Arlon 85NT: The Complete Engineer’s Guide to Ultra-High Tg PCB Material for Extreme Environments

If you’ve ever spec’d a board for avionics, missile defense, or satellite systems, you’ve almost certainly run into the question: “Is FR4 going to survive this?” The honest answer is usually no — and that’s exactly where Arlon 85NT enters the conversation.

I’ve seen engineers default to standard polyimide glass when they need elevated temperature performance, but for applications where CTE mismatch is a real failure mode and board weight actually matters, Arlon 85NT offers a genuinely different solution. This article walks through what makes it tick, when you should use it, and when something else might serve you better.

What Is Arlon 85NT? A Quick Background

Arlon’s 85NT is a pure polyimide with a high glass transition temperature of 250°C laminate and prepreg system, reinforced with a non-woven aramid substrate. The “NT” designation refers to the non-woven aramid (Nomex-type) reinforcement — it’s what makes this material behave fundamentally differently from conventional woven-glass polyimide systems like 85N.

85NT combines the high-reliability features of polyimide — improved PTH reliability and temperature stability — with the low in-plane (X,Y) expansion of 6–9 ppm/°C and outstanding dimensional stability of the aramid reinforcement.

For engineers who work across the Arlon PCB product line, 85NT sits in the “Controlled Thermal Expansion / SMT” category alongside 45NK and 55NT. The polyimide resin base is what separates it thermally from those two epoxy-based siblings.

Core Technical Properties of Arlon 85NT

Before making any material decision, you need numbers. Below is a consolidated property table for Arlon 85NT based on published datasheet values.

Arlon 85NT Key Properties at a Glance

Property	Value	Test Method
Glass Transition Temperature (Tg)	250°C	DSC
Decomposition Temperature (Td)	426°C	TGA
In-Plane CTE (X, Y)	6–9 ppm/°C	TMA
Z-axis CTE	Low (minimizes PTH stress)	TMA
Dielectric Constant (Dk) at 1 MHz	~3.7	IPC-TM-650
Dissipation Factor (Df) at 1 MHz	~0.008	IPC-TM-650
Moisture Absorption	~0.60%	IPC-TM-650
Flammability Rating	HB	UL 94
Weight vs. Glass Laminates	~25% lighter	—
Resin Content (standard prepreg)	~49%	—
IPC Qualification	IPC-4101/53	—
RoHS / WEEE Compliance	Yes	—
Lead-Free Assembly Compatible	Yes	—

A few of these numbers deserve more than just a table entry.

Understanding the Tg of 250°C in Practice

The glass transition temperature is often the headline spec, but it’s worth understanding what it means operationally. At or above Tg, the resin changes from a rigid glassy state to a more rubbery one — dimensional stability drops, Z-axis expansion accelerates, and you start accumulating PTH fatigue with every thermal cycle.

With a Tg of 250°C, Arlon 85NT gives you a very large buffer above lead-free solder reflow temperatures (typically 250–260°C peak, but only for seconds). For boards that will see multiple reflow passes — think double-sided SMT assembly or rework cycles — this margin matters enormously.

Compare that to standard FR4 at 130–170°C Tg. Even high-Tg FR4 (typically 170°C) leaves you with thin margins during lead-free processing. 85NT essentially removes that concern from the conversation.

The Decomposition Temperature of 426°C

High decomposition temperature offers outstanding high-temperature lifetime performance. At 426°C Td, Arlon 85NT far exceeds the 300–360°C typical of high-performance epoxies. This matters most in applications where boards experience sustained elevated temperatures — think engine bay electronics, downhole oil/gas equipment, or high-power amplifier assemblies that run hot continuously.

Why the 6–9 ppm/°C In-Plane CTE Is a Big Deal

This is arguably the single most important property for the SMT applications 85NT is designed around. Low in-plane expansion of 6–9 ppm/°C allows attachment of SMT devices with minimal risk of solder joint failure due to CTE mismatch.

Think about what this means for a BGA. Ceramic packages — common in military and high-reliability electronics — have CTEs in the 6–7 ppm/°C range. Conventional FR4 substrates at 14–17 ppm/°C create significant differential expansion under thermal cycling, which is a primary failure mechanism for solder joints. Arlon 85NT closes that gap dramatically.

85NT is commonly used to replace boards containing Copper-Invar-Copper in traditional CTE control applications, which is a meaningful statement — CIC cores add weight, cost, and fabrication complexity. Getting comparable CTE control from the laminate itself simplifies the stackup considerably.

Arlon 85NT vs. Other High-Performance Laminates

When you’re at the material selection stage, you’ll almost always be comparing 85NT against at least a few alternatives. Here’s how it stacks up honestly:

Comparison Table: Arlon 85NT vs. Common Alternatives

Parameter	Arlon 85NT	Arlon 85N	Standard FR4	High-Tg FR4	Rogers RO4350B
Tg	250°C	250°C	~130°C	~170°C	>280°C
Td	426°C	~407°C	~310°C	~340°C	~390°C
In-plane CTE	6–9 ppm/°C	~14–16 ppm/°C	14–17 ppm/°C	14–17 ppm/°C	~14 ppm/°C
Reinforcement	Non-woven aramid	Woven glass	Woven glass	Woven glass	Woven glass
Board Weight	~25% lighter	Baseline	Heavier	Heavier	Comparable
Laser/Plasma Drilling	Yes (to 25μm)	Limited	No	No	Limited
IPC Qualification	IPC-4101/53	IPC-4101/40,41	IPC-4101/21	IPC-4101/26	—
Typical Application	SMT CTE control, avionics	High-temp rigid boards	General purpose	Reflow-heavy boards	RF/microwave
Relative Cost	High	High	Low	Low-Med	High

The key differentiator between 85NT and 85N comes down to reinforcement type. Arlon 85NT is a composition of polyimide, stiffened with non-woven aramid substrate, which provides dimensional stability without adding additional weight to the laminated sheets. The 85N uses woven glass, which means higher in-plane CTE — perfectly fine for many applications, but not optimal when CTE-matched SMT is the priority.

What Makes the Non-Woven Aramid Reinforcement Special

If you’ve only worked with woven-glass laminates, the aramid reinforcement in 85NT requires a small mental shift. Here’s what changes:

Dimensional stability: Non-woven aramid fibers are randomly oriented, which produces more isotropic in-plane behavior compared to woven glass. There’s no “warp” and “fill” direction to worry about, which simplifies registration management in multilayer stackups. Non-woven aramid reinforcement provides outstanding dimensional stability and enhanced registration for improved multilayer yields.

Weight: Aramid (a polymeric fiber) is significantly less dense than E-glass. Polymeric reinforcement results in PCBs typically 25% lighter in weight than conventional glass-reinforced laminates. For aerospace and satellite applications where every gram matters, this is a non-trivial advantage.

Laser/plasma ablation: Arlon 85NT can be used for laser and plasma processes in the drilling of microvias, and blind and buried vias as small as 25μm. Woven glass is notoriously difficult to laser-drill cleanly — the glass fibers don’t ablate at the same rate as the resin. Aramid is fully organic, so UV laser drilling produces much cleaner sidewalls and smaller feature sizes.

Drilling considerations: The flip side of aramid reinforcement is that it requires specific tooling. Standard profiling parameters may be used, but chip-breaker style router bits are not recommended. Aramid fibers tend to fray rather than cut cleanly with conventional tooling — undercut drill bits are the standard approach for via drilling.

Typical Applications for Arlon 85NT

The material’s combination of properties gives it a fairly specific application niche. If your design doesn’t need at least two or three of these, you’re probably over-specifying:

Military and Defense Electronics

Typical applications include military and commercial avionics, missiles and missile defense, satellites, and other high-reliability SMT applications requiring low in-plane CTE. The controlled CTE is critical here because military ceramic packages (LCCCs, ceramic BGAs) have CTEs that are completely incompatible with FR4 over a -55°C to +125°C military temperature range.

Space and Satellite Systems

The combination of low weight and low CTE is almost tailor-made for satellite electronics. In space, thermal cycling is extreme — a low-earth orbit satellite can experience over 5,000 thermal cycles during a five-year mission as it passes in and out of direct sunlight. Solder joint fatigue is a well-documented failure mode, and minimizing CTE mismatch is one of the primary defenses against it.

Commercial Avionics

Modern avionics boards operate in a harsh combination of vibration, temperature extremes, and altitude-induced outgassing concerns. The PTH reliability improvements of polyimide combined with dimensional stability make 85NT a common choice for flight-critical electronics.

High-Reliability SMT with Fine-Pitch Packages

This material is designed for performance reliability with various interconnect packages including BGA (ball grid array), TSOP (thin small outline package), and FP-SMT (fine-pitch surface mount technology), where conventional substrates are more prone to solder joint cracking under thermal and power cycling due to CTE mismatch.

Semiconductor Burn-In Boards

Burn-in testing exposes boards to sustained elevated temperatures — sometimes 150°C or higher — for extended durations. Standard FR4 would be partially through its Tg range under these conditions. 85NT’s 250°C Tg gives you genuine thermal headroom for burn-in applications.

Fabrication and Processing Guidelines for Arlon 85NT

If you’re sending 85NT files to your fab, make sure they know what they’re working with. This is not FR4, and several process steps require adjustment.

Inner Layer Processing

Process inner layers through develop, etch, and strip using standard practices. Use brown oxide on inner layers and adjust dwell time in the oxide bath to ensure uniform coating. Bake inner layers in a rack for 60 minutes at 107–121°C immediately prior to layup. Vacuum desiccate the prepreg for 8–12 hours prior to lamination.

Lamination Parameters

In the lamination cycle, heat rise should be controlled between 4–6°C per minute. The starting temperature of the curing cycle is kept at 218°C for 2 hours. After curing is completed, cooling at 5°C/min is done. Vacuum lamination is preferred over hydraulic-only lamination for this material.

Drilling and Via Formation

Hole Size	Drill Speed (SFM)	Special Notes
Standard vias	350–400 SFM	Undercut bits recommended for ≤0.023″
Microvias ≥25μm	UV laser / plasma	Preferred method for HDI
Mechanical blind/buried	Plasma de-smear preferred	Alkaline permanganate also compatible

Post-drill baking at 121°C for 1–2 hours is required before HASL or any solder/reflow exposure.

De-smear

De-smear using alkaline permanganate or plasma with settings appropriate for polyimide — plasma is preferred for positive etchback. This is an important distinction from glass epoxy processing: plasma de-smear gives better via wall quality with aramid reinforcement.

Lead-Free Solder Compatibility

Arlon 85NT is fully compatible with lead-free assembly. The 250°C Tg provides the necessary buffer above peak reflow temperatures, and the material carries RoHS/WEEE compliance.

Moisture Absorption: What 0.60% Means in Practice

The moisture absorption of 0.60% is higher than PTFE-based microwave laminates (often <0.1%) but lower than many woven glass-polyimide systems. For most applications this is acceptable, but it does mean proper baking before assembly is non-negotiable.

This laminate is waterproof and has a low rate of water absorption, serving as a barrier to moisture condensation and not allowing the flow of water through its components. That said, for boards going through extended storage before assembly, following the manufacturer’s baking guidelines is essential to avoid popcorning or delamination during reflow.

CAF Resistance and Long-Term Reliability

Conductive Anodic Filament (CAF) formation is a reliability concern in densely packed multilayer boards operating in humid environments. The Arlon 85NT PCB material can withstand the procedures for electrochemical corrosion or migration, aiding its long-term durability through its CAF resistance.

This matters particularly for high-voltage-gradient boards or designs with fine-pitch BGAs where through-hole spacing is tight.

Arlon 85NT Processing Challenges: What Engineers Often Miss

Let’s be real about the parts that aren’t as clean as the datasheet makes them sound:

Tooling cost: Aramid fibers are abrasive in a different way than glass. Drill bits wear differently, and carbide tooling designed for glass laminates will not last as long. Plan for more frequent bit replacement or invest in tooling specifically rated for aramid-reinforced materials.

Routing: Chip-breaker style router bits are not recommended because aramid tends to fray. Standard straight-flute or compression-style bits work better. Your fab should know this, but confirm it.

Cost: High-Tg polyimide with aramid reinforcement is significantly more expensive than FR4 — typically 5 to 10 times more per panel depending on thickness and copper weight. If your design doesn’t need the CTE control or the thermal performance, you’re paying for capability you won’t use.

HB flammability rating: Unlike most FR4 variants which carry UL94 V-0, Arlon 85NT has an HB (horizontal burn) rating. This is worth checking against your design’s flammability requirements early — for some aerospace and industrial applications, V-0 is a hard requirement.

IPC-4101/53 Compliance

85NT is a pure polyimide laminate and prepreg system with Tg = 250°C, reinforced with a non-woven aramid substrate, meeting the requirements of IPC-4101/53. IPC-4101/53 specifically covers polyimide laminate with non-woven aramid reinforcement — this is the qualification standard your procurement team will reference when qualifying the material.

For defense programs operating under MIL-PRF-55110 or similar, the IPC-4101/53 qualification provides the documented traceability path that program offices typically require.

Frequently Asked Questions About Arlon 85NT

Q1: Can Arlon 85NT be used in standard PCB shops, or does it require specialized fabrication?

It requires a fabricator experienced with polyimide and aramid-reinforced materials. The lamination cycle, drill parameters, and de-smear process all differ from FR4. Not every shop has the process controls or tooling knowledge to run it reliably. Always confirm your fab’s experience with IPC-4101/53 materials before committing.

Q2: How does Arlon 85NT compare to Copper-Invar-Copper (CIC) for CTE control?

CIC cores achieve low CTE through a metal-composite structure, which adds significant weight and cost, and complicates drilling (you’re now drilling through metal layers). 85NT achieves similar CTE control through the aramid reinforcement, which is lighter, fully drillable with standard (adjusted) tooling, and doesn’t require the bonding or routing precautions that CIC involves.

Q3: Is the 0.60% moisture absorption a problem for space applications?

Space applications require thorough baking and outgassing qualification before flight. The 0.60% moisture absorption is manageable, but all boards should be baked per the manufacturer’s recommendations and tested for outgassing compliance (typically ASTM E595 for NASA programs). The low in-plane CTE and weight benefits generally make 85NT worthwhile for space use despite the moisture consideration.

Q4: Can I mix Arlon 85NT prepreg with other laminate cores in a hybrid stackup?

Hybrid stackups using 85NT prepreg with other core materials are possible, but CTE matching between layers needs careful analysis. Mixing polyimide-aramid with glass-epoxy in a multilayer can create internal stress concentrations during thermal cycling. Work with your stackup carefully and confirm with your fab before committing to a hybrid design.

Q5: What’s the minimum microvia size achievable with laser drilling on 85NT?

Arlon 85NT can form microvias using laser or plasma processes as small as 25μm. This makes it compatible with HDI designs requiring fine via structures, which is one reason it’s used in advanced packaging substrates with CSP and flip-chip interconnects.

Useful Resources for Arlon 85NT

Here are the key reference documents you’ll want when working with this material:

Resource	Description	Source
85NT Official Product Page	General information, key features, and product links	arlonemd.com
85NT Datasheet (PDF)	Full electrical, mechanical, and thermal property data	arlonemd.com/wp-content/uploads/2020/04/85NT.pdf
85NT Processing Guide v1.3 (PDF)	Detailed fabrication parameters for lamination, drilling, and finishing	arlonemd.com/wp-content/uploads/2020/05/85NT-Processing-Guide-v1.3.pdf
IPC-4101 Standard	Specification for base materials for rigid and multilayer PCBs	ipc.org
MatWeb – 85NT Entry	Third-party compiled property data	matweb.com
Arlon EMD Resources Page	SDS sheets, application notes, certifications	arlonemd.com/resources
Hi-Rel Materials 85NT	Distributor data and alternative datasheet source	hi-relmaterials.com

Who Should Specify Arlon 85NT?

Let me sum this up from a practical standpoint.

Specify Arlon 85NT when:

• Your BGA or LCCC packages have CTEs in the 6–8 ppm/°C range and you’re doing thermal cycling qualification
• Board weight is constrained (aerospace, UAV, satellite)
• You need HDI with microvias down to 25μm in a polyimide system
• Operating temperatures will regularly exceed what high-Tg FR4 can reliably handle
• Your program requires IPC-4101/53 documentation traceability

Look at other options when:

• Cost is a primary driver and CTE mismatch isn’t a validated failure mode in your thermal model
• You need UL94 V-0 flammability rating — check the HB rating carefully against your requirements
• Your fab doesn’t have demonstrated experience with aramid-reinforced polyimide processing
• High-frequency RF performance is the primary need (consider Rogers or Arlon CLTE-XT instead)

Arlon 85NT is a purpose-built material for a specific class of problems. When your application actually fits those problems — fine-pitch SMT on ceramic packages in thermally demanding environments — it’s an outstanding solution. When it doesn’t, the cost and fabrication complexity don’t pay off.

For engineers building boards that have to work in the real world — the kind that launches into orbit, flies in aircraft, or guides a missile — getting the material selection right isn’t an academic exercise. It’s the difference between a board that survives 5,000 thermal cycles and one that doesn’t make it past the first few hundred.

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For more information on high-performance Arlon PCB materials and fabrication capabilities, visit Arlon PCB.