Re: gEDA-user: gEDA and PCB ------

[DJ Delorie <dj@delorie.com>]

> If a board is built in layers there are a few layers that are always
> unique, such as the silk screen, top paste, bottom paste etc.  All
> other layers will be a trace layer.

So far, I've enumerated the following layer types: copper, silk, mask,
antimask, paste, antipaste, outline, and keepaway.  For some, you can
have top, inner, or bottom locations too.  Worst case is 14 special
layers (top antimask, bottom antimask, top keepaway, inner keepaway,
bottom keepaway, etc).

Yes, all the non-special layers will be copper, but there's more than
that.  You need to know which coppers are top and bottom, and for the
inner layers, which ones are paired with which other ones (I think
multilayer boards are etched and drilled in layer pairs before
combining them).

> You are never going to have an internal paste layer for example.

No, but you can have an internal keepaway layer.

> So after handling the unique layers does not unlimited trace layers
> fall out for 'free'?

Yes, but you still need to keep track of stacking order and such.

And "unlimited" is only unlimited if you write the software correctly.
Currently, the design really does limit us to 8 layers.  Changing the
design is part of the work.