Thermal print head and method for manufacturing thermal print head

Abstract

To provide a thermal print head which can suppress sticking.SOLUTION: A thermal print head comprises a base plate, a glaze layer, a wiring layer, a heating element, and a protecting layer. The glaze layer is arranged on the base plate. The wiring layer is arranged on the glaze layer. The wiring layer has a common electrode, and a plurality of individual electrodes. The common electrode has a plurality of projections which are arranged at intervals in a first direction in a plan view and extend in a second direction orthogonal to the first direction in a plan view. The individual electrode has a distal end portion extending in the second direction. The projections and the distal end portions are alternately arranged at intervals in the first direction in a plan view. The heating element extends in the first direction in a plan view, and is arranged on the glaze layer while overlapping the projection and the distal end portion. The protecting layer is arranged on the glaze layer in such a way as to cover the wiring layer and the heating element.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a thermal printhead and a method for manufacturing a thermal printhead. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2023-077118 (Patent Document 1) describes a thermal printhead. The thermal printhead described in Patent Document 1 has a substrate, a glaze layer, a wiring layer, a heating element, and a protective layer.

[0003] The glaze layer is disposed on the substrate. The wiring layer is disposed on the glaze layer. The wiring layer has a common electrode and a plurality of individual electrodes. The common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view. The individual electrodes have tip portions extending in the second direction in a plan view. The protrusions and tip portions are arranged alternately at intervals in the first direction in a plan view. The heating element is disposed on the glaze layer while overlapping with the protrusions and tip portions. The heating element extends in the first direction in a plan view. The protective layer is disposed on the glaze layer so as to cover the wiring layer and the heating element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Document 1: JP 2023-077118 A [Summary] The thermal printhead described in Patent Document 1 may cause sticking (paper to be printed sticks to the surface of the protective layer).

[0005] The thermal printhead of the present disclosure includes a substrate, a glaze layer, a wiring layer, a heating element, and a protective layer. The glaze layer is disposed on the substrate. The wiring layer is disposed on the glaze layer. The wiring layer has a common electrode and a plurality of individual electrodes. The common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view. The individual electrodes have tip portions extending in the second direction. The protrusions and tip portions are arranged alternately at intervals in the first direction in a plan view. The heating element extends in the first direction in a plan view and is disposed on the glaze layer while overlapping the protrusions and tip portions. The protective layer is disposed on the glaze layer so as to cover the wiring layer and the heating element. A recess extending in the first direction so as to overlap the heating element in a plan view is formed on the surface of the protective layer. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a plan view of the thermal printhead 100. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] 1A to 1C are diagrams illustrating the manufacturing process of the thermal printhead 100. [Diagram 5] FIG. 4 is a cross-sectional view illustrating a glaze layer forming step S2. [Figure 6] 11 is a cross-sectional view illustrating a wiring layer forming step S3. FIG. [Figure 7] FIG. 11 is a cross-sectional view illustrating a heating element forming step S5. [Figure 8] FIG. 11 is a cross-sectional view illustrating a first step S71. [Figure 9] FIG. 11 is a cross-sectional view illustrating a second step S72. [Figure 10] FIG. 2 is a cross-sectional view of a thermal printhead 100A. [Figure 11] FIG. 2 is a plan view of a thermal printhead 100B. [Figure 12]12 is a cross-sectional view taken along line XII-XII in FIG. 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Detailed Description] The details of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference characters, and redundant description will not be repeated. A thermal printhead according to an embodiment is referred to as a thermal printhead 100.

[0008] (Configuration of thermal print head 100) The configuration of the thermal printhead 100 will now be described.

[0009] Fig. 1 is a plan view of a thermal printhead 100. In Fig. 1, the protective layer 50 is omitted. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. As shown in Figs. 1 to 3, the thermal printhead 100 has a substrate 10, a glaze layer 20, a wiring layer 30, a heating element 40, and a protective layer 50.

[0010] The substrate 10 has a main surface 10a and a main surface 10b. The main surface 10a and the main surface 10b are end surfaces in the thickness direction of the substrate 10. The main surface 10b is the surface opposite to the main surface 10a. The main component of the material constituting the substrate 10 is a ceramic such as alumina (Al2O3). The main component is a component that occupies more than 50 mass percent of the material.

[0011] The glaze layer 20 is disposed on the substrate 10. More specifically, the glaze layer 20 is disposed on the main surface 10a. The main component of the constituent material of the glaze layer 20 is glass.

[0012] The wiring layer 30 is disposed on the glaze layer 20. The wiring layer 30 has a common electrode 31 and a plurality of individual electrodes 32. The main component of the constituent material of the wiring layer 30 is, for example, gold (Au).

[0013] The common electrode 31 has a strip portion 31a and a plurality of protrusions 31b. The strip portion 31a extends in a first direction DR1 in a plan view. The plan view refers to a view from the main surface 10a along the normal direction of the main surface 10a. The plurality of protrusions 31b are arranged in the first direction DR1 at intervals in a plan view. The protrusions 31b extend in a second direction DR2 in a plan view. The second direction DR2 is a direction perpendicular to the first direction DR1 in a plan view. The protrusions 31b protrude from one side of the strip portion 31a extending in the first direction DR1.

[0014] The individual electrodes 32 are arranged in a first direction DR1 in a plan view. The individual electrodes 32 have a tip portion 32a at one end. The tip portion 32a extends in a second direction DR2 in a plan view. The tip portions 32a and the protrusions 31b are arranged alternately at intervals in the first direction DR1 in a plan view. The individual electrodes 32 have bonding pads 32b at the other end.

[0015] Although not shown, the thermal printhead 100 further has a first wiring and a second wiring. The first wiring is disposed on the glaze layer 20 so as to be connected to the common electrode 31 (strip portion 31a). The second wiring is disposed on the first wiring. The main component of the material constituting the first wiring and the second wiring is, for example, silver (Ag). The first wiring and the second wiring are formed, for example, of a sintered body containing a plurality of silver particles.

[0016] The heating element 40 extends in a first direction DR1 in a plan view. The heating element 40 is disposed on the glaze layer 20 while overlapping with the protrusion 31b and the tip 32a. That is, the adjacent protrusions 31b and tip 32a are electrically connected by the heating element 40. The heating element 40 is formed of a sintered body including, for example, ruthenium oxide (RuO2) particles.

[0017] The protective layer 50 is disposed on the glaze layer 20 so as to cover the wiring layer 30, the heating element 40, the first wiring, and the second wiring. The bonding pads 32b are exposed from the protective layer 50. The main component of the material constituting the protective layer 50 is glass.

[0018] A recess 51 is formed on the surface of the protective layer 50. The recess 51 extends in the first direction DR1 in plan view. The recess 51 overlaps with the heating element 40 in plan view. The width of the heating element 40 in the second direction DR2 is defined as width W1. The width of the recess 51 in the second direction DR2 is defined as width W2. The width W2 is preferably within a range of ±50 μm with respect to the width W1. In other words, the absolute value of the difference between the width W2 and the width W1 is preferably 50 μm or less. In a cross-sectional view perpendicular to the first direction DR1, the bottom surface of the recess 51 is preferably curved and convex upward. "Convex upward" means that the bottom surface is convex toward the opposite side to the substrate 10.

[0019] The protective layer 50 has, for example, a first layer 52 and a second layer 53. The first layer 52 covers the wiring layer 30 and the heating element 40. The second layer 53 covers the first layer 52, avoiding the upper part of the heating element 40. The bottom surface of the recess 51 is composed of the surface of the first layer 52 exposed from the second layer 53. The thickness of the second layer 53 is defined as thickness T. As the thickness T increases, sticking of the paper becomes less likely to occur. On the other hand, if the thickness T is too large, the printing on the paper becomes thin. In consideration of these factors, the thickness T is preferably 10 μm or less. The thickness of the first layer 52 may be equal to or less than the thickness of the protective layer 50 in the configuration shown in FIG. 10. The height of the heating element 40 is the same as the height of the heating element 40 in the configuration shown in FIG. 10.

[0020] The bonding pad 32b is electrically connected to a driver IC (Integrated Circuit) by a bonding wire (not shown). The driver IC selectively supplies a voltage from the bonding pad 32b to the individual electrodes 32 via the bonding wire. On the other hand, a common voltage is supplied to the common electrode 31 via a first wiring and a second wiring. A portion of the heating element 40 connecting the tip 32a of one individual electrode 32 to which a voltage is selectively supplied and the protruding portion 31b adjacent to the tip 32a of the one individual electrode 32 is energized and generates heat. This heat is transferred to a paper in contact with the surface of the protective layer 50 covering the heating element 40, whereby printing on the paper is performed.

[0021] <Modification> The first layer 52 may be formed so as to cover the wiring layer 30 but not cover the heating element 40 (so as to cover the wiring layer 30 while avoiding the heating element 40). The second layer 53 may be formed so as to cover the first layer 52 and the heating element 40.

[0022] (Method of manufacturing the thermal printhead 100) A method for manufacturing the thermal printhead 100 will now be described.

[0023] Fig. 4 is a manufacturing process diagram of the thermal printhead 100. As shown in Fig. 4, the manufacturing method of the thermal printhead 100 includes a preparation step S1, a glaze layer forming step S2, a wiring layer forming step S3, a first wiring forming step S4, a heating element forming step S5, a second wiring forming step S6, a protective layer forming step S7, and a singulation step S8.

[0024] In the preparation step S1, the substrate 10 is prepared. After the preparation step S1, a glaze layer forming step S2 is performed. FIG. 5 is a cross-sectional view illustrating the glaze layer forming step S2. As shown in FIG. 5, in the glaze layer forming step S2, a paste containing glass is applied onto the main surface 10a and the applied paste is fired to form a glaze layer 20. After the glaze layer forming step S2, a wiring layer forming step S3 is performed.

[0025] FIG. 6 is a cross-sectional view for explaining the wiring layer forming step S3. As shown in FIG. 6, in the wiring layer forming step S3, the wiring layer 30 is formed. In the wiring layer forming step S3, first, a resinate paste containing the constituent material of the wiring layer 30 is applied onto the glaze layer 20. Second, the applied resinate paste is baked to form a metal layer. Third, a resist pattern is formed on the metal layer. The resist pattern is formed by applying a photoresist onto the metal layer and exposing and developing the applied photoresist. Fourth, the metal layer is etched using the resist pattern as a mask. As a result, the metal layer is patterned to become the wiring layer 30. After the wiring layer forming step S3 is performed, a first wiring forming step S4 is performed.

[0026] In the first wiring forming step S4, the first wiring is formed. The first wiring is formed by applying a conductive paste containing a plurality of silver particles and baking the applied conductive paste. After the first wiring forming step S4, the heating element forming step S5 is performed.

[0027] Fig. 7 is a cross-sectional view illustrating the heating element forming step S5. As shown in Fig. 7, in the heating element forming step S5, first, a paste containing ruthenium oxide particles is applied onto the glaze layer 20. The paste is applied in a first direction DR1 in a plan view while overlapping with the protruding portion 31b and the tip portion 32a. Second, the applied paste is fired to form the heating element 40. After the heating element forming step S5, a second wiring forming step S6 is performed.

[0028] In the second wiring forming step S6, the second wiring is formed. The first wiring is formed by applying a conductive paste containing a plurality of silver particles and baking the applied conductive paste. After the second wiring forming step S6, a protective layer forming step S7 is performed.

[0029] The protective layer forming step S7 includes a first step S71 and a second step S72. The second step S72 is performed after the first step S71. FIG. 8 is a cross-sectional view illustrating the first step S71. As shown in FIG. 8, in the first step S71, a first layer 52 is formed so as to cover the wiring layer 30, the heating element 40, the first wiring, and the second wiring. In the first step S71, first, a paste containing glass is applied. Second, the applied paste is fired. As a result, the first layer 52 is formed.

[0030] FIG. 9 is a cross-sectional view for explaining the second step S72. As shown in FIG. 9, in the second step S72, the second layer 53 is formed so as to cover the first layer 52. In the second step S72, first, a paste containing glass is applied onto the first layer 52. At this time, the application of the paste is performed while avoiding the area above the heating element 40. Second, the applied paste is fired. As a result, the second layer 53 is formed on the first layer 52 while avoiding the area above the heating element 40. Note that, as a result of the second layer 53 not being formed above the heating element 40, the protective layer 50 has a recess 51 formed so as to overlap the heating element 40 in a plan view. After the protective layer forming step S7 (second step S72), a singulation step S8 is performed.

[0031] In the singulation process S8, the substrate 10, the glaze layer 20, and the protective layer 50 are cut to match the positions that will become the outer periphery of the thermal printhead 100. In this manner, the structure of the thermal printhead 100 shown in Figures 1 to 3 is formed.

[0032] <Modification> In the first step S71, the first layer 52 may be formed so as to cover the wiring layer 30 but not cover the heating element 40. In this case, in the second step S72, the second layer 53 is formed so as to cover the first layer 52 and the heating element 40. This method also makes it possible to form the protective layer 50 having the recesses 51 on its surface.

[0033] (Effects of Thermal Print Head 100) The effects of the thermal printhead 100 will be described below in comparison with comparative examples. The thermal printhead according to comparative example 1 is designated as thermal printhead 100A, and the thermal printhead according to comparative example 2 is designated as thermal printhead 100B.

[0034] Fig. 10 is a cross-sectional view of the thermal printhead 100A. As shown in Fig. 10, the thermal printhead 100A has a substrate 10, a glaze layer 20, a wiring layer 30, a heating element 40, and a protective layer 50. In the thermal printhead 100A, a recess 51 is not formed on the surface of the protective layer 50 so as to overlap the heating element 40.

[0035] In thermal printhead 100A, since recesses 51 are not formed, the contact area between the paper to be printed and the surface of protective layer 50 is likely to be large. As a result, sticking (a phenomenon in which paper sticks to the surface of protective layer 50) can occur with thermal printhead 100A. On the other hand, since recesses 51 are formed in thermal printhead 100, the contact area between the paper to be printed and the surface of protective layer 50 is less likely to be large. Therefore, with thermal printhead 100, it is possible to prevent paper from sticking to the surface of protective layer 50.

[0036] Fig. 11 is a plan view of the thermal printhead 100B. Fig. 12 is a cross-sectional view taken along line XII-XII in Fig. 11. As shown in Fig. 11 and Fig. 12, the thermal printhead 100B has a substrate 10, a glaze layer 21, a wiring layer 30 (a common electrode 31 and a plurality of individual electrodes 32), a heating element 41, and a protective layer 50.

[0037] The glaze layer 21 is disposed on the main surface 10a so as to extend in a first direction DR1 in plan view. In the thermal printhead 100B, the wiring layer 30 is disposed on the main surface 10a except for the protruding portion 31b and the tip portion 32a. The protruding portion 31b and the tip portion 32a extend in a second direction DR2 in plan view so as to reach the glaze layer 21. The protruding portion 31b and the tip portion 32a face each other with a gap in between in the second direction DR2. The heating element 41 is interposed between the substrate 10 or the glaze layer 21 and the wiring layer 30. Since the protruding portion 31b and the tip portion 32a face each other with a gap in between, the heating element 41 is exposed between the protruding portion 31b and the tip portion 32a.

[0038] The protective layer 50 covers the glaze layer 21, the wiring layer 30, and the heating element 41 exposed between the protrusion 31b and the tip 32a. Since the wiring layer 30 is removed between the protrusion 31b and the tip 32a, a step exists in that portion. Due to this step, a step is also formed on the surface of the protective layer 50. Therefore, in the thermal printhead 100B, the contact area between the paper to be printed and the surface of the protective layer 50 is unlikely to be large, and sticking of the paper to the surface of the protective layer 50 is suppressed. However, in the thermal printhead 100B, the heating element 41 exposed between the protrusion 31b and the tip 32a generates heat evenly, and together with the fact that the contact area between the paper to be printed and the surface of the protective layer 50 is unlikely to be large, the printing efficiency is reduced.

[0039] On the other hand, in the thermal printhead 100, the current flows intensively in the center of the heating element 40 in the second direction DR2, so that heat is generated intensively in the center of the heating element 40 in the second direction DR2. Therefore, even if the contact area between the paper and the surface of the protective layer 50 is unlikely to increase as a result of the formation of the recesses 51, it is possible to maintain printing efficiency.

[0040] If the width W2 is too small compared to the width W1, it becomes difficult to bring the paper to be printed into contact with the surface of the protective layer 50 covering the heating element 40 (i.e., the bottom surface of the recess 51), which may cause problems in printing. On the other hand, if the width W2 is too large compared to the width W1, the effect of suppressing the contact area between the paper and the surface of the protective layer 50 from increasing is poor. Therefore, when the width W2 is within a range of ±50 μm or more with respect to the width W1, it becomes possible to perform more appropriate printing while suppressing sticking of the paper. When the bottom surface of the recess 51 has an upwardly convex curved shape in a cross-sectional view in the first direction DR1, it becomes easier to suppress the contact area between the paper and the surface of the protective layer 50 from increasing.

[0041] (Additional Note) The embodiments of the present disclosure include the following features.

[0042] <Appendix 1> A substrate; A glaze layer; A wiring layer; A heating element; A protective layer. the glaze layer is disposed on the substrate; the wiring layer is disposed on the glaze layer, the wiring layer has a common electrode and a plurality of individual electrodes, the common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view; The individual electrodes have a tip portion extending in the second direction, The protrusions and the tip portions are alternately arranged at intervals in the first direction in a plan view, The heating element extends in the first direction in a plan view, and is disposed on the glaze layer while overlapping the protruding portion and the tip portion, the protective layer is disposed on the glaze layer so as to cover the wiring layer and the heating element; The thermal printhead has a surface of the protective layer formed with a recess extending in the first direction so as to overlap the heating element in a plan view.

[0043] <Appendix 2> 2. The thermal printhead of claim 1, wherein the width of the recess in the second direction is within a range of ±50 μm of the width of the heating element in the second direction.

[0044] <Appendix 3> 3. The thermal printhead according to claim 1, wherein a bottom surface of the recess has an upwardly convex curved shape in a cross-sectional view perpendicular to the first direction.

[0045] <Appendix 4> providing a substrate; forming a glaze layer on the substrate; forming a wiring layer on the glaze layer; forming a heating element on the glaze layer; forming a protective layer on the glaze layer so as to cover the wiring layer and the heating element; the wiring layer has a common electrode and a plurality of individual electrodes, the common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view; The individual electrodes have a tip portion extending in the second direction, The protrusions and the tip portions are alternately arranged at intervals in the first direction in a plan view, The heating element extends in the first direction in a plan view, and is disposed on the glaze layer while overlapping the protruding portion and the tip portion, A method for manufacturing a thermal printhead, wherein a recess extending in the first direction is formed on a surface of the protective layer so as to overlap the heating element in a plan view.

[0046] <Appendix 5> the protective layer has a first layer and a second layer, In the step of forming the protective layer, the first layer is formed and then the second layer is formed, the first layer covers the wiring layer and the heating element, The method for manufacturing a thermal printhead described in Appendix 4, wherein the second layer covers the first layer, avoiding an area above the heating element.

[0047] <Appendix 6> the protective layer has a first layer and a second layer, In the step of forming the protective layer, the first layer is formed and then the second layer is formed, the first layer covers the wiring layer; 5. The method for manufacturing a thermal printhead described in claim 4, wherein the second layer covers the heating element and the first layer.

[0048] Although the embodiment of the present disclosure has been described above, the above-mentioned embodiment can be modified in various ways. The scope of the present invention is not limited to the above-mentioned embodiment. The scope of the present invention is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0049] 100 thermal print head, 10 substrate, 10a, 10b main surface, 20, 21 glaze layer, 30 wiring layer, 31 common electrode, 31a strip portion, 31b protrusion portion, 32 individual electrode, 32a tip portion, 32b bonding pad, 40, 41 heating element, 50 protective layer, 51 recess, 52 first layer, 53 second layer, 100A, 100B thermal print head, DR1 first direction, DR2 second direction, S1 preparation step, S2 glaze layer forming step, S3 wiring layer forming step, S4 first wiring forming step, S5 heating element forming step, S6 second wiring forming step, S7 protective layer forming step, S71 first step, S72 second step, S8 singulation step, W1, W2 width, T thickness.

Claims

1. A substrate; A glaze layer; A wiring layer; A heating element; A protective layer. the glaze layer is disposed on the substrate; the wiring layer is disposed on the glaze layer, the wiring layer has a common electrode and a plurality of individual electrodes, the common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view; The individual electrodes have a tip portion extending in the second direction, The protrusions and the tip portions are alternately arranged at intervals in the first direction in a plan view, The heating element extends in the first direction in a plan view, and is disposed on the glaze layer while overlapping the protruding portion and the tip portion, the protective layer is disposed on the glaze layer so as to cover the wiring layer and the heating element; A thermal printhead, wherein a recess is formed on a surface of the protective layer, the recess extending in the first direction so as to overlap the heating element in a plan view.

2. The thermal printhead according to claim 1 , wherein the width of the recess in the second direction is within a range of ±50 μm with respect to the width of the heating element in the second direction.

3. 3. The thermal printhead according to claim 1, wherein a bottom surface of the recess has an upwardly convex curved shape in a cross-sectional view perpendicular to the first direction.

4. providing a substrate; forming a glaze layer on the substrate; forming a wiring layer on the glaze layer; forming a heating element on the glaze layer; forming a protective layer on the glaze layer so as to cover the wiring layer and the heating element; the wiring layer has a common electrode and a plurality of individual electrodes, the common electrode has a plurality of protrusions arranged at intervals in a first direction in a plan view and extending in a second direction perpendicular to the first direction in a plan view; The individual electrodes have a tip portion extending in the second direction, The protrusions and the tip portions are alternately arranged at intervals in the first direction in a plan view, The heating element extends in the first direction in a plan view, and is disposed on the glaze layer while overlapping the protruding portion and the tip portion, A method for manufacturing a thermal printhead, wherein a recess extending in the first direction so as to overlap the heating element in a plan view is formed on a surface of the protective layer.

5. The protective layer has a first layer and a second layer, In the step of forming the protective layer, the first layer is formed and then the second layer is formed, the first layer covers the wiring layer and the heating element, The method for manufacturing a thermal printhead according to claim 4 , wherein the second layer covers the first layer but not above the heating element.

6. The protective layer has a first layer and a second layer, In the step of forming the protective layer, the first layer is formed and then the second layer is formed, the first layer covers the wiring layer; The method for manufacturing a thermal printhead according to claim 4 , wherein the second layer covers the heating element and the first layer.

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