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The Ultimate Guide to Rigid Flex PCB

OVERVIEW

Item Rigid-Flexible PCB
Max Layer 36L
Inner Layer Min Trace/Space 3/3mil
Out Layer Min Trace/Space 3.5/4mil
Inner Layer Max Copper 6oz
Out Layer Max Copper 3oz
Min Mechanical Drilling 0.15mm
Min Laser Drilling 0.1mm
Aspect Ratio(Mechanical Drilling) 12:1
Aspect Ratio(Laser Drilling) 1:1
Press Fit Hole Ttolerance ±0.05mm
PTH Tolerance ±0.075mm
NPTH Tolerance ±0.05mm
Countersink Tolerance ±0.15mm
Board Thickness 0.4-3mm
Board Thickness Tolerance(<1.0mm) ±0.1mm
Board Thickness Tolerance(≥1.0mm) ±10%
Impedance Tolerance Single-Ended:±5Ω(≤50Ω),±10%(>50Ω)
Differential:±5Ω(≤50Ω),±10%(>50Ω)
Min Board Size 10*10mm
Max Board Size 22.5*30inch
Contour Tolerance ±0.1mm
Min BGA 7mil
Min SMT 7*10mil
Surface Treatment ENIG,Gold Finger,Immersion Silver,Immersion Tin,HASL(LF),OSP,ENEPIG,Flash Gold;Hard gold plating
Solder Mask Green,Black,Blue,Red,Matt Green
Min Solder Mask Clearance 1.5mil
Min Solder Mask Dam 3mil
Legend White,Black,Red,Yellow
Min Legend Width/Height 4/23mil
Strain Fillet Width 1.5±0.5mm
Bow & Twist 0.05%
Table of Contents
Primary Item (H2)

Different Types of Rigid Flex PCB Provided By GlobalWellPCBA

Simply select your Rigid Flex PCB below to access the guide.

Introduction

Rigid Flex PCB technology combines rigid PCBs and flexible circuits, combining the former's mechanical stability with the latter's adaptability. 

This hybrid approach allows electronic devices to achieve unprecedented compactness and reliability, making Rigid-Flex PCBs indispensable in modern electronic design.

What is a Rigid Flex PCB?

A Rigid Flex PCB is a hybrid circuit board incorporating rigid and flexible elements within a single, integrated unit. This design enables the PCB to maintain some sections rigidly while allowing others to bend or flex, accommodating various electronic devices' spatial constraints and functional requirements. 

The flexible sections are typically made from high-performance materials like Polyimide, which can withstand repeated flexing without failure. 

The rigid areas, often composed of materials such as FR4, provide structural support and house most electronic components.

Flex vs. Rigid vs. Rigid-Flex PCB

The differences between Flex, Rigid Flex, and Rigid PCBs primarily lie in their construction, flexibility, application suitability, and cost implications.

Rigid PCBs

  • Construction: Made from a solid, inflexible substrate, typically FR4.
  • Flexibility: Do not bend or flex; suitable for applications where the form factor is fixed.
  • Application Suitability: Widely used across various electronic devices due to their durability and cost-effectiveness.
  • Cost: Generally less expensive to produce, especially in high volumes.

Flex PCBs

  • Construction: Built on a flexible substrate, such as Polyimide, the PCB can conform to different shapes.
  • Flexibility: Can bend and fold, making them ideal for space-constrained or uniquely shaped applications.
  • Application Suitability: Best suited for dynamic applications where the PCB may need to flex or for devices where weight and space savings are critical.
  • Cost: More expensive than rigid PCBs due to the specialized materials and manufacturing processes required.

Rigid-Flex PCBs

  • Construction: Hybrid boards that combine rigid and flexible sections within a single PCB.
  • Flexibility: Offer the structural stability of rigid PCBs with the flexibility of flex circuits, allowing for complex designs that can fit into tight or unconventional spaces.
  • Application Suitability: Ideal for complex electronic devices that require both durability and the ability to bend or fold part of the PCB.
  • Cost: Typically the most expensive option due to the design and manufacturing complexity, but they can reduce overall assembly costs by eliminating connectors and discrete wiring.

Advantages of Rigid-Flex PCBs

  • Space Saving: Rigid-Flex PCBs can be bent or folded to fit into tight spaces, enabling more compact device designs by making optimal use of available space within electronic devices.
  • Shock and Vibration Resistance: The flexible sections of Rigid-Flex PCBs absorb shocks and vibrations, enhancing the durability and longevity of electronic devices, especially those exposed to harsh conditions.
  • Lightweight and Cost-effective: By eliminating the need for multiple connectors and cables, Rigid-Flex PCBs reduce both the weight and the manufacturing costs of electronic devices, making them lighter and more cost-efficient.
  • Simple and Fast Assembly Process: Rigid-Flex PCBs streamline the assembly process, reducing production time and minimizing the potential for errors, which leads to faster production timelines and higher-quality products.
  • High Reliability: Reducing solder joints and mechanical connectors lowers the likelihood of failure points, enhancing the reliability and performance of devices equipped with Rigid-Flex PCBs.
  • Easy Testing: Rigid-Flex PCBs can be thoroughly tested before assembly, ensuring any issues are identified and rectified early in the manufacturing process, contributing to the final product's high quality and reliability.

Types of Rigid-Flex PCBs

Rigid-flex printed Circuit Boards (PCBs) have become a cornerstone in modern electronics design, offering the unique advantages of both rigid and flexible PCB technologies.

Here, we delve into the various Rigid-Flex PCBs, exploring their characteristics, applications, and design considerations.

  • Single-Sided Rigid-Flex PCBs

  • Features: One conductive, rigid, or flexible layer with insulating layers on both sides.
  • Applications: Suitable for simple, low-density designs requiring minimal bending.
  • Advantages: Cost-effective and straightforward, ideal for space-saving in uncomplicated applications.
  • Double-Sided Rigid-Flex PCBs

  • Features: Conductive layers on both sides of the flexible substrate, allowing for more complex circuit designs.
  • Applications: Used in consumer electronics and medical devices where moderate complexity and component density are needed.
  • Advantages: Supports additional components and interconnections, balancing complexity and flexibility.
  • Multilayer Rigid-Flex PCBs

  • Features: Multiple layers of rigid and flexible circuits laminated together, accommodating high-density and complex designs.
  • Applications: Ideal for advanced applications in aerospace, military, and medical devices requiring compact form factors and high performance.
  • Advantages: It provides the highest design flexibility and performance and is suitable for integrating multiple functions into a small space.
  • Rigid-Flexible Composite PCB

  • Features: A specialized type where rigid and flexible circuits are intricately interconnected, offering seamless integration.
  • Applications: Custom-designed for specific applications needing robust connections between rigid and flexible sections, such as high-speed communication devices.
  • Advantages: Superior electrical performance and mechanical stability, tailored for complex industrial equipment and communication devices.
  • Design Considerations

When selecting the type of Rigid-Flex PCB for a project, several design considerations must be taken into account, including:

  • Complexity of the Circuit: The more complex the circuit, the more likely a multilayer or composite design will be necessary.
  • Flexibility Requirements: The extent and frequency of bending will influence the choice between single-sided, double-sided, or multilayer designs.
  • Component Density: High-density designs may require double-sided or multilayer Rigid-Flex PCBs to accommodate all components.
  • Cost Constraints: Single-sided Rigid-Flex PCBs are generally less expensive than their double-sided and multilayer counterparts.

Challenges in Designing Rigid-Flex

  • Complex Design Rules: Designing Rigid-Flex PCBs involves navigating intricate rules that balance electrical performance with mechanical constraints, requiring detailed planning and compatibility considerations between rigid and flex sections.
  • Bend Radius Considerations: Ensuring the flexible sections can bend without damage is crucial; a too-tight bend radius can lead to mechanical stress and failure, necessitating optimal bend radius calculations for durability.
  • Material Selection: Selecting appropriate materials is critical to achieving the desired balance of flexibility, durability, and electrical performance, with choices like Polyimide for flex areas and FR4 for rigid sections based on their properties.
  • Signal Integrity and EMI: Maintaining signal integrity while minimizing electromagnetic interference, especially in flex areas, demands careful routing, shielding, and grounding techniques to preserve signal quality.
  • Thermal Management: Effective heat dissipation strategies are essential, considering the different thermal behaviors of rigid and flex sections and employing methods like thermal vias and external cooling solutions.
  • Assembly and Manufacturing: The hybrid structure introduces complexities in assembly and manufacturing, requiring special attention to transition zones and adaptations in assembly lines for unique handling and testing requirements.
  • Mechanical Reliability: Guaranteeing that flex sections withstand repeated bending and flexing involves rigorous mechanical testing and considerations for material selection, trace layout, and protective coatings.
  • Testing and Inspection: Adapting testing methodologies to Rigid-Flex PCBs' unique structure requires specialized testing rigs and inspection techniques to accommodate their dynamic nature.
  • Design for Manufacturability (DFM): Balancing innovative designs with manufacturability challenges designers to consider production capabilities and limitations, often necessitating collaboration with manufacturers to optimize the design.
  • Environmental Factors: Designing PCBs to endure environmental conditions like moisture and temperature fluctuations involves selecting resistant materials, applying protective coatings, and considering ecological impacts on PCB properties.

How To Make A Rigid-Flex PCB Board?

The manufacturing process of Rigid-Flex PCBs is complex and nuanced, combining the techniques used in rigid and flexible PCB fabrication. 

This process requires precision and careful planning at each step to ensure that the final product adheres to the highest quality and functionality standards.

  • Material Selection

The first step in the manufacturing process is selecting the appropriate materials for both the rigid and flexible portions of the PCB. 

Materials like Polyimide are favored for their excellent flexibility and thermal stability in flexible areas. Materials such as FR4 are commonly used for rigid sections due to their mechanical strength and cost-effectiveness.

  • Drilling

Once the materials are selected, the next step is drilling, which involves creating holes for vias and component leads.

The placement and size of the holes are determined based on the design specifications, and it's essential to maintain accuracy to ensure proper alignment of the layers and components.

  • Copper Plating

After drilling, the board undergoes copper plating, which adds a thin layer of copper to the drilled holes and the board's surface. The thickness of the copper plating is carefully controlled to meet the board's electrical requirements.

  • Circuit Patterning

Circuit patterning involves transferring the circuit design onto the board. This can be achieved through various methods, such as photolithography, where a photoresist is applied to the board, exposed to light through a mask representing the circuit pattern, and then developed to remove the unexposed photoresist, leaving the circuit pattern on the board.

  • Etching

The etching removes the unwanted copper from the board, leaving behind the copper forming the circuit pathways.

This is typically done using a chemical etching solution that dissolves the unprotected copper. Care must be taken to ensure that only the unwanted copper is removed and that the remaining circuitry is precisely defined.

  • Inspection

After etching, the board is inspected for defects or deviations from the design specifications. This can involve visual inspections, automated optical inspections (AOI), and electrical testing to ensure the circuit paths are correctly formed and there are no shorts or opens.

  • Solder Mask, Silk Screen, and Surface Finish

The solder mask protects the circuitry and prevents accidental solder bridging between conductive traces during component soldering.

The silkscreen layer is then added to label component positions and other information on the PCB.

Finally, a surface finish is applied to the copper traces to protect them from oxidation and improve solderability.

  • Testing

The final step in the manufacturing process is testing, which verifies the functionality and performance of the PCB. 

This can include continuity tests, insulation resistance tests, and functional tests to ensure that the board meets all the required specifications and performance criteria.

Applications of Rigid Flex PCBs

Rigid Flexible Printed Circuit Boards (PCBs) have carved a niche for themselves across various industries, thanks to their innovative design, which marries the robustness of rigid PCBs with the adaptability of flexible circuits. 

  • Consumer Electronics: Rigid-flex PCBs enable sleek, compact designs in consumer electronics, such as smartphones and portable devices, by optimizing space and enhancing product reliability through their flexible and durable nature.
  • Medical Devices: In the medical sector, Rigid-Flex PCBs are crucial for developing wearable health monitors and diagnostic equipment, offering precision, reliability, and the ability to conform to ergonomic designs while withstanding medical environments.
  • Aerospace: Aerospace applications benefit from Rigid-Flex PCBs due to their resistance to extreme conditions, including vibrations and temperature fluctuations, making them suitable for cockpit instrumentation and satellite systems where reliability is paramount.
  • Automotive: The automotive industry utilizes Rigid-Flex PCBs in dashboard displays, infotainment systems, and advanced driver-assistance systems (ADAS), valuing their robustness and flexibility in dynamic and harsh automotive environments.
  • Wearable Technology: Wearable technology, such as smartwatches and fitness trackers, relies on Rigid-Flex PCBs for their compact, ergonomic designs that are both comfortable for daily wear and durable enough to withstand daily use.

Conclusion

Rigid Flex PCBs represent a pivotal innovation in electronic circuit design, offering a blend of flexibility, reliability, and space efficiency that traditional PCBs cannot match.

As technology continues to advance, their role in enabling the next generation of electronic devices is set to expand, making them a cornerstone of modern electronic design.

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