This is a subject that I am sure will garner a lot of varied response... so
here's my two cents worth.

If it is possible to maintain a trace to trace spacing of at least 2 times
the trace width routed over an intact ground (or power plane) then guard
bands are not overly effective in preventing cross-talk. If your layout will
not lend itself to that large of spacing then guard bands can be useful.

Jeffrey A. McGlaughlin
PCB Designer
Battelle Memorial Institute
Columbus Ohio
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        -----Original Message-----
        From:   Hawes, Adam [SMTP:[log in to unmask]]
        Sent:   Tuesday, 27 July, 1999 04:08
        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