Introduction

Rigid-flex PCBs (Printed Circuit Boards) combine the durability of rigid PCBs with the adaptability of flexible PCBs, making them ideal for challenging environments. These advanced PCBs are favored by industries such as industrial control, medical devices, and military equipment due to their superior resistance to harsh conditions. As a result, manufacturers are increasingly incorporating rigid-flex PCBs into their production. This article will explore the key design considerations for rigid-flex PCBs, including critical areas to focus on during the design process.

Key Design Considerations for Rigid-Flex PCBs

Design Requirements for Flexible Areas

1. Smooth Line Transition: Avoid abrupt changes in trace width. Use teardrop shapes to transition between different trace widths.
2. Pad Design: To meet electrical requirements, maximize pad sizes. Use rounded transition lines between pads and conductors and avoid right angles. Independent pads should have extended pads for added support.

Dimensional Stability

- Copper Addition: Enhance dimensional stability by adding as much copper as possible, especially in waste areas. Design solid copper foils in these regions.

Coverlay Window Design

1. Manual Alignment Holes: Increase the precision of alignment by adding manual alignment holes.
2. Glue Flow Considerations: Design windows considering the flow of adhesive. Typically, the window size should be larger than the original design, as specified by ME standards.
3. Special Mold Designs: For small, dense windows, use special molds like rotary punching or jumping punching.

Transition Zone Design

1. Smooth Trace Transition: Ensure smooth trace transitions in the transition zones. The trace direction should be perpendicular to the bending direction.
2. Uniform Distribution: Distribute conductors evenly across the bending area.
3. Maximized Conductor Width: Maximize conductor width throughout the bending area.
4. Avoid PTH in Transition Zones: Minimize the use of plated-through holes (PTH) in transition areas.
5. Coverlay and No-Flow PP Design: Carefully design the overlay and no-flow prepreg in transition areas.

Design for Air-Gap Requirements

1. No Through-Holes in Bending Areas: Avoid through-holes in areas that need to bend.
2. Protective Copper Lines: Add protective copper lines on both sides of the traces. If space is limited, add them to the inner corners of the bending area.
3. Arched Connection Design: Design the connections within traces as arcs.
4. Maximize Bending Area: The bending area should be as large as possible without interfering with assembly.

Other Considerations

- Separate Tooling Holes: Do not share tooling holes like punch holes, ET, or SMT positioning holes between flexible and rigid parts.

Important Design Precautions

1. Grid Spacing: Ensure grid spacing in large areas is adequate. Too small spacing can lead to film residue during the manufacturing process, causing breakages.
2. Pad Hole Size: Properly size single-sided pad holes to avoid issues during drilling.
3. Electrical and Ground Layers: Avoid mixed use of thermal relief and direct connections.
4. Pad Overlap: Prevent pad overlap to avoid drill bit damage during drilling processes.

Applications of Rigid-Flex PCBs

1. Industrial Applications: Rigid-flex PCBs are used in industrial, military, and medical fields, requiring high reliability, precision, and low impedance loss for accurate signal transmission and durability.
2. Mobile Phones: Commonly used in hinges, camera modules, keypads, and RF modules in mobile phones.
3. Consumer Electronics: Rigid-flex PCBs enhance the performance and structure of devices like DSCs and DVs by enabling three-dimensional connections, reducing signal transmission limits, and improving assembly accuracy.
4. Automotive Applications: Used in steering wheel connections, video systems, door function controls, reverse radar systems, sensors, communication systems, satellite navigation, and more.

Conclusion

Rigid-flex PCBs offer a robust solution for applications requiring a blend of flexibility and durability. By following key design considerations and precautions, manufacturers can optimize the performance and reliability of their products. The Gekun brand remains at the forefront of providing high-quality rigid-flex PCBs, meeting the stringent demands of various high-tech industries.