DuPont Pyralux AP9131R: 1 oz RA Cu / 3 mil PI Laminate — Specs & Flex Circuit Design

If you’ve been sourcing flex circuit materials long enough, you know the number “AP9131R” comes up constantly in rigid-flex stackup discussions. It’s one of those workhorse laminates that sits right in the sweet spot: thick enough to handle impedance-controlled traces reliably, thin enough to flex without cracking copper. This guide breaks down exactly what DuPont Pyralux AP9131R is, its full technical spec sheet, and how to use it effectively in flex and rigid-flex PCB design.

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What Is DuPont Pyralux AP9131R?

DuPont Pyralux AP9131R is a double-sided, copper-clad flexible laminate from DuPont’s Pyralux AP (All-Polyimide) product family. The construction is adhesiveless — the copper foil bonds directly to the polyimide dielectric without an intermediate acrylic or epoxy adhesive layer. That single fact has major downstream consequences for signal integrity, thermal performance, and dimensional stability.

The product code tells you almost everything you need to know once you learn the naming convention:

• AP = All-Polyimide series
• 9 = 1 oz (35 µm) copper foil
• 1 = first offering in that copper weight
• 3 = 3 mil (75 µm) polyimide dielectric
• R = Rolled Annealed (RA) copper foil

So AP9131R: 1 oz RA copper on 3 mil polyimide, double-sided, adhesiveless. Clean and simple.

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DuPont Pyralux AP9131R Full Specifications

Construction Parameters

Parameter	AP9131R Value
Product Code	AP9131R
Copper Thickness	35 µm (1.0 oz/ft²)
Copper Type	Rolled Annealed (RA)
Dielectric Thickness	75 µm (3.0 mil)
Construction	Double-sided, adhesiveless all-polyimide
Total Nominal Thickness	~145 µm (approx. 5.7 mil)
Standard Sheet Sizes	24×36 in, 24×18 in, 12×18 in (610×914 mm, 610×457 mm, 305×457 mm)
IPC Certification	IPC-4204/11
UL Rating	UL 94V-0, UL File E124294
RoHS Compliance	Yes
Max Operating Temp	180°C (356°F)

Electrical Properties

Property	Typical Value	Test Method
Dielectric Constant (Dk) @ 1 MHz	3.4	IPC-TM-650 2.5.5.3
Dielectric Constant (Dk) @ 10 GHz	3.2	ASTM D2520
Loss Tangent (Df) @ 1 MHz	0.002	IPC-TM-650 2.5.5.3
Loss Tangent (Df) @ 10 GHz	0.003	ASTM D2520
Dielectric Strength	200 V/µm	ASTM D149
Volume Resistivity	> 10¹⁷ Ω·cm	IPC-TM-650 2.5.17
Surface Resistance	> 10¹⁶ Ω	IPC-TM-650 2.5.17
Moisture & Insulation Resistance	> 10¹¹ Ω	IPC-TM-650 2.6.3.2

Thermal & Mechanical Properties

Property	Typical Value	Test Method
Glass Transition Temperature (Tg)	220°C	DuPont Method, TMA
CTE (XY-axis, below Tg)	~25 ppm/°C	IPC-TM-650 2.4.41
CTE (XY-axis, above Tg)	~30 ppm/°C	IPC-TM-650 2.4.41
Solder Float (288°C, 10 s)	Pass	IPC-TM-650 2.4.13
Moisture Absorption	0.8%	IPC-TM-650 2.6.2
Tensile Modulus	4.8 GPa	IPC-TM-650 2.4.19
Tensile Strength	345 MPa	IPC-TM-650 2.4.19
Elongation	50%	IPC-TM-650 2.4.19
Flexural Endurance	6,000 cycles (min.)	IPC-TM-650 2.4.3

Copper Peel Strength (Adhesion to Copper)

Condition	Typical Value
As Received	1.4 N/mm (8 lb/in)
After Solder Float	1.4 N/mm (8 lb/in)

The peel strength numbers are particularly important. RA copper combined with a direct polyimide bond gives you strong adhesion that holds up after assembly soldering — which matters a lot when you’re building dynamic flex zones exposed to thermal cycling.

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Where AP9131R Fits in the Pyralux AP Family

The AP series covers a wide range of copper/polyimide thickness combinations. The “3 mil PI / 1 oz Cu” combination that AP9131R represents sits in the middle of the lineup — not the thinnest option, but far from the bulkiest either. Here’s how it compares to its nearest neighbors:

Product Code	Copper Thickness	PI Thickness	Best Use Case
AP9111R	35 µm (1 oz)	25 µm (1 mil)	Ultra-thin flex, HDI, fine-line routing
AP9121R	35 µm (1 oz)	50 µm (2 mil)	General purpose flex, moderate impedance
AP9131R	35 µm (1 oz)	75 µm (3 mil)	Controlled impedance, rigid-flex cores
AP9141R	35 µm (1 oz)	100 µm (4 mil)	Thick-core impedance, low-frequency flex
AP9151R	35 µm (1 oz)	125 µm (5 mil)	High-power, heavy-duty constructions
AP8535R	18 µm (0.5 oz)	75 µm (3 mil)	Low-current, 3-mil PI, finer trace control
AP9232R	70 µm (2 oz)	75 µm (3 mil)	High-current power layers, same PI base

The 3 mil (75 µm) dielectric core is a key reason AP9131R keeps showing up in controlled impedance designs. Thicker dielectrics let fabricators use wider traces to hit target impedances — which means better fabrication yield, fewer open/short defects, and more consistent impedance across the panel.

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Why RA Copper Matters for Flex Circuit Design

The “R” suffix in AP9131R is not cosmetic. Rolled Annealed (RA) copper is manufactured by rolling copper ingots into thin foils and then annealing them to relieve work hardening. The resulting grain structure is elongated and parallel to the foil surface.

This matters in two main ways:

Flex endurance: RA copper bends without cracking far better than electro-deposited (ED) copper. In dynamic flex applications — think fold-down displays, wearable electronics, or connectors that articulate — RA copper can endure thousands of flex cycles where ED copper would develop micro-cracks and eventually fail. The 6,000-cycle minimum flexural endurance on AP9131R reflects the performance of RA foil directly.

Fine line etching: RA copper etches with better sidewall definition than ED copper. If you’re running tight trace/space rules — 3 mil / 3 mil or tighter — RA gives cleaner etch profiles and more predictable impedance results after fabrication.

The trade-off is cost: RA copper is more expensive than ED. But in aerospace, medical, or any high-reliability context, substituting ED to save a few dollars per panel is a risk most engineers won’t take.

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Flex Circuit Design with DuPont Pyralux AP9131R

H3: Controlled Impedance Design

One of the headline use cases for AP9131R is controlled impedance flex circuits. The 3 mil polyimide dielectric with a well-controlled thickness tolerance allows for predictable microstrip and stripline impedance calculations.

For a 50 Ω microstrip using AP9131R:

• Dielectric thickness (H): 75 µm (3 mil)
• Dielectric constant (Dk): 3.2–3.4 @ operating frequency
• Copper thickness (T): 35 µm (1 oz)
• Target trace width: approximately 5–6 mil depending on final plated copper thickness

DuPont’s own application data shows that the thicker 3 mil core outperforms a standard 2 mil core for yield in controlled impedance microstrip design — wider trace widths are possible for the same target impedance, which means etching tolerance has less relative impact on final impedance value.

H3: Minimum Bend Radius Guidelines

When designing flex zones with AP9131R, the total laminate thickness directly determines how tight a bend the circuit can make without copper fatigue. A common rule of thumb for dynamic flex (repeated bending) using RA copper is a minimum bend radius of 10× the total laminate thickness. For AP9131R:

• Total thickness: ~145 µm (~5.7 mil)
• Dynamic bend radius (minimum): ~1.5 mm (10× rule)
• Static bend radius (minimum): ~0.75 mm (5× rule, one-time fold)

These are conservative guidelines — actual limits depend on the number of copper layers, coverlay thickness, and whether stiffeners are present. For dynamic flex zones, always minimize copper layers and keep the neutral axis centered in the bend zone.

H3: Stackup Considerations for Rigid-Flex

AP9131R is commonly used as the flex core in 4-layer rigid-flex constructions. A typical stackup might look like:

Layer	Material
Top rigid prepreg	Standard FR-4 prepreg
Outer copper (rigid)	0.5 oz or 1 oz ED Cu
AP9131R — Cu layer 2	35 µm RA Cu (1 oz)
AP9131R — PI core	75 µm (3 mil)
AP9131R — Cu layer 3	35 µm RA Cu (1 oz)
Outer copper (rigid)	0.5 oz or 1 oz ED Cu
Bottom rigid prepreg	Standard FR-4 prepreg

The adhesiveless construction keeps the total dielectric thickness tight and predictable — important when the flex region needs to pass through a tight chassis gap or hinge.

For alternative high-reliability flex material sourcing, DuPont PCB  laminates are worth evaluating alongside Pyralux AP for multilayer rigid-flex applications.

H3: Processing Compatibility

AP9131R is compatible with all standard flex PCB fabrication processes. Key processing notes:

• Desmearing: Compatible with wet chemical permanganate desmear processes for through-hole plating preparation
• Oxide treatment: No issues; fully compatible before multilayer lamination
• Coverlay lamination: Bonds well with both polyimide and acrylic adhesive coverlays
• Surface finish: Compatible with ENIG, immersion tin, HASL, and OSP
• Assembly temperature: Passes 288°C solder float for 10 seconds — no issues with standard lead-free reflow profiles
• Storage: Keep in original packaging at 4–29°C, below 70% RH; 2-year shelf warranty applies under these conditions

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Applications for DuPont Pyralux AP9131R

This laminate is not a general-purpose choice. It earns its keep in applications where signal integrity, thermal resistance, and reliable flex behavior all have to co-exist:

Aerospace and defense — Avionics where weight reduction, high operating temperature, and controlled impedance RF interconnects are all required simultaneously.

Medical devices — Implantable-adjacent and diagnostic equipment requiring chemical resistance, thermal stability, and dynamic flex capability. (Note: DuPont explicitly flags that Pyralux AP is not for permanent implantation in the human body.)

High-speed data systems — With Dk of 3.2 at 10 GHz and Df of 0.003, AP9131R is a viable flex substrate for multi-gigabit signal routing where insertion loss must stay within spec.

Automotive electronics — Rigid-flex circuits in ADAS sensors, EV battery management systems, and camera modules benefit from the material’s wide thermal operating range and dimensional stability.

5G and RF flex — The consistent dielectric constant across the full 1–6 mil range and predictable loss tangent make the AP series materials a natural fit for millimeter-wave and sub-6 GHz antenna flex structures.

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Useful Resources for DuPont Pyralux AP9131R

Resource	Description	Link
DuPont Pyralux Official Product Page	Current product listings, selector tool	pyralux.dupont.com
Pyralux AP Data Sheet (PDF)	Full technical data sheet with all specs	Available via pyralux.dupont.com or distributor sites
IPC-4204/11 Standard	Flexible metal-clad dielectrics standard for Pyralux AP certification	IPC.org
IPC-TM-650 Test Methods	Reference for test methods cited in datasheets	IPC.org
Cirtech Electronics AP9131R Listing	Distributor page with product comparisons	cirtech-electronics.com
Pragoboard Pyralux AP PDF	Downloadable datasheet with full tables	pragoboard.cz
DuPont Safe Handling Guide	Processing and storage safety guidance	Available via pyralux.dupont.com
Doosan PCB Laminates	Alternative/complementary laminate supplier for rigid-flex	pcbsync.com/Doosan-pcb

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FAQs About DuPont Pyralux AP9131R

Q1: What is the difference between AP9131R and AP9131E?

The construction is identical except for copper type. AP9131R uses Rolled Annealed (RA) copper, which is preferred for dynamic flex applications due to its grain structure and superior bend endurance. AP9131E would use Electro-Deposited (ED) copper, which is better suited for static applications or designs where cost is a higher priority than flex cycle life. If your design involves any repeated bending, stick with the “R” variant.

Q2: Can AP9131R be used as an inner flex layer in a multilayer rigid-flex board?

Yes, and this is actually one of its primary use cases. The low CTE (~25 ppm/°C below Tg) keeps dimensional changes manageable during lamination and thermal cycling, which is critical for registration accuracy in multilayer builds. Its compatibility with oxide treatment processes also makes inner-layer bonding reliable.

Q3: What coverlay should I use with AP9131R?

DuPont offers Pyralux coverlay products designed specifically for use with the AP series. A polyimide coverlay with acrylic or polyimide adhesive is standard. If your application involves high-temperature exposure or tight dimensional tolerances, polyimide-adhesive coverlay is the better choice despite the higher processing temperature requirement.

Q4: Is AP9131R suitable for 5G and high-frequency RF designs?

For moderate RF frequencies (up to ~10 GHz), AP9131R is a solid choice. The Dk is 3.2 at 10 GHz with Df of 0.003, which is significantly better than acrylic-adhesive flex laminates. For mmWave applications (24 GHz+), you may want to evaluate Pyralux TA series or other low-loss alternatives specifically engineered for higher frequencies.

Q5: What are the standard sheet sizes and how is AP9131R supplied?

AP9131R ships in sheet form with standard sizes of 24×36 in (610×914 mm), 24×18 in (610×457 mm), and 12×18 in (305×457 mm). Roll form and custom sizes are available on request through DuPont or authorized distributors. Storage should be in the original sealed packaging at 4–29°C and below 70% RH to maintain the 2-year DuPont warranty.