I know where you are coming from, I had a lot of Eng. asking me to place
ground guard
traces on multilayer designs. I always tell them that I can provide 3 to 1
spacing will do just as well as placing a guard trace. I also believe that
by having dedicated power layers
the use of guard traces is of little benefit or no benefit at all.
Most of cross-talk is inductive and by running traces next to one another
will cause inductive coupling. however by separating the traces this effect
diminishes. Another way of preventing this is by decreasing the height of
the reference plane to the signal layer you are concerned about (strip line
configuration).

ATI Technologies Inc.,
Patrick Jabbaz
Sr. PCB Designer
33 Commerce Valley Drive East,
Thornhill, Ontario, Canada, L3T 7N6
Phone:(905) 882-2600 ext: 8254,   Fax: (905) 882-9339
Email: [log in to unmask]


-----Original Message-----
From: Hawes, Adam [mailto:[log in to unmask]]
Sent: Tuesday, July 27, 1999 4:08 AM
To: [log in to unmask]
Subject: [DC] Ground Shield Tracks


        I feel sure this is probably an issue for a lot of PCB
designers......

        Recently, I have come across an increasing number of engineers who
wish to have certain tracks on multilayer PCB's shielded by ground traces
running adjacently. It seems to be a case of jumping on the bandwagon to me
because we never used to do this until about 12 months ago.

        I was under the impression that ground tracks only served a useful
purpose on 1or 2 layer boards and that on a multilayer they were essentially
a waste of space as most of the capacitive coupling would be straight to the
ground plane.

        I don't like to tell the engineers their jobs obviously so can
anybody put forward their views so I have a more solid argument!

        Thanks all,

Adam Hawes
PCB Design Eng.
GenRad Ltd.

Tel: 0161  491 9290
Fax: 0161 491 9106