Mail Archives: geda-user/2014/06/28/22:18:16
> > I've used both types of tools, and IMHO it's better to have a "canned"
> > geometry that you can reference, as well as making exceptions.
> > Sketchup has a good implementation of this, but lacks a way of finding
> > all features that are exceptions.
>
> Is this in favour of, or against indirecting through reference to a
> separately defined padstack? (We could still choose to copy-on-write, or
> edit-all when modifying vias / pads).
In general, in favor of. The trick is handling the exceptions
properly.
I'm also in favor of storing footprints that way, so you could (for
example) update all your 0603 footprints at once.
> Would a pad-stack definition be explicit for the board stack-up in use,
> or would it more usefully read something like:
>
> TOP PASTEMASK LAYER : Round 2.0mm
> TOP SOLDERMASK LAYER : Round 2.2mm
> TOP (or START?) LAYER : Round 2.0mm Clear Round 2.4mm
> INTERMEDIATE LAYER : Round 2.1mm Clear Round 2.5mm
> BOTTOM (or END?) LAYER : Round 2.0mm Clear Round 2.4mm
> BOTTOM SOLDERMASK LAYER : Round 2.2mm
> BOTTOM PASTEMASK LAYER : Round 2.0mm
I think pad stacks, and footprints in general, need a more "semantic"
stackup (like your example) that can be merged to any actual layer
stack.
> The additive combination of multiple underlying layers is a nuisance
> from a code point of view.. it means we need to combine these various
> data-sources to check for connectivity, and it means some operations can
> be slowed - as the spatial indexes are kept per-layer, not per group.
I think we need additive and subtractive layers, though. Managing
connectivity is no harder than what we have now, if we design suitable
iterators. The only trick will be managing polygons - we'd need to
cache an "effective polygon set" for connectivity purposes.
> IMO, although the history pre-dates my involvement, PCB's layer groups
> only really exist as a substitute for being able to tag objects by
> class, or property.
And pretty colors :-)
> > Photo mode does this too, and OSH Park interprets PCB layouts this
> > way.
>
> Does photo mode use anything other than the outer-layers though?
Yes. If you do a four-layer board, you can see shadows of the inner
layers through the outer layers, just like a real board.
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