DuPont Pyralux AP8545R: Engineer’s Complete Guide to 0.5 oz Copper / 4 mil Polyimide Controlled Impedance Flex

Pick up almost any flex and rigid-flex controlled impedance design guide and you’ll find the same recommendation repeated: use half-ounce copper. The reason is simple once you’ve worked with both options. At 0.5 oz (18 µm), copper traces are thinner, etch more cleanly, and hit controlled impedance targets at line widths that fabricators can hold to tolerance reliably without yield loss. DuPont Pyralux AP8545R — pairing 0.5 oz (18 µm) rolled-annealed copper on both sides of a 4 mil (100 µm) all-polyimide adhesiveless dielectric — is built directly around that principle. The 4 mil core opens up impedance design headroom that thinner cores cannot provide at half-ounce copper, making manufacturable controlled impedance flex circuits achievable across 50Ω single-ended and 100Ω differential pair targets without chasing sub-3 mil trace widths.

This guide covers the full AP8545R specification picture, decodes the part number, explains why the 0.5 oz / 4 mil construction is a deliberate engineering choice rather than a half-measure, positions it correctly within the AP product family, and provides the practical design and fabrication rules that translate material selection into working hardware.

Decoding the DuPont Pyralux AP8545R Part Number

DuPont’s Pyralux AP naming convention encodes the complete laminate construction systematically. Understanding the structure means you can navigate the entire AP family without a catalog.

Code Segment	What It Encodes	AP8545R Value
AP	All-Polyimide, adhesiveless construction	Direct Cu-to-PI bond, no adhesive intermediate
8	Copper weight designator	0.5 oz/ft² (18 µm) copper
5	Product series designator	AP 0.5 oz copper family
4	Dielectric thickness designator	4 mil (100 µm) polyimide
5	Layer structure designator	Double-sided clad
R	Copper foil type	Rolled-Annealed (RA) copper

The “R” suffix is doing more work than it looks. AP8545E (electro-deposited copper) exists in the family, but for controlled impedance flex where surface roughness affects insertion loss at multi-GHz frequencies, and where any flex cycling requires fatigue-resistant copper grain structure, the RA variant is the correct specification. The “E” version is not a substitute in signal-integrity-critical or dynamic-flex applications.

DuPont Pyralux AP8545R Full Technical Specifications

The Pyralux AP all-polyimide dielectric system is consistent across the full 1–6 mil dielectric thickness range. All electrical property data applies equally to the AP8545R construction. The 4 mil (100 µm) core and 18 µm copper together define the mechanical and impedance characteristics of this particular construction.

Confirmed Construction Dimensions

Parameter	AP8545R Value
Top Copper Thickness	18 µm (0.5 oz/ft²), Rolled-Annealed
Polyimide Core Thickness	100 µm (4.0 mil)
Bottom Copper Thickness	18 µm (0.5 oz/ft²), Rolled-Annealed
Total Laminate Core Thickness	~136 µm (before coverlay addition)
Construction Type	Double-sided, adhesiveless all-polyimide

Electrical Properties

Property	Value	Frequency	Test Method
Dielectric Constant (Dk)	3.4	1 MHz	IPC-TM-650 2.5.5.3
Dielectric Constant (Dk)	3.2	10 GHz	ASTM D2520
Loss Tangent (Df)	0.002	1 MHz	IPC-TM-650 2.5.5.3
Loss Tangent (Df)	0.003	10 GHz	ASTM D2520
Dielectric Strength	200 V/µm	—	ASTM D149
Theoretical Isolation Voltage (4 mil core)	~20,000 V	—	Calculated
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

Mechanical and Thermal Properties

Property	Value	Test Method
Peel Strength (as received)	>1.8 N/mm (10 lb/in)	IPC-TM-650 2.4.9
Peel Strength (after solder)	>1.8 N/mm (10 lb/in)	IPC-TM-650 2.4.9
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 (datasheet baseline)	IPC-TM-650 2.4.3
Glass Transition Temperature (Tg)	220°C	DuPont Method, TMA
CTE (XY, below Tg)	25 ppm/°C	IPC-TM-650 2.4.41
CTE (XY, 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
Dimensional Stability (after etch)	±0.04 to ±0.08%	IPC-TM-650 2.2.4

Compliance and Certifications

Standard	Status
IPC-4204/11	Certified
UL 94	V-0 Flame Rating
UL File	E124294
RoHS	Compliant
ISO 9001:2015	Manufactured under certified QMS

Why 0.5 oz Copper and a 4 mil Core Is the Controlled Impedance Sweet Spot

Industry guidance on controlled impedance flex is nearly unanimous on copper weight: the preferred copper thickness for controlled impedance flex is 0.5 oz, which allows for a 2 mil flex core for microstrip and 3 mil cores for stripline. But the AP8545R chooses a 4 mil core with that same 0.5 oz copper. That extra thickness over the 2 mil minimum is not wasted — it delivers specific, measurable improvements in fabrication yield and design flexibility.

Wider, More Manufacturable Trace Widths for 50Ω Targets

The core engineering principle behind every AP core thickness choice for controlled impedance is yield. Thicker cores allow wider traces to hit the same impedance target, and wider traces fabricate more consistently. Using a 4 mil thick all-polyimide substrate, wider trace widths can be used to achieve the same electrical output, which offers a substantial manufacturing yield advantage over designs on thinner cores.

On a 4 mil (100 µm) polyimide core with Dk 3.4 and 0.5 oz copper, a nominal 50Ω microstrip trace comes out to approximately 8–10 mil wide. For common 50Ω single-ended configurations using ½ oz copper, a 4 mil trace width is typical on thinner cores — but on a 4 mil core, the same impedance target shifts to a wider, more tolerant trace geometry. That difference means your fabricator can hold ±1 mil trace width tolerance comfortably, which translates to ±3–5Ω impedance variation rather than ±8–12Ω on tighter traces. For high-speed digital and RF flex circuits where ±10% impedance control is the specification, a 4 mil core delivers it with margin to spare.

The Isotropy Advantage of Glass-Free Polyimide

Pyralux AP does not contain glass, giving it exceptional isotropy. The consistency of dielectric constant is maintained over the entire material, meaning routed signals will see the same dielectric constant no matter which direction they are routed on the circuit board. This matters profoundly for controlled impedance design. Glass-reinforced laminates have anisotropic Dk depending on whether a trace runs parallel or perpendicular to the glass weave — a source of impedance variation that no trace width compensation can fully correct. On AP8545R, what your field solver models is what the fabricated board delivers. That predictability is the foundation of consistent controlled impedance yield.

Tightly Controlled Dielectric Thickness Tolerances

Pyralux AP provides excellent dielectric thickness tolerance and electrical performance. At 100 µm (4 mil) nominal, the dielectric thickness variation across a panel is tighter in absolute terms than on thinner cores — a 5% variation on a 4 mil core is ±0.2 mil, compared to ±0.1 mil on a 2 mil core at the same percentage. But critically, the 4 mil core’s larger absolute thickness means that the same ±0.1–0.2 mil thickness variation causes proportionally less impedance deviation than the same variation on a 2 mil core would. Your impedance strip test results will cluster more tightly around the nominal target on a 4 mil core than on a 2 mil core for this reason alone.

Adhesiveless Construction: No Bondline Degradation in High-Reliability Designs

Adhesive-based three-layer flex laminates add an acrylic or epoxy bondline between the copper and the polyimide film. That bondline has two problems for controlled impedance designs: first, it adds a layer with different Dk characteristics that modifies the effective dielectric constant seen by the signal trace — introducing impedance error that must be characterized and compensated. Second, the adhesive’s low Tg (typically 80–120°C) becomes a reliability failure point in high-temperature operating environments. The AP8545R’s adhesiveless construction eliminates both issues. The copper-to-polyimide interface is direct and stable, Dk is exactly the all-polyimide value (3.4 at 1 MHz, 3.2 at 10 GHz) without adhesive contribution, and the assembly survives lead-free reflow (passes 288°C solder float) without bondline degradation.

AP8545R in the Full Pyralux AP Product Family

Positioning AP8545R correctly within the AP lineup helps designers quickly confirm whether this is the right construction or whether an adjacent option better fits the design constraint.

Standard AP Double-Sided Clad Family — Controlled Impedance Focus

Product Code	Cu (oz / µm)	Dielectric (mil / µm)	50Ω Microstrip Width (approx.)	Best Fit
AP8515R	0.5 oz / 18 µm	1 mil / 25 µm	~2.5 mil	Ultra-thin, chip-on-flex, CoF
AP8535R	0.5 oz / 18 µm	3 mil / 75 µm	~7 mil	Wearables, NFC biosensors
AP8545R	0.5 oz / 18 µm	4 mil / 100 µm	~9 mil	Controlled impedance signal flex
AP9121R	1 oz / 35 µm	2 mil / 50 µm	~6 mil	Standard signal flex
AP9131R	1 oz / 35 µm	3 mil / 75 µm	~9 mil	Balanced, mid-density signal flex
AP9151R	1 oz / 35 µm	5 mil / 125 µm	~13 mil	High-frequency RF controlled impedance

The AP8545R occupies a specific niche: the thinnest practical double-sided construction for controlled impedance flex designs where fabrication yield is a primary concern. Against AP8535R (3 mil core), it gains one extra mil of dielectric that shifts 50Ω microstrip from ~7 mil to ~9 mil trace width — above the reliable minimum for most qualified flex shops. Against AP9131R (1 oz / 3 mil), it offers thinner total stack, better flex endurance, and lower conductor resistance for the same trace width, at the cost of lower current capacity.

Using ½ oz copper allows for narrower line widths, tighter spacing, and thinner flex cores, resulting in more flexible designs. Increasing to 1 oz copper requires wider traces and thicker cores, decreasing bend capability. That trade-off is exactly what the AP8545R is designed to avoid — it gives you all the benefits of half-ounce copper while the 4 mil core provides the impedance headroom that 2 mil and 3 mil cores at 0.5 oz copper require more challenging trace geometries to achieve.

Controlled Impedance Design Reference for AP8545R

This section provides the concrete trace width reference data that engineers need to move from material selection to layout.

Approximate Trace Widths for Common Impedance Targets — AP8545R (0.5 oz Cu, 4 mil PI, Dk 3.4)

Impedance Target	Configuration	Approx. Trace Width	Approx. Spacing (diff pair)
50Ω single-ended	Microstrip	8–10 mil (200–254 µm)	N/A
75Ω single-ended	Microstrip	5–6 mil (127–152 µm)	N/A
90Ω single-ended	Microstrip	3.5–4.5 mil (89–114 µm)	N/A
100Ω differential	Edge-coupled microstrip	4–5 mil trace / 5–7 mil space	5–7 mil
100Ω differential	Edge-coupled microstrip	4 mil trace / 6 mil space	6 mil

These values are approximations from field solver calculations and published design guides for 0.5 oz copper on polyimide substrates with Dk 3.4. Always verify against your fabricator’s impedance calculator or controlled impedance test coupon data before releasing final artwork. Fabrication tolerance on trace width at 0.5 oz is typically ±0.5–1 mil, which translates to approximately ±2–4Ω on a 50Ω target for these geometries.

Cross-Hatch Reference Plane Considerations in Flex

Cross-hatched copper planes are used as reference planes in flex circuit boards. The ratio of cross-hatch conductor width to cross-hatch pitch plays an important role in characterizing the cross-hatch plane. On AP8545R, using a solid copper reference plane in the flex zone increases stiffness and reduces flex endurance compared to a cross-hatch pattern. For dynamic flex zones, use a cross-hatch reference plane with approximately 50% copper fill. For static flex or high-frequency designs where a solid reference plane is needed for shielding or impedance precision, evaluate the bend radius constraints of your total circuit thickness before committing to a solid plane in the flex zone.

Microstrip vs. Stripline in AP8545R Flex Designs

Microstrip designs are preferred for flex areas due to thinner construction and tighter bend radii, while stripline designs provide EMI/RF shielding on both sides but require thicker cores, reducing flexibility.

For most AP8545R applications, the microstrip configuration is the correct choice for the flex zone. It keeps total circuit thickness minimized (critical for bend radius) and eliminates the need for a third polyimide layer. When external shielding or EMI containment is required — common in medical and aerospace RF flex designs — evaluate whether a shielded microstrip with a cross-hatch ground on the back face is sufficient before committing to a full stripline construction that will increase total flex thickness and reduce bend capability.

Real-World Applications for DuPont Pyralux AP8545R

The combination of 0.5 oz copper, 4 mil polyimide, and adhesiveless all-polyimide construction places AP8545R in a well-defined set of application domains.

High-Speed Rigid-Flex Interconnects for Consumer Electronics

Foldable phones, laptop flex interconnects, and compact imaging devices increasingly route PCIe, MIPI, USB 3.x, and other multi-Gbps interfaces through flex sections between rigid subsystems. At these data rates, controlled impedance in the flex zone is not optional — signal reflection and timing skew from uncontrolled impedance in the flex section will degrade eye margins below the specification mask. Polyimide flex materials are very well suited for impedance-controlled designs due to their homogeneous nature, low Dk of 3.2–3.4, uniformity, and tightly controlled thickness. AP8545R’s 4 mil core and 0.5 oz copper give the flex zone of a high-speed rigid-flex the impedance consistency that the signal integrity budget requires.

RF Flex Circuits for Antenna Interconnects and 5G Modules

Sub-6 GHz 5G antenna modules, phased array antenna elements, and GNSS receiver flex antenna circuits all require controlled 50Ω or 75Ω transmission line routing through flex sections. At 0.5 oz copper, the AP8545R’s RA copper surface roughness is lower than ED copper, which reduces skin-effect insertion loss at multi-GHz frequencies. Combined with the all-polyimide Dk of 3.4/3.2 (stable, glass-free, isotropic), AP8545R is a competent substrate for RF flex work in the 1–10 GHz range where the slightly higher Df of 0.003 at 10 GHz is acceptable and the flex form factor is a system-level requirement.

Aerospace and Defense Signal Distribution Flex

Radar signal processing chains, avionics data buses (ARINC 429, MIL-STD-1553, SpaceWire), and electronic warfare antenna harnesses regularly use controlled impedance flex circuits to replace coaxial cable harnesses with lighter, space-efficient flex assemblies. The AP8545R’s ISO 9001:2015 manufacturing pedigree, IPC-4204/11 certification, and full DuPont lot traceability satisfy the materials documentation requirements of AS9100 supply chains.

Medical Imaging Signal Flex — Ultrasound Transducer Arrays

Ultrasound transducer array interconnects route high-frequency (1–15 MHz) acoustic drive and receive signals through dense flex circuits that must maintain controlled impedance across hundreds of channels in a minimum-thickness package. The AP8545R’s thin total stack (approximately 136 µm core before coverlay), 0.5 oz copper for fine-pitch routing, and 4 mil polyimide for consistent 50–75Ω microstrip geometry make it a practical choice for the flex interconnect layers in array transducer assemblies. Note DuPont’s standard caution: Pyralux AP is not approved for permanent implantation in the human body.

Wearable IoT and Compact Sensor Modules

IoT edge devices, industrial RFID tag readers, and compact sensor fusion modules increasingly integrate RF, high-speed digital, and power management in a single rigid-flex assembly. The AP8545R supports the signal integrity requirements of the RF and high-speed digital layers in these designs while maintaining the slim profile and conformability that wearable and space-constrained industrial enclosures demand.

Fabrication Design Rules for AP8545R

Getting the most out of AP8545R in production requires understanding how 0.5 oz copper and a 4 mil core affect the fabrication process.

Etch Process — The 0.5 oz Advantage

At 18 µm copper, wet etching produces significantly cleaner trace sidewalls and lower undercut than at 35 µm (1 oz) or 70 µm (2 oz). The etch compensation requirement on AP8545R is approximately 15–20 µm per trace edge — substantially less than the 50–100 µm compensation needed for 1 oz copper. This means your as-etched trace widths more closely match artwork dimensions, and impedance variation from etching process scatter is lower on AP8545R than on heavier copper constructions.

Bend Radius Calculator for AP8545R

Total finished circuit thickness determines minimum bend radius. For AP8545R with a 25 µm film polyimide coverlay bonded on both faces:

Layer	Thickness
Top coverlay (PI film + adhesive)	~50 µm
Top copper (0.5 oz RA)	18 µm
Polyimide core	100 µm
Bottom copper (0.5 oz RA)	18 µm
Bottom coverlay (PI film + adhesive)	~50 µm
Total finished thickness	~236 µm

Applying IPC-2223 multipliers to the 236 µm finished thickness:

Flex Type	Multiplier	Minimum Bend Radius
Static (bend-to-install, one time)	6×	~1.4 mm
Dynamic (repeated flex cycles)	10×	~2.4 mm
High-cycle dynamic (>10,000 cycles)	15×	~3.5 mm

These are practical values for a bare two-layer AP8545R circuit without stiffeners. Adding stiffeners in component and connector zones increases the radius required at those locations — keep stiffener edges 1–2 mm clear of the flex zone boundary.

Pre-Assembly Moisture Bake-Out

Polyimide is highly hygroscopic. Always bake AP8545R assemblies for a minimum of 4 hours at 120°C before soldering and process within 8 hours of bake completion. Moisture trapped in the polyimide during reflow causes blistering and delamination — particularly damaging at 0.5 oz copper where the thin conductor layer offers less mechanical restraint against gas pressure expansion. This bake-out requirement applies before both the first lamination press cycle and before final reflow assembly.

Coverlay Selection

Film polyimide coverlay (25–50 µm with acrylic or epoxy adhesive) is the standard and recommended choice for AP8545R. At 0.5 oz copper, LPI soldermask is technically more feasible than at 2 oz (because the step height is smaller), but film coverlay still delivers superior adhesion, flexibility, and chemical resistance for most controlled impedance flex applications. Use LPI only where the design requires fine-feature window cutouts that film blanking cannot achieve with sufficient registration accuracy.

Storage

Store AP8545R in original DuPont packaging at 4–29°C (40–85°F) and below 70% relative humidity. Do not freeze. Ensure lamination areas are ventilated with fresh air supply during press cycles to manage trace residual solvents from the polyimide dielectric.

AP8545R vs. Competing Controlled Impedance Flex Laminates

Parameter	AP8545R (DuPont)	AP9131R (DuPont)	Shengyi SHE-FLEX 0.5 oz	Adhesive-Based 3L Flex (0.5 oz)
Cu Weight	0.5 oz / 18 µm	1 oz / 35 µm	0.5 oz / 18 µm	0.5 oz / 18 µm
Dielectric Core	4 mil / 100 µm PI	3 mil / 75 µm PI	1–4 mil PI	1–3 mil PI + adhesive
Adhesiveless	Yes	Yes	Yes	No
Dk @ 1 MHz	3.4	3.4	~3.4–3.5	~3.5–4.2 (adhesive adds)
Dk @ 10 GHz	3.2	3.2	~3.3–3.4	Unknown / variable
Tg	220°C	220°C	~220°C	80–120°C (adhesive Tg)
50Ω Microstrip Width	~9 mil	~9 mil	~7–9 mil	~7–9 mil
Total Flex Flexibility	Higher (0.5 oz)	Lower (1 oz)	Similar	Similar
IPC-4204/11	Certified	Certified	Varies	N/A
ISO 9001:2015 QMS	Full (DuPont)	Full (DuPont)	Factory-dependent	Factory-dependent

The most important comparison is AP8545R vs. AP9131R — both achieve approximately the same 50Ω microstrip trace width (~9 mil) but via different routes. AP9131R uses 1 oz copper on a 3 mil core; AP8545R uses 0.5 oz copper on a 4 mil core. For designs where current capacity above 2 A on signal traces is required, AP9131R wins. For designs where maximum flex endurance, minimum total stack thickness, and lowest insertion loss at multi-GHz frequencies are the priorities, AP8545R is the better choice. The two constructions are complementary, not interchangeable.

Sourcing DuPont Pyralux AP8545R

DuPont supplies Pyralux AP Double-side Clad in standard sheet formats: 24×36 in (610×914 mm), 24×18 in (610×457 mm), and 12×18 in (305×457 mm). Custom sizes are available on special order. Distribution is through DuPont’s authorized global laminate network and through qualified flex PCB fabricators.

When qualifying a fabricator for AP8545R-based controlled impedance designs, verify two things: first, that they perform impedance strip testing on every controlled impedance panel (not just periodic audits), and second, that they have specific process characterization data for 0.5 oz copper on 4 mil polyimide — not just general controlled impedance capability on 1 oz FR4 or standard flex. The trace width/impedance relationship on 0.5 oz PI is different enough from both 1 oz FR4 and 1 oz polyimide that shop-specific data matters.

DuPont PCB  is a substrate supplier worth evaluating alongside DuPont’s Pyralux AP range for polyimide-based controlled impedance rigid-flex stackup combinations, particularly for designs requiring supply chain options beyond single-source dependency.

Useful Resources for Controlled Impedance Flex Designers

Resource	Description	URL
DuPont Pyralux AP Official Product Page	Datasheets, construction options, sample requests	https://www.dupont.com/electronics-industrial/pyralux-ap.html
DuPont Pyralux Laminate Product Selector	Find exact product codes for custom AP constructions	https://pyralux.dupont.com
DuPont Pyralux AP Current Datasheet (PDF)	Full TDS with all standard constructions and properties	https://insulectro.com/wp-content/uploads/2021/09/EI-10124-Pyralux-AP-Data-Sheet.pdf
Epectec Controlled Impedance Flex Design Guide	Practical trace width / spacing data for 0.5 oz and 1 oz flex	https://blog.epectec.com/rigid-flex-pcb-stack-ups-for-impedance-controlled-designs
Sierra Circuits Flex Impedance Stack-Up Guide	Cross-hatch planes, microstrip vs. stripline in flex	https://www.protoexpress.com/blog/how-to-build-a-flex-stack-up-with-controlled-impedance/
Epectec Flex Controlled Impedance Tip Sheet	Line width / spacing reference for common impedance targets	https://cdn.hackaday.io/files/1644617036299424/Flex-and-Rigid-Flex-Controlled-Impedance-Design-Tip-Sheet.pdf
IPC-2223 Flexible PCB Design Standard	Bend radius, DFM rules, and material selection guidance	https://www.ipc.org
IPC-4204/11 Adhesiveless Laminate Specification	Qualification standard for Pyralux AP materials	https://www.ipc.org
IPC-TM-650 Test Method Database	All test methods cited in AP8545R datasheet	https://www.ipc.org/TM
Altium Impedance Design Guide	Practical stackup planning for controlled impedance targets	https://resources.altium.com/p/designing-4-layer-pcb-stackup-50-ohm-impedance

Frequently Asked Questions About DuPont Pyralux AP8545R

1. Why is 0.5 oz copper preferred over 1 oz for controlled impedance flex on AP8545R?

Three reasons drive this preference, and they compound each other. First, using ½ oz copper allows for thinner traces and flex cores, resulting in more flexible designs — thinner copper means lower total stack stiffness and tighter achievable bend radii. Second, 0.5 oz copper etches more cleanly with less undercut, meaning your as-fabricated trace widths track your artwork dimensions more accurately, which directly translates to tighter impedance distribution across a panel. Third, at 18 µm copper thickness, skin-effect conductor losses at multi-GHz frequencies are lower than at 35 µm because the smoother RA copper surface produces less microstructural scattering. For designs where current capacity above 1.5–2 A on signal traces is required, 1 oz copper may be necessary — but for signal-only or low-power RF flex layers, 0.5 oz is the right call.

2. What impedance values can AP8545R reliably achieve in production?

On a 4 mil (100 µm) polyimide core with Dk 3.4 and 0.5 oz (18 µm) RA copper, a 50Ω single-ended microstrip trace requires approximately 8–10 mil trace width. A 100Ω differential pair edge-coupled microstrip uses approximately 4 mil trace with 6 mil spacing. A 75Ω single-ended microstrip falls around 5–6 mil. Most qualified flex fabricators can hold ±10% impedance tolerance (±5Ω on a 50Ω target) across these trace geometries at 0.5 oz copper on a 4 mil core — better tolerance than is achievable on a 2 mil core at the same copper weight. Always confirm target impedances with your specific fabricator using their characterization data for AP or equivalent all-polyimide material.

3. How does the AP8545R handle frequencies above 5 GHz?

The AP8545R’s all-polyimide dielectric — Dk 3.2 and Df 0.003 at 10 GHz — is competitive for designs operating in the 1–10 GHz range. Above 10 GHz, insertion loss becomes more sensitive to copper surface roughness and the material’s Df, and both begin to limit performance in the most demanding mmWave applications. For designs below 10 GHz (5G sub-6 GHz, WiFi 6E, Bluetooth, GNSS, automotive V2X), AP8545R is a capable and practical substrate. For designs requiring consistent performance above 15–20 GHz, Pyralux TK (PTFE/Kapton composite, Dk ~2.3–2.5, Df ~0.002) is the appropriate upgrade — but it sacrifices the broad temperature range and proven processability of the all-polyimide system.

4. Can AP8545R be used in the flex zone of a rigid-flex design alongside FR4 rigid sections?

Yes, and this is one of its primary deployment contexts for high-speed rigid-flex interconnects. The AP8545R flex layers are bonded to FR4 rigid sections (or polyimide-core rigid sections for all-PI builds) using a compatible bondply — typically DuPont Pyralux LF or a low-flow epoxy prepreg — in a single multilayer lamination press cycle. The CTE mismatch between AP8545R (25 ppm/°C XY) and standard FR4 (14–17 ppm/°C XY) must be managed through symmetric stackup design and controlled press cool-down rates. Discuss the rigid-to-flex transition construction — including coverlay edge location, controlled-depth rout parameters, and bondply selection — with your fabricator’s process engineering team before finalizing the stackup specification.

5. What surface finish is recommended for AP8545R in high-frequency controlled impedance flex?

ENIG (electroless nickel immersion gold) is the standard recommendation and the most common surface finish for controlled impedance flex circuits on AP8545R. It provides a flat, uniform surface on pads and traces, is compatible with all standard component assembly processes, and does not introduce the shelf-life limitations of OSP or the barrel stress of hard-electrolytic gold. For applications above 5 GHz where the nickel layer’s higher resistivity contributes measurably to insertion loss through the skin effect, ENEPIG (electroless nickel electroless palladium immersion gold) eliminates the nickel from the current path and reduces high-frequency loss at the conductor surface. Immersion silver is acceptable for lower-frequency designs and offers very flat surface geometry, but requires careful incoming inspection for silver migration risk in high-humidity environments.

Summary

DuPont Pyralux AP8545R is purpose-built for the controlled impedance flex application space. Pairing 0.5 oz (18 µm) rolled-annealed copper — the industry’s preferred copper weight for flex impedance control — with a 4 mil (100 µm) all-polyimide adhesiveless core, it delivers the impedance design headroom, fabrication yield advantage, and mechanical flexibility that the 2 mil and 3 mil core alternatives at the same copper weight cannot match. Its glass-free polyimide dielectric is isotropic, tightly thickness-controlled, and thermally stable to 220°C Tg. Its adhesiveless construction eliminates the Dk uncertainty and low-Tg failure mode of three-layer adhesive-based flex laminates. For high-speed digital rigid-flex, sub-10 GHz RF flex antenna circuits, aerospace signal distribution flex, and medical imaging interconnects where controlled impedance is a hard specification, AP8545R is the construction to put at the center of your flex zone stackup.

For samples and engineering support, contact DuPont Electronics at pyralux.dupont.com or engage a qualified flex fabricator with specific experience in 0.5 oz controlled impedance polyimide construction.