>>But why it is better to insert filler cells after routing?
Still P & R tool might be optimizing the design to meet the timing by moving the cell here and there, that is why filler cells will inserted after routing.
Still P & R tool might be optimizing the design to meet the timing by moving the cell here and there, that is why filler cells will inserted after routing.
But PnR tool can do the same optimization after inserting the filler cells. In that case it will replace the filler cell with std cell or we can say the std cell will swap with filler cell.
I dont know whether it is possible or not for the tool to swap cells.
>>But PnR tool can do the same optimization after inserting the filler cells.
If you insert filler cells before routing, cell placement is fixed and tool cannot move the cells for better placement optimization.