FPC technology trends

     With the diversification and pocketing of applications, FPC used in electronic devices require high-density circuits and require high performance in a qualitative sense. Recent changes in FPC circuit density, A single-sided circuit having a conductor pitch of 30 μm or less can be formed by a subtractive method (etching method), and a double-sided circuit having a conductor pitch of 50 μm or less has also been put into practical use. The conduction aperture between the conductor layers connecting the double-sided circuit or the multilayer circuit is also getting smaller and smaller, and the hole having a via hole diameter of 100 μm or less has now reached mass production scale.

   The possible manufacturing range of high-density circuits based on the position of manufacturing mother-in-law. According to the circuit pitch and the via hole diameter, high-density circuits are roughly classified into three types: (1) conventional FPC; (2) high-density FPC; and (3) ultra-high-density FPC.

    In the conventional subtractive method, an FPC having a pitch of 150 μm and a via hole diameter of 15 μm has been mass-produced. Due to the improvement of materials or processing equipment, a line pitch of 30 um can be processed even in the subtractive method. In addition, due to the introduction of processes such as CO2 laser or chemical etching, it is possible to mass-produce a via of 50um aperture, and most of the high-density FPCs that are currently mass-produced are processed using these techniques.

    However, if the pitch is 25 μm or less and the via hole diameter is 50 μm or less, it is difficult to improve the yield even if the conventional technique is improved, and a new process or a new material must be introduced. The process proposed now has various processing methods, but the semi-additive method using electroforming (sputtering) technology is the most suitable method, and not only the basic processes are different, but also the materials and auxiliary materials used are different.

    On the other hand, advances in FPC bonding technology require FPCs to have higher reliability. With the high density of circuits, the performance of FPCs has been demanded for diversification and high performance, which are largely dependent on circuit processing techniques or materials used.

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