formed on the bottom portion of the dummy via 53 as to prevent voiding on the bottom portion of the via 52 consequently disconnection of the via 52 can be prevented and wiring reliability can be improved the dummy via 53 does not contribute to the electrical connection between the lower wire 44 and the upper wire 51 and hence the void 56 formed on the bottom portion of the dummy via 53 exerts no influence on the electrical connection between the lower wire 44 and the upper wire 51 while the dummy vias 13 a and 13 b are formed correspondingly to the vias 12 a and 12 b respectively in the second embodiment not less than two dummy vias 13 may alternatively be provided correspondingly to each of the vias 12 a and 12 b thus voiding immediately under the vias 12 a and 12 b can be more excellently prevented consequently disconnection of the vias 12 a and 12 b can be more prevented and the wiring reliability can be more improved while the lower wires 4 and 44 the upper wires 13 and 53 the vias 12 a 12 b and 52 and the dummy vias 13 13 a 13 b and 53 are made of cu these elements may not be made of only cu but may be formed by materials containing cu as the main component while the present invention has been described in detail by way of the embodiments thereof it should be understood that these embodiments are merely illustrative of the technical principles of the present invention but.