Compare Arlon 85NT, 55NT, and 35N in this Arlon high Tg comparison — resin systems, aramid vs glass reinforcement, CTE, PTH reliability, and application decision guide.

Picking between Arlon’s high-performance laminate families is one of those decisions that looks simpler than it is. On the surface, Arlon high Tg comparison often comes down to a quick glance at the glass transition temperature — 250°C for 85NT and 35N, 170°C for 55NT — and designers assume the higher Tg product automatically wins. That thinking has caused more than a few expensive redesigns.

The real story is that 85NT, 55NT, and 35N are built around fundamentally different reinforcement strategies, resin systems, and failure modes. Getting this selection right means understanding not just what each material does, but what problem it was actually designed to solve. This guide covers that in depth, from the reinforcement chemistry to specific fabrication requirements, with the kind of detail that’s useful on the shop floor or during a design review.

Why the Reinforcement Material Matters More Than the Resin Alone

Before comparing the three products directly, it’s worth stepping back to understand what separates them at a structural level.

Both 85NT and 55NT use a non-woven aramid substrate — marketed under the DuPont Thermount trade name — as the reinforcement. This is the defining characteristic that sets them apart from 35N, which uses conventional woven fiberglass reinforcement. The aramid fiber is not glass. It’s a synthetic polymer (the same chemical family as Kevlar) with a dramatically lower coefficient of thermal expansion than glass. In-plane X-Y CTE values for aramid-reinforced laminates sit around 6–9 ppm/°C, compared to 14–18 ppm/°C for woven glass/epoxy systems. That single difference in reinforcement fiber is what makes 85NT and 55NT relevant to a whole class of high-density packaging problems that a woven glass polyimide like 35N simply cannot address the same way.

The resin difference matters too. 85NT uses a pure polyimide resin — the same resin family as Arlon’s 85N — giving it a Tg of 250°C. 55NT uses a multifunctional epoxy resin with a Tg around 170°C. 35N uses a pure polyimide resin on woven glass, also hitting 250°C Tg. So the Arlon high Tg comparison within this group is really a three-way trade between: thermal ceiling (resin-driven), dimensional control (reinforcement-driven), and processability/cost (both).

Arlon 85NT: Pure Polyimide on Non-Woven Aramid

Material Construction and Key Properties

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. 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.

The combination is unusual in the PCB laminate world because polyimide and aramid reinforce each other’s weaknesses. Pure polyimide on woven glass (like 35N) is excellent thermally but still subject to the CTE mismatch issues that plague conventional glass-reinforced boards when used with advanced packaging. Aramid fiber on epoxy (like 55NT) gives you the CTE control but not the thermal ceiling. 85NT delivers both simultaneously, at the cost of the highest complexity and typically the highest price of the three.

85NT is commonly used to replace boards containing Copper-Invar-Copper in traditional CTE-controlled constructions. That tells you something important about the application space: if a design previously needed a metal core composite to control CTE, 85NT is the PCB laminate answer. It’s relevant anywhere that LCC (leadless ceramic chip carriers), high I/O count BGAs, and large-die flip-chip packages create severe solder joint stress from CTE mismatch.

Polymeric reinforcement results in PCBs typically 25% lighter in weight than conventional glass-reinforced laminates. For aerospace and space applications where every gram matters, this is not a trivial consideration.

85NT Key Specifications

Property	85NT Value	Notes
Glass Transition Temp (Tg)	235–250°C	Effective Tg with aramid: ~235–245°C on conventional cure cycles
Decomposition Temp (Td)	426°C	Very high — excellent lead-free compatibility
In-plane CTE (X-Y)	6–9 ppm/°C	Matches silicon, ceramic packages closely
Z-axis Expansion (25–250°C)	~2.3%	Better than standard epoxy; benefit of polyimide resin
Moisture Absorption	0.60%	Higher than 35N — store and process carefully
Flammability Rating	HB	Not V-0; design this into system planning
IPC Standard	IPC-4101/53	Qualification reference for buyers
Drill SFM	350–400 SFM	Aramid requires sharp tooling; standard carbide drills smear

One property that catches engineers off-guard is the moisture absorption at 0.60%. This is higher than most woven glass polyimides, because aramid fiber is hygroscopic by nature. The prepreg must be vacuum-desiccated for 8–12 hours immediately before lamination, and inner layers should be baked at 107–121°C for 60 minutes before layup. Skipping these steps is a primary cause of delamination and measling in production.

Where 85NT Is the Right Choice

The cases where 85NT is clearly the right answer: high-layer-count boards with large ceramic or high-CTE-mismatch devices mounted on the surface, military and aerospace applications demanding 250°C Tg plus controlled in-plane CTE, boards replacing Copper-Invar-Copper constructions where weight reduction is also a target, and HDI boards where very fine via structures (down to 25μm blind/buried vias using laser or plasma drill) require a material that doesn’t crack under drill stress the way brittle glass-reinforced laminates can.

Arlon 55NT: Multifunctional Epoxy on Non-Woven Aramid

Material Construction and Key Properties

Arlon 55NT is a unique combination of multifunctional epoxy (Tg 180°C) on DuPont Type E-200 Series non-woven aramid reinforcement with a resin content of 49%. This material is designed for performance reliability with various interconnect packages: BGA, TSOP, FP-SMT, where conventional substrates are more prone to solder joint cracking under thermal and power cycling due to CTE mismatch of the mounted devices.

The multifunctional epoxy resin in 55NT is a step above basic difunctional FR-4 chemistry — it’s a tetrafunctional or multifunctional formulation that pushes Tg to around 170–180°C, well above standard FR-4 (Tg ~130–140°C) and meaningfully compatible with lead-free reflow profiles that reach 260°C peak. It’s not polyimide-level thermal performance, but it’s a practical upgrade for engineers who don’t need 250°C Tg but do need the dimensional stability benefits of aramid reinforcement.

The key differentiator from 85NT is cost and processability. Epoxy-based systems are inherently easier to process than polyimide: shorter cure cycles, less aggressive lamination conditions, and more fabricators who have qualified the full process. 55NT processes on standard epoxy lamination cycles, making it accessible to a broader range of contract manufacturers.

55NT Key Specifications

Property	55NT Value	Notes
Glass Transition Temp (Tg)	~170°C	Multifunctional epoxy; above standard FR-4
Decomposition Temp (Td)	368°C	Lower than polyimide grades
In-plane CTE (X-Y)	6–9 ppm/°C	Same aramid benefit as 85NT
Z-axis Expansion	~3.5%	Higher than 85NT; epoxy resin above Tg expands more
Moisture Absorption	0.30%	Lower than 85NT; easier to manage in production
Flammability Rating	UL94 V-0	Advantage over 85NT; V-0 without additional measures
IPC Standard	IPC-4101/55
Cure Temperature	~182°C (360°F) start	Standard multifunctional epoxy cycle

The V-0 flammability rating of 55NT versus the HB rating of 85NT is a genuine product selection driver in commercial applications. Any design going into consumer electronics, telecom infrastructure, or industrial equipment where UL94 V-0 certification is required at the board level will favor 55NT over 85NT — assuming the 170°C Tg ceiling is adequate for the application. If the system absolutely requires 250°C Tg and V-0 simultaneously, the Arlon 33N (woven glass polyimide, V-0) becomes relevant, though it loses the aramid CTE benefit.

Where 55NT Is the Right Choice

55NT is appropriate when: dimensional stability from the aramid reinforcement is needed for fine-pitch SMT reliability, but the thermal demands don’t justify polyimide-grade resin costs; the design includes high-I/O BGAs, TSSOPs, or LCCCs where solder joint reliability under thermal cycling is a concern; V-0 flame rating is required at the substrate level; and budget and fabricator access are constraints that polyimide processing would strain.

Think of automotive ECUs operating under the hood but below the threshold requiring aerospace polyimide, or telecom line cards with high-density BGA populations where solder joint reliability drives material selection more than raw thermal endurance.

Arlon 35N: Pure Polyimide on Woven Fiberglass

Material Construction and Key Properties

Arlon’s 35N is a 250°C high glass transition temperature polyimide resin system ideal for demanding applications that require low Z-axis directional expansion and resistance to PTH failures during operation in harsh environmental conditions. 35N has reduced temperature and cure times which offers improved throughput during manufacturing compared to traditional polyimide cycles.

The reduced cure time is the specific engineering point that separates 35N from its sibling 33N. Both use similar polyimide resin chemistry, both hit 250°C Tg, both address the same application space — but 35N’s faster cure cycle (90-minute cure at temperature versus longer cycles for 33N or 85N) translates to real throughput improvement in production. On a 16-layer MLB, that time difference compounds across the lamination book.

35N is tougher than conventional polyimides and is less prone to fracture during small hole drilling and profiling. 35N contains no MDA or other potentially carcinogenic diamines. The absence of MDA (methylene dianiline, a carcinogenic diamine historically used in some polyimide formulations) is an environmental compliance and health & safety point that matters in European markets and any supply chain subject to REACH regulations.

35N Key Specifications

Property	35N Value	Notes
Glass Transition Temp (Tg)	250°C	Full polyimide thermal ceiling
Decomposition Temp (Td)	406°C	Excellent; second-best in polyimide family
In-plane CTE (X-Y)	~14–16 ppm/°C	Woven glass — higher than aramid grades
Z-axis Expansion (25–250°C)	~1.5–1.7%	Excellent; low Z-CTE from polyimide resin
Moisture Absorption	0.26%	Lower than 85NT; easier production management
Flammability Rating	UL94 V-1	Flame retardant added; better than HB
IPC Standard	IPC-4101/40, IPC-4101/41	Standard polyimide qualification
Cure Temperature	213°C (415°F)	Standard polyimide cycle
Cure Time	90 min at temperature	Faster than 33N/85N cycles

The X-Y CTE of 35N sitting at 14–16 ppm/°C is the property that most clearly distinguishes it from the NT series. For applications where the primary concern is PTH reliability in a thick, high-layer-count board — not solder joint reliability on large ceramic packages — the Z-axis performance is what counts, and 35N delivers that with woven glass construction that most fabricators can handle with existing equipment.

Where 35N Is the Right Choice

35N is the workhorse of high-reliability commercial and military polyimide applications: oil and gas downhole electronics where sustained high temperatures eliminate FR-4 from consideration; aerospace control boards where 250°C Tg is spec’d but the layer count and component selection don’t justify aramid reinforcement; semiconductor burn-in test fixtures that see hundreds or thousands of thermal cycles; and thick MLBs (>0.093″ finished thickness) where Z-axis expansion control drives PTH reliability.

Applications for 35N include military, aerospace, down hole oil and gas drilling, commercial and industrial electronics. That’s a wide footprint for a single material, and it reflects the fact that 35N hits the sweet spot between maximum thermal performance and practical manufacturability.

Head-to-Head: Arlon High Tg Comparison Table

The following table puts all three materials side by side on the properties that actually drive the selection decision.

Property	Arlon 85NT	Arlon 55NT	Arlon 35N
Resin System	Pure Polyimide	Multifunctional Epoxy	Pure Polyimide
Reinforcement	Non-woven Aramid (Thermount)	Non-woven Aramid (Thermount)	Woven Fiberglass
Glass Transition Temp (Tg)	235–250°C	~170°C	250°C
Decomposition Temp (Td)	426°C	368°C	406°C
In-plane CTE (X-Y)	6–9 ppm/°C	6–9 ppm/°C	14–16 ppm/°C
Z-axis Expansion	~2.3%	~3.5%	~1.5–1.7%
Moisture Absorption	0.60%	0.30%	0.26%
Flammability (UL94)	HB	V-0	V-1
IPC Standard	IPC-4101/53	IPC-4101/55	IPC-4101/40, /41
Lead-Free Compatible	Yes	Yes	Yes
Board Weight vs Glass	~25% lighter	~25% lighter	Standard
Laser/Plasma Drilling	Excellent	Excellent	Standard
CAF Resistance	Very good	Very good	Good
Relative Processability	Most complex	Moderate	Moderate
Relative Cost	Highest	Medium	Medium-High

Fabrication Comparison: What Your CM Needs to Know

All three materials share some common processing requirements that distinguish them from standard FR-4. Understanding these before you send out for quotes will save you from surprises mid-project.

Process Step	Arlon 85NT	Arlon 55NT	Arlon 35N
Inner layer oxide	Brown oxide	Brown oxide	Brown oxide
Prepreg storage	< 30% RH; vacuum desiccate 8–12 hrs	Vacuum desiccate 8–12 hrs	< 30% RH; vacuum desiccate 8–12 hrs
Inner layer pre-bake	60 min at 107–121°C	60 min at 107–121°C	60 min at 107–121°C
Lamination pressure	275–400 PSI (panel size dependent)	Standard epoxy range	275–400 PSI
Cure temperature	218°C (425°F)	~182°C product temp	213°C (415°F)
Cure time at temperature	2 hours	Standard	90 min (faster than 85N)
Drill SFM	350–400 SFM	350–400 SFM	350 SFM
Drill bit style	Undercut bits for vias ≤ 0.023″	Undercut bits	Undercut bits for vias ≤ 0.018″
De-smear method	Plasma preferred	Plasma preferred	Plasma preferred
Pre-reflow bake	1–2 hr at 121°C	1–2 hr at 121°C	1–2 hr at 121°C

One note on drilling all three aramid-reinforced materials (85NT and 55NT): aramid fibers don’t cut cleanly with standard carbide PCB drill bits. They tend to fray rather than shear, which leaves fiber tails in the hole wall. Dedicated drill bits designed for aramid-reinforced composites — often with a compression or brad-point geometry — give significantly cleaner hole walls and improve plating adhesion in the subsequent metallization step. Any fabricator claiming experience with Thermount-based laminates should be able to confirm what tooling they use for aramid drilling.

Application Decision Matrix

Use this as a starting point when evaluating which material fits your design requirements.

Design Driver	Best Choice	Why
Maximum thermal performance (250°C Tg + 250°C+ Td)	85NT or 35N	Both use pure polyimide resin
Solder joint reliability on large BGAs/LCCCs	85NT or 55NT	Low X-Y CTE from aramid reinforcement
Thin, lightweight aerospace board	85NT or 55NT	25% lighter than glass-reinforced
UL94 V-0 flame rating required	55NT (or 33N for glass/polyimide)	85NT is only HB; 35N is V-1
Fastest cure / best production throughput	35N	Reduced cure time vs. 85N/85NT
HDI with laser microvia (≥25μm)	85NT or 55NT	Aramid drills cleanly with laser/plasma
CAF resistance for fine pitch BGA	85NT or 55NT	Non-woven aramid is inherently CAF-resistant
PTH reliability in thick MLB (>0.093″)	35N or 85NT	Low Z-axis expansion from polyimide resin
Cost-sensitive with CTE control	55NT	Epoxy process; lower cost than 85NT
Oil & gas downhole electronics	35N or 85NT	250°C Tg; sustained high temp operation
Bare chip (COB) or flip-chip attachment	85NT	Closest CTE match to silicon die

For Arlon PCB fabrication projects involving any of these three materials, confirming with your manufacturer which grades they have qualified process data for — not just which they claim to stock — is a critical step before committing to a design.

Useful Resources for Engineers

Resource	Description	Link
Arlon 85NT Official Datasheet	Full process parameters and property tables for 85NT	arlonemd.com/arlon_product/85nt
Arlon 35N Official Datasheet	Process guidelines and specifications for 35N polyimide	arlonemd.com/arlon_product/35n
Arlon 55NT Datasheet (PWCircuits)	Full property tables and lamination cycle for 55NT	pwcircuits.co.uk/wp-content/uploads/2024/08/55NT1.pdf
Arlon 35N Datasheet (Midwest PCB)	Alternative datasheet with process cycle details	midwestpcb.com/data_sheets/Arlon35N.pdf
Arlon Laminate Guide (Full PDF)	Comprehensive Arlon technical guide — all material families	arlonemd.com/wp-content/uploads/2020/05/Laminate-Guide.pdf
IPC-4101 Standard	Base materials standard — covers /40, /41, /53, /55 slash sheets	ipc.org
MatWeb Arlon 35N	Material property database entry for Arlon 35N	matweb.com
MatWeb Arlon 85NT	Material property database entry for Arlon 85NT	matweb.com

5 FAQs: Arlon High Tg Comparison — 85NT, 55NT, and 35N

Q1: What is the practical difference between the 250°C Tg of 85NT and the ~170°C Tg of 55NT?

The Tg is the temperature at which the resin transitions from rigid to rubbery state, and it has two major implications. First, Z-axis CTE below Tg is much lower than above Tg — above the Tg, a material can expand 3–4x faster in Z than below it, which is the primary driver of PTH barrel cracking under thermal cycling. A material with 250°C Tg will stay below its transition point throughout any realistic lead-free assembly process (260°C peak, brief), while a 170°C material is already above its transition at reflow temperatures. Second, long-term operating temperature: 55NT with a 170°C Tg shouldn’t be used in applications where the board will regularly operate above 130–140°C. For automotive under-hood or aerospace environments above 150°C sustained, 85NT or 35N are the only valid options from this product group.

Q2: Why does 85NT have a measured Tg of 235–245°C rather than 250°C?

The datasheet Tg for the pure polyimide resin in 85NT is 250°C, measured on the base resin system. However, when the resin is combined with the non-woven aramid reinforcement and cured under standard polyimide lamination cycles, the combined system typically measures 235–245°C by TMA. This is because the reinforcement fiber constrains the resin mobility during the glass transition, giving an effective Tg slightly below the neat resin value. In practice, this is not a reliability concern — 235–245°C is still far above any normal assembly or operating temperature — but it’s worth knowing when reading the datasheet versus test data from fabricated boards.

Q3: Can I substitute 55NT for 85NT to reduce cost if my board operates below 150°C?

Potentially yes, but with important caveats. If sustained operating temperature is below 130°C, 55NT’s 170°C Tg gives reasonable safety margin. The bigger question is usually about solder joint reliability on the specific components in your BOM — both materials share the same aramid reinforcement and thus the same X-Y CTE benefit, so for large-package BGA reliability under thermal cycling, 55NT can substitute for 85NT. The differentiators that remain are Td (368°C for 55NT vs. 426°C for 85NT, which matters if the board sees multiple high-temperature reflow cycles or rework), and flammability rating (55NT is V-0, 85NT is HB). If both those points are acceptable for your application, 55NT is a legitimate cost-reduction step from 85NT.

Q4: When should I choose 35N over 85NT for a high-layer-count aerospace MLB?

35N is the better starting point when: the layer count is high and the concern is PTH barrel reliability rather than solder joint reliability on large packages; the component density doesn’t include the extreme-CTE-mismatch devices (LCCCs, large die flip chips) that motivate aramid reinforcement; the board needs a UL94 V-1 rating rather than HB; or the fabricator doesn’t have qualified aramid drill tooling. The Z-axis expansion performance of 35N (~1.5–1.7%) is actually better than 85NT (~2.3%) because the woven glass constrains Z-direction expansion more effectively than non-woven aramid. For thick boards where PTH aspect ratio is the reliability driver, 35N’s lower Z-expansion is a real advantage. 85NT wins only when X-Y CTE control for surface-mounted devices is the primary concern.

Q5: How do I handle the higher moisture absorption of 85NT in production?

The 0.60% moisture absorption of 85NT (compared to 0.26% for 35N) requires more disciplined material management. Prepreg should be stored in sealed packaging at 60–70°F and below 30% relative humidity. Before lamination, vacuum desiccate the prepreg stack for 8–12 hours. For inner layers, bake at 107–121°C for 60 minutes immediately before layup — not hours before, but immediately before. If boards are being laminated in multiple sequential cycles, each cycle requires the same pre-bake discipline. The root failure mode when moisture management fails is voids in the bond line, which present as delamination or measling — sometimes visible on bare board inspection, sometimes only revealing themselves during thermal stress testing or field operation. A well-run polyimide shop treats moisture control as a first-tier quality control variable, not an afterthought.

Summary: Matching the Material to the Problem

The Arlon high Tg comparison among 85NT, 55NT, and 35N is ultimately a three-way decision between thermal ceiling, dimensional strategy, and practical constraints.

Choose 85NT when you need the full combination of 250°C polyimide thermal performance and low X-Y CTE from aramid reinforcement — typically driven by large ceramic packages, lightweight requirements, or the need for extremely fine via structures. It’s the most demanding material to process and the most expensive, but it’s the right answer for the applications where nothing else works.

Choose 55NT when CTE control from the aramid reinforcement is the primary driver but the application doesn’t demand 250°C Tg — high-density BGA boards operating below 150°C sustained, designs requiring V-0 flammability, or projects where fabricator availability and cost are meaningful constraints. It gives you most of the dimensional benefit of 85NT at significantly lower processing complexity.

Choose 35N when the driving concern is PTH barrel reliability in a thick, high-temperature, high-layer-count board where woven glass construction is acceptable — aerospace, military, and downhole applications where the 250°C Tg ceiling of polyimide is necessary but the component population doesn’t require aramid-level X-Y CTE control. Its faster cure cycle also makes it the most production-friendly of the three polyimide-resin options.