On 09/13/2010 05:07 PM, John Doty wrote:
On Sep 13, 2010, at 2:27 PM, DJ Delorie wrote:
So let me rephrase: Why have seven geometric holes,
one for each layer, when we can have one geometric hole applied to the whole composite?
<snip>
My notion is that you need a general mechanism to align objects between layers.
<snip> Having such a mechanism, you should then use it universally. If
you bypass general general mechanisms for special cases, you risk creating a mess
where general automation procedures fail in
those special cases.
John D has something here -- suppose we start using pcb to model the physical in a way that is used to analyze layer stack up alignment of weirdly processed layers? For instance layers that get folded and stretch some, and so need alignment checking? Perhaps holes get made in one stroke still, but the via pads need a tolerance to be able to hit them close enough to their centers with the drill. Perhaps holes don't even all get made in one stroke! I heard about microvias being made with UV lasers that would be on just a few layers. Also there is a max feasible aspect ratio to a via hole width vs. its depth to drill with carbide bits. Some board makers said they handle this by drilling in from both sides. Take it a little further and you make two composites separately drilled, then bond together.... Sure, all of this is far out, but still worth planning for. John Griessen _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
