Semi Flex PCB Advantages, Limitations, and Applications

Semi flex PCB manufacturing adopts specific manufacturing methods to design a flex-to-install PCB. This PCB can offer an economical solution for some specific applications.

Also, semi flex PCBs can serve as an adequate solution for more advanced applications. The manufacturing process is less complicated. In this article, we will discuss more information on semi flex PCB.

What is a Semi Flex PCB?

Semi flex PCB is a type of board manufactured using a specific process of milling a part of a rigid FR4 down to 0.20mm +/- 0.10mm thickness.  Also, this process allows the PCB to be bendable enough to fit inside a casing. This PCB is mostly utilized for a one-time bend installation.

Semi flex PCB is a flex to install board entirely made of FR4. The flexing element of this board is a thin FR4 core. Also, the FR4 core can bend a limited number of times. Therefore, this board is a suitable option in applications that need to mount two boards in a unit at an angle. A semi flex board is wholly made from FR4. It is cheaper than complex polyimide rigid-flex circuits.

Users can design an Fr4 semi flex board that can bend a number of times. Therefore, this enables installation and maintenance as required. The most important benefit of this PCB is that it can adapt to available space. The fabrication of semi flex PCBs involves removing material from a portion of the board.

The minimum bending radius of a single layer semi flex PCB is 5,0mm. Also, this is beyond polyimide flex.  But, this is adequate for most applications. It is possible to achieve a 180° bending angle in a semi flex board. Also, the number of bending cycles is below 10.

The FR4 semi flex PCB can change its shape based on the space limit. Also, this type of circuit board is bendable without impacting signal transmission.

Advantages of Semi-Flex PCB

Low Cost

Semi-flex PCB manufacturer makes use of epoxy resin FR-4 material. After which depth milling selectively minimizes the traditional material’s thickness. This helps to achieve a good level of flexibility. The fabrication process of semi flex boards minimizes cost. Also, semi flex boards are ideal for cost challenging applications. This PCB is much cheaper than rigid-flex boards.

High Reliability

Semi flex PCBs are widely used in the electronics industry. The manufacturing process of this board can minimize the entanglement of connectors. After completing the assembly, the flexible part can be bent to the final shape without utilizing the flexible substrate. Therefore, this prevents the reliability problem caused by the contraction of the rigid substrate and flexible substrate. Hence, this enhances the reliability of electronic devices.


When it comes to design and assembly, a semi flex PCB can save time. Also, you can easily assembly and integrate this PCB into housings and boxes.


A semi flex PCB provides the enhanced flexibility to fit in a small device. Therefore, you don’t have to design a device based on the PCB specifications. Also, a semi flex board offers a flexible connection when used.

Special installation performance

Semi flex circuit boards can be bent locally. Also, engineers can achieve local bending based on product requirements.

Applications of Semi Flex PCBs

Semi flex PCBs are widely used in several applications. Due to the high reliability and quality of these boards, you will find them in some applications.


The semi flex PCB plays a vital role in the automotive industry. This PCB is ideal for applications in which there is no dynamic stressing of the bending area. You will find a semi flex PCB in automobile parts. This board helps to design some parts of a vehicle like antilock brakes and airbag systems. Also, automotive engine control systems feature this board.

Industrial electronics

A semi flex PCB can be very useful in producing industrial electronics. Also, this board has enhanced flexibility and high reliability.

Consumer electronics

You will find semi flex PCBs in cell phones and hearing aid devices. The semi flex PCBs play a significant role in the consumer electronics industry.

Medical devices

There are several medical devices that feature semi flex boards. Some of these devices include heart monitoring devices and hearing aid devices.


The telecommunication industry also relies heavily on the semi flex boards. Also, these boards are available in satellites and GPS trackers.

Potential Problems and Solutions During FR4 Semi Flex Fabrication

One of the major problems of FR4 semi flex boards is controlling the tolerance and accuracy of depth-control milling. Therefore, rigid PCBs need to have enough flexibility. During the depth-controlling milling process, some factors should be fully considered.

Depth controlled milling test A

The manufacturer uses the mapping method to carry out the remaining thickness milling. Also, the manufacturer can achieve this according to the remaining thickness after testing the board in terms of 90 degree bending. The damage of the glass fiber bundle is the major cause of PCB’s failure.

Depth controlled milling test B

The copper’s dielectric thickness of copper between L2 and solder mask is between 0.188mm to 0.213mm. Also, the manufacturer fails to perform 90 degree bending if the remaining thickness is above 0.283mm. Therefore, you can perform mechanical manufacturing when you control the remaining thickness. This has to be within a tolerance of 0.245mm+-0.213mm.

Depth controlled milling test C

There is a forward effect on machine uniformity and board warpage. This is due to size shrinking. The manufacturer carries out the depth controlled milling according to the set size of 6.3 X 10.5 inches. The mapping point will measure the machine uniformity.

According to FR4 6-layer semi flex PCB fabrication, there is a special production method. The manufacturer applies it and develops it to control depth and maintain the thickness. Therefore, this simplifies manufacturing procedures.


Semi flex boards are widely used in telecommunication, automotive electronics, and other fields. These boards feature low installation cost and high reliability. Semi flex has drastically reduced manufacturing cost and difficulties in the fabrication process. Also, these boards can meet the requirements of local bending of a particular number of times.

    GET A FREE QUOTE PCB Manufacturing & Assembly Service
    File Upload