CuClad 250 PCB | Dk 2.50 PTFE Microwave Laminate

What Is Rogers CuClad 250?

Rogers CuClad 250 is a woven-fiberglass-reinforced PTFE laminate with a dielectric constant (Dk) of 2.50 ± 0.04 and a dissipation factor (Df) of 0.0018, both measured at 10 GHz. It combines low dielectric loss with the dimensional stability that woven reinforcement provides, making it a practical choice for microwave feed networks, GPS patch antennas, satellite downconverters and radar stripline assemblies operating from UHF through Ka-band.

CuClad 250 belongs to the broader CuClad family from Rogers Corporation, which also includes CuClad 217 (Dk 2.17) and CuClad 233 (Dk 2.33). All three use PTFE resin systems but differ in glass-to-resin ratio and weave style, which shifts the Dk and affects how tightly trace widths can be controlled. Among these, CuClad 250 is the most widely specified because its Dk sits close to the 2.50 baseline many legacy designs assume.

Key Electrical and Mechanical Properties

A Df of 0.0018 at 10 GHz means CuClad 250 keeps insertion loss below roughly 0.04 dB/cm for a 50 Ω microstrip on 0.787 mm (31 mil) substrate at 10 GHz—competitive with many non-woven PTFE laminates while offering better drill registration and dimensional stability during lamination.

Why Dk 2.50 Matters for Microwave Design

A Dk of 2.50 produces wider traces for a given impedance compared to higher-Dk substrates, which relaxes fabrication tolerances. For a 50 Ω microstrip on 0.787 mm CuClad 250, the calculated trace width is approximately 2.15 mm (85 mil)—roughly 30 % wider than the same impedance on a Dk 3.48 board. Wider traces reduce conductor loss and are easier to etch repeatably.

Low Dk also shortens the effective electrical length of a quarter-wave transformer or patch element, which can be a layout advantage in tightly packed feed networks. However, a lower Dk means a physically larger patch antenna for a given frequency, so designers working on compact L-band or S-band arrays may prefer a higher-Dk laminate such as Rogers RO3003G2 (Dk 3.00) to shrink element size.

Dk Drift with Temperature and Frequency

CuClad 250’s thermal coefficient of Dk is −125 ppm/°C, meaning the Dk drops slightly as temperature rises. Over a 0–80 °C swing the effective Dk shifts by about −0.025, which can detune a narrowband filter or antenna by several megahertz at C-band. For temperature-sensitive applications, model this drift early.

Use the estimator below to see how much Dk changes across your operating temperature range and evaluate whether the shift stays within your design margin.

If the tool shows a Dk shift that moves your center frequency more than half the passband bandwidth, consider adding a tuning element or switching to a laminate with a flatter thermal Dk profile. For instance, Taconic TLX-8 (Dk 2.55) offers a comparable Dk with a different PTFE/glass system that some designers find more thermally stable in narrow temperature windows.

CuClad 250 vs. Similar Low-Dk PTFE Laminates

Choose CuClad 250 when you need woven-glass dimensional stability, a well-characterized Dk of 2.50 and proven Rogers supply-chain support. Choose DiClad 527 when you need the same Dk but want a non-woven reinforcement for more isotropic Dk behavior, which matters in circular-polarization patch designs. Choose Taconic TLX-0 when budget is the primary constraint and a slight Dk difference (2.45 vs. 2.50) is acceptable.

Fabrication Guidelines for CuClad 250 PCBs

Drilling

PTFE laminates are softer than FR-4, so standard carbide drill bits work but require adjusted parameters. Use entry and backup boards to prevent burring. Recommended spindle speed is 60 000–80 000 RPM with a chip load of 0.025–0.050 mm (1–2 mil) per revolution. Peck drilling cycles help clear PTFE debris from the flute. Hole location accuracy is generally better than on non-woven PTFE because the glass weave resists lateral drill wander.

Plating and Surface Finish

PTFE is chemically inert, so through-hole plating requires a sodium-naphthalenide or plasma etch treatment to roughen the hole wall and promote copper adhesion. Without this step, peel strength in the barrel drops below acceptable levels. After etch-back, electroless copper followed by electrolytic copper plating proceeds normally. ENIG, immersion silver and OSP finishes are all compatible; ENIG is preferred for wire-bondable RF pads.

Lamination for Multilayer Stackups

CuClad 250 can be bonded into multilayer constructions using Rogers CuClad or PTFE-based bonding films (e.g., Rogers 3001 bondply). Typical lamination temperature is 370 °C (700 °F) at 200–400 psi for 60–90 minutes. Registration accuracy benefits from the woven-glass skeleton, which resists in-plane movement during the press cycle better than non-woven alternatives. When hybrid stackups with FR-4 are needed for cost reasons, use a thin PTFE bondply at the FR-4/PTFE interface to manage CTE mismatch. The Rogers CuClad product family page provides detailed lamination profiles for each thickness.

Etching

Standard cupric-chloride or alkaline etchants work. Because CuClad 250 uses electrodeposited (ED) copper by default, etch factors are consistent. For fine-line work below 0.15 mm (6 mil) trace/space, request rolled-annealed (RA) copper cladding for a smoother copper profile and lower conductor loss at millimeter-wave frequencies.

Design Tips and Common Pitfalls

• Dk anisotropy: Woven-glass PTFE laminates exhibit a slight Dk difference between the warp and fill directions of the weave—typically ±0.02. Align critical transmission lines along one axis consistently and characterize that axis during prototyping.
• Moisture uptake is negligible at 0.05 %, but PTFE boards stored in humid environments can trap surface moisture between copper and laminate. Bake at 120 °C for 2 hours before soldering to prevent delamination blisters during reflow.
• Solder mask adhesion: Liquid photoimageable solder mask adheres poorly to bare PTFE. Use a plasma treatment or mechanical abrasion before mask application, or leave RF trace areas mask-free (solder-mask-defined clearances).
• Mixed-dielectric stackups: Combining CuClad 250 with lower-cost PTFE laminates like F4BM for non-critical layers can reduce material cost by 20–35 % in high-layer-count builds, provided the fabricator can manage the differing press profiles.

Typical Applications

• GPS and GNSS patch antennas: The 2.50 Dk gives a good balance between patch size and bandwidth at L-band (1.575 GHz).
• Satellite LNB and downconverter boards: Low Df keeps noise figure contributions from substrate loss below 0.1 dB through Ku-band.
• Radar feed networks: Stripline corporate feeds for X-band and Ku-band slotted waveguide arrays, where amplitude and phase balance across the network depends on low and repeatable Dk.
• Microwave filter and coupler substrates: Edge-coupled and broadside-coupled structures benefit from the wide traces that a Dk of 2.50 allows.
• Test fixtures and calibration standards: The well-documented Dk and Df make CuClad 250 a reliable reference substrate for TRL and SOLT calibration kits up to 33 GHz, as discussed in IEEE microwave calibration literature.

Ordering and Availability

CuClad 250 is available in standard panel sizes of 12 × 18 in (305 × 457 mm) and 18 × 24 in (457 × 610 mm). Thickness options range from 5 mil (0.127 mm) single-layer cores to 125 mil (3.175 mm) for thick ground-plane substrates. Copper weights of ½ oz (17 µm), 1 oz (35 µm) and 2 oz (70 µm) are stocked; heavier claddings are available on request. Lead times for standard thicknesses typically run 4–6 weeks from Rogers distribution; keep this in mind when scheduling prototypes. Consult the IPC-6012 qualification standard to specify the performance class (Class 2 or Class 3) appropriate for your end application.

Frequently Asked Questions

Is CuClad 250 the same as DiClad 527?

No. Both have a Dk of 2.50 and Df of 0.0018 at 10 GHz, but CuClad 250 uses a woven-glass reinforcement while DiClad 527 uses a non-woven (random-fiber) glass structure. The woven version offers better dimensional stability and drill registration; the non-woven version provides more isotropic Dk, which matters for circularly polarized antenna elements.

What is the maximum operating frequency for CuClad 250?

Rogers characterizes CuClad 250 up to 33 GHz. Above that, the woven-glass weave pattern can introduce periodic Dk variation on the scale of the weave pitch (~0.5 mm), which may cause spurious coupling in millimeter-wave circuits. For frequencies above 33 GHz, consider non-woven or ceramic-filled PTFE laminates.

Can CuClad 250 be used in lead-free reflow?

Yes. PTFE has no glass-transition temperature in the conventional sense and remains stable well above the 260 °C peak of lead-free reflow profiles. Ensure adequate bake-out before reflow to avoid trapped-moisture blistering.

How does CuClad 250 compare to FR-4 for RF?

FR-4 has a Dk around 4.2–4.5 and a Df of 0.015–0.025 at 10 GHz—roughly ten times the loss of CuClad 250. For any design above about 2 GHz where insertion loss, phase stability or noise figure matters, CuClad 250 is the superior choice despite its higher material cost.

What bonding materials work with CuClad 250 in multilayer builds?

Rogers 3001 bondply (PTFE-based, Dk 2.28) and Rogers CuClad bonding film are the standard choices. FEP (fluorinated ethylene propylene) film at 0.025–0.050 mm thickness is a lower-cost alternative that bonds at around 300 °C. Avoid epoxy-based prepregs unless the RF layers are isolated from the epoxy interface, as the Dk mismatch creates impedance discontinuities.