As the Rigid-Flex PCB Market Expands, Traditional PCB Designers Are Paying More Attention to Rigid-Flex PCBs

The growing market for rigid-flex PCBs, along with increasing attention from traditional PCB designers, highlights a significant trend in the industry. This shift is driven by the shrinking demand for rigid PCBs, prompting PCB manufacturers to seek solutions for filling their manufacturing facilities. OEMs may also search for ways to simplify, enhance reliability, and reduce the number of components in new product manufacturing.

Designers of rigid PCBs might be interested in understanding how to select a rigid-flex PCB supplier and how to initiate this process. If you are placing your bets on the next generation of rigid-flex designs for OEMs, you will want to partner with the best manufacturer for these designs. New rigid-flex designs need to be entrusted to the right factory to leverage the best manufacturing solutions.

Let’s explore the expertise, processes, and materials used in manufacturing rigid-flex PCBs. Rigid-flex PCBs, as a hybrid solution combining rigid and flexible circuits, can be produced by two main types of factories in North America:

1. Flexible Circuit Factories Specializing in Flexible Circuits and Rigid-Flex PCBs

2. Rigid PCB Factories Producing Rigid-Flex PCBs or Transitioning Toward Rigid-Flex PCB Manufacturing

Both types of factories compete for customers’ rigid-flex PCB business. From a high-level perspective, some rigid-flex PCBs are best produced in rigid PCB factories, while others should be made in specialized flexible circuit factories. For PCB designers, understanding the differences between these two types of factories can help in selecting the right supplier and achieving better quality and delivery times.

Rigid PCB Factories

Rigid PCB factories generally offer multi-layer FR-4 solutions, where about 95% of the circuits are on non-flexible, rectangular substrates. The paneling for these products is relatively straightforward, and in many cases, the material layers are ready-made. Rigid PCB factories excel at complex stacking, high-density interconnections (HDI) for blind and buried vias, and multiple lamination cycles, with stable, repeatable processes and design rules that have been used for years. However, as rigid PCBs become more complex, the available board area decreases while the number of components increases.

Flexible Circuit Factories

In contrast to rigid PCB factories, flexible circuit factories mainly provide custom mechanical solutions that can bend without breaking. Once electrical features, component placements, supports, contour shapes, copper grain direction, and cover layers are added, the rigid-flex PCB becomes a completely new product. The design and manufacturing rules for flexible circuits differ significantly from those for rigid PCBs. Flexible circuit manufacturing is more labor-intensive and involves a variety of materials for each operation.

Materials

Suppliers for rigid PCBs and flexible circuits are quite different, dealing with substrates, adhesives, and material processing. PCB factories typically use FR-4, prepreg, and electrodeposited (ED) copper. If HDI is offered, the material choices can include photoresists, resins, and dry films. Flexible circuit factories primarily use polyimide substrates, adhesives, and rolled annealed (RA) copper foil. Thin materials are used to achieve flexibility.

Copper Plating

PCB factories employ traditional full-panel or patterned copper plating techniques. Copper is plated on both sides of the panel and through vias, then etched away to leave the circuit design and plated holes. Flexible circuit factories use pad or pattern plating techniques, plating only on pads and plating through holes. If copper is plated on a flexible trace designed for bending, it is likely to crack. For rigid-flex PCBs with small bend radii, it is crucial to ensure that the manufacturer uses pattern plating for the flexible sections.

Design Considerations

Both PCB and flexible circuit designs have unique considerations. For instance, there are specific rules for through-holes.

Bend Radius

In most cases, PCB suppliers do not have to worry about bending rigid boards. However, for flexible circuits, bending is a major concern. During the design and layout phases, considerations include material selection, bending location, bend radius, and component placement.

IPC-2223 provides a chapter specifically on calculating bend radii, generally recommending a bend radius of 12 times the thickness of the material. The stiffness of a flexible board is mainly determined by copper weight, but the thickness of the polyimide is also crucial.

Layout Design Factors

Flexible circuit design considerations are diverse and distinct from those for rigid PCBs.

Chamfering: It is best to add a chamfer (teardrop) to vias in the bending area to distribute stress over a wider area, which improves reliability.

Through-Hole Placement in Rigid-Flex PCBs: Vias in the flexible areas of a rigid-flex PCB should be at least 0.050” away from the rigid-flex junction and 0.050” from the beginning of the bending area. The same 0.050” rule applies on the rigid side of the rigid-flex PCB.

Trace Routing: For bending and folding areas in a single metal layer, it is optimal to route conductors vertically.

Routing in Multi-Flex Layers: Avoid routing over the top of traces between layers to prevent I-beam effects.

HDI: PCB suppliers are actively providing blind vias, buried vias, staggered vias, and stacked vias. The progress in high-layer counts and HDI in the PCB industry is impressive. Flexible circuits have smaller features and vias and achieving blind vias, buried vias, and staggered vias is more challenging. However, the flexible market is advancing with better support for flexible technologies.

Conclusion

Rigid-flex PCBs are a hybrid solution combining rigid PCBs and flexible circuits. Both rigid PCB and flexible circuit companies offer high-quality solutions for client needs. As an OEM circuit designer, design engineer, or procurement manager, understanding the requirements and selecting the right manufacturer is crucial for achieving successful outcomes.

If the rigid-flex design you are working on features more traditional PCB aspects, such as high layer counts, dense assembly requirements, HDI needs, and blind or buried vias, a rigid PCB manufacturer might be the best choice.

On the other hand, if the rigid-flex PCB involves more flexible circuit functions, such as small bend radii, fine features, and thin stack requirements, it may be necessary to contact a flexible circuit supplier.

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Gekun Rigid-Flex PCB Manufacturer

Gekun stands out as a leading rigid-flex PCB manufacturer in the electronics industry with its innovative technology and superb craftsmanship. We focus on producing high-performance rigid-flex circuit boards, renowned for their excellent electrical performance, flexible design, and durability. Gekun employs advanced manufacturing techniques to ensure precision and reliability in every detail, meeting the demands of complex electronic devices. We are dedicated to ongoing technological innovation to provide customized solutions for our customers, driving industry development, and achieving mutual success.

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