Arlon AD250C PCB: Properties, Design & Selection

What Is the Arlon AD250C PCB Laminate?

The Arlon AD250C PCB substrate is a woven-fiberglass-reinforced PTFE laminate with a nominal dielectric constant (Dk) of 2.50 ± 0.04 at 10 GHz. Its combination of low dissipation factor (Df ≈ 0.0018 at 10 GHz), tight Dk tolerance, and the mechanical rigidity contributed by E-glass reinforcement makes it a proven choice for microstrip and stripline circuits operating from UHF through Ka-band. If you need a substrate that machines like a conventional glass-reinforced PTFE board yet keeps insertion loss close to unreinforced PTFE, the Arlon AD250C PCB material sits in the sweet spot between processability and RF performance.

Key Electrical and Mechanical Properties of Arlon AD250C

The table below consolidates the parameters most relevant to an RF designer evaluating an Arlon AD250C PCB stackup. All values are typical unless noted, drawn from the manufacturer’s published datasheet.

The woven-glass architecture keeps the in-plane CTE close to copper (≈ 17 ppm/°C), which matters for plated-through-hole reliability across thermal cycles. Compare that with pure unreinforced PTFE, where x/y CTE can exceed 70 ppm/°C and drilling becomes problematic.

Understanding the Dk Tolerance and Its Design Impact

A ± 0.04 Dk tolerance on a nominal 2.50 means your actual board could land anywhere from 2.46 to 2.54. For a 50 Ω microstrip on a 20 mil core, that swing shifts the required trace width by roughly ± 1 mil—well within standard etch tolerances. However, at Ka-band (26–40 GHz), even that small Dk variation can shift a filter passband by tens of MHz. If your Arlon AD250C PCB design includes narrowband filters above 20 GHz, request lot-specific Dk data from your laminate supplier and adjust your artwork per lot, or add a tuning element.

Loss Budget: Dielectric vs. Conductor

At 10 GHz on a 20 mil AD250C core with 1 oz rolled copper, total microstrip loss is approximately 0.15 dB/inch, split roughly 40 % dielectric and 60 % conductor. The dielectric contribution scales almost linearly with frequency, so by 30 GHz it approaches 50/50. Switching to ½ oz electrodeposited copper increases conductor loss by about 15 % due to higher surface roughness (typically 1.8 µm RMS vs. 0.5 µm for rolled foil). When loss is critical, specify rolled or reverse-treated foil on your Arlon AD250C PCB fabrication drawing.

Why Choose AD250C Over Competing Dk 2.50 Laminates?

Several PTFE laminates cluster around Dk 2.50, including Rogers DiClad 527 and Taconic TLX-9. The decision usually comes down to loss, dimensional stability, cost, and supply chain familiarity.

Choose AD250C when you need the lowest possible loss among woven-glass Dk 2.50 substrates and your fabricator is already qualified for Arlon’s PTFE product line. Choose DiClad 527 when faster procurement matters more than a fraction of a dB in loss. Choose Taconic TLX-9 when you want a second-source woven-glass option with near-identical performance.

Within the Arlon Family

If your design can tolerate a slightly higher Dk, Arlon AD255C (Dk 2.55) shares the same resin system and processing steps, so you can switch without requalifying the fabrication process. For higher-Dk antenna designs requiring broader bandwidth, Arlon AD300D at Dk 3.00 is worth evaluating. Both alternatives use the same woven-glass PTFE construction, so a shop set up for AD250C can handle them with minimal process changes.

Selecting the Right Arlon Grade for Your Arlon AD250C PCB Project

Arlon’s microwave portfolio spans Dk values from roughly 2.17 to 10+. Use the selector below to compare AD250C against other Arlon grades based on your target frequency, Dk range, and loss budget. Enter your operating frequency and maximum acceptable Df, and the tool ranks every Arlon grade by suitability.

If AD250C appears near the top of the results, confirm the available thickness matches your impedance target. For example, if you need a 10 mil core for a compact Ka-band feed network and AD250C is not stocked in that gauge, AD255C or a ceramic-filled thermoset such as Arlon 25N may be a practical alternative. When AD250C ranks lower—typically because your frequency exceeds 40 GHz or you need Dk below 2.3—the tool will surface grades like AD250A (non-woven, Dk 2.50) or AD217 (Dk 2.17) that better fit those constraints.

Design Considerations for an Arlon AD250C PCB

Impedance and Line Width

At Dk 2.50, a 50 Ω microstrip on a 20 mil (0.508 mm) core with 1 oz (35 µm) copper requires a trace width of approximately 55 mil (1.40 mm). That relatively wide trace is an advantage for power-handling and etch tolerance but can be a constraint in dense layouts. Moving to 10 mil (0.254 mm) core halves the trace width to about 27 mil (0.69 mm). Always run a field solver rather than relying on closed-form approximations when your frequency exceeds 10 GHz, because the woven-glass weave pattern introduces slight Dk anisotropy between warp and fill directions.

Worked Example: 50 Ω Microstrip at 24 GHz

Consider a 24 GHz ISM-band radar front-end on 10 mil AD250C with ½ oz (17.5 µm) rolled copper. A 2.5-D field solver (e.g., Altium’s impedance calculator) returns a 50 Ω trace width of approximately 26.5 mil (0.67 mm). At this frequency, the guided wavelength in microstrip is about 7.8 mm, so a quarter-wave matching stub is roughly 1.95 mm long. The total microstrip loss over a 25 mm feed line is around 0.45 dB—acceptable for most radar receiver noise budgets. If you route the same 25 mm line on DiClad 527 (Df 0.0022), loss rises to about 0.50 dB: a small but measurable difference in a cascaded receive chain.

Drilling and Plating

Woven-glass PTFE drills cleanly with carbide bits at moderate chip loads. Use a backup board to prevent burring, and de-smear with a sodium-etch or plasma cycle to promote copper adhesion in the hole barrel. AD250C’s peel strength of ≥ 8 lb/in after solder float indicates that the copper-to-PTFE bond survives standard lead-free reflow profiles (peak ≈ 260 °C). For multilayer builds, bond plies from Arlon’s 6700 series maintain impedance continuity between AD250C cores.

Moisture and Environmental Stability

With moisture absorption below 0.04 %, AD250C is well-suited to outdoor antenna radomes and marine radar applications where humidity cycling is a concern. PTFE’s inherent chemical inertness adds resistance to salt spray and industrial solvents. The IPC-6012 Class 3 reliability requirements for high-performance electronics are achievable on AD250C stackups when the fabricator follows proper PTFE processing protocols.

Flex and Rigid-Flex Considerations for AD250C Builds

AD250C is a rigid laminate, not a flex film. However, some designers combine thin AD250C cores (10 mil) with polyimide flex layers in hybrid rigid-flex stackups for phased-array antenna feeds where the RF signal path must remain on a low-loss PTFE layer while the interconnect folds. In such builds, the minimum bend radius of the flex portion—not the AD250C—governs the mechanical design. Use the calculator below to verify the flex section meets your bending requirements. Enter the number of flex layers, copper weight, and polyimide thickness.

For a typical 2-layer polyimide flex section with 1 mil (25 µm) copper and 2 mil (50 µm) polyimide, the tool will return a minimum bend radius around 10–15 mil for a dynamic bend application. Keep the AD250C rigid zones well outside that bend area, and use controlled-depth routing or scoring to define the rigid-to-flex transition cleanly. A common mistake is routing the rigid-to-flex boundary through a via field; leave at least 50 mil (1.27 mm) clearance between the nearest via and the score line to avoid stress cracking during flexing.

Fabrication Process Flow for Arlon AD250C PCBs

1. Incoming inspection — Verify Dk and thickness per the Arlon certificate of conformance. Spot-check with a resonant cavity or split-post dielectric resonator at 10 GHz.
2. Imaging and etching — Standard photolithographic process. Minimum feature/space of 4 mil / 4 mil (100 µm) is comfortable; finer geometries require LDI exposure.
3. Drilling — Carbide drills, 300–500 surface feet per minute, entry/exit boards. Aspect ratio up to 8:1 for standard through-holes.
4. Hole preparation — Sodium-naphthalene etch or plasma treatment to activate the PTFE surface for electroless copper adhesion.
5. Plating — Electroless copper seed, followed by electrolytic copper to final wall thickness per IPC-A-600 Class 2/3 requirements.
6. Solder mask and finish — ENIG, immersion silver, or bare copper with OSP. HASL is less common on PTFE because the thermal shock can stress the copper-to-laminate bond on thinner cores.
7. Routing and profiling — Diamond-coated router bits or scoring for panel arrays.
8. Electrical test — Flying probe or fixture test per IPC-9252 for continuity and isolation.

Common Fabrication Pitfalls

• Skipping sodium etch — Without proper PTFE surface activation, electroless copper will not nucleate reliably, leading to barrel cracks after thermal cycling. This is the single most common failure mode on any PTFE-based board, including AD250C.
• Excessive lamination pressure — Over-pressing during multilayer bonding can squeeze out the 6700-series bond ply, thinning the dielectric and raising the local Dk. Target 150–200 psi per Arlon’s processing guidelines.
• Wrong drill stack — Stacking too many PTFE panels in one drill hit causes smearing and hole-wall roughness. Limit to two panels per hit for holes smaller than 15 mil (0.38 mm).

Typical Applications for Arlon AD250C PCB Designs

• Patch antenna arrays — The low Dk yields wider patches for a given frequency, easing manufacturing tolerances on element dimensions.
• GPS and GNSS front-ends — L-band receivers benefit from AD250C’s low loss and stable Dk across temperature.
• Radar feed networks — Corporate and series feed lines on AD250C maintain amplitude and phase balance across wide temperature swings.
• Satellite communication BFNs — Beam-forming networks at Ku- and Ka-band exploit the tight Dk tolerance for repeatable phase matching.
• Test fixtures and calibration standards — Stable Dk and low moisture absorption make AD250C a reliable reference material for TRL and SOLT calibration substrates, as described in IEEE microwave measurement standards.
• Military EW and SIGINT receivers — Wideband antenna feeds spanning 2–18 GHz exploit the flat Dk-vs-frequency curve of PTFE to maintain consistent impedance across multiple octaves.

Storage and Handling

PTFE laminates are less sensitive to moisture than FR-4, but best practice still applies. Store panels flat in their original packaging at 15–30 °C and below 60 % RH. If panels have been exposed for more than 72 hours, a 2-hour bake at 120 °C is a reasonable precaution before lamination or plating to drive off adsorbed surface moisture that could cause delamination during reflow. Avoid stacking heavy items on top of thin AD250C panels—PTFE is softer than epoxy-glass and can take a permanent set under sustained pressure, which locally changes the dielectric thickness and shifts impedance.

FAQ

What frequency range is the Arlon AD250C PCB suitable for?

AD250C performs well from below 1 GHz up to approximately 40 GHz. Beyond 40 GHz, the woven-glass weave pitch (typically around 1 mm for standard 1080 glass) can introduce measurable Dk variation across the trace width, so designers targeting W-band (75–110 GHz) typically move to non-woven or ceramic-filled substrates.

Can AD250C be used in multilayer RF stackups?

Yes. Multiple AD250C cores can be bonded with Arlon 6700-series PTFE prepregs to create stripline or dual-stripline configurations. Hybrid stackups combining AD250C with FR-4 or polyimide cores for digital layers are also common, though the CTE mismatch at the bonding interface must be managed with appropriate prepreg selection.

How does an Arlon AD250C PCB compare to Rogers RO4003C?

RO4003C is a ceramic-filled thermoset (Dk 3.38) that processes like FR-4, while AD250C is a PTFE-based laminate (Dk 2.50) requiring sodium etch for hole preparation. AD250C wins on raw insertion loss and lower Dk; RO4003C wins on ease of fabrication and cost. The choice depends on whether your loss budget or your production budget is tighter.

Is AD250C RoHS compliant?

AD250C itself is an inorganic composite (PTFE + glass + copper) and does not contain restricted substances under RoHS. Confirm the specific copper foil and surface finish with your fabricator to ensure full-stack compliance.

What surface finishes work best on AD250C?

ENIG is the most common finish for RF applications on PTFE substrates because it provides a flat, solderable surface without the thermal stress of HASL. Immersion silver is a lower-cost alternative with good RF performance but requires careful handling to avoid tarnish before assembly.