Printed circuit boards (PCBs) denote boards just before electric components are mounted. In such a PCB, a circuit line pattern is printed on an insulation board using a conductive material such as copper. That is, the PCB denotes a circuit board in which an installation position of each of the components is decided and a circuit pattern connecting the components to each other is printed and fixed on a surface of the flat plate to densely mount various electric devices on the flat panel.
Specifically, a multi-layer PCB may be used to be built in a cellular phone, a video camera, a notebook, etc., in which high-integration and compact size are required in recent years. The multi-layer PCB (MLB) is manufactured by building up the PCB one by one. In the build-up process, the board may be manufactured and evaluated one by one to improve yield of the multi-layer PCB. Also, the layers may be precisely connected to each other using a wire to realize a small-sized PCB. Hereinafter, a PCB buried within the multi-layer PCB will be referred to as an inner PCB.
For example, in case of a PCB including ten layers, eight inner PCBs may be provided.
Also, an insulation layer may be disposed between the multi-layer PCBs. A circuit pattern metal part, a via hole metal part electrically connected to the inner PCB, and a pad metal part disposed on the via hole metal part may be disposed on a surface of the insulation layer. A trench process using a laser may be performed as a process of forming engraved patterns (i.e., circuit pattern, via hole, and pad part) in which the metal part, the via hole metal part, and the pad metal part are disposed in the insulation layer.