MULTILAYER WIRING SUBSTRATE AND MANUFACTURING METHOD THEREOF

To provide a multilayer wiring board that ensures sufficient adhesion between a resin insulating layer and a conductor layer and is excellent in connection reliability. The multilayer wiring board 10 has a multilayered build-up construction where a plurality of resin insulating layers 33 to 36 and a plurality of conductor layers 42 are alternately laminated. The resin insulating layers 33 to 36 are formed of the lower insulating layer 51 and the upper insulating layer 52 disposed on the lower insulating layer 51. The conductor layer 42 is formed on the surface of the upper insulating layer 52. The upper insulating layer 52 is formed thinner than the lower insulating layer 51. The silica filler occupying the upper insulating layer 52 has a lower volume proportion than the volume proportion of the silica filler and the glass cloth that are occupying the lower insulating layer 51.