When the FPC flexible circuit board is bent, different types of stress are experienced on each side of its center line. The inside of the curved surface endures pressure, while the outside experiences tension. The magnitude of the stress is dependent on the thickness and bending radius of the FPC flexible circuit board. Excessive stress can lead to delamination of FPC flexible circuit boards, as well as breakage of copper foil. Therefore, it is important to carefully design the laminate structure of the FPC flexible circuit board to ensure that the two ends of the center line of the curved surface are as symmetrical as possible. Additionally, the minimum bending radius must be calculated based on the specific application.
The minimum bending radius can be calculated using the following formula: R=(c/2)[(100-Eb)/Eb]-D where: R=minimum bending radius (unit µm), c= copper thickness (unit µm), D = cover film thickness (unit µm), EB = allowable deformation of copper skin (measured in percentage). Different types of copper have different allowable deformations of copper skin, with crushed copper having a maximum deformation of ≤16% and electrolytic copper having a maximum deformation of ≤11%. Additionally, the value of the deformation of the copper skin may vary based on the specific use occasion. For one-time bending, the limit value of the critical state of fracture is used (for rolled copper, the value is 16%). For bending installation design, the minimum deformation value specified by IPC-MF-150 is used (for rolled copper, the value is 10%). For dynamic flexible applications, 0.3% of the copper deformation is used, while for magnetic head applications, 0.1% of copper deformation is used. By setting the allowable deformation of the copper skin, the minimum bending radius can be calculated.
Dynamic flexibility refers to applications where the copper skin experiences deformation, such as the phosphor copper shrapnel in the IC card socket, which contacts the chip after the IC card is inserted. The shrapnel undergoes constant deformation during the insertion process, making this application scenario flexible and dynamic.
The minimum bending radius can be calculated using the following formula: R=(c/2)[(100-Eb)/Eb]-D where: R=minimum bending radius (unit µm), c= copper thickness (unit µm), D = cover film thickness (unit µm), EB = allowable deformation of copper skin (measured in percentage). Different types of copper have different allowable deformations of copper skin, with crushed copper having a maximum deformation of ≤16% and electrolytic copper having a maximum deformation of ≤11%. Additionally, the value of the deformation of the copper skin may vary based on the specific use occasion. For one-time bending, the limit value of the critical state of fracture is used (for rolled copper, the value is 16%). For bending installation design, the minimum deformation value specified by IPC-MF-150 is used (for rolled copper, the value is 10%). For dynamic flexible applications, 0.3% of the copper deformation is used, while for magnetic head applications, 0.1% of copper deformation is used. By setting the allowable deformation of the copper skin, the minimum bending radius can be calculated.
Dynamic flexibility refers to applications where the copper skin experiences deformation, such as the phosphor copper shrapnel in the IC card socket, which contacts the chip after the IC card is inserted. The shrapnel undergoes constant deformation during the insertion process, making this application scenario flexible and dynamic.
