Re: [SI-LIST] : GND on the outer layers

Steve Weir (weirsp@a.crl.com)
Tue, 13 Jul 1999 20:41:22 -0700

Jon,

I would not recommend swapping the top layer as a reflection plane. The
top layer usually is so full of large voids for components that you will
get significantly larger current loops than routing signals on top with a
nice much more solid reflection plane underneath. Once the top layer is
committed to signal, and the one beneath it is a plane, it is a good idea
to mirror that arrangement on the bottom to prevent warping.

Regards,

Steve Weir.

At 12:40 PM 7/14/99 +1000, you wrote:
>I'd be interested in opinions on whether placing tracks "inside" and
>putting GND planes on the outer layers reduces raditation.
>
>It seems to me that there is little difference regarding the high
>frequency magnetic component: the return current in an outer plane runs
>parallel with the track, and the materials have little effect on the
>field.
>
>The E field is different in that the conductivity of the outer GND
>planes would confine this component completely within the PCB.
>
>Has anybody modelled this?
>
>Jon Keeble.
>
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