JPS5922675B2 - Method of manufacturing thermal head - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a thermal head.

In general, thermal recording is performed by applying a recording signal current to a resistor provided on a substrate and applying heat to thermal paper according to the Joule heat generated at that time. Conventionally, there are three types of thermal heads, depending on the material of the resistor and its manufacturing method: a thin film resistor type, a semiconductor resistor type, and a thick film resistor type.

Each type has advantages and disadvantages in terms of characteristics and manufacturing methods. In other words, in the thin film type, a resistor base is basically formed by vapor deposition or sputtering of a metal or its oxide or nitride, and then the resistor base is finished into a desired shape by photo-etching means, and the heat generating element is formed. Although it has excellent properties, it has the disadvantage that its manufacturing method requires a large number of steps and large-scale manufacturing equipment.

Next, in the semiconductor type, for example, low resistance diffusion is applied to the negative part of a silicon substrate to form a resistor, and this series of manufacturing steps is almost the same as the manufacturing process of normal semiconductor devices.
It requires equipment and has the same drawbacks as the thin film type. Furthermore, a long thermal head such as a facsimile thermal head also has the disadvantage that it cannot be constructed using a single substrate due to the silicon substrate size limitations. On the other hand, for the thick film type, a paste-like resistor is used, and the pattern is immediately formed by screen printing on which the desired pattern has been formed in advance.
It only needs to be fired after this, and has the advantage that it can be manufactured at a lower cost using an extremely simple method and equipment compared to the former two.

However, this thick film type is because of its manufacturing method! For example, it is extremely difficult to arrange a fine resistor of 6 dots/- or more, or the spacing between resistor dots is large relative to the dot width. It is inferior to the two. Since thermal recording utilizes Joule heat generated by the resistor, if the resistance value of each dot varies, differences in color density will occur, resulting in unsightly recording.

Currently, this variation is ±5 to 1 for thin film and semiconductor types.
0%, and the thick film type is said to have a tolerance of ±15 to 30917. Although the thick film type is one step inferior, it has become one of the mainstream thermal heads because of its low cost.

Also, when looking at the cross section of a resistor dot that has a thick film shape, it has a semicircular shape due to the influence of paste sag during printing and the surface tension of the paste. With this shape, the contact pressure of the resistance dots against the recording paper becomes weaker toward the periphery of the dots, so that heat transfer also becomes weaker, making it difficult to make an impression of a normal dot area and making the dots appear smaller. In order to compensate for this drawback, a method is usually used to increase the size of the impression dot by inputting excessive power, and this method has problems in terms of longevity. Also, the distance between the resistor dots is, for example, 5
In the case of dot/Tfm, the practical limits of the screen printing method are a dot width of 100 μm and a dot spacing of 100 μm.

If the dot spacing is large, the recording becomes mottled with black and white, making it difficult to see, and the halftone effect also reduces the visual density, resulting in a disadvantage that the recording quality is not very good. The present invention investigates the cause of the resistance variation in the thick film type and devises the manufacturing method to improve it to a thin film type or even lower, and the shape is also a dot shape with good flatness suitable for thermal recording. In addition, the dot spacing can be narrower than in conventional printing methods, improving recording quality and providing a thermal head with excellent cost performance without sacrificing low cost due to the simplicity of the manufacturing method. It is something.

Hereinafter, specific examples of the method for manufacturing a thermal head according to the present invention will be described in detail.

Generally, the resistance value R of a resistor is expressed by the following formula.

Here, ρ: Specific resistance of the resistor material (Ω-Cm), L: Length of the resistor (Cm), S: Cross-sectional area of the resistor (Cr!i). However, if the uniformity of the resistor paste is satisfied, the resistance value and the variation among the resistors are determined by the shape of the resistor paste, such as length and cross-sectional area.

However, in a thick film resistive element manufactured by a screen printing method, the shape of the pattern, especially the width cross-sectional area in the length direction, is not uniform.

This is, so to speak, a fate of the screen printing method.
This is because a screen plate has a desired emulsion pattern made of a thin resin or metal film formed on a fine mesh surface made of thin resin or metal wires, but especially at the pattern edges, the emulsion edges and the mesh line edges are It is impossible to match the mesh perfectly, and for this reason, the mesh openings at the ends of the emulsion are not uniform but jagged. Resistance patterns printed with such screen plates also exhibit similar shapes. In addition, since the screen printing method is used to print with a fluid paste, the printed cross section becomes semi-cylindrical due to sagging of the paste or the influence of surface tension, etc., as described above.

As mentioned above, it is virtually impossible to make the cross-sectional shape of thick film resistive elements made by the screen printing method uniform across multiple elements, and as a result, compared to pattern-format methods using photo-etching such as thin film type, there is a possibility of variation. It is natural that there are many.

The present invention is based on the above-mentioned viewpoints of screen printing thick film elements, and provides a manufacturing method that reduces the variation to the same level or lower than that of thin film elements and makes the shape suitable for thermal recording. It is something. FIG. 1 is a plan view of a thermal head manufactured in the first step of a specific embodiment of the method for manufacturing a thermal head according to the present invention.

The first step is performed as follows.

On one plane of the insulating substrate 100, which is made of ceramic, glass, or metal, and which holds electrical insulation on its surface, a conductive paste containing a precious metal as a main component is printed in a desired pattern arrangement by a screen printing method. After baking or depositing a non-oxidizing metal on the entire surface or a part of the surface of the insulating substrate 100 by vapor deposition or plating in a single layer or multiple layers so that the non-oxidizing metal is on the surface, photoetching means is applied. A plurality of current-carrying electrode leads 101 are provided. Second
The figure is also a plan view of the thermal head produced in the second step of this embodiment. The second step is carried out as follows: A thick film resistor paste is applied to a desired thickness by screen printing or a doctor blade method so as to span a portion of the plurality of current-carrying electrode leads 101, and repelling is performed. Let dry.

Thereafter, in the third step, the temperature (200℃) is set to burn off the organic binder in the thick film resistor paste.
~300°C), or a temperature near the softening temperature of the binder glass in the paste (500~600°C), or a complete firing temperature of the resistor paste (700~85°C).
A resistor layer 201 fired at a temperature of 0° C.) is provided. FIG. 3 is a plan view of the thermal head similarly prepared in the third step of this embodiment.

The third step is performed as follows. In the resistor layer 201 created in the second step, since the pairs of current-carrying electrode leads 101 facing each other are not separated, the separation of pixels is poor during recording, and the resolution is degraded.

Therefore, it is necessary to insulate and separate the resistance between the pair of current-carrying electrode leads 101. As described above, in the case of thick film elements manufactured using the ordinary screen printing method, insulation separation is automatically performed because the desired pattern is already formed during printing, but the screen printing method has poor printing accuracy.

The method for manufacturing a thermal head according to the present invention has its most distinctive feature in this third step. As a specific method for implementing this third step, two methods can be used depending on the firing temperature of the resistor layer 201 performed in the second step.

That is, as a first method of a specific embodiment of the third step, if the resistor layer 201 in the second step is fired at a temperature that burns off the organic binder, the resistor layer 201 A suitable photoresist is applied to the surface of the substrate including the layer 201, prebaked at a suitable temperature, and then exposed to light using a photomask on which a desired resistor shape is formed. Thereafter, when the resistor layer 201 is developed while applying ultrasonic waves in a developer solution compatible with the photoresist, the resistor layer 201 becomes porous because the organic binder is burnt off, and there is no contact between the particles and the substrate. Since the adhesion strength is weakened, it dissolves together with the developed photoresist, and unnecessary portions are removed, forming a plurality of resistor dots 301 which are insulated and separated from each other and shaped into a desired resistance pattern. The second method of the specific embodiment of the third step is applicable when the resistor layer 201 in the second step is fired at a temperature higher than the softening point of the glass binder or at a complete firing temperature. An acid-resistant photoresist is applied to the surface of the substrate including the resistor layer 201 formed in the second step, dried, and exposed with a photomaster in which a pattern of the desired resistor shape is formed. First, a resist pattern is formed, which can be obtained by development or by printing an etching-resistant resist with a screen printing method so that the edges are sharp by using a metal mask screen plate without a mesh. .

Next, the excess resistor layer in the portions not covered by the resist pattern is removed using an etching solution that is selectively non-corrosive to the current-carrying electrode lead material and corrosive to the resistor layer material. A plurality of shaped resistor dots 301 are formed which are insulated and isolated from each other. Of course, if the resistor layer is not completely fired, it is necessary to perform another firing after the etching to complete the firing. Here, as the etching liquid, since the binder glass in the thick film resistor paste is likely to be easily corroded by acid, an appropriate concentration of 91% acid, sulfuric acid, or fluoric acid should be used. I can do it.

The shape of the resistor dot created by the method described above is
Since it is reproduced with an accuracy similar to the pattern accuracy of a photomask, variations due to differences in shape are reduced, and the cross-sectional shape has been changed from the conventional semicircular semicircle shape to an almost flat shape, and the distance between resistors is reduced. Since the interval between the resistor dots and the resistor dots can be arbitrarily set and narrowed at the photomask forming stage, resistor dots are formed that are extremely suitable for thermal recording.

FIG. 4 is a plan view of the thermal head produced in the fourth and final step of this embodiment.

The fourth step is performed as follows. In thermal recording, the resistor dot surface is conveyed in pressure contact with the thermal paper and is subjected to its abrasive action, so if the third step is continued, the resistor will be polished and its life will be extremely short. .

In order to prevent this, in the fourth step, all of the resistor dots 301 are included, and the energizing electrode lead 101 is removed.
A wear-resistant layer 401 is provided by printing low-melting point glass on all parts except for a part thereof using, for example, a screen printing method and then baking the glass. As described in detail above, although the thermal head manufactured by the manufacturing method of the present invention is a thick film resistor element, it can be made to have high performance by adding photoetching means, which is one of the means for forming a thin film resistor element, to an intermediate process. Since a resistor pattern that is accurate and suitable for thermal recording is formed, the resulting recording is of high quality.

Furthermore, the equipment and process costs required for this level of photoetching process are much smaller than those required for forming thin film resistive elements, and a thermal head with excellent cost and efficiency can be obtained.

Although the present invention has been described above with reference to a thermal head,
It goes without saying that the basic concept of the present invention can be directly applied to thermal heads and thick film integrated circuits, which are a technical field.

Brief Explanation of Section 1 Figures 1 to 4 are plan views of a thermal head obtained in each step of the method for manufacturing a thermal head according to the present invention.
Throughout the figure, 100 is an insulating substrate, 101 is a current-carrying electrode lead, 201 is a resistor layer, 01 is a resistor dot, 4
01 indicates an abrasion resistant layer.

Claims (1)

[Scope of Claims] 1. In the manufacture of a thermal head that conducts thermal recording using Joule heat by passing current through a plurality of resistor dots, the plurality of resistor dots are made of thick film resistors. 1. A method for manufacturing a thermal head, which comprises forming a thermal head larger than a desired shape, firing it at a temperature higher than a complete firing temperature, and then shaping it into a desired shape by etching means. 2. In manufacturing a thermal head that conducts thermal recording using Joule heat generated by passing current through a plurality of resistor dots, the plurality of resistor dots are formed using a thick film resistor to be larger than the desired shape. . A method for manufacturing a thermal head, which comprises firing at a temperature below the complete firing temperature, shaping it into a desired shape by etching means, and firing it again at a temperature above the complete firing temperature.