JPH1044485A - Thermal head - Google Patents

Abstract

(57) [Summary] When printing is performed for a long time, heat storage in a region immediately below an insulating substrate becomes extremely large, and uneven density and unnecessary printing are formed. A heat generating resistor and a concave groove are provided on an upper surface of an insulating substrate, and the heat generating resistor is provided in the concave groove.
Driver IC4 for selectively generating Joule heat
And a metal layer 5a is attached to at least the bottom surface of the concave groove 1a of the insulating substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thermal head incorporated as a printer mechanism of a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism of a word processor or the like is, as shown in FIG. 4, an insulating substrate made of alumina ceramics on which a plurality of heating resistors 12 and a driver IC 13 are mounted. 11 is mounted and fixed on a support plate 14 made of aluminum or the like.
When the heating resistor 12 is driven, the heating resistor 12 is selectively caused to generate Joule heat, and the generated heat is conducted to the thermosensitive recording medium to form a predetermined printed image on the thermosensitive recording medium, thereby functioning as a thermal head.

In the above-described conventional thermal head, a concave groove 11a is formed on the upper surface of an insulating substrate 11 and a driver IC 13 is provided therein so that printing can be performed on a medium that is difficult to bend such as a plastic card. By burying it, the surface in contact with media etc. was made flat.

When printing is performed using a thermal head, the heat generated by the heating resistor 12 is transmitted not only to the medium but also to the insulating substrate 11 and accumulated therein.
For this reason, the insulating substrate 1 located near the heating resistor 12
In order to prevent the temperature of 1 from becoming excessively high due to the above-mentioned heat storage effect, it is necessary to diffuse the heat from the heating resistor 12 over the entire insulating substrate 11 and to conduct the heat to the support plate 14 side. is there.

However, in the above-described conventional thermal head, a concave groove 11a is formed on the upper surface of the insulating substrate 11, and the thickness of the insulating substrate 11 is partially reduced by the concave groove 11a. The diffusion of heat in the interior of the substrate 11 is blocked by the concave groove 11a, and when printing is performed for a long time or when high-speed printing is performed, the amount of heat stored in the region directly below the insulating substrate 11 becomes extremely large. In addition, the insulating substrate 11 has a drawback that the temperature becomes excessively high and uneven density and unnecessary printing are formed.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks. The present invention provides a heating resistor and a concave groove on an upper surface of an insulating substrate and selectively connects the heating resistor in the concave groove. A thermal head having a driver IC for generating Joule heat embedded therein, wherein a metal layer is applied to at least a bottom surface of the concave groove of the insulating substrate.

The thermal head according to the present invention is characterized in that the metal layer is connected to a ground electrode for connecting one end of the heating resistor to a reference potential via a driver IC.

Further, the thermal head of the present invention is provided with a heating resistor and a concave groove on an upper surface of an insulating substrate, and a driver IC for selectively causing the heating resistor to generate Joule heat is embedded in the concave groove. A thermal head, wherein a solder wetting layer is applied to at least a bottom surface of a concave groove of the insulating substrate and a lower surface of a driver IC, and a solder wetting layer on a lower surface of the driver IC is soldered to a solder wetting layer on a bottom surface of the concave groove. Driver I
C is embedded in the concave groove.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a plan view showing an embodiment of a thermal head according to the present invention, and FIG. 2 is a sectional view taken along line X--X in FIG.
1 is an insulating substrate, 1a is a concave groove, 2 is a heating resistor, 4 is a driver IC, 5a is a metal layer, 5b is a ground electrode, 6 is a resin material, and 7 is a support plate. The insulating substrate 1 is formed of an electrically insulating material having a thermal conductivity of 0.9 to 26 W / m · k, for example, glass or alumina ceramics.
In the case of forming a ceramic raw material powder of alumina, silica, magnesia, etc., an appropriate organic solvent and a solvent are added and mixed to form a slurry, and this is formed by adopting a conventionally well-known doctor blade method, a calendar roll method, or the like. It is manufactured by forming a ceramic green sheet and then punching the ceramic green sheet into a predetermined shape and firing at a high temperature.

On the upper surface of the insulating substrate 1, a plurality of heating resistors 2 arranged linearly,
The common electrode 3a and the individual electrode 3b connected to both ends are respectively attached.

Since the heating resistor 2 is made of tantalum nitride or the like and has a predetermined electric resistivity, power from an external power source is applied through the common electrode 3a and the individual electrode 3b. Then, Joule heat is generated, and heat is generated at a predetermined temperature required for forming a print image on the thermosensitive recording medium, for example, a temperature of 200 to 350 ° C.

On the other hand, the common electrode 3a and the individual electrode 3b
Is made of a metal such as aluminum or copper, and acts to apply a predetermined power to the heating resistor 2 described above. still,
At the time of printing, a predetermined potential difference is provided between the common electrode 3a and the individual electrode 3b. For example, the common electrode 3a is connected to an external power supply (not shown) and is held at a potential of 24V. The individual electrode 3b is connected to a driver I to be described later.
It is connected to the ground electrode 5b via C4 and is held at a reference potential (for example, a potential of 0 V).

The heating resistor 2, the common electrode 3a, and the individual electrode 3b are respectively attached to the upper surface of the insulating substrate 1 with a predetermined pattern and a predetermined thickness by employing a conventionally known sputtering method and photolithography technique. .

On the upper surface of the insulating substrate 1 on which the heating resistors 2 and the like are attached, a concave groove 1a is formed substantially in parallel with the arrangement of the heating resistors 2, and the inside of such a concave groove 1a is formed. A plurality of driver ICs 4 are embedded so that their upper surfaces are arranged in the same plane as the upper surface of the insulating substrate 1.

The driver IC 4 is for controlling on / off of electric power applied to the heating resistor 2 via the common electrode 3a and the individual electrode 3b, and is internally connected to each individual electrode 3b. A plurality of output terminals 4a for connecting the output side of the switching transistor to the individual electrode 3b, and a reference potential side of the switching transistor to the ground electrode 5b are provided on the upper surface thereof. Ground terminal 4b for connection and a plurality of input terminals (not shown) for inputting an external print control signal into driver IC 4
Are provided. The ground electrode 5b is for applying electric power to each heating resistor 2 via the individual electrode 3b or the switching transistor of the driver IC 4, etc. By holding this at a reference potential, the ground electrode 5b is connected to the common electrode 3a. A predetermined potential difference is provided between them.

The concave groove 1a of the insulating substrate 1 is formed by cutting the upper surface of the insulating substrate 1 with a predetermined diamond blade, for example, to a depth of 0.5 mm and a width of 3.0 m.
m and the driver IC 4
The electrical connection between the output terminal 4a and the individual electrode 3b is made by first embedding the driver IC 4 in the concave groove 1a of the insulating substrate 1 so that its upper surface is arranged in the same plane as the upper surface of the insulating substrate 1, The individual electrodes 3b are formed by the above-described forming method (sputtering method and photolithography technique) so that one end thereof extends to the output terminal 4a.

A gap formed between the concave groove 1a and the driver IC 4 is filled with a resin material 6 made of epoxy resin or the like. The upper surface of the IC 4 is the insulating substrate 1
It is set to the same height as the upper surface of. At this time, the material for forming the resin material 6 is preferably such that the coefficient of thermal expansion thereof is between alumina ceramics for forming the insulating substrate 1 and silicon for forming the driver IC. Breakage of the individual electrode 3b due to a change in the volume of the resin material 6 and the like can be effectively prevented.

Then, the concave groove 1a of the insulating substrate 1 is formed.
A metal layer 5a made of aluminum or the like is formed on at least the bottom surface (the surface facing the driver IC 4) of 5 to 100 μm.
It is attached in a belt shape with a thickness of.

The metal layer 5a is pulled out to the upper surface of the insulating substrate 1 at a plurality of locations and is electrically connected to the ground electrode 5b at the lead-out portion, thereby electrically reinforcing the ground electrode 5b. The heat accumulated inside the insulating substrate 1 is transferred to one side of the concave groove 1a (the side of the heating resistor 2).
It acts to make the conduction more quickly to the other side.

In such a thermal head of the present invention, since the metal layer 5a is applied to at least the bottom surface of the concave groove 1a of the insulating substrate 1, the heat of the insulating substrate 1 located near the heating resistor 2 Is well conducted to the end of the insulating substrate 1 (the region on the right side of the groove 1a in FIG. 2) via the metal layer 5a, and the heat from the heating resistor 2 is transferred to the entire insulating substrate 1. Can be spread well.
As a result, printing for a long time, or
Even if high-speed printing is performed, the temperature of the insulating substrate 1 located in the vicinity of the heating resistor 2 can always be maintained at a temperature suitable for printing, and a good printed image without density unevenness can be formed. Becomes possible.

The metal layer 5a is formed not only at the time of printing but also during the manufacturing process of the thermal head so as to make the temperature distribution inside the insulating substrate 1 uniform.
A large stress is not concentrated on the corners of the insulating substrate 1 and cracks and the like can be effectively prevented from being generated on the insulating substrate 1.

Further, as described above, if the metal layer 5a is connected to the ground electrode 5b, the ground electrode 5b through which a large current flows can be electrically reinforced by the metal layer 5a, and the power at the ground electrode 5b can be increased. Clear print images can be formed with minimal loss.

Further, in this case, since the driver IC 4 is electromagnetically shielded by the metal layer 5a, electromagnetic waves such as noise coming from the outside are absorbed by the metal layer 5a connected to the ground electrode 5b, and the malfunction of the driver IC 4 is effectively performed. Can also be prevented. Therefore, the thermal head can always be operated accurately.

The above-mentioned insulating substrate 1 is placed on the upper surface of a support plate 7 made of a good heat conductive material such as aluminum via an adhesive member 9 such as a double-sided tape. The insulating substrate 1 having the above is fixed on the support plate 7.

Thus, in the above-described thermal head, a predetermined power is applied between the common electrode 3a and the individual electrode 3b with the driving of the driver IC 4, and the heating resistor 2 is selectively heated by the Joule heating based on the print signal. At the same time, the generated heat is conducted to the thermosensitive recording medium to form a predetermined printed image on the thermosensitive recording medium, thereby functioning as a thermal head.

(Second Embodiment) Next, another embodiment of the thermal head of the present invention will be described. The same parts as those in the above-described first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

In the thermal head of the present embodiment, a heating resistor 2 and a concave groove 1a are provided on the upper surface of an insulating substrate 1, and a driver IC 4 for selectively causing the heating resistor 2 to generate Joule heat is provided in the concave groove 1a. Embedded in the insulating substrate 1 and at least the bottom surface of the concave groove 1a and the driver IC.
The driver IC 4 is embedded in the concave groove 1a of the insulating substrate 1 by applying solder wetting layers 10b and 10c to the lower surface of the insulating substrate 1 and soldering them together (solder: 10a).

The solder wetting layers 10b and 10c are formed on the bottom surface of the concave groove 1a of the insulating substrate 1 and the lower surface of the driver IC 4 by using a material having good solder wetting properties such as nickel and gold.
The solder 10a for bonding the solder wetting layers 10b and 10c is completely filled between the concave groove 1a of the insulating substrate 1 and the driver IC 4. It is interposed between 10b and 10c.

In the thermal head of the second embodiment as described above, the heat of the insulating substrate 1 located near the heating resistor 2 is transferred to the end of the insulating substrate 1 via the metal layer 10a (FIG. 3).
Medium, to the right side of the groove 1a),
Since the heat from the heating resistor 2 can be satisfactorily diffused over the entirety of the insulating substrate 1, the insulating substrate 1 located near the heating resistor 2 as in the first embodiment described above.
Can be maintained at a temperature suitable for printing, and the solder 10 joining the two solder wetting layers 10b and 10c can be maintained.
a has a low coefficient of thermal expansion, even if the thermal head becomes high temperature due to the heat generated by the heating resistor 2 during printing,
The volume of the solder 10a does not greatly change, and the driver IC 4 can always be arranged at a predetermined position in the concave groove 1a. Therefore, the terminal electrode 4 of the driver IC 4
a, 4b and the individual electrodes 3b and the ground electrode 5b can be maintained in good electrical connection over a long period of time.

The solder 10a is first attached to the insulating substrate 1
A solder wetting layer 10 made of nickel on the bottom surface of the groove and the lower surface of the driver IC 4 by a conventionally known electroless plating method or the like.
b and 10c are applied, respectively, and then the required amount of cream solder is filled into the concave groove 1a, and the driver IC 4 is pushed from above, and then the cream solder is applied to the groove 1a.
The solder wetting layer 10b on the bottom surface of the concave groove and the solder wetting layer 10c on the lower surface of the driver IC are joined by heating and melting at a temperature of about 120 ° C. At this time, since the solder wetting layers 10b and 10c made of nickel or the like are previously applied to the bottom surface of the concave groove of the insulating substrate 1 and the lower surface of the driver IC, when the cream solder is heated and melted, the surface tension of the melted solder causes The driver IC 4 is positioned substantially at the center of the groove 1a. The exposed surface of the solder 10a is covered with a resin material 6 'made of an epoxy resin or the like.
A thermal head pattern such as an individual electrode 3b, a ground electrode 5b, etc. is formed on the upper surface by sputtering, photolithography, or the like.

At this time, since the driver ICs 4 are all positioned at the center of the concave groove 1a as described above, when forming the thermal head patterns such as the individual electrodes 3a and the ground electrodes 5b by the photolithography technique,
It is not necessary to separately form the thermal head pattern on the upper surface of the insulating substrate 1 and the upper surface of the driver IC 4, but the thermal head pattern may be formed on the upper surface of the insulating substrate 1 and the driver IC 4 by one photomask. It is possible.

In this case, the solder 10a filling the gap between the concave groove 1a of the insulating substrate 1 and the driver IC 4 has a relatively small coefficient of thermal expansion. Does not shift significantly.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the spirit of the present invention. 2 and electrodes may be covered with a protective film 8 made of glass, silicon nitride, or the like.

[0035]

According to the present invention, since the metal layer is applied to the bottom surface of the concave groove of the insulating substrate, the heat of the insulating substrate located near the heating resistor is transferred to the insulating substrate via the metal layer. As a result, the heat from the heating resistor can be satisfactorily diffused throughout the insulating substrate. As a result, even if printing is performed for a long time or high-speed printing is performed, the temperature of the insulating substrate located in the vicinity of the heating resistor can always be maintained at a temperature suitable for printing, and density unevenness can be maintained. It is possible to form a good printed image without any problem.

Further, according to the present invention, the metal layer makes the temperature distribution inside the insulating substrate uniform not only in printing but also in the manufacturing process of the thermal head.
A large stress does not concentrate on the corners of the concave groove and the like, and it is possible to effectively prevent cracks and the like from occurring on the insulating substrate.

Further, according to the present invention, if the metal layer is connected to the ground electrode, the ground electrode through which a large current flows can be electrically reinforced by the metal layer, and the power loss at the ground electrode can be minimized. And a clear printed image can be formed.

Further, in this case, since the driver IC is electromagnetically shielded by the metal layer, electromagnetic waves such as noise coming from outside are absorbed by the metal layer connected to the ground electrode, and malfunction of the driver IC is effectively prevented. You can also. Therefore, the thermal head can always be operated accurately.

Still further, according to the present invention, a solder wetting layer is applied to at least the bottom surface of the concave groove of the insulating substrate and the lower surface of the driver IC, and the solder wetting layer on the lower surface of the driver IC is soldered on the bottom surface of the groove. By soldering to the layer, the driver IC can always be arranged at a predetermined position in the concave groove, and the electrical connection between the terminal electrodes of the driver IC and the individual electrodes can be maintained well over a long period of time. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of a thermal head according to the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a sectional view showing a second embodiment of the thermal head of the present invention.

FIG. 4 is a sectional view of a conventional thermal head.

[Explanation of symbols]

 1 Insulating substrate 1a Groove 2 Heating resistor 4 Driver IC 5a, 10a Metal layer 5b ... Ground electrode

Claims (3)

[Claims] 1. A thermal head comprising a heating resistor and a groove provided on an upper surface of an insulating substrate, and a driver IC for selectively causing the heating resistor to generate Joule heat in the groove. A thermal head, wherein a metal layer is applied to at least a bottom surface of the concave groove of the insulating substrate. 2. The thermal head according to claim 1, wherein the metal layer is connected to a ground electrode for connecting one end of the heating resistor to a reference potential via a driver IC. 3. A thermal head comprising a heat generating resistor and a concave groove provided on an upper surface of an insulating substrate, and a driver IC for selectively causing the heat generating resistor to generate Joule heat is embedded in the concave groove. At least a bottom surface of the concave groove of the insulating substrate and a driver I
The driver IC is embedded in the concave groove by applying a solder slim layer to the lower surface of each of the Cs and bonding the solder slim layer on the lower surface of the driver IC to the solder slim layer on the bottom surface of the concave groove. Thermal head.