Arlon 33N PCB | Polyimide High-Temperature Boards

What Is Arlon 33N?

Arlon 33N is a woven-E-glass-reinforced polyimide laminate designed for PCBs that must survive sustained operating temperatures above 200 °C. It offers a glass-transition temperature (Tg) of approximately 250 °C, a dielectric constant (Dk) near 4.2 at 1 GHz, and a dissipation factor (Df) around 0.013. These properties make Arlon 33N PCB a standard selection for aerospace avionics, military radar, down-hole drilling electronics, and other harsh-environment applications where conventional FR-4 (Tg 130–180 °C) cannot survive.

Because 33N uses a pure polyimide resin system rather than a blended epoxy, it retains mechanical integrity and electrical stability well beyond the temperatures that would degrade most mainstream laminates. The trade-off is higher material cost, tighter process windows during fabrication, and the need for moisture management before and during lamination.

Key Material Properties

A Dk of roughly 4.2 is comparable to standard FR-4, which simplifies impedance calculations when migrating an existing design to a high-temperature laminate. However, the slightly higher Df means insertion loss is greater than what you would see on a low-loss RF laminate such as a Taconic TLX-8 board (Df ≈ 0.0019). For applications below a few GHz where thermal survival is the primary driver, 33N’s loss is perfectly acceptable.

Why Choose Arlon 33N Over FR-4?

Standard FR-4 epoxy systems begin to soften near 130–180 °C and decompose around 300 °C. In environments such as jet-engine nacelles, under-hood automotive radar, or geothermal well-logging tools, ambient temperatures can reach 200 °C or higher for extended periods. Arlon 33N’s polyimide resin survives these conditions with minimal property drift. Specific advantages include:

• Thermal endurance: Continuous operation above 200 °C without delamination, blistering, or measling.
• Low Z-axis expansion: A CTE of ~55 ppm/°C (below Tg) protects plated through-holes during thermal cycling, critical for boards that see –55 °C to +260 °C qualification profiles per IPC-6012 Class 3/A.
• Stable Dk over temperature: The dielectric constant shifts less than 2 % across the –55 °C to +200 °C range, keeping impedance-controlled traces within spec.
• Lead-free reflow compatible: Peak reflow temperatures of 260 °C sit well below 33N’s Td of 390 °C, giving ample margin for multiple reflow cycles.

The primary reason not to choose 33N is cost: polyimide laminates can run 3–5 × the price of mid-Tg FR-4 on a per-panel basis, and processing costs are also higher. If your operating environment stays below 150 °C, a high-Tg FR-4 or a material like Isola IS550H may be a more economical path.

Arlon 33N vs. Arlon 35N and Other Polyimides

Arlon’s polyimide family includes several grades. The most common comparison is between 33N and Arlon 35N, which uses a modified polyimide resin with slightly different flow and fill characteristics.

35N’s lower Z-axis CTE (~45 ppm/°C) gives it a slight edge in PTH reliability for thick multilayer boards (≥ 16 layers). 33N is often preferred when better resin flow during lamination is needed or when the design uses thinner cores. Both outperform any FR-4 variant above 200 °C.

For applications where RF loss is the primary concern rather than temperature, consider PTFE-based alternatives. A Rogers CuClad 250 laminate delivers Df around 0.0018 at 10 GHz but has a much lower maximum operating temperature. Material selection always balances thermal, electrical, and mechanical requirements against cost.

Arlon Material Selector

Use the tool below to compare Arlon 33N against other Arlon grades and competing high-temperature laminates. Enter your target Dk range, operating temperature, and layer count to see which materials qualify.

If the selector returns both 33N and 35N as candidates, the deciding factors are usually Z-axis CTE (favor 35N for thick boards with many PTHs) and resin flow behavior (favor 33N for thinner, more complex lamination stacks). When neither polyimide meets your loss budget, the tool may suggest a hybrid stackup—polyimide cores for structural layers bonded with low-loss prepreg on signal layers.

Fabrication Guidelines for Arlon 33N PCBs

Lamination

Polyimide resins require higher lamination temperatures (typically 220–250 °C platen temperature) and longer press cycles (90–120 minutes at full pressure) compared with FR-4. Ramp rates must be controlled to 2–3 °C/min to avoid resin starvation or void formation. Because polyimide absorbs moisture readily, panels and prepreg sheets should be pre-baked at 105 °C for a minimum of 4 hours immediately before layup.

Drilling

The abrasive E-glass reinforcement combined with tough polyimide resin accelerates drill-bit wear. Use carbide micro-grain bits with a high helix angle, reduce hit counts per bit by roughly 30 % compared with FR-4, and back-drill thick boards to minimize stub lengths that degrade signal integrity above a few GHz. Entry and backer materials rated for polyimide (e.g., aluminum entry sheets) help control burr formation.

Plating and Surface Finish

Desmear is critical: polyimide smear is harder to remove than epoxy smear. A permanganate or plasma desmear cycle tuned for polyimide ensures reliable copper-to-barrel adhesion. For high-temperature end-use, ENIG (electroless nickel / immersion gold) or hard gold finishes are preferred because they withstand repeated thermal excursions without oxidation. OSP and immersion tin are generally not recommended for boards that will see continuous service above 150 °C.

Solder Mask and Markings

Standard LPI solder masks are rated to roughly 130–150 °C. For Arlon 33N boards expected to operate above that range, use a high-temperature polyimide-based solder mask or, in extreme cases, leave pads unmasked and rely on conformal coating. Silkscreen inks must likewise be rated for the service temperature; standard epoxy inks will discolor and flake above 200 °C.

Design Considerations for High-Temperature RF Circuits

Impedance Control

With a Dk near 4.2, impedance calculations for 33N are almost identical to those for FR-4. A 50 Ω microstrip on 10 mil (0.254 mm) 33N with ½ oz copper requires a trace width of approximately 18 mil (0.46 mm)—very close to the same geometry on standard FR-4. The advantage is that this impedance remains stable across the full operating temperature range, whereas FR-4 Dk can drift 5–8 % between room temperature and 150 °C.

Thermal Management

Polyimide’s thermal conductivity is low (~0.25 W/m·K in-plane for the composite), similar to FR-4. For power-dissipating components, use thermal vias tied to internal copper planes, or consider a metal-core or alumina ceramic substrate beneath high-power devices while keeping 33N for the rest of the interconnect.

Moisture Sensitivity

Arlon 33N absorbs roughly 0.35 % moisture by weight—about twice that of FR-4. In humid storage, absorbed moisture can cause delamination during reflow (“popcorning”). Best practice is to bake bare boards at 120 °C for 2–6 hours before assembly and store them in moisture-barrier bags with desiccant per J-STD-033 moisture sensitivity guidelines.

Typical Applications

• Aerospace avionics: Engine-area electronics, flight-control actuators, and sensor modules exposed to sustained 200 °C+ environments.
• Military radar and EW: High-power transmit/receive modules where board-level temperatures exceed FR-4 limits during continuous operation.
• Down-hole drilling: Measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools operating at 175–230 °C ambient for hundreds of hours.
• Automotive under-hood: Proximity sensors and power-management boards near exhaust manifolds or turbocharger housings.
• Industrial controls: Boards inside furnaces, kilns, or smelting equipment where ambient temperatures far exceed consumer norms.

Cost Drivers and Procurement Tips

Arlon 33N is a specialty laminate. Expect longer lead times (6–10 weeks for raw material in standard thicknesses) and higher per-panel costs compared with volume FR-4. Key cost drivers include:

• Panel utilization: Standard Arlon sheet sizes may not match your fabricator’s preferred panel format; check with the supplier early.
• Layer count and thickness: Thicker multilayers require more prepreg sheets and longer press cycles, compounding cost.
• Copper weight: Heavy copper (2 oz+) on polyimide demands tighter etch control and more aggressive desmear.
• Surface finish: ENIG or hard gold adds cost but is usually necessary for high-temperature reliability.

To manage cost, consider a hybrid stackup: use Arlon 33N for the core layers closest to heat sources and bond them with a less expensive high-Tg prepreg on outer layers that see lower temperatures. Discuss this approach with your fabricator’s materials engineer before finalizing the stackup, as CTE mismatches between dissimilar materials can introduce reliability risks. For comparison, see how other high-frequency laminates like Taconic RF-301 balance cost and performance in mixed-material builds.

Frequently Asked Questions

Can Arlon 33N be used for multilayer PCBs?

Yes. Arlon 33N is available in core and prepreg forms suitable for multilayer constructions exceeding 20 layers. The key requirement is precise lamination cycle control—higher temperatures and longer dwell times than FR-4—along with pre-baking to remove absorbed moisture.

What is the maximum continuous operating temperature for 33N?

Arlon 33N boards are routinely qualified for continuous operation at 200–230 °C. Short excursions to 260 °C (e.g., lead-free reflow) are well within its capability, given a Td above 390 °C. Long-term reliability at the upper end depends on copper adhesion, surface finish, and solder-mask selection.

Is Arlon 33N suitable for RF and microwave frequencies?

At frequencies up to 2–3 GHz, 33N performs well for impedance-controlled interconnects. Above 10 GHz, its Df of ~0.013 introduces meaningful insertion loss compared with PTFE or hydrocarbon ceramic laminates (Df < 0.003). For millimeter-wave front ends, use a low-loss laminate for signal layers and 33N only where thermal performance is the priority.

How does Arlon 33N compare with DuPont Pyralux for flex circuits?

33N is a rigid laminate; Pyralux is a flexible polyimide film. They share the polyimide chemistry and similar Tg values, but 33N’s woven-glass reinforcement makes it unsuitable for flex or rigid-flex bend zones. For high-temperature flex sections, Pyralux or equivalent adhesiveless polyimide films are the correct choice, with 33N used in the rigid portions of a rigid-flex assembly.

Does Arlon 33N meet IPC-4101 slash-sheet requirements?

Arlon 33N conforms to IPC-4101 slash sheets for polyimide laminates (commonly /40, /41, or /42 depending on specific construction). Always confirm the exact slash-sheet designation with the laminate supplier for your chosen thickness and copper configuration.