Which NDR to use? Can we use 2w2s till leaf cells?

o   NDRs Used: The most common NDR applied was Double Width, Double Spacing (2W2S) for the main trunk and branch lines of the clock tree. For very critical top-level clock spines, sometimes Triple Width (3W) or wider rules were considered, depending on EM requirements and foundry recommendations.

o   Using 2W2S Till Leaf Cells:

o    Generally NO. not necessary and highly undesirable.

o    Congestion: number of leaf-level clock nets is enormous. Applying 2W2S universally would consume excessive routing resources, especially on lower layers where usually pin connections occur

o    NDR is required for longer and nets with high current density which drives heavy load. Leaf nets are usually shorter and doesn’t need NDR.

o    Power: Wider wires have higher capacitance, increasing the dynamic power consumption of the clock tree.