A partitioning method for partitioning a group of power-ground (PG) cells is disclosed. The method includes: placing at least one out-boundary PG cell on a substrate, wherein power strips of the at least one out-boundary PG cell are aligned with corresponding power rails on the substrate; and placing at least one in-boundary PG cell on the substrate, wherein power strips of the at least one in-boundary PG cell are aligned with corresponding power rails on the substrate.