Copper surface profile can materially affect conductor loss at high frequencies. A low-loss dielectric does not remove this contribution.
What to consider
The copper foil variant and its treatment belong in the stackup specification. Compare insertion-loss predictions with a suitable roughness model and the actual conductor geometry. Very fine routing also increases conductor resistance, so increasing routing density can create an electrical tradeoff.
A practical review example
Compare two foil options at the same pressed thickness and route width. If the channel budget is sensitive to the difference, control the foil choice as a released material requirement.
Checks before release
- Specify the intended copper foil system.
- Use an appropriate roughness model.
- Review manufacturability of any foil substitution.
Connect this decision to fabrication
Use the material selector 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.
- Identify the exact grade, glass style, resin content and copper foil.
- Compare Dk and Df only with their frequency and test method.
- Confirm the material system is qualified for the proposed via structure.
Technical references
FR408HR material and processing resourcesMEGTRON6 material family and test conditionsRO4000 laminate data and processing resourcesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.