Re: gEDA-user: General Layers questions

[Stephan Boettcher <boettcher@xxxxxxxxxxxxxxxxxx>]

John Doty <jpd@xxxxxxxxx> writes:

> On Mar 16, 2011, at 4:24 AM, Stephan Boettcher wrote:
>
>>> Ok. So "via" should be a circle element on "hole" typed layer.
>> 
>> No.  A Via is a composit, consisting of a circle on the hole layer, and
>> various circles on copper layers, and circles on mask layes, and
>> thermals.
>
> The "layer" concept should be physical, not a metaphysical
> abstraction. Objects in a layer may contain holes, but a "hole layer"
> is nonsensical, a toxic conceptual shortcut. An "outline" layer is
> similarly bad: the insulating layers may all have the same shape
> sometimes, but not always.

So, a via needs a separate hole in each copper and insulating layer?  And
each layer needs its own discription of it's shape?

> Trying to model things that aren't layers as if they were layers is
> one common mistake in this kind of tool. Equally common is leaving out
> layers: the insulating layers in a PCB are just as important as the
> copper, and have their own properties (shape, thickness, material,
> etc.). They're a critical part of the layer stack.
>
> The description language needs to be able to express "feature p in
> layer x is aligned with feature q in layer y" in order to build up
> composites. This is the geometrically sensible way to describe the
> result of drilling through several layers. But the geometric
> description language should not be tied to any particular fabrication
> procedure.

This is all too physikal for my taste.

Why are you so attached to the concept of drilling?  For the design of a
layout, all that matters is that there are conductive connections
between layers. 

For me, a layer is something that the designer puts shapes on.  Shapes
with atributes, if required.  The semantics of these shapes on a given
layer shall all be the same.  Some of these are required for netlisting,
some are steering the physical checkout.

-- 
Stephan


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