[SI-LIST] Re: Conductor loss reduction at High Frequency

  • From: olaney@xxxxxxxx
  • To: kgrhoads@xxxxxxxxxxxx
  • Date: Thu, 30 Aug 2007 16:44:48 -0700

We're agreed, and the humor is reciprocated.  Copper is pretty darn good,
so there isn't much you can do to improve the metal beyond the marginal
benefit of silver flash.  Some designs do resort to that for critical
communications circuits that need every last tenth of a dB, but that is
not an applicable concept for digital signaling.  That leaves everything
else as the low hanging fruit, as you wisely pointed out.  BTW, though
superconductors are exactly that at DC, for RF other loss terms kick in. 
You can still get some mighty impressive resonant Q values, but the sky
is not the limit...

On Thu, 30 Aug 2007 23:26:32 +0000 "Kevin G. Rhoads"
<kgrhoads@xxxxxxxxxxxx> writes:
> > "silver tarnishes easily"
> >So does copper, which is why standard PWB practice is to either 
> plate
> >over it or solder mask it or both.  Silver flash would need solder 
> mask.
> >I don't think the HT semiconductors etch very well, being ceramic 
> and
> >all, but if you go for the 4 Kelvin metal ones, lead traces would 
> melt
> >when you tried to solder.  Niobium-Tin costs more, but maybe it's 
> more
> >amenable to a multilayer process.  What are your other 
> suggestions?
> Well, while copper tarnishes, it doesn't as easily or as fast as 
> does silver,
> and silver can tarnish even UNDER certain coatings.  
> But mostly I was trying to say, with some humor, to the OP that 
> concentrating
> upon a "better" conductor material than copper is usually and 
> largely a total
> waste of time and effort.  Yes, there are some exceptions, e.g., 
> CeBAF, with
> superconducting resonating cavities.  But, usually the improvement 
> is from
> conductor layout, and surface finish, and avoiding surface 
> contamination on
> the conductor side, and on dielectric losses & other non-conductor 
> related 
> loss issues (e.g., mismatch, or excessive VSWR for RF).
> So, my suggestions were to NOT look at the conductor materials, but 
> to
> look elsewhere, such as the many excellent suggestions in other 
> posts.
> But rather than just TELLING the OP that, I thought perhaps I could 
> provide
> sufficient information that OP could/would realize the truth of it 
> directly.
> Knowledge gained that way means more, helps more and tends to stay 
> with 
> people.  Just telling someone the answer is less effective (and 
> others
> were doing that quite excellently).
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