JPH08310028A - Thermal head - Google Patents

Abstract

PURPOSE: To provide a thermal head having high reliability wherein a short circuit does not occur between electrode patterns. CONSTITUTION: A glaze layer 2 having a mountain-shaped cross section is provided on a surface of a ceramic substrate 1 and heating resistors 6 are formed on a top portion of the glaze layer 2. A glaze layer 4 formed from a material of which main component is a glass having a softening point lower than that of the glaze layer 2 is provided at least one of foot sections 2a of the glaze layer 2 such that one part of each foot sections is overlapped to the glaze layer 4. A conductive layer 5 to be individual electrode patterns and a common electrode pattern is formed on a surface of the glaze layer 4. The glaze layer 4 is formed so that it is possible to prevent a short circuit of the electrode patterns due to the irregularities or zigzag lines on the foot sections 2a of the glaze layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head.

[0002]

2. Description of the Related Art A thermal head having a heating resistor provided on the surface of a glaze layer having a chevron cross section has been proposed as a partial glaze thermal head (for example, Japanese Patent Publication No. 63-19358). . The thermal head will be described with reference to FIG.

In FIG. 3, a first glaze layer 2 and a second glaze layer 3 each having a chevron cross section are formed on the surface of a ceramic substrate 1. The second glaze layer 3 has a flat cross-sectional shape. Then, the conductor layer 5 is formed on the surface of the ceramic substrate 1 including the surfaces of the first and second glaze layers. This conductor layer 5 is formed by photoetching or the like.
It is formed as a wiring pattern for each individual electrode, common electrode, and the like.

Next, a heating resistor 6 is formed on the first glaze layer 2, and a protective film 7 is formed on the heating resistor 6.
Then, a driver IC 8 for controlling energization of the heating resistor 6 is mounted on the thermal head substrate on the second glaze layer 3, and a gold wire 9 is provided for the individual electrode and the driver made of the conductor layer 5 and the driver. The bonding pad of the IC 8 is connected by wire bonding.

At this time, the purpose of arranging the second glaze layer 3 having a flat cross-sectional shape is provided to increase the adhesion strength of the individual electrode composed of the conductor layer 5 at the time of bonding. 3 is not essential. Further, this thermal head substrate is an external wiring connection substrate, connector, and
Attach a cover etc. to make a thermal head.

When the thermal head is manufactured, the first glaze layer 2 is formed by a printing method, and the ceramic substrate 1 is formed at the skirt 2a of the first glaze layer 2.
At the boundary portion between and, large irregularities appear due to the non-linearity of the edge line of the screen mask during printing and the non-smoothness of the surface of the ceramic substrate.

Explaining this problem in detail with reference to FIG. 4, the skirt portion 2a of the first glaze layer 2 has large irregularities as described above, and the glaze skirt line is not a straight line but a zigzag state. Then, in order to pattern the individual electrodes and the common electrode, a gold paste is printed and baked on the entire surface to form a conductor film. At this time, the viscosity of the gold paste is adjusted so as to level after printing in order to improve printability.

For this reason, after printing, the gold paste flows into the recesses 2a of the first glaze layer 2 by leveling in the recesses, and the thickness of the gold paste locally increases.

Then, a gold conductor is formed in the pattern of each individual electrode 10 and the common electrode 11 by the photoetching method. The gold conductor is locally thickened in the concave portion of the skirt portion 2a of the first glaze layer 2. Therefore, it is difficult to etch, excess gold other than the above pattern remains, and a short-circuit portion 12 occurs particularly in the pattern on the individual electrode side. For this reason, this short-circuited portion 12 needs a correction work for electrically cutting it, and the processing cost thereof increases.

Further, as another problem, the background of the ceramic substrate 1 is exposed in the portion sandwiched between the first glaze layer 2 and the second glaze layer 3, and the ceramic substrate is exposed in this portion. There is no choice but to form the conductor layer 5 directly on the substrate 1 by printing and firing a gold paste, for example.

At this time, as shown in FIG. 5, the surface of the ceramic substrate 1 is not smooth, and countless recesses 1a are formed. When gold paste is printed on the depressions 1a, air is entrapped in the depressions 1a, and when the paste is fired, the entrained air expands due to the heating during firing to expand the conductive layer 5. 13 occurs.

The bubbles 13 cause the film peeling of the conductor layer 5 because the conductor layer 5 and the ceramic substrate 1 do not adhere to each other, and the conductor layer 5 in such a state is etched so that individual electrodes and a common electrode are formed. Patterning the electrodes will impair the reliability of the thermal head.

[0013]

SUMMARY OF THE INVENTION The present invention provides a thermal head capable of forming an electrode pattern which eliminates the unevenness at the skirt portion 2a of the first glaze layer 2 having the chevron cross-section and which does not generate the bubbles 13. In point.

[0014]

A thermal head according to the present invention comprises a glaze layer having a chevron cross section on the surface of an insulating substrate, and a heating resistor array on the surface of the glaze layer. An insulating layer mainly composed of glass having a softening point lower than that of the mountain-shaped cross-sectional glaze layer is formed on the surface of the insulating substrate so that one side or both sides of the skirt of the mountain-shaped cross-sectional glaze layer overlap. An electrode is formed on the surface of the insulating layer.

[0015]

1 shows a cross section of an embodiment of the device according to the invention. The same parts as those in the conventional example will be described with the same reference numerals. In FIG. 1, a first glaze layer 2 having a chevron cross section and a second glaze layer 3 having a flat cross section are formed on the surface of a ceramic substrate 1.

The third glaze layer 4 is formed so as to partially overlap the skirt portions 2a and 3a of the first glaze layer 2 and the second glaze layer 3. The third glaze layer 4 is the first
The glaze layer 2 and the second glaze layer 3 are made of an insulating material whose main component is glass having a lower softening point.

Then, as the material of the first glaze layer 2 and the second glaze layer 3, a material paste having a softening point of 900 to 950 ° C. is printed and baked at 1300 to 1400 ° C. to form a glaze layer. . In particular, since the cross-sectional shape of the first glaze layer 2 affects the contact state between the platen roller and the heating resistor 6 and the concentrated state of the platen pressure, it is necessary to maintain the initial cross-sectional shape.

Therefore, unless the third glaze layer 4 is fired at a firing temperature lower than the softening points of the first glaze layer 2 and the second glaze layer 3, the first glaze layer 2
Also, the second glaze layer 3 flows out during firing of the third glaze layer 4, causing sagging, which makes it impossible to maintain a predetermined shape.

Therefore, as the material of the third glaze layer 4, the softening point is 780 ° C. or lower and the firing temperature is 900 ° C.
Select the following glass materials. At the same time, since the surface roughness of the third glaze layer 4 is required to be smooth, an insulating material containing glass as a main component is used. By using glass as the main component, the surface of the third glaze layer 4 after firing has good smoothness, and the unevenness of the background of the ceramic substrate 1 can be smoothed at the same time.

The unevenness of the skirt portion 2a of the first glaze layer 2 is also eased by the third glaze layer 4 due to the overlap with the first glaze layer 2, so that the short circuit of the electrode pattern occurs (FIG. 4). 12) can be prevented.

In this case, since the short circuit at the skirt portion 2a of the first glaze layer 2 is particularly likely to occur on the individual electrode side, the third glaze layer 4 may be formed only on the individual electrode side.

Further, the second glaze layer 3 has the first glaze layer.
Since the glaze width is wider than that of the glaze layer 2 and the unevenness of the skirt portion 3a is also small, it is possible to implement without overlapping with the third glaze layer 4.

Next, after the conductor layer 5 is formed by printing and firing a gold paste, for example, the conductor layer 5 is formed into individual wiring patterns such as individual electrodes and common electrodes by a photoetching method or the like. Then, the heating resistor 6 is arranged near the top of the first glaze layer 2, and the protective film 7 is formed thereon.

A driver I is mounted on the thermal head substrate.
C8 is mounted, the bonding pad of the driver IC 8 and the individual electrode bonding pad are connected by wire bonding with the gold wire 9, and this bonding portion is sealed with resin. Further, the thermal head substrate is fixed on a heat dissipation plate (not shown), and an external wiring substrate, a connector, a cover, etc. are attached to form a thermal head.

In the above embodiment, the first glaze layer 2 and the second glaze layer 2
Although the structure of the thermal head having the glaze layer 3 has been described, as another embodiment, as shown in FIG. 2, the glaze layer 14 is formed on the ceramic substrate 1 except for the second glaze layer 3 in the first embodiment. Alternatively, the conductive layer 5 may be continuously provided on the glaze layer 14 to form the individual electrodes and the common electrode by patterning the conductor layer 5, and the driver IC 8 may be fixed on the glaze layer 14. In addition,
The other structure of the second embodiment is the same as that of the first embodiment, and the description thereof will be omitted.

[0026]

According to the thermal head of the present invention, since the insulating layer is formed on the ceramic substrate so as to partially overlap with the skirt of the glaze layer having the chevron section provided with the heating resistor, the glaze layer of the glaze layer is formed. It is possible to prevent a defect due to a short circuit of the electrode pattern in the skirt portion, and as a result, the work for correcting the short circuit and the processing cost are unnecessary. Further, since the conductive film forming the electrode is formed on the insulating layer, it is possible to prevent generation of bubbles due to the unevenness of the surface of the ceramic substrate as in the conventional case, and it is possible to supply a highly reliable thermal head.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of a thermal head of the present invention.

FIG. 2 is a sectional view of a second embodiment of the thermal head of the present invention.

FIG. 3 is a sectional view of a conventional thermal head.

FIG. 4 is a perspective view of a main part for explaining a problem of a conventional thermal head.

FIG. 5 is a cross-sectional view of essential parts for explaining another problem of the conventional thermal head.

[Explanation of symbols] 1 ceramic substrate 2 chevron cross-section glaze layer 2a foot of chevron cross-section glaze layer 4, 14 insulating layer 5 made of glass material having a lower softening point than the chevron cross-section glaze layer 5 conductor layer 6 heat generation Resistor

Claims (6)

[Claims] 1. A thermal head comprising a glaze layer having a chevron cross section on the surface of an insulating substrate, and a heating resistor provided on the surface of the glaze layer having the chevron cross section, wherein the foot of the glaze layer having the chevron cross section is provided. A thermal head, characterized in that an insulating layer is formed on the surface of the insulating substrate so as to partially overlap one side or both sides of the portion, and an electrode pattern is formed on the surface of the insulating layer. 2. The thermal head according to claim 1, wherein the insulating layer is an insulating layer formed of a material whose main component is glass having a lower softening point than that of the glaze layer having a chevron cross section. 3. The thermal head according to claim 1, wherein the electrode patterns are an individual electrode pattern and a common electrode pattern. 4. The thermal head according to claim 1, wherein the insulating substrate is a ceramic substrate. 5. The thermal head according to claim 1, wherein a driver IC is fixed on the insulating layer. 6. The thermal head according to claim 1, wherein a glaze layer for fixing the triver IC is provided on the insulating substrate so that one of the skirts thereof overlaps the insulating layer.