Abstract: A fabrication method of a multilayer PWB is provided, which realizes a satisfactorily-high adhesion strength between a mounting pad and a cured resin of a prepreg layer located in a surface via hole. A first surface via hole is formed in a first subboard, and a second surface via hole is formed in a second subboard. Then, the first and second subboards are laminated together while placing an inner structure including a prepreg layer between the first and second subboards. The first and second surface via holes are filled with a resin contained in the prepreg layer. Filler particles are buried into first and second surface regions of the resin which are located in the first and second surface via holes, respectively. The filler particles buried into the first and second surface regions of the resin are removed by dissolving the filler particles, thereby roughening the first and second surface regions of the resin.