Distinguish copper geometry from mask geometry
A copper pad and its solder-mask opening are separate design objects. In a non-solder-mask-defined land, the opening exposes the copper perimeter; in a solder-mask-defined land, the opening limits the exposed area. Follow the component's applicable land-pattern guidance and assembly review. Do not change from one approach to the other by adjusting a global expansion merely to silence a design-rule warning. That change can alter the solder joint geometry.
Calculate the remaining web
For neighboring circular features on the same pitch, the nominal mask web equals the pitch minus the opening diameter. If both openings are expanded equally from copper lands, the opening diameter is the land diameter plus twice the radial expansion. Altium documents this radial expansion behavior and supports local overrides. Use the formula to understand a warning, then check the process-agreed minimum web and registration assumptions. A positive nominal web does not by itself prove that the mask feature will survive production.
Review via treatment independently
A tented via, a filled via, and a capped solderable via describe different structures. Decide which result the design needs and state it in the fabrication requirements. At a BGA land, the assembly goal may require a planar solderable surface; a mask setting alone does not create it. For vias near component pads, inspect whether the opening permits unintended solder movement or merges with a neighboring land. Coordinate the decision with both fabrication and assembly.
Inspect the released layers
Export the manufacturing data and review top and bottom mask against copper, drills, and the assembly footprint. Look for local pad overrides, unintended gang openings, missing exposure, and silkscreen intrusions. Check dense packages separately from general board rules. If the fabricator proposes a mask adjustment, review the actual revised geometry rather than accepting an undocumented global change. Preserve the approved output with the release so later library changes can be compared against it.
Adjacent-layer access, one connection at a time
Dielectric · geometry + material
Core or build-up dielectric
Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.
Common questions
Is zero mask expansion always the most accurate choice?
No. The required opening depends on the intended land definition, package guidance, registration, and process. A software default is not a fabrication requirement.
Can I merge mask openings when a web is too small?
Possibly, but that changes the assembly geometry. Obtain review of the specific component region rather than merging every flagged opening automatically.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.