Arlon 38N Laminate: The PCB Engineer’s Complete Guide to 2nd-Gen Low-Flow Polyimide

There’s a specific problem that keeps coming up in high-reliability rigid-flex designs: you need to bond multilayer polyimide stackups together, but you can’t afford to have resin flowing into component clearance areas, relief zones, or across exposed Kapton surfaces. Standard prepregs — even standard polyimide prepregs — have too much flow for this job. That’s exactly the problem Arlon 38N laminate was built to solve, and it does it better than most alternatives on the market.

I want to be direct here: 38N is a prepreg-only product. It’s not a copper-clad laminate like 35N or 85N. Its role in the stack is as a bonding layer — a very precisely controlled bonding layer — in applications where resin flow discipline matters as much as thermal performance. Once you understand that distinction, the rest of this material’s properties make a lot more sense.

What Is Arlon 38N Laminate? The Second-Generation Low-Flow Story

Arlon’s 38N is the second-generation 200°C glass transition temperature polyimide low-flow resin system, designed to improve adhesion and bond strength to Kapton® polyimide films, copper, and other metals. The “second-generation” label is worth paying attention to — 38N was specifically developed to address real shortcomings in first-generation low-flow polyimide prepregs, most notably bond strength to Kapton surfaces and cure consistency.

Novel chemistry ensures faster and more uniform resin cure for minimal and consistent resin flow, preventing excessive flow into clearance and relief areas. In a rigid-flex design, those clearance areas are where your flexible segments need to remain free to bend. Any resin bleed into those zones can stiffen or crack the flex region during service — a failure mode that typically doesn’t show up until field conditions.

The first-generation product in this design space was Arlon 37N. Both 38N and 37N polyimide resins have a glass transition temperature of 200°C and are specifically designed for high-layer-count rigid-flex where thermal performance is required. However, 38N is specifically engineered for greater adhesion to Kapton® surfaces used in rigid-flex printed circuit boards. If your application is a high-reliability military or aerospace rigid-flex where delamination at the polyimide interface is a failure mode, the upgrade from 37N to 38N for the bonding layer is a straightforward engineering call.

The Low-Flow Concept: Why Resin Flow Control Matters in Rigid-Flex PCBs

Most PCB engineers are familiar with prepreg flow as something to manage, not eliminate. For standard multilayer builds, you want the resin to flow enough to fill gaps, wet out inner-layer copper topography, and produce a void-free bond. The IPC-4101 specification sets minimum flow requirements for standard materials for exactly this reason.

Low-flow materials invert that logic. In rigid-flex construction, you’re bonding layers together across a structure that includes both rigid sections and flexible Kapton-based flex sections. Standard prepreg flow would push resin across the flex-to-rigid transition boundary, locking down areas that need to remain flexible. Controlled-flow prepreg keeps resin exactly where you put it — and nowhere else.

Attaching boards to a heat sink is a secondary lamination process that requires special materials and processes. This usually requires the absolute minimum flow possible so that the resin from the prepreg does not flow onto areas where components need to be attached. The metal and the board usually have different expansion rates, creating process difficulties to maintain flatness of the final assembly. Arlon 38N handles both of these use cases — rigid-flex bonding and heat sink attachment — with a single material system.

Arlon 38N Laminate: Complete Technical Specifications

These are the properties that matter for design and fabrication decision-making. Values are drawn from Arlon’s published datasheet and cross-referenced against MatWeb and the IPC-4101/42 standard.

Thermal Properties

Property	Value	Test Method
Glass Transition Temperature (Tg)	200°C	DSC & TMA
Decomposition Temperature (Td)	>311°C	TGA
Td at 5% Weight Loss	~330°C	TGA
Cure Temperature (minimum)	182°C (360°F)	Process
Cure Temperature (typical platen)	188–193°C (370–380°F)	Process
Cure Time at Temperature	90 minutes	Process
T-260 (time to delamination)	Exceeds standard	IPC TM-650
Lead-Free Reflow Compatible	Yes	—

Electrical Properties

Property	Value	Test Condition
Dielectric Constant (Dk)	~4.2	1 MHz
Dissipation Factor (Df)	~0.014	1 MHz
Surface Resistivity	High — meets IPC-4101/42	C-96/35/90
Volume Resistivity	High — meets IPC-4101/42	C-96/35/90
Dielectric Strength	>1000 V/mil	—
Arc Resistance	Meets IPC-4101/42	—

Mechanical Properties

Property	Value
Peel Strength to Copper (after thermal stress)	8.5 lb/in (1.5 N/mm)
Peel Strength to Copper (after process solutions)	8.5 lb/in (1.5 N/mm)
Peel Strength to Kapton (as received)	5.9 lb/in (1.0 N/mm)
Peel Strength to Kapton (after soldering)	5.2 lb/in (0.9 N/mm)
Flexural Strength	60 kpsi (414 MPa)
Water Absorption (24 hr)	<1.0%

Compliance & Certification

Standard	Status
IPC-4101/42	Meets requirements
UL 94	V-0 Rated
RoHS / WEEE	Fully Compliant
Lead-Free Soldering	Compatible
Halogen-Free	Yes

One item in that compliance table deserves special attention: the V-0 flammability rating. Unlike Arlon 35N which carries a V-1 rating, Arlon 38N laminate achieves V-0. For military and aerospace programs with strict flammability requirements, this distinction can affect your material qualification paperwork significantly.

The Kapton Bond Strength Advantage: What Makes 38N Different

This is the engineering detail that separates 38N from its predecessor and from generic low-flow alternatives. Improved bond strength to Kapton® polyimide of up to 50% compared with conventional polyimide low-flow or no-flow products. A 50% improvement in peel strength to the Kapton interface isn’t a minor refinement — in multilayer rigid-flex applications, that peel strength is your primary protection against delamination at the flex-to-rigid transition.

The typical failure mode in multilayer rigid-flex boards during thermal cycling is delamination at exactly this interface. The Kapton film has a Z-axis CTE that differs from the prepreg bonding layer, and every thermal excursion puts stress on that bond line. Conventional low-flow polyimide prepregs bond adequately at room temperature but tend to weaken faster under thermal cycling conditions. The 38N chemistry was designed with this specific failure mode in mind.

The peel strength to Kapton is 5.2 (0.9) lb/in (N/mm) after soldering. It is 5.9 (1.0) lb/in (N/mm) as received. Note that the post-solder peel strength — which is the value that actually matters for a board going into service — is still 5.2 lb/in. For a low-flow prepreg bonding to polyimide film, that’s a strong number and it’s driven by the novel chemistry in the 38N resin formulation.

Arlon 38N Laminate vs. Competing Low-Flow Materials: Side-by-Side

Understanding how Arlon 38N laminate fits into the broader low-flow prepreg landscape will help you make better material selections across different programs.

Arlon 38N vs. Arlon 37N: The Generation-to-Generation Upgrade

Property	Arlon 37N	Arlon 38N
Tg	200°C	200°C
Generation	1st Gen	2nd Gen
Bond Strength to Kapton	Baseline	Up to 50% higher
Cure Temperature (min)	177°C (350°F)	182°C (360°F)
Flammability Rating	V-0	V-0
IPC Compliance	IPC-4101/42	IPC-4101/42
Primary Advantage	Lower cure temp	Superior Kapton adhesion

Arlon’s 37N is a 200°C glass transition temperature polyimide low-flow resin system designed for bonding multilayer rigid flex, heat sink attachment to MLBs or other applications where minimal and uniform resin flow is required. 37N can be cured as low as 350°F and has excellent thermal stability. The practical decision between 37N and 38N comes down to your bonding substrate. If you’re bonding primarily to copper and glass, 37N’s slightly lower minimum cure temperature may offer a small processing advantage. If you’re bonding to Kapton film surfaces — as you typically are in polyimide rigid-flex — 38N’s superior adhesion chemistry is worth the 10°F cure temperature increase.

Arlon 38N vs. Arlon 49N Epoxy Low-Flow

Arlon’s 49N is a low-flow epoxy prepreg engineered for bonding multilayer epoxy rigid-flex or attaching heat-sinks to multilayer epoxy PCBs. With a high glass transition temperature of 170°C, the prepreg can be used in high-performance or high-temperature applications compared to a standard difunctional epoxy low-flow.

Property	Arlon 49N (Epoxy)	Arlon 38N (Polyimide)
Tg	170°C	200°C
Resin System	Epoxy	Polyimide
Max Operating Temp	~155°C	~185°C
Cost	Lower	Higher
Kapton Bond Strength	Moderate	Excellent
Best For	Epoxy rigid-flex	Polyimide rigid-flex

The matching principle matters here. The 37N and 38N are polyimide low-flow prepregs that match up well with PWBs manufactured with polyimide resin systems that require higher operating temperatures with the finished PWB. Primarily used in military or aerospace applications. If your base laminate is polyimide-based, 38N is the correct bonding prepreg. Using an epoxy low-flow to bond a polyimide multilayer creates a mismatched CTE interface that will underperform under thermal stress.

Arlon 38N vs. Arlon 35N: Understanding the Different Roles

Engineers occasionally ask whether they can use 35N prepreg for the same applications as 38N. The short answer is: they serve different purposes, and substituting one for the other is a process error, not a valid material swap.

Characteristic	Arlon 35N	Arlon 38N
Form Available	Laminate & Prepreg	Prepreg only
Tg	>250°C	200°C
Resin Flow	Standard	Low-flow / controlled
Purpose	Full stackup layers	Bonding layer only
Heat Sink Bonding	Not designed for	Yes, primary use case
Kapton Adhesion	Not optimized	Specifically engineered

35N is what you use for the core layers and standard prepreg layers in a high-temperature multilayer stackup. 38N is what you use at the bonding interface when you’re joining that polyimide stackup to a flex section or a heat sink. In a complex rigid-flex board, you may well have both materials in the same stackup — 35N for the structural layers, 38N at the flex bonding interface.

Where Arlon 38N Laminate Gets Used: Real Application Breakdown

Military and Aerospace Rigid-Flex PCBs

Arlon’s 38N and 37N polyimide resins are primarily used in military or aerospace applications and are specifically engineered for greater adhesion to Kapton® surfaces used in rigid-flex printed circuit boards. Military avionics systems routinely use high-layer-count rigid-flex boards to reduce connector counts, improve reliability, and fit complex circuitry into constrained 3D packages. When those boards need to survive temperature ranges from -55°C to 200°C — as many mil-spec boards do — you need a bonding prepreg that maintains peel strength through the full thermal excursion. 38N is designed for exactly this operating profile.

Heat Sink Bonding for Polyimide Multilayer Boards

Improved bond strength to copper and other metals for excellent performance in heat sink bonding applications. When you’re directly laminating a PCB to an aluminum or copper heat spreader, the resin in the bonding prepreg needs to wet the metal surface, develop high peel strength, and survive the CTE mismatch between the metal slug and the board material. 38N’s adhesion chemistry was specifically improved for this application. The low-flow characteristic is equally critical here — excessive resin flow would contaminate the component placement areas surrounding the heat sink zone.

Semiconductor Testing Equipment and Burn-In Boards

Typical applications for these materials include advanced commercial and military electronics such as avionics, semiconductor testing, heat sink bonding, high-density interconnect, and microvia PCBs. Burn-in boards are subjected to hundreds or thousands of thermal cycles between ambient and elevated temperatures, often with elevated voltage stress simultaneously. The combination of 200°C Tg and strong bonding to the metal retention hardware makes 38N a well-suited bonding prepreg for burn-in board assemblies.

High-Density Interconnect (HDI) and Microvia Applications

In HDI board construction, the controlled-flow characteristic of 38N prevents resin migration into the micro-drilled blind via structures during lamination. If resin flows into an unfilled blind via during the bonding lamination step, you lose the via connection and potentially create a void that won’t show up until you have field failures. Low-flow prepreg eliminates this failure mode at the lamination stage.

Space Electronics

Applications include military, aerospace, space, commercial and industrial PWB electronics. Space-grade PCB programs face the additional challenge that there’s no field servicing. A board that delaminated at the rigid-flex bonding interface because the prepreg bond strength degraded over a 15-year mission is not a problem you can recover from. The combination of 200°C Tg, V-0 flammability, polyimide chemistry, and strong Kapton bond strength makes 38N one of the go-to materials for space-qualified rigid-flex builds.

Processing Arlon 38N Laminate: Step-by-Step Fabrication Notes

These processing notes are drawn from Arlon’s published processing guide and should be treated as starting points — your actual parameters will depend on your specific press equipment, panel size, and stackup configuration.

Prepreg Storage and Pre-Lamination Preparation

Because of varying storage conditions, it is recommended that 38N prepreg be dried at 29″ (736mm) Hg for 12 to 24 hours. This vacuum-drying step is non-negotiable. Polyimide resins are more hygroscopic than standard epoxies, and moisture trapped in the prepreg at lamination becomes steam at cure temperature, creating voids and delamination blisters in the final panel. If you skip the pre-dry, you will eventually pay for it in scrap or field failures.

Store 38N prepreg at 60–70°F at 30% RH or below. Material that has been exposed to higher humidity should be given the full 24-hour vacuum dry before use regardless of appearance.

Lamination Process Parameters

38N Low-Flow prepreg is very process tolerant. It laminates well with either a cold platen press start or with a hot start. Vacuum or vacuum assist lamination is recommended for the removal of moisture and air. Low-Flow products do not displace air voids as well as standard prepregs, and vacuum will help assure a void-free final product.

The key process steps for lamination are as follows:

Vacuum draw down the package for 30 minutes at less than 29″ Hg prior to applying pressure in the press. Maintain the vacuum beyond the resin set point — above 320°F (160°C). Use a platen temperature in the range of 370°F–380°F (188°C–193°C). Control the heat rise to about 8°F–12°F per minute (4.5°C–6.5°C) between 210°F and 300°F. Cure time is 90 minutes at temperature.

That heat rise rate control window — 8°F to 12°F per minute between 210°F and 300°F — is where most press operators make mistakes. Too fast and you’ll trap volatiles as the resin gels prematurely. Too slow and you may not develop full bond strength. Use a calibrated press with verified platen temperature uniformity.

Post-Lamination Processing

The subsequent processing should be the same as those normally used for rigid-flex PCBs. After lamination, use standard polyimide-compatible desmear chemistry — alkaline permanganate or plasma (plasma preferred for positive etchback). Drill parameters should follow polyimide recommendations, not FR-4 defaults. Plating processes are compatible with standard polyimide board lines.

Available Prepreg Configurations for Arlon 38N

Arlon 38N is available in multiple glass cloth styles with different resin content levels. Selecting the right style depends on the gap fill and thickness requirements of your specific bonding application.

Style	Glass Cloth	Resin Content	Typical Use Case
38N0672	106	High	Thin bonding layers, HDI
38N8063	1080	Medium-High	Light gap fill needs
38N2650	2116	Medium	Standard multilayer bonding
38N2840	7628	Lower	Maximum thickness, larger gaps

For rigid-flex bonding applications, the 106 and 1080 styles are most commonly used because they keep the bonding layer thin and minimize total laminate thickness at the transition zone. For heat sink bonding where some gap fill is needed to accommodate surface irregularities, the 2116 or 7628 may give you better results.

Useful Resources for Arlon 38N Laminate

Resource	Description	Link
Arlon 38N Official Product Page	Full product description and features	arlonemd.com
Arlon 38N Datasheet (PDF)	Complete specs and lamination process guide	arlonemd.com PDF
Arlon Controlled Flow Prepreg Application Page	Comparison of all Arlon low-flow products	arlonemd.com
Arlon Heat Sink Bonding Application Guide	Detailed guidance on heat sink bonding with low-flow prepregs	arlonemd.com
MatWeb Arlon 38N Datasheet	Cross-reference database for material properties	matweb.com
UL Prospector — Arlon 38N	UL compliance data and property comparisons	ulprospector.com
IPC-4101 Standard Page	Base specification for rigid/multilayer base materials	IPC.org
PCBSync Arlon PCB Resource	Practical guide to the full Arlon PCB material family	Arlon PCB — PCBSync

Common Design Mistakes When Specifying Arlon 38N Laminate

Before the FAQ section, it’s worth calling out a few design and specification errors that come up repeatedly in practice. These are the mistakes that cause rework, qualification failures, or field issues.

Specifying 38N as a core laminate. 38N is a prepreg — it doesn’t come as a clad laminate with copper foil on both sides. If your BOM calls for 38N as a core layer with copper, your fabricator will come back to you with a problem. Use 35N, 85N, or another Arlon copper-clad laminate for your rigid core layers.

Using 38N with an epoxy-based board system. As discussed earlier, 38N is optimized for bonding within polyimide systems. If your core laminates are standard FR-4 or another epoxy system, you want an epoxy-based low-flow prepreg (49N or 51N) for compatibility. Mixing resin families at bonding interfaces creates CTE mismatch and adhesion problems.

Skipping the pre-dry step. The 12–24 hour vacuum dry at 29″ Hg before lamination is in the Arlon process guide for a reason. Shops that batch-process standard FR-4 without pre-drying often carry that habit over to polyimide materials. Don’t.

Incorrect drill parameters. Polyimide is tougher than cured epoxy and requires different drill bit geometry and speed settings. Using FR-4 drill parameters on 38N will cause hole wall damage, smear, and interconnect reliability problems downstream.

Frequently Asked Questions About Arlon 38N Laminate

1. What is the difference between Arlon 38N and Arlon 37N?

Both are low-flow polyimide prepregs with a 200°C Tg that meet IPC-4101/42, so on paper they look similar. The critical difference is that Arlon 38N provides improved bond strength to Kapton® polyimide of up to 50% compared with conventional polyimide low-flow or no-flow products. Arlon 37N can cure at a slightly lower minimum temperature (350°F vs. 360°F for 38N), but if your application involves bonding to Kapton film — as most polyimide rigid-flex designs do — 38N’s chemistry upgrade is worth the negligible process difference.

2. Can Arlon 38N laminate be used as a standard prepreg for building up core layers?

No. 38N is specifically a controlled low-flow bonding prepreg. Its resin flow is intentionally restricted, meaning it will not fill the topography gaps from inner-layer copper features the way a standard prepreg is designed to do. Using 38N as a standard prepreg layer in your stackup will result in voids and poor inner-layer bonding. Use it only where controlled low-flow is the design intent: flex-to-rigid bonding interfaces and heat sink attachment applications.

3. Is Arlon 38N laminate compatible with lead-free soldering?

Yes. Arlon 38N is compatible with lead-free solder processing and is RoHS/WEEE compliant. With a Tg of 200°C, the material has meaningful headroom above the 260°C peak temperature of lead-free reflow. The standard pre-bake before reflow (1–2 hours at 121°C) is recommended to drive out absorbed moisture before the board goes through the reflow oven.

4. What is the flammability rating of Arlon 38N?

Arlon 38N meets the UL 94 V-0 flammability standard. This material contains no halogen or lead components. V-0 is the most stringent standard flammability rating, requiring self-extinguishing in under 10 seconds and no dripping of burning resin. This is important for military and aerospace qualification, where V-0 is frequently called out as a minimum requirement in program specifications.

5. How does Arlon 38N perform in heat sink bonding versus rigid-flex bonding?

It was designed for both, but the chemistry was specifically upgraded for Kapton adhesion rather than metal adhesion. That said, Arlon 38N features improved bond strength to copper and other metals for excellent performance in heat sink bonding applications. For polyimide boards requiring direct lamination to aluminum or copper heat spreaders, 38N delivers higher metal adhesion than its predecessor. The 37N and 38N are polyimide low-flow prepregs that match up well with PWBs manufactured with polyimide resin systems that require higher operating temperatures. If your heat sink-bonded board is FR-4 or another epoxy system, 47N or 49N may be a better fit than 38N.

The Bottom Line on Arlon 38N Laminate

Arlon 38N laminate has a very specific job: bonding multilayer polyimide stackups — specifically polyimide rigid-flex — with controlled resin flow, excellent thermal performance, and genuinely superior adhesion to Kapton surfaces. It does that job better than its predecessor (37N) and better than generic alternatives in the low-flow polyimide space.

If you’re designing a high-reliability rigid-flex PCB for military, aerospace, or space applications, and your stackup includes Kapton-based flex sections, 38N belongs in your bonding prepreg spec. If you’re attaching a polyimide MLB to a metal heat sink and need the bond to survive long-term thermal cycling, 38N delivers the peel strength and CTE-matched performance to do it reliably.

The V-0 flammability rating, IPC-4101/42 qualification, and RoHS compliance round out the package for engineers who need a material that meets the procurement documentation requirements for regulated programs as well as the physical performance requirements for demanding environments.

For a broader look at the full range of materials available in the family, the Arlon PCB resource at PCBSync provides a useful overview of where each grade fits within the complete portfolio — worth bookmarking if you’re making material selections across multiple programs.