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

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From: Muhammad S. Sagarwala (msagarwa@san-jose.tt.slb.com)
Date: Wed Nov 01 2000 - 09:41:40 PST


Sorry...I guess I should have been a bit more precise...

My response is given below:

>...
>> 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"?
Two of each kind and the behaviour is very very consistent.

>
>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?

The stackup is exactly the same...the decoupling is exactly the same...the
component placement is exactly the same...
the routing is different but the routing the rules are exactly the same...
>
>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?
I did not measure and compare the ground bounce...this is just an
observation of the end result..
The conditions were exactly the same.... There is a possibility that we are
pretty close to the threshold and that is the
reason I posed this question...I wanted to find out whether ground bounce on
the board would significantly improve
if I change the weight of copper and whether you people think (based on
experience) change in trace width contribute
significantly to improve the quality of the signal...

>
>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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