JPH0781116A - Thermal printing head - Google Patents

Abstract

PURPOSE:To provide a thermal printing head which can obtain uniform printing quality without any irregularity in printing density and is suitable for miniaturization. CONSTITUTION:A heating element 5 formed along a longitudinal end part of one side of an insulating substrate 1, a plurality of divided common electrodes 14, 14a formed by dividing into a plurality parts, a plurality of common leads 16, 16a connected to the heating element 5 by being drawn out from those divided common electrodes 14, 14a, a plurality of individual leads 3 connected to the heating element, and a continuous common electrode 15 which is formed along a longitudinal end part of the other side on the insulating substrate 15 and the common leads 16, 16a are connected to, are provided. Then, a block 18 which contains one electrode of the common leads 16, 16a and a plurality of individual leads 3, is formed. A bonding pad 127 which is bonded with wire to a driving element, is provided to the individual leads 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to thermal printheads.

[0002]

2. Description of the Related Art A conventional thermal print head is shown in FIG.
As shown in FIG. 4B and FIG. 4, the individual electrode 3 on the insulating substrate 1 and the common electrode 4 along the longitudinal end portion of the insulating substrate 1 are formed by the conductor pattern 2 mainly using gold. A heating resistor 5 is formed at the intersection of the electrode 3 and the common electrode 4.
Further, the auxiliary common electrode 6 is formed so as to overlap the common electrode 4, but this is formed in order to increase the current capacity of the common electrode 4, and a silver-based electrode material is mainly used.

The insulating substrate 1 is fixed on a heat radiating plate (not shown), and a printed wiring board 7 made of a glass cloth substrate, an epoxy resin laminated plate or the like is fixed so as to come into contact with the insulating substrate 1, and After the drive element 5 is mounted on the substrate 1 or the printed wiring board 7 and wire bonding 9a is performed, a protective film 10 of silicon resin coat for protecting the drive element 8 is applied.

However, in the conventional thermal print head, the wire bonding 9b between the common electrode 4 and the common electrode (not shown) on the printed wiring board 7 side is designated by the reference numeral 4a on the insulating substrate 1 of the common electrode 4. There are two end portions shown, and the conductor resistance value of the common electrode 4 increases toward the central portion of the head substrate 11, and the voltage drop increases toward the central portion, so that the central portion of the head substrate 11 is printed. The density became light and uneven printing density occurred.

As a remedy for this, a thermal print head as described in Japanese Patent Publication No. 4-17797 has been proposed. In this known thermal print head, a ground electrode is provided with a connection terminal to a printed wiring board on the side opposite to the common electrode, the common electrode has a higher conductor resistance toward the center of the head substrate, and the ground electrode is the head substrate. The conductor resistance value increases toward the end of, and the difference in both conductor resistance values is canceled out, and unevenness in printing density is corrected. However, the size of the insulating substrate must be increased in order to provide the ground electrode in the insulating substrate, which raises the material cost and is not suitable for downsizing.

By the way, in order to eliminate the print density unevenness, it is originally desirable to adopt a common electrode structure in which the conductor resistance values of the common electrodes for supplying a voltage to the respective elements of the heating resistor are the same. Is. As one example thereof, as disclosed in Japanese Patent Application Laid-Open No. 1-2047664, a thermal print head having a structure in which a common electrode (return electrode) is provided in two elements in one pattern is known. However, this thermal print head is a thin film type thermal print head, and is made possible because each element of the heating resistor is independent from its basic structure.

On the other hand, in the thick film type thermal print head, the heating resistor is formed as a continuous and integrated body. Therefore, in each element, all the elements are connected as a parallel circuit to the common electrode, so that one common electrode pattern is arranged for each element in order to connect the common electrode to each element. The density becomes high.

As a structure for solving this problem, the structure shown in FIG.
It is possible to arrange 12a. However, in such a structure, for example, when the extraction common electrode 12 is cut at the cutting point 13 in the manufacturing process, it can usually be found by measuring the resistance value between the common electrode 4 and the individual electrode 3, Since the other lead-out common electrode 12a is connected, it becomes impossible to identify the open portion, and it is possible to find it only by printing it as a finished product, but at this point it cannot be corrected. There is a problem that it becomes a waste product.

[0009]

SUMMARY OF THE INVENTION In view of the above problems, the present invention is to provide a thermal print head which is capable of identifying the open portion of the common electrode for extraction without uneven printing density and at the same time being capable of being miniaturized. .

[0010]

A thermal print head according to the present invention comprises an insulating substrate, a heating resistor and a first common electrode formed on one end of the insulating substrate in the longitudinal direction, and the first common electrode. A plurality of common extraction electrodes that are drawn out from the common electrode and connected to the heating resistor, a plurality of individual extraction electrodes that are connected to the heating resistor and drawn out, and the other longitudinal end on the insulating substrate. A thermal printhead comprising a second common electrode formed along a portion and connected to the plurality of common extraction electrodes, the block including one common extraction electrode and a predetermined number of the individual extraction electrodes. The first common electrode is divided so as to form Then, a bonding pad for performing wire bonding with a drive element is provided at the end of the individual extraction electrode on the side of the second common electrode.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In particular, in order to solve the problems of the thermal print head having the structure of FIG. 3, the present invention divides the common electrode 4 of FIG.
By constructing 14a and dividing it into blocks, it is possible to find a disconnection point when measuring the resistance value. Further, since the voltage drop is reduced in each divided electrode, it is not necessary to provide the auxiliary common electrode 6 (B in FIG. 2) in the common electrode 4 as in the conventional case, and the formation area of this auxiliary common electrode pattern is deleted. Can be achieved. From the above, each element to bonding pad 1
By adopting a structure in which the number of extraction common electrodes 16 drawn out to the 7 side is thinned out to one for several elements, it is possible to simultaneously improve the unevenness of printing density and reduce the size of the head substrate.

The above embodiment will be described in detail below with reference to FIGS. 1 and 2A. The divided common electrodes 14 and 14a, the lead-out common electrodes 16 and 16a, the individual electrode 3, the heating resistor 5, and the protective film 10 are formed on the insulating substrate 1 to form the head substrate 11a. At this time, the extraction common electrode 1
6 and 16a extend to the bonding pad 17 side at a rate of one in four elements, pass between the bonding pads 17 to which the individual electrodes 3 are extended, and the head is located at the end of the head substrate 11a from the bonding pad 17. Lead-out common electrodes 16 and 16a extended to the bonding pad 17 side on a continuous common electrode 15 installed parallel to the substrate longitudinal direction.
Are connected. The divided common electrode 14 is divided into adjacent divided common electrode blocks 18 for every four elements centering on the extraction common electrode 16.

By adopting this configuration, even if the lead-out common electrode 16 is temporarily cut, when the resistance value is measured between the individual electrode 3 and the divided common electrode 14, the cut lead-out common electrode 16 is used. The heating resistor 5 directly connected to the electrode 16 corresponds to the lead-out common electrode 1 connected to another heating resistor element 19 of the divided common electrode block 18.
The measured current circulates from 6a, and the adjacent element is connected in series to the element being cut, and the resistance value is measured as a value more than double, and the cutting point can be specified. It can be modified to make it a good product.

In the above embodiment, the number of elements applied to the lead-out common electrode 16 is four, but the number is not limited to this number, and the number of elements can be increased as long as it is within the current capacity range of the lead-out common electrode. Is. Standard 8 dots / mm
Considering the power consumption per device of about 7 mA in a thermal print head with a resistance of 3000 Ω, 8 devices
Block division is appropriate. In addition, the pattern pitch in this case is 0.125 mm × 8 elements / 9 electrode pattern = 0.111 mm pitch because one extraction common electrode is added to 8 elements, which is easy with the current resolution technology in pattern formation. Can be manufactured.

In the case of an 8 dot / mm thermal print head, a bonding pad width of 80 μm and an inter-pad gap of 20 μm are required, but since these can be sufficiently secured, the bonding pad array can be arranged at the same time, and the bonding can be performed. It is possible to reduce the size of the head substrate in the lateral direction of the pad portion.

As described above, since the heating resistor elements are adjacent to each other within the range of the divided common electrode block 18, the common electrode conductor resistance value difference is almost zero, and the print density unevenness is generated without causing the voltage drop difference. There is no. In addition, between the blocks, the printed wiring board 7 is connected via the common electrode 15 and the common electrode 16 pattern of the same number of distances and is connected to the heating resistor 5, so that the conductor resistance values are the same. No uneven printing density occurs. Together, Figure 2
Although the auxiliary common electrode 6 for increasing the current capacity is formed by printing on the common electrode 4 of the related art as shown in (B), the current is dispersed in the respective extraction common electrodes in this embodiment.
Since the auxiliary common electrode 6 is not necessary, it is possible to reduce the printing processing cost of the silver-based paste material and the auxiliary common electrode.

[0017]

According to the present invention, the common electrode is divided into a predetermined number of elements, and one drawn common electrode is provided on the divided common electrode, so that the print density unevenness is eliminated and at the same time, the head is removed. The substrate can be downsized, the auxiliary common electrode can be removed, and an inexpensive thermal print head can be supplied.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part of a thermal head of the present invention.

FIG. 2 is a cross-sectional view of essential parts of a thermal head of the present invention and a conventional example.

FIG. 3 is a plan view of relevant parts showing a state of disconnection in a conventional example.

FIG. 4 is a plan view of a conventional thermal head.

[Explanation of symbols]

 1 Insulating Substrate 3 Individual Electrode 5 Heating Resistor 7 Printed Wiring Board 8 Driving Element 14, 14a Divided Common Electrode 16, 16a Leading Common Electrode 17 Bonding Pad

Claims (2)

[Claims] 1. An insulating substrate, a heating resistor formed along one longitudinal end of the insulating substrate and a first common electrode, and the heating resistor drawn from the first common electrode. A plurality of common extraction electrodes connected to each other, a plurality of individual extraction electrodes connected to the heating resistor and extracted, and a plurality of common extraction electrodes formed along the other longitudinal end of the insulating substrate. Second with the extraction electrode connected
In the thermal print head including the common electrode, the first common electrode is divided so as to form a block including one common extraction electrode and a predetermined number of the individual extraction electrodes. Thermal print head. 2. The thermal print head according to claim 1, wherein a bonding pad for performing wire bonding with a driving element is provided at an end of the individual extraction electrode on the side of the second common electrode.