Abstract: A circuit substrate includes a board, a plurality of metal layers and an insulator. The board has a plurality of conductive traces layers and a via formed therein. The metal layers are formed on the inner wall of the via and each of the metal layers is electrically connected to its corresponding conductive traces layer. The via is filled with the insulator so that each of the metal layers is electrically isolated from each other. In addition, this invention also provides a fabrication method of the circuit substrate.

Abstract: A method of making a multilayer substrate comprising: (a) providing an interlayer circuit board having conductor circuits thereon; (b) forming a dielectric layer on the interlayer circuit board; (c) mechanical drilling (or laser drilling) through the dielectric layer to the conductor circuits at predetermined positions thereof so as to form blind-vias; (d) electrolessly plating a conductive layer on the surface of the dielectric layer and the blind-vias; (e) forming an etch resist on the conductive layer, followed by formation of outer conductor circuits on the conductive layer by selectively etching; and (f) removing the etching resist. Since the blind-vias of the present invention are formed by drilling instead of photosensitive polymer technology, the processing steps are minimized thereby significantly improving the production efficiency. Furthermore, since the mechanical drilling (or laser drilling) has better accuracy, the blind-vias can be formed with better accuracy.