PURPOSE: To provide a high quality flexible printed wiring board with favorable adhesion and insulation quality by a method wherein molding materials, which are respectively pinched between cushioning materials and mirror plates and sealed onto a surface plate by being covered by a vacuum bag film, are housed in a pressure vessel so as to be enclosed therein and finally joined and cured under heat and pressure by evacuating the interior sealed by the vacuum bag film.

CONSTITUTION: A molding material consists of an inner layer printed wiring board 29 and overfilms 28. First, an air permeable plate 25, a mirror plate 26, a cushioning plate 27, the overfilm 28, the inner layer printed wiring board 29, the overfilm 28, a cushioning plate 27 and a mirror plate 26 are seated in the order named onto a surface plate 20 and then covered by a vacuum bag film 32. Secondly, each molding material 1 assembled in such a manner as just described above is inserted in the shelf 21 of a molding material equipment member E on a truck 22. Thirdly, a vacuum pump 16 is put into actuation in order to evacuate the interior sealed by the vacuum bag film. Fourthly, high pressure heated gas is circulated along a wind tunnel plate through each molding material 1 in a pressure vessel 2 by rotating a fan 12. In this case, each molding material 1 is pressurized over the whole surface of the vacuum bag film 32 and heated from its underside and four side faces. As a result, the overfilms 28 are softened and made an inroad in the circuitry parts 34 of the inner layer printed wiring board. The employment of gas pressure makes the uniform pressurizing of the molding material possible.