I’m trying to find a way to define minimum microvia hole-to-hole clearances on different layers that would be caught by DRC. Basically, I’d like to be warned if staggered microvias are too close to eachother so that I can make sure that their hole diameters have a minimum distance between them.
There doesn’t seem to be a setting for that in Settings -> Design Rules -> Constraints. And, if I try to use ‘Custom Rules’ they don’t apply to microvias because they are not ‘drilled’; see ‘hole_to_hole’ and ‘physical_hole_to_hole’ below, from here:
I attempted to test the following rule, that indeed does not work (the measurement is wrong), probably because KiCad treats microvia holes differently than ‘regular’ holes.
(rule microvia-microvia-hole-clearance
(constraint physical_hole_clearance (min 0.01mm))
(condition "A.isMicroVia() && B.isMicroVia()"))
I’ve also tried to convert the microvias to buried/blind vias (that are assumed to be ‘drilled’), but then the much larger ‘hole to hole’ clearance from the constraints setting (useful for through-vias) kicks in.
I’d appreciate any pointers on how to achieve what I’m after, or knowing that it is indeed not possible 
.
Thanks!