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

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From: Heard, Chris (cheard@cereva.com)
Date: Tue Oct 31 2000 - 18:45:52 PST


Muhammad,
 
What are the lengths of the 9 and 7.5mil lines?
What is the risetime of these signals?
Are both of them bussed or pt-to-pt?
How are they terminated?
 
The difference between 7.5 and 9 mil might be noticable at lengths over 24"
and at risetimes under 150ps, assuming a differential pair pt-to-pt line.
 
Chris

-----Original Message-----
From: Muhammad S. Sagarwala [mailto:msagarwa@san-jose.tt.slb.com]
Sent: Tuesday, October 31, 2000 8:34 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : effect of trace width on the performance

Hi SI Gurus,
 
I am in a big problem. I designed two boards which are pretty much the
same.
The changes between them are:
 
(1) One has traces that are 7.5 mils wide and the other has 9 mils wide
traces (both have a characteristic impedence of 50 ohms)
(2) The one that has 9 mil wide traces has 1 oz copper for the pwr planes
and the one with 7.5 mil wide traces has 0.5 oz. copper
     on pwr planes.
 
The stackup is pretty much the same.
The Frequency of signals on the boards is 400 Mhz.
The decoupling scheme on both boards is pretty much the same.
 
 
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.
 
My question is "do you think these changes make a big difference or is there
another variable(s) that I am missing?????"
 
Comments suggestions are most welcome....(I need to be sure before I make a
decision to respin the board )
 
Muhammad
 
 
 
 
 
 
 
 
Muhammad S. Sagarwala
Schlumberger SABER
Ph. (408) 586 7065
Fax (408) 586 4668

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