A rigid circuit member fabricated by bending a composite sheet comprising a circuit conductor made of metal foil and polyethylene naphthalate films having an elastic modulus of more than 450 kg/mm and sandwiching the circuit conductor. A circuit board which is connected to a conductor on a hard board and whose circuit conductor is sandwiched between polyethylene naphthalate films. A printed circuit board which is fabricated by joining with adhesive a polyethylene naphthalate film which have an elastic modulus of not less than 500 kg/mm<2>, a thermal expansion coefficient of not larger than 1.5 x 10<-5>/ DEG C, a humidity expansion coefficient of not larger than 1.2 x 10<-5>/%RH, a water vapor permeability of not larger than 15 g/m<2>/mil<.>day, a moisture absorption coefficient of not larger than 2 % and a melting point of not higher than 280 DEG C to a circuit conductor.
