- Insulating substrate
The insulating substrate is a flexible insulating film. As the insulation carrier of FPC flexible circuit board, the flexible dielectric film is required to comprehensively investigate the heat resistance, covering performance, thickness, mechanical properties and electrical properties of the material. Polyimide film, polyester film and polytetrafluoroethylene film are commonly used now.
- Adhesive sheet
The function of the adhesive sheet is to bond the film to the metal foil, or to bond the film to the covering film. Different types of adhesive sheets can be used for different film substrates. For example, the adhesive sheets for polyester and polyimide are different. The adhesive sheets for polyimide substrates can be divided into epoxy and acrylic. The flow property and thermal expansion coefficient of the material were mainly investigated when the adhesive sheet was selected.
- Copper foil
Copper foil is a conductive layer covered and bonded on the insulating substrate, which is then selectively etched to form a conductive circuit. The vast majority of such copper foil is rolled copper foil or electrolytic copper foil. The ductility and bending resistance of calendered copper foil are better than electrolytic copper foil. The elongation of calendered copper foil is 20%~45%, and that of electrolytic copper foil is 4%~40%.
The covering layer is an insulating protective layer covering the surface of FPC flexible circuit board, which protects the surface conductor and increases the strength of the substrate. The protective materials for the outer layer graphics generally fall into two categories: dry film type (covering film) and photosensitive developing type.
- Reinforcing plate
The reinforcing plate is bonded to the plate at the local position of the flexible plate, which can super support and strengthen the flexible film substrate and facilitate the connection, fixation or other functions of the FPC flexible circuit board. Reinforcing plate materials are selected according to different uses, commonly used polyester, polyimide sheet, epoxy fiberglass cloth board, phenolic paper board or steel plate, aluminum plate, etc.