RO4350B is a reinforced hydrocarbon/ceramic laminate used for RF circuits. It is not a metal alloy, and an RF layer alone does not define an HDI construction.
What to consider
A hybrid board may combine RF laminate with other dielectric systems. The press sequence, bonding material, thickness balance and via process must be compatible. Distinguish process Dk from design Dk when selecting simulation inputs, and use the construction and test conditions relevant to the actual board.
A practical review example
If the outer RF route uses RO4350B while the core uses another material, ask the factory to confirm the bond system and microvia process through the outer dielectric. Recalculate the route geometry using the approved pressed thickness.
Checks before release
- Identify the exact material and thickness.
- Confirm hybrid bonding and drilling compatibility.
- Use the manufacturer’s RF design and processing guidance.
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
RO4000 laminate data and processing resourcesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.