low
>>thermoelectric voltages (or voltage differences).
>>
>>Is that right? If so, which alloy has to be used?
>>
>>Thanks
>>
>>Volker
>>

Within LT AN86 Cd60Sn40 is recommended for a limited temperature range of 0 
to around 40 degrees.
http://cds.linear.com/docs/en/application-note/an86f.pdf

But: the thermal EMF is only zero against copper.
Most precision integrated (hermetical) cirquits use Kovar. (39uV/K against 
copper)
Relay contacts will be either copper berillium or another material.
So in most cases a optimized solder for copper/copper connections will not 
be useful.

On the other side Cd containing solders create very poisonous damps when 
being heated.

With best regards

Andreas