Engineer’s guide to Arlon polyimide PCB laminates: 85N vs 84N specs, when to use polyimide over FR4, fabrication tips, aerospace applications, and material comparison tables.

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If you’ve been specifying FR4 for every board you design, you’re not alone — it covers maybe 80% of all PCB applications without complaint. But that other 20%? That’s where FR4 quietly fails you, often mid-qualification, sometimes in the field. Arlon polyimide laminates exist for exactly those situations: the boards that run hot, live in harsh environments, need to survive thousands of thermal cycles, or carry signals into the GHz range without falling apart.

This guide is written from a PCB engineering perspective. We’ll cover what makes Arlon polyimide laminates different, which grades to use when, how they process in fab, what they cost, and where they’re being used in real applications today.

What Is Arlon Electronic Materials?

Arlon Electronic Materials Division is a veteran-owned business founded in 1969 and is a major manufacturer of specialty high-performance laminate and prepreg materials used in a wide variety of printed circuit board applications. That’s over 50 years of focused development on materials that standard laminate suppliers simply don’t prioritize.

The company has built over 50 years of experience in PTFE-based microwave laminates and more than 30 years in polyimide and specialty epoxy systems. Unlike commodity FR-4, Arlon materials are engineered for specific performance characteristics — whether that’s surviving extreme temperatures, maintaining signal integrity at microwave frequencies, or providing dimensional stability in multilayer constructions.

Their product portfolio spans four main categories: polyimide systems, low-flow prepregs, epoxy-based laminates, and PTFE/microwave substrates. For this guide, we’re focusing on the polyimide family — the materials that get called in when thermal performance is non-negotiable.

Why Polyimide? Understanding the Chemistry

Polyimide is a family of polymers built around imide linkages in their backbone chain. That molecular structure is what gives polyimide its legendary thermal resistance. The bonds don’t break down at the temperatures that destroy standard epoxy systems.

Polyimide is a polymer composed of imide monomers from the high-performance plastics category. Because of its great heat resistance, the material can be used in a variety of applications that require tough organic ingredients — high-temperature displays, fuel cells, military applications, and more.

In practical PCB terms, this translates to:

• Glass transition temperature (Tg) above 250°C, compared to 130–170°C for most FR4 grades
• Decomposition temperature (Td) pushing above 400°C
• Low z-axis CTE, meaning through-holes survive aggressive thermal cycling without cracking

The trade-off is that polyimide absorbs more moisture than FR4 and costs significantly more. It also requires more careful processing — longer bake cycles, specific lamination protocols, and plasma desmear rather than permanganate for some grades. But for the applications that need it, those trade-offs are entirely acceptable.

The Arlon Polyimide Product Line: A Practical Overview

Understanding which Arlon polyimide grade fits your application requires knowing what each one is actually optimized for. Here’s a breakdown:

Arlon 85N — The Gold Standard Pure Polyimide

Arlon’s 85N is a 250°C high glass transition pure polyimide resin system which provides superior thermal resistance to high temperature end-use electronics. Coupled with the high temperature stability and the pure resin formulation, 85N is the best choice for high layer count multilayers.

What makes 85N stand out in the polyimide market is its purity. 85N is the ultimate pure polyimide laminate and prepreg system. Bromine-free chemistry provides best-in-class thermal stability for applications with sustained high in-use temperatures as well as for use in lead-free soldering applications. It meets IPC-4101/40 and /41 specifications with pure polyimide — no secondary resin, no epoxy added, blended or reacted.

The key specs for 85N at a glance:

Property	Arlon 85N	Typical FR4
Glass Transition Temp (Tg)	≥250°C	130–170°C
Decomposition Temp (Td)	>407°C	~300–330°C
T300 (time to delaminate at 300°C)	>60 min	<5 min
Z-axis CTE (50–260°C)	~1.2%	~3.5–4.5%
Dielectric Constant (Dk) @ 1 GHz	~3.8–4.0	~4.2–4.6
Loss Tangent (Df) @ 1 GHz	~0.010–0.013	~0.018–0.025
Flammability	HB	V-0
IPC Spec	IPC-4101/40 & /41	IPC-4101/21

85N is the default choice for aerospace avionics, military electronics, and any application that must survive lead-free assembly and then live at elevated temperatures for years.

Arlon 84N — Ceramic-Filled Polyimide for Hole Filling

84N is a high performance ceramic-filled polyimide prepreg based on Arlon’s 85N pure polyimide system, designed for use in filling etched areas in polyimide multilayers that contain thick copper layers and for filling clearance holes in metal cores. The ceramic filler in the resin serves to reduce shrinkage and inhibit crack formation during through-hole drilling in filled clearance areas.

84N inherits the same Tg and Td as 85N (>250°C and >400°C respectively) but adds the ceramic filler for a specific fabrication purpose: when your stackup has thick copper planes or metal cores with clearance holes that need to be filled before drilling. The filler helps control resin flow and prevents the cracking that can occur around drilled holes in high-copper-density designs.

Low z-expansion of 1% between 50–250°C offers superior PTH reliability through manufacture, assembly and in service. Up to 50% or more reduction in cure time compared with traditional polyimide cycles.

If your design is a standard multilayer without metal cores, stick with 85N. If you’re dealing with metal-core construction or extremely thick internal copper layers (2 oz+), 84N is the right prepreg.

Arlon 85HP — Higher Thermal Conductivity Polyimide

High Performance Polyimide (Arlon 85HP) has Tg >250°C, Td of 430°C, HB flammability rating, and moisture content of 0.19%. Its thermal conductivity is double that of standard polyimide.

85HP is the right choice when you need the thermal endurance of 85N but with better heat dissipation through the laminate itself — useful in power electronics or designs where junction temperatures need to be managed not just at the component level, but through the board stack.

Arlon 37N — Low-Flow Polyimide Prepreg

37N is designed specifically for situations where you need bonding between layers but cannot tolerate significant resin movement during lamination. Low-flow polyimide prepreg (Arlon 37N) has Tg of 199°C, Td of 320°C, and a V0 flammability rating.

In rigid-flex constructions, any excess resin flow can encroach on the flex areas or cause registration issues. 37N prevents that by limiting how far the resin migrates under heat and pressure. It’s a specialized prepreg, not a laminate, so it’s always used in combination with a core material like 85N.

Arlon 38N — Low-Flow Polyimide Prepreg (Electrical Focus)

Arlon 38N, with a dielectric constant of 3.8, balances cost-effectiveness with strong electrical and thermal performance for high layer count, high density interconnect boards.

38N occupies an interesting middle ground: it gives you better layer-to-layer registration control than standard prepregs while still delivering good electrical properties for HDI designs where tight via registration is critical.

Full Comparison: Arlon Polyimide Grades at a Glance

Grade	Type	Tg (°C)	Td (°C)	Key Feature	Primary Application
85N	Pure polyimide laminate + prepreg	≥250	>407	No additives, best thermal	Aerospace, military, high-layer MLBs
84N	Ceramic-filled polyimide prepreg	≥250	>400	Hole fill, crack resistance	Metal-core boards, thick Cu MLBs
85HP	Enhanced thermal conductivity polyimide	>250	430	2× thermal conductivity	Power electronics, heat management
37N	Low-flow polyimide prepreg	199	320	Controlled resin flow	Rigid-flex, fine-feature MLBs
38N	Low-flow polyimide prepreg	~200	~320	Better electrical properties	HDI, high layer count

When to Choose Arlon Polyimide Over FR4

This is the practical question most engineers are asking. The short answer: when any of the following conditions apply to your design, you should be evaluating polyimide seriously.

Sustained Operating Temperature Above 130°C

Unlike FR4, which begins to struggle beyond 130–150°C, Arlon 84N (and 85N) remains stable even at temperatures exceeding 250°C. If your board lives near an engine, under a hood, in a server rack with poor cooling, or inside a power supply enclosure, the delta between FR4’s Tg and your operating temperature shrinks fast. Polyimide gives you margin.

Lead-Free Assembly on High-Layer-Count Boards

Lead-free solder peaks at 260°C. A 20+ layer board with standard FR4 (Tg 150–170°C) is being laminated multiple times and then hit with a thermal excursion that exceeds its Tg during reflow. The result can be measling, delamination, or barrel cracking in through-holes. 85N’s Tg of 250°C+ means the material stays well below transition during even the most aggressive lead-free assembly profiles.

High Thermal Cycling Applications

Electronics used in fields like military, aerospace, and telecommunications often encounter extreme temperature changes, vibrations, and thermal cycling. These stresses can weaken standard PCB materials, leading to performance issues or even failure. However, Arlon 84N (and 85N) stands up to these challenges by offering better resistance to thermal cycling and mechanical deformation compared to traditional materials.

The z-axis CTE is what determines PTH survival over thermal cycles. Arlon 85N’s ~1.2% z-axis expansion across the 50–260°C range versus FR4’s 3.5–4.5% means dramatically less stress on your copper barrels.

Long Service Life in Elevated Temperature Environments

Applications requiring significant lifetimes at elevated temperatures — such as aircraft engine instrumentation, down hole drilling, under-hood automotive applications, industrial sensor systems and burn-in testing of ICs — are prime candidates for 84N/85N.

The T300 spec (time to delaminate at 300°C) is particularly telling here. FR4 fails in minutes at 300°C. 85N exceeds 60 minutes. In terms of long-term reliability at elevated temperatures, that’s not a marginal improvement — it’s a different category.

Rigid-Flex Constructions Requiring Precise Layer Registration

When you’re bonding rigid sections to flex in a multilayer rigid-flex design, resin control is critical. Low-flow grades like 37N and 38N prevent resin bleed into flex areas while still providing full polyimide thermal performance in the rigid sections.

Arlon Polyimide vs. FR4 vs. Rogers: Where Does Each Fit?

A lot of engineers land on this question when they’re selecting materials for a new design. Here’s a practical positioning framework:

Scenario	Best Material Choice	Why
General commercial PCB, <130°C	Standard FR4 (e.g., Isola IS410)	Cost-effective, well-characterized, easy to fab
High-layer MLB, lead-free, >150°C	Arlon 85N	High Tg, low z-CTE, proven reliability
RF/microwave >3 GHz, low loss priority	Rogers RO4350B / RO4003C	Lower Dk/Df, tighter Dk tolerance
High-temp + RF in same stackup	Arlon 85N + Rogers hybrid	Polyimide cores with RF outer layers
Metal-core PCB with thick copper	Arlon 84N prepreg	Ceramic fill controls resin, prevents cracking
Under-hood automotive, 175–200°C	Arlon 85N or Isola IS620	Both offer high Tg; compare Td and PTH reliability
Space flight electronics	Arlon TC600 or 85N	NASA-qualified supply chains, extreme Td

Rogers materials like RO4350B are often used in RF and microwave applications due to their low-loss properties, but Arlon 85N holds up well in hybrid stackups where polyimide layers are needed. Isola laminates like IS620 offer high Tg values, but Arlon 84N/85N still delivers superior thermal endurance in multi-layer applications.

The honest engineering answer: Rogers wins on raw RF performance at microwave frequencies, but if your design also needs to survive extreme temperatures or aggressive thermal cycling, a hybrid stackup using Arlon polyimide for structural cores and Rogers for the signal layers is often the right call.

Fabrication Considerations: What Changes When You Process Arlon Polyimide

This is where a lot of engineers get surprised. Polyimide is not FR4, and your fab needs to know that before they quote your job. Here’s what changes:

Pre-Lamination Bake

Polyimide absorbs more moisture than FR4. All Arlon polyimide prepregs should be vacuum-desiccated for 8–12 hours before lamination. Skipping this step risks steam-induced delamination or blistering during the lamination cycle.

Lamination Cycle

For 85N: pre-vacuum for 30–45 minutes, control heat rise to 4.5–6.5°C per minute between 100–150°C, set cure temperature at 218°C, start cure time when product temperature exceeds 213°C, cure at temperature for 120 minutes, and cool down under pressure at ≤5°C/min.

This is a significantly longer and more controlled cycle than FR4. The slow ramp rate prevents thermal shock, and the 120-minute cure at temperature ensures full cross-linking. If your fab isn’t set up for this, they’ll struggle.

Inner Layer Preparation

Use brown oxide on inner layers and ensure uniform coating. Bake inner layers at 107–121°C for 60 minutes immediately before lay-up to drive out absorbed moisture. This step is often skipped with FR4; with polyimide, it’s not optional.

Drilling

Drill at 350–500 SFM (depending on grade). Undercut bits are strongly recommended for vias 0.45mm and smaller. Polyimide is tougher than FR4, so standard drill parameters will result in more bit wear and potentially rougher hole walls.

Desmear

Plasma desmear is preferred over permanganate for polyimide. Permanganate can work, but plasma gives more consistent etchback and better copper adhesion in the PTH barrel. If your fab quotes you on permanganate-only desmear for a polyimide job, push back.

Pre-Assembly Bake

Bake for 1–2 hours at 121°C prior to solder reflow or HASL. Again, moisture management. Polyimide that has picked up moisture during board fab will outgas violently during reflow and can cause delamination that looks like a material defect but is actually a process failure.

Real-World Application Areas

Aerospace and Defense

For aerospace applications, Arlon supports AS9100 certified supply chains. Specific MIL-spec qualifications depend on the material — 85N, for instance, is commonly used in MIL-PRF-31032 qualified boards.

Avionics boards in flight computers, radar systems, electronic warfare equipment, and missile guidance systems all see thermal extremes, vibration, and humidity cycling that would degrade FR4 within the design life. 85N is the de facto standard for these applications.

Space Electronics

The NASA Goddard Space Flight Center has extensively qualified and utilizes TC600 for high reliability space flight electronics applications. TC600 (a polyimide-based system) sits at the top of the thermal performance ladder within the Arlon range, with Tg above 260°C and the documentation trail needed for space qualification.

Down-Hole Oil and Gas

Downhole drilling tools operate at temperatures that can exceed 175°C continuously, combined with mechanical shock and vibration. Down hole drilling is explicitly listed as a primary application for ceramic-filled polyimide grades like 84N, where the combination of thermal endurance and mechanical stability is non-negotiable.

Automotive Under-Hood Electronics

As EV powertrains push more electronics into high-heat zones, the under-hood environment is increasingly demanding. Engine management modules, power inverters, and high-current motor controllers can see sustained temperatures above 150°C near heat sources. Arlon 85N provides the Tg headroom that standard automotive-grade FR4 cannot.

Semiconductor Test and Burn-In

Semiconductor testing and burn-in PCBs are a classic Arlon polyimide application, because burn-in chambers operate at 125–150°C for extended periods, and the test boards need to survive hundreds or thousands of cycles without degrading.

High-Density Interconnect (HDI) and Microvia PCBs

Microvia PCBs used in mobile communication products benefit from Arlon’s polyimide systems when combined with demanding thermal requirements, particularly in advanced packaging where die temperatures are high and board z-expansion must be minimized to protect fragile microvias.

Compliance, Certifications, and Standards

When specifying Arlon polyimide for a program, you’ll need to understand the applicable standards:

Standard	Relevance to Arlon Polyimide
IPC-4101/40	Polyimide laminate and prepreg specification (base requirement)
IPC-4101/41	High-performance polyimide (covers 85N explicitly)
MIL-PRF-31032	Military PCB qualification; 85N commonly used
RoHS / WEEE	All polyimide grades are compliant
REACH	Compliant; no SVHCs in current formulations
UL94	Most grades carry HB rating; some V-0
AS9100	Arlon supports AS9100-certified supply chains for aerospace

Arlon EMD is the first U.S. laminator recognized under IPC’s Quality Product Listing. That’s a meaningful credential when you’re building a qualified supply chain for a defense or aerospace program.

Cost Considerations: What to Expect

Let’s be direct about cost, because it matters in real designs.

Arlon materials cost more than standard FR-4 — typically 2–5x for electronic substrates and 5–10x for microwave materials. The exact premium depends on the specific product and order volume. However, consider total cost: for high-reliability applications, the cost of field failures, rework, or warranty claims often far exceeds the material premium.

For a typical 12-layer aerospace board, the material delta between standard FR4 and Arlon 85N might add $50–$150 per panel depending on board size and volume. Against the cost of a field failure on an avionics assembly — which can run into five or six figures counting engineering investigation, rework, retest, and schedule impact — the polyimide premium is trivially justified.

Many engineers use a hybrid approach — Arlon for performance-critical layers, FR-4 for standard routing layers — to optimize the cost-performance balance. This is particularly effective in thick multilayers where only a subset of layers are thermal-critical.

How to Order and Work with Arlon Polyimide PCBs

If you’re ready to move forward with an Arlon PCB design, here are the practical steps:

1. Confirm your fab is qualified for polyimide processing. Not all shops are. Ask specifically about their polyimide lamination experience, plasma desmear capability, and whether they have run 85N before.
2. Share the full stackup including all prepreg grades and laminate part numbers. Don’t just say “polyimide” — specify 85N, 84N, or whatever grade you’ve selected.
3. Include processing notes referencing the Arlon data sheet lamination cycle parameters. This protects you if there’s a process deviation.
4. Specify IPC-4101/41 on your drawing for 85N-class materials. This gives the fab a clear spec to certify against.
5. Plan for longer lead times. Arlon polyimide materials are specialty items. Lead time for raw material can run 4–6 weeks versus 1–2 weeks for standard FR4. Factor this into your schedule.

Useful Resources for PCB Engineers

Here are direct links to datasheets, standards, and technical references you’ll actually use when working with Arlon polyimide:

Resource	Description	Link
Arlon 85N Official Datasheet	Full specs, lamination cycle, drill parameters	arlonemd.com
Arlon 84N Datasheet (PDF)	Ceramic-filled prepreg specs	epectec.com/downloads
IPC-4101 Standard	Laminate and prepreg specifications	ipc.org
Arlon EMD Product Page	Full product portfolio overview	arlonemd.com
MIL-PRF-31032	Military PCB performance specification	everyspec.com
IPC J-STD-001	Soldering requirements (relevant for lead-free assembly on polyimide)	ipc.org
PCBSync Arlon Guide	Independent engineer-focused material guide	pcbsync.com/arlon-pcb

FAQs: Arlon Polyimide PCB Laminates

Q1: Can I use Arlon 85N in the same fab shop that runs standard FR4?

Yes, provided the shop has polyimide processing capability. The key differentiators are: vacuum lamination (not all presses have this), plasma desmear capability, and experience with the longer lamination cycles polyimide requires. Always ask your fab directly whether they have 85N experience before committing.

Q2: Is Arlon polyimide compatible with lead-free assembly?

Absolutely — this is one of its primary advantages. With a Tg ≥250°C, 85N sits well above the 260°C peak temperature of lead-free assembly profiles. Compare that to standard FR4 (Tg ~150°C) being pushed through a 260°C reflow cycle, and you understand why polyimide is the correct choice for high-reliability lead-free assemblies.

Q3: What’s the difference between Arlon 84N and 85N?

85N is a pure polyimide laminate and prepreg system — it’s the core material for most applications. 84N is a ceramic-filled polyimide prepreg derived from 85N, designed specifically for filling clearance holes in metal-core boards or etched areas in multilayers with thick copper planes. In most standard multilayer polyimide designs, you use 85N throughout. You’d only bring in 84N when your stackup has metal cores or 2+ oz internal copper requiring hole fill.

Q4: How does Arlon polyimide compare to Rogers in an RF/microwave application?

Rogers materials (like RO4350B) have tighter Dk control and lower Df at microwave frequencies, making them the first choice for pure RF/microwave designs above 3 GHz. However, Arlon polyimide has significantly better thermal endurance. For hybrid applications — where a board needs both RF performance and high-temperature reliability — the solution is often a hybrid stackup: Rogers outer signal layers with Arlon 85N inner core layers.

Q5: What is the typical shelf life of Arlon polyimide prepreg?

Arlon 85N prepreg has a rated shelf life of approximately 6 months when stored at ≤21°C (70°F) and ≤50% relative humidity. Proper storage is critical — prepreg that has picked up moisture will not laminate correctly and can cause voids or delamination. Always check the date code on incoming prepreg and vacuum-desiccate before use regardless of age.

Conclusion

The polyimide PCB laminate guide question that most engineers are really asking is: “Is this expensive material worth it for my application?” The answer depends entirely on what your board needs to do and where it needs to do it.

For boards that live in benign environments, run below 130°C, and don’t face aggressive thermal cycling, standard FR4 is almost certainly the right answer. It’s well-characterized, universally processed, and inexpensive.

But for the boards that need to survive — avionics, military systems, downhole tools, high-current automotive electronics, semiconductor test fixtures — Arlon polyimide isn’t a luxury specification. It’s the correct engineering choice. The material premium is real, but it’s a fraction of the cost of qualifying a redesign after a field failure.

The key is matching the grade to the requirement: 85N for high-layer MLBs needing maximum thermal performance, 84N when you have metal cores or thick copper fill requirements, 85HP when thermal conductivity is part of the equation, and the low-flow grades (37N, 38N) when rigid-flex or HDI layer registration demands controlled resin movement.

Get the specification right, partner with a fab that knows polyimide, and Arlon gives you a board that will outlast most of the systems it’s built into.