Designing electronics for environments with constant motion, extreme temperatures, or limited space is no easy task. Whether you’re building devices for aerospace, medical, or military applications, traditional boards often fail to meet the durability and flexibility required in these conditions. You need a solution that can perform reliably under pressure.
Rigid flex PCBs offer a solution by combining the strength of rigid boards with the adaptability of flex circuits, all in a lightweight, space-saving format.
In this guide by All Flex, we’ll explore practical rigid flex PCB design guidelines to help you confidently navigate material choices, stackup configurations, bend radius, trace routing, and more, so your next project is engineered for performance and longevity.
What Problems Do These Hybrid PCBs Solve?
When electronics must perform in tight quarters or harsh conditions, like constant vibration, high shock, extreme temperatures, or repeated bending, traditional circuit boards often fall short. That’s where rigid flex design excels. Used across aerospace, medical, and defense, these hybrid circuits reduce failure points, eliminate bulky connectors, and fit into compact spaces without sacrificing performance.
When to Use Hybrid PCBs?
As you explore potential applications, think about where space is limited, reliability is essential, and components must perform in challenging environments. These PCBs are especially effective when routing circuitry between multiple rigid sections, removing the need for bulky connectors or flexible cabling. They are ideal for compact layouts where the board must conform precisely to the device design.
By consolidating multiple hard boards into a single streamlined assembly, this configuration supports greater design efficiency and mechanical reliability. Its lightweight structure is a strong fit for drones, wearables, and aerospace systems, while its resilience under shock, vibration, and thermal stress makes it a dependable choice in mission-critical settings.
Applications range from hearing implants and pacemakers to satellites and unmanned aerial systems, offering dependable performance where flexibility, durability, and weight reduction are priorities.
To explore field-tested solutions for real-world conditions, visit the All Flex Valu Build program.
What Are The Rigid Flex PCB Design Guidelines?
Use this essential rigid flex design guide to help ensure performance, reliability, and manufacturability in your rigid flex projects.
1. Plan Flex-to-Rigid Transitions Carefully
The flexible layers in your board run continuously through the rigid sections. There’s no physical connector, so smooth transitions are essential. Avoid stressing the flex at the rigid interface, and follow fabricator-defined keep-out zones. Don’t place pads, vias, or traces near these margins. Position drill holes far enough from the edge to prevent structural issues during fabrication.
2. Respect Minimum Bend Radius
The flex areas must bend without stressing the copper or substrate. Use a bend radius of at least 6x the flex thickness for 1–2 layer designs, and 12x for designs with 3+ layers. Following these ratios helps prevent stress on your copper circuits, or in extreme cases, delamination during use. For high-cycle applications, All Flex Solutions offers ultralight, rugged constructions built to withstand repeated bends.
3. Material Selection
Material choice directly impacts flexibility, thermal resistance, and long-term reliability. You’ll typically use polyimide for the flex layers and FR4 or polyimide for the rigid sections. Be sure to specify no-flow prepregs to prevent resin from seeping into the flexible areas during lamination, which would limit bend performance. Since not all laminate systems include no-flow options, reference the All Flex Rigid Flex Design Guide for Manufacturing or connect with your fabricator early to align on the right material stackup.
We have the largest library of rigid flex constructions, all approved to UL 94 V-0 and RoHS compliant. Get your All Flex Solutions rigid flex design for manufacturing guide today.
4. Layer Count and Stackup Planning
Your layer count and stackup influence mechanical flexibility, impedance control, and signal integrity. Flex layers must be continuous and symmetrically placed within the stack to maintain balanced construction. Typical builds range from 1–4 flex layers, but All Flex supports configurations with over 20 layers for high-density designs.
Ensure flex and rigid transitions are aligned properly during lamination to prevent registration issues. Plan for selective stiffeners or EMI shielding if required by your application. For stackups with mixed dielectric requirements or high-speed constraints, simulate performance early in the design cycle. Additional guidance is available in the All Flex Rigid Flex Design Guide for Manufacturing.
5. Trace Routing and Via Placement
Trace routing must accommodate both mechanical movement and electrical requirements. In flex regions, use wider trace widths and increased spacing to reduce stress concentration. Avoid right angles or abrupt bends in traces. Maintain uniform routing paths and use curved or teardrop transitions where possible.
Impedance control is challenging in regions with trace width variation. Place neckdowns after traces exit the rigid area and clear the keep-out margin. Avoid placing vias within 0.050″ (1.27 mm) of the flex-to-rigid boundary to prevent cracking under mechanical strain. Use anchor vias or tie-downs in transition areas if mechanical reinforcement is needed.
6. Thermal Management
Thermal properties vary between rigid and flex sections due to material composition and copper distribution. Components with high thermal output should be placed in the rigid zones, where heat sinking, copper planes, or thermal vias can aid in dissipation.
Flex sections inherently trap less heat due to their lower mass and density, but they also have fewer options for passive or active cooling. Consider thermal simulations for mixed-material assemblies, and ensure the placement of heat-generating components does not compromise the mechanical reliability of the flex regions.
Get Started With All Flex!
Designing with confidence starts with the right partner. At All Flex Solutions, we offer the engineering insight, manufacturing experience, and proven design resources to help you move forward with clarity. Whether you’re refining an existing concept or starting fresh, we’re here to support your goals with performance-driven solutions built to last.
Contact us today to request a quote and take the next step toward bringing your design to life.