How to Select the Right Arlon PCB Laminate for Your RF Design

If you’ve spent any time doing RF or microwave PCB work, you already know that laminate selection is not a footnote in the design process — it is the design process. Pick the wrong material and no amount of clever layout will recover your insertion loss budget. Pick one that’s overkill and your BOM cost and fabrication lead time balloon for no functional gain.

When engineers ask how to select an Arlon PCB laminate for RF design, the honest answer is: it depends on five specific things — your operating frequency, how much insertion loss you can tolerate, the thermal environment, how many layers your stack-up needs, and what your fabricator can actually process reliably. This guide walks through each of those factors methodically, maps them to the right materials in Arlon’s RF laminate portfolio, and gives you the decision framework to get it right the first time.

Why Arlon Laminates Matter in RF Design

Before getting into selection criteria, it’s worth anchoring on why Arlon PCB materials are frequently specified for RF and microwave work in the first place. Standard FR-4 typically delivers a dielectric constant (Dk) between 4.2 and 4.8 at 10 GHz, with a dissipation factor (Df) ranging from 0.015 to 0.025. Those numbers translate to high conductor loss, significant dielectric absorption, and Dk variation with both frequency and temperature — all of which degrade signal integrity in ways that are difficult to compensate in layout.

Arlon’s RF laminate portfolio spans several resin chemistries: ceramic-filled PTFE composites (the CLTE and AD series), non-PTFE thermoset systems (the 25N/25FR family), and filled PTFE composites with enhanced thermal management (TC350). Each family targets a different sweet spot on the frequency-cost-processability curve.

Understanding where your application sits on that curve is the first step to making a smart material choice.

Step 1 — Define Your Operating Frequency Range

Frequency is the starting gate. It determines which material families are physically capable of delivering the Dk and Df your transmission lines require, and it influences which loss mechanisms — dielectric or conductor — will dominate your insertion loss budget.

As a practical rule of thumb for RF laminate selection:

Frequency Range	Typical Laminate Category	Arlon Options
< 1 GHz	Standard or high-Tg FR-4	Arlon 45N, 55NT
1 GHz – 6 GHz	Low-loss thermoset epoxy	Arlon 25N/25FR
6 GHz – 18 GHz	PTFE/ceramic composite	Arlon CLTE, AD series
18 GHz – 40 GHz	Low-loss ceramic PTFE	Arlon CLTE-XT, AD300
40 GHz – 77 GHz+	Ultra-low-loss PTFE	Arlon CLTE-XT

Below 1 GHz, the insertion loss difference between Arlon 45N and a true RF laminate is negligible for most practical circuit lengths. Above 6 GHz, the difference becomes significant enough that it affects link budget calculations. Above 18 GHz, you are almost certainly in PTFE territory unless your traces are very short or your system margin is unusually large.

The boundary isn’t hard — an 8 GHz filter on a 25N board often works perfectly well. But once you start pushing through Ku band (12–18 GHz), the 25N’s Df of approximately 0.002–0.003 starts contributing meaningfully to your loss, and moving to CLTE or CLTE-XT becomes justifiable.

Step 2 — Understand the Five Key Electrical Parameters

Every RF laminate datasheet lists a set of electrical properties, and not all of them get equal weight in real design decisions. Here’s how to read them from an RF engineering perspective.

Dielectric Constant (Dk)

Dk directly sets the propagation velocity of signals in your transmission lines and therefore determines the physical length of impedance-controlled structures. A lower Dk means faster propagation and physically larger structures, which can be an advantage or a disadvantage depending on your design.

For impedance control, what matters more than the absolute value is batch-to-batch consistency. A material with Dk of 3.0 ±0.05 is more valuable to a production engineer than one with Dk of 2.6 ±0.15. Arlon’s CLTE-XT is notable for exceptionally tight Dk control across temperature, which matters in phased array and radar applications where phase consistency is a first-order requirement.

Dissipation Factor (Df)

Df — sometimes listed as loss tangent or tan δ — is the dominant driver of dielectric insertion loss. It tells you how much signal energy is absorbed by the dielectric as heat per unit length. At frequencies above 5 GHz, the Df difference between a standard epoxy laminate and a PTFE composite becomes the primary determinant of whether a long transmission line will work.

The table below shows Df values for Arlon’s RF laminate family alongside standard FR-4 for context:

Material	Dk @ 10 GHz	Df @ 10 GHz	Resin System
Standard FR-4	4.2–4.5	0.015–0.025	Epoxy/glass
Arlon 55NT	3.9	~0.010	Epoxy/aramid
Arlon 25N	3.38	0.0025	Ceramic-filled PTFE
Arlon CLTE	2.94–3.0	0.0025	Ceramic-filled PTFE
Arlon TC350	3.5	0.004	Ceramic-filled PTFE
Arlon CLTE-XT	2.94	0.0009–0.0012	Low-loss ceramic PTFE
Arlon AD300	3.0	~0.002	PTFE/woven glass

Thermal Coefficient of Dk (TCDk)

This property — how much Dk shifts with temperature — rarely gets attention in early design reviews but bites engineers on phase-sensitive circuits. If your board will operate from -40°C to +85°C (a common industrial range), a material with poor TCDk stability will shift the electrical length of your transmission lines with temperature. For filters, combiners, and phased arrays, that translates to gain variation, phase error, and resonant frequency drift.

The CLTE and CLTE-XT families are specifically engineered for temperature-stable Dk. The ceramic loading in these materials counteracts the natural Dk drift of the PTFE matrix, resulting in TCDk values close to zero — critical for satellite ground stations and radar systems that operate through wide temperature swings.

Copper Foil Roughness

This is the parameter most RF engineers underweight until they’ve dealt with its consequences at Ka band or above. At frequencies above 10 GHz, conductor losses increasingly dominate total insertion loss, and copper surface roughness is the primary driver of conductor loss beyond the theoretical skin effect.

Standard electrodeposited (ED) copper has an RMS roughness of 2–4 μm, which is fine for low-frequency work. For RF designs above 10 GHz, specifying low-profile (LP), very-low-profile (VLP), or ultra-low-profile (HVLP) copper foil reduces conductor loss meaningfully. Arlon’s CLTE-XT is paired with smooth microwave-grade copper specifically to match its ultra-low dielectric loss — there is little point using Df = 0.001 dielectric material with rough copper that overwhelms the dielectric advantage.

Moisture Absorption

RF laminates that absorb moisture shift their Dk — water has a Dk of approximately 78, so even small amounts of moisture uptake can move your effective dielectric constant enough to cause measurable impedance variation. For outdoor antennas, shipboard electronics, and any application without hermetic enclosure, moisture absorption should be explicitly checked in material selection.

PTFE-based laminates (CLTE, CLTE-XT) absorb very little moisture (typically < 0.02%). The 25N ceramic-filled thermoset absorbs slightly more but still far less than epoxy-based materials. CLTE-XT specifically achieves the lowest moisture absorption of any material in the Arlon microwave line.

Step 3 — Map Arlon’s RF Laminate Families to Your Application

Arlon 25N / 25FR — The Entry Point to RF Performance

The 25N is built on a ceramic-filled PTFE matrix reinforced with woven glass, giving it Dk approximately 3.38 and Df around 0.0025 at 10 GHz. It processes much closer to FR-4 than pure PTFE laminates — your fab shop can handle it on standard equipment with some modifications to the lamination profile. That processability is its main advantage over the harder PTFE materials.

The 25FR variant adds a flame retardant to the formulation (UL94 V-0 rated), which matters for commercial communications equipment that must carry regulatory certifications. The 25N without flame retardant is preferred for aerospace and defense applications where UL certification is not required but maximum thermal performance is valued.

Best fit for: Antenna feeds, power dividers, low-noise amplifiers (LNAs) in L- and S-band, base station components up to 6 GHz, and any RF design where standard FR-4 has been identified as the loss bottleneck but cost pressures exist.

Arlon CLTE Series — The Workhorse of Microwave PCB Design

CLTE (Ceramic Laminate Thermoset Epoxy) is Arlon’s ceramic-filled PTFE composite designed for high-volume commercial microwave applications. Its Dk of approximately 2.94–3.0 and Df around 0.0025 put it in the same performance class as Rogers RO4003C, making it a natural cross-reference for engineers already familiar with Rogers materials.

The CLTE series offers reliable multilayer capability — this is a significant advantage over some pure PTFE laminates, which can be challenging to bond reliably in multilayer constructions. CLTE’s CTE characteristics are better controlled than unloaded PTFE, improving plated through-hole reliability over thermal cycling.

CLTE-XT is the premium variant. It delivers Df as low as 0.0009 at 10 GHz — among the lowest of any commercially available laminate in this class. It also provides the highest phase stability over temperature, best-in-class moisture resistance, and a CTE optimized to minimize dimensional shift. If you’re designing Ka-band phased arrays, satellite communications downconverters, automotive radar at 77 GHz, or any application where phase consistency over temperature is non-negotiable, CLTE-XT is where you start.

Best fit for: C-band through Ka-band circuits, satellite communication infrastructure, 5G mmWave front-end modules, phased array radars, high-performance antenna arrays where phase stability matters.

Arlon TC350 — When Thermal Management and RF Performance Both Matter

TC350 occupies a unique position in the Arlon RF portfolio: it combines ceramic-filled PTFE dielectric performance (Dk ~3.5, Df ~0.004) with thermal conductivity of approximately 1.0 W/mK — roughly five to seven times the thermal conductivity of standard PTFE laminates.

For power amplifier boards, where transistors can dissipate tens of watts and the substrate temperature rise directly affects gain, efficiency, and device lifetime, TC350’s thermal conductivity allows heat to be conducted to the chassis or heatsink through the laminate itself rather than relying entirely on thermal vias. This design approach reduces junction temperature, extends MTBF, and reduces the reliance on copper coin or embedded heatsink structures.

The Dk stability of TC350 over temperature is also excellent, which matters for power amplifier designers who need consistent load impedance as the board heats up during operation. Phase and impedance stability translate directly to consistent gain flatness across operating temperature — a specification that matters in cellular base station power amplifiers.

Best fit for: Base station power amplifiers, gallium nitride (GaN) amplifier boards, RF front-end modules with integrated PA stages, any design where dielectric loss and thermal resistance are simultaneously constrained.

Arlon AD Series — PTFE/Glass Composites for Multilayer Microwave

The AD250, AD255, and AD300 are woven fiberglass-reinforced PTFE composites. Their strength is CTE control: the higher glass-to-PTFE ratio compared to unloaded PTFE gives them better dimensional stability and improved X-Y plane CTE, which matters for large multilayer boards where registration accuracy across many layers is critical.

AD300 in particular is rated for use up to 77 GHz and provides ultra-low X-Y CTE for reliable plated through holes. The AD series is used extensively in satellite ground station equipment and communication infrastructure where large panel multilayer boards require both microwave performance and manufacturing reliability.

Best fit for: Large-panel multilayer microwave boards, satellite ground station equipment, antenna array feed networks, designs where CTE matching to copper and via reliability are as important as electrical performance.

Step 4 — Consider the Thermal and Environmental Requirements

Material selection for RF designs isn’t purely electrical. The deployment environment shapes which materials are physically viable.

Operating Condition	Requirement	Arlon Options
Outdoor / unenclosed	Low moisture absorption	CLTE-XT, 25N
High ambient temp (>85°C)	Tg margin, thermal stability	TC350, CLTE series
Cryogenic cycles	TCDk stability, low CTE	CLTE-XT
High-power (>10W/cm²)	Thermal conductivity	TC350
Military/space	Outgassing, CTE stability	CLTE-XT, AD series
Commercial certification (CE/UL)	V-0 flame rating	25FR

For avionics and space applications, outgassing is a design input that can eliminate some laminate options entirely. NASA’s outgassing database is a useful reference for confirming that your selected Arlon material is acceptable for space-qualified hardware. The CLTE-XT is widely used in satellite applications where its combination of thermal stability, dimensional precision, and low outgassing has been verified through qualification testing.

Step 5 — Evaluate Fabrication Constraints Early

The most common mistake in RF laminate selection is specifying a material before confirming that your chosen PCB fabricator can process it reliably. PTFE-based materials require modifications to standard processing steps that not every shop handles with the same competence.

Key fabrication considerations when selecting Arlon RF laminates:

Lamination profile: PTFE-based materials (CLTE, AD series) require controlled temperature ramp rates — typically 2–3°C per minute — and vacuum pull-down before pressing. Materials like 25N/25FR are softer than FR-4 and require guide plates and careful handling to prevent dimensional distortion.

Inner layer preparation: Brown oxide or black oxide treatment on inner copper layers is recommended before lamination to ensure adequate bond strength. Skipping this step can lead to delamination under thermal cycling.

Drilling: CLTE and ceramic-filled PTFE materials are slightly abrasive due to the ceramic filler, which can reduce drill bit life compared to FR-4. Confirm your fabricator’s drill parameter guidelines for the specific material and panel thickness you’re using.

Hole cleaning and plating: Potassium permanganate or plasma desmear is effective on these materials. No special plating chemistry is required beyond standard parameters.

Surface finishes: ENIG, HASL (lead-free), immersion silver, immersion tin, and OSP are all compatible. For maximum RF performance above 10 GHz, immersion silver (ImAg) or OSP are preferred because they introduce the lowest additional conductor loss at the surface. ENIG introduces a nickel layer with higher resistivity than copper, which contributes to conductor loss — the effect becomes measurable above 5–6 GHz on long lines.

If your selected fab house hasn’t processed CLTE or CLTE-XT before, ask for coupon data from a previous run. Material properties from the datasheet only translate to actual board performance when the fabricator understands how that specific material behaves at their press, drill, and plate lines.

Step 6 — Evaluate Hybrid Stack-Up Strategies

For mixed-signal boards where RF and high-speed digital share the same panel, a hybrid stack-up approach is often the most cost-effective path. The premise is straightforward: use Arlon RF laminate (CLTE, 25N, or TC350) only on the layers that carry RF signals, and use standard high-Tg FR-4 or a modified epoxy for the layers handling digital logic, power distribution, and structural thickness.

This approach can reduce material cost by 40–60% compared to a full RF laminate stack-up while still delivering the RF performance you need where it actually matters. The challenge is compatibility between materials at the bonding ply interfaces — you need prepreg and bonding film systems that are compatible between the two laminate types without creating delamination risk or impedance discontinuities at layer transitions.

When designing hybrid stack-ups with Arlon materials, always confirm the lamination compatibility of your specific material combination with the fabricator. Some pairings require specific bonding films or intermediate prepreg layers that aren’t obvious from the base material datasheets.

Arlon RF Laminate Selection Summary

Design Scenario	Recommended Material	Key Reason
Antenna / power divider, 1–6 GHz	Arlon 25N / 25FR	Low Df, FR-4-compatible processing
LNA / filter board, 6–18 GHz	Arlon CLTE	Low Dk, reliable multilayer
Phased array, 18–40 GHz	Arlon CLTE-XT	Phase stability, ultra-low Df
77 GHz automotive radar	Arlon CLTE-XT	Stable Dk, fine-line capability
GaN power amplifier board	Arlon TC350	RF + thermal management combined
Satellite multilayer (large panel)	Arlon AD300	CTE, PTH reliability
Mixed RF/digital board	Hybrid: CLTE + FR-4	Cost-performance balance
Rigid-flex RF assembly	Arlon 55NT + polyimide	Dimensional stability, flex compatibility

Useful Resources for RF Laminate Selection

These are the references worth bookmarking before finalizing any Arlon laminate selection:

• Arlon EMD Product Datasheets — arlonemd.com/resources/#data-sheets — Official datasheets for every current Arlon laminate, including CLTE-XT, TC350, AD series, and 25N/25FR. Always pull the current version before designing.
• Arlon Microwave Materials Guide (PDF) — Available through arlonemd.com — Comprehensive overview of the microwave product line with typical application mapping.
• IPC-4101 Standard — ipc.org — Qualification standard for PCB base materials. Confirms which slash sheet each Arlon material is qualified to (e.g., /26, /40, /98).
• PCB Directory Laminate Database — pcbdirectory.com — Searchable database for comparing Dk, Df, Tg, and CTE across manufacturers, useful for cross-referencing Arlon materials against Rogers, Taconic, and Isola equivalents.
• Isola RF Material Selection Guide (PDF) — isola-group.com — A useful reference even for non-Isola designs, covering fundamental RF material selection methodology.
• Sierra Circuits RF PCB Design Guide — protoexpress.com — Practical coverage of copper foil selection, CTE, and thermal requirements for RF boards.
• Altium High-Frequency PCB Material Selection — resources.altium.com — Good coverage of conductor loss modeling and copper roughness effects.
• Arlon PCB Materials Overview at PCBSync — pcbsync.com/arlon-pcb/ — Covers the full Arlon family with application-oriented guidance and procurement context.

5 FAQs on Selecting Arlon PCB Laminates for RF Design

Q1: Can I replace Rogers RO4350B with Arlon CLTE in my existing design without retuning?

In most cases, yes — with a caveat. CLTE and RO4350B have similar Dk (nominally 2.94–3.0 for CLTE vs. 3.48 for RO4350B depending on the specific CLTE variant and glass weave). If the Dk values are close, your impedance-controlled trace widths will be nearly identical and retuning should be minimal. However, always verify by running your stack-up through an impedance calculator with both the CLTE and RO4350B Dk values for the specific glass style you’ll be using. A ±0.05 shift in Dk at 50 Ω typically shifts trace width by less than 0.1 mm — usually within fabrication tolerance. For resonant structures like patch antennas or coupled-line filters, verify the resonant frequency shift before going to production.

Q2: Does CLTE-XT really justify its cost premium over standard CLTE?

That depends entirely on your frequency and phase requirements. Below 18 GHz, standard CLTE’s Df of ~0.0025 is often sufficient, and CLTE-XT’s Df of ~0.001 provides margin that you may not need. Above 18 GHz, or in any design where phase variation over temperature must be tightly controlled (phased arrays, radar, mmWave communications), CLTE-XT’s combination of ultra-low Df, near-zero TCDk, and lowest moisture absorption in its class translate to measurable design margins. Run your link budget with both Df values over your trace length and temperature range — if the margin difference is less than 1 dB over your worst-case scenario, standard CLTE may be sufficient. If it exceeds that, CLTE-XT is worth the premium.

Q3: What surface finish should I specify for an Arlon CLTE board at 24 GHz?

At 24 GHz, surface finish becomes a meaningful contributor to conductor loss. ENIG introduces a nickel layer (resistivity approximately 6.9 × 10⁻⁸ Ω·m, compared to 1.7 × 10⁻⁸ Ω·m for copper), which increases conductor loss on high-frequency signal surfaces. Immersion silver (ImAg) or OSP are the preferred finishes for performance-critical RF layers above 10 GHz. ImAg has the added benefit of offering solderability and wire bondability while maintaining near-copper surface resistivity. OSP is the lowest-loss option but has a shorter shelf life and isn’t suitable for multiple reflow cycles without refresh. If your board requires ENIG for mechanical reasons (e.g., connector pads, press-fit interfaces), consider specifying selective ENIG only on those pads while using ImAg on RF signal areas.

Q4: How do I handle the mismatch between Arlon PTFE laminate and FR-4 prepreg in a hybrid stack-up?

Mixed dielectric stack-ups require careful attention to the bond ply at the interface between dissimilar materials. For Arlon CLTE-to-FR-4 hybrid constructions, specify a bonding film or prepreg that is compatible with both surfaces — Arlon’s application engineering team can recommend specific products for your material combination. The general rule is to avoid having impedance-sensitive signal layers reference two different dielectric materials simultaneously. If a microstrip line references both CLTE and FR-4 within its field distribution, you’ll get an effective Dk that is somewhere between the two materials, making impedance calculation less predictable. For robust hybrid designs, keep RF signal layers fully within the CLTE section of the stack-up and use FR-4 only for layers outside the RF field region.

Q5: Arlon 25N is listed as “FR-4 compatible process” — does that mean any PCB fab can run it?

Not quite. “FR-4 compatible” means 25N can use standard press equipment and doesn’t require the specialized PTFE handling procedures needed for pure PTFE laminates. But there are still differences from standard FR-4 that not every fabricator handles correctly without experience: the material is softer and more prone to dimensional distortion during handling, it requires a specific lamination ramp rate, and the pre-bake requirement before HASL must be followed to avoid voiding. Ask your fab shop specifically whether they have prior production experience with 25N or 25FR, and request a certificate of conformance and impedance coupon measurement on the first article run. A fabricator that has run these materials before will know exactly what you’re asking for — one that hasn’t may need to run engineering samples before committing to production quantities.

Final Thoughts on Arlon PCB Laminate Selection for RF Work

The right way to select an Arlon PCB laminate for your RF design is to start with frequency and loss budget, let those drive the material family (thermoset, ceramic PTFE, or CLTE-XT), then layer in thermal, mechanical, and fabrication requirements to narrow to the specific product. Don’t let cost drive the decision before you’ve confirmed whether a cheaper material actually closes your link budget — a board respin costs far more than the material upgrade.

The Arlon RF portfolio is well-structured to cover the range from 1 GHz to 77 GHz, with clear performance escalation at each tier. Once you’ve mapped your requirements to the family, the datasheet comparisons and fabricator conversations become straightforward rather than overwhelming. Build the habit of pulling actual datasheet values at your operating frequency (not the 1 MHz values that still appear in some datasheets), and always confirm copper foil options alongside the dielectric — above 10 GHz, they’re inseparable parts of the same performance decision.