Well, just some very general observations.

If nothing else is changed, going from a single
layer 2 sided board to a 4 layer board (again
assuming the trace layouts don't change and full
board size ground and power plane) could give you
automatically a 10dB reduction in emissions. But,
that's such a general statement there are probably
plenty of counterexamples.

I personally have designed (EMC-wise now) a product
that was similar to an existing one that was marginal
for FCC, but the new one (thank god) was under the
limit by 20 to 25 dB under. The existing one needed
all sorts of ferrites and grounding to be done. The
new one needed nothing extra.

So to answer your question, yes, ground management,
if you want to call it that, is very important.

I have very little experience with flex circuits,
but my advice would be to keep as large a ground
layer as you can, try to keep the traces both power
and signal over that ground area.  If you are able
to sandwich the power and signal between 2 ground
layers - do it. Make sure the ground plane (if you
can) has several connections to ground through the connector.

----------
> From: APeder01 <[log in to unmask]>
> To: [log in to unmask]
> Subject: [TN] Design: Shield Layer Relief and Shielding Effectiveness
> Date: Friday, October 31, 1997 1:55 PM
>
>      Does anybody have data they're willing to share which shows the
>      relationship between shielding effectiveness over frequency vs.
>      various ground plane/shield layer relief schemes?
>
>      For instance, in a flex design I'd want to remove copper in a plane
>      for flexibility.  In a rigid design, I might want to remove copper
to
>      better achieve balance.  But, I can't do either if "putting holes"
in
>      the plane causes shielding problems.
>
>      Thanks for any help.
>
>      Andy Pedersen
>      Harris Corp.
>      [log in to unmask]
>
>      p.s. The shielding effectiveness question holds for silver filled
>      epoxy over-coats.
>
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