New one to me...........
I have a board where we have decided to put a few non-plated holes around the board to be used for debug purposes incase we need to run some wires from the bottom layer to the top layer for modifications and such. I have a mechanical hole that when I place it anywhere on the board, the solid copper layers produce a void of a square instead of a circle. I have other holes of similar nature used for the mounting holes that were placed the same way but give me a nice circular void.
So, why the square void vs the circular void? Both pad stacks have the same structure except the drill diameter is smaller fo one vs the other. Both holes are non-plated and have pad sizes smaller then the drill size so the pads get drilled away.