DuPont Pyralux AP8525E: 2 mil Adhesiveless Polyimide with ED Copper — Full Specs

If you’ve been specifying flex or rigid-flex laminates long enough, you’ll recognize the moment when a part number stops being just digits and starts telling you something useful. DuPont Pyralux AP8525E is one of those part numbers — once you know how to read it, every character is doing real work.

This article breaks down exactly what AP8525E is, what its numbers mean, what properties you can count on in production, and where it belongs (and doesn’t belong) in your stack-up. We’ll also touch on how it compares to the RA variant and why the choice between ED and RA copper matters more than most datasheets let on.

What Is DuPont Pyralux AP8525E?

DuPont™ Pyralux® AP is an all-polyimide double-sided copper-clad laminate considered the industry standard for thermal, chemical, and mechanical properties, making it ideal for rigid-flex and multilayer flex applications requiring advanced performance.

The AP8525E is a specific construction within that family:

Code Segment	Meaning
AP	All-Polyimide (adhesiveless) series
85	2 mil (50.8 µm) polyimide dielectric thickness
25	1 oz (35 µm) copper weight, each side
E	ED — Electrodeposited copper foil type

So when you order AP8525E, you’re getting a double-sided, adhesiveless laminate: 2 mil polyimide core, 1 oz ED copper cladding on both sides. No adhesive layer between the copper and the dielectric. That distinction is important, and we’ll get to why shortly.

AP8525E Full Specifications

The table below consolidates the key electrical, mechanical, and thermal properties for the AP8525E construction. These reflect typical values from DuPont’s official Technical Data Sheet for the AP double-sided clad series.

Electrical Properties

Property	Value	Test Method
Dielectric Constant (Dk) @ 1 MHz	3.4	IPC-TM-650 2.5.5.3
Dissipation Factor (Df) @ 1 MHz	0.002	IPC-TM-650 2.5.5.3
Dielectric Strength	>3,000 V/mil	IPC-TM-650 2.5.6
Surface Resistivity	>10¹³ Ω	IPC-TM-650 2.5.17.1
Volume Resistivity	>10¹⁵ Ω·cm	IPC-TM-650 2.5.17.1

Mechanical Properties

Property	Value	Notes
Polyimide Thickness	2.0 mil (50.8 µm)	±10% tolerance
Copper Thickness	1 oz / 35 µm per side	ED foil
Total Laminate Thickness (approx.)	~3.5 mil (88.9 µm)	Both copper layers included
Peel Strength (as received)	≥1.4 N/mm (8 lb/in)	IPC-TM-650 2.4.9
Tensile Strength (MD/TD)	~165 / 140 MPa	Film only
Elongation at Break	~70%	Film only

Thermal Properties

Property	Value	Standard
Glass Transition Temperature (Tg)	>300°C	DSC
Maximum Operating Temperature	180°C (356°F)	UL rating
Coefficient of Thermal Expansion (CTE)	~12–16 ppm/°C (X/Y)	IPC-TM-650 2.4.41
Flammability Rating	UL 94V-0	UL 796
Solder Float (288°C, 10s)	Pass	IPC-TM-650 2.4.13

Dimensional & Physical Properties

Property	Value
Dielectric Thickness Tolerance	±10%
Standard Sheet Size	12″ × 18″, 18″ × 24″ (custom available)
IPC Certification	IPC-4204/11
Quality System	ISO 9001:2015
Moisture Absorption	~2.5% (24 hr immersion)

Why “Adhesiveless” Changes Everything

This is something that gets glossed over in a lot of laminate comparisons, so let’s be direct about it.

Conventional flex laminates bond copper to polyimide using an acrylic or epoxy adhesive layer. That adhesive adds thickness, lowers the Tg significantly (often down to 90–130°C), and introduces a material with different CTE and moisture behavior into the stack-up. When you’re designing rigid-flex boards that will see multiple thermal cycles through assembly or harsh operating environments, that adhesive layer becomes your weakest link.

The 2 mil DuPont™ Pyralux® AP adhesiveless laminate supports advanced circuit designs through its core polyimide chemistry — including a low thermal expansion coefficient for rigid-flex fabrication and assembly, excellent thermal resistance to high-temperature assembly, and superior mechanical and electrical properties for severe environment applications.

With AP8525E, the copper is bonded directly to the polyimide through a chemical treatment process. You get a single-material dielectric system with:

• Higher effective Tg (polyimide Tg >300°C, no limiting adhesive layer)
• Lower and more predictable CTE
• Better dimensional stability through heat cycling
• Thinner total cross-section for the same copper and dielectric spec

For PCB engineers sourcing flex laminate for mil-aero, medical implantables (with appropriate certification), or high-density interconnect applications, this is not a small thing.

ED vs. RA Copper: Why the “E” Suffix Matters

The E in AP8525E means electrodeposited (ED) copper. The alternative — rolled annealed (RA) copper — would be designated AP8525R.

Property	ED Copper (AP8525E)	RA Copper (AP8525R)
Grain Structure	Columnar (vertical)	Rolled (horizontal)
Surface Profile	Rougher (higher Rz)	Smoother
Flex Endurance	Lower	Higher
Etching Behavior	Excellent uniformity	Good, slightly anisotropic
Cost	Lower	Higher
Typical Application	Rigid-flex, static flex, HDI	Dynamic flex, high-cycle flex

If your flex circuit is a static bend-to-install design, AP8525E (ED) works well and costs less. If it’s a dynamic application — think actuators, printer heads, or wearable sensors that flex thousands to millions of cycles — you want the AP8525R (RA copper).

For the majority of rigid-flex and multilayer flex boards where controlled impedance and thermal performance are the primary drivers, AP8525E is the appropriate call.

Controlled Impedance Design with AP8525E

For high-speed, high-frequency designs, the substrate choice is critical to success. The Pyralux AP material is weave-free, providing a smoother, homogeneous medium for improved signal integrity and a consistent dielectric constant for controlled impedance requirements.

The 2 mil dielectric with a Dk of 3.4 is well-suited for 50 Ω microstrip and 100 Ω differential pair designs. Unlike glass-reinforced substrates, there is no woven fiber texture — meaning signal propagation velocity is consistent across every routing direction. For RF flex circuits or high-speed differential pairs crossing the flex region, that isotropy is valuable.

DuPont’s own data shows that with a 2 mil thick AP core in a 50 Ω microstrip circuit, copper traces with 2× greater line/space resolution can achieve identical electrical performance while greatly reducing yield loss from fine-line imaging.

Fabrication Compatibility

AP8525E behaves consistently through standard flex circuit fabrication processes:

• Oxide treatment: Compatible
• Wet chemical PTH desmearing: Compatible
• Fine-line photolithography: Excellent — consistent dielectric thickness means tight impedance tolerance
• Coverlay lamination: Standard polyimide coverlay and bondply
• Multilayer press lamination: Lamination areas should be well ventilated with fresh air supply to avoid buildup from trace quantities of residual solvent (typical of polyimides) that may volatilize during press lamination.
• Lead-free solder assembly: Passes 288°C solder float

DuPont’s AP laminate is manufactured under a certified ISO 9001:2015 Quality Management System. Each manufactured lot is identified for reference traceability, and the packaging label serves as the primary tracking mechanism including product name, batch number, size, and quantity.

Typical Applications for DuPont Pyralux AP8525E

The 2 mil / 1 oz ED construction hits a sweet spot that makes it the most widely specified Pyralux AP SKU for a reason. It’s thick enough to handle without excessive care, thin enough for tight bend radii, and electrically consistent enough for impedance-controlled designs.

You’ll find AP8525E specified in:

• Aerospace and defense flex circuits — where thermal cycling range and Tg headroom are non-negotiable
• Rigid-flex HDI boards — in smartphones, tablets, cameras, and wearables
• Medical electronics — diagnostic equipment flex interconnects (not permanent implants)
• Automotive ADAS modules — radar and sensor flex circuits requiring dimensional stability
• High-frequency RF flex — antenna structures, mmWave test cables, and radar front ends
• Satellite and space electronics — for the combination of radiation stability and weight reduction

Boards manufactured from materials like AP8525E, including complex rigid-flex and HDI constructions, are sourced from specialized manufacturers. One well-regarded supplier in this space is DuPont PCB , which works with premium polyimide laminates for demanding flex and rigid-flex applications.

AP8525E vs. Other Common Pyralux AP Constructions

Part Number	Polyimide Thickness	Copper Weight	Copper Type	Common Use
AP7525E	1 mil (25 µm)	1 oz / 35 µm	ED	Ultra-thin HDI flex
AP8525E	2 mil (50.8 µm)	1 oz / 35 µm	ED	General rigid-flex, RF flex
AP8525R	2 mil (50.8 µm)	1 oz / 35 µm	RA	Dynamic flex applications
AP9125E	3 mil (76.2 µm)	1 oz / 35 µm	ED	Thicker cores, impedance control
AP8565E	2 mil (50.8 µm)	2 oz / 70 µm	ED	High-current flex circuits

Useful Resources for Designers and Fabricators

These are the primary sources worth bookmarking when working with DuPont Pyralux AP8525E:

Resource	Description	Link
DuPont Pyralux AP Official Page	Product overview, selector tool, and contact	dupont.com/pyralux-ap
Pyralux AP Technical Data Sheet (PDF)	Full electrical, mechanical, thermal tables	pragoboard.cz/download/pyralux_ap.pdf
IPC-4204/11 Standard	Flexible metal-clad dielectric specification	ipc.org
IPC-TM-650 Test Methods	Test methods referenced in the datasheet	ipc.org/TM
DuPont Safe Handling Guide	Handling, storage, and ventilation guidelines	pyralux.dupont.com
UL Product iQ	Verify UL 94V-0 / UL 796 certifications	iq.ul.com

Frequently Asked Questions About DuPont Pyralux AP8525E

Q1: What does the “E” suffix mean in Pyralux AP8525E — and when should I choose AP8525R instead?

The “E” designates electrodeposited (ED) copper foil. ED copper is produced by electroplating onto a rotating drum, which creates a columnar grain structure. It etches cleanly and consistently, making it the preferred choice for fine-line imaging and controlled-impedance traces. Choose AP8525R (rolled annealed copper) when the flex circuit will endure repeated dynamic bending, as RA copper’s horizontal grain structure offers significantly better fatigue resistance.

Q2: Is DuPont Pyralux AP8525E compatible with lead-free reflow assembly?

Yes. The all-polyimide construction of AP8525E has a Tg well above 300°C. It passes the standard 288°C solder float test per IPC-TM-650 2.4.13. Lead-free peak reflow temperatures (typically 245–260°C) are well within its operating window. The bigger concern in lead-free assembly is board-level warpage on the rigid-flex junction — manage this with appropriate core sequencing and carrier frames during reflow.

Q3: What is the minimum bend radius for AP8525E in a static flex application?

DuPont does not publish a single universal bend radius figure, as it depends on trace coverage, copper weight, and whether the flex is single or double sided. As a general guideline for double-sided 1 oz copper on 2 mil polyimide, a static bend radius of 10–15× the total laminate thickness is a conservative design rule. That works out to approximately 35–55 mils (0.9–1.4 mm) for this construction.

Q4: Can AP8525E be used for multilayer flex (more than 2 signal layers)?

Absolutely. AP8525E is a core laminate that can be stacked with additional AP cores and DuPont Pyralux bondply (such as FR8110 or LF8110 series) to build multilayer flex constructions. Fabricated circuits can be cover coated and laminated together to form multilayers or bonded to heat sinks using polyimide. Just ensure your layer count and copper distribution are balanced to control warpage.

Q5: What are the storage and handling requirements for AP8525E?

Pyralux AP is fully cured when delivered. Store rolls or sheets in original packaging, in a temperature-controlled environment (15–25°C, <70% RH), and away from direct UV exposure. Before processing, allow panels to equilibrate to shop floor temperature to avoid condensation. Lamination presses should be well ventilated — trace solvent residuals in the polyimide can volatilize under heat. When cutting or routing, use adequate dust extraction to minimize operator exposure.