JPH02179765A - Thermal head substrate - Google Patents

Abstract

PURPOSE:To minimize a difference in applied voltages caused by printing positions by connecting a thick-film conductor part made of a good conductor to a thin-film common electrode which directly supplies a printing current to thin-film heating resistors. CONSTITUTION:A resistant layer 2 is formed on an alumina substrate 1, and thereon an aluminum conductor layer 3 is formed. Thereafter, a patterning is performed using a photoresist, and thin-film heating resistors 4 made of a part of the resistant layer 2 and a thin-film common electrode 3a and thin-film discrete electrodes 3b made of the aluminum conductor layer 3 are formed by selective etching. After the photoresist is removed, one area of the electrode 3a is masked with a photoresist and thereon a nickel-plated layer 6a is formed. After non-conductor part of the substrate 1 is activated, the plated layer 6a is further formed on the side and rear faces. A copper-plated layer 5 is formed on the plated layer 6a and, thereon, a nickel layer 6b is plated. A wear-resistant layer 7 made of a silicon oxide film is formed, thereafter being coated with an insulating resin film 8. In this manner, voltage values to be applied to the heating resistors according to printing positions can be remarkably uniformized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head substrate, and more particularly to a thermal head substrate in which heating resistive elements, electrodes, and other connection wiring are formed by thin film technology.

[Conventional technology]

FIGS. 3(a) and 3(b) are a partial plan view and a sectional view taken along the line AA' of a conventional thin film thermal head substrate, respectively. In this way, in the conventional thermal head substrate, the printing current is supplied to the thin film heating resistor element 4 through the thin film common electrode 3a and the thin film individual electrodes formed of a conductor film of the same thickness on one main surface of the alumina substrate 1. 3b.

Here, 2 is a thin film resistance layer provided on the alumina substrate IF and forms the thin film heating resistance element 4.

[Problem to be solved by the invention]

Generally, when this thermal head substrate prints on large size paper such as A4 or B4, it is necessary to supply a large current to the thin film common electrode 3a. When is about 250Ω,
It is necessary to supply a maximum current of around 20 amperes so that these can generate sufficient heat. At this time, even if the radio waves are divided into two parts and supplied from both sides of the common electrode 3a, each part is as large as about 10 amperes, so the resistance value of the electrode conductor film becomes a problem. The material of the electrode conductor film is usually aluminum (AIL) or gold (Au) in consideration of bonding connections with mounted components. For those with a structure in which the electrode conductor film is formed only on the electrode, the width of the common part is 4 mm, and the conductor film thickness is 2 gm.
Calculating the conductor resistance value per 10 cm of length of the 8-film common electrode 3a in the case of
Specific resistance p = 2.4X 10-8 am],
They are 344mΩ and 300mΩ, respectively. Therefore,
The voltage drop when a current of 10 amperes flows is 3.
The value is around V/10c, and since the voltage applied to the thin film heating resistor element 4 becomes smaller as it approaches the center of the substrate, there is a tendency for the print density to become lighter toward the center. Such a drawback of uneven print density can be improved by increasing the conductor film thickness by ten times or more, but this is not economical in terms of the equipment capacity of the film forming apparatus and cannot be easily realized.

In view of the above circumstances, an object of the present invention is to provide a thermal head substrate that solves the conventional problem of uneven print density near the center of the substrate.

[Means to solve the problem]

According to the present invention, the thermal head substrate includes an alumina substrate, thin film heating resistance elements arranged in a row on one main surface of the alumina substrate, and common and individual electrodes for the t11i film heating resistance elements. the common electrode conductor film includes a tJ film body forming an electrode portion on one main surface of the alumina substrate; one of its ends is overlapped and connected to the thin film conductor portion; The thick film conductor portion extends onto the other main surface of the alumina substrate.

[Effect]

According to the present invention, the thick film conductor portion made of a good conductor added to the conventional thin film common electrode significantly lowers the conductor resistance value of the common electrode and sufficiently reduces the difference in voltage applied to the thin film heating resistor element depending on the printing position. Since it is made small, the printing density can be made uniform over the entire surface of the substrate.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a partial cross-sectional view of a thermal head substrate showing an embodiment of the present invention. According to this embodiment, the thermal head substrate includes an alumina substrate l and an alumina substrate l, as in the conventional example. # Arranged in rows on one main surface! It is equipped with an I heating resistor element 4, a thin film common electrode 3a and a thin film individual electrode 3b which directly supply a printing current to this thin film heating resistor element 4, and furthermore, one end of the thin film common electrode 3a is overlapped with the other end. It includes a thick film conductor section made of a copper (Cu) plating layer 5 that extends to the other main surface (back surface) of the alumina substrate l to effectively form a low resistance current path to the thin film common electrode 3a. Ru. Here, 6a and 6b are nickel (Xi) plating layers each serving as an intermediate layer for forming the copper plating layer 5.

It is extremely easy to obtain the structure of this example. Figure 2 (
A) to (f) show one method of the manufacturing method in order of steps.

First, a thin film resistor layer 2 is placed on a glued alumina substrate l.
is formed to a thickness of 1000~200 OA by sputtering method, and then an aluminum (AM) conductor N3 is formed thereon to a thickness of about 1.0 μm by sputtering method.
As shown in FIG. 2(a)), this multilayer metal layer is then subjected to a patterning process using a well-known photoresist technique. The thin film resistance layer 2 is selectively etched using a mixed acid etchant of hydrofluoric acid and nitric acid, and a part of the thin film resistance layer 2 is formed into a thin film heating resistance element 4 and an aluminum conductor layer 3 is formed. A thin film common electrode 3a and a thin film individual electrode 3b are formed (FIG. 2(b)).
Then, after peeling off the photoresist from the previous step and masking a partial area of the thin film common electrode 3a with photoresist, the nickel (old) plating layer 6a is approximately removed by an electroless plating method using a known zinc substitution method. 1000-200
The alumina substrate 1 is formed to a thickness of 0A (Fig. 2 (C)), and after activating the nonconducting portions on the side and back surfaces of the alumina substrate 1 using a catalytic treatment method, it is immersed in a known electroless plating solution. Then, a nickel (Ni) plating layer 6a is formed on the side and back surfaces [FIG. 2(d)]. The nickel (Xi) plating on the alumina substrate l by this catalytic treatment method is performed in the next step. It is.

Degreasing → Acid cleaning → Sensitizing → Activation →
Ni electroless plating.

Next, a copper (Cu) plating layer 5 is formed on this Ni plating layer 6a to a thickness of 3 to 1 Opm by using a known electrolytic plating method [FIG. 2(e)]. A nickel (Xi) layer 6 is formed on 5 using an electroless plating method.
b to a thickness of about 1000 to 200 OA [Fig. 2 (f
)) Finally, a wear-resistant layer 7 made of a silicon oxide film (Si02) is formed to a thickness of about 7 μLm by sputtering, and then a thin common electrode 3 is formed using a conventional screen printing method.
The desired thermal head substrate is obtained by coating the side surfaces and back surfaces of the individual electrodes a, the individual electrodes 3b, and the alumina substrate l with an insulating resin film 8, respectively.

The thermal head board in this example uses nickel (
The old) layers 6a and 6b serve as intermediate layers for forming the copper (Cu) plating layer 5, and this allows thick film plating using a copper (Cu) material with a significantly lower resistivity. Realized.

〔Effect of the invention〕

As described in detail below, according to the present invention, a thick copper (Cu) plating layer is newly connected to the thin film common electrode that directly supplies printing current to the thin film heating resistor element, and the common electrode Since the resistance value of the entire surface can be kept low, it is possible to make the voltage applied to the heating resistor element extremely uniform depending on the printing position on the thermal head substrate. Therefore, it is possible to sufficiently improve the print density unevenness near the center of the substrate, which occurs in conventional thermal head substrates. Furthermore, since the side and back surfaces of the alumina insulating substrate are used as surfaces for forming the electrode portions, it is possible to narrow the conductor width of the thin film common electrode formed on the -main surface (front surface). Therefore, it is also possible to achieve miniaturization of the thermal head substrate.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of a thermal head substrate showing an embodiment of the present invention, FIGS. Figures (a) and (b) are a partial plan view and an AA' cross-sectional view of a conventional thin film thermal head substrate, respectively. l...Alumina substrate, 2...Thin film resistance layer, 3...Aluminum (A pattern) conductor layer. 3a... Thin film common electrode, 3b... Thin film individual electrode, 4... Thin film heating resistor element. 5... Copper (Cu) plating layer, 6a, 6b... Nickel (Xi) plating layer, 7...
Wear-resistant layer, 8... Insulating resin film.

Claims (1)

[Claims] an alumina substrate, thin film heating resistance elements arranged and formed in a row on one main surface of the alumina substrate, and common and individual electrode conductor films for the thin film heating resistance elements, the common electrode conductor film is a thin film conductor portion forming an electrode portion on one main surface of the alumina substrate, and a thickness that allows one of the end portions to be overlapped and connected to the thin film conductor portion and the other end extends onto the other main surface of the alumina substrate. A thermal head substrate comprising a membrane conductor section.