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	Wed, 27 Jan 2016 05:13:40 -0800 (PST)
Date:	Wed, 27 Jan 2016 14:13:34 +0100
From:	"Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Subject:	Re: [geda-user] The nature of gEDA users
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> >> > I am probably on same track. A via or hole is: drilled cut out thru
> >> > all layers with plating
> >> 
> >> No.  A via is a collection of circles, negative circles, thermals on
> >> conductive layers, and a circle on a layer connecting the copper circles.
> >> 
> >> The technology and DRC ruleset knows that the circles shall be drilled
> >> at slightly larger diameter and filled with plating, and check the
> >> copper circles accordingly.  But that is several orders up in the
> >> abstractions stack.
> >> 
> >> -- 
> >> Stephan
> >
> > I got slightly wrong and would only add the circle connecting the
> > copper circles really is a cut out or negative circle as you call it.
> 
> No.  The circle connecting the copper circles is on a different layer,
> and is not negative, i.e., not a cutout.  The gerber export of a copper
> layer has no hole where the drill hits.

The circles connecting the layers are drilled thru board and are hence a cut out in the board which is later plated. The gerber export of a copper layer has no hole where the drill hits but it does not matter because the drill will make a hole, a proper model of layer would however have a hole there the drill hits.

> It is the overlap of an object on the copper layer and an object on the
> via layer that provides the connection.

There is no via layer, a via is a composite of objects on different layers. pcb however know the plated hole in via and pin connect all layers or that it connect the copper annular ring on all layers.

If electrical connectivity and DRC look at geometry made by the drawing primitives on the electrical layers it does not matter what logical object they are part of. Ordinary vias connect annular copper ring on all layers and if buried/blind via is implemented electrical connectivity and DRC need to know which layers are connected and I guess this would be the hardest part if implementing blind/buried vias.

> > I assume the following objects are equal and give the same result:
> > drilled hole, negative object, cut out.
> >
> > To drill a hole thru only some of the layers I consider a little bit
> > more involved. If I got objects wrong is less important. Do you think
> > it would be good with possibility to draw on any layer inside element,
> > pin, via, pad for those special cases that are a little bit different?
> 
> Any object shall be allowed everywhere.  But the GUI does not need to
> support that initially, if that is difficult, orclutters the user
> experience.

No GUI does need to support any object everywhere but data model need. What is missing in GUI to draw any object on any layer is circle and possibility to select if it should be a cut out.

> ... Nor do I see a problem to move Element pads from the
> nominal component layer to a flex surface layer with a text editor.  The
> data structures must support that.

As is now it is possible to place element on upper layer or upside down on bottom layer. If data model could put element on any layer either up or down it would be possible to make boards with embedded elements. I do not suggest to implement anything new in pcb but if data model is changed it would however make sense to make it this way.

> The data structures must efficiently represent the geometry and the
> connectivity.  Everything else can be defined in tools that operate on
> the data structures ...

Correct. Data structures model the geometries on the different layers which usually end up in gerber files but it also group some of the geometries in pin/pad/via-->element-->layout. It would also be nice with a feature to group elements and other layout objects user add in sub layouts which could be handled with the same ease as an element.

> Stephan


Nicklas Karlsson

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