Finished board thickness combines copper, pressed dielectric, mask and other construction details. A thickness target must leave a feasible microvia geometry.
What to consider
Thin build-up dielectrics can help microvia aspect ratio but change achievable impedance width and resin-flow requirements. A thick core can increase mechanical drilling demands. Ask for the pressed construction rather than adding nominal prepreg sheet values without considering resin flow and copper coverage.
A practical review example
For a 0.10 mm nominal laser diameter and a 0.075 mm dielectric depth, the geometric depth-to-diameter ratio is 0.75. That arithmetic is an input to process review, not evidence that the via is qualified.
Checks before release
- Specify overall thickness tolerance and measurement convention.
- Use pressed rather than unprocessed dielectric values.
- Coordinate mechanical fits with impedance and via geometry.
Connect this decision to fabrication
Use the stackup planner 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.
- Give every signal layer a defined return-path strategy.
- Review material and copper balance about the board center.
- Specify every via span and the factory-approved lamination sequence.
Technical references
HDI construction types and definitionsFabrication design guidelinesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.