Patent ID: 7140103

Claim:
A process for the production of a high-density printed wiring board, comprising the steps of (1) providing an ultrathin-copper-foil-clad board having a through hole and/or a blind via hole formed therein and having an outermost copper foil thickness of 5 μm or less, plating the surface thereof including the inside of the hole by electroless copper plating to form an electroless copper plating layer having a thickness of 0.1 to 1 μm, (2) forming an electrolytic copper plating layer having a thickness of 0.5 to 3 μm by using the electroless copper plating layer as an electrode, (3) forming a plating resist layer for pattern electrolytic copper plating on a necessary portion of the copper plating layer, (4) forming a pattern copper plating layer having a thickness of 6 to 30 μm on the copper surface in a portion where the plating resist layer is not formed, by electrolytic copper plating, (5) removing the plating resist layer, and (6) etching the entire surface to dissolve and remove the thin electrolytic copper layer, the electroless copper layer and the ultrathin copper foil layer in at least a portion where the pattern copper plating layer is not formed.