Net Classes to specify layer-specific differential geometry

[Victor W]

It would be very helpful if it were possible to uniquely specify zone clearances for specific nets.

This would be useful in effectively routing differential grounded coplanar waveguides.

In such cases, it's useful to separately specify the trace-to-trace gap and the trace-to-ground.

Presently, in order ensure the correct trace-to-ground clearance when pouring polygons, we constantly adjust the netlist clearance depending on whether we are routing (in which case we make it smaller), or pouring polygons (in which case we make it the trace-to-trace gap).

The problem is that when specifying the larger trace-to-ground clearance, then DRC and routing (with DRC enabled) doesn't work because the complimentary traces is marked as being 'too close'.

This problem would be completely solved if we could associate layer-specific differential geometries (trace width and gap) and clearances within a netclass. When running DRC, it would then also be able to flag incorrect trace geometries, and apply clearance rules to the trace pair, instead of individual tracks.

Not only would this solve our immediate problem (that we can't uniquely specify trace-to-trace clearances from trace-to-ground clearances), it would also allow us to accommodate and specify unique trace geometries for different layers (our trace geometry varies depending on routing layer, due to changes in geometry and dielectric).

[Maciej Suminski (orsonmmz)]

We plan to refactor DRC in v6. There is a blueprint [1] in progress, in case you are interested in details.

1. https://docs.google.com/document/d/1qvCH9aHwCzp5qtKTna4jJXuloNU0b96gAxAHSKPuXpU/edit?usp=sharing