[volt-nuts] cadmium solder alloy for low thermal emf?
m1k3k1 at hotmail.com
Fri May 31 17:04:28 EDT 2013
> From: john at devereux.me.uk
> To: volt-nuts at febo.com
> Date: Fri, 31 May 2013 14:05:39 +0100
> Subject: Re: [volt-nuts] cadmium solder alloy for low thermal emf?
> "Andreas Jahn" <Andreas_-_Jahn at t-online.de> writes:
> > 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?
> > 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.
> I have never understood why it matters anyway. The conductors being
> soldered together end up in very good thermal contact. So there should
> be no thermocouple generated by the solder-conductor interfaces (since
> there is no temperature difference between the ends of the wires being
> So if you have copper-solder-copper, say, then the copper-solder
> junction is microns away from the solder-copper junction and is
> surrounded by metal. So surely they will be at the same temperature
> unless there is a huge heat flow.
> The referenced AN86 even suggests introducing balancing
> copper-solder-copper junctions, by cutting tracks and bridging with
But then why does it make a difference to stop the air currents around sensitive/accurate circuits?
> John Devereux
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