The present invention relates to a thermal print head, particularly to packaging of the elements of a thermal print head.
The thermal print system is widely adopted in facsimile and printers. Thermal print means a system in which Joule heat is given to a printing medium such as heat-sensitive paper and plain paper through ink sheet (transcription paper) by heating elements (heating resistors) to cause direct color development or fusion thereby to perform transcriptional print.
A thermal print head usually comprises a plurality of heating elements disposed in a line on a ceramic substrate, and each heating element is heated by the electric current corresponding to a picture signal.
A Japanese Patent Laid-Open No. 31778/1983 discloses an example of the construction of such a thermal print head.
The thermal print head which has been known up to date, as shown in FIG. 2 of the above Patent Laid-Open No. 31778/1983, has a construction that the driver IC's for the heating resistors (driver IC's) are packaged on a ceramic substrate by the so-called face-up packaging so that the face having the connecting terminals takes the upside position, and the connecting terminals provided on the lead wires from the heating resistors are wire-bonded to the connecting terminals of the driver IC's by gold or aluminum wires.
In recent years, printed pictures of high definition having 8 lines/mm or more resolution have been required, and miniaturization of the print head itself has also been required. In this situation, it is necessary to densely package the electic elements constituting the print head, but there is a limit in the above-mentioned conventional construction. That is, to perform wire bonding, the distance between the connecting terminals needs to be at least 1 mm or so in view of the nature of the work, and even if the driver IC can be miniaturized, this space for wire bonding cannot be reduced. In addition, if the lead wires from the heating resistors are made narrower and thinner, electric resistance will increase and the fluctuation of resistance due to the differences in wire length cannot be ignored. Further, fall of the production yield due to pattern defects in the manufacture process is inevitable.