JP3451008B2 - Thermal head - Google Patents

Description

Description: 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. 2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism such as a word processor has a glass glaze layer having a mountain-like cross-section partially formed on the upper surface of a ceramic substrate made of alumina or the like. A plurality of heating elements are formed on the top of the glaze layer, and a plurality of individual electrode wirings electrically connected to the heating elements are formed in parallel from above the glaze layer to the surface of the ceramic substrate. It has a structure in which the element and the individual electrode wiring are further covered with a protective film made of silicon nitride or the like,
Applying power to the heating element via individual electrode wiring or the like while transporting the thermal recording medium in a direction substantially orthogonal to the arrangement of the heating elements and sliding the thermal recording medium on the surface of the protective film on the heating element row, The heat generating element functions as a thermal head by selectively generating Joule heat individually and forming an image on a thermosensitive recording medium by the generated heat. The glaze layer is for accumulating and dissipating the heat generated by the heating element to an appropriate temperature to maintain good thermal response characteristics of the thermal head. For example, a predetermined glass paste may be used. 20 to 60 μm on a predetermined area of the upper surface of the ceramic substrate by well-known screen printing, etc.
And partially baked at a high temperature. The surface of such a glaze layer is a smooth surface having a center line average roughness Ra of about 50 to 150 °. In general, the ceramic substrate of the above-mentioned thermal head has a relatively low surface smoothness.
Specifically, the surface roughness has a center line average roughness Ra of 0.2 to 0.1.
Those of about 4 μm are most often used. However, the surface of such a ceramic substrate has a diameter of 30 to 40 μm.
m, a large number of depressions of about 5 to 10 μm are formed.Thus, when a thin individual electrode wiring having a thickness of about 0.5 to 2.0 μm is to be patterned by a conventionally known photolithography technique or the like, the thickness of the photoresist layer is reduced. However, although it is substantially constant in the area where the glaze layer is applied, it becomes non-uniform in the other areas due to the influence of the above-mentioned depressions. In some cases, short-circuits occurred between the wirings. For this reason, in the conventional thermal head, for example, as shown in FIG.
More specifically, a constricted portion A is provided near the edge of the glaze layer 12, and the line width of the individual electrode wiring 14 directly attached on the ceramic substrate 11 is reduced to reduce the distance between adjacent individual electrode wirings. It was widened to prevent short circuit. The reason why the individual electrode wiring 14 on the glaze layer 12 is formed wide in such a thermal head is to reduce the wiring resistance of the individual electrode wiring 14 as much as possible. [0005] However, according to the conventional thermal head, the constricted portion A of each individual electrode wiring 13 is linearly arranged along the edge of the glaze layer 12. The internal stress tends to concentrate on the protective film formed on the constricted portion A, especially on the corner. Therefore, when an external force is applied to the protective film due to sliding contact of a thermal recording medium or biting of a foreign substance, a crack occurs along the arrangement of the constricted portions A in the protective film, and the protective film functions as a protective film. In some cases, the thermal head may not be used. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and a thermal head according to the present invention has a glaze layer formed partially on a ceramic substrate, and the glaze layer is formed on the ceramic substrate. A plurality of heating elements are formed on the top, and a plurality of individual electrode wirings electrically connected to the heating elements are formed in parallel from the glaze layer to the surface of the ceramic substrate. In the thermal head in which the wiring is covered with a protective film, the individual electrode wiring has a constricted portion for reducing the line width in a part thereof, and the constricted portion is staggered along the edge of the glaze layer. It is characterized by being arranged. Hereinafter, a thermal head according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing one embodiment of the thermal head of the present invention, and FIG. 2 is an enlarged view of a main part showing the upper surface of the thermal head of FIG. 1, wherein 1 is a ceramic substrate, 2 is a glaze layer, 3 is a heating element, Reference numeral 5 denotes an individual electrode wiring, 6 denotes a protective film, and A denotes a constricted portion provided in the middle of each individual electrode wiring 5. The ceramic substrate 1 is made of a ceramic material such as alumina, and has a glaze layer 2, a heating resistor 3, common electrode wiring 4, individual electrode wiring 5, a protective layer 6, and the like on its upper surface. Acts as When the ceramic substrate 1 is made of, for example, alumina, a ceramic raw material powder such as alumina, silica, magnesia or the like is mixed with a suitable organic solvent and a solvent to form a slurry. A ceramic green sheet is formed by adopting a calender roll method or the like, and then the ceramic green sheet is punched into a predetermined shape and fired at a high temperature. The surface roughness of the ceramic substrate 1 thus obtained is about 0.2 to 0.4 μm in center line average roughness Ra, and a large number of depressions having a diameter of 30 to 40 μm and a depth of about 5 to 10 μm are formed on the surface. Will be done. On the upper surface of the ceramic substrate 1, a glaze layer 2 having a mountain-like cross section is partially adhered and formed. The glaze layer 2 is made of a material having a low thermal conductivity such as glass.
Since it is formed to a thickness of 60 μm, the heat generated by the heating element 3 is accumulated and dissipated to maintain a good thermal response characteristic of the thermal head, and a plurality of heating elements 3 arranged on the top are It protrudes upward to effectively increase the pressing force (printing pressure) on the thermosensitive recording medium. When the glaze layer 2 is made of, for example, glass, a predetermined glass paste obtained by adding and mixing an appropriate organic solvent and a solvent to a glass powder is formed on a predetermined area of the upper surface of the ceramic substrate 1 by a conventionally known screen printing or the like. From 20 to
Print and apply to a thickness of 60 μm, and heat it up to about 900 ° C
Is partially adhered / formed on the upper surface of the ceramic substrate 1 by baking. The surface of the glaze layer 2 thus obtained has a center line average roughness Ra of 50 to 150 °.
The surface becomes as smooth as possible. On the top of the glaze layer 2, a plurality of heating elements 3 are attached and formed in a line, and a common electrode wiring 4 is commonly connected to one end of each of the heating elements 3. Individual electrode wirings 5 are individually connected to the other ends. The heating element 3 is made of, for example, TaSiO, TaSiNO, TiSiO, TiSiCO, NbSiO.
System resistance material is applied to a thickness of 0.01 to 0.5 μm,
Since itself has a predetermined electric resistivity, when electric power from an external power supply is applied through the common electrode wiring 4 and the individual electrode wiring 5, Joule heat is generated, and a print is formed on the thermosensitive recording medium. Required temperature, for example 150-300 ° C
Joule heat is generated at the temperature. On the other hand, the common electrode wiring 4 and the individual electrode wiring 5 connected to the heating element 3 are formed by coating a metal such as Al or Cu to a thickness of 0.5 to 2.0 μm. The function of applying a predetermined power required to cause the heating element 3 to generate Joule heat through the heating element 3 is provided. The individual electrode wires 5 among such wires are led out and formed in parallel from the glaze layer 2 to the surface of the ceramic substrate 1, and a constricted portion A is provided in the middle of each individual electrode wire 5. . The constricted portions A are arranged in two rows along the edge of the glaze layer 2 in a staggered manner. The constricted portions A are part of the line width of each individual electrode wiring 5, specifically, a ceramic substrate. By shortening the line width of the portion directly adhered on 1 and widening the space between adjacent individual electrode wirings, an effect of preventing a short circuit between the individual electrode wirings is achieved. For this reason, the internal stress in the protective film 6 covering the individual electrode wirings 5 and the like is dispersed in the plane direction as compared with that in FIG. 7 in which the constricted portions A are arranged in a straight line. In addition, it is possible to effectively prevent a large stress from being concentrated on a predetermined portion of the protective film 6. Therefore, even if a large external force is applied to the protective film 6 due to sliding contact of the heat-sensitive recording medium or biting of a foreign substance, the protective film 6 does not crack, and the protective film 6 is separated from the individual electrode wiring 5 and the like. By attaching the thermal head in a good condition, the reliability of the thermal head can be improved. The reason why the individual electrode wiring 5 is made wider on the glaze layer 2 is to reduce the wiring resistance of the individual electrode wiring 5 as much as possible. Such individual electrode wirings 5 are patterned together with the above-mentioned heating element 3 and common electrode wiring 4 by a conventionally known thin film forming technique. Specifically, first, the ceramic substrate 1 on which the glaze layer 2 is partially applied is provided.
And a resistive material such as TaSiO and a metal material such as Al are sequentially deposited on the entire upper surface thereof by a conventionally known sputtering method to form a resistive layer having a thickness of 0.01 to 0.5 μm and a thickness of 0.01 to 0.5 μm.
A metal layer of 0.5 to 2.0 μm is laminated. Next, a photoresist layer is applied on the metal layer by a well-known spin coating method or the like, and the photoresist layer is dried. Then, the thermal head pattern (heating element 3, common electrode wiring 4 and individual electrode wiring 5) shown in FIG. Developing with the same exposure pattern as in the above, and thereafter immersing in a predetermined etching solution containing phosphoric acid or the like to pattern the metal layer, and then immersing this in a predetermined etching solution containing hydrofluoric nitric acid The resistance layer is patterned into the same shape as the metal layer. At this time, the thickness of the photoresist layer becomes non-uniform due to the above-mentioned depression in a region where the glaze layer 2 does not exist, but is directly adhered to the surface of the ceramic substrate 1 by the constricted portion A in the middle. In this case, the distance between the adjacent patterns is sufficiently large, so that the short circuit of the patterns is effectively prevented. Next, the photoresist layer is peeled off from the metal layer, a new photoresist layer is applied, and development is performed so that a portion where the heating element 3 is to be formed is opened. Finally, the metal layer located within the window of the photoresist layer is removed by etching by contacting it with a predetermined etchant, and the resistive layer is partially exposed, thereby forming a plurality of heating elements 3 and common electrode wiring 4. And the individual electrode wiring 5 are formed. Then, a protective film 6 is further applied to the upper surfaces of the heating element 3, the common electrode wiring 4, the individual electrode wiring 5 and the like formed as described above. The protective film 6 is made of an abrasion-resistant electrically insulating material such as Si ₃ N ₄ or SiON.
When the heating element 3 and the individual electrode wiring 5 are covered with the protective film 6, corrosion due to contact with moisture and the like contained in the atmosphere and the heat-sensitive recording medium are formed. The heating element 3 and the individual electrode wiring 5 are protected from wear due to sliding contact. Since the constricted portions A of the individual electrode wirings 5 covered with the protective film 6 are provided so as to be staggered along the edge of the glaze layer 2 as described above, the protective film 6 The internal stress therein is satisfactorily dispersed in the plane direction, so that cracking of the protective film 6 due to the use of the thermal head is effectively prevented. When the protective film 6 is made of, for example, Si ₃ N ₄ , a predetermined thickness of Si ₃ N ₄ is applied to the upper surface of the heating element 3, the individual electrode wiring 5, etc. by a conventionally known sputtering or the like. Formed by Thus, in the above-described thermal head of the present embodiment, the heat-sensitive recording medium is conveyed by the external platen roller in a direction substantially perpendicular to the arrangement of the heating elements, and the heat-sensitive recording medium is slid on the surface of the protective film on the heating element 3. Meanwhile, an external power is applied between the common electrode wiring 4 and the individual electrode wiring 5 based on the printing signal, and the heating elements 3 are individually and selectively caused to generate Joule heat, and the generated heat is transferred to the thermosensitive recording medium. It functions as a thermal head by causing conduction and forming a print on a thermosensitive recording medium. 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. Although the constricted portions A are staggered in two rows, the constricted portions A of the individual electrode wires 5 may be staggered in three rows instead, as shown in FIG. In the above embodiment, the individual electrode wiring 5
The constricted portion A is formed in a tapered shape so that the individual electrode wiring 5 is gradually narrowed. Alternatively, the constricted portion A of the individual electrode wiring 5 may be rapidly narrowed as shown in FIG.
The shape may be a gentle curve as shown in FIG. In the case of the embodiment shown in FIG. 5, since the corners are eliminated from the constricted portion A, the stress concentration in the protective film is further alleviated. Further, as shown in FIG. 6, constricted portions A and B of the individual electrode wiring 5 are provided on the glaze layer 2 and the ceramic substrate 1, respectively. May be reduced only at the boundary between the glaze layer 2 and the ceramic substrate 1 where the thickness of the glaze layer 2 tends to increase.
If the upper constricted portion A and the constricted portion B on the ceramic substrate 1 are arranged in a staggered manner, the stress in the protective film deposited thereon can be dispersed well, and It is possible to effectively prevent the occurrence of cracks. According to the thermal head of the present invention, since the constricted portions of the individual electrode wirings are arranged in a staggered manner along the edge of the glaze layer, these individual electrode wirings and the like are covered. The internal stress in the protective film is satisfactorily dispersed in the plane direction, so that a large stress can be effectively prevented from being concentrated on a predetermined portion of the protective film. Therefore, even if a large external force is applied to the protective film due to sliding contact of the thermal recording medium or biting of foreign matter, the protective film does not crack, and the protective film is kept in good condition with respect to the individual electrode wiring and the like. By attaching the thermal head, the reliability of the thermal head can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of a thermal head according to the present invention. FIG. 2 is an enlarged view of a main part showing an upper surface of the thermal head of FIG. 1; FIG. 3 is an enlarged view of a main part showing another embodiment of the thermal head of the present invention. FIG. 4 is an enlarged view of a main part showing another embodiment of the thermal head of the present invention. FIG. 5 is an enlarged view of a main part showing another embodiment of the thermal head of the present invention. FIG. 6 is an enlarged view of a main part showing another embodiment of the thermal head of the present invention. FIG. 7 is an enlarged view of a main part showing an upper surface of a conventional thermal head. [Description of Signs] 1 ... Ceramic substrate 2 ... Glaze layer 3 ... Heating element 5 ... Individual electrode wiring 6 ... Protective films A and B ... Constricted portion

Continuation of the front page (56) References JP-A-6-155786 (JP, A) JP-A-4-78546 (JP, A) JP-A-60-3045 (JP, U) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B41J 2/335 B41J 2/345

Claims (1)

(57) [Claim 1] A glaze layer is partially formed on a ceramic substrate, and a plurality of heating elements are provided on the top of the glaze layer from the glaze layer to the surface of the ceramic substrate. A plurality of individual electrode wirings which are individually electrically connected to the heating elements are formed in parallel, and in the thermal head in which these heating elements and the individual electrode wirings are covered with a protective film, the individual electrode wirings are A thermal head having a constricted portion having a narrow line width in a part thereof, wherein the constricted portions are arranged in a staggered manner along the edge of the glaze layer.