Patent ID: 7763809

Claim:
A substrate of multilayered structure having a plurality of sets of an insulation layer and a wiring line layer, and having one face for mounting a semiconductor element thereon and the other face on which external connection terminals are to be provided, the face for mounting the semiconductor element being provided with semiconductor element-mounting pads to be bonded to an electrode terminal of the semiconductor element, the other race being provided with pads to be bonded to the external connection terminal, and the wiring wine layers on both sides of an insulation layer being connected with each other by vias made of a metal material piercing the insulation layer, wherein the wiring line layers and the insulation layers are alternately laminated from the face for mounting the semiconductor element thereon to the face on which external connection terminals are to be provided, and the vias are formed to pierce through the insulation layer so as to have a bottom at the side of the insulation layer facing the face of the substrate for mounting the semiconductor element and an opening a the side of the insulation layer facing the face of the substrate on which the external connection terminals are to be provided, wherein the semiconductor element-mounting pad has a first side and a second side opposite the first side, the first side being exposed to be bonded to the electrode terminal of the semiconductor element, and the second side being located at the bottom of the via of the insulation layer at the side of the substrate on which the semiconductor element is to be mounted, and being connected to the metal material of the via, the semiconductor element-mounting pad having a multilayered structure of Cu/Ni/Pd/Au or Cu/Ni/Au, the layers of Au and Cu forming the first and second sides of the semiconductor element-mounting pad, respectively, and the metal material of the via being copper, wherein the diameter of the semiconductor element-mounting pad is greater than the bottom of the via.