Name the dimensions before dividing
Record where depth begins and ends and which diameter enters the calculation. A laser opening may have different entrance and target dimensions. A ratio calculated from the largest opening can tell a different story from a process rule based on another measured feature.
Altium documents an IPC-2226A microvia definition with explicit dimensional references. Consult the applicable definition and revision for a project; do not combine a depth convention from one source with a diameter convention from another.
Work a simple screening example
Using illustrative dimensions only, a depth of 60 micrometers divided by an agreed diameter of 100 micrometers gives 0.60. If the relevant depth becomes 75 micrometers while the diameter stays unchanged, the ratio becomes 0.75. This arithmetic does not establish that either structure is manufacturable.
Include tolerances in the real review. The nominal ratio can conceal a deeper dielectric region or a smaller opening at a permitted extreme. Ask the fabricator which combination should govern its acceptance and design rules.
Evaluate the alternatives beyond the ratio
Reducing depth may affect impedance geometry or stack thickness. Increasing diameter may consume the capture-pad margin or routing channel. Splitting a deeper connection into separate microvias adds interfaces and may require another construction stage. Compare these consequences before selecting the lowest calculated number.
- Use the same units for depth and diameter.
- Document the measurement convention alongside the result.
- Check target-land coverage and neighboring clearances.
- Review the entire multi-level path after changing one feature.
Use calculators as review aids
A calculator can expose arithmetic errors and compare scenarios quickly. It cannot know whether the selected material, laser process, metallization, and via stack have been qualified. Export the inputs with the result so the manufacturing reviewer can replace illustrative assumptions with the actual approved dimensions.
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
Does a ratio below a published limit guarantee reliability?
No. A geometry limit is one constraint. The interfaces, materials, manufacturing process, and expected exposures still require review.
Should I use the finished board thickness as depth?
For a microvia, use the defined depth of that particular structure. Full board thickness applies to a different span and would give the wrong calculation.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.