FPC's main raw materials are divided into four categories:

1. Substrate, 2. Cover film, 3. Reinforcement, 4. Other auxiliary materials.
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1. Base material

1.1 Adhesive substrate

Adhesive substrates mainly consist of three parts: copper foil, adhesive, and PI. There are two types of substrates: single-sided substrates and double-sided substrates. Materials with only one copper foil are single-sided substrates, while materials with two copper foils are double-sided substrates.

1.2 Non adhesive substrate

Non adhesive substrate refers to a substrate without a glue layer. Compared to ordinary adhesive substrates, it lacks a middle glue layer and only consists of copper foil and PI. It has the advantages of thinner, better dimensional stability, higher heat resistance, higher bending resistance, and better chemical resistance than adhesive substrates. It is now widely used.

Copper foil: Currently, commonly used copper foil thicknesses include the following specifications: 1OZ, 1/2OZ, and 1/3OZ. Thinner copper foils with a thickness of 1/4OZ are now available, but this material is already being used in China to make ultra-fine (line width and spacing of 0.05mm or less) products. With the increasing demands of customers, this specification of material will be widely used in the future.

2. Cover film

It mainly consists of three parts: release paper, adhesive, and PI. Only the adhesive and PI parts remain on the product. The release paper will be torn off during the production process and will no longer be used (its function is to protect foreign objects on the adhesive).

3. Strengthening

For FPC specific materials, they are used in a specific part of the product to increase support strength and compensate for the relatively "soft" characteristics of FPC.

There are currently several commonly used reinforcement materials:

1) FR4 reinforcement: The main components are glass fiber cloth and epoxy resin adhesive, which are the same as the FR4 material used in PCB;

2) Steel sheet reinforcement: composed of steel, with strong hardness and support strength;

3) PI reinforcement: Similar to the cover film, it consists of three parts: PI and release paper, except that its PI layer is thicker, and can be produced in ratios ranging from 2MIL to 9MIL.

4. Other auxiliary materials

1) Pure adhesive: This adhesive film is a thermosetting acrylic adhesive film composed of protective paper/release film and a layer of adhesive. It is mainly used for laminated boards, soft hard bonding boards, and FR-4/steel reinforcement boards, playing a bonding role.

2) Electromagnetic protective film: pasted on the board surface to provide shielding effect.

3) Pure copper foil: composed only of copper foil, mainly used in the production of hollow boards.

4、 Types of FPC

There are six types of FPC distinctions:

A. Single panel: Only one side has wiring.

B. Double sided board: There are lines on both sides.

C. Hollow board: also known as window board (finger face opening window).

D. Layered board: Two sided circuit (separated).

E. Multilayer board: Two or more layers of circuits.

F. Soft hard combination board: a product that combines soft and hard boards.

5、 FPC process flow