DuPont Pyralux AP9242R — 2 oz RA copper / 4 mil all-polyimide adhesiveless laminate for multilayer rigid-flex PCB design. Explore specs, stack-up guidance, current capacity, controlled impedance tables, fabrication tips, and FAQs from a PCB engineer’s perspective.
Specifying a flex core material for a multilayer rigid-flex stack-up is never a one-size-fits-all decision, but if your design carries higher current loads, demands robust thermal management, and still needs controlled impedance performance, DuPont Pyralux AP9242R is a construction worth putting at the top of your evaluation list. The combination of a 4 mil all-polyimide dielectric with 2 oz rolled-annealed (RA) copper on both sides hits a practical crossover point: thick enough copper for real power distribution work, a dielectric core that’s manageable for impedance control, and all-polyimide construction that holds up through multiple thermal cycles in a rigid-flex assembly. This article walks through what AP9242R actually is, where it earns its place in a stack-up, and the practical fabrication considerations every PCB engineer needs before they commit to it.
What Is DuPont Pyralux AP9242R?
DuPont Pyralux AP9242R is a double-sided, adhesiveless copper-clad laminate from DuPont’s flagship Pyralux AP all-polyimide flexible circuit materials family. Decoding the part number is straightforward once you understand the AP naming convention: “92” indicates 2.0 oz (70 µm) RA copper on both sides, “4” identifies the 4.0 mil (100 µm) polyimide dielectric thickness, and “R” designates rolled-annealed copper foil. The result is a symmetrical construction — same copper weight on both faces — bonded adhesiveless to a 4 mil polyimide film.
The adhesiveless architecture is the defining characteristic of the entire AP series. Conventional three-layer flex laminates sandwich an acrylic or epoxy adhesive between the copper and the polyimide film. That adhesive layer introduces additional Z-axis stress during thermal cycling, a higher dielectric loss contribution, and — critically for high-current applications — a thermal resistance that limits how efficiently heat moves through the stack. Removing it eliminates all three problems simultaneously, making AP9242R a fundamentally more thermally capable and dimensionally stable base for demanding multilayer designs.
AP9242R Core Construction Summary
| Parameter | AP9242R Value |
| Product Code | AP9242R |
| Dielectric Material | All-polyimide, adhesiveless |
| Dielectric Thickness | 4.0 mil (100 µm) |
| Copper Foil — Side 1 | 2.0 oz / ft² (70 µm) RA |
| Copper Foil — Side 2 | 2.0 oz / ft² (70 µm) RA |
| Construction | Double-sided, symmetrical |
| Dielectric Constant (Dk) | ~3.4 (1 MHz) |
| Dissipation Factor (Df) | ~0.002 (1 MHz) |
| Maximum Operating Temp | 180°C (356°F) continuous |
| Flammability Rating | UL 94V-0 |
| UL Listing | UL 796, File E124294 |
| IPC Certification | IPC-4204/11 |
| Quality System | ISO 9001:2015 |
Why 2 oz RA Copper Changes the Design Equation
The jump from 1 oz to 2 oz copper is not trivial from a design or fabrication standpoint. At 70 µm of copper versus 35 µm, you get roughly double the cross-sectional conductor area per unit trace width. The practical consequences for a design spec are real.
From a current-carrying perspective, a 10 mil trace at 1 oz copper can handle approximately 0.3–0.4 A before approaching the IPC-2152 temperature rise limits. The same 10 mil trace at 2 oz carries significantly more current with a lower resistive voltage drop. For power distribution layers in a multilayer rigid-flex assembly — supplying motor drivers, high-current bus bars, or RF PA supply rails — that copper weight difference can eliminate the need to widen traces to the point where they conflict with signal routing density.
The thermal conductivity argument is equally important. Thicker copper is a better lateral heat spreader. In a rigid-flex assembly where component dissipation is high and the flex zone passes close to hot components, 2 oz copper on the flex core layers conducts heat away from local hot spots better than 1 oz copper can. This is particularly relevant in automotive powertrain electronics and aerospace power conditioning modules where junction-to-ambient thermal resistance is a hard requirement.
The RA designation matters here exactly as it does in any flex application. Rolled-annealed copper has a grain structure parallel to the foil surface, which gives it superior resistance to fatigue cracking when the flex zone sees repeated mechanical deflection. For a power flex layer that also needs to survive several thousand flex cycles in service — think hinge connectors in foldable devices, or articulated robot arm interconnects — RA copper is not optional. Electro-deposited copper with its columnar grain structure will crack under cyclic flex stress long before RA copper does.
Decoding the AP9242R in the Context of the Pyralux AP Product Matrix
Understanding where AP9242R sits within the broader Pyralux AP lineup helps clarify when to specify it versus adjacent constructions. The table below shows the 2 oz copper family at various dielectric thicknesses, along with a few neighboring constructions for reference.
Pyralux AP 2 oz Copper Series vs. Adjacent Constructions
| Product Code | Side 1 Cu | Dielectric | Side 2 Cu | Cu Type | Primary Use Case |
| AP 9222R | 2 oz (70 µm) | 2 mil (50 µm) | 2 oz (70 µm) | RA | Very thin, high-current dual-sided |
| AP 9232R | 2 oz (70 µm) | 3 mil (75 µm) | 2 oz (70 µm) | RA | Moderate impedance, high current |
| AP9242R | 2 oz (70 µm) | 4 mil (100 µm) | 2 oz (70 µm) | RA | Multilayer rigid-flex, power flex |
| AP 9252R | 2 oz (70 µm) | 5 mil (125 µm) | 2 oz (70 µm) | RA | Wider trace impedance, heavy current |
| AP 9142R | 1 oz (35 µm) | 4 mil (100 µm) | 2 oz (70 µm) | RA | Asymmetric, mixed power/signal |
| AP 9141R | 1 oz (35 µm) | 4 mil (100 µm) | 1 oz (35 µm) | RA | Signal-optimized, same dielectric |
The 4 mil dielectric in AP9242R sits at a useful middle ground. Thinner cores (2 or 3 mil) with 2 oz copper become mechanically challenging — the copper-to-dielectric thickness ratio is very high, which can induce bow and twist in the panel during fabrication and makes controlled impedance calculations more sensitive to copper thickness variation. The 4 mil core restores the balance. It gives the polyimide enough body to control panel flatness and enough dielectric height that trace width tolerances don’t dominate impedance variation.
Key Electrical Properties for Multilayer Rigid-Flex Stack-Up Design
The electrical fundamentals of AP9242R mirror the rest of the Pyralux AP family: a Dk of approximately 3.4 and a Df of approximately 0.002 at 1 MHz. These are excellent numbers for any material, and for a DuPont PCB carrying high-speed differential pairs alongside power distribution, the low loss tangent keeps signal integrity manageable even as trace lengths extend across the flex zone.
The all-polyimide construction eliminates glass fiber weave from the dielectric, which matters for signal integrity in two specific ways. First, the Dk is isotropic — signals routed in any direction through the flex core see the same dielectric constant. Second, there is no periodic fiber-weave effect to create spatial variation in the effective Dk, which in glass-reinforced laminates creates a small but measurable insertion loss spike at specific spatial frequencies. On a 4 mil AP core, neither of these effects is present, and your pre-layout simulation Dk values stay accurate through fabrication.
For the power layers in a multilayer rigid-flex using AP9242R, the relevant electrical specification is not Dk but resistance. The sheet resistance of 2 oz (70 µm) RA copper is approximately 0.25 mΩ/square, which is exactly half that of 1 oz copper. That 2x reduction in resistance translates directly to lower I²R heating in power distribution traces, less voltage drop on supply rails, and better EMI containment from power plane copper pours.
Controlled Impedance Reference: AP9242R (4 mil PI, 2 oz RA Cu)
The following values are approximate and should always be verified with a field solver using actual fab process copper weights and dielectric tolerances.
| Impedance Target | Topology | Approx. Trace Width | Notes |
| 50 Ω single-ended | Microstrip (2 oz Cu) | ~6–7 mil | Wider than 1 oz equivalent due to copper thickness |
| 50 Ω single-ended | Stripline | ~4–5 mil | Depends on coverlay/bondply stack |
| 100 Ω differential | Microstrip edge-coupled | ~4 mil / 4 mil space | Tighter than 1 oz microstrip |
| 75 Ω single-ended | Microstrip | ~9–10 mil | Common for coax transition matching |
Note that 2 oz copper changes trace impedance predictions significantly compared to 1 oz. The copper thickness is no longer negligible relative to the dielectric height, and the trapezoidal cross-section of an etched trace becomes an important factor. Always use a field solver — not a simple closed-form model — when targeting ±5% impedance tolerance with 2 oz copper.
Where AP9242R Gets Specified
The particular balance of heavy copper and a mid-weight polyimide core puts AP9242R into a set of applications that standard 1 oz flex materials simply can’t address.
Military and Aerospace Avionics — Power distribution buses in avionics assemblies need flex interconnects that carry 5–30 A in confined spaces, survive –55°C to +125°C thermal cycling, and pass vibration screening. The all-polyimide construction handles the thermal range; 2 oz RA copper handles the current; the low CTE keeps the rigid-flex dimensionally stable through lamination and cycling.
Automotive Power Electronics — EV inverter gate drive boards, battery management flex interconnects, and ADAS control modules combine power distribution with signal layers in a single rigid-flex assembly. AP9242R used as the power flex cores, with lighter copper AP cores for signal layers, is a common hybrid stack-up approach.
Industrial Motor Drives and Robotics — Articulated robot arms and servo drives use rigid-flex assemblies to eliminate connectors across flex zones. Heavy copper flex cores carry motor phase currents; the RA copper handles millions of flex cycles in service.
High-Power RF and Microwave — PA bias distribution in phased array radar and 5G base station modules requires flex layers that supply significant DC current to power amplifier stages while coexisting with GHz-range RF routing on adjacent signal layers. The low Df of AP9242R keeps the RF signal layers behaving as the simulation predicted even when the power layers are running hot.
Fabrication and Processing Considerations
AP9242R is fully cured when delivered and compatible with all standard PWB fabrication processes — oxide treatment, wet chemical etching, mechanical drilling, and lamination. The 2 oz copper weight introduces some fabrication-specific notes that differ from working with 1 oz AP materials.
Etching: At 70 µm copper, etch factor becomes more significant. Trace edge undercut with 2 oz copper is larger in absolute terms than with 1 oz copper, so line width design rules need to account for the additional etch compensation the fabricator will require. Always confirm etch compensation targets with your flex fabricator before releasing artwork — standard 1 oz compensation tables do not apply to 2 oz copper.
Drilling: Via aspect ratio calculations need to include the full copper layer thickness. In multilayer rigid-flex constructions using multiple AP9242R cores, the total copper contribution to z-axis thickness increases substantially and affects drill feed/speed recommendations for mechanical drilling.
Panel Flatness: As mentioned above, the symmetrical 2 oz / 4 mil / 2 oz construction helps maintain panel flatness during fabrication. Asymmetric copper removal during patterning — removing large areas of copper from one side only — can introduce bow. Discuss copper balance requirements with your fabricator early if large copper pours are on only one layer.
Lamination: AP9242R is fully compatible with DuPont’s AP bondply materials for multilayer constructions. Lamination areas should be well-ventilated to manage trace residual solvents that can volatilize during press cycles, consistent with standard AP series processing guidance.
AP9242R Mechanical Properties at a Glance
| Property | Typical Value |
| Peel Strength (2 oz RA Cu) | ≥ 1.4 N/mm (8 lb/in) |
| Tensile Strength (PI film) | ~165 MPa |
| Dimensional Stability (MD/TD) | ≤ 0.10% |
| CTE (x/y plane) | ~16–20 ppm/°C |
| Moisture Absorption | ≤ 2.8% |
| Storage Conditions | 4–29°C, below 70% RH |
| Shelf Life (sealed) | 2 years from manufacture |
Useful Resources for Engineers Specifying AP9242R
- DuPont Pyralux AP Official Product Page — dupont.com/electronics-industrial/pyralux-ap.html — The primary source for current TDS downloads, the AP product selector tool, and fabrication guidelines. Always verify you are working from the most current revision of the datasheet.
- DuPont Pyralux AP Technical Data Sheet (PDF) — Available directly from DuPont and through authorized distributors including Suntech Circuits, Cirexx International, and Multi-Circuit-Boards. The TDS includes the full product code table, electrical test data, and peel strength data for all AP constructions.
- DuPont Pyralux Safe Handling Guide — Covers storage conditions, shelf life, lamination area ventilation requirements, and drill/route dust management. Essential reading before processing AP9242R for the first time.
- IPC-4204/11 — The IPC specification to which all Pyralux AP laminates are certified. Reference this specification when writing incoming material acceptance criteria, supplier qualification requirements, or process control plans.
- IPC-2223 — Sectional design standard for flexible printed boards. Contains conductor spacing rules, bend radius guidelines, and via design rules specifically applicable to flex and rigid-flex constructions using AP-series materials.
- IPC-2152 — The standard for determining current-carrying capacity in printed board design. Particularly important when using 2 oz copper and sizing power distribution traces on AP9242R flex cores.
- Polar SI9000 / Polar CITS880s — Field solver and test equipment widely used in the industry for controlled impedance calculation and coupon measurement on rigid-flex stack-ups using AP series materials.
Frequently Asked Questions About DuPont Pyralux AP9242R
Q1: What is the practical difference between AP9242R and AP9241R in a rigid-flex stack-up? AP9241R has 1 oz (35 µm) RA copper on side 2 versus the 2 oz (70 µm) RA copper on both sides in AP9242R. The asymmetric AP9241R is sometimes chosen when one layer is signal-only and the other is a power plane, allowing the fabricator to use slightly finer line widths on the signal face while still getting the current capacity of 2 oz copper where it matters. AP9242R with its symmetrical 2 oz / 2 oz construction gives more consistent panel bow behavior and is the natural choice when both faces carry significant current.
Q2: Is AP9242R compatible with standard FR-4 prepregs in a hybrid rigid-flex stack-up? You can bond AP9242R flex cores into a hybrid stack-up with FR-4 rigid sections, but CTE mismatch between the polyimide core (~16–20 ppm/°C x/y) and standard FR-4 (~14–17 ppm/°C x/y) needs to be evaluated for your specific thermal cycle profile. For most commercial rigid-flex designs the mismatch is manageable. In high-reliability aerospace or military applications, using DuPont Pyralux AP bondply and polyimide-based rigid prepregs throughout the stack eliminates the CTE mismatch concern entirely.
Q3: How does 2 oz copper affect the minimum bend radius for AP9242R flex zones? Heavier copper increases the required minimum bend radius in the flex zone. The general IPC-2223 guideline for static flex is a minimum bend radius of 6–10x the total flex zone thickness; for dynamic flex the guideline tightens to 20x or more. At 2 oz copper per side, the total copper contribution to flex zone thickness is significant — approximately 140 µm of copper plus the 100 µm polyimide core. Adding coverlay brings the total above 300 µm even without additional bonding layers. Plan bend radius accordingly and avoid routing traces in the bend zone perpendicular to the bend axis.
Q4: Can AP9242R be used in dynamic flex applications? Yes, RA copper is specifically suited to dynamic flex. The rolled-annealed grain structure resists fatigue cracking under cyclic bending. However, the 2 oz copper weight means the flex zone will be stiffer than a comparable 1 oz or 0.5 oz construction, and the achievable minimum dynamic bend radius will be larger. For applications requiring very tight dynamic bend radii or very high flex cycle counts (>1 million), evaluate whether a lighter copper weight AP variant meets the current requirements before committing to the 2 oz construction.
Q5: What is the shelf life of AP9242R, and are special storage conditions needed? DuPont warrants a two-year shelf life when AP9242R is stored in the original sealed packaging at 4–29°C (40–85°F) and below 70% relative humidity. No refrigeration is required. The material should not be frozen, and should be kept clean, dry, and protected from physical damage. Before processing, condition the material to room temperature to avoid moisture condensation on the copper surfaces.
