RE: [SI-LIST] : effect of trace width on the performance

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From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Wed Nov 01 2000 - 08:38:18 PST


...
> The problems is the board with 9 mil wide traces and 1oz. copper is
> performing very good and the other board with 7.5 mil wide
> traces and 0.5 oz. copper is behaving very very bad.
...
 
To make this a fair comparison you need to be more precise and scientific.
Any number of things could cause the difference you are seeing. It is quite
possible that there is something else wrong that has nothing whatsoever to
do with the trace widths.

How many boards of each kind were built and tested, and found to be "very
good" versus "very very bad"?

Is the stackup "pretty much the same" or exactly the same? Is the
decoupling "pretty much the same" or exactly? How about the component
placement and trace routing patterns?

What exactly do you mean by "performing very good" and "behaving very very
bad"? Did you measure and compare the ground bounce, or is this an
observation of the end result, perhaps BER? Did you use the same
conditions? Might you be real close to a threshold, such that a very small
difference in (say) ground bounce could cause this big difference in
performance?

The trace width difference alone, given the same impedances, doesn't seem
significant enough to cause this, unless you already were right on the edge.

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