JP2001315370A - Thermal printing head and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal printing head mounted with high-density heating units which is more compact, operates with a lower power, has a higher resolution and is lower in cost than the prior art. SOLUTION: A plane and highly heatproof glass base material 21 with a metallic thin film 22 formed to one surface is used as a substrate 20 for manufacturing. This thermal printing head is manufactured through a first process of forming a protecting film 11 to a surface of the metallic thin film 22 with the substrate 20 being used as a base, a second process of setting a heating element 12 and a wiring electrode 13 to a surface of the protecting film 11, a third process of forming a glass substrate 14 of a small thermal conductivity and forming a plurality of vias 15 to the glass substrate 14, a fourth process of mounting a driver IC 17b with a solder bump 17a to the glass substrate 14, and a fifth process of melting the metallic thin film 22 by etching thereby separating the substrate 20 and the thermal printing head 10 from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal print head.

[0002]

2. Description of the Related Art A printer using a thermal print head has a simple mechanism and has no noise, and a printer having a large number of heating elements as recording elements can be easily manufactured. Therefore, high-speed printing is made possible and widely used for business use. Further, since the printer can be reduced in size and weight, its use has been expanded to portable use.

FIG. 7 is a sectional view showing an example of a conventional thermal print head. This thermal printhead is a substrate in which a heat storage layer glass is glazed on the entire upper surface of a ceramic substrate, a heating element and wiring electrodes are formed on the glass, and a driver IC (semiconductor integrated circuit) is mounted. The cylindrical platen supplies a print medium, and components other than the heating element of the thermal print head are arranged so as not to contact the platen. For this reason, the driver IC needs to be arranged at a place far away from the heat generating element, which increases the size of the glass-glazed ceramic substrate, which causes a cost increase.

[0004] In recent years, demand for printers has increased, and the market for small color printers for consumer use has grown remarkably. As a feature of this field, a product with high printing quality and a low price is required. 2. Description of the Related Art With the spread of digital cameras, there has been a demand for the development of smaller, lower-priced, high-print-quality color printers as digital photo hard copy printers.

[0005] Printers other than thermal printers have been further densified, and ink jet printers have realized 600 elements per inch, and laser printers have realized 2400 elements / inch. However, in the thermal print head, the output terminal pitch of the driver IC is 75 μm, which is the minimum, and if it is less than this, the terminals cannot be easily connected. Therefore, this is the limit, and generally 300 elements /
It is at the limit where thermal printheads with inch density can be mass-produced. By placing driver ICs on both sides of the heating element as a special one, double density 600d
A pi thermal printhead has also been developed, but as described above, the size of a glass-glazed ceramic substrate is twice or more the size of a normal glass substrate, which significantly increases the cost and is limited to special applications. Recently, 600 dpi
Compatible driver ICs have been developed, but the output terminal pitch is narrow, resulting in poor wiring yield.
The difficulty in high-definition patterning is an obstacle to practical application.

[0006] Further, recently, as computer devices have become mobile, demand for portable printers has increased, and therefore, there has been a demand for lower battery consumption. In the conventional thermal print head as shown in FIG. 7, the heat remaining in the glass near the heating element is dissipated to the ceramic substrate.
Furthermore, this heat becomes reactive energy because it is released to the aluminum radiator. To remedy this, the glass is made thicker to reduce the escape of heat to the ceramic substrate. Furthermore, thermal print heads using glass as the substrate itself have been commercialized, but since the heat accumulated near the heating elements affects the next print cycle and impairs the print quality, sufficient print quality can be secured. Not.

In order to solve such a problem, the present inventor has already developed a thermal print head as shown in FIG. 8 (Japanese Patent Application No. 11-346614). FIG.
FIG. 9 is an enlarged cross-sectional view illustrating a periphery of a heating element formed on a multilayer glass substrate used in the thermal print head of FIG. 8. As shown in FIG. 9, a heating element and an electrode are formed on a multilayer glass substrate, an insulating layer is provided on the surface of the electrode, and a common electrode is further provided on the insulating layer. Is composed.

In this thermal print head, a glass substrate having a thickness of 0.05 mm or less functions as a protective film, thereby enabling a two-layer circuit to be provided in the vicinity of the heating element, and connecting the glass substrate to the outside. Terminal pitch can be widened, and connection with the outside is facilitated. The width of the glass substrate is determined by the printing length, but the height is 5 mm.

As shown in FIG. 8, the multi-layer glass substrate on which the heating element and the electrode circuit are formed is held on glass for heat insulation and attached to a support, and the recess of the support surrounds the heating element. ing. By performing thermal insulation in the air gap in this manner, the heat capacity of the thermal print head is reduced, and a print density equivalent to one-third of the heat generation energy is obtained as compared with the conventional thermal print head having the structure shown in FIG. Has been realized.

Further, in order to obtain high print density while maintaining high resolution, one pixel constituting one pixel as shown in FIG.
Two heating resistors divided into two and arranged in the main scanning direction
A thermal head has been proposed in which two current paths are formed, and narrow portions are formed at different positions in the sub-scanning direction in each of the two current paths, thereby forming two heat-generating portions in one pixel. JP-A-10-181061). FIG. 3A is a partially enlarged plan view showing an arrangement pattern of electrodes and heating elements, and FIG. 3B shows a state of print dots of each heating element.

[0011]

However, in the thermal print head of FIG. 8, an epoxy resin or polyimide which is easy to process is mainly used as an insulating layer of a multilayer glass substrate, and the mechanical strength required for printing is a protective film. It also depends on the strength of the glass substrate that functions. Further, since it is difficult to process a thin glass substrate, the glass substrate is processed with a thickness of about 0.7 mm, and after assembling into the structure of FIG. 8, the glass surface of the multilayer glass substrate is polished to a required thickness. Finished. Under these circumstances, the thickness of the glass substrate functioning as a protective film of the completed thermal print head is about 0.03 to 0.05 mm.
Therefore, in comparison with a thermal print head having a protective film having a thickness of 5 to 10 μm, more heat energy is required to obtain the same print density. In addition, due to the structure with a multilayer glass substrate and a flexible substrate on which a driver IC is mounted, miniaturization of the thermal print head has achieved a size of about 5 mm x 120 mm x 10 mm with a print length of 4 inches. In order to be built in a cellular phone or the like or a wristwatch structure, further reduction in size and power consumption is required.

In order to mount the heating elements at a high density, when the heating elements as shown in FIG. 10 are formed, the printing dots become elongated due to the elongated shape of the heating elements. Since the wide portion and the narrow portion are provided, there is a problem that when trimming by a high voltage pulse, current is concentrated on the narrow portion and disconnection is likely to occur.

The present invention has been made in view of such a conventional problem, and realizes a more compact and lower power than before.
Another object of the present invention is to provide a low-cost, high-density thermal printhead.

[0014]

In order to solve the above-mentioned problems, a thermal print head of the present invention uses a highly heat-resistant glass substrate provided with a metal thin film on one surface as a manufacturing substrate, and uses the glass substrate for manufacturing. A protective film, a heating element, an electrode, and a glass substrate are sequentially formed on the metal thin film surface, and a thermal print head is formed on the upper surface of the manufacturing substrate. Then, the metal thin film is dissolved by etching, and the manufacturing substrate and the thermal print head are formed. And means for separating them from each other. Also,
A via is formed on the glass substrate to connect the heating element and the driver IC that electrically drives the heating element, and the via is filled with hard metal, so that the driver IC is mounted on the substrate and the overall strength of the thermal print head is increased. Measures to reinforce it. In addition, a heating element is formed on the upper surface of the protective film, and an electrode is formed on the upper surface of the heating element, so that a means is provided for disposing the heating element closer to the protective film than the electrode. Furthermore, one wiring electrode is branched into two branch electrodes near the heating element,
Two heating elements constituting one pixel are arranged on the two branch electrodes so as to be shifted in the sub-scanning direction, and a large number of heating elements are continuously arranged at equal intervals in two rows in the main scanning direction. Means is provided for forming the shape of each heating element into a rectangular shape.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermal print head of the present invention uses a highly heat-resistant glass substrate 21 having a flat surface and a metal thin film 22 on one surface thereof as a manufacturing substrate 20, and using the manufacturing substrate 20 as a substrate. As a base, a first step of forming the protective film 11 on the surface of the metal thin film 22, a second step of providing the heating element 12 and the wiring electrode 13 on the surface of the protective film 11, and a glass substrate 14 having a small thermal conductivity A third step of forming and forming a plurality of vias 15 in the glass substrate 14, and a driver I having a solder bump 17a in the glass substrate 14;
It is manufactured through a fourth step of mounting the C17b and a fifth step of separating the manufacturing substrate 20 and the thermal print head 10 by dissolving the metal thin film 22 by etching.

With the above configuration, in the first step, the protective film 11 of glass or the like having an arbitrary thickness can be formed on the surface of the metal thin film 22 with high precision. Next, the second
In the process, the heating elements 12 and the wiring electrodes 13 can be formed at a high density on the surface of the protective film 11 by a thin film technique. Next, in the third step, a plurality of vias 15 are provided in the glass substrate 14 and each via is filled with a hard metal such as nickel, so that the strength of the entire thermal print head can be enhanced. Next, in the fourth step, a driver IC having solder bumps was directly mounted on the via, thereby minimizing the component area and enabling high integration. Next, in a fifth step, the metal thin film 22 is melted by etching to separate the manufacturing substrate 20 and the thermal print head 10, thereby completing the thermal print head and reusing the manufacturing substrate 20. .

As described above, a protective film, a heating element, an electrode, and a glass substrate are sequentially formed on a manufacturing substrate to form a thermal print head. By separating the print head from the print head, a thermal print head having a strong structure while having a thin protective film of about 5 μm is manufactured.

Further, since the heating element is provided in contact with the protective film, heat conduction from the heating element to the printing medium through the thin protective film is extremely good. Furthermore, since the heating element and the electrode are formed on the surface of the protection film after the formation of the protection film, the protection film itself is not affected by the unevenness of the pattern of the heating element and the electrode. The outer surface of the protective film of the print head is extremely flat.
In addition, one wiring electrode is branched into two in the vicinity of the heating element, and a heating element is arranged at each branch electrode so as to be shifted in the sub-scanning direction, so that one pixel is constituted by the two heating elements, and in the main scanning direction. By arranging a large number of heating elements continuously at equal intervals in two rows, the heating elements can be arranged at a high density. In addition, since the shape of each heating element is formed in a rectangular shape, the shape of the printing dot by the heating element becomes substantially a round dot, and the printing dot is equalized in both the main scanning direction and the sub-scanning direction.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a typical embodiment of the present invention, a thermal print head for a color video printer having a heating dot density of 800 dots / inch and a printing length of 2 inches will be described with reference to the drawings. FIG. 1 is a sectional view showing the structure of the thermal print head of the present invention. In FIG. 1, a thermal print head 10 has a heating element 12 formed on a protective film 11 and an electrode 13 formed on the heating element 12.
Is formed, and a heat-resistant insulating thin film 19 is formed on the wiring electrode 13.
Is formed on the insulating thin film 19 to form a laminated circuit including the glass substrate 14, the via 15, and the common electrode 16. The via 15 is formed by subjecting the insulating thin film 19 and the glass substrate 14 to a hole process, and is filled with nickel and gold plating.
Then, the driver IC 17a is mounted with the positions of the via 15 and the solder bump 17b aligned, and the case 18 is mounted. The thermal print head 10 is manufactured as described above.

FIG. 2A is a sectional view of a manufacturing substrate 20 used when manufacturing a thermal print head.
The manufacturing substrate 20 is a flat glass substrate 21 having high heat resistance.
The metal thin film 22 is formed on the entire surface of one of the surfaces. The metal thin film 22 is formed of a material having high heat resistance and easy to be etched. In this embodiment, the metal thin film 22 is made of nickel 1
An alloy of 0% and 90% tungsten is formed to a thickness of 1 μm by plating. In this embodiment, an example in which the glass substrate 21 is used as the manufacturing substrate 20 is shown. However, from the viewpoint of strength and heat resistance, as shown in FIG. You may use what was done.

FIG. 3 is a sectional view when the thermal print head 10 is formed on the manufacturing substrate 20. As a first step of manufacturing a thermal print head, a manufacturing substrate 20 is used.
The protective film 11 of 5 to 10 μm is formed on the surface of the metal thin film 22 of FIG. The thickness of the protective film 11 is large in the case of an industrial card printing application in which abrasion resistance is important, and conversely, the printing medium is smooth and the protective film is less worn like a video printer. If it is required, make it thinner. Since this embodiment is for a video printer, a glass paste is applied and baked to form a glass film having a thickness of 5 μm.

In the second step, a heating element 12 and a wiring electrode 13 are formed on the surface of the protective film 11. In this embodiment, the heating element 12 and the wiring electrode 13 were formed by a thin film technique in order to realize a high density. FIG. 5A is a partially enlarged plan view of the pattern of the heating element 12 and the electrode 13. The wiring electrode 13 has a branch electrode 93 and a branch electrode 94 immediately adjacent to the heating element.
, And are connected to a heating element 91 and a heating element 92, respectively, which are displaced in the sub-scanning direction.
As shown in the figure, a large number of two heating elements, which are displaced in the sub-scanning direction, are arranged on each branch electrode in two rows in the main scanning direction, and the wiring electrodes 13 have a pitch of 63.5 μm. The pitch of each heating element is 31.75 μm, which is a double density. Further, since the shape of each heating element is formed in a rectangular shape, as shown in FIG. 5 (B), the printing dots become substantially round dots, so that high-definition image printing can be obtained, and the width of the heating element is constant. Therefore, the current does not concentrate on a part of the heating element during the trimming, and there is no breakage of the wire. In the thermal print head of this embodiment, a total of 1536 rectangular heating elements each having a size of about 0.025 mm × 0.035 mm are arranged in two rows in the main scanning direction.
By printing through a thin protective film of about 5 μm,
The size of the printing dot by one heating element is about 0.
A substantially circular print result of 03 mm was obtained.

In the third step, a glass substrate 14 having vias is formed as a thermal print head substrate. The vias 15 serve to electrically connect the wiring electrodes 13 separately provided on both surfaces of the glass substrate 14 and the driver IC 17a, and to maintain the strength of the entire print head at a high level. First, an insulating thin film 19 is formed on the surfaces of the heating element and the electrodes by a thin film technique, a glass paste is applied to the surface of the insulating thin film 19, and the via 15 is processed.
The glass substrate 14 is formed by sintering at about 0 ° C. Thereafter, a hole is formed in a portion of the insulating thin film 19 that contacts the via 15 by dry etching, so that the surface of the wiring electrode 13 is exposed. The reason why the insulating thin film 19 is formed first is to prevent the heating elements and the electrodes from being oxidized when firing at a high temperature. In this embodiment, the insulating thin film 19 is made of Si by thin film technology.
O ₂ was formed to a thickness of 2 μm. Next, the via 15 was filled with nickel by plating, and the surface was plated with gold. Then, a conductive paste was applied on the glass substrate 14 as a common electrode, and dried at 150 ° C. to form the common electrode 14. In this embodiment, the thickness of the glass substrate 14 is about 0.10 mm, and about four hundred vias 15 are mounted at intervals of about 0.15 mm.

As a fourth step, the gold-plated via 1
The solder bump 17b of the driver IC 17a is aligned with 5 and temporarily fixed with a high-concentration flux and soldered. In this way, the thermal print head of this embodiment has a thickness of 3 mm by forming a laminated circuit and employing a driver IC 17a having a solder bump 17b which does not require a wiring area to achieve high integration. With a width of 55 mm and a height of 1 mm in the printing direction, the size was dramatically reduced as compared with the conventional one.

In a fifth step, the thermal print head 10 is separated from the manufacturing substrate 20 by dissolving the metal thin film 22 by etching, and the thermal print head 10 is completed. For the metal thin film made of the nickel-tungsten alloy of this embodiment, a mixed solution of caustic soda and hydrogen peroxide was used as an etching solution. FIG. 4 shows the state after the metal thin film 22 is dissolved and removed by etching.
FIG. 2 is a cross-sectional view showing a state where a thermal print head 10 and a manufacturing substrate 20 are separated. The manufacturing substrate separated at this time can be repeatedly used as the manufacturing substrate 20 of the thermal print head of the present invention by forming a metal thin film again.

In the above embodiment, the wiring electrode 13 is formed of a thin film. When the glass paste is sintered at a high temperature of 600 ° C. when forming a glass substrate, the wiring electrode 13 is formed so as not to be oxidized. Although the example in which the insulating thin film 19 is provided between the substrate 13 and the glass substrate 14 is shown, when the electrode is formed as a thick film and sintered at a high temperature of 600 ° C. or more, the insulating thin film 19 is formed.
Becomes unnecessary. In addition, although the case where the protective film 11 of the above embodiment is formed of thick glass is shown, an inorganic film may be formed by a thin film technique. Similarly, instead of the metal thin film 22 of the manufacturing substrate 20, an inorganic film such as silicon nitride having high heat resistance and good etching properties may be formed.

[0027]

According to the present invention, a protective film having an arbitrary thickness can be formed on a metal thin film by using a high heat-resistant glass substrate previously coated with a metal thin film as a substrate for manufacturing a thermal print head. As a result, the thickness of the protective film could be reduced to about 5 μm. Therefore, heat conduction from the heating element to the print medium through the thin protective film is good, and a thermal print head with high energy efficiency is realized.

Further, in each step of sequentially assembling a thermal print head from a protective film on a manufacturing substrate coated with a metal thin film in advance, an adhesive member between the glass substrate of the manufacturing substrate and the thermal print head portion. And effectively produced a high-precision, high-density thermal printhead. Furthermore, after creating a thermal print head on a manufacturing substrate, the thin metal film is melted by etching to separate the manufacturing substrate from the thermal printer head, making the glass substrate of the manufacturing substrate reusable. did.

By filling the vias of the glass substrate of the thermal print head with hard metal, the glass substrate itself was reinforced and the mechanical strength of the entire thermal print head could be increased while the protective film was thinned. In addition, the provision of vias in the glass substrate makes it possible to mount a driver IC on the glass substrate, and the use of a driver IC with solder bumps eliminates the need for a wiring area, thus reducing the size of the thermal print head. Was reduced in size to 3 mm × 1 mm in cross-sectional area. This increases the number of pieces taken from a fixed-size substrate and contributes to cost reduction.

Since the protective film is thin and the heating element is formed directly on the protective film, heat conduction to the print medium through the protective film is good, and energy efficiency is high. Further, since the flatness of the surface of the protective film is good, it is possible to prevent the occurrence of wrinkles of the ink ribbon, and it is possible to reduce the thickness of the ink ribbon. As an example, in a fusion type thermal transfer ink ribbon, the thickness of the conventional base film is 3.5 μm and the thickness of the ink is 1.2 μm.
m was the thinnest, but 2.5 μm and 0.5 μm, respectively.
m, which enables printing with less heat generation energy.

One electrode is branched into two in the vicinity of the heating element, and two heating elements are shifted from each other in the sub-scanning direction per electrode, and a large number of elements are continuously arranged in the main scanning direction. High-density arrangement of heating elements is now possible. In addition, since the heating element was formed in a rectangular shape, the print dots were formed into extremely small round dots, and the problem of disconnection breakage during trimming could be solved. With such a heating element and electrode structure, high-quality and high-definition printing required for digital photography and the like can be realized, and the electrode spacing can be matched to the terminal pitch of the conventional driver IC, so that component costs and manufacturing costs are reduced. Made it possible to keep it low.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a thermal print head of the present invention.

FIG. 2A is a cross-sectional view illustrating a structure of a substrate for manufacturing a thermal print head. (B) is a sectional view showing the structure of the manufacturing substrate according to claim 2.

FIG. 3 is a cross-sectional view showing a state in which a thermal print head is formed on a manufacturing substrate.

FIG. 4 is a cross-sectional view showing a state where a thermal print head and a manufacturing substrate are separated.

FIG. 5A is an enlarged plan view showing a pattern of a heating element and an electrode. (B) is a diagram showing a state of a print dot of each heating element.

FIG. 6 is a circuit diagram showing electrical connection between a heating element and electrodes according to the present invention.

FIG. 7 is a sectional view showing an example of the structure of a conventional thermal print head.

FIG. 8 is a sectional view showing an example of the structure of an improved thermal print head.

FIG. 9 is an enlarged cross-sectional view showing the vicinity of a heating element of the thermal print head of FIG.

FIG. 10A is an enlarged plan view showing an arrangement of heating elements of a conventional thermal head. (B) is a diagram showing a state of a print dot of each heating element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Thermal print head 11 ... Protective film 12 ... Heating element 13 ... Wiring electrode 14 ... Glass substrate 15 ... Via 16 ... Common electrode (conductor paste) 17a ... Driver IC 17b ... Solder bump 18 ... Case 19 ... Insulating thin film 20 ... Manufacturing Substrate 21 ... Glass base material 22 ... Metal thin film 23 ... Ceramic base material 24 ... Glass 91,92 ... Branch electrode 93,94 ... Heating element

Claims (6)

[Claims] 1. A manufacturing substrate (2) comprising a flat glass substrate (21) having a metal thin film (22) on one surface.
0) A protective film (11) is formed on the surface of the metal thin film (22), a thermal print head (10) is assembled on the surface of the protective film (11), and then the metal thin film (22) is dissolved by etching. A method for manufacturing a thermal print head, comprising separating a substrate for use (20) and a thermal print head (10). 2. The manufacturing substrate (20) has a glass (24) glazed on one surface of a planar ceramic substrate (23) and a metal thin film (2) on a surface of the glass (24).
2. The method according to claim 1, wherein the method (2) is formed. 3. A method for manufacturing a thermal print head according to claim 1, wherein a first step of forming a protective film (11) on a surface of the metal thin film (22) of the manufacturing substrate (20); A second step of providing a heating element (12) and a wiring electrode (13) on the surface of the protective film (11), and a glass substrate (14)
Forming a plurality of vias (15) in the glass substrate (14) and a driver IC (17) having solder bumps (17b) in the glass substrate (14).
b) mounting a thermal printhead, and a fifth step of dissolving the metal thin film (22) by etching to separate the manufacturing substrate (20) from the thermal print head (10). Manufacturing method of print head. 4. A thermal print head in which a plurality of heating elements forming one pixel are continuously arranged at equal intervals in a main scanning direction, wherein the heating elements forming one pixel are positioned in a sub-scanning direction. Two heating elements (91,
92), and each heating element (91, 92) is connected to a branch electrode (93, 94) that branches one wiring electrode (13) into two near the heating element.
A thermal printhead, wherein each heating element is formed in a rectangular shape. 5. A thermal print head comprising a heating element (12), a wiring electrode (13), a driver IC (17a) and a glass substrate (14), wherein a plurality of vias (15) are provided in the glass substrate (14). ) And vias (1)
5) A thermal print head, wherein the holes are filled with a hard metal. 6. The thermal print head according to claim 4, wherein the thermal print head is manufactured by the manufacturing method according to claim 3.