Why timing may degrade after CTS?

o   Clock groups might be updated after CTS based on new tree topologies causing new violation.

o   Physical Detours and Congestion: The newly inserted clock buffers and routing can create congestion, forcing data path signals to take longer routes (detours) around the clock tree structures, thereby increasing their delay.

o   CTS might trigger ECO fixes or buffer legalization that shifts data path buffers or cells.

o   Actual skew values achieved is more than expected and considered in uncertainty, causing mismatch.

o   CTS fixes DRC. And move around cells can cause timing violation.

o   Very tight CTS constraint can cause CTS to add more buf/inv creating congestion and shifting nonCTS cells.