A power delivery network (PDN) engineering change order (ECO) approach for repairing IR-drop failures after the routing stage

PDN evaluation/synthesis techniques have been used to facilitate the planning/construction of PDNs in integrated circuits at early physical implementation stages. They are rarely relevant after the routing stage when few routing resources are left and hence call for a repair strategy. The reason is that the traditional methods often apply wire widening or wire density increment directly without taking signal routing into account. Moreover, intuitively adding connections to the PDNs using the entire space available is quite time-consuming and eventually leads to lack of routing resources for later design ECO. Therefore, in this paper, we propose an approach to efficiently repairing the PDNs at the signoff stage. The greedy-Pareto-optimal (GPO) method is used to select the most effective regions to enhance the power rail connectivity. Maximizing the IR-drop improvement and minimizing the use of routing resources are considered at the same time. The method has been incorporated in our backend design flow and verified by leveraging a commercial P&R tool. On a test case of image signal processor, the experimental results show that the proposed PDN ECO approach can improve the worst IR-drop from 9.34% to 3.84% (i.e., 58.9% improvement) in the post-routing stage, where the ECO wire pitch is 3.5 times the minimal routing pitch.