| abstract |
An opening is formed in the resin 20 by a laser and a via hole is formed accordingly. At this time, in order to lower thermal conductivity, the copper foil 22 processed by the etching to 3 micrometers in thickness is used as a conformal mask. Therefore, even if the number of irradiation of the pulsed laser beam decreases, the opening 20a is formed in the resin 20. Therefore, occurrence of undercut of the resin 20 which performs interlayer insulation of the resin layer is prevented. As a result, the reliability of the via hole connectivity is improved.n n n n Multilayer printed wiring board |