A printed wiring board includes an uppermost insulating layer, first pads positioned to mount an IC chip on the insulating layer, second pads positioned to mount a second printed wiring board on the insulating layer, metal posts formed on the second pads, respectively, such that the metal posts mount the second board over the chip, and a solder resist layer formed on the uppermost insulating layer and having first and second openings such that the first openings exposes the first pads and that the second openings exposes the second pads, respectively. The metal posts are formed such that each of the metal posts has a diameter which is smaller than a diameter of each of the second opening portions, and the second opening portions are formed such that the diameter of each of the second opening portions is smaller than a diameter of each of the second pads.