An area 5 for mounting a magnetic head is formed on a metal board 1, a conductive layer 4 is formed as a circuit pattern via an insulation layer 2 interposed outside this area and up to a metal board 1. A pattern end 4 to be a connection terminal for connection with the terminal of the magnetic head is formed on the circuit pattern, an end face 4a of the pattern end 4 is aligned with an end face 2a of the insulation layer 2 directly beneath it or protruded in the terminating direction from the end face 2a, thereby providing a structure preventing irradiation of a laser beam on the insulation layer 2. Preferably, a stepped-part is formed on the upper surface of the pattern end, two ridge-shaped protrusion parts are formed on a lower level surface on the tip side of the stepped-part, with which the position of a solder ball is stabilized. By this constitution, even when a laser beam is irradiated around the solder ball, it does not easily hit the insulation layer, and dispersion in the solder ball placing positions is minimized.