In PCB design, the flexural performance of FPC is very important, and the factors that affect it can be described in two ways:

First, the FPC material itself, the following points have an important impact on the flexural properties of FPC.
1.The molecular structure and orientation of copper foil (i.e. copper foil)
The bending resistance of rolled copper is obviously better than that of electrolytic copper foil.
2.Thickness of copper foil
With a variety of copper foil thickness Qinai flexural performance will be better.
3.The type of glue used in the base material
Generally speaking, epoxy resin is more flexible than acrylic rubber. Therefore, the epoxy system is the main choice in the selection of high flexibility materials. And tensile modulus (tensilemodulvs) of higher glue can improve flexibility.
4.The thickness of the adhesive used
The thinner the thickness, the better the softness of the material. It can increase the flexibility of FPC.
5.Insulating Substrate
The thinner the thickness of the insulating material PI, the better the flexibility of the material, and the flexibility of the FPC is improved. The lower the amount of modolos (tensile) PI, the better the flexural performance of the FPC.
The main factors affecting the deflection of the material are summarized as two major aspects: the type of material chosen and the thickness of the material.

Second, from the process of FPC analysis of its flexibility.
1.Symmetry of FPC combinations
When the base material is bonded to the covering film, the better the symmetry of the copper foil material, the better its flexibility. Because the stress is consistent when it is bent. The thickness of PI on both sides of the PCB plate tends to be uniform, and the thickness of the adhesive on both sides of the PCB plate tends to be uniform
2.Control of pressing process
In the coverlay pressing requirement to completely fill the gum line intermediate, has no stratification (sections). If there is a stratification phenomenon, which is equivalent to bare copper in flexure, the deflection will decrease in flexure.