JPH0920026A - Thermal printing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electrode for driving from becoming separated at the time of replacing an IC by connecting the individual electrodes of thermal resistors to a driving integrated circuit by wire-bonding and also electrically connecting part of the electrode for driving as a lead-out terminal to an external area to an external circuit. SOLUTION: Heating resistors 3 and individual electrodes 4 which supply an electric current to the former are provided on an alumina ceramic substrate 2. In addition, an IC 6 which turns on/off the electric current to be supplied to the heating resistors is mounted through a connecting member on a substrate 11 for a driving circuit. Further, an electrode 5 for driving which transmits a picture signal, a control signal and the electric current which are fed to the IC 6 from an external circuit through a connector 10 for connection, is provided on the substrate 11 for a driving circuit. The individual electrodes 4 are connected to the IC 6 by a wire bonding method 12. Consequently, a flexible circuit used for connecting to the external circuit is no longer required and therefore, the number of parts to be used is reduced. Besides, an insulating film on the electrode for driving is not necessary, so that the electrode for driving is prevented from being damaged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal print head equipped with a driving circuit.

[0002]

2. Description of the Related Art Generally, a direct drive type thermal print head (hereinafter referred to as DD type thermal print head) equipped with a driving integrated circuit (hereinafter referred to as IC).
Is an integrated circuit in which a plurality of heat generating resistors, individual electrodes for supplying current to these heat generating resistors, logic circuits such as shift registers, latches, gates, etc., and an independent transistor driver for each heat generating resistor are integrated. And this IC
A thermal print head main body in which a driving electrode for transmitting a power supply, an image signal, a control signal, etc. externally supplied to the substrate is formed on a ceramic substrate, and the thermal print head main body and an external circuit are electrically connected. And an interface section including a flexible circuit board or the like.

By the way, the above-mentioned DD type thermal print head has the following problems.

First, in order to electrically connect the flexible circuit board and the drive electrodes of the thermal print head body, pressure contact is used. Usually, it is difficult to secure reliability unless gold (Au) is used for this pressure contact. However, the use of this gold raises the price of the thermal print head, which goes against the trend of the low price era. In addition, during pressure contact, a contact failure may occur between the flexible circuit board and the driving electrode due to temperature change or the like, which makes it difficult to ensure high reliability.

Secondly, since the IC is mounted on a ceramic substrate (usually an alumina ceramic substrate is used), the area occupied by the expensive alumina ceramic substrate is increased, leading to an increase in cost and a batch process in the thin film forming process. The workability when performing is reduced.

Third, when the IC is mounted on the ceramic substrate, since the wiring is densified, a multi-layer wiring is used. Therefore, an insulating film is formed on the driving electrode of the ceramic substrate. However, forming this insulating film
This leads to complicating the process of producing the thermal print head, and eventually destroys the insulating film when a defective IC is replaced, and when it is conspicuous, there is a risk that even the drive electrodes below the insulating film are damaged.

Therefore, there is a split type thermal print head which solves the second and third problems. This thermal print head includes a substrate on which a heating resistor is mounted and an IC.
It is formed by a different substrate from the substrate on which is mounted. According to this thermal print head, it is possible to reduce the area of the substrate on which the heating resistors for batch processing are placed, and it is possible to process a large number of substrates at the same time.

However, the substrate on which the IC is mounted usually requires thick film wiring made of matrix wiring. In order to make reliable electrical connection between the board on which the IC is mounted and an external circuit, it is necessary to press-connect a flexible circuit board provided with a connecting means such as a connector. Therefore, the first problem is still unsolved.

Techniques for solving the above-mentioned problems have been put into practice
It is disclosed in Japanese Patent No. 8949. The basic structure of the thermal print head disclosed in this publication is that a common signal input conductor is provided on a glass epoxy substrate and a set of driving electrodes connected to an electronic component mounted on one tape carrier and adjacent thereto. The common electrode is connected to the signal input conducting wire and the common signal input conducting wire on the epoxy substrate through one tape carrier.

The following effects can be obtained by using this thermal print head. That is, since the glass epoxy substrate excels in mechanical workability, it is possible to easily install a connecting means such as a connector with an external circuit. Therefore, an inexpensive thermal print head can be obtained.

[0011]

However, when the present inventor made a prototype of this thermal print head and conducted an experiment, it was found that there were the following problems.

First, since a tape carrier is used for connecting ICs, the area of the connecting portion is increased as compared with wire bonding, resulting in an increase in size, which runs counter to the trend of the technology seeking for miniaturization.

Second, the tape carrier is peeled off when the defective IC is replaced after being mounted on the thermal print head. In this case, there is a risk that the wiring layer on the substrate will be separated together with the tape carrier.

Thirdly, metallization such as Au-Sn or solder-solder is generally used for connection by a tape carrier, but since the temperature of the wiring layer rises near the heating resistor, solder or solder is used. A low melting point metal such as Sn cannot be used.

In order to avoid this problem, the present inventors have considered two methods of metallizing the wiring layer for supplying a current to the heating resistor. (1) Entirely made of Au, tape carrier and Au-S
n Method of making connection by eutectic. (2) The whole is made of a metal having a relatively high melting point such as Al,
A method in which Sn or a solder layer is formed at the connection portion with the tape carrier and the tape carrier is connected with Sn-Au or solder-solder.

However, the first method not only increases the cost because metallization is performed on the entire substrate with expensive Au, but also uses wet etching in the etching process. For this reason, it is difficult to form the lead wire and the heating resistor accurately in shape due to over-etching. Can not stand.

In the second method, a cheap and dry-etchable metal such as Al can be used, and the shape and size of the heating resistor can be accurately formed. However, Sn or solder must be partially adhered as a connection layer with the tape carrier, which complicates the process and lowers the productivity, and also increases the cost, which is suitable for the actual production of a thermal print head. Absent.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a reliable thermal print head.

[0019]

In order to achieve the above-mentioned object, the thermal print head of the present invention is an alumina in which a plurality of heating resistors and individual electrodes electrically connected to the heating resistors are arranged. A ceramic substrate, a driving integrated circuit that opens and closes according to an image signal supplied to the heating resistor, and a driving electrode that transmits an image signal, a control signal, and a power source input from an external circuit to the driving integrated circuit. And a drive circuit substrate composed of a glass-epoxy substrate, and
The individual electrode and the drive integrated circuit are electrically connected by wire bonding, and a part of the drive electrode serves as an external lead terminal, and the external circuit and the drive electrode are connected through the external lead terminal. Is characterized by being electrically connected.

By adopting the above-mentioned structure, the thermal print head of the present invention does not need to use a tape carrier or the like, so that reliability is deteriorated such as peeling of a wiring layer or the like which occurs when a defective IC or the like is replaced. Never.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a thermal print head of the present invention will be described below with reference to the drawings. FIG.
In (a) and (b), an alumina ceramic substrate (2) is fixed to one end of a support plate (1) surface made of iron via an adhesive member (not shown). A drive circuit board (11) having a glass-epoxy laminate as a base material is fixed to the other end of the surface of the support plate (1) via an adhesive member (not shown). A plurality of heating resistors (3) and individual electrodes (4) for supplying current to these heating resistors (3) are formed on the alumina ceramic substrate (2). An IC (6) that opens and closes the current supplied to the heating resistor according to an image signal and a control signal is mounted on the drive circuit board (11) via an adhesive member (not shown). There is. A driving electrode (5) for transmitting an image signal, a control signal, and a current input from an external circuit via a connector (10) for connection to the IC (6) is formed on a driving circuit board (11). ing. The individual electrode (4) and the IC (6) are electrically connected to each other using an electrical connection means such as wire bonding (12).

The thermal print head shown in FIG.
Since the flexible circuit used for connecting the conventional thermal print head and the external circuit is unnecessary, the number of parts can be reduced. In addition, A required for the pressure contact part
Since u metallization is not required, material cost and man-hours can be reduced, and a cheap thermal print head can be provided. Further, since the contact failure of the pressure contact portion due to the temperature change does not occur, it is possible to provide the thermal print head with extremely high reliability.

Further, it is not necessary to install the IC on the ceramic substrate. For this reason, the area per expensive thermal print head of the expensive alumina ceramic substrate can be greatly reduced, and when batch processing is performed, the number of products to be manufactured per batch (such as heating resistors from one alumina ceramic plate is sputtered). The number of alumina ceramic substrates having a heat generating portion used in the thermal print head formed in (1) can be increased, productivity and workability can be improved, and material costs can be reduced.

Further, the IC is directly attached to the glass-epoxy substrate.
By mounting the IC, the insulating film on the drive electrode is not necessary because the structure is such that productivity and workability are not deteriorated even if the IC is not mounted on the lower part of the drive electrode. As a result, not only is the process simplified, but there is no risk of damaging the drive electrodes below the IC when replacing a defective IC.

Moreover, in this embodiment, since wire bonding is used for all the electrical connection means, the area required for connection can be reduced and the base material of the individual electrodes can be dry-etched such as Al. It can be a possible and cheap metal. As a result, an accurate heating resistor shape and size can be formed without using a complicated metal structure. Therefore, according to the thermal print head of the present invention, recording can be performed with a uniform and accurate pixel size.

In addition to the glass-epoxy substrate described above, in the thermal print head of the present invention, the IC may be placed on a metal or resin film or the like.
Further, it goes without saying that the same effect as the thermal print head shown in FIG. 1 can be obtained by mounting the combination on the substrate.

Next, another embodiment of the present invention will be described with reference to FIG.

The same members as those in FIG. 1 are designated by the same reference numerals.

In FIG. 2, if a part of the driving electrode (5) is used as an external lead-out terminal (21), the thermal print head can be directly connected to an external circuit. In addition, (22) indicates a common electrode, (23) indicates a signal electrode for supplying a current to the common electrode (22), and (24) indicates an IC.
The cover which protects (6) is shown.

[0030]

With the above-mentioned structure, the thermal print head of the present invention can prevent the risk that the driving electrodes are peeled off due to replacement of defective ICs, such as when the tape carrier is no longer used. High reliability can be obtained very easily.

[Brief description of the drawings]

1A is a simplified sectional view showing an embodiment of a thermal print head of the present invention, and FIG. 1B is a partially cutaway plan simplified view of FIG. 1A.

FIG. 2 is a partially cutaway schematic perspective view showing another embodiment of the thermal print head of the present invention.

[Explanation of symbols]

 2 Alumina ceramic substrate 3 Heating resistor 4 Individual electrode 5 Driving electrode 6 Driving integrated circuit 11 Glass-epoxy substrate 12 Wire bonding

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[Procedure amendment]

[Submission date] April 26, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG. 1 is a partially cutaway schematic perspective view showing an embodiment of a thermal printer head of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Kobayashi 72 Horikawacho, Saiwai-ku, Kawasaki-shi, Kanagawa Higashi Shiba Horikawacho Factory

Claims (1)

[Claims] 1. An alumina ceramic substrate on which a plurality of heating resistors and individual electrodes electrically connected to the heating resistors are arranged, and for driving to open / close according to an image signal supplied to the heating resistors. An integrated circuit; and a drive circuit substrate made of a glass-epoxy substrate on which a drive electrode for transmitting an image signal, a control signal, and a power source input from an external circuit to the drive integrated circuit are arranged. The driving integrated circuit is electrically connected by wire bonding, and a part of the driving electrode serves as an external lead terminal, and the external circuit and the driving electrode are electrically connected through the external lead terminal. The thermal print head is characterized by being connected to.