i can see where this might break, but i don't know that it will be a problem. basically, if it's a 2-layer board and you need both layers through that junction, things could get ugly quickly. my feeling is though, that unless there's a lot of desire for a standalone numpad, this isn't something we should bother with. if it there is, however, then we might as well just do it right and build both up as one separate-able pcb with a uc placed on both ends and a flex connector that can allow them to be plopped into the same chassis