Rigid-flex Board : 5 Unforgettable Things That Make You Love and Hate

With the rapid development and continuous evolution of electronic products, innovation and flexibility have become key words for designers. To meet the growing demands, traditional rigid  PCBs no longer fully satisfy the design requirements of various complex electronic devices. In this context, rigid-flex boards have emerged as a crucial component of innovative design in the new era, thanks to their unique characteristics and advantages.

What is rigid-flex board?

Rigid-flex board is an increasingly common innovative technology in electronic devices. The emergence and development of FPC and PCB have led to the creation of this new product, which combines flexible and rigid boards. Through processes such as lamination, the flexible circuit board and rigid circuit board are combined according to relevant technological requirements, resulting in a combination of the characteristics of rigid boards and flexible circuit boards. This combination provides both strong mechanical stability and reliability, as well as flexibility and adaptability. The advent of rigid-flex boards has changed the design and application of traditional rigid circuit boards, bringing many new opportunities and challenges to the electronics industry. Compared to traditional rigid circuit boards, FPCBs have significant advantages in terms of shape, weight, and space utilization. This provides designers with greater freedom, enabling them to achieve more innovative and precise product designs.

Common types of rigid-flex board

Type 1: Flexible-Rigid Board. A flexible PCB  and a rigid PCB are bonded together without plated-through holes (PTH) connections, and the number of layers is more than one.

Type 2: Multi-Layer Flexible-Rigid  Board. This type has plated-through holes (PTH) and includes more than two conductor layers.

A coin has two sides, and rigid-flex board is no exception. Let's first discuss the advantages of rigid-flex boards .

Advantages of rigid-flex board

Flexibility - With their unique design and manufacturing process, FPCBs demonstrate excellent flexibility and adaptability. These boards can be bent, folded, or flexed to the desired shape to meet various product design requirements. For example, when designing smartphones or wearable devices, FPCBs can be freely bent and molded to accommodate complex shapes. This flexibility provides designers with greater freedom to create more intricate and elegant products. The flexibility of rigid-flex board makes it an ideal choice for wearable device design. For instance, devices like smartwatches, health monitors, and smart glasses need to adapt to various sizes and shapes of wrists, bodies, or faces. The flexibility and bendability of rigid-flex boards allow these devices to snugly fit the user's body contours, providing a comfortable wearing experience.

Rigid-flex boards play a crucial role in the design of curved display screens. Modern devices such as smartphones, televisions, and automotive displays are increasingly adopting curved designs to provide a better visual experience. The flexibility of boards allows the display screen to bend along the curve without the need for rigid connectors, enabling seamless curved designs. The adaptability of rigid-flex boards makes it an essential component of foldable devices. For example, products like foldable smartphones and foldable tablets require the circuitry to maintain connectivity when opened and folded. The design of  boards allows the circuit board to bend and fold smoothly, enabling seamless transitions between various forms of the device while maintaining reliable circuit connections. The flexibility and adaptability of rigid-flex boards provide innovative solutions for the design of automotive electronic systems. Electronic devices in automobiles need to adapt to narrow spaces and complex shapes while withstanding environmental factors such as automotive vibrations and temperature variations. The flexibility of rigid-flex boards allows circuit boards to be installed compactly within various shaped vehicle components while providing reliable electrical connections.

From wearable devices to curved displays, and even foldable devices and automotive electronic systems, the flexibility and adaptability of rigid-flex boards enable electronic products to accommodate different shapes, sizes, and environmental conditions, providing enhanced user experience and functionality. In addition, rigid-flex boards also offer higher reliability. Compared to traditional rigid boards, rigid-flex boards eliminate connectors or plug-in connections, thereby reducing potential points of failure. This design also reduces issues with inter-circuit connectivity and the risk of electrical noise, providing a more stable and reliable electronic device. In the aerospace field, rigid-flex boards are widely used in equipment such as aircraft and satellites. These devices face harsh operating conditions, including high temperatures, low temperatures, vibrations, and impacts. The high-temperature resistance of rigid-flex boards allows them to operate stably in high-temperature environments while maintaining the reliability of circuit connections. At the same time, their vibration and impact resistance enable them to withstand the intense vibrations and impacts experienced during flight, ensuring the normal operation of electronic equipment. In medical devices such as pacemakers, implanted sensors, and wearable medical devices, the reliability of rigid-flex boards is crucial. These devices need to operate steadily for extended periods, while also requiring durability and resistance to corrosion. The special design and material selection of rigid-flex boards enable them to adapt to changes in the body's environment and withstand the influence of bodily fluids and chemicals. This ensures long-term reliability and stability of medical devices. Industrial control systems often face harsh working environments, including high humidity, corrosive gases, and vibrations, among others. Rigid-flex boards are widely used in these systems to meet their requirements for reliability and durability. The special materials and protective measures of rigid-flex boards enable them to resist moisture intrusion in high humidity environments, while also providing corrosion resistance and oxidation resistance. Furthermore, the vibration resistance of rigid-flex boards ensures the normal operation of the system in vibrating environments, preventing circuit interruptions or malfunctions. Another factor that makes rigid-flex boards popular is their space efficiency. Due to their flexibility and thin design, rigid-flex boards occupy less space in compact electronic devices. This is crucial for modern consumer electronics such as smartphones, tablets, and wearable devices. The use of rigid-flex boards makes the devices thinner and lighter while still meeting complex circuit connectivity requirements. In modern smartphones, space is crucial. The use of rigid-flex boards allows for more compact and lightweight phone designs. These boards can bend and fold according to the shape of the phone, accommodating various tight spaces and closely integrating with other electronic components. Rigid-flex boards can connect different modules within the phone, such as the display screen, camera, battery, and touchpad, resulting in a more compact device structure while providing stable electrical circuit connections. Rigid-flex boards are also widely used in the field of wearable devices. Traditional rigid boards cannot meet the requirements of wearable devices as they need to adapt to the curvature and movement of the human body. Rigid-flex boards can be bent, folded, and rolled to fit the shape of the wrist, arm, or other body parts. This makes wearable devices more comfortable and reduces the space occupied on the body. In the field of automotive electronics, spatial efficiency is one of the key factors. The use of rigid-flex boards allows for more compact automotive electronic modules, thus freeing up more space for other functions and designs. For example, on the car dashboard, rigid-flex boards can connect various instruments and displays in a compact manner, reducing the space requirements for wiring. Additionally, rigid-flex boards can bend and adapt to the curved surfaces inside the vehicle, enabling better space utilization. Medical devices often need to accommodate multiple electronic components and sensors within limited space. The application of rigid-flex boards allows for a more compact design of medical devices, thereby saving space. For example, in implantable medical instruments, rigid-flex boards can bend and flex to conform to the shape of the instrument and establish reliable connections with other components. As a result, medical instruments can better adapt to the patient's internal environment and provide accurate medical monitoring and treatment. Rigid-flex boards are highly favored for their excellent reliability and durability. These boards undergo special treatment and possess characteristics such as vibration resistance, impact resistance, and high-temperature resistance. This makes rigid-flex boards highly suitable for applications that require high reliability and stability, such as aerospace, medical devices, and industrial control systems. Rigid-flex boards are also capable of operating in harsh environmental conditions, such as high humidity, extreme temperatures, and chemical corrosion, without losing performance or causing failures. After discussing the advantages, let's look at the drawbacks of rigid-flex boards.

The drawbacks of rigid-flex board

Despite having numerous advantages, the manufacturing process of flexible printed circuit boards  is complex. Compared to traditional rigid boards, manufacturing rigid-flex boards requires higher technical requirements and specialized manufacturing equipment. This can result in a more expensive and time-consuming manufacturing process. Additionally, the manufacturing of rigid-flex boards involves multiple processes and the combination of different materials, which may increase the difficulty of quality control during the manufacturing process. Let's have a brief understanding of the production process of rigid-flex boards , and when choosing a manufacturer, we should select one that has both FPC production equipment and PCB production equipment. First, electronic engineers draw the circuit and outline of rigid-flex boards according to the requirements. Next, the drawings are sent to the production manufacturer, where the CAM engineers process the files. Third, the boards production line produces the required rigid-flex boards, and the PCB production line produces the required PCBs. Fourth, after the flexible and rigid boards are produced, they are seamlessly bonded together using a laminating machine, following the requirements specified in the drawings. Finally, through a series of detailed processes, the final product, the flexible and rigid combined board, is manufactured. In the manufacturing process of rigid-flex boards, it is necessary to select and handle different types of materials. For example, flexible parts typically use polyimide (PI) film as the substrate, while rigid parts may use FR4 or other rigid substrates. This involves understanding and selecting different material properties to ensure they can be compatible and reliably function together in the manufacturing process and final application. Rigid-flex boards are typically composed of multiple layers of materials, including laminated combinations of rigid and flexible parts. During the manufacturing process, precise lamination and bonding steps are required to ensure the adhesion and connection quality between different material layers. This may involve the use of precision bonding equipment and control of lamination parameters to ensure reliability and consistency between each layer. The flexibility of the board comes from its ability to bend and conform to the desired shape. During the manufacturing process, precise bending and shaping operations are required to ensure that the board maintains its electrical performance and reliability after bending. This may involve the use of specialized equipment and molds, as well as precise control parameters, to avoid excessive stress and damage. During the manufacturing process of rigid-flex boards, wiring and circuit design also become more complex. Due to the flexible portion's bending and folding capabilities, restrictions on circuit paths and wiring rules need to be considered. Designers must determine the optimal paths for circuit connections and adhere to minimum bend radius limitations to ensure reliability and stability of the circuit connections. Strict quality control and testing are required in the manufacturing process of  boards. Due to the combination of multiple materials and layers involved, the challenges of quality control increase. Manufacturers must ensure the quality of each manufacturing step, such as material processing, lamination quality, accuracy of bending and forming, and reliability of circuit connections. This may require the use of high-precision detection equipment and techniques, such as X-ray inspection, infrared detection, and electrical performance testing. Rigid-flex boards have certain limitations in some design respects, which can be a reason for some people to dislike them. For instance, rigid-flex boards have certain restrictions on wiring rules, especially in circuit connections and signal transmission. Additionally, rigid-flex boards often have limitations on the minimum bending radius, which means that curve constraints need to be considered during the design process. These limitations can pose challenges for certain specific applications and innovative designs, requiring designers to carefully weigh the pros and cons during the design process. Due to the complexity of the design and manufacturing of rigid-flex boards, repairing and replacing them can be more challenging. If a board malfunctions or requires replacement, it may necessitate the involvement of specialized technicians for repair. Furthermore, due to the unique design and customization of rigid-flex boards, longer repair times and higher costs may be incurred.

Applications of rigid-flex board

Rigid-flex board have a wide range of applications, such as high-end smartphones like the iPhone, high-end Bluetooth headphones (which require signal transmission over a distance), smart wearable devices, robots, drones, curved displays, high-end industrial control equipment, aerospace satellites, and more. As smart devices continue to develop towards higher integration, lightweight design, and miniaturization, and with the new requirements for personalized production brought by Industry 4.0, rigid-flex board offer both the stability of rigid boards and the ability to be assembled three-dimensionally, making them highly promising. In 2019, the global market size of rigid-flex board was approximately 1.66 billion US dollars, accounting for only about 2.8% of the overall circuit board market. However, products such as smartphones, wireless headphones, drones, cars, AR/VR devices, etc., all experienced the highest growth rates in 2019. With the increasing number of subsequent applications, rigid-flex board remains one of the most promising products with growth potential in 2020. It is estimated that the global market value of rigid-flex board will reach 2.3 billion US dollars in 2022, accounting for approximately 3.3% of the global circuit board production value. Mobile device applications were the largest software and hardware board market in 2019, accounting for approximately 43% of the overall software and hardware integrated board market. Applications such as camera lenses, screen signal connections, and battery modules for smartphones have significantly increased the demand for software and hardware integrated boards. In particular, the application of smartphone camera lenses has seen a significant rise in demand due to the trend of multi-camera smartphones among various brands. This increase in both the quantity and average unit price of software and hardware integrated boards will contribute to a higher share in the mobile device application market. The development of mobile phone lens software and hardware integrated boards is mainly driven by the lightweight, thin, and high-density requirements of smartphone lenses, all of which require the utilization of software and hardware integrated boards. Additionally, factors such as placement position, orientation, signal interference, heat dissipation, and specification requirements are taken into consideration. Furthermore, some lenses adopt a periscope-like structure design due to optical zoom requirements, further exacerbating the stringent spatial limitations for smartphone lenses. As a result, various form factors have emerged in terms of appearance, placing more rigorous demands on software and hardware integrated boards, and expanding their application scope.