Footprint TO_SOT_Packages_SMD:TO-263-3_TabPin2 is for big surface mount power components such as MOSFETS and regulators with three pins and a huge square pad. In the library footprint, the pad appears both as one big square pad, and as four smaller squares underneath it. All are marked as Pin 2.
DRC is happy with this, but FreeRouter considers it a violation. Is there some reason for that? Is there a pad size limitation somewhere? I created a similar symbol with one big pad, and it seems to work fine. Somebody was trying to do something special, but what?
(Interestingly, it is a clearance violation in FreeRouter to have two pads of the same footprint with the same number touching. KiCAD itself allows that. However, FreeRouter will connect two pads with the same number that don’t touch.)
The segmented PCB design facilitates the solder paste flux outgassing during reflow, thereby promoting a lower voiding level of the completed solder joint. At the same time, the maximum size of a single solder void is limited by the dimensions of a single matrix segment.