JPH0712696B2 - Lead forming method for partial glaze type thermal head - Google Patents

Description

The present invention relates to a lead forming method for a thermal head used as a printing apparatus such as a facsimile or a printer, and more particularly to a lead forming method for a partial glaze type thermal head.

<Prior Art> There are two types of thermal heads, a full-glaze layer type in which a glaze layer is provided on the entire surface of a substrate such as a ceramic, and a partial glaze layer type in which a glaze layer is provided only in the vicinity of dots.

The general reason for providing the glaze layer on the thermal head is to speed up printing by blocking the heat conduction between the dots and the substrate, and to miniaturize and thin the lead wiring due to the smoothness of the glaze layer surface. There is a place to plan.

Therefore, the reason why the partial glaze layer type thermal head is particularly proposed and implemented is that, in addition to the above reason, a glaze layer having an arcuate surface is provided only under the vicinity of the dot, and as a result, the dot portion is projected. That is, the contact with the thermal paper is extremely good, and the thickness of the glaze layer is controlled according to the printing speed so that efficient characteristics with less blurring are exhibited.

The following description is for a partial glaze type thermal head.

FIG. 4 is a flowchart of the steps of the lead forming method in the prior art.

The resistor layer on the substrate with the glaze layer formed at a predetermined place,
After laminating the conductor layers, a photoresist layer is applied on the conductor layers (FIG. 4 (a)).

In order to form individual leads and common leads on the ceramic substrate and the glaze layer, a mask is placed on the substrate and exposed to ultraviolet light (FIG. 4 (b)).

Development is performed to remove the exposed portion of the resist layer (FIG. 4 (c)).

Etching is performed to remove the conductor layer and the resistor layer directly below the resist layer. By removing the conductor layer and the resistor layer, the individual leads and the common leads are formed at once on the ceramic substrate and the glaze layer (FIG. 4 (d)).

<Problems to be Solved by the Invention> Generally, the surface roughness of the surface of the glaze layer and the surface of the ceramic substrate is significantly different from about 0.01 μRa in the glaze layer to about 0.3 μRa in the ceramic substrate. Therefore, since the ceramic substrate has a substantially larger surface area than the glaze layer, the etching rate in the etching step tends to be smaller in the glaze layer than in the ceramic substrate under the same conditions. From this, it can be said that when the individual lead or the common lead is formed, by setting the etching rate corresponding to the glaze layer, there is little risk of short-circuiting between the leads due to unetched portions.

However, on the other hand, it is common that a large number of fine void-like voids exist inside the ceramic substrate. Therefore, even if the ceramic substrate is mirror-polished, irregularities of about 30 to 150 μm remain on the surface.

Therefore, the resistor layer formed on the ceramic substrate,
Since the photoresist layer of the conductor layer and the photoresist layer is formed by coating, the thickness of the uneven portion tends to be different from other portions. In particular, in the recessed portion, the thickness tends to be thicker than other portions due to the surface tension of the photoresist.

If there is the above-mentioned recessed portion between the adjacent leads, the photoresist is applied to that portion thicker than the other portions. Since this thickly applied photoresist cannot be completely removed by exposure and development, the separation between the leads, which should be separated by etching, may be incomplete, resulting in a short circuit between the leads. It also causes a decrease in the production efficiency of the thermal head.

In order to completely remove the photoresist, it is necessary to perform either so-called overexposure or overdevelopment.
On the other hand, in order to make the printing of the thermal head clear, it is better that the dots are fine and the adjacent dots are as close as possible. For that purpose, the interval of the lead pattern connected to the dot becomes fine,
To form such fine intervals, the overexposure,
If any of the overdevelopment is performed, the processing accuracy of the dot portion cannot be maintained, which is a problem.

That is, if it is attempted to perform etching with high accuracy in the vicinity of the dot portion, which is the printed portion of the thermal head, the photoresist in the concave portion on the ceramic substrate cannot be completely removed. On the contrary, if the photoresist in the concave portion on the ceramic substrate is to be completely removed, the dots cannot be etched with high precision.

Therefore, it is very difficult to perform exposure, development, or etching that can satisfy both of them, so that the yield of the thermal head cannot be improved.

The present invention has been made in view of the above circumstances, and provides a lead forming method for a thermal head, which can form a highly accurate and near-dot dot parine without being influenced by irregularities on the surface of the ceramic substrate. Is intended.

<Means for Solving Problems> A method for forming leads of a partial glaze type thermal head according to the present invention is a method for forming leads of a thermal head in which a lead pattern is formed on a ceramic substrate on which partial glazes are formed by a lithography technique. In the first step, a first step of performing resist patterning only on the lead portion on the ceramic substrate and a second step of performing resist patterning on the lead portion in a superimposed manner and performing resist patterning on the dot connection portion on the glaze layer. I'm out.

<Example> FIG. 1 shows a process drawing and a schematic plan view of a lead forming method of a partial glaze type thermal head according to the present invention. Second
FIG. 3 is a schematic plan view of a mask used in the present invention, and FIG. 3 is a partial schematic perspective view of a thermal head on which dots are formed. Embodiments of the present invention will be described below with reference to the drawings.

A resistance layer is formed on the entire surface of the ceramic substrate having the glaze layer 20 formed at a predetermined position. This resistance layer is made of TaSi or
A thin film resistance material such as TaN is formed by means such as vapor deposition or sputtering. Then, a conductor layer is formed on the resistance layer. This conductor layer is, for example, Au, Cu, aluminum or the like, and is formed by the same means as described above. After applying the positive photoresist layer 50 on the conductor layer, soft baking is performed in a baking oven.

Here, when the photoresist layer 50 is applied, the photoresist layer 50 is applied on the concave portion 11 existing on the surface of the ceramic substrate 10 in a thick state as compared with other places because of its surface tension. (Fig. 1 (a)).

As shown in FIG. 2 (a), individual and common leads are formed on the ceramic substrate 10 coated with the photoresist 50.
The mask 60 as shown in FIG. In this mask 60, a pattern 601 covering the individual leads 411, the common leads 412 and the glaze layer 20 is a light shielding part (shown by diagonal lines), and the other patterns 602 are through holes. That is, the mask 60 is adapted to pattern the ceramic substrate 10 excluding the glaze layer 20. When ultraviolet exposure is performed in this state, the portion corresponding to the pattern 602 is exposed, and the exposed photoresist layer in this portion
Only 50 undergo a photochemical reaction to form a latent image (first
(Figure (b)).

The ceramic substrate 10 that has been exposed to the first ultraviolet ray is developed using, for example, an alkaline aqueous solution (see FIG. 1).
(c)). As a result of this development, as shown in FIG. 1 (g), the photoresist layer 50 in the region where the photochemical reaction has occurred is removed, the conductor layer 40 is exposed, and the other region (indicated by diagonal lines) is used for individual lead in the future. The photoresist layer 50 in the regions to be the 411 and the common leads 412 (the regions are shown by (411) and (412)) or the regions to be the dots is not removed.

However, in this case, since the concave portion 11 is located on the surface of the ceramic substrate 10 at a position where it crosses the insulating isolation band of the lead (shown by hatching), and therefore the concave portion 11 has a thick photoresist layer in advance, In some cases, it may not be removed sufficiently by the ultraviolet light exposure once, and may remain.

The above steps 1 to 4 are the first steps for performing resist patterning on the lead portion of the ceramic substrate 10.

Next, the second UV exposure is performed (Fig. 1 (d)). For this exposure, the mask 61 shown in FIG. 2 (b) is used. The mask 61 is substantially the same as the mask 60. That is, in FIG. 2 (b), the pattern 602 'is a through hole, and the other patterns are light shielding parts. However,
The tip 603 'of the insulating separation band between the individual leads 411 (this tip is hung on the glaze layer 20) has a convex shape, and the tip 604' of the common lead 412 (this tip is hung on the glaze layer 20). Is a convex through hole that is laterally leftward in the drawing at a position corresponding to the tip 603 '. The width W'of the insulating separation band on the ceramic substrate is slightly wider than or equal to that of the mask 60.

The ceramic substrate 10 is developed (FIG. 1 (e)). As a result of this development, the photoresist layer in the recess 11 left behind is completely removed because it has undergone a photochemical reaction in the second exposure. At the same time, dot portion neighborhood patterns 421 and 422 are formed at the position of the glaze layer 20 (see FIG. 1).
(h)). Since the dot portion vicinity patterns 421 and 422 are formed on the glaze layer having a very smooth surface, the above-mentioned inconvenience due to the uneven thickness of the photoresist layer does not occur.

The above steps correspond to the second step of performing the resist patterning of the lead portion one after another and the resist patterning of the dot portion vicinity pattern on the glaze layer.

After that, the ceramic substrate 10 is etched (FIG. 1 (f)). As a result, the conductor layer 40 and the resistor layer 30 which are directly below the photoresist layer 50 removed by the first and second steps are etched to expose the surface of the ceramic substrate 10. Moreover, as described above, the recess 11
However, since the resist layer is completely removed, the conductor layer 40 and the resistor layer 30 in that portion are completely etched in this etching step.

Thus, the individual leads 411, the common leads 412 and the dot portion vicinity patterns 421 and 422 are formed.

Photoresist is again applied to the ceramic substrate 10 on which the individual lead and common lead patterns are formed in this manner, and a mask (not shown) having a through-hole pattern corresponding to the dots 31 is overlaid for exposure and development steps. By further performing selective etching capable of removing only the conductor layer 40, the resistor layer 30 corresponding to the dots 31 is exposed on the surface of the conductor layer 40, and a thermal head pattern as shown in FIG. 3 is formed. To manufacture.

It should be noted that, in the above-mentioned embodiments, the photoresist is described as a positive type, but the same pattern as the above embodiment can be obtained by reversing the opening pattern of the mask used also in the negative type photoresist. .

The concave patterns 603 'and 604' are not always necessary.

<Advantages of the Invention> According to the lead forming method of the partial glaze type thermal head according to the present invention, it is possible to simultaneously form the lead in the vicinity of the dot which requires a highly precise forming process and to etch the lead on the end face substrate. Therefore, highly accurate lead patterning can be performed. Furthermore, the photoresist thickly applied to the concave portion of the ceramic substrate can be completely removed. Therefore, the yield of the thermal head can be improved as compared with the conventional method.

[Brief description of drawings]

FIG. 1 is a process diagram of a lead forming method according to the present invention, FIG. 2 is a schematic plan view of a mask used in the present invention, and FIG. 3 is a thermal head in which dots are formed after a pattern is formed by the present invention. 4 is a partial schematic perspective view, and FIG. 4 is a process drawing of a conventional lead forming method. 10 …… ceramic substrate, 20 …… glaze layer, 30 …… resistor layer, 31 …… dot, 40 …… conductor layer, 411 …… individual lead, 412 …… common lead, 50 …… photoresist.

Claims (1)

[Claims] 1. In a lead forming method of a thermal head for forming a lead pattern on a ceramic substrate on which a partial glaze is formed by a lithography technique, a first step of performing resist patterning only on the lead portion on the ceramic substrate, And a second step of performing resist patterning of the lead portion in a repeated manner and resist patterning of the lead portion on the glaze layer.