Antipad size on non-functional layer

[v923z]

What is the canonical way of setting the antipad size on a non-functional layer? In particular, I have an 8-layer board, where the high-speed (10 GHz) signals run on the outer layers, which are connected by vias. Now, for reasons related to impedance control, I’ve removed the pads on all non-functional layers like so:

The problem is that the antipads are now defined by the diameter of the via, and not anything else. (This can be seen in the fact that the hole on the green layer, which is the first inner layer, is smaller than the hole on the red layer, which is the top layer.) However, I’d like to be able to control the antipad size. (Some even recommend elongated antipads.) What is the correct way of doing this in KiCAD?

[craftyjon]

What you call antipad here is just copper clearance in KiCad. You are talking about the clearance between the copper zone and the via hole wall (which is plated with copper). So, if you want to define a specific clearance rule, you would do that with the custom rules system. Figure out a constraint that applies to the nets in question and the layers in question, and set the minimum clearance to what you want.

Defining custom shapes for copper clearance can be done using Rule Areas.

[v923z]

Many thanks for the pointer!