FPC Flexible Circuit Boards: Types and Processes Detailed Explanation

FPC (Flexible Printed Circuit) boards are printed circuit boards made of polyimide or polyester film as the base material. With advantages such as high wiring density, light weight, and thin thickness, they are widely used in mobile phones, tablets, medical equipment, LEDs, automotive electronics, smart wearables, and other products. Their "family members" are mainly divided into single-sided FPC, double-sided FPC, and multilayer FPC, with the process characteristics of each category as follows:

1. Single-sided FPC: The "Transformation" of Basic Models
Single-sided FPC has a conductive pattern formed by chemical etching (made of rolled copper foil). Insulating substrates can be polyimide, polyethylene terephthalate, etc. Although it is a basic model, it can be divided into four "sub-branches":
Single-sided connection without cover layer:The conductor pattern is directly attached to the insulating substrate with no cover layer on the surface. Circuit connection is achieved through soldering, fusion welding, or pressure welding.
Single-sided connection with cover layer: Compared to the above, it has an extra "protective coat" (cover layer), but the pads need to be exposed, and the end area can be simply processed without coverage.
Double-sided connection without cover layer: Its advantage is that it can "work on both sides"—connection pad interfaces can be connected on the front and back of the conductor. There are via holes made by stamping, etching, etc., on the insulating substrate at the pads.
Double-sided connection with cover layer: It has a cover layer on the surface with specially reserved via holes, enabling double-sided termination while retaining the "protective coat". It is made of two layers of insulating material and one layer of metal conductor.

2. Double-sided FPC: The "Wiring Expert" with Doubled Capacity
There is an etched conductive pattern on each side of the insulating base film, which is equivalent to "doubling" the wiring space, allowing more circuits to be accommodated per unit area. Metallized holes act like "bridges" to connect the patterns on both sides to form conductive pathways, meeting flexure requirements. The cover film protects the conductors and indicates the placement of components.


3. Multilayer FPC: The "Master" Formed by Superposition
Three or more layers of single-sided or double-sided flexible circuits are "laminated" together, and then metallized holes are made through drilling and electroplating, enabling easy conduction between different layers and eliminating complex welding processes. Its advantages are significant: the base film is lightweight, and it has excellent electrical performance. There are also two "characteristic members" in the family:
Flexible insulating substrate products: Made on flexible insulating substrates, they are naturally "flexible" (specified to be flexural). Structurally, they are similar to bonding the two ends of many single-sided or double-sided microstrip flexible FPCs, with the middle unbonded, thus having extremely strong flexibility.
Soft insulating substrate products: Made on soft insulating substrates, they are relatively "stable" (not specified to be flexural).

4. Rigid-Flex FPC: Advantages of the "Hybrid King"
It belongs neither to FPC nor PCB boards but is a combination of flexible and rigid boards. Flexible circuit boards and rigid circuit boards are "combined" through processes such as lamination according to technical requirements, forming a special circuit board that has both the "flexibility" of FPC and the "rigidity" of PCB. It is particularly suitable for products with special requirements, featuring both bendable areas and rigid parts, which can help products save space, reduce volume, and improve performance, with extensive applications.
For more information on the classification and processes of FPC flexible circuit boards, please send a message to our email: sales06@kbefpc.com. Visitors are welcome to consult.