A common electrode and a signal electrode are separately formed on two major
faces
of each of tabular piezoelectric actuator elements arrayed on a substrate. On a
flexible printed circuit board, formed are electric bonding pads, which are to
be electrically connected with the substrate of the actuator elements. A semi-spherical
bump including a conductive core and a conductive sealant is formed on each of
pads. The actuator elements having substrate is made to face the flexible printed
circuit board, and heated under pressure to thereby electrically bond the signal
electrodes (at their electric bonding area) to the corresponding bumps. Thus bonded,
there exists a gap around the core, and it allows the actuator area of the signal
electrode to act completely free, not interfered with any other.
