Identify connected and unconnected layers

For every via type, list the layers on which it connects and those it only passes or approaches. Define capture and target lands where relevant, and specify clearances to unconnected copper. Do not assume that one circular padstack shape is appropriate on every layer.

Review unused-pad removal as a deliberate design and manufacturing choice. A CAD option can change geometry that was assumed in an electrical model or fabrication review, so the resulting padstack should be inspected in the released data.

Budget the land for actual variation

The nominal radial difference between land and opening is only one part of the connection margin. Include the agreed positional and dimensional allowances. Altium's drill-size discussion relates pad selection to hole size, ring requirements, and tolerance; use the supplier's definitions for the exact structure.

An illustrative larger land can improve landing margin but close a neighboring escape channel. When that happens, compare routing changes or a different transition rather than shrinking the land until it merely looks convenient in CAD.

Treat the antipad as electrical geometry

Increasing clearance can change coupling to a reference plane and consume plane area. Decreasing it can create a manufacturing or isolation concern. Dense fields of clearances may interact, leaving narrow copper connections or forcing return current around an obstacle.

  • Check clearance to all nearby copper, not only the named plane.
  • Inspect merged clearances in dense via fields.
  • Maintain useful reference connections near critical transitions.
  • Model demanding transitions using the actual released geometry.

Review complete padstacks in section and plan

Use a cross-section to understand layer connections and a plan view to see spacing and plane continuity. Neither view is sufficient alone. For differential or otherwise sensitive paths, compare the neighboring structures too; symmetry and the local return environment may matter as much as the dimensions of one via.

DESIGN NOTE / SCHEMATIC

Adjacent-layer access, one connection at a time

Signal copper

Dielectric · geometry + material

Reference copper

Core or build-up dielectric

Signal copper

Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.

Common questions

Is a larger antipad always better for high-speed signals?

No. It changes the transition and reference plane. Evaluate the complete structure rather than optimizing one clearance in isolation.

Can I use the same pad on every layer?

Sometimes, but it should be an intentional approved choice. Connected layers, unused layers, and different targets can need different geometry.

References & further reading

Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.