JPH07321445A - Thick-film circuit board, its manufacturing method, and thermal head using thick-film circuit board - Google Patents

Abstract

PURPOSE:To minimize a contact area, prevent the increase in resistance due to the diffusion of silver to a metal layer, and achieve a reliable connection with a low resistance by forming a thick-film layer mainly consisting of the silver of an electrode- reinforcement part so that the thick-film layer contacts a wiring pattern consisting of the thick-film layer mainly consisting of gold at the end face. CONSTITUTION:An individual electrode 3 consisting of a gold thick-film pattern with a film thickness of 0.1-0.5mum being aligned in a line is provided on an alumina ceramic substrate 1 via an undergraze layer 2. A common electrode 4 with a comb-shaped tip part 4a so that the tip of the comb teeth is located is formed between the individual electrodes 3. Also, a heat-generation resistor layer 5 consisting of ruthenium oxide layer crossing the individual electrode and a common electrode is provided at the upper layer of the individual electrode and the common electrode. A silver layer 7 with a film thickness of 20-50mum whose only end face is in contact is formed on the outer-periphery part of a body part 4b of the common electrode. Also, an external frame part 4c consisting of a gold film-thickness pattern is formed at an outermost periphery so that it contacts only at the end face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick film circuit board, a method for manufacturing the same, and a thermal head, and more particularly to an electrode lead-out structure for a thermal head used in a recording section of a facsimile or printer.

[0002]

2. Description of the Related Art Usually, when printing is performed using a thermal head, a heating resistor forming the thermal head is energized to generate heat. At this time, energization is achieved by passing an electric current between a common electrode whose tip is branched into a plurality of electrodes and an individual electrode facing or facing the common electrode. In addition, since the individual electrodes are selectively energized, it is desirable that the common electrode to which a power is collectively applied is made of a conductive material having a small resistance value in order to satisfy a predetermined power capacity. Usually, the root portion of the common electrode, that is, the common electrode body portion is reinforced by a method such as securing a large area of the body portion of the common electrode or increasing the film thickness in order to satisfy a desired power capacity. However, in order to secure the area of the common electrode main body, an insulating substrate having a large area is required, which causes drawbacks such as high cost and large thermal head.

Therefore, in order to solve this problem, in the common electrode body, a silver layer is laminated on a thick film pattern using a gold paste or a metalloorganic paste to reinforce the conductive layer to improve its conductivity and its resistance. A method for suppressing the increase in value has been proposed (Japanese Patent Publication No. 4-62867).

By using this method, it is possible to reduce the cost because the silver layer is inexpensive even if it is formed thick. However, when the gold layer and the silver layer come into contact with each other, silver having a small atomic radius becomes gold. There is a problem in that the resistance value of the contact portion rises due to diffusion into the inside, and high electric power must be supplied in order to secure the current necessary to heat the heating resistor.

For example, as shown in FIG. 5 and FIG. 6 which shows a main part of a conventional thermal head, in both cases, a silver layer is laminated on a gold layer forming a common electrode main body to form an electrode reinforced portion. The contact area between the gold layer and the silver layer is large, and the contact between the gold layer and the silver layer causes the silver layer to diffuse into the gold layer, increasing the resistance value of the main body of the common electrode, which enables good printing. There was a problem that I could not.

[0006]

When the silver layer is laminated on the upper layer of the common electrode body to form the electrode reinforced portion as described above, the resistance value increases due to the diffusion of silver, and high power must be supplied. There is also a problem that good printing cannot be performed. Further, the occurrence of such a problem is not limited to the formation of the thermal head, and is the same in other thick film circuits.

The present invention has been made in view of the above circumstances, and prevents an increase in the resistance value of an electrode reinforced portion in a thick film circuit,
It is an object of the present invention to provide a thick film circuit board having low cost and high reliability.

Another object of the present invention is to provide a thermal head which is inexpensive and highly reliable, which prevents an increase in the resistance value of the common electrode body.

[0009]

A first thick film circuit board of the present invention is characterized by a wiring pattern comprising an insulating substrate and a thick film layer containing gold as a main component formed on the insulating substrate. And an electrode reinforced portion composed of a thick film layer containing silver as a main component, which is arranged in parallel on the surface of the insulating substrate so as to be in contact with the wiring pattern at its end face.

A second feature of the present invention is a first printing step of forming a wiring pattern containing gold as a main component on the surface of an insulating substrate by a thick film printing method using a first mask, The second mask is mask-aligned with a slight overlap such that the overlapping portion with the wiring pattern is 1 mm or less, and the insulation is performed by a thick film printing method so as to contact the wiring pattern at its end face. And a second printing step of forming an electrode reinforced portion composed of a thick film layer containing silver as a main component on the surface of the flexible substrate.

A third feature of the present invention is that an insulating substrate and a branch portion which is composed of a gold thick film pattern formed on the surface of the insulating substrate, is branched into a plurality of pieces, and extends like a comb. A common electrode composed of a common electrode body portion integrally connecting the roots of the branch portions, and individual electrodes arranged between the branch portions extending in a comb shape or arranged so as to face the branch portions, A heating resistor layer is formed on the common electrode branch portion and the individual electrode so as to cross them, and an electrode reinforced portion made of a silver layer is formed on an upper layer of the common electrode body portion. The main body is in contact with the end face, and the overlap is 1
It is arranged side by side so that it is less than mm.

[0012]

According to the present invention, since the thick film layer containing silver as a main component of the electrode-reinforced portion is configured to be in contact with the wiring pattern formed of the thick film layer containing gold as its end face. Since the contact area is minimized and the resistance value is prevented from increasing due to the diffusion of silver into the gold layer, a low resistance and highly reliable connection is possible. The thick film layer containing silver as the main component may have a slight overlap with the wiring pattern formed of the thick film layer containing gold as the main component, but it is preferable that the thick film layer is formed so as to contact only the end face as much as possible.

According to the method of the present invention, in thick film printing,
The mask is aligned with a slight overlap so that the overlap of the mask patterns is 1 mm or less, and the thick film layer containing silver as the main component of the electrode-reinforced portion is separated from the thick film layer containing gold as the main component. Since it is formed so as to be in contact with the wiring pattern with the end face, the contact area is minimized, the resistance value is prevented from increasing due to the diffusion of silver into the gold layer, and low resistance and highly reliable connection is possible. Become. According to the thermal head of the present invention, the thick film layer containing silver as a main component of the electrode-reinforced portion of the common electrode is configured to be in contact with the wiring pattern made of the thick film layer containing gold as its main end face. The contact area is minimized to prevent the resistance value from increasing due to the diffusion of silver into the gold layer, so that a low resistance and highly reliable connection is possible.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1A is a plan view of a main part of a thermal head according to an embodiment of the present invention, and FIG. 1B is a view showing an X-Y cross section of FIG. 1A. This thermal head comprises an alumina ceramic substrate 1 and an underglaze layer 2 having a thickness of 60 to 70 μm.
Individual electrodes 3 made of a gold film pattern having a film thickness of 0.1 to 0.5 μm arranged in a row with a comb formed so that the tips of the comb teeth are located between the individual electrodes 3. A common electrode 4 including a tooth-shaped tip portion 4a and a main body portion 4b, and a heating resistor layer 5 made of a ruthenium oxide layer formed on and above the individual electrodes and the common electrode so as to cross the electrodes.
And a film thickness of 20 to 50 μm by the thick film method so that the outer surface of the common electrode 4b of the common electrode is contacted only at the end face.
It is characterized in that a silver layer 7 of m 3 is formed. The outermost circumference is also constituted by an outer frame portion 4c made of a thick gold film pattern so as to contact only the end face. 6 is an overglaze layer which covers these upper layers.

According to this structure, since the gold layer and the silver layer 7 forming the electrode body 4b are in contact with each other only at the end faces,
It is possible to obtain an electrode structure having low resistance and high strength without causing the diffusion of silver into the gold layer, and also possible to obtain a highly reliable thermal head at low cost.

Next, the manufacturing process of this thermal head will be described.

First, a glass paste is applied on an alumina ceramic substrate 1 to form an underglaze layer 2 having a film thickness of 60 to 70 μm (FIG. 2 (a)).

Subsequently, a gold paste was used for the upper layer by a screen printing method to form a film having a thickness of 0.1 arranged in a line.
An individual electrode 3 consisting of a gold thick film pattern of ˜0.5 μm,
A common electrode 4 including a comb-teeth-shaped tip portion 4a formed so that the tip of the comb-teeth is located between the individual electrodes 3, a main body portion 4b, and an outer frame portion 4c are formed (FIG. 2). (b)).

Thereafter, a heating resistor layer 5 made of a ruthenium oxide layer is formed on the individual electrodes and the common electrode so as to cross the individual electrodes and the common electrode by a screen printing method (FIG. 2 (c)).

Finally, the mask is aligned so that the outer periphery of the main body 4b of the common electrode and the inner periphery of the outer frame 4c have an overlap of about 1 mm or less, and a film thickness of 20 to 20 is obtained by screen printing. A silver layer 7 of 50 μm is formed (FIG. 2 (d)). As a result of such mask alignment, there is no overlap here, and only the ends are formed in good contact. Finally, the overglaze layer 6 is formed.

In this way, the thermal head shown in FIGS. 1A and 1B is formed.

Here, the gold layer and the silver layer 7 as the common electrode body portion 4b are formed so as to have an overlap of 1 mm or less as shown in FIG. 2 (d) (FIGS. 3 (a) and (b)). You can
As shown in FIGS. 1 (a) and 1 (b), it is ideal that the contact should be made only at the end faces.

FIG. 3 (a) is a plan view of an essential part of a thermal head of an embodiment of the present invention in which an overlap is formed, and FIG. 3 (b) is FIG. 3 (a).
It is a figure which shows the XY cross section of. This thermal head
It is formed in the same manner as the thermal head shown in FIGS. 1 (a) and 1 (b), except that the main body 4b of the common electrode and the silver layer 7 have an overlapping portion of about 1 mm.

With such a structure, it is possible to obtain a thermal head having low resistance, low cost and high reliability.

Next, as a modification of the present invention, as shown in FIG.
(b) shows a pattern structure in which the individual electrode 3 and the common electrode 4 face each other. Also in this structure, the common electrode main body is formed by stacking a silver layer on the gold layer so that the overlapping portion is 1 mm or less, as in the embodiment shown in FIG.

Here, if it is possible to secure the conduction between the gold layer and the silver layer, it is desirable to make the contact area between the gold layer and the silver layer as small as possible. There is a risk that good contact may not be achieved and electrical connection may not be achieved. By the way, the thermal head is usually formed by a screen printing method, but the screen printing method has a problem that the printing accuracy is not good although the process is simple and the productivity is excellent. Generally, the positional accuracy at the time of printing is about 0.1 mm, and the linearity at the time of printing varies depending on the number of meshes of the plate making, but a wavy pattern is generated, and the difference between the maximum and the minimum is about 0.2 mm.

That is, when the silver layer of the common electrode body is formed by using the screen printing method, a deviation of printing accuracy of about 0.5 mm occurs at the maximum.

Therefore, it is necessary to secure a contact width equivalent to the maximum printing accuracy of screen printing of 0.5 mm when the silver paste is used. The printing accuracy of screen printing of 0.5 mm when silver paste is used is the maximum value. Therefore, if the contact width between the gold layer and the silver layer is kept at 0.5 mm + 0.5 mm = 1 mm, the gold layer and the silver layer of the common electrode body can be satisfactorily joined, and the contact area can be reduced. The increase in resistivity due to the diffusion of silver into the layer can be suppressed.

The contact between the gold layer and the silver layer of the common electrode body contacts at each outer peripheral portion of the common electrode body, and the contact width is 1 mm.
If it is the following, it is possible to suppress an increase in the resistance value caused by the shape of the common electrode body.

The full glaze substrate in which the underglaze layer is formed on the entire surface of the ceramic substrate has been described.
Needless to say, the present invention is not limited to this, and can be applied to a partial glaze substrate in which an underglaze layer is selectively formed only in the heating resistor portion.

Further, the reason why the gold layer is used for the outer frame portion is that
This is to improve the connection with the external circuit.

Further, although the thermal head has been described in the above-mentioned embodiment, it is particularly effective for other thick film circuits, especially for a circuit using a large power.

[Brief description of drawings]

FIG. 1 is a diagram showing a thermal head according to an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a thermal head according to an embodiment of the present invention.

FIG. 3 is a diagram showing a modification of the thermal head according to the embodiment of the present invention.

FIG. 4 is a diagram showing a modification of the thermal head according to the embodiment of the present invention.

FIG. 5 is a diagram showing a conventional thermal head.

FIG. 6 is a diagram showing a conventional thermal head.

[Explanation of symbols]

 1 Ceramic Substrate 2 Underglaze Layer 3 Individual Electrode 4 Common Electrode 5 Heating Resistor 6 Overglaze Layer 7 Silver Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiya Omori 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Works (72) Inventor Yasuo Takayama 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business (72) Inventor Masaaki Araki 2274 Hongo, Ebina City, Ebina, Kanagawa Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor, Yasushi Miyajima 2274, Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd., Ebina Business Office

Claims (3)

[Claims] 1. An insulating substrate, a wiring pattern made of a thick film layer containing gold as a main component formed on the insulating substrate, and a surface of the insulating substrate so as to be in contact with the wiring pattern at an end face thereof. A thick film circuit board, comprising: an electrode reinforced portion composed of a thick film layer containing silver as a main component, which are arranged in parallel. 2. A first printing step of forming a wiring pattern containing gold as a main component on a surface of an insulating substrate by a thick film printing method using a first mask, and an overlapping portion of the wiring pattern is 1 mm. The second mask is aligned with a slight overlap as shown below, and a silver film is mainly formed on the surface of the insulating substrate by a thick film printing method so as to contact the wiring pattern at its end face. And a second printing step of forming an electrode reinforced portion composed of a thick film layer as a component. 3. An insulating substrate, a thick film pattern of gold formed on the surface of the insulating substrate, branching into a plurality of branches and extending like comb teeth, and a root of the branching portion. A common electrode composed of a common electrode main body that is integrally connected; individual electrodes arranged between the branch portions extending in a comb shape or facing the tip of the branch portion; and the common electrode branch portion And a heating resistor layer formed on the individual electrode so as to traverse them, and an electrode reinforced part made of a silver layer is formed on the upper layer of the common electrode body part, and the electrode reinforced part and the body part are The thermal heads are arranged side by side so that the overlap is less than 1 mm at most.