A method for I/O pins partitioning targeting 3D VLSI circuits

This paper presents an algorithm for I/O pins partitioning and placement targeting 3D circuits. The method starts from a standard 2D placement of the pins around a flat rectangle and outputs a 3D representation of the circuit composed of a set of tiers and pins placed at the four sides of the resulting cube. The proposed algorithm targets a balanced distribution of the I/Os that is required both for accommodating the pins evenly as well as to serve as an starting point for cell placement algorithms that are initially guided by I/O's locations, such as analytical placers. Moreover, the I/O partitioning tries to set pins in such a way the it allows the cell placer to reach a reduced number of 3D-Vias. The method works in two phases: first the I/O partitioning considering the logic distances as weights; second, fix the I/Os and perform partitioning of the cells. The experimental results show the effectiveness of the approach on balance and number of 3D-Vias compared to simplistic methods for I/O partitioning, including traditional min-cut algorithms. Since our method contains the information of the whole circuit compressed in a small graph, it could actually improve the partitioning algorithm at the expense of more CPU time. Additional experiments demonstrated that the method could be adapted to further reduce the number of 3D-Vias if the I/O pin balance constraint can be relaxed.