Matthew,
Here is my guidelines on ML boards.

Setup - Find the amount of connections you have. The reason
most planes are "power planes" are due to their large number
of connections and this IS the most efficent way of connecting them.

*Note-Your question about "why put the planes on the inside if you use them
to protect the signals" is correct. The standard of protection seems to have
changed over the years. If you have low level of interference you can place
the planes on the outer layers, but this does nothing for the components.
Many military board used ground planes on the externals to protect it.
You should use a different ground from you board ground or you could
stand the chance of injecting noise into the ground of your components.

The planes are necessary when you have a large number of connections
to one net (and it doesn't have to be a power source!) that would make
the board otherwise unrouteable. (or very difficult) You may use any
power or signal net on a plane. (put the net name in text on your plane
do help you note what net the plane is connected to)
Remember your copper to board edge clearance.......
You may also split a plane into several different sections to reduce the
number of planes needed.

Materials; Look at the resource page at www.robertsondne.com for
a stackup calculator/general resource spreadsheet.
ML are primarly foil stackups (external layers) as opposed to core
stackup. This means that layer 2 and 3 are part of a core then there
is prepreg between 1-2 and 3-4. Layer 1 and 4 will be a sheet of
foil, then plated up. (consult you fabricator or look as the resource sheet
for available materials.)
Attempt to use the same style on either side of the core (ex
plane-core-plane or
signal-core-signal) I ocassionaly don't and never had any problem with
warpage
but it is recommended.

Routing; Attempt to alternate direction of layers. This reduces the
possibility
of crosstalk and noise. It also increases your route-ability.

Read up on ML material specifications (or visit www.robertsondne.com for
a modular notes w/ML notes) for materials.

Trace and space; Remember trace width minimums increase on internal layers,
but spacing mins are less. Use worse case for both unless you have
"define-by-
layer" capabilities.

B & B vias; Stay away from them. Thy cost much more. This technology is for
those doing high technology board that maxed out on layers or room.

This is the thimble full of knowledge I have.

HTH

Chris Robertson
[log in to unmask]








> Hi there again, thanks for all the tips folk's, theyre pouring in...
>
> "Input, need more input"
>
> What exactly is a power plane then?
> Never having used one I'm not too sure.
>
> Is it like a ground plane?
> Is it used to route the power connections only, with +v signals going only
> to those
> places its supposed to and the 0v as a groundplane for the rest of that
> layer ?
>
> I suppose that I could do that and then use the other 2 available layers
for
> routing the signals.
>
> Why would the powerplane be a middle layer? if it has groundplaning/emc
> reduction effects
> wouldn't it be better nearer the outside?
>
> Thanks again....
>
> P.S. I like the wallchart etc Senthil, thanks.
>
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