Re: [SI-LIST] : Ground gap problem

Christian S. Rode (csrode@mediaone.net)
Wed, 24 Mar 1999 10:48:40 -0800

Question? Would the width of the ground return path essentially be
the width of the trace, plus the height (or some fraction thereof) plus
the skin depth? "High frequencies" in copper being anything over
10MHz?

Thanks in advance,
Chris Rode
RCI

Jon Keeble wrote:

> >At 02:09 PM 3/23/99 -0800, you wrote:
> >>>>>
> >> Hi all,
> >> I am trying to find the effects of the gaps on the ground plane for
> >> the high-speed circuits.
> >> Even though I have a couple of references about the via, which has the
> >> ground gap problem, I need more specific data about the ground gap
> >> problem regarding the gap size, gap location.....
> >> Either measured data or simulated data will be fine ( papaers or
> >> refernce book...)
> >> Looking forward to your answers.
> >>
> >> Thanks
> >> Sangil Lee
>
> The high frequency component of return current in a plane is concentrated
> under the track.
>
> I recall a number of 90% within 1.5 times the track-plane distance.
>
> So intuitively one might expect less effect if the track is close to the
> plane.
>
> Say the vias are 50 drilled 16 with 10 clearance. This makes a bridge of
> copper between voids of
>
> 50 - (16 + 2x10) = 14.
>
> Best result would be obtained if the track follows the centre line of the
> bridge (good argument for gridded routing).
>
> If the above is correct, then the above geometry would support a track to
> plane distance of upto 10.
>
> Jon Keeble
>

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