Patent ID: 7144472

Claim:
A method for producing a thin prepreg for use in producing a printed wiring board having a backbone material impregnated with a thermosetting resin, comprising the steps (1) to (5): (1) a liquid resin coat forming step for forming a liquid resin layer as a coat having a predetermined thickness on a flat work plane by use of a liquid thermo setting resin and a solvent; (2) a pre-drying step for drying the liquid resin layer on the work plane as it is, to form a dry resin layer; (3) a backbone material pre-adhesion step for overlapping the backbone material on the surface of said dry resin layer on the work plane, pre-heating and pressure bonding to form a dry resin layer with backbone material; (4) a resin impregnation step for heating the resin, while the dry resin layer with backbone material remains on the work plane, at a temperature where the resin is reflowable, and impregnating said backbone material with a thermosetting resin component; and (5) a cooling step for carrying out a temperature decreasing operation immediately after finishing the resin impregnation without curing the thermosetting resin completely to form the prepreg by maintaining a half-cured state of the thermosetting resin impregnated in the backbone material.