>
>On this subject, why, on a four layer board (or 6 or 8 or 16), do the power
>planes usually go in the centre and the signal layers on the outside.  Isn't
>it more logical to put plane on the outside to catch EMI/RFI?

You'd think so, but it makes modifying the PCB practically impossible, and
copper sheets are reflectors, not magic black holes.  Proper routing means
you don't radiate nearly as much to start with. I produce multi-processor
designs at >10MHz with switcher power supplies, that pass part 15 with only
a plastic enclosure and two layer boards. No shields, coatings etc.

>Why have power planes at all.  If you used them as signal layers you would
>have almost an extra 2 layers.

In my experience, layer three is worth about .5 layer for routing, and it
goes down from there.
I don't use blind or buried vias though.


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