FPC (Flexible Circuit Board) mainly uses Polyimide (PI) Copper Clad Laminate (FCCL) or Polyester (PET) Copper Clad Laminate.

Flexible Copper Clad Laminate (FCCL) has two types of PI: adhesive and non adhesive.

The adhesive is applied to the PI film and then bonded to the copper foil.

There are two methods for making non adhesive soft copper-clad laminates. One is to use PI film as the carrier and dip copper foil on its surface. The other method is to use copper foil as the carrier, coat liquid PI on the surface of the copper foil, and then cure it.

The adhesive free substrate is relatively thin and cannot be distinguished on the surface. Only by conducting slice analysis can it be distinguished.