### Mask Opening on Shapes

Checks the minimum open area.

When a solder mask or cover lay covers a large area of a design, more often a large copper area, air can be trapped between the mask and the PCB surface during fabrication. When heated, the expanding air pushes the mask away from the PCB and forms a bubbling appearance, as there is no relief hole for the air to escape. This is common in dry film solder mask processes, not commonly found in the Liquid Photo Imageable (LPI) masks.

This constraint specifies the minimum area that must be open to reduce air bubbling. This check is valid for shapes with area larger than specified in the DFF options page.

#### DRC Code: %2