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Date: Thu, 28 Jan 2016 16:45:55 -0500
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From: DJ Delorie <dj AT delorie DOT com>
To: geda-user AT delorie DOT com
CC: geda-user AT delorie DOT com
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Subject: Re: [geda-user] The nature of gEDA layers
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Reply-To: geda-user AT delorie DOT com

> >  - pad stacks, with differnet pad sizes on middle layers
> 
> Everyone seems to want these, to be honest I don't understand what
> pads on middle layers are for.  Not mounting components for sure.  If
> it's just a node what's wrong with a trace or poly?

Internal pads provide structural integrity to the hole plating.
However, the alignment accuracy for internal pads is not the same as
for external pads, so the DRC rules are different, but OTOH you
sometimes want big outer pads for strength but smaller inner pads to
allow more traces between pins.  Etc.

> >  - hierarchical layout
> 
> It can be done now...

PCB doesn't support it, you need to flatten the design first, and
using external scripts (which I've done) to replicate the design is
just hacks.

> I've never done these.  I guess the flexing connector layer is on
> top, but only where it exists so you can still have components on
> the layer below?  There's still only one top layer at any given
> point?

It depends - there's lots of options for how flex assemblies are put
together.  There might, indeed, be multiple "top" layers for one X,Y
coordinate.