JPS61255872A - Thermal head - Google Patents

Abstract

PURPOSE:To remedy the thermal strain of ceramic substrate and at the same time, to improve the adhesive property to the cooling base, by establishing a thermal expansion regulation layer on the back surface of ceramic substrate. CONSTITUTION:The substrate 1 is connected to the cooling base 8 with the adhesives layer 9 via the thermal expansion regulation layer 10. Materials forming the thermal expansion regulation layer 9 include metals, alloys, ceramics, thermet, etc. The thermal expansion rate on the surface side on which a thermal head function part is provided and that on the back surface side having the thermal expansion regulation layer 9 are coordinated thereby. The ceramic substrate 1 has the flatness having no thermal strain even at room temperature and the back surface has a suitable surface roughness profitable for adhesion. Therefore, a high-reliable, well-durable thermal head can be provided without using especially complicated jigs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal head used in various printers, facsimile machines, and the like.

2. Description of the Related Art The thermal head used in conventional facsimiles, printers, etc. has a typical configuration as shown in FIG. In FIG. 4, 1 is an insulating ceramic substrate, 2 is a heat storage glass layer, 3 is an etching prevention layer, 4 is a resistor, 6 is a pair of electrodes and conductor wiring, e is a wear-resistant layer, and 7 is a driving I
It is C. 8 is a cooling board, which is attached to the board 1 by an adhesive layer 9.
is attached to the back side of the

Problems to be Solved by the Invention Due to the demand for higher speed and higher recording density, thermal heads have generally been constructed in such a way that a heat storage glass layer is provided only on the upper surface of a ceramic substrate, as shown in FIG. moreover,
In addition to the thermal head such as the driving IC 7, a pair of electrodes, and the conductor wiring 6, the driving circuit and wiring are also mounted on the base ring to achieve compactness.

In such a structure in which the functional parts are stacked only on one side of the ceramic substrate, distortion occurs due to the difference in thermal expansion between the upper and lower portions of the ceramic substrate.

Fig. 6 shows the degree of distortion when the functional part of the thermal head as shown in Fig. 4 is provided on an extremely flat ceramic substrate 1 with a width of 16.7 ff, a length of 275 jff, and a thickness of 0.66 jff. For the length of 9.27tswy,
Approximately 1.5-2. Off distortion will occur.

This distortion occurs when the head part is 400% when using a thermal head.
~esolv, so if the distortion is further expanded by 2 to 3 times, it becomes a button. Also, the thickness of the base was 1, around 1973.
What used to be 6~2.53ff has recently become 0.65~
1.20, and it is predicted that it will become 0.4 to 0.5 silk in the near future. As the substrate becomes thinner, thermal strain tends to be further magnified.

Such thermal distortion can be prevented by using an etching prevention layer (thickness 500~10m).
Since this will have a negative effect on the thermal head) and the resistor (thickness 1000x to 5000x), a special jig is used to prevent the distortion of the thermal head from being applied to the solid and heavy cooling board 8 as shown in Figure 4. While being straightened, it is fixed via a bonding layer 9 using a heat-resistant adhesive containing a heat conduction improver.

Because such operations are performed at room temperature, thermal heads that are straightened and bonded at room temperature have no room for thermal expansion to escape during actual use, and this has a significant negative impact on the reliability and durability of the thermal head. giving.

Furthermore, when bonding the thermal head to the cooling substrate 8, in addition to the difficulty of adhesion due to thermal strain as described above, the surface roughness of the back surface of the ceramic substrate 1 is generally RmO01 to 0.5 μm.
It has been wrapped or polished,
The surface is too smooth for adhesion.

Therefore, the present invention aims to correct the thermal distortion of the ceramic substrate and improve the adhesiveness with the cooling substrate.

Means for Solving the Problems The technical means of the present invention for solving the above problems is to provide a thermal expansion adjustment layer on the back side of the ceramic substrate.

Here, the thermal expansion adjustment layer is made of a material such as ceramic, cermet, metal, or alloy, and has a thickness of 5 to 60 μm.
It is preferable to form a film having a centerline surface roughness Ra of 1 to 10 μm.

The thermal expansion coefficients of the front side where the functional part of the thermal head is provided and the back side with the thermal expansion adjustment layer are matched, and the ceramic substrate has flatness without thermal distortion even at room temperature, and the back side has a moderate expansion coefficient that is advantageous for adhesion. Since it has a surface roughness of , it is possible to provide a thermal head with high reliability and excellent durability without using a particularly complicated jig as in the past.

Embodiment FIG. 1 shows the structure of a thermal head according to the present invention. 1
2 is an insulating ceramic substrate, 2 is a heat storage glass layer, 3 is an etching prevention layer, 4 is a resistor, 6 is a pair of electrodes and conductor wiring, 6 is a wear-resistant layer, 7 is a driving IC, and 8 is a cooling board. These are the same as the conventional example. 1o is a thermal expansion adjustment layer formed on the back surface of the ceramic substrate 1, and the substrate 1 is bonded to the cooling substrate 8 by an adhesive layer 9 via the thermal expansion adjustment layer 1o. Here, the functional parts of the thermal head main body from the heat storage glass layer 2 to the wear-resistant layer 6 laminated on the ceramic substrate in FIG. 1 are represented by M.

2a, b, and c show examples of forming the thermal expansion adjustment layer 10. FIG.

3a, b, and c are respective cross-sectional views of the corresponding FIG. 2. FIG.

In these figures, a shows an example in which the thermal expansion adjustment layer is provided on the entire back surface of the base, and b shows an example in which the layer 10 is provided only on both sides of the back surface of the base, leaving the central part. C has a layer 10 provided at the center of the back surface of the base.

In addition, a diagonal striped pattern (zebral band) may be provided.

Next, preferred conditions for effectively implementing the present invention will be explained.

Materials forming the thermal expansion adjustment layer include metal 9 alloys, ceramics, cermets, and the like. Specifically, Ni, Or, F
s, Cu, τa, MuJ, Ti, Hf', Z
r, Mo.

There are single metals such as W and alloys of these metals.

Also, as ceramics, Mu120s, 5i02
, ZrO2.

TiO2 and Mu/205・5in2. Mu1205・T
Examples include composite oxides such as iO2 and glass. Cermets are Or, Fe, Ni, Ti, τ
Metals such as a, Zr, Mu7, Mo, Wb, W, and alloys thereof are mainly used. Also,
Oxide is an insulator that makes up cermet.

Use ceramics such as carbides and nitrides.

In order to effectively form the thermal expansion adjustment layer, the surface roughness of the back surface of the base 1 is important. For this reason, it is preferable that the surface roughness of the back surface of the substrate 1 be in the range of 1 to 10 μm, particularly preferably in the range of 2 to 4 μm, as measured by a Taliser 7 surface roughness meter.

Next, the thickness of the thermal expansion adjustment layer is preferably 3 to 60 μm, particularly preferably 6 to 30 μm.

Next, regarding the insulating substrate used in the present invention, an alumina substrate, a glazed alumina substrate, a hollow substrate, etc. can be used. Mullite substrates and cordierite substrates are also available as alternatives to alumina substrates.

It is also possible to use a glass substrate.

Methods for forming the thermal expansion forming layer include plasma method, L
P(j plasma method, sputtering method, EB evaporation method, evaporation method,
There is also a method of baking after screen printing. Among these, the plasma method and the LPO plasma method are most preferred from the viewpoints of speed, cost, and mass productivity.

Next, a specific example will be described.

As the substrate 1, a ceramic substrate with a width of 16.73 ff, a length of 275 fl, a wall thickness of 0.66 ml, and a glaze layer of 80 μm thick on one side is used. A thermal expansion adjustment layer was formed under various conditions on the side opposite to the glaze layer (back side) of this substrate, and a thermal head functional section was formed on the glaze layer.

(The following is a blank space.) The table compares the formation conditions of the thermal expansion adjustment layer and the thermal strain of the obtained thermal head. A plasma spraying machine and an XB vapor deposition apparatus were used to form the thermal expansion adjustment layer. The material is T
a, illusion 205. Illusion 203. TiO2, cermet made of glass/aluminum, Or-Ou gold alloy, etc. were used. The surface roughness was adjusted using grinding paper and a surface polisher.

The pattern example shown in FIG. 2 was used as the pattern example of the thermal expansion adjustment layer.

The film thickness was adjusted by changing the film formation time. The thermal strain is the result of measuring the height of the strain rate shown in FIG. 5 using a surface plate. ? On the contrary, thermal distortion occurred in 11kL14 to Nagi16, so negative numbers were written.

Regarding adhesion, with the exception of Nagi 1 (conventional example), which requires a jig to press the head and correct thermal distortion when bonding to the cooling plate, the others require a special jig. It was possible to easily join the thermal head and the cooling plate without using.

Comprehensively judging the results in the table, it can be seen that the surface roughness may be approximately 2 to 4 μm, and the thickness of the thermal expansion adjustment layer is preferably 6 to 30 μm.

It has also been found that forming a thermal expansion adjustment layer significantly reduces the thermal strain rate and at the same time makes it easier to bond the thermal head to the cooling substrate.

Effects of the Invention According to the present invention, thermal distortion of the ceramic substrate can be solved, and the bonding strength between the cooling substrate and the thermal head can be improved. As a result, it is possible to make the ceramic substrate even thicker, and it is also possible to improve reliability and durability.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an example of the structure of a thermal head according to the present invention, FIG. 2 is a plan view showing an example of a pattern of a thermal expansion adjustment layer formed on the back surface of a ceramic substrate, and FIG. FIG. 4 is a longitudinal cross-sectional view of a conventional thermal head, and FIG. 5 is a cross-sectional view showing the state of thermal distortion thereof. 1...Ceramic base, 2...Heat storage glass layer, Etching prevention layer, 4...
...Resistor, 6...Conductor wiring, 6...
Wear-resistant layer, 7... Drive I (j. 8... Cooling board, 9... Adhesive layer, 1
0...Thermal expansion adjustment layer. Name of agent: Patent attorney Toshio Nakao and one other person f.
,, Board figure 2

Claims (3)

[Claims] (1) An insulating substrate, a heating resistor and its electrode formed on the surface of the substrate, a wear-resistant layer formed to cover the heating resistor and the electrode, and a thermal expansion layer formed on the back surface of the substrate. A thermal head having an adjustment layer. (2) The thermal head according to claim 1, wherein the thermal expansion adjustment layer is made of ceramic, cermet, metal, or alloy. (3) The thermal expansion coefficient of the thermal expansion adjustment layer is (30 to 140) x 1
The thermal head according to claim 2, which has a temperature of 0^-^7cm/°C.