Wired circuit board for controlling characteristic impedances of a connection terminal

A wired circuit board for connecting to an external circuit that includes external read wires and external write wires, the wired circuit board comprising:

• an insulating layer having a first surface and a second surface that oppose each other;
• a plurality of read lines formed on the first surface of the insulating layer;
• a plurality of write lines formed on the first surface of the insulating layer;
• a connection terminal portion formed on the first surface of the insulating layer to electrically couple the wired circuit board and the external circuit, the connection terminal portion comprising:
• first terminals that are connected to the plurality of read lines and are configured to be electrically coupled to the external read wires of the external circuit;
• and
• second terminals that are connected to the plurality of write lines and are configured to be electrically coupled to the external write wires of the external circuit;
• a ground layer formed on the second surface of the insulating layer;
• and
• an opening formed in the ground layer proximate to the connection terminal portion and positioned to overlap with one of the first terminals or the second terminals and not to overlap with the other of the first terminals or the second terminals, wherein the opening is adapted to control characteristic impedances at the connection terminal portion between the first terminals and the external read wires and between the second terminals and the external write wires;
• wherein the ground layer comprises:
• a stiffener board, and
• a conductive board interposed between the insulating layer and the stiffener board, wherein the opening is formed in the conductive board;
• wherein the conductive board comprises a metal foil selected from the group consisting of copper, nickel, gold, solder and alloys thereof.