Electronics Manufacturing Service, PCB Manufacturing

Semi-Rigid PCBs: The Future of Compact and Durable Electronics

Semi-flex PCB

Electronic devices, over the past decade or so, have become increasingly slim and smart taking up as little space as possible. In a race to occupy minimum space and utilize it to the maximum, semi-flex PCBs are the wave to ride. The demand for adaptable and versatile circuit boards makes the perfect headroom for the development of such PCBs that can occupy space efficiently.

What is Semi flex PCB?

Semi-flex PCBs are printed circuit boards made of rigid laminates, usually FR4 material, but they can be bent at a certain part by thinning to a thickness of 0.3mm or less. This kind of PCB strikes the perfect balance between rigid PCBs and flexible PCBs, possessing the features of both conventional rigid PCBs and modern flex PCBs. Rigid PCBs essentially provide a solid, flat structure while flex PCBs offer extreme foldability.

Semi-flex PCBs are rigid throughout most of the routing and component area but also have some flexible joints allowing them to be bent or folded in certain areas. They allow the PCB to flex to some extent while maintaining the strength and structural integrity of the board. This balance allows semi flexible PCBs to fit inside a smaller finished product while not requiring extremely advanced technology, as in flex PCBs.

Construction of Semi flex PCB

Employing a combination of rigid and flexible materials, the semi flex PCBs are produced. Generally, the components are placed on the rigid area of the board, while the routing may pass through the bent area, as it is extremely expensive and difficult to find such components that can be placed on the bent areas.

The rigid core, made up of conventional materials, provides the structural integrity to the board. FR4 material is used for the manufacture of the flexible area. FR4 is a PCB base material made from flame retarded epoxy resin while providing up to 180° bend angle. This material also possesses phenomenal thermal resistance capabilities. In other words, FR4 is a material that makes the idea of 3D PCBs a reality and provides the most basic foundation of semi flexible PCBs.

Construction of semi flex PCB

As in the diagram above, the left and right parts are rigid parts and the area in the middle is flexible, allowing the PCB to be bent.

The manufacturing process to artistically thin the PCB down to have the flex zone, a process called controlled depth routing or milling down is conducted, where the thickness is decreased enough to provide flexibility while maintaining the structural integrity and strength.

Advantages of Semi flex PCBs

Semi flexible PCB has many advantages because it combines the good features of both rigid and flexible PCBs, such as space-saving, cost-saving, and high reliability.

  • Space Saving

The main feature or the USP (unique selling point) of semi rigid PCBs is space-saving. To be able to produce compact and space-efficient products, semi-flex PCBs provide enough leverage to the producer, which rigid PCBs can not provide. They are agile enough to accommodate multiple other components than the PCB, reducing the overall size of the package. Conventional PCBs are known to be the center of attention in electronic goods around which other components are adjusted, while the case is fairly different for semi flexible PCB type.

  • Cost Efficient

Furthermore, semi rigid PCBs are cost-efficient as compared to flex PCBs or rigid-flex PCBs as the advanced technology and materials, which are expensive, do not need to be used in the overall PCB. Instead, the flexibility of semi rigid flex PCB is achieved by thinning the rigid areas where the board is to be bent. This can easily be predetermined during the design of how the PCB is going to be placed inside the product and how the component placement is going to be done, such that it minimizes the area to be bent and hence being as cost-effective as possible.

  • High Reliability

While maintaining this versatility, the materials used in semi flex PCBs provide high reliability. They offer great signal integrity, strength, thermal resistance and low-noise solutions. They provide the design engineer enough leverage to design the product as efficiently as possible without worrying about the cost and board quality. This creates room for the product designers to design an aesthetically pleasing and ergonomically efficient product, with increased utility for the end user.


Applications of Semi flex PCB

Semi rigid flex PCBs are used widely in a lot of industries, such as wearable devices, industrial robotics and automation, vehicles and automotive, telecommunications, aerospace, medical equipment, military, etc. Here we will list a few of them.

  • Wearable Devices

Semi-flex PCBs are the greatest asset to wearable technology, as these devices require them to be as compact as physically possible, to feel lightweight and to be easily manageable. While saving space, wearable devices on a large scale have to be affordable, hence their manufacturing costs must be low as well. Semit rigid flex PCBs provide a perfect bridge between the flexibility of flex PCBs and the cost-effectiveness of the rigid PCB. Devices such as smart watches, earphones and health monitoring devices are major applications for the semi flex type PCB.

  • Industrial Robotics and Automation

Control panels, industrial robots, sensors and machinery interfaces employ semi-flex PCBs due to their vibration, shock and temperature resistance. The versatility offered by them provides a reliable platform for industrial automation machinery which requires robustness and strength from the components. As industries are becoming increasingly automated, the demand for semi flex PCBs will continue to rise.

  • Vehicles and Automotives

The need for premium parts will only grow as the automotive industry shifts more and more toward electric vehicles (EVs). Modern cars with fuel engines also place a greater emphasis on the extras and luxuries found inside, like ADAS, cruise control, GPS, driving modes, screens with more apps, and improved entertainment systems. High performance and dependability in hardware are essential requirements for all these technologies. Semi-flex PCBs, due to their vibration resistance and ability to fit into small structures, are a perfect choice for motherboards of these modern systems used in vehicles.

Semi flex PCB

Key Considerations in Semi flex PCBs Design and Production

It is essential to maintain some rules and regulations while designing and manufacturing semi flex PCBs.

  • Mechanical Design Consideration

First and foremost, the mechanical design is to be considered. The mechanics of the design are important as the PCB is required to operate mechanically and have flexibility. During this, the flexural strength, fatigue resistance and bend radius are to be considered, so the structural integrity of a semi flex PCB is not compromised.

  • Manufacturing Difficulties

Secondly, the manufacturing process of this PCB is more complex and detailed than a conventional rigid PCB, as it requires the incorporation of flexible FR4 materials and controlled depth routing, which is critical for semi-flex PCBs.

  • Materials Selection

In addition, the materials selected should also be suitable for the application, such that they maintain the signal quality and strength of the PCB.

  • Sufficient Tests

Towards the end, there need to be rigorous tests, both mechanical and electrical to ensure a reliable end product.



Semi-flex PCBs are an elegant modern-day invention in the electronics world. As appliances, electronics and devices become increasingly smart, the demand for such PCBs will continue to rise. In addition, the innovative designs of existing appliances will be aided by semi flex PCBs, as they will allow maximum adaptability leverage to product designers, in terms of effective space occupation and cost-friendly outcomes. By embracing the characteristics, advantages and applications of semi flex PCBs, engineers can utilize their complete potential in creating and producing innovative, modern-day and future electronics.

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