# Rigid-Flex PCB Design Guide: From Stack-up to Production

In medical devices, aerospace, and high-end consumer electronics, rigid-flex PCBs are becoming increasingly common. They enable 3D routing in tight spaces, reduce connectors and solder joints, and improve overall system reliability.

But rigid-flex PCBs are far more demanding to design and manufacture than standard rigid boards. A poorly chosen bend radius can crack copper in the flexible region. A poorly planned stack-up can delaminate during lamination.

Drawing on AnyPCBA's experience in small-to-medium volume rigid-flex manufacturing, this guide covers the key design considerations, common pitfalls, and production recommendations for rigid-flex PCBs.

## **1\. What Is a Rigid-Flex PCB?**

A rigid-flex PCB combines rigid and flexible regions in a single board. The rigid areas carry components and provide mechanical support, while the flexible areas allow bending and 3D routing.

Typical structure:

*   **Rigid layers:** FR-4 or high-Tg material, carrying components
    
*   **Flexible layers:** Polyimide (PI) material, supporting bending
    
*   **Bonding layers:** Bonding rigid and flexible regions together
    
*   **Coverlay:** Protecting flexible region traces
    

Key advantages of rigid-flex PCBs:

*   Fewer connectors and solder joints, improving reliability
    
*   3D routing, saving space
    
*   Fewer assembly steps, reducing overall cost
    
*   Suitable for high-frequency, high-speed signal transmission
    

## **2\. Key Design Considerations for Rigid-Flex PCBs**

### **2.1 Bend Radius Design**

Bend radius is one of the most critical parameters in rigid-flex design.

*   **Dynamic bending:** Bend radius should be ≥ 10× the flexible region thickness
    
*   **Static bending:** Bend radius should be ≥ 5× the flexible region thickness
    

Too small a bend radius can crack copper and coverlay. Designers should maximize bend radius and avoid vias and components in the bend area.

### **2.2 Stack-up Design**

Rigid-flex stack-ups are far more complex than standard rigid boards.

*   **Symmetrical stack-up:** Keep it as symmetrical as possible to avoid warpage during lamination
    
*   **Flexible layer position:** Place flexible layers in the middle of the stack-up to reduce stress
    
*   **Bonding material selection:** Choose low-flow bonding materials to avoid resin squeeze-out during lamination
    
*   **Coverlay opening:** Open the coverlay in the bend area to reduce bending stress
    

### **2.3 Routing in Flexible Regions**

Routing in flexible regions requires special attention:

*   **Trace direction:** Route traces perpendicular to the bend line, not parallel
    
*   **Copper thickness:** Keep copper thin in flexible regions (1/3 oz or 1/2 oz) to improve bend performance
    
*   **Grid copper:** Use grid copper in bend areas to reduce stress
    
*   **Avoid vias:** Avoid vias in bend areas to prevent stress concentration
    

### **2.4 Rigid Region Design**

Rigid region design is similar to standard rigid boards, but note:

*   **Component placement:** Keep heavy components away from flexible regions
    
*   **Via design:** Keep vias in rigid regions away from flexible boundaries
    
*   **Panelization:** Rigid-flex panelization must account for flexible region support
    

## **3\. Common Manufacturing Issues in Rigid-Flex PCBs**

| **Issue** | **Cause** | **Solution** |
| --- | --- | --- |
| Copper cracking in flexible region | Bend radius too small | Increase bend radius, optimize trace direction |
| Delamination during lamination | Improper bonding material | Choose low-flow bonding materials |
| Coverlay cracking | Stress concentration in bend area | Open coverlay in bend area, use grid copper |
| Impedance instability | Dk variation in flexible material | Choose PI materials with stable Dk |
| Poor dimensional stability | CTE mismatch between materials | Choose matched material systems |

## **4\. Industry Applications for Rigid-Flex PCBs**

| **Industry** | **Typical Applications** | **Key Requirements** |
| --- | --- | --- |
| Medical devices | Endoscopes, implantable devices | High reliability, small size, biocompatibility |
| Aerospace | Satellites, radar | High-temperature resistance, vibration resistance, lightweight |
| Consumer electronics | Foldable phones, TWS earbuds | Thin form factor, high bend life |
| Automotive electronics | Sensors, camera modules | High-temperature resistance, vibration resistance |

## **5\. AnyPCBA's Rigid-Flex Manufacturing Capabilities**

AnyPCBA has over ten years of experience in small-to-medium volume PCB manufacturing, and rigid-flex is one of our key process focuses.

Our capabilities:

*   **Layer count:** 2–64 layers, including rigid-flex
    
*   **Materials:** FR-4, polyimide (PI), high-Tg materials
    
*   **Processes:** Laser cutting, depth-controlled slots, half-hole/edge plating
    
*   **Inspection:** AOI, X-Ray, 100% functional testing
    
*   **Certifications:** ISO 13485 (medical), IATF 16949 (automotive)
    

Our engineers check bend radius, stack-up structure, and flexible region routing during DFM review, helping you anticipate manufacturing risks at the design stage.

## **6\. Conclusion**

Rigid-flex PCBs are a key technology for achieving 3D routing and improving system reliability. But their design and manufacturing demands are far higher than standard rigid boards, requiring systematic control of bend radius, stack-up structure, flexible region routing, and rigid region design.

If you're working on a rigid-flex project, or want to learn more about our manufacturing capabilities, contact us through [our website](https://www.anypcba.com/).

**What challenges have you encountered in rigid-flex PCB design? Share your experience in the comments.**