Arlon 85NT laminate: full specs (Tg 240–245°C, CTE 6–9 ppm/°C, Td 426°C), polyimide on aramid prepreg configs, fabrication guide & avionics/satellite applications.

One correction before anything else: Arlon 85NT is not a cyanate ester laminate. It is a pure polyimide laminate and prepreg system reinforced with DuPont THERMOUNT® non-woven aramid fabric. Cyanate ester (also written BT or bismaleimide-triazine) is an entirely different resin family. If you have a spec sheet in front of you that labels 85NT as cyanate ester, it is incorrect. The Arlon datasheet and IPC-4101/53 qualification are unambiguous: this is pure polyimide on non-woven aramid. Making the wrong call here means ordering and processing the wrong material, so the distinction matters.

What Arlon 85NT actually delivers is the intersection of two performance axes that no other standard PCB laminate covers simultaneously. The first is extreme thermal stability — a pure polyimide resin with Tg of 250°C (resin), developing 240–245°C Tg in the finished laminate, with a decomposition temperature of 426°C. The second is aggressive CTE control — an in-plane (X,Y) coefficient of thermal expansion of just 6–9 ppm/°C, achieved through the DuPont THERMOUNT® non-woven aramid reinforcement. Neither glass-reinforced polyimide (Arlon 85N) nor epoxy/aramid (Arlon 55NT) delivers both axes together. That combination is precisely what the most demanding PCB applications — military avionics, missile guidance, satellite electronics, on-engine instrumentation — require.

This guide covers what Arlon 85NT is, its complete verified specifications, how it differs from closely related Arlon materials, its fabrication requirements, and the real engineering situations where it is the correct and sometimes only viable laminate choice.

What Is Arlon 85NT?

Arlon 85NT is a pure polyimide laminate and prepreg system with a glass transition temperature of 250°C, reinforced with DuPont Type E-200 Series THERMOUNT® non-woven aramid substrate. The resin content of the standard prepreg formulation is 49%. Arlon is a licensed laminator of the THERMOUNT® reinforcement system, meaning the non-woven aramid fabric is a DuPont product processed under license by Arlon Electronic Materials Division.

The material meets the requirements of IPC-4101/53 — the slash sheet specification for non-woven aramid fabric with polyimide resin laminates — and carries RoHS/WEEE compliance and lead-free processing compatibility. Arlon EMD is the first U.S. laminator recognized under IPC’s Quality Product Listing, and the only laminator to have achieved certification for all three slash sheets on polyimide materials (IPC-4101/40, /41, and /42), underscoring the depth of their polyimide process knowledge that 85NT inherits.

The polyimide resin formulation is non-MDA — it contains no methylene dianiline or other potentially carcinogenic diamines. This is an important qualification for aerospace and defense supply chains where material chemistry documentation is mandatory.

Understanding what THERMOUNT aramid reinforcement brings to the table is fundamental to understanding 85NT. Standard E-glass fibers have a CTE of approximately 5 ppm/°C along the fiber axis, but woven glass fabric produces in-plane laminate CTEs of 14–18 ppm/°C due to the woven geometry and the high resin content between fiber bundles. DuPont THERMOUNT aramid uses high-strength para-aramid fibers with a meta-aramid binder in a non-woven random distribution. The in-plane CTE of the finished laminate drops to 6–9 ppm/°C. This places the substrate CTE within close range of ceramic packages, copper, and many solders — reducing the CTE mismatch that is the root cause of solder joint fatigue failure in fine-pitch and area-array packages.

For engineers evaluating Arlon PCB materials for the highest-reliability applications in aerospace, defense, and industrial extremes, Arlon 85NT represents the ceiling of what conventional PCB laminate technology delivers without moving to exotic composite constructions.

Arlon 85NT Key Features at a Glance

Feature	Detail
Resin Type	Pure polyimide (non-MDA)
Reinforcement	DuPont THERMOUNT® Type E-200 non-woven aramid
Tg (Resin)	250°C
Tg (Finished Laminate, TMA)	240–245°C
Decomposition Temperature (Td)	426°C
In-Plane CTE (X, Y)	6–9 ppm/°C
IPC Qualification	IPC-4101/53
Weight vs. Glass-Reinforced	~25% lighter
Microvia Capability	Laser and plasma ablatable to 25 µm
Lead-Free Compatibility	Yes
RoHS/WEEE Compliance	Yes
Non-MDA Chemistry	Yes

The decomposition temperature of 426°C is notably higher than Arlon’s glass-reinforced polyimide 85N (Td 407°C). The aramid reinforcement itself contributes to this improvement. Higher Td means greater processing margin during multi-lamination sequences, lead-free assembly, and rework operations — directly reducing the risk of delamination in service.

Complete Arlon 85NT Electrical Properties

The dielectric constant stability of Arlon 85NT across frequency and construction is one of the less-discussed but practically important benefits of the non-woven aramid reinforcement architecture.

Electrical Property	Value	Test Method / Condition
Dielectric Constant (Dk) @ 1 MHz	3.8	IPC TM-650 2.5.5.3, C23/50
Dissipation Factor (Df) @ 1 MHz	0.015	IPC TM-650 2.5.5.3, C23/50
Volume Resistivity (C23/50)	>1.0 × 10³ MΩ·cm	IPC TM-650 2.5.17.1
Volume Resistivity (C96/35/90)	>1.0 × 10⁶ MΩ·cm	IPC TM-650 2.5.17.1
Surface Resistivity (C23/50)	>1.0 × 10³ MΩ	IPC TM-650 2.5.17.1
Surface Resistivity (C96/35/90)	>1.0 × 10⁴ MΩ	IPC TM-650 2.5.17.1
Electric Strength	1,300 V/mil	IPC TM-650 2.5.6.2

The Dk of 3.8 at 1 MHz is lower than glass-reinforced polyimide (Arlon 85N, Dk ~4.2 at 1 MHz) and lower than both standard FR-4 (4.2–4.8) and the epoxy/aramid Arlon 55NT (Dk 4.0). Aramid fibers have an intrinsically lower dielectric constant than E-glass, and that characteristic carries through to the laminate. For high-density digital designs where signal propagation delay across long signal paths on large boards matters, the lower Dk reduces latency and can simplify timing closure.

The absence of a periodic weave structure in the non-woven aramid reinforcement means there is no weave-induced Dk variation across the laminate surface. Woven glass FR-4 and polyimide laminates have measurably higher Dk over glass yarn bundles versus resin-rich regions between bundles — this creates impedance variation along the trace path that is a known issue in very high-speed signal integrity work. Arlon 85NT’s random fiber distribution eliminates this source of Dk non-uniformity.

The Df of 0.015 at 1 MHz is lower than epoxy-based materials (standard FR-4 at ~0.020–0.025) and consistent with the pure polyimide resin chemistry.

Arlon 85NT Full Thermal and Mechanical Properties

Thermal Properties

Thermal Property	Value	Notes
Tg (Resin system)	250°C	DSC
Tg (Finished laminate, TMA)	240–245°C	With conventional polyimide cure cycles
Decomposition Temperature (Td)	426°C	Higher than 85N (407°C) — aramid reinforcement contribution
CTE X-Axis (25°C to 125°C)	6–9 ppm/°C	IPC TM-650 2.4.41
CTE Y-Axis (25°C to 125°C)	6–9 ppm/°C	IPC TM-650 2.4.41
CTE Z-Axis	80–90 ppm/°C	Z-axis dominated by resin
Thermal Conductivity	0.25 W/mK	ASTM E-1225, 50°C
Solder Float (10 sec @ 288°C)	Pass	IPC TM-650 2.4.23
Solder Float (60 sec @ 288°C)	Pass	IPC TM-650 2.4.23

The gap between the resin Tg (250°C) and the finished laminate Tg (240–245°C TMA) reflects the interaction between the polyimide resin cure and the aramid reinforcement. This is consistent across the THERMOUNT product family and is well understood. For design purposes, the conservative value to use is 240°C — this still provides enormous thermal headroom above any lead-free soldering profile (peak ~260°C for brief duration) or realistic operating temperature environment.

The Z-axis CTE of 80–90 ppm/°C is notably better than the equivalent Arlon 55NT (110–120 ppm/°C). The polyimide resin inherently has better Z-axis thermal dimensional stability than multifunctional epoxy, and this translates to better plated-through hole reliability in thick multilayer constructions under repeated thermal excursions. For boards above 0.093″ finished thickness with high aspect ratio via holes, the improved Z-axis CTE of Arlon 85NT relative to 55NT is a meaningful reliability advantage.

Mechanical Properties

Mechanical Property	Value	Test Method
Tensile Strength	114 MPa (16.5 kpsi)	ASTM D-3039, A, 23°C
Tensile Modulus	15.6 GPa (2.26 Mpsi)	ASTM D-3039, A, 23°C
Flexural Strength	234 MPa (34 kpsi)	ASTM D-790, A, 23°C
Flexural Modulus	7.3 GPa (1.06 Mpsi)	A, 23°C
Shear Modulus	4.8 GPa (0.7 Mpsi)	ASTM D-3039, A, 23°C
Peel Strength	3.5 lb/in (0.6 N/mm)	IPC TM-650 2.4.8, Condition A
Specific Gravity	1.25 g/cm³	ASTM D-792, A, 23°C
Laminate Smoothness	2,200 Å	—
Water Absorption	0.60%	IPC TM-650 2.6.2.1

The specific gravity of 1.25 g/cm³ produces the advertised ~25% weight reduction versus conventional E-glass/polyimide laminates. At typical PCB thicknesses of 0.062″, a 12″ × 18″ panel of 85NT weighs roughly 25% less than the same panel in 85N (glass-reinforced polyimide). In aerospace and missile applications where every gram of payload is quantified, this weight reduction has direct program value.

Peel strength of 0.6 N/mm (3.5 lb/in) is lower than glass-reinforced laminates. Aramid fibers are organic polymer and bond to polyimide resin with less chemical affinity than the silica surface chemistry of E-glass. This is a known, characterized property and should inform copper pad design, surface finish selection, and any application where direct peel forces on copper features are a concern. For soldered assemblies on standard-size copper pads processed within normal design rules, peel strength is not a limiting factor.

Water absorption of 0.60% is the highest in the THERMOUNT product family (55NT is 0.45%, 55RT is 0.32%). The aramid polymer itself is modestly hygroscopic. Vacuum desiccation of prepreg before lamination and mandatory pre-solder bake are both essential process controls — not optional best practices.

The laminate surface smoothness of 2,200 Å is identical to 55NT and reflects the smooth surface generated by the random fiber distribution of non-woven reinforcement. This enables fine-line circuit definition with minimum photolithography exposure issues from surface topography, supporting trace widths below 75 µm (3 mils) and HDI circuit patterns.

Arlon 85NT Prepreg Configurations and Availability

Arlon 85NT prepreg is available on three DuPont THERMOUNT E-200 Series reinforcement styles, all at 49% resin content. The controlled flow of 7% — notably lower than Arlon 55NT’s 12% — means 85NT prepreg flows considerably less during lamination. This low flow characteristic is an important processing consideration in dense multilayer constructions where excessive resin bleed would compromise via clearances or inner layer feature geometry.

Arlon Part Number	MIL-S-13949 Designation	Reinforcement Style	Resin %	Ply Thickness (mils)	Flow %
85NT147	PBINA10xxxx49	E210	49%	1.8	7%
85NT247	PBINA16xxxx49	E220	49%	3.1	7%
85NT347	PBINA20xxxx49	E230	49%	3.9	7%

The three prepreg styles differ only in ply thickness (1.8 / 3.1 / 3.9 mils), providing designers with flexibility to achieve target dielectric thicknesses for controlled impedance stack-ups. The consistent 49% resin content and 7% flow across all three styles means any combination of ply styles within a multilayer stack produces uniform laminate properties — no Dk or CTE gradients from mixed prepreg styles.

Standard laminate cladding uses 1/2 oz and 1 oz HTE copper foil. Laminate sheet sizes up to 36″ × 48″ are available. Common core thicknesses are 0.005″, 0.006″, 0.008″, and 0.010″. The MIL-S-13949 qualification designations are available for programs requiring mil-spec material traceability.

Where Arlon 85NT Is Specified: Core Applications

Military and Commercial Avionics

Avionics PCBs operate in environments that combine high sustained operating temperatures, aggressive thermal cycling between cold soak and high-altitude operation, and the requirement for multi-decade service life with zero tolerance for field failures. Arlon 85NT’s Tg of 240–245°C provides complete thermal margin above any realistic avionics operating or processing temperature. Its CTE of 6–9 ppm/°C in the X-Y plane matches the CTE of ceramic LCCCs, ceramic BGAs, and flip-chip packages used extensively in avionics designs — preventing the solder joint fatigue failures that plague FR-4 and even standard glass-reinforced polyimide substrates in long-life thermal cycling applications.

The MIL-S-13949 qualification of Arlon 85NT prepreg provides the material traceability documentation that defense avionics programs require for supply chain qualification.

Missiles and Missile Defense Electronics

Missile and missile defense electronics demand materials that pass extremely demanding thermal shock and shock/vibration qualification profiles. The combination of lightweight construction (25% weight savings over glass-reinforced equivalents) and CTE-controlled solder joint performance makes Arlon 85NT particularly attractive for missile guidance and seeker electronics where both weight and reliability are mission-critical constraints. The high Td of 426°C also provides margin against the brief high-temperature exposure events that some missile electronic compartments experience.

Satellite and Spacecraft Electronics

Satellite thermal cycling in low earth orbit (LEO) can produce 15–16 thermal cycles per day between sun exposure and eclipse, with temperature swings from –40°C to +85°C or beyond depending on orbit and satellite position. Over a 10-year satellite lifetime, this amounts to 50,000–60,000 thermal cycles — a fatigue budget that FR-4 solder joint reliability cannot support for fine-pitch packages without underfill or other mitigations. Arlon 85NT’s CTE of 6–9 ppm/°C dramatically reduces the per-cycle solder joint strain, extending fatigue life by orders of magnitude relative to FR-4.

The material’s laser and plasma ablation capability for microvias down to 25 µm directly supports the high-density interconnect requirements of small satellite electronics, where board area is at an absolute premium. The ~25% weight reduction is directly valued in spacecraft mass budgets.

On-Engine and Aircraft Engine Instrumentation

Aircraft engine instrumentation boards sit closer to heat sources than almost any other avionics application. Exhaust gas temperature sensors, engine management units, and structural health monitoring electronics on modern turbofan engines can see sustained temperatures of 150°C+ with transient peaks well above 200°C. Standard polyimide (Arlon 85N on E-glass) handles the pure thermal performance requirement, but fine-pitch SMT packages on those boards face CTE mismatch fatigue from the engine’s own thermal cycling. Arlon 85NT solves both problems simultaneously — polyimide thermal performance plus CTE-matched substrate.

Copper-Invar-Copper (CIC) Replacement

Copper-Invar-Copper core constructions were historically used in high-reliability SMT boards specifically to reduce the effective in-plane CTE of the substrate assembly toward ceramic package CTE values. CIC adds significant weight and cost, requires specialized mechanical drilling (the hard Invar layer is difficult to drill cleanly), and adds procurement complexity. Arlon 85NT achieves comparable CTE values (6–9 ppm/°C) without any metal core constraint, using standard (for polyimide) PCB fabrication processes. Programs that specified CIC historically now have a lighter, potentially lower-cost path to equivalent CTE performance through Arlon 85NT.

High-Layer-Count Multilayer Boards

The combination of excellent Z-axis CTE (80–90 ppm/°C) and the high Tg of 240–245°C makes Arlon 85NT one of the most capable materials for very thick, high-layer-count multilayer constructions. The low Z-axis expansion during lead-free reflow preserves plated-through hole barrel integrity in boards exceeding 0.125″ thickness and layer counts above 24. The 7% prepreg flow is also appropriate for dense inner layer constructions where uncontrolled resin bleed would compromise feature geometry.

High-Density Interconnect (HDI) and Microvia Applications

Arlon 85NT is laser and plasma ablatable for microvia formation down to 25 µm (0.001″). The non-woven aramid reinforcement is essential for consistent microvia quality at small diameters — woven glass reinforcement produces variable via diameters because the laser encounters variable resistance at glass yarn bundles versus resin-rich inter-yarn regions. The random fiber distribution of non-woven aramid means the laser ablates material at a consistent rate, producing round, dimensionally consistent microvias hole after hole. For HDI build-up layers where microvia reliability and uniformity directly drive multilayer yield and reliability, this is a practical process advantage that justifies the material choice in its own right.

Arlon 85NT vs. Related Arlon Polyimide and Aramid Materials

Knowing which Arlon material to specify requires understanding where 85NT sits relative to closely related products.

Thermal and CTE Comparison: Arlon Polyimide and Aramid Family

Property	FR-4	Arlon 55NT	Arlon 35N	Arlon 85N	Arlon 85NT
Resin System	Difunctional epoxy	MF epoxy	Pure polyimide	Pure polyimide	Pure polyimide
Reinforcement	Woven E-glass	Non-woven aramid	Woven E-glass	Woven E-glass	Non-woven aramid
Tg °C (TMA/laminate)	130–145	170	>250	>250	240–245
Td (°C)	~300	368	407	407	426
CTE X,Y (ppm/°C)	14–17	7–9	14–16	14–16	6–9
CTE Z (ppm/°C)	60–70	110–120	51–60	50–60	80–90
Dk @ 1 MHz	4.2–4.8	4.0	4.2	~4.2	3.8
Df @ 1 MHz	0.020–0.025	0.018	0.010	~0.010	0.015
Water Absorption	0.15–0.25%	0.45%	0.26%	~0.25%	0.60%
Weight vs. FR-4	Baseline	~25% lighter	Baseline	Baseline	~25% lighter
Microvia Capable	No	Limited	No	No	Yes, to 25 µm
IPC-4101	/21	/55	/40, /41	/40, /41	/53

Reading this table, the choice context becomes clear. Arlon 85N (E-glass polyimide) achieves excellent Z-axis CTE and the highest Tg but has standard 14–16 ppm/°C in-plane CTE — fine for high-layer-count multilayers where the primary concern is barrel integrity, not SMT package solder joint reliability. Arlon 55NT achieves the CTE control but with an epoxy resin limited to 170°C Tg. Arlon 85NT is the only product that delivers both polyimide Tg and CTE-controlled substrate performance simultaneously.

Arlon 85NT Detailed Fabrication Guidelines

Inner Layer Preparation and Storage

Process inner layers through develop, etch, and strip using standard industry practices. Use brown oxide on inner layers, adjusting oxide bath dwell time to ensure uniform coating. Bake inner layers in a rack for 60 minutes at 107°C–121°C (225°F–250°F) immediately prior to lay-up.

Store prepreg at 60–70°F (16–21°C) at or below 30% relative humidity. Vacuum desiccate the prepreg for 8–12 hours prior to lamination. With 0.60% water absorption capability, Arlon 85NT prepreg is more hygroscopic than comparable epoxy materials — moisture control is not optional.

Lamination Cycle

Step	Parameter
Pre-vacuum	30 minutes
Heat rise rate	4.5–6.5°C (8–12°F) per minute between 100°C and 150°C (210°F and 300°F)
Cure temperature	218°C (425°F)
Cure start condition	When product temperature reaches 218°C
Cure time	3.0 hours
Cool down	Under pressure at ≤6°C/min (10°F/min)

The 3.0-hour cure time at 218°C is one of the most significant process distinctions from multifunctional epoxy laminates (which typically cure in 90 minutes at 185°C). This longer, higher-temperature polyimide cure cycle is what fully develops the 250°C Tg and the associated thermal and mechanical properties. Incomplete cure — attempting to shorten the cycle — directly compromises Tg and long-term reliability. Vacuum lamination is preferred.

Lamination Pressures by Panel Size

Panel Size (inches)	Pressure (psi)	Pressure/29″ (psi)	Vacuum (psi)
12 × 18	275	200	—
16 × 18	350	250	—
18 × 24	400	300	—

Drilling

Drill at 350–400 SFM. Undercut bits are recommended for vias 0.023″ (0.9mm) and smaller — note this threshold is larger than for woven-glass polyimide materials (0.018″), reflecting the aramid fiber characteristics. Standard carbide tooling is compatible, and tool life is dramatically extended compared to E-glass drilling. The non-woven random fiber distribution also reduces drill wander, improving hole location accuracy on fine-pitch via patterns. Chip-breaker style router bits are not recommended for profiling.

For microvias below 0.010″ diameter, laser ablation (CO₂ or Nd:YAG) is the preferred and most reliable method. Plasma ablation is also viable for microvia formation. Arlon 85NT achieves feature sizes down to 25 µm (0.001″) — a capability relevant for HDI satellites and high-density military electronics.

Desmear

Use alkaline permanganate or plasma desmear with settings appropriate for polyimide. Plasma is preferred when positive etchback is specified (common in high-reliability aerospace and military programs). Polyimide resin is more resistant to permanganate chemistry than standard epoxy, requiring longer dwell times or elevated process temperatures to achieve equivalent etchback. Process qualification runs should verify smear removal and etchback depth before production.

Post-Process and Pre-Assembly

Conventional electroless and electrolytic copper plating processes are compatible with Arlon 85NT without modification. Standard profiling parameters apply. Bake boards for 1–2 hours at 121°C (250°F) before solder reflow or HASL. Given the 0.60% water absorption, this bake is especially critical for 85NT compared to lower-absorption materials — moisture absorbed during storage or post-plate drying will cause delamination or blistering events during lead-free reflow if not driven off prior to solder exposure.

Useful Resources for Arlon 85NT Engineers

Resource	Description	Link
Arlon 85NT Official Product Page	Product description, IPC qualification, fabrication overview	arlonemd.com
Arlon 85NT Official Datasheet (PDF)	Full typical properties table, prepreg availability, lamination cycle	arlonemd.com (PDF)
Arlon 85NT/55NT/55RT THERMOUNT Family Datasheet	Side-by-side property comparison of all three non-woven aramid products	cadxservices.com (PDF)
MatWeb: Arlon 85NT Material Entry	Searchable properties database with unit conversions	matweb.com
UL Prospector: Arlon 85NT	Material entry with property data (free registration required)	ulprospector.com
Arlon Controlled CTE/SMT Application Page	Application context for 85NT and 55NT in SMT reliability designs	arlonemd.com
Arlon “Everything You Wanted to Know” Laminate Guide	Deep technical reference covering polyimide, CTE, Tg, and material selection	arlonemd.com (PDF)
ScienceDirect: Non-woven aramid-polyimide for spacecraft electronics	Peer-reviewed study of THERMOUNT polyimide (85NT-class) in HDI spacecraft PCBs	sciencedirect.com
IPC-4101 Specification	PCB laminate base specification; 85NT qualifies to /53 slash sheet	ipc.org

Frequently Asked Questions About Arlon 85NT

1. Is Arlon 85NT the same material as a cyanate ester laminate?

No. Arlon 85NT is pure polyimide, not cyanate ester. This confusion appears in informal sources and some vendor listings. Cyanate ester (BT) resin is a triazine-based system used in certain high-frequency and specialized packaging substrates — it is a completely different resin chemistry from polyimide. Arlon 85NT uses a Non-MDA pure polyimide resin (the same resin family as Arlon 85N) coated on DuPont THERMOUNT® non-woven aramid reinforcement. The correct resin classification is polyimide; the correct IPC designation is IPC-4101/53. Any specification referencing Arlon 85NT as cyanate ester should be flagged and corrected before placing a purchase order.

2. When should I specify Arlon 85NT instead of Arlon 85N?

The decision between 85NT (non-woven aramid polyimide) and 85N (E-glass polyimide) comes down to whether in-plane CTE control is a design requirement. Both materials deliver essentially identical polyimide thermal performance (Tg ~250°C, Td ~407–426°C), high-reliability PTH performance, and lead-free compatibility. The difference is the reinforcement. Arlon 85N on E-glass has in-plane CTE of 14–16 ppm/°C — correct for high-layer-count boards where the primary need is Z-axis expansion control and barrel reliability. Arlon 85NT on non-woven aramid drops in-plane CTE to 6–9 ppm/°C — necessary when fine-pitch ceramic packages, LCCCs, or high-I/O BGAs on the board will experience thermal cycling that would cause solder joint fatigue on a higher-CTE substrate. Specify 85NT when you need polyimide thermal performance AND CTE-matched substrate for SMT reliability. Specify 85N when you need polyimide performance for high-temperature processing and thick multilayers without the premium cost of aramid reinforcement.

3. What is the practical drilling difference between Arlon 85NT and standard glass-reinforced polyimide?

Non-woven aramid reinforcement in 85NT drills fundamentally differently from E-glass polyimide. Aramid fibers are organic polymer (aromatic polyamide) — they are much less abrasive to carbide tooling than silica-based E-glass, so drill tool life increases dramatically, commonly 3–5× or more compared to equivalent hit counts on glass-reinforced materials. Drill wander is also reduced because non-woven random fiber distribution eliminates the periodic high-resistance regions of woven glass yarn bundles that deflect drill tips laterally. For hole diameters above 0.023″, undercut bits are recommended — a slightly larger threshold than the 0.018″ cutoff for E-glass. Below 0.010″, laser ablation is preferred over mechanical drilling. One caution: the aramid fiber surface does not bond as aggressively to permanganate desmear chemistry as glass, so desmear qualification with the actual chemistry and dwell times used in production should be run before committing to a production process.

4. Does Arlon 85NT’s 0.60% water absorption create problems in standard PCB fabrication?

It can if moisture control is neglected. Arlon 85NT absorbs more moisture than lower-absorption materials in the product family (55NT at 0.45%, 55RT at 0.32%), and significantly more than glass-reinforced polyimide (85N at ~0.25–0.27%). The consequence of moisture entering a PCB laminate before soldering is steam generation at solder reflow temperatures. Above Tg, polyimide resin is in its rubbery phase and steam pressure will cause delamination or blistering that may not be visible externally but creates internal laminate defects that compromise reliability. The mitigations are straightforward: vacuum desiccate prepreg for 8–12 hours before lamination, store at 60–70°F at or below 30% RH, and bake fully processed boards for 1–2 hours at 121°C before any soldering operation. These are standard best practices for any polyimide laminate and must be followed with 85NT.

5. Can Arlon 85NT be used in a hybrid stack-up with standard FR-4 inner layers?

Hybrid constructions combining 85NT outer layers (or near-outer layers under fine-pitch SMT areas) with FR-4 inner cores are technically feasible but require careful analysis. The challenges are lamination cycle compatibility (85NT’s 218°C/3.0-hour polyimide cure will exceed the thermal capability of uncured FR-4 prepreg in the same press cycle — sequential lamination is typically required), Dk mismatch between the two materials (85NT Dk 3.8 versus FR-4 Dk 4.2–4.8, requiring separate impedance calculations for signal layers in each dielectric), and CTE mismatch between the inner and outer layer dielectrics during lamination. Sequential lamination approaches — laminating the 85NT layers onto a cured FR-4 core — are the most common hybrid construction method. For boards where the CTE control benefit of 85NT is localized to the outer surface layer (where fine-pitch packages are mounted) and the inner layers carry only power/ground planes, hybrid construction can be cost-effective. Consult with your laminate supplier and PCB fabricator before committing to a hybrid stack-up design.

Summary

Arlon 85NT is the pure polyimide on DuPont THERMOUNT® non-woven aramid laminate and prepreg system that occupies the most demanding corner of Arlon’s electronic substrate portfolio — simultaneously delivering Tg of 240–245°C (finished laminate), Td of 426°C, in-plane CTE of 6–9 ppm/°C, laser/plasma microvia capability to 25 µm, and ~25% weight reduction versus conventional glass-reinforced laminates.

No other standard PCB laminate combines polyimide thermal performance with CTE values in the range of ceramic packages and solder alloys. For avionics engineers designing boards that must pass MIL-SPEC thermal cycling, for satellite electronics engineers building hardware that must survive tens of thousands of orbit cycles, for guidance electronics engineers needing both lightweight construction and solder joint reliability with fine-pitch ceramic packages — Arlon 85NT is not one option among several. In many of these applications, it is the correct engineering answer.

It requires polyimide processing discipline: longer cure cycles at higher temperatures, mandatory vacuum desiccation, rigorous moisture management, plasma-preferred desmear, and careful drill parameter control. For fabrication shops with established polyimide process flows, these are normal controlled conditions. For shops new to polyimide, process qualification on Arlon 85NT before production is essential.

All property values are typical values sourced from official Arlon 85NT documentation. These are not specification limits. Properties may vary with design and application. Always verify against the current Arlon 85NT datasheet before finalizing a design specification.