Your rigid flex PCB material directly affects your product’s performance, reliability, and lifecycle. While most rigid flex materials are standardized across the industry, you’ll be able to create more intentional designs if you understand what’s beneath the surface.
In this article by All Flex, you’ll learn what rigid flex PCB materials are made of and how each one impacts real-world functionality. This breakdown will give you the insight you need to design with confidence.
The Core Rigid Flex PCB Materials
Rigid flex PCB materials have a layered construction combining both rigid and flexible sections into a unified circuit. Each material serves a specific role, whether it’s supporting flexibility, maintaining structural integrity, or enabling high-performance electrical function.
Here’s what you need to know about the core materials and how they impact your design:
1. The Flexible Core: Polyimide Film
Polyimide is the foundation of the flexible sections chosen for its excellent thermal resistance, mechanical flexibility, and chemical stability. This makes it ideal for dynamic environments where the circuit will bend or flex during use, and reliability under extreme conditions is non-negotiable.
2. The Rigid Core: FR4 and Polyimide Laminates
The rigid sections of your circuit rely on a strong, stable backbone typically made from FR4 or poyimide laminates.
FR4 is a glass-reinforced epoxy laminate that provides structural strength and routing support to hold connectors, components, and vias in place without deformation. Polyimide offers similar structural benefits but with enhanced thermal performance. It can withstand higher temperatures than FR4 and maintain integrity in extreme environments.
Combining the structural strength of FR4 and polyimide enables you to meet stringent performance requirements without compromising manufacturability.
3. No Flow Prepregs
Rigid flex manufacturers use no-flow prepregs, which are glass-reinforced resin systems that are designed to bond all of the components together without resin flowing out onto the flexible parts of the board. It is a critical component in rigid flex designs and the most significant cost factor in their manufacturing.
4. Conductive Layers: Copper Foil
Copper foil forms the electrical pathways in both rigid and flexible sections. There are two main types: rolled annealed (RA) and electro-deposited (ED). RA copper is preferred in flexible areas due to its superior ductility, while ED copper is often used in rigid zones for its strength and cost efficiency.
Copper weight and type directly affect signal integrity, current-carrying capacity, flexibility, and impedance. The copper thickness and the dielectric properties of adjacent materials determine how signals behave. Precision here ensures your circuit meets performance specs without signal loss or noise.
5. Protective Layers: Coverlay and Soldermask
Coverlay is a polyimide-based film used to encapsulate and protect the flexible portions of your circuit. It shields the copper from moisture, abrasion, and environmental stress. In contrast, flexible soldermask is a photo-imaged polymer that can be applied in thinner layers and is better suited for detailed geometries. Both offer protection, but coverlay is typically favored in high-wear, high-flex, or harsh environments.
6. Supporting Materials: Adhesives and Stiffeners
Adhesives bond the various flexible layers together, with polyimide and acrylic being the most common. Polyimide adhesives are ideal for high-temperature applications, while acrylics offer better flexibility. Stiffeners may be used to reinforce mechanical components, typically near connectors, mounting points, or components. Common stiffener materials include FR4, polyimide, and stainless steel.
How These Rigid Flex PCB Materials Impact Performance in the Real World
Thermal and Mechanical Stress – Polyimide’s high thermal tolerance and the structural strength of FR4 allow your circuit to survive extreme environments.
High-Density Interconnects – With flexible layers and laser-drilled vias, you can pack more functionality into smaller spaces without sacrificing signal integrity.
Electrical Reliability Over Flex Cycles – RA copper and durable polyimide help maintain consistent performance even after thousands of bends.
Save Space and Reduce Weight – Rigid flex construction eliminates bulky connectors and excess wiring to minimize weight and maximize free space.
Durability and Reliability in Harsh Environments – Coverlay protection, adhesive bonding, and mechanical stiffeners are proven in military-grade systems and mission-critical controls.
Failure Points – Integrating rigid and flex sections into a single, continuous board eliminates the need for interconnects and connectors between parts. Fewer components mean fewer things that can go wrong.
Design With All Flex!
Understanding rigid flex PCB materials is essential to building reliable, high-performance products, especially in demanding fields like aerospace, medical, and defense. Every material plays a critical role in how your design performs under pressure.
Remember:
- Polyimide film for flexibility and thermal stability
- FR4 and polyimide laminates for structural strength
- No flow prepregs to bond the components together
- Copper foil for electrical conductivity
- Coverlay and soldermask for protection
- Adhesives and stiffeners for mechanical integrity
When you partner with All Flex, you get a team that understands your application and builds to meet exact specifications. We’re by your side through everything from material selection to final delivery.