buffer vs delay cells to fix hold violations

i) When local congestion is not there at endpoint:

generally delay cells are big compared to buf and 1 delay cell can give 80ps (for e.g.) and buf cell can give only 20ps => so instead of putting 4 buf cells (area of 4 buf cells is more than 1 delay cells for the same delay), it it better to put 1 delay cell.


ii) When local congestion is there, 80ps delay cell may not fit there and 4 buf cells can be inserted 1 top on other on different routing tracks.

So, it is difficult say which is put to fix and which is advantageous to have to fix certain ECO.