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How do we envision Pad Stacks?
I had been assuming that you could define a separate shape for each layer. Full flexibility, but time-consuming to edit (even with commands such as “push current layer to other layers”).
Most users are looking to route traces on inner layers between tight pads. This is commonly done with the definition of a “capture pad”. The constraint on inner layers that have connecting tracks is simply not to have a butt joint between the track and the plated hole. A capture pad is therefore a circular pad with an annulus width of the drill wander plus 1 or 2 mils; other capture pad shapes get you nothing more.
There were also a few requests for SMD pads on a single inner layer (or perhaps multiple) — but importantly not for different shapes on different layers.
So one could imagine allowing the pad shape to be placed on any number of layers, and a capture annulus width for any other connected layers. While it doesn’t have same flexibility, it would be a lot easier to edit.
Another possible complication is wanting a different shape for mask (or paste) layers. Is this ever required?