— Since re-designing and re-optimizing existing logic, memory, and IP blocks in a 3D fashion significantly increases design cost, nearterm three-dimensional integrated circuit (3D IC) design will focus on reusing existing 2D blocks. One way to reuse 2D blocks in the 3D IC design is to first perform 3D floorplanning, insert signal through-silicon vias (TSVs) for 3D inter-block connections, and then route the blocks. In this paper, we propose algorithms (finding signal TSV locations, assigning TSVs to whitespace blocks, and manipulating whitespace blocks) for post-floorplanning signal TSV planning in the block-level 3D IC design. Experimental results show that our signal TSV planner outperforms the state-of-the-art TSV-aware 3D floorplanner by 7% to 38% with respect to wirelength. In addition, our multiple TSV insertion algorithm outperforms a single TSV insertion algorithm by 27% to 37%.