FPC, also called flexible printed circuit board for short, is commonly known as FPC in the industry. It is a printed circuit board made of flexible insulating substrate (mainly polyimide or polyester film). It has many advantages that rigid printed circuit boards do not have, such as it can be bent, rolled and folded freely. Using FPC can greatly reduce the volume of electronic products, and it is suitable for the development of electronic products in the direction of high density, miniaturization and high reliability. Therefore, FPC is widely used in aerospace, military and military affairs.
The process of producing FPC is complicated, from cutting and drilling to packing and shipping, there are more than 20 processes in the middle. In this long process of producing FPC, according to the customer’s demand, a variety of auxiliary materials will be used. The substrate of FPC is usually double-sided or single-sided copper foil, which is the foundation 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:
1. FR4- is hard in texture, with different thicknesses of 0.15-2.0mm, and is mainly used on the opposite side of FPC welding, as a reinforcement, which facilitates stable and reliable welding;
FR-4 is a code name of a fire-resistant material grade, which means that the resin material must be able to extinguish itself after burning. It is not a material name, but a material grade. Therefore, at present, there are many kinds of FR-4 grade materials used in general circuit boards, but most of them are composite materials made of so-called Tera-Function epoxy resin, Filler and glass fiber.
2. PI tape-the texture is soft and flexible, and it is mainly used for thickening and strengthening in the golden finger area, which is easy to plug;
PI tape, the full name of which is polyimide tape. PI tape is based on polyimide film, imported from pressure sensitive adhesives, silicone, and has high and low temperature resistance, acid and alkali resistance, solvent resistance, electrical insulation (H grade), radiation protection and other properties. It is suitable for wave soldering tin shielding of electronic circuit boards, insulation of gold fingers and high-grade electrical appliances, insulation of motors, and fixing of positive and negative lugs of lithium batteries.
3. Steel sheet-hard in texture, same in function as FR4, used for reinforcing the welded joint, more beautiful than FR4, grounding, and higher in hardness than FR4;
Steel sheet, made of imported stainless steel by heat treatment and fine grinding, has the characteristics of high precision, strong tension, good smoothness, toughness and not easy to break.
4. TPX resist film-a high-performance and high-temperature resistant resin barrier release film, which is used in the pressing process of circuit boards. After special process design, it can be used in many laminating processes of burying holes and blind through holes after blocking resin overflow, and has a good effect of blocking glue and plugging holes.
5. EIM electromagnetic film-attached to the surface of FPC for shielding signal interference;
EIM electromagnetic film is a vacuum sputtering method, which can coat shielding materials on different substrates (PET/PC/ glass, etc.) to achieve EMI electromagnetic interference shielding with extremely low resistance.
6. Conductive adhesive-used for the connection and pressing of steel sheet and FPC, which is conductive and can realize the grounding function of steel sheet;
Conductive adhesive is an adhesive with certain conductivity after curing or drying. It is mainly composed of resin matrix, conductive particles, dispersing additives and auxiliaries. 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 indispensable new material.
7. 3M adhesive tape-mainly used for bonding FR4 and FPC with thickness of 0.4mm or 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.