Multilayer wiring board and method of fabrication thereof

A method of fabricating a multilayer wiring board comprising a plurality of integrally-stacked resin sheets each having one surface thereof formed with a conductor pattern;

• wherein each of the resin sheets includes a pair of film-like thermosetting resin layers adapted to exhibit the bonding properties when heat treated at a predetermined temperature, a resin film having a lower coefficient of linear expansion than, and sandwiched between, the thermosetting resin layers, a conductor pattern formed on one surface of the sandwich, and a plurality of vias each having an end thereof coupled to the reverse surface of the conductor pattern and the other end thereof exposed to the other surface of the sandwich,
• the method comprising the steps of:
• stacking a plurality of the resin sheets in such a manner that the exposed end of each of the vias of each resin sheet is in contact with a predetermined portion of the conductor pattern of an adjacent resin sheet;
• and
• heat treating the resin sheets at a temperature enabling the thermosetting resin layers to exhibit the bonding properties thereby to integrate a plurality of said resin sheets.