FPC circuit board is also called flexible circuit board, referred to as "soft board, the industry commonly known as FPC, battery FPC is used in the flexible insulating substrate (mainly polyimide or polyester film) made of printed circuit board, has many hard printed circuit board does not have the advantages, such as it can be free bending, winding, folding, using FPC can greatly reduce the volume of electronic products, It is suitable for the development of electronic products in the direction of high density, miniaturization and high reliability. Therefore, FPC has been widely used in aerospace, military, mobile communication, laptop, computer peripherals, PDA, digital camera and other fields or products.
The production process of FPC is complicated, from opening and drilling to packaging and shipping, the intermediate process needs more than 20 processes, in this long production process, according to customer needs, will use a variety of auxiliary materials. The base material of FPC is generally double-sided or single-sided copper foil, which is the foundation of the entire FPC, and the electrical performance of the FPC is determined by it. Other auxiliary materials are only used to assist installation and adapt to the operating environment. There are mainly the following kinds:
1. FR4- is hard in texture, with different thickness of 0.15-2.0mm. It is mainly used on the opposite side of FPC welding, as a strengthening, to facilitate stable and reliable welding.
FR-4 is a kind of inflammable material grade code, on behalf of the resin material after combustion state must be able to self-extinguish a material specification, it is not a material name, but a material grade, so the general circuit board used FR-4 grade materials there are very many kinds, But most are composites made with a so-called Tera-Function Filler made with epoxy and fiberglass.
2, PI tape - soft texture, flexible, mainly used in the gold finger area thickening and strengthening, easy to plug and pull;
PI tape, full name is polyimide tape. PI tape is based on polyimide film as the base material, using imported silicone pressure sensitive adhesive, with high and low temperature resistance, acid and alkali resistance, solvent resistance, electrical insulation (H class), radiation resistance and other properties. Suitable for circuit board wave soldering shield, protective gold finger and high-grade electrical insulation, motor insulation, and lithium battery positive and negative ear fixation.
3, steel sheet - hard texture, function and FR4, used for welding reinforcement, than FR4 beautiful, earthing, hardness is higher than FR4.
The steel sheet is made of imported stainless steel by heat treatment and fine grinding. It has the characteristics of high precision, strong pulling force, good finish, toughness and not easy to break.
4, TPX blocking film - a high performance and high temperature resistant resin blocking release film, used for circuit board pressing process, after special process design, can be used to block the resin overflow after buried holes and blind hole multiple laminating process, with good adhesive blocking, plugging effect.
5, EIM electromagnetic film - attached to the surface of FPC, for shielding signal interference;
EIM electromagnetic film is a method of vacuum sputtering, can be in different substrates (PET/PC/ glass, etc.) substrate plating shielding material, with very low resistance to achieve EMI electromagnetic interference shielding.
6, conductive adhesive - used for steel sheet and FPC connection pressing, conductive, can realize the steel sheet grounding function;
Conductive adhesive is a kind of 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, so that the connected materials form an electrical path. In the electronic industry, conductive adhesive has become an indispensable new material.
7, 3M adhesive paper - mainly used for the thickness of 0.4mm and above FR4 and FPC paste, and FPC and customer product assembly fixed.
The use of FPC auxiliary materials, ultimately according to the customer's use environment and functional requirements to decide.