PCB Blog - What is a Rigid-Flex PCB?

The birth and development of FPC and PCB have given birth to the new product of Rigid-Flex PCB. Therefore, a soft hard combination board refers to a circuit board with FPC and PCB characteristics formed by combining flexible circuit boards and hard circuit boards through pressing and other processes according to relevant process requirements.

Rigid-Flex PCB

Production process

Because the Rigid-Flex PCB is a combination of FPC and PCB, the production of Rigid-Flex PCB should have both FPC production equipment and PCB production equipment. Firstly, the electronic engineer draws the circuit and appearance of the Rigid-Flex PCB according to the requirements and then sends it to the factory that can produce soft and hard bonding boards. After the CAM engineer processes and plans the relevant documents, the FPC production line is arranged to produce the required FPC and PCB production lines for PCB production. After these two types of soft and hard boards are produced, according to the planning requirements of the electronic engineer, the FPC and PCB are seamlessly pressed together through a pressing machine, After a series of detailed steps, a soft and hard combination board was finally made. A very important aspect is that due to the difficulty and numerous details of the Rigid-Flex PCB, a full inspection is generally required before shipment, as its value is relatively high to avoid causing losses to both the supply and demand parties.

The characteristics of the Rigid-Flex PCB

1. Lightly important, with a thin interlayer.

2. Short transmission path and small conduction aperture.

3. Low noise and high reliability.

4. High and low-temperature resistance, good flame resistance, and foldable without affecting signal transmission function.

5. Stable chemical changes, stability, and high reliability.

6. It can reduce the volume of application products, significantly reduce weight, increase functionality, and reduce costs.

7. The design of related products can reduce assembly time and errors, and improve the product's service life.

8. It can prevent static interference and has flexible flexibility, allowing for three-dimensional wiring and changing shape according to space limitations.

Application fields of Rigid-Flex PCB

1. Industrial use: including industrial, military, and medical fields. The requirements for soft and hard boards in these fields include high reliability, high accuracy, low impedance loss, complete signal transmission quality, and durability. Due to the complexity of the manufacturing process and low output, the production cost is high.

2. Mobile phone: The application of a soft and hard combination board in a mobile phone, commonly including the turning point of a foldable phone, image module, buttons, and RF module.

3. Consumer electronics products: The most representative is the soft and hard boards used in DSC and DV. In terms of performance, its soft and hard boards can connect differently PCB hard boards and components in a three-dimensional manner. At the same circuit density, it can increase the total usable area of the PCB, improve its circuit carrying capacity, and reduce the signal transmission limit and assembly error rate of the contacts. Structurally speaking, soft and hard boards are lightweight and thin, allowing for flexible wiring, which is essential for reducing volume and weight.

4. Car: Commonly used include buttons for connecting the motherboard on the steering wheel, connections between the car's video system screen and control panel, operation connections for audio or function keys on the side door, reverse radar imaging system, sensors, car communication system, satellite navigation, rear seat control panel and front-end controller connection board, exterior detection system, etc. 

Advantages and disadvantages of Rigid-Flex PCB

Advantage

1. The Rigid-Flex PCB has both the characteristics of FPC and PCB, so it can be used in some products with special requirements, including a certain flexible area and a certain rigid area, which is very helpful in saving internal space, reducing finished product volume, and improving product performance.

2. Rigid-Flex PCB can replace connectors, reduce the number of connectors, and not only save costs; More importantly, the electrical performance can be maintained even after repeated bending for over 100000 times; It can achieve impedance control of the thinnest insulated carrier board, and reduce weight, installation time, and cost; the material has high heat resistance and also has better thermal diffusion ability.

Disadvantage

The production process of soft and hard combination boards is diverse, with high production difficulty, low yield rate, and a large number of materials and manpower required. Therefore, their prices are relatively expensive and the production cycle is relatively long.

Design requirements for Rigid-Flex PCB

Layout requirements

1. The device is placed in a hard area and the flexible area is only used for connection, which has a long bending life and can improve reliability.

2. When the device is placed in a hard area, the distance between the edge of the device and the soft hard junction is greater than 1mm.

3. If the soft zone goes deep into the hard zone, the distance between the two should be at least 1mm.

Wiring requirements for Rigid-Flex PCB

1. The direction of the flexible zone route is perpendicular to the bending line, and the route at the bending point can be connected by an arc to avoid the pattern cracking in a certain direction during the bending test.

2. The soft area graphics should be at least 10 miles away from the board edge, and holes should not be punched. The distance between the through-hole and the soft hard joint should be at least 2mm.

3. If there is an internal electrical layer in the soft area, isolation can be placed in the soft area to improve its softness without affecting the power supply connection, current value, and impedance value.

4. To facilitate production differentiation, soft area markings should be added to the soft area of the mechanical auxiliary layer.

5. If the design requires impedance design and impedance lines need to be arranged in the soft area, it must be noted that when formulating the impedance structure diagram, the soft area wiring layer must have a corresponding reference layer on evry single chip.

The Rigid-Flex PCB is mainly used in consumer electronics. The demand for the use of soft and hard bonding plates for camera lenses, screen signal connections, battery modules, etc., including smart phones, has increased significantly. Especially in the use of smartphone camera lenses, as multi-lens phones have become a design trend for various mobile phone brands, the demand for both soft and hard combination boards has increased.