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.
Using 2W2S Till Leaf Cells:
Generally NO. not necessary and highly undesirable.
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
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.
Power: Wider wires have higher capacitance, increasing the dynamic power consumption of the clock tree.