Which PCB materials are used for RF?
RF laminate choice is driven by dielectric constant (Dk) and its tolerance and stability, loss tangent (Df), copper roughness, thermal properties and cost. Standard FR-4 (Dk ≈ 4.2–4.7, Df ≈ 0.015–0.02) is adequate for many sub-3 GHz designs; hydrocarbon-ceramic laminates such as Rogers RO4350B (design Dk 3.66, Df 0.0037 at 10 GHz) and PTFE laminates such as RT/duroid 5880 (Dk 2.20, Df 0.0009 at 10 GHz) are used for lower loss and tighter control.[1][2]
How do materials compare?
| Material class | Dk (typical) | Df (typical) | Notes |
|---|---|---|---|
| Standard FR-4 | 4.2–4.7 | 0.015–0.02 | Low cost; Dk varies with resin content and frequency |
| Low-loss FR-4 variants | 3.5–4.0 | 0.005–0.01 | High-speed digital laminates |
| Hydrocarbon ceramic (e.g., RO4350B) | 3.48 process / 3.66 design | ~0.0037 | FR-4-like processing |
| PTFE glass (e.g., RT/duroid 5880) | 2.2 | ~0.0009 | Lowest loss; special processing |
| Ceramic-filled PTFE | 3–10+ | 0.001–0.003 | Size reduction |
Values from manufacturer datasheets for the named products; others indicative.
What is the difference between process and design Dk?
Manufacturers report Dk measured by a specific test method (such as the IPC-TM-650 clamped stripline method) and sometimes a separate “design Dk” derived from circuit measurements, which better predicts microstrip impedance and phase. Use the design value for simulation.[3][1]
What else matters?
- Glass weave effect: fiber bundles create local Dk variation, causing skew in differential pairs; spread glass helps.
- Copper roughness: see skin effect.
- Thermal coefficient of Dk (TCDk) for filters and phase-critical lines.
- Moisture absorption and CTE for reliability; hybrid stackups combine RF laminate with FR-4.
Frequently asked questions
Can I use FR-4 at 5 GHz?
Often yes for short lines and non-critical designs, accepting higher loss and Dk uncertainty.
Why is PTFE harder to fabricate?
It needs special surface preparation for plating and is soft and dimensionally less stable.
What is a hybrid stackup?
A board combining RF laminate on outer layers with FR-4 inner layers.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “RO4000 Series High Frequency Circuit Materials data sheet (RO4350B)”. Rogers Corporation. data sheet.
- “RT/duroid 5870/5880 High Frequency Laminates data sheet”. Rogers Corporation. data sheet.
- “IPC-TM-650 Test Methods Manual (incl. 2.5.5.5 stripline dielectric constant test)”. IPC. current.