Mail Archives: geda-user/2017/11/04/09:19:39
(... padstack announcement continued)
because a padstack already has to be able to look up its pad shape on a
per layer group (physical layer) basis, it was sort of trivail to add
blind/buried vias too.
The hole starting layer group and ending layer group is specified in a way
that is transferrable between different pad stacks. The simplest thing to
describe is the all-way throuh hole (needs no extra parameter). The second
simplest is a blind hole (needs one parameter). A buried hole needs 2.
Following the best pcb-rnd traditions, things are not entangled: whether
a padstack has a hole or not does not depend on whether it has shapes on
copper or other layers. Whether a hole is plated does not depend on if
it's through, blind or buried.
This gives the user maximum flexibility of combining the features, even
building things that we would normally regard broken constructs, like an
unplated buried hole between two inner layers, with a pad on each layer.
Again following the best pcb-rnd traditions, we are not to outsmart the
user. We let the user do what the user finds useful. Later on we will
provide DRC to warn for strange looking constructs, but it's the user's
responsibility to use or abuse a feature.
*** CALL FOR HELP ***
now that the core started to support bbvias, I started to look after how
this needs to be exported for fab houses. I found contradicting
recommendations and considerations. Thus I am calling for help: if you
ever sent boards including blind and/or buried vias to fab and you have
actual experience on what the fab wanted, please contact me.
Regards,
Igor2
P.S. because of the low user demand, I originally did not plan to
implement bbvia. But while doing padstacks, I figured it was very easy to
add it as an elegant, integral part of padstacks. Instead of trying to
duct tape them as a kludge onto the existing pinvia infrastructure, which
would have been the plan without padstacks. So whenever I coded something
for the shapes, I also cared a bit about bbvias. At the end, when shapes
already worked, bbvia needed less than 1 hour of extra testing and
bugfixing to pass the initial smoke tests.
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