[SI-LIST] Re: stitched via shielding

Paul...

In my boards, I use lambda/10 or lambda/20 and get good results.

Those two transmission lines are pretty close - in symmetrical stripline 
(ground plane above and below), the stitched vias would do a good job of 
isolating them.  If this is open microstrip and if the lines run parallel for a 
long distance, you'll have a problem no matter what the spacing of the vias.

Ray

Raymond W. Waugh
Agilent Technologies

-----Original Message-----
From: Denomme, Paul S. [mailto:Paul.Denomme@xxxxxxxxxxxxxx]
Sent: Thursday, March 27, 2003 9:10 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] stitched via shielding



Hi All,

I am looking to shield a trace using stitched vias.  What is the general
practice for stitching vias around a trace in order to obtaining shielding
from the rest of the system?
 
Here is my scenario:

I have .2mm wide 10Ghz signal trace going down a PWB.  The nearest trace
running parallel to it is 0.2mm and the edge to edge distance of the traces
are 0.9mm. I will have stitched 0.3mm DIA ground vias located directed
between the two traces.  What would the center to center spacing for the
vias need to be to virtually contain the 10GHz signal?  

In practice I have seen via stitching rules of Lambda/20, and I have heard
of people using Lambda/30.  This is not a production board, but a test
vehicle, so I am looking for what people are using today that helped them
obtain acceptable results.  


Regards,

Paul S. Denomme
Design Engineer
Viasystems 
804-226-5155
804-226-5193 (Fax)





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