Cell padding for routability

Cell padding for routability. The cells are placed in a fixed order, packed tight. A cluster of pin-heavy cells in the middle is a local routing hotspot: too many pins fall in one window for the router to reach them. The fix is cell padding - reserving extra space around the crowded cells so their pins spread out.

• Local density under limit - click a cell to add padding; it spreads the cluster and drops the local pin density (the heat) under the limit.
• Wirelength under target - every pad you add lengthens the nets, so do not over-pad.
• Row fits in core - padding also pushes the row wider; it must stay inside the core edge.

Pad just enough to clear the hotspot without blowing the wire or the row, then Submit design.