JPH05229156A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain practically sufficient bonding strength and to enhance reliability by providing a bonding strength enhancing layer consisting of a lower metal membrane layer and an upper insulating film layer between a head- resistant resin layer and a resistor. CONSTITUTION:A polyimlde layer with a thickness of several mum-20mum is formed on a metal substrate as a heat-resistant resin layer and a metal film 12 with a thickness of 0.1-1mum is formed on the layer 2 and, further, a bonding strength enhancing layer composed of an insulating film 14 with a thickness of about 1mum is formed on the metal film 12. A resistor film 3 with a thickness of several 100-300Angstrom composed of Ta2N is formed on the insulating film 14 and electrodes 4,5 are formed on the resistor film 3. Each of the electrodes 4,5 is composed of an aluminum film or a laminated film of NiCr and gold and has a thickness of 8000Angstrom -1mum. The electrode 4 is a common electrode formed into a shape continuing in the direction vertical to a drawing and the 5 is arranged as a selection electrode arranged in the direction vertical to the drawing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used as a thermal print head or a bubble jet head used in printers, facsimiles and the like.

[0002]

2. Description of the Related Art As a substrate of a thermal head, a ceramic substrate whose surface is covered with a glassy glaze layer is generally used. In order to operate the thermal head at high speed and reduce power consumption, for example, to comply with G4 standard of facsimile, one method is to provide a heat insulating layer between the heating element and the substrate. A heat resistant resin layer such as polyimide is promising as the heat retaining layer. The thermal conductivity of the polyimide layer is a fraction of that of the glass glaze layer.

Various thermal heads provided with a polyimide layer as a heat retaining layer have been proposed (for example, Japanese Patent Laid-Open No. 2-78).
573-6). An example of a thermal head provided with a polyimide layer as a heat retaining layer is shown in FIG. Reference numeral 1 is an insulating substrate made of ceramic or the like or a metal substrate made of stainless steel or the like, the surface of which is covered with a polyimide layer 2. A resistor 3 is formed on the polyimide layer 2, and a common electrode 4 and a selection electrode 5 are formed on the resistor 3.
Are formed. The resistors in the portions exposed from the electrodes 4 and 5 serve as heating elements. 6 is a protective film. Reference numeral 7 denotes a support plate, and the substrate 1 on which the heating element is formed is mounted on the support plate 7, and the printed wiring board 8 is further mounted on the support plate 7. A driving IC on the printed wiring board 8
9 is mounted, the drive IC 9 and the selection electrode 5 are connected by a wire 10a, and the drive IC 9 and the wiring of the printed wiring board 8 are connected by a wire 10b. The common electrode 4 is also connected to the wiring on the printed wiring board 8 by a wire (not shown).

[0004]

In a thermal head having a heat-resistant resin layer as a heat-retaining layer, the adhesion between the heat-resistant resin layer and the resistor formed thereon is weak, which is a reliability problem. An object of the present invention is to provide a thermal head having a heat-resistant resin layer as a heat retaining layer, by increasing the adhesive force between the heat-resistant resin layer and the resistor to obtain a highly reliable thermal head.

[0005]

According to the present invention, a heat-resistant resin layer is formed on a substrate, and an adhesion-strengthening layer having a lower metal film and an upper insulating film is formed on the heat-resistant resin layer. A heating element, an electrode connected to the heating element, and at least a protective film covering the heating element are formed on the adhesion strengthening layer. In a preferred embodiment, a contact hole is provided in the insulating film of the adhesion enhancing layer, the common electrode is connected to the metal film of the adhesion enhancing layer through the contact hole, and the metal film is also used as the common electrode.

As the substrate, various substrates such as a metal substrate such as stainless steel or an insulating substrate such as ceramic or glass can be used. The heat-resistant resin layer is preferably polyimide,
Polyamide and the like can also be used. A suitable thickness of the heat resistant resin layer is about several μm to 20 μm. The lower metal film of the adhesion strengthening layer is made of Al, Cr, Ni, Cu, Ti, T.
a, V, Mn, Fe, Co, Mo or W, or an alloy thereof. The thickness of this metal film is preferably 0.1 to several μm, and may be thin for the purpose of strengthening the adhesive force. It is more convenient to form a thick metal film when it is also used as a common electrode. is there. A silicon oxide film, a silicon nitride film, or SiAlO is used as the insulating film above the adhesion enhancing layer.
Various insulating films such as N film can be used, and the thickness is 1μ
m is suitable. The resistor film that becomes the heating element is Ta ₂ N.
Various resistor films used in thermal heads such as or Ta-SiO ₂ can be used.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment. The same parts as those in FIG. 3 are designated by the same reference numerals. A polyimide layer 2 is formed as a heat-resistant resin layer on the metal substrate 1 to a thickness of several μm to 20 μm, and a metal film 12 of 0.1 to 1 μm and an insulating film 14 of about 1 μm thereon are further formed thereon. An adhesion enhancing layer is formed. A resistor film 3 made of Ta ₂ N or the like is formed on the insulating film 14 to have a thickness of several hundred to 3000 Å, and electrodes 4 and 5 are formed thereon. Electrodes 1,5
Is an aluminum film or a laminated film of NiCr and gold,
Its thickness is 8000Å-1 μm. The electrode 4 is a common electrode formed in a continuous shape in the direction perpendicular to the paper surface, and the electrode 5 is a selection electrode arranged in the direction perpendicular to the paper surface. Electrodes 4 and 5
The part exposed between the two becomes the heating element. The heating elements are arranged in the direction perpendicular to the paper surface of the figure. 6 is SiAlON or S
It is a protective film such as i ₃ N ₄ and has a thickness of 1 to 2 μm.

Similar to FIG. 3, the substrate 1 on which the heating element is formed
Is mounted on the support plate 7, and the printed wiring board 8 is further mounted on the support plate 7.
A driving IC 9 is mounted on the upper side, and the driving IC 9 and the selection electrode 5 are connected by a wire 10a.
And the wiring of the printed wiring board 8 are connected by a wire 10b, and the common electrode 4 is also connected to the wiring on the printed wiring board 8 by a wire (not shown).

Here, as an example, the substrate 1 is a stainless steel substrate (SUS304), the heat-resistant resin layer 2 is a polyimide layer having a thickness of about 15 μm after curing, the insulating film 14 is a silicon oxide film having a thickness of about 1 μm, and a resistor. The body film 3 has a thickness of about 500 Å Ta ₂ N, the electrodes 4 and 5 have a thickness of about 1 μm, and the protective film 6 has a thickness of about 1 μm.
m of SiAlON was used, and four types of Al, Cr, NiCr, and Ti were used as the metal film 12 of the adhesion strengthening layer, and four types of test heat generation substrates were manufactured. Metal film 12
Was about 1 μm for Al and about 1000 Å for other metals. Further, as a comparative example, a heat-generating substrate having the same structure as that of the above-mentioned example except that the metal film of the adhesion-strengthening layer was removed was prepared and evaluated. The evaluation test was performed by a high temperature and high humidity storage test (85 ° C., relative humidity 85%).

As a result of this evaluation test, on the heat-generating substrate having no metal film of the adhesion strengthening layer, no abnormality occurred in the 100-hour test, but film peeling occurred in the 200-hour test. On the other hand, no abnormality occurred in the four types of heat generating substrates provided with the metal film of the adhesion strengthening layer even after 1000 hours of testing. From this result, it can be seen that it is effective to provide the metal film in order to improve the adhesive force.

FIG. 2 shows a heat generating substrate of the second embodiment. Compared with the heat generating substrate in the embodiment of FIG. 1, the contact hole 16 is formed in the insulating film 14 of the adhesion enhancing layer.
Is provided and the common electrode 3 is connected to the metal film 12 of the adhesion strengthening layer through the contact hole 16. The metal film 12 is formed to have a large thickness of about 1 μm and also serves as a common electrode.

The invention is not limited to the examples. For example,
The thermal head is not limited to the type in which a heat generating substrate and a printed wiring board are mounted on a supporting plate as shown in FIG. 1, but an integrated type thermal head in which a driving IC is also mounted on the heat generating substrate or a heat generating element is arranged on an inclined surface. The present invention can be applied to various types of thermal heads such as the inclined surface type thermal head.

[0013]

According to the present invention, an adhesive strength layer having a lower metal film and an upper insulating film is provided between the heat resistant resin layer and the resistor, so that a practically sufficient adhesive strength can be obtained. It will be possible and reliability will be improved. When the metal film of the adhesion strengthening layer is used as the common electrode, the width of the common electrode on the heating substrate can be narrowed and the heating element can be provided at the end of the substrate. If the heating element is provided at the end portion of the substrate, the contact with the platen roller is improved, and the printing quality can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment.

FIG. 2 is a sectional view showing a heat generating substrate in another embodiment.

FIG. 3 is a sectional view showing a conventional thermal head.

[Explanation of symbols]

 1 substrate 2 polyimide layer 3 resistor film 4 common electrode 5 selection electrode 6 protective film 12 metal film 14 insulating film

Claims (3)

[Claims] 1. A heat-resistant resin layer is formed on a substrate, an adhesion-strengthening layer having a lower metal film and an upper layer an insulating film is formed on the heat-resistant resin layer, and a heating element is formed on the adhesion-strengthening layer. A thermal head comprising: an electrode connected to the heating element; and a protective film covering at least the heating element. 2. The metal film of the adhesion enhancing layer is made of Al, Cr,
Ni, Cu, Ti, Ta, V, Mn, Fe, Co, Mo
Alternatively, the thermal head according to claim 1, which is made of W or an alloy thereof. 3. A contact hole is provided in the insulating film of the adhesion enhancing layer, and the common electrode of the electrodes is connected to the metal film of the adhesion enhancing layer through the contact hole, and the metal film also serves as the common electrode. The thermal head according to claim 1 or 2.