What is Rigid Flex PCB ? – Design, Manufacturing & Cost

Rigid Flex PCB Manufacturing Process

Producing a reliable rigid-flex PCB requires advanced manufacturing techniques and processes. Here is an overview of rigid-flex fabrication:

1. Materials Preparation

The process starts with raw rigid and flexible core materials being prepared. The materials are cleaned, coated, and conditioned to optimize adhesion and processing performance.

2. Imaging

The individual inner and outer layers are imaged with the conductive pattern using lithography and etching processes. This forms the traces, pads, and features on each layer.

3. Hole Formation

Holes are drilled or punched through the core layers. This includes component holes, tooling holes, and through vias between layers. The holes are plated with copper to form the vertical interconnects.

4. Lamination

The rigid and flexible core layers are precisely aligned and bonded using high temperature and pressure. The bond line between materials is critical to performance. Advanced adhesives are used.

5. Outer Layer Imaging

After lamination, the outer layer traces and features are imaged using lithography and etching. This completes the conductive patterning on the PCB.

6. Solder Mask and Finish

Solder mask is applied to exposed copper surfaces. The edges of pads and traces are exposed. The PCB surface is finished with treatments like ENIG, immersion tin, or OSP.

7. Singulation

The large panel is precision routed to separate into individual PCBs. Rigid-flex PCBs often have complex board shapes.

8. Testing

Each completed PCB goes through electrical testing and inspection to verify function and workmanship. Automated optical inspection checks feature accuracy.

9. Assembly

Components are mounted on the rigid portions using soldering or adhesive attachment. The PCB can then be dynamically flexed into the 3D shape as required.

Rigid-flex PCB fabrication requires expertise in advanced processes like:

• Surface preparation and adhesion promotion

• High-accuracy imaging and pattern transfer

• Controlled lamination of dissimilar materials

• Mitigation of thermal and mechanical process stresses

• Precise techniques for routing, drilling, and hole plating

• DFM techniques for optimizing manufacturability

Rigid Flex PCB Cost Factors

Here is a detailed analysis of the key factors that influence the cost of rigid-flex PCBs. These PCBs typically incur higher costs than standard rigid PCBs due to the use of specialized materials, complex processes, and lower production volumes:

1. Layer Count The cost increases significantly with the addition of more conductive layers due to the increased material requirements, lamination complexity, and fabrication difficulty. High layer count rigid-flex PCBs are exponentially more expensive than simpler 2-4 layer versions.

2. Panel Utilization Rigid-flex PCB panels often exhibit lower utilization rates due to their intricate geometries, leading to higher costs. Optimal panel layout and utilization are crucial for cost efficiency.

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3. Finishing and Coatings Specialized solder masks, coverlays, and surface finishes add to the cost compared to standard FR-4 finishes. Techniques like thick copper plating and buried vias further escalate expenses.

4. Flexible Material Type The choice of flexible dielectric materials, such as polyimide, LCP (Liquid Crystal Polymer), or PEN (Polyethylene Naphthalate), influences the cost. More durable and heat-resistant materials tend to be more expensive.

5. Registration Accuracy Achieving precise alignment of layers and high drilling/routing accuracy adds to the cost. Tighter tolerances necessitate advanced equipment and sophisticated processes.

6. Design Complexity Complex routing, high component density, HDI (High-Density Interconnect) features, and impedance control requirements increase fabrication difficulty and costs.

7. Low Volume Production The relatively smaller market for rigid-flex PCBs prevents the realization of economies of scale. Consequently, shorter production runs lead to higher per-unit costs.

8. Testing and Inspection Extensive inspection and electrical testing are required to ensure the quality of rigid-flex PCBs, adding to the overall cost compared to basic PCB validation processes.

In addition to fabrication costs, there are significant engineering costs associated with the specialized design, simulation, prototyping, documentation, and qualification of rigid-flex PCBs. These costs reflect the advanced expertise and precision required to produce reliable and high-performing rigid-flex PCB assemblies.

Rigid Flex PCB Applications

Here are some of the major application areas taking advantage of rigid-flex PCB technology:

Consumer Electronics

Wearables, smartphones, laptops, tablets, cameras, and other connected consumer gadgets utilize rigid-flex PCBs to achieve folding, compact size, rugged cabling, and dynamic positioning.

Automotive Electronics

Automotive camera systems, powertrain electronics, LED lighting, and in-vehicle infotainment systems employ rigid-flex PCBs for shape conformability and vibration resistance.

Medical Equipment

Hearing aids, blood analyzers, surgical tools, and implants use rigid-flex PCBs to fit within tight, curved spaces and provide dynamic interconnections.

Industrial

Industrial rigid-flex applications include robotics, motion control, telemetry devices, and navigation systems that require ruggedized, shape-conforming PCBs.

Military/Aerospace

Avionics systems, guidance controls, communications, and navigation electronics in defense and aerospace applications utilize rigid-flex PCBs for compact, rugged performance.

Advanced HDI

Rigid-flex PCBs are commonly used as integrated carrier boards for ultra-high density interposers and multi-chip modules (MCMs) for applications like ASIC packaging.

From small wearable gadgets to large avionics systems, rigid-flex PCB technology enables solutions not possible with standard rigid boards – supporting dynamic motion, flexing, wrapping, and 3D shaping.