JPH0890813A - Thermal head - Google Patents

Abstract

(57) [Abstract] [Purpose] All individual lead wires can be easily patterned, and high reliability that a small driving IC can always be firmly bonded to an electrically insulating substrate. Providing a good thermal head. A plurality of heating elements linearly arranged on the upper surface of an electrically insulating substrate, a plurality of individual lead wires 4 connected to one end of each of the heating elements, and an individual lead wire 4 A thermal head comprising a driving IC 5 having a plurality of electrodes 5a bonded to each other via a conductive adhesive, the driving IC 5 having electrodes 5a.
The number of the electrodes 5 is larger at the end portion Y than at the center portion X, and the distance between the adjacent electrodes 5a is set such that the center portion X is short and the end portion Y is long.

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 for a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, a thermal head incorporated as a printer mechanism for a word processor or the like has an electrically insulating substrate 1 made of alumina ceramics or the like.
1, a plurality of heating elements 12 made of tantalum nitride or the like and linearly arranged at a constant interval P1, and a plurality of individual lead wires 15 connected to one end of each heating element 12
And a common electrode 13 commonly connected to the other end of each heating element 12 and each of the individual lead wires 15 via a conductive adhesive material such as solder, and the heating element 12
Drive IC 15 having a plurality of electrodes 15a arranged substantially parallel to the arrangement direction of the drive ICs for selectively heating the plurality of heating elements 12 by Joule heat.
A predetermined electric power is applied between the common electrode 13 and the individual lead wire 14 in accordance with the driving of 15 to cause the heating element 12 to selectively generate Joule heat based on the print signal, and the generated heat is transferred to a thermal paper or the like. It conducts to the recording medium, and functions as a thermal head by forming a predetermined print image on the recording medium.

The plurality of electrodes 15a are used for driving I
To reduce the size of C15, the arrangement interval P1 of the heating elements 12 is set.
The individual lead wires 1 are arranged at a narrower interval P2 than
Reference numeral 4 connects the corresponding heating element 12 and the electrode 15a through the shortest distance between them.

The plurality of heating elements 12 are 8 do.
The heating elements 12 and the individual lead wires 14 are arranged at a high density of t / mm or more, and the heat generating elements 12 and the individual lead wires 14 are usually formed on the upper surface of the electrically insulating substrate 11 by using a thin film forming technique such as a sputtering method and a photolithography technique. Each is deposited.

[0005]

However, in this conventional thermal head, the electrodes 15a are arranged at an interval P2 narrower than the arrangement interval P1 of the heating elements 12, and each individual lead wire 14 includes the heating element 12 and the electrode 15a. Since the two are connected through the shortest distance between them, the distance H between the adjacent individual lead wires 14 in the vicinity of the driving IC 15 becomes short in the vicinity of both ends Y of the driving IC 15. Will end up. Therefore, in the vicinity of both ends Y of the driving IC 15, the distance H between the adjacent individual lead wires 14 is increased.
However, there is a drawback that it is extremely difficult to accurately pattern each individual lead wire 14 by a photolithography technique or the like.

Therefore, in order to solve the above-mentioned drawbacks, the distance between the adjacent electrodes 15a is set to be shorter at both ends Y than the central portion X of the driving IC 15, and the distance is set near both ends Y of the driving IC 15. It is conceivable to increase the distance H between the individual lead wires 14 arranged.

However, when the distance between the adjacent electrodes 15a is set to be longer at both ends Y than the central portion X of the driving IC 15, the number of electrodes 15a existing at both ends Y of the driving IC 15 is set. Drive IC15
The joint strength between the electric insulating substrate 11 and the electric insulating substrate 11 is lower at both end portions Y than in the central portion X of the driving IC 15. Further, the coefficient of thermal expansion of alumina ceramics forming the electrically insulating substrate 11 is 9.8 × 10 ⁻⁶ 1 / ° C., while the driving IC 15
Coefficient of thermal expansion of the silicon forming the film is 2.6 × 10 ^-6 1 / ℃
Since the two differ greatly from each other, when the thermal head reaches a relatively high temperature (about 60 ° C. or more) due to Joule heat generation of the heating element 12 during high-speed printing or the like, the driving IC
15 generates a large thermal stress between the electrically insulating substrate 11 and, as a result, the thermal stress causes the joint portion between the driving IC 15 and the electrically insulating substrate 11 to be coupled with the decrease in the joint strength described above. The drawback of destruction is triggered.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object of the present invention is to make it possible to easily pattern all the individual lead wires and use a small driving IC on an electrically insulating substrate. It is to provide a highly reliable thermal head that can always be firmly bonded.

[0009]

A thermal head according to the present invention comprises a plurality of heating elements linearly arranged on an upper surface of an electrically insulating substrate, and a plurality of heating elements connected to one end of each heating element. A thermal head comprising a plurality of individual lead wires and a driving IC having a plurality of electrodes joined to each of the individual lead wires via a conductive adhesive, the thermal head comprising: It is characterized in that a large number of electrodes are present at the end portion as compared with the central portion of the driving IC, and the distance between adjacent electrodes is set such that the central portion is short and the end portion is long.

The thermal head of the present invention further comprises a plurality of heating elements linearly arranged on the upper surface of the electrically insulating substrate, and a plurality of individual lead wires connected to one end of each heating element. A driving head having a plurality of electrodes bonded to each of the individual lead wires via a conductive adhesive material, wherein the electrodes of the driving IC have the same area. It is characterized in that the end portion is larger than the central portion of the IC for use, and the distance between adjacent electrodes is set to be short in the central portion and long in the end portion.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of a thermal head according to the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, 1 is an electrically insulating substrate, 2 is a heating element, 3 is a common electrode, Reference numeral 4 is an individual lead wire, 5 is a driving IC, and 5a is an electrode.

The electrically insulative substrate 1 is made of electrically insulative material such as alumina ceramics. For example, ceramic material powder such as alumina, silica, magnesia, etc. is mixed with an appropriate organic solvent and solvent to form a sludge-like material. A ceramic green sheet is formed by employing a conventionally known doctor blade method, and then the ceramic green sheet is punched into a predetermined shape and fired at a high temperature (about 1600 ° C.).

A heat storage layer (not shown) made of glass or the like is deposited on the upper surface of the electrically insulating substrate 1, and the heat storage layer accumulates and dissipates heat generated by a heating element 2 described later. It works to keep the thermal response characteristics of the thermal head good.

When the heat storage layer is made of, for example, glass, a glass paste obtained by adding and mixing an appropriate organic solvent and a solvent to glass powder is applied to the upper surface of the electrically insulating substrate 1 by a conventionally known screen printing method or the like. To a predetermined thickness, and then baked at a high temperature to be applied in a strip shape on the electrically insulating substrate 1.

On the upper surface of the heat storage layer, a constant space P
A plurality of heating elements 2 arranged linearly with 1;
A plurality of individual lead wires 4 connected to one end of each heating element 2 and a common electrode 3 connected to the other end of each heating element 2 are respectively attached.

The heating element 2 is made of, for example, tantalum nitride, titanium nitride, or the like. Since the heating element 2 made of tantalum nitride or the like itself has a predetermined electric resistivity, the common electrode 3 and individual When a predetermined electric power is applied through the lead wire 4, Joule heat is generated, and heat is generated at a temperature required to form a printed image, for example, a temperature of 200 to 350 ° C.

The common electrode 3 and the individual lead wire 4 connected to the heating element 2 are made of a metal material such as aluminum, silver, and copper, and the common electrode 3 and the individual lead wire 4 are connected to the heating element 2. It has a function of applying a predetermined electric power necessary for causing Joule heat generation.

The heating element 2 and the individual lead wires 4 are formed on the upper surface of the electrically insulating substrate 1 in a predetermined pattern by using a thin film forming technique such as a sputtering method and a photolithography technique.

Each of the individual lead wires 4 also forms a predetermined angle θ with respect to the arrangement direction A1 of the heat generating elements 2, specifically, the direction in which the electrodes 5a provided on the driving IC 5 are arranged. Is derived linearly.

The driving IC 5 has a rectangular shape, and has a plurality of electrodes 5a on the lower surface, which are joined to each of the individual lead wires 4 via a conductive adhesive material such as solder. To produce Joule heat selectively on the basis of the print signal, specifically to control the on / off of the electric power applied to the heating element 2 via the common electrode 3 and the individual lead wire 4.

The electrodes 5a of the driving IC 5 all have the same area, and are arranged substantially parallel to the arrangement direction A1 of the heat generating elements 2 at an interval narrower than the arrangement interval P1 of the heat generating elements 2. The driving IC 5 and the individual lead wire 4 are electrically and mechanically connected by soldering each of the electrodes 5a to the corresponding individual lead wire 4.

Further, the electrode 5a has an array for driving I
The central portion X of C5 has two steps and the end portions Y have three steps, and all the electrodes 5a existing in the central portion X and the electrodes 5a existing in both end portions Y from the side closer to the heat generating element 2 are connected. The distance between the adjacent electrodes 5a is different from that of the electrodes 5a forming the stepped array according to the sine value (sin θ) of the angle θ formed by the array direction A1 of the heating elements 2 and the lead-out direction of the individual lead wires 4. It is set. Specifically, the sine value is set to be small at both ends Y of the driving IC 5 and large at the center X, and the distance between the adjacent electrodes 5a is set to the driving IC 5.
At both ends Y and at the central part X are short. For example, the distance at the center X of the driving IC 5 is about 70 μm.
If m, the distance at both ends Y is set to about 140 μm. In this way, the distance between the adjacent electrodes 5a is set to be long at both ends Y of the driving IC 5 and short at the central portion X. It becomes long in the vicinity of the portion Y, and it becomes possible to pattern each individual lead wire 4 surely and easily by the photolithography technique or the like.

Further, the electrodes 5a are present in large numbers at both ends Y of the driving IC 5 compared to the center X thereof. For example, the central portion X has a linear density of 14.3 pieces / mm and both ends thereof. In the portion Y, the linear density of 17.9 pieces / mm exists.

Therefore, the number of joints between the driving IC 5 and the electrically insulating substrate 1 is larger at both ends Y than in the central portion X of the driving IC 5, and the joint strength of the driving IC 5 to the electrically insulating substrate 1 is high. It becomes particularly strong at both ends Y of the driving IC 5. Therefore, even if the thermal head becomes relatively hot when high-speed printing is performed and a large thermal stress is applied to both ends Y of the driving IC 5, the driving IC 5 and the electrically insulating substrate 1
The joint portion with and is effectively prevented from being destroyed by the thermal stress, and the thermal head can be satisfactorily operated for a long period of time.

The drive IC 5 and the individual lead wire 4 are connected by a conventionally known face-down bonding method or the like.

Thus, in the thermal head of the present invention, the common electrode 3 and the individual lead wires 4 are driven as the driving IC 5 is driven.
Predetermined electric power is applied between the heating elements 2 to selectively cause Joule heat generation based on a print signal, and the generated heat is conducted to a recording medium such as thermal paper to form a predetermined print image on the recording medium. It functions as a thermal head.

Next, another embodiment of the thermal head of the present invention will be described.

FIG. 3 (a) is an enlarged view of the essential parts showing another embodiment of the thermal head of the present invention. The thermal head shown in FIG. 3 differs from the thermal heads shown in FIGS. Electrodes 5a arranged at both ends Y of the driving IC 5 are arranged in a row of three stages, two of which are driving I.
The point is that they are arranged in a zigzag pattern along one side of the heating element 2 side of C5, and the remaining one step is arranged along the other side opposite to the one side. Further, FIG. 3B is an enlarged view of a main part showing another embodiment of the thermal head of the present invention. The thermal head shown in FIG. 3 differs from the thermal heads shown in FIGS. The area of the electrodes 5a arranged at both ends Y of the IC 5 is larger than that of the electrodes 5a arranged at the central portion X, and each electrode 5a has a quantity of conductive adhesive (for example, a conductive adhesive material corresponding to each area). , Solder) to the individual lead wires, and for example, the area of the electrodes 5a (diameter φ84 μm) arranged at both ends Y is 5.5 × 10 ⁻³ mm ² , the central portion X. The area of the electrode 5a (diameter φ70 μm) arranged in the area is 3.8 × 10 ⁻³ m
m ² and the amount of solder that joins the individual lead wire 4 to the electrode 5a at both ends Y is 1.6 × 10 ⁻⁴ mm ³ , and the amount of solder that joins the individual lead wire 4 to the electrode 5a at the center portion X The amount is 9.0
It is × 10 ^-5 mm ³ .

In the thermal head of the other embodiment as well, similar to the thermal heads shown in FIGS. 1 and 2, the driving IC 5 is firmly bonded to the electrically insulating substrate 1 at both ends Y, so that high speed is achieved. Even if a large thermal stress is applied to both ends of the driving IC during printing or the like, the joint between the driving IC and the electrically insulating substrate is effectively prevented from being destroyed by the thermal stress. It Therefore, the thermal head can function well for a long period of time.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the spirit of the present invention.

[0032]

According to the thermal head of the present invention, since the bonding strength between the driving IC and the electrically insulating substrate becomes particularly strong at both ends of the driving IC, the thermal head is driven when high-speed printing or the like is performed. Even if a large thermal stress is applied to both ends of the IC for
The joint portion between the driving IC and the electrically insulating substrate is effectively prevented from being destroyed by the thermal stress. Therefore, the thermal head can function well for a long period of time.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a thermal head of the present invention.

FIG. 2 is an enlarged view of a main part of the thermal head shown in FIG.

3 (a) and 3 (b) are enlarged views of a main part showing another embodiment of the thermal head of the present invention.

FIG. 4A is a plan view of a conventional thermal head,
(B) is an enlarged view of a main part of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrically insulating substrate 2 ... Heating element 3 ... Common electrode 4 ... Individual lead wire 5 ... Driving IC 5a ...

Claims (2)

[Claims] 1. A plurality of heating elements linearly arranged on the upper surface of an electrically insulating substrate, a plurality of individual lead wires connected to one end of each of the heating elements, and a plurality of individual lead wires. A thermal head comprising a driving IC having a plurality of electrodes bonded to each other through a conductive adhesive material, wherein the driving IC has its electrodes in comparison with a central portion of the driving IC. The thermal head is characterized in that there are many end portions and the distance between adjacent electrodes is set such that the central portion is short and the end portions are long. 2. A plurality of heating elements linearly arranged on the upper surface of an electrically insulating substrate, a plurality of individual lead wires connected to one end of each of the heating elements, and the individual lead wires. A thermal head comprising a driving IC having a plurality of electrodes bonded to each other via a conductive adhesive material, wherein the electrode of the driving IC has an area in the central portion of the driving IC. On the other hand, the thermal head is characterized in that the ends are large, and the distance between adjacent electrodes is set to be short in the central part and long in the ends.