FR4 vs Rogers PCB Material
FR4 is the workhorse of the PCB industry — inexpensive, widely available, and suitable for most digital and low-frequency analog designs. Rogers (and similar high-frequency laminates like Isola and Taconic) offer stable dielectric constant, low loss tangent, and better performance at microwave frequencies — at 5–10× the cost of FR4.
FR4 (Standard PCB Laminate)
FR4 is a woven glass-reinforced epoxy laminate. Its dielectric constant varies from ~4.3 at 1 MHz to ~4.0 at 10 GHz, and its loss tangent (tan δ) is 0.015–0.025 — acceptable to about 2–4 GHz.
Advantages
- Very low cost — standard material for most PCB fabricators
- Short lead times — widely available globally
- Well-characterized for digital and RF designs below 2 GHz
- Compatible with all standard PCB processes
Disadvantages
- High loss tangent (0.015–0.025) — significant dielectric loss above 5 GHz
- Variable εr — woven glass causes local εr variation, affecting controlled-impedance traces
- Moisture absorption changes εr — problematic in outdoor and humid environments
- Not suitable for designs above 5–10 GHz
When to use
Use FR4 for all digital designs, mixed-signal boards, and RF up to 2.4 GHz WiFi/Bluetooth. With careful design, FR4 can be used to 5 GHz for low-loss-tolerance applications.
Rogers High-Frequency Laminate (RO4003, RO3010, etc.)
Rogers materials are ceramic-filled PTFE or hydrocarbon/ceramic composites with stable εr (3.5–10.2 depending on grade) and very low loss tangent (0.0013–0.004). εr varies < 0.5% with temperature and frequency.
Advantages
- Low loss tangent (0.001–0.004) — essential above 5 GHz
- Stable εr over temperature and frequency — critical for tight-tolerance filters
- Low moisture absorption — reliable outdoor and space performance
- Available in multiple εr values for impedance and antenna design
Disadvantages
- 5–10× more expensive than FR4
- Longer lead times — specialty material
- Harder to etch and process — fewer fabricators
- Higher coefficient of thermal expansion (CTE) mismatch with connectors in some grades
When to use
Use Rogers for microwave and mmWave PCBs (5–77 GHz+), precision RF filters, phased array antennas, automotive radar (77 GHz), satellite transceivers, and any application requiring low insertion loss or stable impedance above 5 GHz.
Key Differences
- ▸Loss tangent: FR4 = 0.015–0.025; Rogers RO4003 = 0.0027 — nearly 10× lower
- ▸FR4 εr varies with frequency and moisture; Rogers εr is stable to < 0.5%
- ▸FR4 cost: ~$1–2/in²; Rogers: ~$10–20/in² — 5–10× premium
- ▸FR4 acceptable to ~2–4 GHz; Rogers used from 5 GHz to 77 GHz and above
- ▸Most designs use FR4 with Rogers only for the RF stackup layers (hybrid stackup)
Summary
Use FR4 for everything below 2.4 GHz and digital layers in multilayer RF boards. Switch to Rogers (or equivalent: Isola, Taconic, PTFE) when loss, εr stability, or frequency demands it — typically above 5 GHz. Hybrid stackups (FR4 + Rogers) are common in mixed RF/digital designs to contain cost while achieving RF performance where needed.
Frequently Asked Questions
What Rogers material should I use for 2.4 GHz WiFi?
FR4 is sufficient for 2.4 GHz WiFi. Rogers is generally not needed below 5 GHz unless you require very low insertion loss, high-Q resonators, or tight impedance tolerances. Rogers RO4003C (εr = 3.55, tan δ = 0.0027) is a common starting point when upgrading from FR4.
Can I mix FR4 and Rogers in one PCB?
Yes — hybrid stackups combine Rogers high-frequency layers with FR4 digital layers. The Rogers layers handle RF routing; FR4 handles power, ground, and digital signals. This reduces cost while achieving the RF performance needed. The stackup must be carefully designed to match CTE of the materials.
What is the dielectric constant of FR4?
FR4 εr ≈ 4.2–4.4 at 1 MHz, dropping to ~3.8–4.1 at 10 GHz due to frequency dispersion. The woven glass weave also causes local εr variations. For controlled-impedance design, most fabricators use 4.2 ± 0.2. Compare this to Rogers RO4003C: εr = 3.55 ± 0.05 at 10 GHz.
What material is used for 77 GHz automotive radar?
77 GHz automotive radar PCBs use Rogers RO3003 (εr = 3.0, tan δ = 0.001) or similar ultra-low-loss materials. The strict wavelength tolerances at 77 GHz (λ ≈ 2 mm in air) require εr stability of < 0.5% and very low loss. Some designs use liquid crystal polymer (LCP) for flexibility.