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From:	Bdale Garbee <bdale AT gag DOT com>
To:	Peter Clifton <pcjc2 AT cam DOT ac DOT uk>, geda-user AT delorie DOT com
Subject:	Re: [geda-user] pcb: Patch for arcs with different radii for x and y on screen
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Peter Clifton <pcjc2 AT cam DOT ac DOT uk> writes:

> How would you select from/to layers? Would we constrain the end-points
> to physically realisable ones? IE... should I allow modelling a via that
> would not be possible to achieve, e.g. from layer 1-5 in a 6 layer
> board?

Real-world blind and buried vias always connect a range of layers from N
to M.  The tricky bit in my experience in large-layer-count boards was
always when there were multiple buried vias with the same X-Y
coordinate.  In other words, something like layers 2-3 and 6-7 connected
in an 8-layer board.

> How does all this interact with moving objects etc.. between layers?

If you move a trace off a layer where the via exists, it disconnects.
If you move a trace onto a layer where a via exists, it connects.  What
over interesting cases can you think of?

> How are blind and buried vias represented for manufacturing? Different
> drill-files for each of the from-to layer pairs?

Good question.  I don't know, but we could find out.

> Should we pre-define a list of legal vias (like pad-stacks), and then
> allow choice between them, or should each one be completely
> independently defined?

Good question.  In the past, the tools I used mostly thought in terms of
pad stacks.  But it has been years since I worked on a board where I
actually needed blind or buried vias.=20=20

Bdale

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