Interposers, semiconductor packages and methods of producing the same

An interposer, comprising:

• an inner layer structure including at least one inner wiring layer;
• a first outer layer structure disposed on a first surface of the inner layer structure, the first outer layer structure having rigidity higher than that of the inner layer structure;
• and
• a second outer layer structure disposed on a second surface of the inner layer structure, the second outer layer structure having rigidity higher than that of the inner layer structure, wherein
• the first outer layer structure covers at least the first surface of the inner layer structure,
• the second outer layer structure covers at least the second surface of the inner layer structure,
• the inner wiring layer includes wiring disposed on a surface of a first insulating resin layer, which is a photosensitive insulating resin, and a conductive member penetrating the first insulating resin layer and connected to the wiring,
• the first outer layer structure includes a second insulating resin layer and a conductive member penetrating the second insulating resin layer,
• the second outer layer structure includes a third insulating resin layer and a conductive member penetrating the third insulating resin layer,
• the second insulating resin layer is a non-photosensitive resin containing a filler and no fiber substrate,
• the third insulating resin layer is a non-photosensitive resin containing a filler and a fiber substrate, and
• the first outer layer structure and/or the second outer layer structure includes a terminal connectable to a semiconductor device on a surface opposite to that connected to the inner layer structure, the terminal being capable of being subjected to electrical inspection.