Blockages

Soft (Non buffer blockage)

• Only buffers can be placed and standard cells cannot be placed.

Hard (Std-cell blockage)

• Blocks all std-cells and buffers to be placed. 
• Std-cell blockages are mostly used to:
• Avoid routing congestion at macro corners
• Restrict std-cells to certain regions in the design
• Control power rails generation at macro cells

Partial blockages

• By default a placement blockage has a blockage factor of 100%. No cells can be placed in that area, but flexibility of blockages can be chosen by partial blockages.
• To reduce placement density without blocking 100% of the area, changing the blockage factor of an existing blockage to lower value will be a better option.

Benefits 

• Reduce the congestion by spreading the logic

Disadvantages

• It may leads to timing violations
• Hard blockages will west the core area

Commands to create the placement blockages

• create_placement_blockage -coordinates { {x1 y1} {x2 y2}} -type hard/Soft -name blockagename
• create_placement_blockage -coordinates { {x1 y1} {x2 y2}} -type partial -blocked_percentage x -name blockagename.