Distinguish process Dk from design Dk when specifying RO4350B or RO4003C, then document the construction assumptions used for your RF layout.
Use the exact material designation
A drawing that says only “Rogers PCB” leaves the material requirement incomplete. Specify the laminate family and grade, the intended construction and whether any substitutions are permitted. The board fabricator also needs the nominal core thickness, copper choice and bonding arrangement. For a mixed-material multilayer board, show which layers use which material.
Process Dk and design Dk are different entries
The Rogers RO4000 data sheet lists process Dk and design Dk separately. For RO4003C, the listed values are 3.38 ± 0.05 for process Dk and 3.55 for design Dk. For standard RO4350B, they are 3.48 ± 0.05 and 3.66 respectively. The process measurement is specified at 10 GHz and 23°C; the design value uses a different method and frequency range. The data sheet also notes an exception for 4 mil RO4350B. Check the exact construction and notes before using a number.
These values are not interchangeable labels for an identical test. Put the selected dielectric model, its source and its frequency assumptions in the simulation record. When sharing an impedance calculation, include that record with the physical stackup so another engineer can understand why the geometry was chosen.
Make the stackup review reproducible
| Record | Question it should answer |
|---|---|
| Signal layer and reference plane | Which conductor pair defines the modeled transmission line? |
| Dielectric construction | What material and finished separation are assumed? |
| Copper | What foil and finished conductor thickness were used in the model? |
| Geometry | What trace width, spacing and solder mask assumptions were used? |
| Verification | What impedance or RF measurement will check the finished build? |
Ask the fabricator to distinguish a suggested manufacturing adjustment from an approved design change. If the trace width is changed to reach an impedance target, retain both the original requirement and the final agreed geometry. Do not accept an unexplained “equivalent stackup” when material choice is part of the RF design.
Handle material substitutions as engineering changes
Availability may prompt a proposed alternative material, copper foil or bonding product. Review the proposal against the design model and the product requirements. A nominally similar dielectric constant does not, on its own, establish equivalent behavior. Document which calculations, coupons or prototype measurements must be repeated before accepting the change.
A useful approval record identifies the original requirement, the proposed construction, the technical reason, the supporting data and the revision or lot to which approval applies. This keeps a one-time exception from silently becoming the default for every future order.
What to send with an inquiry
- The board data and a layer-by-layer construction drawing.
- Material grade, copper specification and any restricted substitutions.
- The nets requiring controlled impedance and the targets with tolerances.
- The RF operating range and the relevant verification plan.
Use the stackup guide and impedance planning page to organize the request. Supplier data describe material properties; actual manufacturability and acceptance need agreement for the released board.
References
Move from reading to a build-ready project
Use the fabrication and assembly checklists to prepare drawings, production files and test requirements.
Open the DFM checklist