Arlon 25FR PCB | Flame Retardant RF Laminate

What Is Arlon 25FR?

Arlon 25FR is a woven-fiberglass-reinforced PTFE composite laminate with a dielectric constant (Dk) of 3.58 ± 0.04 at 10 GHz and a dissipation factor (Df) of approximately 0.0035 at the same frequency. It carries a UL 94 V-0 flame rating, which separates it from many unfilled or ceramic-loaded PTFE laminates that only achieve HB or V-1. That combination of controlled RF performance and fire safety makes Arlon 25FR PCB a go-to material for avionics, defense, and commercial telecom assemblies where both electrical specifications and regulatory compliance are non-negotiable.

Key Electrical and Mechanical Properties

The table below summarizes the published parameters engineers need when evaluating Arlon 25FR against other RF-grade laminates. All values are typical unless otherwise noted.

A Dk of 3.58 is higher than many pure or ceramic-filled PTFE options—compare it with Rogers DiClad 527 at Dk 2.50 or a hydrocarbon ceramic laminate at Dk 3.38—but the trade-off buys you a robust flame-retardant system embedded in the resin rather than relying on external shielding or enclosures to meet fire codes.

Why Flame Retardancy Matters in RF Laminates

Many high-frequency PTFE laminates achieve excellent Dk and Df numbers but carry only a UL 94 HB (horizontal burn) rating. That is acceptable for bench prototypes or sealed metallic enclosures, but not for applications governed by:

• FAA/EASA airworthiness directives — avionics PCBs generally require V-0.
• IEC 61010-1 — measurement and control equipment mandates V-1 or better for certain risk classes.
• EN 45545-2 — rail transport fire-safety standard.
• Telecom cabinet standards (NEBS GR-63-CORE) — carrier-grade equipment must pass flame tests.

Arlon 25FR addresses these by incorporating a halogenated flame-retardant additive into the PTFE matrix. The engineering trade-off is a slight increase in Df relative to an unfilled PTFE of similar Dk, plus a marginally higher moisture-absorption figure. For most designs operating below 10 GHz, that penalty is insignificant compared to the cost and schedule risk of failing a flammability audit.

Where Arlon 25FR PCBs Are Used

Avionics and Defense

Radar feed networks, GPS patch antenna substrates, and IFF (Identification Friend or Foe) transponder boards frequently specify Arlon 25FR because the laminate meets MIL-grade flame requirements while keeping insertion loss manageable through L- and S-band frequencies (1–4 GHz).

Commercial Telecom

Base-station power amplifier pallets and filter boards that sit inside outdoor cabinets use 25FR to satisfy NEBS testing. The woven-glass reinforcement also gives the laminate better dimensional stability during reflow than unreinforced PTFE, reducing warpage in multi-up panel processing.

Industrial and Medical

ISM-band (2.4 GHz, 5.8 GHz) sensor modules and medical telemetry devices benefit from the V-0 rating, especially when the end product must carry a UL listing for flammability of plastic materials.

Arlon 25FR vs. Alternative RF Laminates

Use the selector below to compare Arlon 25FR against other Arlon grades and see which material best fits your frequency, Dk, and compliance requirements.

If the tool suggests a lower-Dk option and flame retardancy is not mandatory, consider Arlon 55NT, a non-PTFE thermoset with Dk 3.50 and very low Z-axis CTE, or a ceramic-loaded PTFE for frequencies above 20 GHz. If you need high-temperature polyimide construction instead, Arlon 85N offers pure-polyimide multilayer capability with a different set of trade-offs.

Rogers RO4350B matches 25FR on flame rating and is easier to fabricate because it processes like FR-4, but its slightly higher Df at lower frequencies and its different resin chemistry may not suit every legacy design originally qualified on PTFE. Taconic TSM-DS3 wins on loss but lacks V-0, which may rule it out for avionics. The right choice depends on whether your bottleneck is loss budget, flame compliance, or fabrication cost.

Fabrication Considerations for Arlon 25FR PCBs

Drilling and Via Preparation

PTFE-based laminates are softer than epoxy-glass systems, so drill bit selection matters. Use carbide-tipped bits with a lower chip load (0.001–0.002 in per revolution) to avoid smearing. Plated through-holes in PTFE require a sodium-naphthalenide etch (or equivalent plasma desmear) to activate the PTFE surface before electroless copper deposition. Skipping this step is the single most common cause of barrel cracking and pad lift in PTFE boards.

Lamination and Hybrid Stackups

Arlon 25FR can be laminated with FR-4 or polyimide cores in hybrid stackups using compatible bonding films (e.g., Arlon 6700 or similar low-flow prepregs). Hybrid construction places the RF layers on 25FR and the digital/power layers on lower-cost epoxy-glass, cutting material cost without compromising the RF interface. Keep bonding temperatures within the recommended 350–375 °F (177–191 °C) range and apply 200–300 psi to achieve reliable adhesion. Consult the IPC-6012 qualification standard for acceptance criteria on plating thickness and registration in mixed-dielectric builds.

Surface Finish

ENIG and immersion silver are the most common finishes for Arlon 25FR RF boards. HASL is generally avoided on RF traces because the uneven solder profile degrades impedance control at frequencies above a few GHz.

Cost Positioning

Arlon 25FR sits in the mid-to-upper tier of RF laminate pricing. It is more expensive than standard FR-4 or basic hydrocarbon-ceramic laminates, but typically less costly per panel than ultra-low-loss ceramic-filled PTFE grades used at millimeter-wave frequencies. The primary cost drivers are:

• Raw laminate price — PTFE resin systems cost more than epoxy or hydrocarbon resins.
• Fabrication complexity — sodium etch, controlled drill parameters, and lower panel utilization (PTFE is more prone to dimensional movement during etching).
• Volume — Arlon 25FR is a specialty product; lead times can stretch to 4–6 weeks for non-stocked thicknesses.

Use the cost index tool below to get a relative sense of how Arlon 25FR compares to other laminates in your target thickness and copper weight.

If the index shows 25FR at 2–3× the cost of FR-4, that is typical. The question is whether a hybrid stackup—RF layers on 25FR, everything else on FR-4—can bring the overall board cost closer to budget while still meeting your flame and electrical requirements. In most telecom and avionics designs, that hybrid approach is exactly what gets built.

Design Tips and Common Pitfalls

• Account for Dk tolerance in impedance calculations. A Dk of 3.58 ± 0.04 means your 50 Ω microstrip width can shift by roughly ±1 mil (0.025 mm) depending on the panel. Always run a sensitivity analysis.
• Do not assume FR-4 etch factors. PTFE laminates etch differently; the undercut profile is typically less predictable. Request etch-factor data from your fabricator for the specific copper weight.
• Specify the copper type. Rolled-annealed (RA) copper gives lower insertion loss at higher frequencies than electrodeposited (ED) copper because of its smoother surface profile. For designs above 5 GHz, RA copper on Arlon 25FR can recover 0.5–1.0 dB of loss per foot of trace.
• Mind the moisture. Although 0.06 % absorption is low, PTFE laminates can absorb moisture along drilled hole walls. Bake panels at 250 °F (121 °C) for 2–4 hours before lamination or soldering if they have been stored in a humid environment.
• Mark the flame-retardant requirement on your fab drawing. If V-0 is the reason you chose 25FR, call it out explicitly so the fabricator does not substitute a non-FR PTFE grade during procurement.

Comparing Arlon 25FR with Other Flame-Retardant RF Options

Arlon 25FR is not the only V-0 RF laminate. Rogers RO4000-series laminates (RO4003C, RO4350B) also carry V-0 and are easier to process. Isola IS680-AG offers low Dk with halogen-free flame retardancy for high-speed digital/RF crossover designs. The deciding factors are usually:

• Choose Arlon 25FR when your design is already qualified on a PTFE substrate, flame retardancy is mandatory, and operating frequency is below 10 GHz.
• Choose RO4350B when you want FR-4–compatible processing, V-0 compliance, and operation up to 20 GHz or higher.
• Choose a ceramic-filled PTFE (e.g., Rogers CLTE-MW) when CTE matching to copper is critical and you can work around the HB flame rating with enclosure-level fire protection.

Frequently Asked Questions

Is Arlon 25FR the same as Arlon 25N?

No. Arlon 25N is a non-flame-retardant woven-glass PTFE laminate with a similar Dk (~3.38) but a UL 94 HB rating. The “FR” suffix specifically denotes the flame-retardant formulation, which adds a small amount of loss and raises the Dk slightly.

Can Arlon 25FR be used above 10 GHz?

Physically, yes—PTFE remains low-loss well into millimeter-wave frequencies. However, the Df of 0.0035 and the Dk tolerance become more significant above 10 GHz. For frequencies beyond 10 GHz, lower-loss PTFE or ceramic-loaded laminates are usually a better engineering choice unless the V-0 mandate leaves no alternative.

What bonding film works with Arlon 25FR in hybrid stackups?

Arlon 6700 (a fluoropolymer-based bonding film) is the manufacturer’s recommended option. Third-party FEP or modified-PTFE bonding films also work, provided the lamination temperature and pressure are matched. Always run a peel-strength coupon test on the specific combination before committing to production.

Does Arlon 25FR meet RoHS requirements?

Arlon 25FR uses a halogenated flame-retardant system, so it is not halogen-free. It does meet IEC 62321 RoHS substance restrictions (no lead, cadmium, mercury, hexavalent chromium, PBB, or PBDE above threshold), but if your program requires halogen-free construction, you will need a different laminate.

What is the typical lead time for Arlon 25FR panels?

Stocked thicknesses (20 mil, 31 mil, 62 mil with 1 oz ED copper) typically ship within 1–2 weeks. Non-standard thicknesses or rolled-annealed copper cladding may require 4–6 weeks. Always confirm availability before locking your BOM.