From: Zabinski, Patrick J. (firstname.lastname@example.org)
Date: Tue Oct 31 2000 - 18:48:15 PST
This alone would make me think the 7.5 mil wide trace board would
work better than the 9 mil wide trace board due to the lower crosstalk.
This assumes single-ended lines, but the opposite would be true
for differential lines. Are the lines differential or single ended?
If this isn't it, my next best guess is the attenuation of the lines.
With cyanate ester, the loss tangent is quite low (around 0.001 if I
recall??), so I don't think you'll be running into much dielectric
loss at 400 MHz. However, the wider/thicker traces will have much
less loss at both DC and higher freqs than the narrower/thinner
traces (at least a factor of two better).
Have you looked at the signal degradation differences between the
two boards? Are the edge rates on the two board different?
If this isn't it, then I'm clueless.
> Exactly the same...
> >How about center-to-center pitch on routing tracks?
> >> I am sorry Patrick,
> >> I forgot to mention ... the thickness of the boards is
> >> different. The one
> >> with 9 mil wide traces is thicker than the one
> >> with 7.5 mil wide traces.
> >> As regards other possibilities, the boards use the same
> >> dielectric material
> >> (Cynate Ester), the power planes on them
> >> are exactly the same, and the stackup is the same too and the
> >> placement of
> >> the decoupling caps is pretty much the same too
> >> (both the physical location and quantity)..
> >> Muhammad
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