Arlon 25N PCB: Properties, Design & Selection

What Is an Arlon 25N PCB?

An Arlon 25N PCB is a printed circuit board built on Arlon 25N, a ceramic-filled, woven-glass-reinforced thermoset laminate designed for RF and microwave circuits operating from UHF through X-band (roughly 300 MHz to 10 GHz). It offers a dielectric constant (Dk) of 3.38 ± 0.05 at 10 GHz, a dissipation factor (Df) of 0.0025, and a low Z-axis coefficient of thermal expansion (CTE) thanks to its ceramic filler loading. Unlike pure PTFE laminates, an Arlon 25N PCB can be fabricated with standard FR-4-class tooling—no sintering, no sodium etch for via prep—which significantly lowers fabrication cost and cycle time for mid-frequency RF boards.

The material sits in the same Dk bracket as Rogers RO4350B (Dk 3.48) and Taconic TLF-35 (Dk 3.50), but its thermoset resin system and ceramic filler give it a distinct balance of electrical performance, mechanical rigidity, and manufacturability. Engineers choose an Arlon 25N PCB when they need tighter Dk tolerance than standard FR-4 and lower loss, but do not require the sub-0.002 Df of pure PTFE.

Key Electrical and Mechanical Properties of Arlon 25N

The Tg above 250 °C is notably higher than many hydrocarbon-ceramic blends (RO4350B has a Tg around 280 °C by TMA for comparison). This makes Arlon 25N compatible with lead-free reflow profiles peaking at 260 °C without delamination risk, an important consideration for RoHS-compliant assemblies.

Dk Stability Across Frequency and Temperature

Ceramic fillers reduce the resin’s inherent Dk drift with temperature. Arlon 25N holds its Dk within ± 0.02 from −40 °C to +85 °C, which keeps filter center frequencies and antenna impedance matches stable in outdoor and automotive environments. Across frequency, the Dk drops by roughly 0.03 between 1 GHz and 10 GHz—tighter than FR-4 but wider than pure PTFE materials like Nelco N9000, which is essentially flat across that range. For designs above 10 GHz where even small Dk drift matters, a PTFE or LCP-based laminate is usually the better choice.

Arlon 25N PCB Fabrication and Processing Advantages

The biggest practical benefit of an Arlon 25N PCB over PTFE-based alternatives is fabrication simplicity. Because it is a thermoset system, it can be drilled, routed, plated, and laminated using the same equipment and chemistry lines as FR-4. Specific advantages include:

• No plasma desmear required. Standard permanganate desmear cleans drill holes effectively, unlike PTFE which often needs plasma or sodium-naphthalenide treatment for reliable plating adhesion.
• Conventional multilayer lamination. Arlon 25N bonds well with standard FR-4 prepregs and with Arlon’s own 25N prepreg, enabling hybrid stackups where RF layers use 25N and digital layers use lower-cost FR-4.
• Tight drill registration. The ceramic filler and woven glass keep dimensional stability under ±0.05 mm over a 457 × 610 mm (18 × 24 in) panel, supporting fine-pitch vias down to 8 mil (0.2 mm) mechanical drill.
• Lead-free compatible. The high Tg and low moisture absorption mean the material survives multiple lead-free reflow cycles (peak 260 °C, 10 s above 255 °C) without blistering.

For engineers familiar with Arlon 25FR, the 25N variant trades the flame-retardant halogenated resin for a non-halogenated thermoset, achieving UL 94 V-0 through the ceramic loading itself rather than brominated additives. This matters for designs subject to IEC 61249-2 halogen-free requirements.

Typical Applications for Arlon 25N PCBs

Antenna Feed Networks and Patch Arrays

Arlon 25N’s Dk of 3.38 produces moderately compact patch antennas—about 18 % smaller than the same design on a Dk 2.55 substrate—while keeping bandwidth acceptable. GPS L1/L2 patches, ISM-band (2.4 GHz, 5.8 GHz) antenna arrays, and WiMAX panel antennas are common uses. The low Dk tolerance ensures consistent gain and return loss across production lots.

Filters, Couplers, and Power Dividers

Coupled-line bandpass filters and Wilkinson dividers at 1–6 GHz benefit from 25N’s combination of low loss, tight Dk, and the ability to hold etch tolerances on fine coupled gaps. The thermoset resin’s rigidity prevents the dimensional creep that softer PTFE substrates sometimes exhibit under thermal cycling.

Hybrid RF/Digital Boards

Because 25N laminates and bonds with FR-4 prepreg, designers can build mixed-dielectric stackups: 25N cores for the RF signal layers and FR-4 cores for power distribution and digital routing. This cuts material cost substantially compared to an all-PTFE stackup while keeping RF performance where it is needed.

Arlon 25N PCB vs. Competing High-Frequency Laminates

The table below compares Arlon 25N against materials engineers most often evaluate in the same design window. Use the selector tool below to explore other Rogers-family options side by side.

Choose an Arlon 25N PCB when you need a non-halogenated, ceramic-filled thermoset with Dk near 3.4, your frequency stays below 10 GHz, and your fabricator already has Arlon-qualified processes. Choose RO4350B when the broader global supply base and slightly higher Dk are acceptable—RO4350B is stocked by more distributors worldwide. Choose Isola Astra MT77 when you are designing above 20 GHz and need the lowest loss in a thermoset-processable material. Choose Taconic TLC-32 when you want the lowest Z-axis CTE for high-reliability via structures and can work with a Dk of 3.20.

Arlon 25N PCB Cost Positioning and Supply

An Arlon 25N PCB typically falls in the mid-range of high-frequency laminate pricing—less expensive than pure PTFE materials such as Rogers RT/duroid 5880 or alumina ceramic substrates, but more expensive per panel than FR-4 or basic hydrocarbon blends. The ceramic filler loading, specialty resin, and smaller production volumes compared to mass-market FR-4 drive the premium. Use the cost index tool below to get a relative sense of where 25N sits against other laminate families.

A realistic example: a 4-layer hybrid stackup with two 25N cores (20 mil each) and two FR-4 cores will cost roughly 1.5–2× what a pure FR-4 build costs at the same layer count, depending on panel utilization and volume. Going all-PTFE could push that multiplier to 3–5×. The hybrid approach is the most common cost optimization strategy for designs where only one or two signal layers carry RF traces.

Arlon materials are distributed through specialty channels; lead times can run 4–8 weeks for non-stock thicknesses. Confirm availability early in the design phase, especially for thicknesses outside the standard 20 mil and 30 mil range. For programs requiring a second-source option, Arlon 35N (a polyimide-based variant with higher Tg but different Dk) or Rogers RO4350B are the most common alternatives, though neither is a drop-in replacement—trace widths must be recalculated for the Dk difference.

Design and Stackup Guidelines

Impedance Control

With Dk = 3.38 and a 20 mil (0.508 mm) core, a 50 Ω microstrip line on 1 oz (35 µm) copper is approximately 45 mil (1.14 mm) wide. For 50 Ω grounded coplanar waveguide (GCPW) on the same core, a 20 mil signal trace with 8 mil gaps is a reasonable starting point. Always verify with a 2D field solver using the manufacturer’s Dk at your operating frequency, not the 1 MHz datasheet value—Arlon 25N’s Dk at 1 MHz is closer to 3.45, which would give misleadingly wide traces if used for a 5 GHz design.

Hybrid Stackup Example

A common 4-layer RF/digital hybrid using Arlon 25N:

1. Layer 1 (Top): RF signal — microstrip on 25N core.
2. Layer 2: Ground plane — continuous copper, stitching vias at λ/20 spacing.
3. Layer 3: Digital / power — FR-4 core.
4. Layer 4 (Bottom): Ground / mixed signal — FR-4 prepreg bond to Layer 3.

The 25N-to-FR-4 bond layer uses a compatible thermoset prepreg (Arlon 25N prepreg or a low-flow FR-4 prepreg). Confirm with your fabricator that their lamination profile accommodates both materials’ cure windows. Mismatched cure temperatures are the most common source of delamination in mixed-dielectric builds.

Thermal Management

Arlon 25N’s thermal conductivity of 0.62 W/m·K is roughly twice that of standard FR-4 (~0.3 W/m·K), courtesy of the ceramic filler. For power amplifier pallets dissipating several watts, this helps spread heat laterally toward thermal vias. However, it is still far below alumina ceramic (25–30 W/m·K), so high-power designs above ~5 W per device typically need metal-backed or coin-insert solutions regardless of the laminate choice.

Quality and Standards Compliance

Arlon 25N meets IPC-4101 slash sheet requirements for ceramic-filled thermoset laminates. It carries UL 94 V-0 flammability, and its non-halogenated formulation satisfies IEC 61249-2-21 for halogen-free status. For military and aerospace programs, verify the specific slash sheet designation with Arlon’s current datasheet, as IPC-4101 revision updates can shift slash sheet numbering. The material has a long history in defense radar and avionics feed networks where IEEE standard terminology for dielectric characterization applies.

Frequently Asked Questions

Is Arlon 25N the same as Arlon 25FR?

No. Both share the ceramic-filled thermoset family and a similar Dk (~3.38), but Arlon 25FR uses a halogenated resin system for flame retardancy, while 25N achieves UL 94 V-0 without halogens. Electrically they are close, but 25N is preferred for halogen-free compliance.

Can an Arlon 25N PCB be used above 10 GHz?

It can function at frequencies somewhat above 10 GHz, but insertion loss rises noticeably past X-band because Df of 0.0025 becomes significant relative to lower-loss PTFE and LCP alternatives. For Ku-band and above, evaluate materials with Df below 0.002.

Does Arlon 25N require special via preparation?

No. Standard mechanical drilling and permanganate desmear produce reliable plated-through holes. Plasma desmear is not required, unlike most PTFE-based laminates.

What surface finishes work with Arlon 25N?

ENIG, immersion silver, immersion tin, OSP, and hard gold are all compatible. ENIG is the most common choice for RF boards because it provides a flat, solderable surface with minimal impact on skin-effect losses at microwave frequencies.

Where can I get the official Arlon 25N datasheet?

Arlon (now part of Rogers Corporation’s Advanced Electronics Solutions division) publishes datasheets through its distributor network. Contact Rogers or an authorized distributor for the latest revision.