Interposer substrate and method of fabricating the same

An interposer substrate, comprising:

• a second dielectric material layer having opposing first and second surfaces;
• a first wiring layer embedded in the second dielectric material layer and exposed from the first surface of the second dielectric material layer;
• a first dielectric material layer formed on the first surface of the second dielectric material layer and the first wiring layer, wherein a portion of the first wiring layer extends continuously into the first dielectric material layer from the second dielectric material layer, and the first dielectric material layer has a plurality of openings, from which a portion of the first wiring layer is exposed;
• a plurality of first conductive blocks embedded in the second dielectric material layer and having first terminal surfaces connected to the first wiring layer and second terminal surfaces opposing to the first terminal surfaces and flush with the second surface of the second dielectric material layer;
• a second wiring layer formed on the second surface of the second dielectric material layer and having a first side connected to the second terminal surfaces of the first conductive blocks and a second side opposing to the first surface of the second wiring layer;
• a plurality of second conductive blocks formed on the second side of the second wiring layer;
• and
• an insulative protection layer formed on the second surface of the second dielectric material layer, the second wiring layer and the second conductive blocks, wherein an end of the second conductive blocks is exposed from the insulative protection layer, and the insulative protection layer has at least a concave portion formed between two of the second conductive blocks.