I’m using KiCad 7.0.9 on Ubuntu to design a PCB with 0.4mm pitch BGA components. I’ve set up rule areas around the BGAs to allow for neckdown and smaller clearances for breakout, compared to the rest of the board for routing.
According to the documentation and to past forum posts (such as DRC custom design rule question (again)) it seems like the global minimum clearance should not be able to be overridden.
I have the global minimum clearance set to 0.076 mm (3 mils) as per the fabricator’s capabilities, and put the clearance inside by BGA breakout rule area to 0.05mm. However it seems that the 0.05mm clearance was used when filling zones based on the feedback from the fabricator.
I’ve resolved this issue by setting the custom rule clearance to 3 mils as well. However, I’m wondering if this is the intended behaviour, or if this should be investigated further.