JPH06191077A - Electrode structure of thermal head and its forming method - Google Patents

Abstract

PURPOSE:To provide a thermal head having an electrode structure which can reduce common drop and is good in productivity, and its manufacturing method. CONSTITUTION:A filmy common electrode 7 is formed on a substrate 3, and a heating resistor 1A and lead electrodes 6a, 6b are formed on the common electrode 7 via an insulation film 10. The common electrode 7, the insulation film 10, the heating resistor 1A, and the lead electrodes 6a, 6b are formed by a thin film-forming technique.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a thermal head used for thermal recording or thermal transfer recording and a method for forming the same.

[0002]

Prior Art and Problems to be Solved by the Invention FIG.
(A) is a side view showing an example of a conventional thermal head having an integrated structure, (B) is a plan view, and (C) is a partial equivalent circuit diagram. As shown in FIG. 3 (A), the integrated structure of the server
The round head is a ceramic heating element array forming substrate 3 made of alumina or the like having a heating element 1 and a driving IC 2 for energizing the heating element provided on the surface thereof, and a circuit board 4 for external connection.
Is attached to the heat sink 5 made of an aluminum plate or the like by adhesion or by using an appropriate fixing tool such as a screw or a rivet.

As shown in FIG. 3B, the heating elements 1 are arranged linearly to form a heating element row, and the heating elements 1 are energized on the surface of the substrate 3. The lead electrode 6 and the common electrode 7 for wiring are formed by a film forming technique or the like. An end portion of each lead electrode 6 opposite to the heating element 1 is connected to the driving IC 2 by wire bonding or the like, and the driving IC 2 controls energization to each heating element 1. Each heating element 1 generates heat when energized and performs heat-sensitive recording or thermal transfer recording on a recording medium such as a card or paper that slides and passes over the upper surface of the heating resistor array.

The common electrode 7 is formed by a film forming technique or the like so that the heating element 1 is formed between the common electrode 7 and the lead electrode 6. The common electrode 7 is connected to the heating resistor array through each lead electrode 6. The structure has a current capacity necessary for all the current flowing.

As shown in FIG. 3C, the voltage at both ends of the common electrode 7 is V ₀ , the current flowing through the k-th heating resistor from the end is i _k , and the common electrode 7 between the heating resistors is in common electrode 7. Assuming that the resistance value is r, the voltage V _n applied to the nth heating resistor from the end is V _n = V ₀ -r (i ₁ + i ₂ + ... + i _n ) -r (i ₂ + i ₃ + ...... + i _n) - represented by ...... -ri _n, the voltage drop in the common electrode 7 is increased as the distance from the power supply, the voltage Vn phenomenon (common drop) occurs become smaller.

If this common drop voltage difference is large,
When both ends of the common electrode are connected to a power source, there is a difference in heat generation of the heating element 1 between the end portion of the thermal head and the central portion, and printing,
Since a problem that the printing is not uniform occurs, in order to prevent this, the cross-sectional area of the common electrode 7 in the current direction is secured to a certain extent or more, thereby reducing the resistance value r of the common electrode 7 and reducing the common drop. There is a need.

However, since the common electrode 7 must be formed in a narrow space between the heating element 1 and the tip of the substrate 3, the width dimension cannot be increased so much that the common electrode 7 is cut off. To secure the area, a certain thickness or more was required. Therefore, when the common electrode 7 is formed by the thin film forming technique, it takes a long time to form the common electrode 7 to have a required thickness.
There was a problem that productivity deteriorates.

Further, as a conventional common electrode forming method,
There was a method of forming the heating element 1 by a printing method in the final step after forming the heating element 1, but this method requires two different film forming steps, a thin film method and a thick film method, which complicates the process and increases productivity. There was a problem that was worse.

In order to solve the above problems, FIG. 4 shows an electrode structure of a conventional thermal head provided with a U-turn structure electrode having a large number of common electrode lead wires.
Is a side view, (B) is a partial plan view, and (C) is an enlarged view of (B). As shown in FIG. 4A, in the thermal head of this example, the driving IC 2 is mounted on a circuit board 4 which is separate from the board 3, and the common electrode 7 is a lead electrode with respect to the heating element 1. 6
The drive IC 2 on the circuit board 4 is connected to the lead electrode 6 by a bonding wire 15 across the common electrodes 7 and 4 between the substrates 3 and 4. . The lead electrode 6 is connected to the heating element 1b via the heating element 1a and the turn electrode 8, and the heating element 1b is connected to the common electrode 7 via the branch portion 7c. Also,
The common electrode 7 has pads 7d at a plurality of positions (illustration is for driving I
The same number of pads 7d as C are shown), and the pads 7d are connected to a conductor pattern (not shown) of the circuit board 4 by a bonding wire 15A.

As described above, in the thermal head provided with the U-turn structure electrodes, the current flowing through the heating elements 1a and 1b flows through the pads 7d at a plurality of positions of the common electrode 7, so that the heating element rows are formed. There is no difference in the voltage drop of the common electrode 7 when viewed in the direction, and even if the common electrode 7 is a thin film and has a large resistance,
The common drop described above can be prevented.

However, since the common electrode 7 and the lead electrode 6 are provided on the same side with respect to the heating element 1, each lead electrode 6
Since the space for forming the conductor pattern is narrow, the conductor pattern pitch must be reduced, the pattern width must be narrowed, and the pattern interval must be narrowed. For this reason, there is a problem in that the photo-etching process of the conductor pattern is likely to have a problem, the patterning is difficult, and the productivity is poor.

As a conventional common electrode forming method,
There is also a method in which a separate metal common bar is attached to the substrate 3 by soldering, but since the step of forming a soldering metal and the step of attaching the common bar are required, the problem is that productivity is also poor. was there.

In view of the above problems, it is an object of the present invention to provide a thermal head having an electrode structure capable of reducing common drops and having good productivity, and a method for forming the electrodes.

[0014]

In order to achieve the above object, the electrode structure of the thermal head of the present invention has a film-shaped common electrode formed on a substrate, and heat is generated via an insulating film on the common electrode. It is characterized in that a resistor and a lead electrode are formed.

Further, in the method of forming the electrode of the thermal head of the present invention, the common electrode is formed on the substrate by a thin film forming technique, and the insulating film, the heat generating resistor and the lead electrode are formed on the common electrode in a thin film. It is characterized by being formed by a film forming technique.

[0016]

In the electrode structure of the thermal head of the present invention, as described above, since the common electrode layer is formed under the heating resistor and the lead electrode via the insulating layer, the common electrode film is formed. A large flow passage cross-sectional area is secured even if the thickness is thin. Further, according to the electrode forming method of the present invention, all film formation after the common electrode is formed by the thin film forming method (vapor phase film forming method).

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a sectional view showing a heating element forming portion of an embodiment of a thermal head according to the present invention, FIG. 1B is a sectional view taken along line EE of FIG. 1A, and FIG. It is a top view of the Example.

In FIGS. 1A and 1B, only the heating element forming portion on the upper surface of the ceramic substrate 3 of the thermal head is shown, and 9 is a glaze layer formed on the substrate 3. , 7 are resistors 1A serving as heating elements on the glaze layer 9
A common electrode formed over the entire width of the formation region (hereinafter referred to as a heating resistor), 10 is an insulating layer interposed between the common electrode 7 and the heating resistor 1A, and 6a is the driving I.
A lead electrode 6b connected to C2 is a lead electrode formed by being partially laminated on the common electrode 7. The heating resistor 1A portion between the lead electrodes 6a and 6b serves as a heating point. The method of forming this electrode will be described below with reference to the manufacturing process diagram of FIG. 2 (partial plan view of the substrate 3).

First, in FIG. 2, the glaze layer 9 is formed on the upper surface of the substrate 3 by a screen printing method or a dipping method.
(A), and a common electrode 7 made of aluminum, gold, nickel, copper, tantalum, titanium, tungsten, molybdenum, chromium or an alloy thereof, and further, tungsten silicide, molybdenum silicide, or the like is formed into a thin film. Formed by a technique (b), an insulating layer 10 such as SiO ₂ is formed thereon (c), and a heating resistor 1A made of, for example, polycrystalline silicon is formed thereon by a low pressure CVD method (d). .

Then, a part of the heating resistor 1A and a part of the insulating layer 10 are removed by an etching process such as photo-etching to expose a part of the common electrode 7 at the end of the substrate. An exposed portion T is formed (e), and a metal conductor layer 6 made of the same material as or different from the common electrode 7 is formed thereon by a thin film deposition technique (f).

Subsequently, the metal conductor layer 6 is etched into a predetermined shape by photo-etching or the like to expose a part of the insulating layer 10 and a part of the heating resistor 1A to expose the lead electrode. 6a and 6b are formed (g), and the protective film 11 is formed thereon by, for example, the plasma CVD method.

As described above, the common electrode 7 is formed under the lead electrode 6a and the heating resistor 1A with the insulating layer 10 interposed therebetween, so that the common electrode 7 can be formed over a wide area.
Can be formed, and even if it is a thin film, a large cross-sectional area of the flow path of the current can be taken, so that the common drop can be reduced and the film thickness of the common electrode 7 can be made thin, so that the film forming time can be shortened.

Although the common electrode 7 may be formed by a printing method, the lead electrodes 6a and 6b and the heating resistor 1A may be formed.
By using the same thin film deposition technique as above, it is possible to fabricate in a consistent deposition process.

Further, the common electrode 7 and the lead electrode 6
Since the pattern widths of a and 6b can be made larger than in the case where the U-shaped structure electrode is provided, the patterning becomes easy.

[0025]

According to the first aspect, since the common electrode can be formed in a wide area, the cross-sectional area of the common electrode is increased and the common drop can be reduced. Moreover, since the film thickness of the common electrode can be reduced, the film formation time of the common electrode can be shortened and the productivity can be improved.

According to the second aspect, the common electrode can be manufactured consistently in the same film forming process as the lead electrode and the heating resistor, and the patterning of the lead electrode and the common electrode can be facilitated. Productivity is improved.

[Brief description of drawings]

FIG. 1A is a cross-sectional view showing a heating resistor forming portion of an embodiment of a thermal head according to the present invention, and FIG.
6B is a sectional view taken along line EE in FIG.

FIG. 2 is a manufacturing process diagram showing an embodiment of an electrode forming method of the present invention in a partial plan view.

3A is a side view showing an example of a conventional integral type thermal head, FIG. 3B is a plan view, and FIG. 3C is a partial equivalent circuit diagram.

FIG. 4A is a side view showing an example of a conventional thermal head provided with a U-turn structure electrode, FIG. 4B is a partial plan view, and FIG. 4C is an enlarged view of FIG. 4B. Is.

[Explanation of symbols]

 1A Heating resistor 2 Driving IC 3 Heating element row formation substrate 4 Circuit board 5 Heat sink 6a, 6b Lead electrode 7 Common electrode 9 Glaze layer 10 Insulating layer 11 Protective film

Claims (2)

[Claims] 1. An electrode structure of a thermal head comprising a film-shaped common electrode formed on a substrate, and a heating resistor and a lead electrode formed on the common electrode via an insulating film. . 2. A thermal head characterized in that a common electrode is formed on a substrate by a thin film forming technique, and an insulating film, a heating resistor and a lead electrode are formed thereon by the thin film forming technique. Method of forming the electrode.