I have used 3oz. Copper on both inner and outer layers successfully.
Having planes on the outer layers can help reduce EMI but if the
board is very dense, the planes get chopped up so much that it may
not be worth the effort.  Routing 10 amp traces on inner layers can
also be very difficult.  If you do use planes on the outer layers
with heavy copper, make sure you add thermal reliefs to the smd pads.
John Woodford


>From: Mark Holmes <[log in to unmask]>
>Reply-To: "DesignerCouncil E-Mail Forum." <[log in to unmask]>,
>Mark Holmes <[log in to unmask]>
>To: [log in to unmask]
>Subject: [DC] Planes on external layers.
>Date: Mon, 21 Jun 1999 09:14:12 +0100
>
>Hello all,
>
>I am currently working on a very interesting board which has quite a few
>high current carrying tracks (around 10A). The scheme suggested by the
>engineer is to have the planes on the outer layers (for EMC reasons) and
>the
>tracking on the inner layers. There are surface mount components on both
>sides.
>
>Is EMC performance improved by having planes on outer layers? Are there any
>problems are associated with mounting surface mount parts on 2oz copper
>pads? Can I have 2oz copper as inner layer? All the trace width calculators
>I have seen use copper weight for the calculations, but PCB manufacturers
>often talk of "plating up" and "finished weight" presumably this it not the
>same as 2oz of copper - any advice?
>
>My view is I could get a more complete plane using the inner layers
>(because
>of the surface mount pads) and I am concerned that high current tracks on
>the inner layer, being much wider than if the were on the outer layers, may
>be difficult to route.
>
>Any advice or comments on the above would be most appreciated!
>
>Regards,
>
>Mark.
>
>Mark Holmes


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