Abstract: A flexible printed board is which has increased bonding strength, with which dispersion of the bonding strength can be prevented, the quality of which can be uniformed, with which curling can satisfactorily be prevented, which exhibits excellent dimensional stability and with which a precise circuit can satisfactorily be formed. A flexible printed board has a copper foil on which first and second polyimide-resin layers are sequentially laminated. The first polyimide layer made contact with the copper foil is formed by forming, turning into an imide, a polyimide precursor which contains polyamic acid components prepared owing to reactions of acid anhydride and amine and polyimide components prepared owing to reactions of acid anhydride and isocyanate.

Abstract: A flexible printed circuit board that is intended to minimize curling is formed having a first polyimide-resin layer with a conductor pattern formed on one surface thereof and supporting that conductor pattern. A second polyimide-resin is formed on another surface of the conductor pattern and covers and protects the circuit of the conductor pattern. The polyimide-resin layers are chosen so that a difference between a coefficient of linear thermal expansion of the first polyimide-resin layer and the coefficient of linear thermal expansion of the second polyimide-resin layer is 3×10−6/K or smaller.

Abstract: The present invention aims to obtain a flexible printed wiring board with good flatness. According to the present invention, a copper-clad film 3 is formed by applying a polyamic acid solution on one surface of a copper foil 2 and thermally contracting the polyamic acid layer la so that the other surface of the copper foil 2 may form a convex surface of a curling surface to form a polyimide film 1. A polyamic acid solution is applied on the other surface of the copper foil 2 of the copper-clad film 3, and then the polyamic acid layer 5a is thermally contracted to form a protective film 5, whereby a flexible printed wiring board 10 is obtained.