Working with the Paste Mask Expansion Design Rule on a PCB in Altium Designer

Rule category: Mask

Rule classification: Unary

Summary

The shape that is created on the paste mask layer at each pad site is the pad shape, expanded or contracted radially by the amount specified by this rule.

Constraints

Default constraints for the Paste Mask Expansion rule

• Expansion - the value applied to the initial pad shape to obtain the final shape on the paste mask layer.
• Measure Method - use this drop-down to specify the paste mask as an absolute expansion or as a percentage of the pad area. When the option is set to Percent, the Expansion is defined as a percentage of the pad area. You can set the Expansion as follows:
  • Expansion = 0 - the paste mask opening is the same size as the pad.
  • Expansion < 0 - enter a negative value to define a paste mask area that is <Value> percent smaller than the pad area.
  • Expansion > 0 - enter a positive value to define a paste mask area that is <Value> percent larger than the pad area.
• Use Paste - check the box to enable the chosen expansion value by default throughout all designs. The expansion value will be reflected in the Paste Mask Expansion region of the Pad Properties panel. Clear the checkbox to remove the paste from the targeted/selected pad(s). If this option is disabled, the expansion value will default to 0.

How Duplicate Rule Contentions are Resolved

All rules are resolved by the priority setting. The system goes through the rules from highest to lowest priority and picks the first one whose scope expression matches the object(s) being checked.

Rule Application

During output generation.

Notes

• The paste mask expansion can be defined for pads on an individual basis. While browsing properties for a selected pad through the Properties panel, options are available to follow the expansion defined in the applicable design rule, or to override the rule and apply a specified expansion directly to the individual pad in question.
• Paste mask expansion can also be defined at the individual level for the following objects (through the Properties panel, when browsing the properties of a selected object): Track, Region, Fill, Arc. Options are available to follow the expansion defined in the applicable design rule, to override the rule and apply a specified expansion directly to the individual object in question, or to have no mask at all.