1. Field of the Invention
The present invention relates to a combined circuit unit constructed by combining a flexible printed circuit film and a rigid printed circuit board. The present invention also relates to an inkjet printer.
2. Description of the Related Art
An inkjet head used in an inkjet printer distributes ink supplied from an ink tank to a plurality of pressure chambers, pushes out the ink from a selected pressure chamber by applying pressure to the selected pressure chamber, and discharges the ink pushed out from the selected pressure chamber from a corresponding nozzle. The nozzle that discharges the ink can be selected by selecting the pressure chamber to which the pressure is applied. An actuator unit utilizing a piezoelectric sheet made from piezoelectric ceramics is used to apply pressure to any pressure chamber that may be arbitrarily selected from the pressure chambers.
One example of an inkjet head is described in Japanese Laid-Open Patent Application Publication No. 2003-311953. An actuator unit described in the publication uses a piezoelectric sheet that straddles and extends across a plurality of pressure chambers, a common electrode spreading out on one surface of the piezoelectric sheet, and a plurality of individual electrodes formed on the other surface of the piezoelectric sheet. Each of the individual electrodes is disposed to face each of the individual pressure chambers.
A plurality of individual electrodes dispersed on the surface of the piezoelectric sheet is electrically connected to a driver IC through a plurality of wiring patterns formed on a flexible printed circuit film. The driver IC is mounted on a surface of the flexible printed circuit film. The driver IC selects any individual electrode from the plurality of individual electrodes and applies a driving voltage to the selected individual electrode. When the driving voltage is applied to the selected individual electrode, the thickness of the piezoelectric sheet in the location that corresponds to the selected individual electrode changes by a so-called piezoelectric longitudinal effect. Accordingly, the volume of the pressure chamber that corresponds to the selected individual electrode changes, and the ink is discharged from a nozzle linked to that pressure chamber. The flexible printed circuit film is frequently abbreviated as FPC. This specification will follow this common notation and refer to the flexible printed circuit film as FPC. The “Printed” included in the abbreviation FPC means that a wiring pattern is formed, and it is not limited to those with wiring patterns formed by a method of “Print.”
In the recent years, higher resolution of inkjet heads is being desired. When an attempt is made to seek higher resolution by increasing the density of nozzles, the densities of pressure chambers and individual electrodes also increase. Consequently, the number of individual electrodes increases. Along with this, the heat release value generated by the driver IC also increases. An active site of the actuator unit operates electrically as a capacitive load such as a condenser, and consumes energy proportional to the product of the capacitance, the square of a driving voltage, and a driving cycle. As energy consumed by the actuator unit increases, energy consumed by the driver IC also increases. If the driver IC is overheated, the inkjet head is overheated and the discharge property of the ink varies. Sufficient printing quality cannot be obtained.
To handle this problem, an inkjet head described in Japanese Laid-Open Patent Application Publication No. 2003-311953 provides a large-scale heat sink, and pushes a driver IC to the heat sink by an elastic member such as a sponge. By doing so, heat generated from the driver IC is transferred to the heat sink, and the heat is dissipated to the exterior (such as into the atmosphere).