Other worries which will limit-> towards gridlessness. (Routing-1)

To handle various cost functions and constraints of deep sub micron layouts, the router will need to have the capability to perform

1. variable wire widths
2. variable spacing requirements
3. shielding/interleaving capabilities.

These requirements lead towards gridlessness.

When designing a detailed router utmost care needs to be taken so that interconnect parasitics after detailed route do not render the existing design useless.

(optimization in most tools happens with an elmore delay model and global route parasitic extraction). So the deviation even beyond ripup and reroute stage has to limit towards the pre-exisiting global route while fixing as many opens/spacings and shorts as possible.