| 摘要 |
PROBLEM TO BE SOLVED: To accurately form a fine pattern containing via holes in a multilayered printed wiring board such as build-up board. SOLUTION: A resined copper foil 4 as an outer layer is laminated on a core substrate. The copper foil 4 as the outer layer is etched to form an outer layer circuit pattern except for at least peripheries of land holes of via holes. Since the circuit pattern is previously formed, the etching step can be provided as separated from an etching step for the plated layer 5 to be later formed, and thus an etching time can be shortened. A circuit pattern of an inner layer can be externally confirmed. Since the circuit pattern is not formed in the vicinity of the via holes, an edge of the pattern will not be exposed to a laser beam. Thereafter the pattern is irradiated with the laser beam having a diameter corresponding to a diameter of the via hole to make an opening reaching the inner layer in the resin layer. Since the laser beam is not diffracted at the edge of the copper foil 4, a vertical section of the hole has an inverted- trapezoid shape, whereby the good plated layer 5 can be formed and the reliable via hole can be made. |
