Problems that need to be paid attention to in the design of the flex PCB !

Based on one of our products, because the FPC needs to be bent frequently, it will cause poor contact or direct breakage after a period of use. Therefore, for the PCB design of the FPC, the FPC manufacturer needs to pay attention to some problems, which are summarized here.

1. Use electrolytic copper (ED) or rolled copper (RA) Among them, the bending resistance of ED is weaker than that of RA, and it is particularly prominent in single-sided FPC. In double-sided, even RA, the actual The bending resistance is not much different from that of ED. According to the process of the board factory, the vias are basically processed by electroplating copper, so even if it is RA, it is made of RA+ED.

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If 1/3 ounce copper foil is used, the thickness of the raw copper foil is only about 12um. Generally, the copper foil must be blackened before FPC electroplating, and the surface of the copper foil should be removed and roughened. The surface of the foil is electroplated with a thickness of about 10um of electroplated copper, so there was originally 12um of RA copper. Due to the planing treatment, only 2 to 6um of RA copper may remain. Coupled with the electroplating operation, the original copper crystal will be crushed. The rearrangement of the grid arrangement tends to the vertical direction of the electrolytic copper, that is to say, after the original rolled copper is electroplated, the bending resistance of the rolled copper is almost gone, so the FPC above the double-layer circuit does not use rolling Copper or electroplated copper is used as the material, and the final FPC characteristics are actually similar to those of electroplated copper. Of course, some people may use 1/2 ounce copper foil with a thickness of about 18um. Even if it is removed and then electroplated, the original rolled copper horizontal lattice arrangement should remain more, but the disadvantage is that the thicker the copper The harder the foil is. A flexible printed circuit board (FPC Flexible Printed Circuit) is a form of circuit made on a flexible cut-off surface, which may or may not have a cover layer (usually used to protect the FPC circuit). Compared with ordinary rigid boards (PCBs), FPCs have the advantages of lightness, thinness, flexibility, etc., because they can be bent, folded or repeated in various ways, so their applications are becoming more and more extensive.

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