WIRING BOARD AND ITS MANUFACTURE

PROBLEM TO BE SOLVED: To manufacture a wiring board provided with viahole conductor having high conductivity which is excellent in burying property of metal conductor in a viahole and conductivity and free from appearance deterioration and insulation deterioration due to oozing conductor paste. SOLUTION: Via holes 2 are formed in an insulating sheet 1 which contains at least thermosetting resin and is in an uncured or semicured state. A metal ball 3a and conductor paste are buried in the viahole. The ball 3a has a diameter within ±5 μm to the distance between two wiring conductor layers 5 to be connected. The conductor paste contains organic binder containing photo- setting resin component 3b, e.g. ultraviolet-curing epoxy resin, and photo- crosslinker like bis-azide compound. The insulating sheet 1 is irradiated with ultraviolet rays 4, and the resin 3b in the conductor paste buried in the via hole 2 is cured. The wiring conductor layers 5 are stuck and formed on the surfaces of the insulating sheet 1 containing viahole 2 forming parts, and the sheet 1 is thermoset.