The process of producing FPC is complicated. There are more than 20 processes required from material drilling to packaging and shipment. In this long production process, a variety of auxiliary materials will be used according to the needs of customers. The base material of FPC is generally double-sided or single-sided copper foil, which is the basis of the whole FPC, and the electrical performance of FPC is determined by it. Other auxiliary materials are only used to assist installation and adapt to the use environment. There are mainly the following materials:

1. FR4 - has a hard texture and different thickness of 0.15-2.0mm. It is mainly used on the reverse side of FPC welding as reinforcement, which is convenient for welding, stable and reliable;
FR-4 is a code for the grade of flame resistant material, which means that the resin material must be able to extinguish itself after combustion. It is not a material name, but a material grade. Therefore, there are many kinds of FR-4 grade materials used in general circuit boards at present, However, most of them are composites made of so-called Tera function epoxy resin, filler and glass fiber.

2. PI tape - soft and bendable, mainly used for thickening and strengthening the golden finger area, easy to plug in and out;
PI tape, the full name is polyimide tape. PI tape is based on polyimide film and imported silicone pressure-sensitive adhesive. It has the properties of high and low temperature resistance, acid and alkali resistance, solvent resistance, electrical insulation (Class H), radiation protection and so on. It is suitable for shielding wave soldering tin of electronic circuit board, protecting golden finger and high-grade electrical insulation, motor insulation, and fixing the positive and negative lugs of lithium battery.

3. Steel sheet - hard in texture and the same function as FR4. It is used for reinforcement of welding joints. It is more beautiful than FR4, can be grounded and has higher hardness than FR4;
The steel sheet is made of imported stainless steel after heat treatment and fine grinding. It has the characteristics of high precision, strong tensile strength, good finish, toughness and not easy to break.

4. TPX glue blocking film - a high-performance high-temperature resistant resin barrier release film, which is used in the pressing process of circuit board. After special process design, it can be used in the multiple lamination process of buried hole and blind through hole after resin overflow. It has good glue blocking and hole plugging effect.

5. EIM electromagnetic film - pasted on the surface of FPC to shield signal interference; EIM electromagnetic film is a method of vacuum sputtering. Shielding materials can be plated on substrates of different substrates (PET / PC / glass, etc.) to realize EMI electromagnetic interference shielding with very low resistance.

6. Conductive adhesive - used for the connection and pressing of steel sheet and FPC. It is conductive and can realize the grounding function of steel sheet; Conductive adhesive is a kind of adhesive with certain conductivity after curing or drying. It is mainly composed of resin matrix, conductive particles, dispersion additives and additives. It can connect a variety of conductive materials together to form an electrical path between the connected materials. In the electronic industry, conductive adhesive has become an essential new material.

7. 3M adhesive tape - mainly used for pasting FR4 and FPC with a thickness of 0.4mm and above, and assembling and fixing FPC and customer products; The use of FPC auxiliary materials is ultimately determined according to the customer's use environment and functional requirements.