FreeLists / si-list / [SI-LIST] Re: Gigabit traces on Backplane

["Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>]

I would wonder why your antipads are so large.  If there is room to run a
trace between pins, there is room to have a plane web underneath the
traces.  The impedance of the trace will certainly go up in this area and
if there are several sets of pads in a row, you will see an impedance
increase.

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just used the energy it took to be angry to write some blues.
Count Basie


> [Original Message]
> From: steve weir <weirsi@xxxxxxxxxx>
> To: <jain.nitin@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 12/8/2005 1:08:31 AM
> Subject: [SI-LIST] Re: Gigabit traces on Backplane
>
> Nitin, FYI attachments don't generally make it to postings.  Variation in 
> channel geometry does cause impedance variations.  Whether it is enough
to 
> be a problem or not depends on a number of other factors.
>
> Steve.
> At 02:12 PM 12/8/2005 +0530, jain.nitin@xxxxxxxxx wrote:
>
> >=0D
> >Hello,
> >
> >Enclosed is the snapshot of Gigabit traces (differential) running on the
> >Backplane in my design. The Blue color shows the traces in one signal
> >layer and green color shows the ground plane.=0D
> >
> >Now if you look closely, you will find that at some places, the plane is
> >not there for the differential trace because of the Antipads. Although
> >this for a short segment only.
> >
> >Could somebody let me know if this is okay or any problems are expected
> >because of this. Will this cause any impedance discontinuity.
> >
> >With regards,
> >Nitin Jain
> >
> >
> >
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