Polyimide films can be chemically etched using chemical etching agents such as Naoh,koh and other alkali solutions to produce various through holes. This is often used in the two-layer tab, which is only poly (imide) and metal. The through hole is formed by etching the poly-phenylenediamine film after covering the metal layer. If the poly-phenylenediamine film cannot pass through the caustic.
Especially in the near future, the high frequency circuit flexible FPC which is higher than GHz needs more emphasis on the low permittivity of the substrate, low water absorption and reliability. The polyimide film has the problems such as the dielectric constant (in ε=3.0), the high water absorption rate, the lower tensile strength of copper foil during high temperature welding, the larger size change rate after the substrate hygroscopicity. These can not meet the requirements of the current high-performance FPC. In addition, the use of polyimide film produced by the two-layer FPC at present in the adhesive strength is low, low alkali resistance problem, still need to be further resolved. At the same time, in environmental protection, polyimide film as FPC substrate, it is also difficult to be able to recycle the use of.
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