FORMATION METHOD OF VIA HOLE AND MANUFACTURE OF MULTILAYER WIRING BOARD AS WELL AS MULTILAYER WIRING BOARD AND ELECTRONIC APPARATUS

PURPOSE:To reduce the interlayer connection resistance of a wiring layer formed on a resin thin-film multilayer wiring board by a method wherein, by utilizing the laser etching threshold value of a metal forming a barrier layer and of a metal forming the wiring layer, the barrier layer formed between a resin thin film and the wiring layer is removed simultaneously. CONSTITUTION:A sample 5 in which a copper film 2 and a chromium film 3 have been laminated and formed sequentially on a glass substrate 1 by using a sputtering method and in which a polyimide film 4 has been formed on them is placed on an X-Y stage for a laser irradiation apparatus. A mask 7 in which light-transmitting regions 9 have been formed is placed on the sample 5, a laser at an energy intensity of 0.5 to 0.55J/cm .pulse is irradiated from a laser oscillator 8 by utilizing the difference in a laser etching threshold value between chromium anal copper. As a result, the chromium film 3 inside the via holes 9 can be removed completely without damaging the copper wiring layer 2. Consequently, an upper wiring layer and a lower wiring layer in the via holes are connected directly, and their interlayer connection resistance is reduced.