Arlon 25N Laminate: The Complete Engineer’s Guide to This Low-Loss Thermoset for RF and Microwave PCBs

If you’ve been looking for a substrate that bridges the performance gap between standard FR-4 and expensive PTFE laminates, the Arlon 25N laminate deserves a close look. It’s one of the more pragmatic choices in the RF materials world — not because it’s cutting-edge, but because it solves a very real problem: how do you get low dielectric loss, stable electrical properties across temperature, and compatibility with standard thermoset PCB processing without paying PTFE prices?

This guide breaks down what Arlon 25N actually is, what its real-world electrical and mechanical properties look like, how it compares to competing materials, and when it genuinely makes sense to specify it. Written from the engineering bench rather than a marketing brochure, the goal is to give you the working knowledge to make a confident material decision.

What Is Arlon 25N? Clearing Up a Common Misconception

Before diving into specs, it’s worth clarifying what Arlon 25N actually is — because it is sometimes incorrectly described as a polyimide material in shorthand discussions. Arlon 25N is not a polyimide laminate. It is a woven fiberglass-reinforced, ceramic-filled thermoset composite, based on a non-polar olefinic (hydrocarbon) resin system. The ceramic filler is what provides dimensional control and pulls the Dk down to the low-3 range.

Arlon’s actual polyimide product family — materials like 33N, 35N, and 85N — are entirely different resin systems with Dk values around 3.9–4.3 and Tg values exceeding 250°C, targeted at thermal management and reliability-driven applications. The 25N sits in a completely different design space: it’s Arlon’s cost-effective microwave thermoset solution for RF circuit boards, where PTFE is overkill on price and standard FR-4 is insufficient in electrical performance.

The full designation is 25N/25FR — the “25” references the nominal dielectric constant family, and the “FR” variant adds UL 94V-0 flame retardancy. For the purposes of this article, 25N refers to the base grade.

Arlon PCB materials span a wide product family from polyimides to PTFE composites to ceramic-filled thermosets, and understanding which subfamily you’re working with is the starting point for any successful design.

Arlon 25N Laminate: Key Electrical Properties

The datasheet numbers for Arlon 25N come from IPC TM-650 test methods and represent typical values measured at defined conditions. The table below uses official published data — not estimates.

Table 1: Arlon 25N — Core Electrical Properties

Property	Test Method	Condition	Arlon 25N Value
Dielectric Constant (Dk) @ 10 GHz	IPC TM-650 2.5.5.5	C23/50	3.38
Dissipation Factor (Df) @ 10 GHz	IPC TM-650 2.5.5.5	C23/50	0.0025
Thermal Coefficient of Er (ppm/°C)	IPC TM-650 2.5.5.5 Adapted	-10°C to +140°C	-87
Volume Resistivity (MΩ·cm)	IPC TM-650 2.5.17.1	A	1.98 × 10⁹
Surface Resistivity (MΩ)	IPC TM-650 2.5.17.1	A	4.42 × 10⁸
Water Absorption (%)	IPC TM-650 2.6.2.1	E1/105 + D24/23	0.09

That dissipation factor of 0.0025 at 10 GHz is where the material earns its place. Standard FR-4 can run as high as 0.020–0.025, meaning signal loss through dielectric absorption is roughly 8–10 times higher. Arlon’s published laminate guide confirms that 25N occupies an intermediate position with Df values in the 0.0025–0.003 range — well below traditional thermosets, but above the most capable PTFE composites which can reach 0.0009. For a large portion of commercial RF work, that’s exactly where you need to be.

The low thermal coefficient of Er (-87 ppm/°C) means the dielectric constant doesn’t drift dramatically as board temperature changes. In a system where you’re relying on a quarter-wave matching section or a filter response to stay within spec across a -10°C to +60°C outdoor operating range, this stability matters more than the raw Dk value.

Arlon 25N Laminate: Mechanical and Thermal Properties

Table 2: Arlon 25N — Mechanical and Thermal Properties

Property	Test Method	Value
Tensile Strength (kpsi)	ASTM D-882, 23°C	16.1
Flexural Strength (psi)	ASTM D-790, 23°C	30,195
Specific Gravity (g/cm³)	ASTM D-792 Method A	1.7
CTE — X Axis (ppm/°C)	IPC TM-650 2.4.24	15
CTE — Y Axis (ppm/°C)	IPC TM-650 2.4.24	15
CTE — Z Axis (ppm/°C)	IPC TM-650 2.4.24	52
Thermal Conductivity (W/mK)	ASTM E-1225 @ 100°C	0.4
Total Mass Loss (%)	ASTM E-595-90	0.17 (max 1.00%)
Collected Volatile Condensable Material (%)	ASTM E-595-90	0.01 (max 0.10%)

The outgassing data is worth flagging for any engineer working on space or sealed-cavity applications. With a Total Mass Loss of only 0.17% and Collected Volatile Condensable Material (CVCM) of just 0.01%, Arlon 25N passes the NASA ASTM E-595 outgassing standard. Very few cost-effective thermoset laminates can make that claim, which opens 25N up to satellite and space-adjacent applications that would normally demand PTFE.

The Z-axis CTE of 52 ppm/°C is higher than many PTFE-based alternatives, which is an important consideration for through-hole reliability in thermally demanding applications. X-Y plane expansion at 15 ppm/°C in both axes reflects the dimensional stability provided by the ceramic filler.

Available Thicknesses and Copper Weights

Arlon 25N ships as copper-clad laminate or as B-stage bonding plies (prepregs), making it usable across single-sided, double-sided, and multilayer circuit builds including dual-offset stripline configurations.

Table 3: Standard Laminate Thicknesses for Arlon 25N

Thickness (inches)	Thickness Tolerance (inches)
0.006″	± 0.0007
0.008″	± 0.0010
0.010″	± 0.0010
0.012″	± 0.0015
0.018″	± 0.0020
0.020″	± 0.0020
0.024″	± 0.0020
0.030″	± 0.0030
0.060″	± 0.0040

Table 4: Available Prepreg Styles

Prepreg Style	Thickness (inches)
106	0.0020
1080	0.0039
2112	0.0057

Laminates are supplied standard with ½ oz, 1 oz, or 2 oz electrodeposited (HTE) copper on both sides. Rolled copper foil and heavier copper weights are available on request — important for power-handling designs where thermal management is a concern.

Why Arlon 25N Exists: The Design Space It Fills

To understand why 25N is engineered the way it is, you need to appreciate the problem it was created to solve. In the RF laminate world, you broadly have three tiers:

Tier 1 — Standard FR-4: Cheap, ubiquitous, processable with any shop in the world. But Dk varies from ~4.0 to 4.8 depending on frequency and temperature, Df runs 0.018–0.025, and above a few gigahertz, signal loss becomes unmanageable. For anything at X-band or above, FR-4 is effectively ruled out.

Tier 2 — Ceramic-filled thermosets: Materials like Arlon 25N, Rogers RO4350B, and similar. These use hydrocarbon or olefinic resin systems with ceramic loading to pull Dk down to the 3.0–3.6 range and Df to 0.002–0.004. They process on standard thermoset PCB equipment — no sodium etch, no specialized drills for PTFE, no exotic lamination cycles. This is the practical sweet spot for commercial RF work.

Tier 3 — PTFE composites: Materials like Rogers RT/duroid 5880, Arlon IsoClad 933, Taconic TLY. Best-in-class electrical performance with Df as low as 0.0009, but they require specialized fabrication (sodium etch or plasma for plating adhesion, PTFE-specific drill parameters), are significantly more expensive, and are mechanically softer and harder to handle.

Arlon 25N sits firmly in Tier 2. Its key design intent, as stated by Arlon directly, is to serve applications where PTFE costs are prohibitive but where the electrical and stability shortcomings of traditional thermosets are unacceptable. The ceramic filler does three things simultaneously: lowers the Dk, tightens the Dk tolerance, and controls dimensional expansion — creating a substrate that’s electrically capable and manufacturable at scale.

Arlon 25N vs. Competing RF Thermoset Laminates

The Tier 2 thermoset space has several well-established competitors. Here’s how 25N stacks up against the most commonly specified alternatives.

Table 5: Arlon 25N vs. Competing Low-Loss Thermoset RF Laminates

Material	Manufacturer	Dk @ 10 GHz	Df @ 10 GHz	Flame Rating	FR-4 Compatible Process	Key Differentiator
Arlon 25N	Arlon (Rogers)	3.38	0.0025	N/A	Yes	Ceramic-filled, low TCEr, outgassing qualified
Arlon 25FR	Arlon (Rogers)	3.58	0.0035	UL94 V-0	Yes	Flame retardant variant of 25N
Rogers RO4350B	Rogers Corp	3.48	0.0037	UL94 V-0	Yes	Widest industry adoption, mature supply chain
Rogers RO4003C	Rogers Corp	3.55	0.0027	N/A	Yes	Tight Dk tolerance, dual glass fabric styles
Arlon 55NT	Arlon (Rogers)	3.5	~0.003	V-0	Yes	Non-woven aramid reinforced, flex-capable
Taconic RF-35	Taconic	3.5	0.0018	V-0	Partial	Ceramic PTFE, lower Df, higher cost
Standard FR-4	Various	~4.3	~0.020	V-0	Yes	Low cost only, poor RF performance

A few honest observations from this comparison:

Arlon 25N vs. RO4350B: Rogers’ RO4350B is arguably the dominant Tier 2 thermoset substrate in the industry by sheer volume of usage, and for good reason — it has the broadest fabricator support and most documented field history. Its Dk of 3.48 and Df of 0.0037 are slightly worse than 25N’s 0.0025, meaning 25N has a measurable loss advantage. For loss-sensitive designs, this is a real number. However, RO4350B’s supply chain is larger and more globally distributed, which can be a practical tie-breaker in production.

Arlon 25N vs. RO4003C: These two are close rivals. Both target the 3.38–3.55 Dk range, both process on standard thermoset equipment, and both offer Df values in the 0.0025–0.0027 range. The differences are in process nuance, available prepreg styles, and supply availability. For designers who have historically used Rogers materials, RO4003C is the natural comparison point.

Arlon 25N vs. PTFE laminates: If Df of 0.0009 vs. 0.0025 matters for your application — for instance, at Ka-band or in very long feed networks where every fraction of a dB of insertion loss compounds — then 25N is the wrong material and a PTFE composite is the right one. 25N is not positioned to compete with PTFE on loss; it’s positioned to compete on processability and cost.

Primary Applications for Arlon 25N Laminate

Cellular Base Station Antennas

This is the single largest application segment for Arlon 25N by volume. Base station antenna feed networks need low-loss substrates with consistent Dk across production lots, because impedance tolerance and gain patterns depend directly on transmission line electrical lengths. Arlon calls this out explicitly in the 25N datasheet as a primary target application. The combination of low Df, low TCEr (so the antenna doesn’t detune with temperature), and thermoset processability at production scale makes 25N commercially viable for antenna manufacturers.

Power Amplifier Boards

In power amplifier designs, substrate loss contributes directly to output power reduction and efficiency degradation. Every 0.1 dB of substrate insertion loss in the matching network is 0.1 dB less delivered to the load. The Df of 0.0025 on 25N keeps substrate-induced losses tight, and the material’s thermal conductivity of 0.4 W/mK (modest but better than standard FR-4 at around 0.25 W/mK) helps manage the thermal environment around dissipating transistors.

Down Converters and Low Noise Amplifiers

Receiver front-end circuits are particularly sensitive to loss, since every fraction of a dB of loss in front of an LNA increases the system noise figure by the same amount. The low Df of 25N keeps front-end circuitry performing close to the theoretical limit of the active devices without the cost penalty of PTFE substrates.

High-Speed Digital Backplanes

While 25N is primarily positioned as an RF/microwave substrate, its low Df and stable Dk also make it useful in high-speed digital applications — specifically backplanes where signal integrity at multi-gigabit rates is critical and standard FR-4 materials create unacceptable intersymbol interference (ISI) from dielectric loss. The material’s flat Dk versus frequency response maintains consistent group delay across the signal bandwidth, which reduces eye pattern degradation on high-speed serial links.

Mixed Dielectric Multilayer Boards

One of 25N’s practical advantages is that its prepreg has identical chemical composition and physical properties to its laminate core. This means a fully homogeneous multilayer structure, with consistent Dk through the entire stackup. In mixed-dielectric designs where RF layers are combined with digital layers, 25N prepregs bond to 25N cores predictably, without the adhesion concerns that arise when trying to bond dissimilar resin systems.

Satellite and Space-Adjacent Applications

The ASTM E-595 outgassing performance noted above (TML 0.17%, CVCM 0.01%) qualifies 25N for applications where outgassing is tightly controlled. Sealed microwave assemblies, satellite subsystems, and near-space electronics that can’t afford to have condensable vapors depositing on optical surfaces or sensitive components can use 25N where many other thermosets would fail the qualification test.

Fabrication and Processing: What to Know Before You Build

One of Arlon 25N’s most practically valuable features is that its processing is explicitly documented as consistent with standard high-temperature thermoset PCB substrates. Unlike PTFE materials, there is no sodium etch requirement for through-hole plating, no exotic drill parameters, and no specialized press cycles. Your standard FR-4-capable fabricator can, in principle, process 25N.

That said, “in principle” comes with important caveats.

Lamination Process

Arlon 25N uses an olefinic-based (peroxide cure) resin system, which differs from standard epoxy chemistry. The lamination process requires a modified cycle compared to standard FR-4 lamination — specifically in temperature ramp rates and press profile. Arlon’s processing guide documents these requirements, and fabricators who are new to 25N should obtain the Arlon processing specification before setting up production.

Drilling

The material drills similarly to standard woven-glass FR-4 in terms of tool selection, but the ceramic filler content means drill bit wear rates are somewhat higher than pure epoxy-glass laminates. Published fabrication guidance for ceramic-filled hydrocarbon laminates (across several manufacturers, not just Arlon) suggests reducing the drill bit service life by approximately 20% compared to FR-4 baselines.

Etching and Feature Definition

Chemical etching follows standard processes. The material holds fine features well due to its dimensional stability, and tight impedance control is achievable with proper artwork compensation. Because the Dk tolerance is well-controlled in 25N (a key design intent of the ceramic filling), the material tends to produce consistent impedance results lot-to-lot when fabrication parameters are stable.

Surface Finish Compatibility

25N is compatible with the full range of standard PCB surface finishes: HASL, ENIG (electroless nickel/immersion gold), immersion silver, and OSP. For RF applications where skin depth effects make surface finish roughness a performance variable at higher frequencies, ENIG is typically preferred for its smooth, consistent surface.

Moisture Handling

With water absorption at only 0.09%, Arlon 25N is notably resistant to moisture uptake — significantly better than standard FR-4 (which typically absorbs 0.1–0.5%). However, the prepreg should still be handled per Arlon’s storage guidelines. Arlon recommends vacuum desiccation of all prepregs before use to ensure consistent resin flow during lamination.

Understanding 25N vs. 25FR: The Flame Retardancy Question

The 25FR designation adds a flame retardant system to the 25N base chemistry, achieving UL 94 V-0 certification. The trade-off is in electrical properties: Dk rises from 3.38 to 3.58, and Df increases from 0.0025 to 0.0035. The thermal coefficient of Er also changes sign, from -87 ppm/°C (for 25N) to +50 ppm/°C for 25FR.

Table 6: Arlon 25N vs. Arlon 25FR — Key Differences

Property	25N	25FR
Dk @ 10 GHz	3.38	3.58
Df @ 10 GHz	0.0025	0.0035
Thermal Coefficient of Er (ppm/°C)	-87	+50
UL 94 Flammability	N/A	V-0
Z-axis CTE (ppm/°C)	52	59
Water Absorption (%)	0.09	0.09

For applications where UL 94 V-0 is required by a product safety standard, 25FR is the correct choice despite its higher loss. For applications where flame retardancy is not a regulatory requirement — which is common in aerospace, defense, and test equipment contexts — 25N’s superior electrical properties make it the better specification.

The TCEr sign change is particularly important: 25N’s negative TCEr (-87 ppm/°C) means Dk decreases slightly with increasing temperature, while 25FR’s positive TCEr (+50 ppm/°C) means Dk increases. Depending on your thermal operating profile and whether you’re designing a filter or a broadband matching network, this can affect frequency response drift in opposite directions between the two variants.

Useful Resources for Engineers Specifying Arlon 25N

Resource	Description	Link
Arlon 25N/25FR Official Datasheet (via Integrated Test)	Full property table, thickness chart, prepreg styles	https://integratedtest.com/wp-content/uploads/2021/08/Arlon25n.pdf
Arlon 25N/25FR Datasheet (via Cirexx)	Alternative hosted copy of the Dk/Df spec sheet	https://www.cirexx.com/wp-content/uploads/25N25FR.pdf
Arlon 25N/25FR Datasheet (via PCBApeak)	Production data including prepreg styles	https://www.pcbapeak.com/wp-content/uploads/2023/12/Arlon-25N-25FR.pdf
Arlon Microwave & RF Materials Guide	Full portfolio guide with 25N positioning and copper cladding options	https://integratedtest.com/wp-content/uploads/2021/08/ArlonMaterials.pdf
Arlon “Everything You Wanted to Know” Laminate Guide	In-depth technical FAQ covering thermoset resin systems, processing, and material selection	https://www.arlonemd.com/wp-content/uploads/2020/05/Laminate-Guide.pdf
IPC TM-650 Test Methods	Standard test procedures referenced in all Arlon datasheets	https://www.ipc.org/committee/2-5
Northwest Engineering Solutions RF Materials Chart	Independent comparison of RF PCB materials by Dk, Df, and type	https://www.nwengineeringllc.com/rf-pcb-materials-for-microwave-electronics.php
UL Prospector — Arlon 25N Entry	Material database listing with registration for full data access	https://www.ulprospector.com/plastics/en/datasheet/120881/arlon-25n

Common Design and Specification Mistakes With Arlon 25N

Confusing 25N with Arlon’s polyimide line: As noted at the outset, 25N is not a polyimide. Specifying it expecting polyimide-grade Tg performance (>250°C) will produce a design that is mismatched to the actual material. If you genuinely need a polyimide substrate for extreme thermal environments, look at the Arlon 85N or 33N families instead.

Ignoring the TCEr in temperature-compensated designs: The -87 ppm/°C thermal coefficient is large enough to matter in filters or resonators that must hold frequency across wide temperature ranges. If your passband needs to stay within ±10 MHz across -40°C to +85°C, you need to run the numbers on how much Dk change that temperature range produces and whether it shifts your filter response unacceptably.

Using 25N above its loss comfort zone: Arlon 25N’s Df of 0.0025 is excellent for a thermoset material, but it’s still roughly 2–3 times higher than the best PTFE composites. For millimeter-wave work above 30 GHz, or for very long feed networks where insertion loss compounds significantly, 25N may produce disappointing results that a PTFE substrate would have avoided. Simulate the insertion loss budget before committing to the material.

Underestimating drill bit wear: A 20% reduction in effective drill life sounds minor until you’re tooling up a production run of thousands of panels. Factor this into tooling cost when quoting the board, particularly for dense multilayer designs with high via counts.

Not validating impedance with test coupons: The nominal Dk of 3.38 is measured at a specific condition and thickness. Your actual effective Dk for microstrip or stripline transmission lines will differ from the bulk material value due to copper surface roughness, solder mask loading, and glass weave effects. Always design test coupons with your critical impedance values into the panel and validate with TDR before releasing production.

Frequently Asked Questions About Arlon 25N

Q1: Is Arlon 25N a polyimide laminate?

No. This is a common point of confusion. Arlon 25N is a ceramic-filled thermoset composite based on an olefinic (hydrocarbon) non-polar resin system reinforced with woven fiberglass. It is not a polyimide. Arlon’s polyimide products are the 33N, 35N, 84N, and 85N series, which have very different Dk values (around 3.9–4.3) and are engineered specifically for extreme thermal environments and high Tg performance. Arlon 25N is engineered for low dielectric loss and stable Dk in RF and microwave circuit applications — a completely different design objective.

Q2: Can Arlon 25N be processed using standard FR-4 equipment?

Largely yes, but with important process adjustments. Standard PCB drilling, etching, and plating equipment are compatible. Through-hole plating does not require sodium etch treatment (unlike PTFE laminates) — which is one of 25N’s key practical advantages over PTFE substrates. However, the peroxide-cure resin system requires a modified lamination cycle that differs from standard FR-4 epoxy chemistry. Fabricators should obtain Arlon’s published processing guidelines and validate their lamination parameters before production.

Q3: How does Arlon 25N compare to Rogers RO4350B?

Both are ceramic-filled thermoset laminates that process on standard equipment, target similar application spaces, and have comparable Dk values. The key difference is in dissipation factor: 25N at 0.0025 versus RO4350B at 0.0037. For loss-sensitive designs, 25N has a meaningful edge. For supply chain breadth and fabricator familiarity, Rogers RO4350B is more widely stocked and processed globally. The practical choice often comes down to which material your preferred fabricator has the most experience running at your required tolerances.

Q4: What frequency range is Arlon 25N suitable for?

The published electrical properties are characterized at 10 GHz, which is the standard IPC TM-650 test frequency for RF laminates. In practice, Arlon 25N is routinely used from the low gigahertz range up through X-band (8–12 GHz) and in some cases into Ku-band (12–18 GHz). Above Ku-band, the dissipation factor and surface roughness effects of standard electrodeposited copper begin to create measurable insertion loss penalties, and PTFE-based substrates become the preferred choice. Below 1 GHz, the RF performance advantage over high-quality FR-4 variants narrows, and the cost premium may not be justified.

Q5: Is Arlon 25N suitable for multilayer PCB builds?

Yes. Arlon 25N is explicitly designed for multilayer use. The prepregs (available in 106, 1080, and 2112 glass styles) have identical chemical composition to the laminate core, ensuring a fully homogeneous dielectric structure throughout the multilayer stackup. This homogeneity is critical for predictable signal integrity in multilayer RF designs. Arlon recommends using 25N prepregs with 25N cores — mixing 25N laminates with prepregs from different resin systems (including standard FR-4 prepregs) can introduce interface bonding issues and Dk discontinuities at the layer interfaces that affect impedance control.

When to Choose Arlon 25N — and When to Look Elsewhere

Choose Arlon 25N when your application needs RF-grade dissipation factor (Df ≤ 0.003), consistent Dk across temperature, standard thermoset processability without the sodium etch requirement of PTFE, outgassing performance for sealed or near-space applications, and a cost point below PTFE laminates. It’s the pragmatic choice for base station antennas, power amplifiers, LNAs, down converters, and high-speed backplanes where FR-4’s limitations are a real problem but PTFE’s cost or process requirements are barriers.

Look elsewhere when your design demands the absolute lowest possible dielectric loss (choose IsoClad 917 or RT/duroid 5880), you need Tg above 200°C and extreme thermal reliability (choose Arlon 85N or 33N polyimide), you need UL 94 V-0 with full 25N-level electrical performance (there is a trade-off in 25FR), or your operating frequency is above 20 GHz and every tenth of a dB matters (choose PTFE composites).

Arlon 25N has been in production long enough that its properties are well-characterized, its process behavior is understood by experienced RF fabricators, and its use in base station and wireless infrastructure hardware has been validated at large production volumes. That track record — combined with thermoset processability and a dissipation factor that beats standard FR-4 by a factor of 8 — is why it remains a relevant specification choice for RF and microwave PCB engineers today.

All property values in this article are typical properties from published Arlon datasheets (Arlon 25N/25FR, Rev 0201-R3). They are not specification limits and should be verified with current manufacturer documentation before finalizing any design.