When soldering a package having an electrode on which Ni/Au or AgPd alloy is plated, to a printed circuit board having a Cu electrode or an electrode on which Cu is plated, a solid-phase diffusion layer is formed within a layered solder material for bonding different species of electrodes. The layered solder material is composed of a solder material of SnAgCu series or SnSb series and a solder material of SnAgCuNi series or SnPb series. The electrode on which Ni/Au or AgPd alloy is plated and the Cu electrode or the electrode on which Cu is plated are soldered with the solder material of SnAgCu series or SnSb series being attached to the Cu electrode and the solder material of SnAgCuNi series or SnCu series being attached to the electrode on which Ni/Au or AgPd alloy is plated. This restrains formation of intermetallic compounds and provides high bonding reliability.

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.