METHOD OF MANUFACTURING FLEXIBLE PRINTED CIRCUIT BOARD

PROBLEM TO BE SOLVED: To provide a method of manufacturing a flexible printed circuit board, capable of suppressing degradation in adhesion strength caused by diffusion of copper under long-term thermal load, having excellent heat resistance against thermal load of long period, as well as heat resistance and solder heat resistance against thermal load during short period at a high temperature, with no heating after formation of an electroless nickel plating layer at a high temperature, nor a plurality of times of steps are required for forming the electroless nickel plating layer.SOLUTION: After formation of an electroless nickel plating layer having thickness of more than 0.1 μm to less than 0.3 μm on both surfaces of a polyimide film by single plating, both-sided nickel plating laminate polyimide film that has been heated is used to manufacture a flexible printed circuit board, by wiring process, in which one surface (A) of the polyimide film contains wiring while the other surface (B) has a portion where the polyimide film is exposed at a part of or across the entire surface of it. Otherwise, after formation of the electroless nickel plating layer by a single plating on both surfaces of a polyimide film having been subjected to thermal treatment at 530°C or higher of maximum heating temperature for imide-formation or the polyimide film having been subjected to thermal treatment at 490°C or higher, the both-sided nickel plating laminate polyimide film having been heated for 2.5 hours or longer at 100-180°C is used to manufacture the flexible printed circuit board by wiring process.