Pros and Cons of NDR

Pros: greater width reduces crosstalk (glitch and delay) and net delay, and also helps with electromigration.

• report_timing -crosstalk_delay -net -input shows the total net delay on each cell's input pin.
• That delay component is the sum of net delay and crosstalk delay; the -crosstalk_delay option prints the crosstalk portion separately. Cons: NDR causes congestion and adds extra route length.

KEY NDR cuts crosstalk, net delay and EM risk, but increases congestion and route length.

Taller Metal Layers in Lower Nodes

Shrinking the wire width raises its resistance by the same scaling factor. To bring that resistance back down, the cross-sectional area must be increased. Since the width is fixed by the technology, the only way to enlarge the cross-section is to make the metal taller.

KEY Narrower wires raise resistance, so metal height is increased to restore cross-sectional area.

Non-Default Routing (NDR)

An NDR is any deviation from the default routing rules, such as a change to the minimum spacing or minimum width. Increasing width helps by improving electromigration robustness and lowering wire resistance. Increasing spacing helps by reducing crosstalk coupled from data nets onto the clock net.

• Extra spacing matters mainly in the specific case where a data net switches faster than the clock net, since that situation can inject crosstalk onto the clock; wider spacing suppresses it.

KEY NDR changes default width/spacing - width aids EM and resistance, spacing cuts clock crosstalk.