DuPont Pyralux AP-PLUS is a thick-core all-polyimide laminate built for high-speed flex PCB design. Learn specs, fabrication tips, applications, and expert design insights.

If you’ve ever spent a late night chasing impedance drift across a flex layer or fighting signal attenuation on a multi-gigabit trace, you already know how brutally unforgiving substrate selection can be at high frequencies. The DuPont Pyralux AP-PLUS is one of those materials that actually solves a real engineering problem rather than just checking a spec sheet box — and understanding exactly what it does (and why) can save you a lot of rework.

What Is DuPont Pyralux AP-PLUS?

DuPont Pyralux AP-PLUS is a thick-core, all-polyimide, copper-clad laminate designed specifically for high-speed, high-frequency flexible and rigid-flex PCB applications. It belongs to the broader DuPont PCB Pyralux AP family — a product line that has been the industry benchmark in adhesiveless flexible laminates for over three decades.

The key differentiator in the AP-PLUS variant is its thicker dielectric construction. While standard Pyralux AP products offer dielectric cores ranging from 0.5 to 6 mils, AP-PLUS extends to 8 mils and beyond. That extra thickness sounds counterintuitive for a flex product, but it opens significant advantages for controlled impedance circuit design — and that’s the crux of why this material exists.

AP-PLUS all-polyimide thick copper-clad laminates are ideal for double-sided, multilayer, and rigid-flex applications requiring advanced material performance and high reliability.

Why Thick Dielectric Matters in High-Speed Designs

Here’s something that trips up engineers moving from low-speed to high-speed design: as signal frequencies climb, the dielectric thickness isn’t just a mechanical property — it becomes a primary electrical parameter that directly governs your trace geometry, signal loss, and manufacturing yield.

For high-speed, high-frequency designs, the substrate choice is critical to success. Attenuation can be reduced by using AP-PLUS all-polyimide thick copper-clad laminates to create wider lines. Also, using low profile, smooth copper foil reduces attenuation by minimizing losses from the skin effect.

Think about what that means practically. A 75-ohm microstrip on a 4 mil substrate forces you down to extremely fine line/space geometries — we’re talking 4 mil lines on a 4 mil space, right at the edge of many fabricators’ capabilities. With an 8 mil thick AP-PLUS substrate, the same electrical output can be realized with 8–9 mil line/space traces, which offers a substantial manufacturing yield advantage. That’s the same impedance target, but with traces twice as wide and far easier to image reliably.

For any PCB engineer who has watched yield numbers crater on fine-line controlled impedance layers, that’s not a minor detail. That’s potentially the difference between a viable production process and a costly headache.

Key Technical Properties of DuPont Pyralux AP-PLUS

Electrical Performance

Pyralux AP delivers outstanding signal integrity and electrical performance, with a dielectric constant (Dk) of 3.4 and a low dissipation factor (Df) of 0.002. For a polyimide substrate, those numbers are competitive and stable across a wide frequency range.

One property that’s worth calling out specifically: AP-PLUS does not contain glass, which gives it exceptional isotropy. Routed signals will see the same dielectric constant no matter which direction they are routed on the circuit board. On glass-reinforced laminates, the weave pattern creates localized variations in Dk that can be a real problem for skew-sensitive differential pairs. That issue simply doesn’t exist with Pyralux AP-PLUS.

Dimensional and Thickness Tolerance

AP-PLUS provides designers a consistent dielectric constant for controlled impedance circuit requirements, with tight thickness tolerance choices in contrast to other products at 15–20% thickness tolerance. When you’re targeting a specific impedance, that tolerance feeds directly into your final result. A 10% dielectric thickness variation on a 50-ohm trace can translate into several ohms of impedance error — enough to cause reflections on fast edges.

Thermal and Mechanical Properties

Pyralux AP offers low CTE for rigid-flex multilayers, excellent thermal resistance, and full compatibility with PWB industry processes. It is IPC-4204/11 certified, UL 94V-0, UL 796 listed, with a maximum operating temperature of 180°C (356°F).

The material’s low coefficient of thermal expansion (CTE) is particularly relevant for rigid-flex assemblies that undergo solder reflow. Mismatch between the flex section and the rigid laminate can cause delamination or trace cracking over time. The AP chemistry’s CTE brings the flex layer much closer in line with the rigid sections, improving long-term reliability.

Pyralux AP-PLUS Product Specifications at a Glance

The table below summarizes the core specifications for the AP-PLUS family alongside the standard AP series for comparison:

Property	Pyralux AP (Standard)	Pyralux AP-PLUS
Dielectric Construction	All-polyimide, adhesiveless	All-polyimide, adhesiveless
Dielectric Thickness	0.5 – 6.0 mils (standard)	7.0 – 8.0+ mils (thick core)
Copper Thickness Range	6 – 70 µm (0.25–2.0 oz)	18 – 70 µm (0.5–2.0 oz), RA or ED
Dielectric Constant (Dk)	~3.4 @ 1 MHz	~3.4 @ 1 MHz
Dissipation Factor (Df)	~0.002 @ 1 MHz	~0.002 @ 1 MHz
Glass Reinforcement	None (isotropic)	None (isotropic)
Thickness Tolerance	±5–10%	±5–10% (tighter than industry avg.)
Max Operating Temp	180°C (356°F)	180°C (356°F)
IPC Certification	IPC-4204/11	IPC-4204/11
UL Rating	UL 94V-0, UL 796	UL 94V-0, UL 796
Quality System	ISO 9002	ISO 9002

Available Constructions and Sheet Sizes

Standard AP product codes follow a straightforward naming convention. The suffix “R” indicates rolled-annealed (RA) copper foil, while “E” denotes electro-deposited (ED) foil. “D” suffix indicates rolled-annealed double-treat foil. RA copper is generally preferred for dynamic flex applications due to its better fatigue resistance. ED copper offers a smoother surface profile, which is relevant for high-frequency signal loss.

AP-PLUS all-polyimide thick copper-clad laminates are supplied in standard sheet sizes. Custom sizing up to 100 inches in length (2.54 meters) is available through request to your DuPont representative, as are additional copper types and double-sided constructions. Specialty dielectric thickness constructions can also be accommodated.

The table below shows representative AP-PLUS construction options:

Product Code	Dielectric Thickness (mil)	Copper Thickness (µm / oz)	Copper Type
AP-PLUS 8535R	8.0	18 / 0.5 oz	RA
AP-PLUS 9131R (thick)	8.0	35 / 1.0 oz	RA
AP-PLUS 9232R (thick)	8.0	70 / 2.0 oz	RA
Custom constructions	7.0–20.0	Per spec	RA or ED

Note: Always confirm current product codes and availability with your DuPont or authorized distributor representative, as the product line is periodically updated.

Fabrication and Process Compatibility

One of the practical selling points of the AP-PLUS series is that you don’t need to retool your shop to use it. AP-PLUS all-polyimide thick copper-clad laminates handling and processing requirements are identical to standard AP clads. They are fully compatible with all conventional flexible circuit fabrication processes.

That means wet chemical plated-through-hole, oxide treatment, standard lamination processes with polyimide, acrylic, or epoxy adhesives — all of it carries over without modification. For fabricators already running Pyralux AP in production, qualification of AP-PLUS is a straightforward process rather than a ground-up process development exercise.

AP-PLUS copper clads are manufactured under a quality system registered to ISO 9002. The clads are certified to IPC-4204/11. Complete material and manufacturing records, which include archive samples of finished product, are maintained by DuPont. Each manufactured lot is identified for reference and traceability.

That lot traceability matters in aerospace, medical, and defense programs where material certification is not optional.

Storage Requirements

AP-PLUS does not require refrigeration and should be stored in the original packaging at temperatures of 4–29°C (40–85°F) and below 70% relative humidity. The product should not be frozen and should be kept dry, clean, and well protected.

Compared to some pre-preg materials that need temperature-controlled warehouses, that’s a practical advantage for shops without specialty storage infrastructure.

Where DuPont Pyralux AP-PLUS Gets Used

High-Speed Digital and RF Applications

Controlled electrical impedance is required in a large portion of high-performance circuit designs. Packaging density, increasing clock frequencies, and interconnection demands have generated the need for differential impedance designs of 100 ohms and greater. AP-PLUS’s thick dielectric and consistent Dk make it the material of choice when those targets need to be hit reliably in production.

Industry Application Summary

Industry	Typical Use Case
Aerospace & Defense	Avionics flex assemblies, satellite systems, radar interconnects
Automotive	ECUs, ADAS sensor flex circuits, in-cabin control interfaces
Medical Devices	Diagnostic imaging equipment, wearable sensors, implant-adjacent electronics
Telecommunications / 5G	Antenna flex circuits, base station interconnects, mmWave modules
High-Speed Computing	Server backplane flex sections, GPU interconnects, co-packaged optics

Pyralux AP-PLUS vs. Standard Pyralux AP: When to Choose Which

Choosing between standard Pyralux AP and AP-PLUS comes down primarily to your controlled impedance requirements and your fabricator’s capability for fine-line imaging.

Design Scenario	Best Choice
Standard multilayer flex, moderate impedance tolerances	Pyralux AP (standard)
High-speed differential pairs, tight impedance control	Pyralux AP-PLUS
Ultra-thin flex with fine-line traces	Pyralux AP (thin core)
Improved manufacturing yield on controlled impedance layers	Pyralux AP-PLUS (thick core)
RF/mmWave antenna flex	Pyralux AP or AP-PLUS depending on Dk requirements
Rigid-flex with thermal cycling requirements	Either (both have excellent CTE performance)

Useful Resources for Designers and Fabricators

• DuPont Pyralux AP Official Product Page: https://www.dupont.com/electronics-industrial/pyralux-ap.html
• Pyralux AP-PLUS Datasheet (PDF via Cirexx): https://www.cirexx.com/wp-content/uploads/Pyralux_AP-Plus_DataSheet1.pdf
• Pyralux AP Full Laminate Datasheet (PDF): https://pwcircuits.co.uk/wp-content/uploads/2024/08/PyraluxAPclad_DataSheet.pdf
• IPC-4204/11 Flexible Metal-Clad Dielectrics Standard: Available via IPC.org
• DuPont Electronics & Industrial Materials Portal: https://www.dupont.com/electronics-industrial.html
• RayPCB – DuPont PCB Materials Guide: https://www.raypcb.com/Dupont-pcb/

Frequently Asked Questions About DuPont Pyralux AP-PLUS

1. What makes Pyralux AP-PLUS different from standard Pyralux AP?

The primary difference is dielectric thickness. AP-PLUS targets the 7–8+ mil range (thick core), while the standard AP series covers 0.5–6 mils. That thicker core is specifically engineered to improve controlled impedance manufacturing yield by allowing wider trace geometries for the same target impedance.

2. Does Pyralux AP-PLUS require any special fabrication equipment?

No. AP-PLUS is fully process-compatible with standard AP and conventional flexible circuit fabrication lines. There’s no need for new tooling, modified drilling parameters, or specialty lamination presses. If your shop already runs Pyralux AP, AP-PLUS drops in without major process changes.

3. Is AP-PLUS suitable for dynamic flex applications?

AP-PLUS with rolled-annealed (RA) copper can be used in flex-to-install applications. However, the thicker dielectric does increase the bending stiffness of the laminate. For continuous dynamic flex (high flex-cycle count), a thinner AP core is generally more appropriate. Always confirm the specific flex requirements with your fabricator.

4. What copper foil types are available on AP-PLUS?

Both rolled-annealed (RA) and electro-deposited (ED) copper foils are available, depending on the specific product code. RA copper is generally preferred for flex applications due to its improved fatigue resistance, while ED copper’s smoother surface profile offers marginal improvements in high-frequency signal loss due to reduced skin effect roughness.

5. How does the glass-free construction of AP-PLUS affect signal routing?

Because AP-PLUS contains no glass reinforcement, the dielectric constant is completely uniform throughout the material. This means routed signals — regardless of the angle at which they traverse the board — see the same Dk value. On glass-woven laminates, the weave pattern creates periodic Dk variation that can cause skew between differential pair lanes. That problem is eliminated with AP-PLUS, which is an important advantage in tight-tolerance differential impedance designs.

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