Printed wiring board having highly reliably via hole and process for forming via hole

摘要

Disclosed are a printed wiring board having micro-via holes highly reliable for conduction and a method of making the micro-via hole by providing a coating or sheet of an organic substance containing 3 to 97% by volume of at least one selected from a metal compound powder, a carbon powder or a metal powder having a melting point of at least 900° C. and a bond energy of at least 300 kJ/mol on a copper foil as an outermost layer of a copper-clad laminate having at least two copper layers, or providing a coating or sheet of the same after oxidizing a copper foil as an outermost layer, irradiating the coating or sheet with a carbon dioxide gas laser at an output of 20 to 60 mJ/pulse, thereby removing a micro-via-hole-forming portion of at least the copper foil as the outermost layer, then irradiating micro-via-hole-forming portions of the remaining layers with a carbon dioxide gas laser at an output of 5 to 35 mJ/pulse to make a micro-via hole which does not penetrate through the copper foil in a bottom of the micro-via hole, and electrically connecting the copper foil as the outermost layer and the copper foil in the bottom of the micro-via hole with a metal plating or an electrically conductive coating composition.