Calculate microvia aspect ratio from the relevant dielectric depth and via diameter using a consistent convention. Obtain the factory limit for the actual shape, material and filling process.
What to consider
A tapered laser hole has different top and bottom diameters. The measurement convention matters when comparing capability tables. Copper filling, target preparation and plating quality also affect reliability; an acceptable geometric ratio alone does not qualify a microvia stack. Treat examples as calculations, not universal manufacturing limits.
A practical review example
With 75 µm depth and 100 µm diameter, the nominal ratio is 0.75. If the depth becomes 100 µm while the diameter stays unchanged, the ratio becomes 1.0. Confirm the factory’s accepted depth and diameter definitions before evaluating either option.
Checks before release
- Use one unit system.
- Identify top, bottom, drilled or finished diameter.
- Confirm supported ratio and reliability evidence together.
Connect this decision to fabrication
Use the design checklist to organize the initial discussion. Keep proposed values separate from the approved drawing and document the effect of any change on the rest of the construction.
- Record depth and diameter using the same units and measurement convention.
- Check capture lands, target lands and registration together.
- Match the test coupon to the actual interconnect construction.
Technical references
Fabrication design guidelinesHistorical IPC microvia reliability warning (2019)References checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.