@User a negative fill area error during placement means that (design area /

PLACEMENT_DENSITY

) >

CORE_AREA

. In other words, you are trying to place the design in a core area that is too small.

PLACEMENT_DENSITY

must always be greater than

CORE_UTILIZATON

. Anecdotally, simple processes can get a clean solution with up to ~50% placement density. The most complex processes we have tested (sub-20nm) require ~20% placement density.