Re: Via exact size DRC rule
In my personal experience, the vias in IO pad are no larger than standard vias. They are generally grouped into a diamond-shaped array to allow more current flow.
Also, there are several things I think might be helpful to you.
First, the size of standard via grows as the metal layer level increases.
Second, vias can be stacked in contemporary processes. That is, the via from metal2-to-metal3 can be directly on the via metal1 to metal 2.
Third, generally speaking, all available metals have to be used in IO pads.
Correct me if I am wrong, thank you
ceyjey