Polyimide Flex PCB
Dk 3.2-3.5 | -269C to +400C | 200,000+ bend cycles — the foundation material for flexible and rigid-flex circuit construction.
3.2-3.5
Dk
-269/+400
C Temp Range
200K+
Bend Cycles
25-125
um Thickness
What is Polyimide (Flex/Rigid-Flex)?
Polyimide is the primary substrate material for flexible printed circuits, offering an extraordinary combination of mechanical flexibility (200,000+ bend cycles), thermal endurance (-269C to +400C), and chemical resistance that no other organic substrate can match. DuPont Kapton and equivalents form the foundation of all modern flex and rigid-flex PCB construction.
Flexible circuits enable three-dimensional packaging that rigid boards cannot achieve: folding smartphone displays, wearable health sensors that conform to skin, satellite solar array harnesses that deploy in orbit, and medical implants that flex with body movement. Each application exploits polyimide's unique ability to maintain electrical reliability under repeated mechanical stress.
Rigid-flex construction combines polyimide flex layers with FR-4 rigid sections in a single integrated assembly, eliminating connectors and cables between board-to-board links. This reduces weight, improves reliability (fewer connection points), and enables compact 3D packaging for aerospace, military, and high-end consumer applications.
200K+ Bend Cycles
Dynamic flex applications — hinges, sliders, and rotating connections.
-269C to +400C
Widest operating temperature range of any organic substrate.
Ultra-Thin 25-125um
Minimum thickness enables compact folding and tight bend radii.
Rigid-Flex Integration
Eliminate connectors with integrated rigid and flex sections.
Polyimide (Flex/Rigid-Flex) Key Properties
Representative values from the manufacturer datasheet.
| Property | Value | Why it matters |
|---|---|---|
| Dielectric constant (Dk) | 3.2-3.5 @ 1 GHz | Lower Dk than FR-4 — actually better for high-speed flex. |
| Dissipation factor (Df) | 0.002-0.008 @ 1 GHz | Low loss suitable for multi-GHz signaling on flex. |
| Temperature range | -269C to +400C | Cryogenic to extreme heat — space and industrial. |
| Bend endurance | 200,000+ cycles | Dynamic flex rated for continuous movement applications. |
| Thickness range | 25-125 um (1-5 mil) | From single-film to built-up multilayer flex. |
| Chemical resistance | Excellent | Resists solvents, acids, and harsh cleaning processes. |
| Moisture absorption | 1.5-3.0% | Higher than FR-4 — bake before assembly. |
| Dimensional stability | Good | Controlled expansion with proper film handling. |
| Copper adhesion | Adhesive or adhesiveless | Both construction types available for different needs. |
Flex vs Rigid-Flex: When to Use Each
Single-sided and double-sided flex circuits are cost-effective alternatives to wire harnesses and ribbon cables. A flex circuit replaces a connector + cable + connector assembly with a single integrated component — saving space, weight, and eliminating two failure-prone connection points. Most consumer flex applications (phone interconnects, laptop hinges) use simple 1-2 layer flex.
Multilayer flex (3-8 layers) provides complex routing in tight spaces while maintaining full flexibility. Applications include dynamic medical probe cables, robotic arm signal harnesses, and spacecraft solar array wiring that must survive deployment and thermal cycling in orbit.
Rigid-flex combines the best of both worlds: rigid sections for component mounting and complex routing, connected by flex sections that fold, bend, or accommodate mechanical movement. The elimination of board-to-board connectors improves reliability dramatically — from MTBF limited by connector cycles to MTBF limited only by solder joint integrity.
Dynamic Flex
Continuous-motion applications: printer heads, disk drives, robotic joints.
Rigid-Flex Integration
3D packaging eliminating connectors and reducing assembly points.
Cryogenic Rated
-269C operation for space, scientific, and superconducting applications.
Medical Grade
Biocompatible with sterilization resistance for implantable devices.
Flex Material Options Comparison
Polyimide versus alternative flexible substrate materials.
| Material | Dk | Df | Best For |
|---|---|---|---|
| Polyimide (Kapton)This page | 3.4 | 0.004 | Standard flex — best balance of properties, widest use. |
| LCP (Liquid Crystal Polymer) | 2.9 | 0.002 | Low-loss flex — 5G AiP, mmWave, moisture-resistant. |
| PEN (Polyethylene Naphthalate) | 3.2 | 0.005 | Budget flex — lower temp, consumer wearables. |
| PET (Polyester) | 3.3 | 0.010 | Lowest cost — single-use, non-solderable applications. |
| FR-4 Thin Core | 4.3 | 0.020 | Rigid — limited flex capability, lowest cost. |
Polyimide (Flex/Rigid-Flex) Applications
Flex circuits, rigid-flex assemblies, wearables, medical implants, aerospace harnesses, foldable devices
Consumer Foldables
Smartphone hinges, foldable displays, laptop flex interconnects.
Medical Devices
Catheter sensors, implantable electrodes, surgical tool connections.
Aerospace Harnesses
Satellite solar array wiring and spacecraft internal interconnects.
Automotive Sensors
Under-hood flex connections, battery management harnesses.
Defense Electronics
Conformal antenna arrays and compact avionics packaging.
Industrial Robots
Multi-axis robotic arm signal and power harnesses.
Flex and Rigid-Flex Design Guidelines
Minimum bend radius depends on construction: static flex allows bend radius of 6x material thickness, dynamic flex requires 12-20x thickness minimum. Route traces perpendicular to the bend axis and avoid placing vias in flex zones to maximize bend cycle life.
For rigid-flex, define rigid and flex zones early in design. Flex sections should be as thin as possible (ideally 2 layers) while rigid sections can be any layer count. Stagger copper layers through the transition zone to prevent stress concentration at rigid-flex boundaries.
Get Instant QuoteBend Radius Rules
Static: 6x thickness. Dynamic: 12-20x minimum for reliability.
Trace Routing
Perpendicular to bend axis. No vias in flex zones.
Rigid-Flex Transitions
Stagger copper layers through boundaries to reduce stress.
Pre-Assembly Bake
Polyimide absorbs moisture — bake 4h at 120C before soldering.
Genuine Polyimide (Flex/Rigid-Flex), Verified on Every Order
Material CoC
Certificate of Conformance with lot number ships with every order.
Stock Verified
We confirm laminate availability before order confirmation.
No Substitutions
Specified material guaranteed — never swapped without written approval.
FAQ
Polyimide (Flex/Rigid-Flex) Questions
What is polyimide flex PCB?
A flexible printed circuit built on polyimide film (DuPont Kapton or equivalent) — capable of 200,000+ bend cycles and -269C to +400C operation.
Flex vs rigid-flex — which do I need?
Flex alone for cable replacement and simple interconnects. Rigid-flex when you need component mounting plus mechanical flexing in a single integrated assembly.
What is the minimum bend radius?
Static applications: 6x material thickness. Dynamic (repeated bending): 12-20x thickness. Tighter bends possible with careful design optimization.
Can flex circuits carry high-speed signals?
Yes. Polyimide Dk 3.4 and Df 0.004 are actually better than FR-4 for high-speed. Many 25G+ designs use flex interconnects.
What is AtlasPCB's flex capability?
1-8 layer flex circuits and rigid-flex assemblies with up to 20+ rigid layers. Prototype to production with no minimum order.
Need flex or rigid-flex fabrication?
Polyimide flex and rigid-flex — from simple 1-layer flex cables to complex 3D rigid-flex assemblies. No MOQ.
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