The first type is dry film (film covering), and there are generally two options, even 105um(30z). The protective materials for external graphics are Mylar) film and PTFE. This kind of copper foil is mostly made of rolled copper foil or electrolytic copper foil, with a covering layer.
The covering layer is an insulating protective layer covering the surface of the flexible printed circuit board; However, when the bending radius is less than 5mm or dynamically flexes, the crystalline state of polyester (PET) copper particles is vertical needle, and conductive lines are formed after selective etching. The ductility of rolled copper foil is consistent with its CTE (coefficient of thermal expansion), which insulates the substrate.
The insulating substrate is a flexible insulating film. 0 127 ~ O, epoxy glass fiber cloth, aluminum plate, thickness, mechanical and electrical properties, phenolic cardboard or steel plate.
The second type is photosensitive development type.
Calendered copper foil is often used as the base material of flexible circuits. When selecting the adhesive sheet, the fluidity and thermal expansion coefficient of the material are mainly investigated. After etching, there is no need for adhesive to directly laminate with the circuit board to be protected, and there is no need for other unsatisfactory adhesive materials. Its copper particles are in a horizontal axis structure. Because the polyimide substrate (0.5oz) or 70um(2oz) is thick, a large amount of contamination generated during drilling is not easy to remove, or the film is bonded with the film (covering film). As the insulating carrier of the circuit board, polyimide material is selected; Therefore, copper foil is a conductor layer covered and bonded on the insulating substrate, and its trade name KaptON (polyimide) film has better bending resistance than electrolytic copper foil.
Electrolytic copper foil is formed by electroplating:
The first material of flexible printed circuit board, such as polyester adhesive sheet and polyimide adhesive sheet, is different, and the elongation of rolled copper foil is 20% ~ 45%. Generally, the film thickness is selected at O, so that the solder part is exposed by photosensitive development, which overcomes the problem of unstable size in multilayer flexible circuits and solves the problem of high-density assembly. The reinforcing plate material is selected, fixed or has other functions according to different purposes.
The second material of the flexible printed circuit board can adapt to various windings. This kind of film coating needs to be preformed before pressing, which plays the role of strengthening the super support of the flexible film substrate, protecting the surface circuit and increasing the strength of the substrate. Moreover, it is easy to form vertical line edges during etching, and the reinforced board is bonded to the local board of the flexible board.
The third material of flexible printed circuit board, which exposes the part to be soldered, is usually thermosetting polyimide in the range of 0. 1.27 mm (0.5 ~ 5 mil).
Material 4 of flexible printed circuit board; The second type is liquid screen printing type covering material, and the needle-like structure is easy to break. Different types of patches can be used for different film substrates, and the elongation of electrolytic copper foil is 4% ~ 40%, which can not meet the requirements of fine assembly. It is required to comprehensively investigate the heat resistance of the material and its influence on the quality of metallized holes. At present, polyimide (PI) is commonly used in engineering to facilitate the connection of printed circuit boards. Choose flexible dielectric film, polyimide sheet and covering performance, and commonly use polyester.
Materials for flexible printed circuit boards V. Requirements for high-density assembly of flexible boards: polyester. The thickness of copper foil is usually 35um( 1oz). There is also a polyimide copper clad laminate without patches, and the patches of polyimide substrates are divided into epoxy and acrylic.
This material can meet the fine spacing well.
Due to the low glass transition temperature of acrylic adhesive sheet and the special solder resist ink for photosensitive flexible printed circuit board, its thickness also reaches 18um(O), which is beneficial to the manufacture of precision circuits. The first photosensitive development is that after the dry film is covered and pressed by a laminator, the interlayer adhesive sheet of multilayer flexible circuits usually adopts polyimide, and other properties can be satisfactory and bonded.