Arlon CuClad 250 is a cross-plied woven PTFE/fiberglass laminate with Dk 2.40–2.60 and low loss for military radar, ECM, and microwave filter PCBs. Complete guide to CuClad 250 properties, GT vs GX vs LX grades, fabrication tips, and comparison with CuClad 217 and Rogers RT/duroid 5880.

There’s a reason Arlon CuClad 250 keeps showing up on defense radar BOMs, ECM system stackups, and filter board specs that have been refreshed multiple times over the decades. It isn’t the flashiest microwave laminate on the market — it won’t win a Df shootout against the latest ceramic/PTFE composite — but it hits a combination of mechanical robustness, dimensional stability, in-plane electrical isotropy, and low loss that keeps earning its spot when designers have to balance fabrication practicality with genuine RF performance.

This guide gives you the complete picture: what CuClad 250 actually is, what its properties mean in practice, how it compares to the rest of the CuClad family and to competing materials, and where it genuinely earns its place in a design.

What Is Arlon CuClad 250?

Arlon CuClad 250 is a woven fiberglass/PTFE composite laminate engineered for use as a microwave printed circuit board substrate. Within the CuClad product family, it occupies the high-fiberglass-ratio end of the spectrum — using a higher fiberglass/PTFE ratio than CuClad 217 or CuClad 233 to provide mechanical properties approaching those of conventional substrates.

That higher glass loading has a direct effect on Dk. Where CuClad 217 sits at Er = 2.17–2.20, CuClad 250 ranges from Er = 2.40 to 2.60 depending on the specific grade and thickness specified. The increase in Dk relative to the lower-glass CuClad grades is the direct result of more fiberglass in the matrix — glass has a higher dielectric constant than PTFE, so more glass means higher Dk.

What you gain from that tradeoff is a laminate that behaves much more like FR-4 from a mechanical standpoint — better dimensional stability, lower thermal expansion in all directions, and a substrate that handles more like a conventional epoxy laminate during fabrication. For shops that routinely build FR-4 multilayers but occasionally take on microwave work, that processability difference matters enormously.

The Cross-Ply Construction That Sets CuClad Apart

If there’s one technical differentiator that genuinely sets the CuClad family apart from competing woven PTFE laminates, it’s the cross-plied construction. CuClad laminates are crossplied — alternating layers of coated fiberglass plies are oriented 90° to each other. This provides true electrical and mechanical isotropy in the XY plane, a feature unique to CuClad. No other woven or nonwoven fiberglass-reinforced PTFE-based laminates make this claim.

What does in-plane isotropy actually mean for a PCB engineer? In a standard unidirectional-ply laminate, the dielectric constant is slightly different depending on whether you’re measuring along the fiber direction or perpendicular to it. That anisotropy is small — typically less than 1% — but in circuits sensitive to dielectric constant uniformity, it translates to measurable variation in characteristic impedance and signal propagation velocity depending on trace orientation. For filters, couplers, and low noise amplifiers where Dk uniformity is critical, that variation matters.

Designers have found this degree of isotropy critical in some phased array antenna applications. In a large planar phased array, you’ll have traces running in multiple orientations across the aperture. If your substrate has directional Dk variation, elements oriented along the fibers will have slightly different electrical performance from elements oriented perpendicular to them — and that manifests as phase and amplitude imbalance across the array.

CuClad 250’s cross-plied construction eliminates that variable by making the electrical properties identical in both X and Y axes. It’s a structural detail that makes a real difference in precision circuits.

Arlon CuClad 250 Key Properties and Datasheet Overview

Electrical Properties

Property	Value	Notes
Dielectric Constant (Dk)	2.40 – 2.60	Varies by grade and thickness
Dissipation Factor (Df)	0.0009 – 0.0022	X-band (10 GHz)
Dk Stability vs. Frequency	Stable across RF/microwave range
Dk Uniformity	Excellent	Cross-ply construction
XY Plane Isotropy	True electrical isotropy	Unique to CuClad family

Mechanical and Physical Properties

Property	Value / Description
Construction	Cross-plied woven fiberglass / PTFE composite
Dimensional Stability	Better than non-woven PTFE laminates
Thermal Expansion	Lower in all directions vs. lower-glass CuClad grades
Water Absorption	Very low (PTFE-based)
Mechanical Strength	Approaches conventional substrates (higher glass loading)
Copper Cladding	½ oz, 1 oz electrodeposited; other weights available

Available Grades: GT, GX, and LX

One source of confusion for engineers specifying CuClad 250 for the first time is the suffix letters. These designate different testing protocols, not fundamentally different materials:

Grade Suffix	Test Frequency	Use Case
GT (e.g., CuClad 250GT)	1 MHz	General procurement, standard QC
GX (e.g., CuClad 250GX)	10 GHz	Preferred for microwave design verification
LX (e.g., CuClad 250LX)	Per-sheet, with certificate of analysis	Critical performance applications

The electrical properties of CuClad 250GT and CuClad 250GX are tested at 1 MHz and 10 GHz respectively. For critical performance applications, CuClad products may be specified with the “LX” testing grade — this designates that each sheet will be tested individually and a test report will be issued with the order.

For any serious microwave design work, GX (10 GHz tested) is the relevant specification. GT figures measured at 1 MHz don’t reflect the Dk your design will see at microwave frequencies. If you’re quoting from a datasheet that only shows 1 MHz data, you’re working from numbers that don’t represent real operating conditions for RF circuits.

The LX grade is worth the premium on programs where lot-to-lot dielectric constant consistency is a hard requirement — defense production programs with tightly controlled electrical performance specs, for example.

Available Thicknesses and Dk Options

From the Arlon Microwave & RF Materials Guide, CuClad 250GX is available in the following standard configurations:

Thickness (inches)	Thickness (mm)	Available Dk Options
0.004″	0.102	2.40
0.010″	0.254	2.48, 2.55
0.015″	0.381	2.44, 2.48, 2.55
0.020″	0.508	2.45, 2.48, 2.50, 2.55
0.030″	0.762	2.40, 2.45, 2.50, 2.55
0.031″	0.787	2.45, 2.50, 2.55
0.047″	1.194	2.50
0.060″	1.524	2.40, 2.45, 2.50, 2.55

Master sheet sizes are 36″ × 48″ (non-cross-plied) and 36″ × 36″ (cross-plied configuration). When ordering, always specify dielectric constant, thickness, cladding weight, panel size, and testing grade. Since the Dk range for this material is 2.40–2.60, you’re selecting a specific nominal Dk within that range — not a fixed value like single-Dk materials.

The CuClad 250 Design Advantage: Higher Glass Loading in Practice

The headline spec on CuClad 250 is that it uses a higher fiberglass/PTFE ratio to provide mechanical properties approaching those of conventional substrates, with better dimensional stability and lower thermal expansion in all directions compared to lower-glass CuClad grades.

Let’s unpack why that matters for real PCB designs.

Dimensional Stability and Registration

High layer count multilayer boards depend on consistent layer-to-layer registration to meet controlled impedance tolerances and via-to-pad alignment requirements. PTFE materials with very low fiberglass content can be dimensionally unstable during processing — they shrink and move more than higher-glass materials as they’re processed through lamination, etching, and drilling.

CuClad 250’s higher glass content acts as a dimensional stabilizer. The woven fiberglass structure constrains in-plane movement during thermal processing steps. Compared to nonwoven PTFE laminates of similar dielectric constants — which use random-fiber reinforcement — the woven glass structure provides greater dimensional stability and better Dk uniformity across the panel.

Lower Thermal Expansion

Lower thermal expansion in all directions, compared to the lower-glass CuClad grades, translates directly to reduced stress on plated-through holes and solder joints during thermal cycling. CuClad 250 is still a PTFE-based material, so it doesn’t match the Z-axis CTE performance of ceramically loaded PTFE laminates like CLTE. But within the woven PTFE family, the higher glass loading in CuClad 250 gives it measurably better CTE characteristics than CuClad 217, making it a more reliable choice for multi-layer boards that will see significant thermal cycling.

Processability

One practical advantage that doesn’t get enough attention in datasheets: CuClad 250 is easier to fabricate than low-glass PTFE materials. Its higher fiberglass content gives it better rigidity and drill response. Boards are less prone to the micro-tearing and smearing that can occur when drilling very soft, high-PTFE-ratio materials. For shops doing low-volume defense microwave work alongside higher-volume standard build work, the reduced process complexity of CuClad 250 compared to pure PTFE products is a real operational benefit.

Where Arlon CuClad 250 Fits: Applications

The combination of low loss, X-Y isotropy, and mechanical robustness makes Arlon CuClad 250 a natural match for specific application categories:

Military Electronics: Radars, ECM, and ESM Systems

CuClad 250’s primary defense application history is in military electronics — radars, electronic countermeasure (ECM) systems, and electronic support measures (ESM). These systems typically require microwave PCBs that combine good RF performance with genuine mechanical durability: they get mounted in aircraft, ships, and ground vehicles that impose vibration and shock loads that bench-top electronics never see. CuClad 250’s near-conventional-substrate mechanical properties help boards survive those environments while maintaining electrical performance.

Microwave Filter, Coupler, and LNA Designs

These properties make CuClad an attractive choice for filters, couplers, and low noise amplifiers. For these circuits, Dk uniformity across the panel is critical — variations in local dielectric constant translate directly to center frequency shift in filters and to loss and directivity variation in couplers. CuClad 250’s cross-plied woven construction, combined with Arlon’s PTFE-coating process control, delivers the Dk consistency these designs require.

In LNA designs specifically, the low dissipation factor of CuClad 250 (as low as 0.0009 at X-band in the lower-Dk grades) matters for noise figure. Every tenth of a dB counts in an LNA front end, and laminate insertion loss contributes directly to cascaded noise figure.

Phased Array Antenna Substrates

True X-Y isotropy is critical in some phased array antenna applications. Large phased arrays — particularly those using distributed corporate feed networks or beamforming networks etched directly into the substrate — are precisely the applications where directional Dk variation shows up as measurable array performance degradation. CuClad 250’s cross-ply construction is designed to eliminate this concern.

Power Dividers and Combiners

In power divider and combiner networks, consistent Dk and low loss across the full circuit area determine port-to-port balance and insertion loss respectively. CuClad 250’s panel-wide Dk uniformity enables reproducible power divider performance across production lots — a significant advantage in defense production programs where every board must pass the same electrical acceptance test.

For a comprehensive view of the broader Arlon PCB laminate portfolio — including the ceramic-filled CLTE family, polyimide products, and high-frequency epoxy systems — it’s worth reviewing the full lineup to understand where CuClad 250 fits relative to other design options.

CuClad 250 vs. CuClad 217 and CuClad 233: How to Choose Within the Family

Engineers new to the CuClad family sometimes aren’t sure which grade to spec. Here’s the practical guidance:

Parameter	CuClad 217	CuClad 233	CuClad 250
Dk (nominal)	2.17 – 2.20	2.33	2.40 – 2.60
Df (X-band)	~0.0009 (lowest)	~0.0013	~0.0015–0.0022
Fiberglass/PTFE ratio	Low	Medium	High
Dimensional stability	Moderate	Better	Best in family
Thermal expansion	Higher	Moderate	Lowest in family
Mechanical rigidity	Lower	Moderate	Best in family
Signal propagation speed	Fastest	Moderate	Slower vs. 217
Best for	Lowest loss, fastest propagation	Balanced loss / mechanical	Mechanically demanding, ECM/radar

CuClad 217 is the right choice when you need the absolute lowest Dk and loss — the fastest signal propagation and best Df in the CuClad family. CuClad 233 balances both. CuClad 250 is the right choice when mechanical durability, dimensional stability, and fabrication robustness matter as much as electrical performance — which is most defense hardware.

CuClad 250 vs. Rogers RT/duroid 5880

Since Rogers acquired Arlon in 2015, CuClad 250 effectively competes with Rogers’ own RT/duroid 5880 in some applications. The comparison is informative:

Parameter	Arlon CuClad 250	Rogers RT/duroid 5880
Dk (10 GHz)	2.40 – 2.60	2.20
Df (10 GHz)	~0.0015–0.0022	0.0009
Construction	Cross-plied woven glass/PTFE	PTFE/microfiber glass
XY Isotropy	True (cross-ply)	Good but non-woven
Dimensional stability	Better (woven)	Moderate
Mechanical strength	Higher	Moderate
Primary strength	Dk uniformity, isotropy, mechanicals	Ultra-low loss

RT/duroid 5880 wins on raw Df and Dk. CuClad 250 wins on dimensional stability and cross-ply isotropy. They’re different tools for different jobs, and understanding which axis matters most for your circuit determines which belongs on your BOM.

Fabrication Guidelines for CuClad 250 PCBs

CuClad 250 processes similarly to other woven PTFE laminates, but the higher glass content makes it somewhat more forgiving than pure PTFE or very-high-PTFE-ratio materials.

Drilling

Use highly polished carbide tools. Repointed (resharpened) bits are not recommended on PTFE-based materials because even small amounts of dulling lead to smearing of the PTFE matrix around hole walls. Panels can be drilled in stacks based on total thickness — standard entry and backup board materials apply. Use firm clamping to prevent material lift during drilling.

Surface Preparation for Bonding

PTFE surfaces require activation before bonding or plating. Inert gas plasma or sodium etch processes are standard approaches. Adhesion to copper surfaces can be improved with an aggressive micro-etch such as ammonium persulfate prior to bonding. It is best to proceed to lamination as quickly as possible after surface activation — PTFE surfaces relax over time and adhesion windows are finite.

Routing

Use two-flute, slow-spiral, micrograin carbide upcut endmills for routing. Support PTFE material with rigid entry and backup materials to prevent lifting and tearing at the routed edge. Typical routing parameters for a 0.062″ cutter: spindle speed around 15,000 rpm, table feed rate approximately 15 inches per minute — adjust based on your specific machine and material thickness.

Storage

Store CuClad 250 flat in a cool, dry location away from direct sunlight. Avoid copper oxidation and panel contamination. Unlike moisture-sensitive thermoset prepregs, PTFE materials have minimal moisture sensitivity, but maintaining clean, oxidation-free copper surfaces is important for downstream bonding steps.

Useful Resources for Engineers Working with CuClad 250

Resource	Description	Where to Find It
Arlon CuClad Series Datasheet	Full electrical, mechanical, and dimensional specs	midwestpcb.com/data_sheets/ArlonCuClad.pdf
Rogers CuClad 250 Product Page	Current Rogers-era product info and Laminate Properties Tool	rogerscorp.com/advanced-electronics-solutions/cuclad-series-laminates/cuclad-250-laminates
Arlon Microwave & RF Materials Guide	Full PTFE laminate portfolio comparison and thickness/Dk tables	integratedtest.com/wp-content/uploads/2021/08/ArlonMaterials.pdf
Fabrication Guidelines: DiClad, CuClad, IsoClad	Process guidelines for PTFE woven laminates	Available via rfglobalnet.com/doc/rf-microwave-laminates-cuclad-0001
MatWeb — Arlon CuClad 250	Material property database with key specs	matweb.com
Hughes Circuits CuClad Overview	Fabricator’s material reference with CuClad family data	hughescircuits.com
IPC-4103 Specification	Industry standard covering PTFE-based laminates	ipc.org

Always pull the latest revision of the Rogers/Arlon datasheet directly from Rogers Corporation or an authorized distributor — specifications have been updated since the original Arlon publications and Rogers-era documentation is authoritative for current production material.

Frequently Asked Questions About Arlon CuClad 250

Q1: What is the difference between CuClad 250GT and CuClad 250GX?

The GT and GX suffixes designate the test frequency at which the dielectric constant is measured and certified. CuClad 250GT is tested at 1 MHz, which is standard for broad material qualification but not particularly relevant to microwave circuit performance. CuClad 250GX is tested at 10 GHz — the frequency range your circuits are actually operating in. For any microwave PCB design work, always specify and design from GX data. The 10 GHz Dk value is what your EM simulator needs to produce accurate results.

Q2: Why does CuClad 250 have a range of dielectric constants (2.40–2.60) rather than a single fixed value?

The Dk range reflects the fact that the fiberglass/PTFE ratio — and therefore the composite dielectric constant — varies slightly across the thickness range of available materials. Thinner substrates tend toward the lower end of the range, while thicker substrates can achieve higher Dk values due to changes in the glass volume fraction. When you specify CuClad 250, you select a specific nominal Dk option (e.g., 2.50) from the available options at your chosen thickness. Your design and EM simulations should use that specific nominal value with an understanding of the typical lot-to-lot tolerance.

Q3: Can CuClad 250 be processed in a standard FR-4 shop?

Partially. CuClad 250’s higher glass content makes it more FR-4-like than lower-glass PTFE laminates, but important process differences remain. PTFE surfaces require specific surface activation (plasma or sodium etch) before plating or bonding — standard FR-4 oxide processes don’t apply. Lamination bonding plies for PTFE multilayers require much higher press temperatures than standard epoxy prepreg. Drilling with repointed bits is not recommended. A shop with some PTFE experience can handle CuClad 250, but a pure FR-4 shop without PTFE process knowledge will run into surface adhesion and multilayer bonding problems. Always verify your fabricator’s PTFE process capabilities.

Q4: What bonding materials are used to build CuClad 250 multilayers?

CuClad products can be bonded using Arlon’s CuClad 6700 and CuClad 6250 thermoplastic bonding films, or Arlon’s CLTE-P bonding ply (the same prepreg used with the CLTE laminate family), or Arlon’s GenClad 280 hybrid thermoset/thermoplastic prepreg. Each has different process temperature requirements and Dk properties. For circuits where the bondline Dk must match the laminate Dk closely — stripline designs, controlled impedance inner layers — CLTE-P or GenClad 280 with a well-characterized Dk are the better choices over bare bonding films.

Q5: How does the CuClad 250 cross-ply construction benefit filter and coupler designs specifically?

Bandpass filters and directional couplers are among the most Dk-sensitive circuits in microwave design. A small change in local dielectric constant shifts the resonant frequency of filter stubs and the coupling coefficient of gap couplers. If your laminate has directional Dk variation — higher along the fiber direction than perpendicular to it — traces parallel to the fibers will have slightly different electrical length than identical traces oriented 90° away. In a filter or coupler that combines orthogonally oriented elements, this shows up as asymmetry in the frequency response. CuClad 250’s cross-ply construction ensures the Dk your circuits see is the same regardless of trace orientation, so the only Dk variables left in your design are the well-characterized tolerances from lot to lot — not the orientation-dependent variation that complicates other PTFE laminate designs.

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Arlon CuClad 250 is a cross-plied woven PTFE/fiberglass laminate with Dk 2.40–2.60 and low loss for military radar, ECM, and microwave filter PCBs. Complete guide to CuClad 250 properties, GT vs GX vs LX grades, fabrication tips, and comparison with CuClad 217 and Rogers RT/duroid 5880.