In modern electronic device design, the types and structures of PCBs are becoming increasingly diverse to meet the ever-changing technological demands. Rigid-Flex PCBs, an innovative design that combines both rigid and flexible materials, typically involve a manufacturing process where pattern plating is performed on both rigid and flexible substrates, and then adhesive is used to bond the two together. The adhesive is usually a non-flowable prepreg material. However, flexible materials are more expensive, and the manufacturing process is more complex, causing the cost of multi-layer Rigid-Flex PCBs to be 5 to 7 times higher than that of traditional multi-layer rigid PCBs, which limits the widespread application of Rigid-Flex PCBs. Additionally, compared to rigid materials, flexible materials have a greater degree of expansion and contraction. This inconsistency in dimensional changes can lead to misalignment of the circuit patterns between the rigid and flexible materials during lamination, thereby reducing the product's reliability.

Therefore, although Rigid-Flex PCBs offer significant advantages in many high-end applications, their high cost and complex manufacturing process remain the main factors limiting their widespread adoption. In this context, Semi-Flex PCBs have emerged as an alternative. Unlike traditional Rigid-Flex PCBs, Semi-Flex PCBs achieve flexible areas by locally removing material (such as through deep milling) on a rigid PCB material, allowing certain regions to bend while the majority of the board remains rigidly supported. This design approach satisfies the need for flexible connections in some applications, while significantly reducing production costs and manufacturing complexity.

How is the minimum bending radius of a Semi-Flex PCB calculated?

The minimum bending radius (R) of a Semi-Flex PCB is calculated as R = W * T.

This is an approximate calculation formula.

For single-sided boards, W is 6.

For double-sided boards, W is 12.

For multi-layer boards, W is 24.

T is the board thickness.

The minimum bending radius is no less than 1.60 mm.

Advantages of Semi-Flex PCBs

Semi-Flex PCBs offer many benefits to electrical engineers and designers.

1. Space-saving: Like flexible PCBs, Semi-Flex PCBs excel in space-saving. Since they can bend during installation, larger PCBs can fit into smaller and more confined spaces.

2. Cost-reducing: Semi-Flex PCBs can significantly reduce costs compared to flexible PCBs. The flexible areas of Semi-Flex PCBs are achieved by precisely milling FR4 material, while flexible PCBs rely on more expensive polyimide substrates to achieve higher flexibility. Although flexible PCBs are required in certain special applications where greater bending capabilities are needed, in many cases, Semi-Flex PCBs offer a better way to control costs.