Thermal print head

Abstract

To provide a thermal print head capable of reducing an electric resistance value of a common electrode while securing difference of elevation between a resistor and a common electrode.SOLUTION: A thermal print head includes a substrate, a wiring layer, embedded wirings and a resistor. The substrate has a principal plane. A concave part is formed on the principal plane. The concave part extends along a first direction in a planar view. The wiring layer includes a plurality of first wirings and a plurality of second wirings. One side end part of each of the plurality of first wirings and one side end part of each of the plurality of second wirings are opposed in the first direction or in a second direction vertical to the first direction in the planar view. The embedded wirings are embedded in the concave part and are electrically connected with the other side end part of each of the plurality of second wirings. The resistor is arranged on the principal plane so as to extend along the first direction while overlapping with the one side end part of each of the plurality of first wirings, and the one side end part of each of the plurality of second wirings.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to thermal printheads. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open No. 2023-115544 (Patent Document 1) describes a thermal printhead. The thermal printhead described in Patent Document 1 has a substrate, a heat storage layer, an electrode layer, a resistor, and a protective layer. The electrode layer has a first layer and a second layer. The heat storage layer is disposed on the substrate.

[0003] The first layer is disposed on the heat storage layer. The first layer has a common electrode and a plurality of individual electrodes. The common electrode has a strip portion and a plurality of protrusions. In a plan view, the strip portion extends along a first direction. The plurality of protrusions are arranged at intervals along the first direction. Each of the plurality of protrusions protrudes from the strip portion along a second direction. The second direction is a direction perpendicular to the first direction in a plan view. The plurality of individual electrodes are arranged at intervals along the first direction. Each of the plurality of individual electrodes has a tip portion extending along the second direction. The protrusions and the tip portions are arranged alternately in the first direction. The resistor extends along the first direction. The resistor is disposed on the heat storage layer while overlapping with the protrusions and the tip portion. The second layer is disposed on the first layer except for a portion of the first layer overlapping with the resistor. The protective layer is disposed on the heat storage layer so as to cover the electrode layer and the resistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-115544 A [Summary] In the thermal printhead described in Patent Document 1, the electrode layer is composed of a first layer and a second layer, so that the electrode layer is thick and the electrical resistance of the electrode layer is reduced. However, as a result, the height difference between the surface of the electrode layer and the surface of the resistor is small or the surface of the electrode layer is higher than the surface of the resistor, so that when the paper to be printed is brought into contact with the protective layer on the resistor, the paper may also come into contact with the protective layer on the electrode layer.

[0005] The thermal printhead of the present disclosure includes a substrate, a wiring layer, embedded wiring, and a resistor. The substrate has a main surface. A recess is formed in the main surface. The recess extends along a first direction in a plan view. The wiring layer has a plurality of first wirings and a plurality of second wirings. One end of each of the plurality of first wirings and one end of each of the plurality of second wirings face each other in the first direction or in a second direction perpendicular to the first direction in a plan view. The embedded wiring is embedded in the recess and is electrically connected to the other end of each of the plurality of second wirings. The resistor is disposed on the main surface so as to extend along the first direction while overlapping with one end of each of the plurality of first wirings and one end of each of the plurality of second wirings. [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 plan view of a thermal printhead 100A. [Figure 4] 2A to 2C are process diagrams illustrating a method for manufacturing the thermal printhead 100. [Diagram 5] FIG. 4 is a cross-sectional view illustrating a ceramic layer forming step S2. [Figure 6] FIG. 11 is a cross-sectional view illustrating a glaze layer forming step S3. [Figure 7] 11 is a cross-sectional view illustrating a wiring layer forming step S4. FIG. [Figure 8] FIG. 11 is a cross-sectional view illustrating a resistor forming step S5. [Figure 9] 11 is a cross-sectional view illustrating a first protective layer forming step S6. FIG. [Figure 10] 11 is a cross-sectional view illustrating an embedded wiring forming step S7. [Figure 11] 11 is a cross-sectional view illustrating a second protective layer forming step S8. FIG. [Figure 12] FIG. 2 is a plan view of a thermal printhead 200. [Figure 13] 13 is a cross-sectional view taken along line XIII-XIII in FIG. 12.

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

[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. Note that protective layers 50 and 60 are omitted from Fig. 1. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. The thermal printhead 100 has a substrate 10, a wiring layer 20, embedded wiring 30, a resistor 40, and protective layers 50 and 60.

[0010] The substrate 10 has a main surface 10a and a main surface 10b. The main surface 10b is the surface opposite to the main surface 10a. The main surfaces 10a and 10b are both end surfaces of the substrate 10 in the thickness direction. When the thermal printhead 100 is viewed from the main surface 10a side along the normal direction of the main surface 10a, this is referred to as a planar view. For example, the longitudinal direction of the substrate 10 in the planar view is defined as a first direction DR1. A direction perpendicular to the first direction DR1 in the planar view is defined as a second direction DR2.

[0011] A recess 10c is formed on the main surface 10a. A raised portion 10d may be further formed on the main surface 10a. The recess 10c extends along a first direction DR1. The main surface 10a is recessed toward the main surface 10b at the recess 10c. The main surface 10a is raised toward the opposite side to the main surface 10b at the raised portion 10d. The raised portion 10d extends along the first direction.

[0012] The substrate 10 has, for example, a ceramic substrate 11, a ceramic layer 12, and a glaze layer 13. The ceramic substrate 11 forms a main surface 10b. The ceramic layer 12 is disposed on the ceramic substrate 11. The glaze layer 13 is disposed on the ceramic layer 12. The main surface 10a is composed of a surface of the ceramic layer 12 and a surface of the glaze layer 13. The recess 10c is formed in the ceramic layer 12. In the illustrated example, the ceramic substrate 11 is exposed from the recess 10c, but the ceramic substrate 11 does not have to be exposed from the recess 10c. The raised portion 10d is composed of the glaze layer 13.

[0013] The main component of the constituent material of the ceramic substrate 11 and the main component of the constituent material of the ceramic layer 12 are ceramics. The main component refers to a component that accounts for more than 50 mass percent of the constituent material. The main component of the constituent material of the glaze layer 13 is glass. The thickness of the ceramic layer 12 is thickness T. The thickness T is preferably 30 μm or more. The thickness T may be, for example, 50 μm or less. The thickness T corresponds to the depth of the recess 10c.

[0014] The wiring layer 20 is disposed on the substrate 10. More specifically, the wiring layer 20 is disposed on the main surface 10a. The wiring layer 20 has a plurality of first wirings 21 and a plurality of second wirings 22. The main component of the constituent material of the wiring layer 20 is, for example, a metal material. Specific examples of the main component of the constituent material of the wiring layer 20 include, for example, gold or silver. The wiring layer 20 is, for example, a sintered body of gold particles or silver particles.

[0015] The multiple first wirings 21 are arranged at intervals along the first direction DR1. One end and the other end of the first wiring 21 are referred to as end 21a and end 21b, respectively. The end 21a extends along the second direction DR2 so as to reach a position overlapping with the raised portion 10d in a plan view. The end 21b forms a bonding pad.

[0016] The second wirings 22 are arranged at intervals along the first direction DR1. One end and the other end of the second wirings 22 are referred to as end 22a and end 22b, respectively. The second wirings 22 extend along the second direction DR2 so that the end 22a reaches a position where it overlaps with the raised portion 10d in a plan view, and the end 22b reaches the recessed portion 10c. The end 22a faces the end 21a at an interval in the second direction DR2 at a position where it overlaps with the raised portion 10d in a plan view.

[0017] The embedded wiring 30 is disposed in the recess 10c. As described above, the second wiring 22 extends so that the end 22b reaches the recess 10c, and therefore the embedded wiring 30 is electrically connected to the end 22b (second wiring 22). The embedded wiring 30 and the multiple second wirings 22 constitute a common electrode of the thermal printhead 100. On the other hand, each of the multiple first wirings 21 constitutes an individual electrode of the thermal printhead 100. The main component of the material constituting the embedded wiring 30 is, for example, a metal material. A specific example of the main component of the material constituting the embedded wiring 30 is silver. The embedded wiring 30 is, for example, a sintered body of silver particles. The electrical resistance value of the common electrode of the thermal printhead 100 is preferably 100 mΩ or less.

[0018] The resistor 40 extends along the first direction DR1. The resistor 40 is disposed on the main surface 10a while overlapping the end 21a and the end 22a. More specifically, the resistor 40 is disposed on the protruding portion 10d (the glaze layer 13) while overlapping the end 21a and the end 22a. This allows electrical connection between the adjacent end 21a and the end 22a. It is preferable that the height difference between the resistor 40 and the embedded wiring 30, that is, the distance DIS between the surface of the resistor 40 and the surface of the embedded wiring 30, is a negative value. From another perspective, it is preferable that the surface of the embedded wiring 30 is lower than the surface of the resistor 40. The main component of the constituent material of the resistor 40 is a conductive material. The resistor 40 is, for example, a sintered body of ruthenium oxide particles.

[0019] The protective layer 50 is disposed on the substrate 10 (principal surface 10a) so as to cover the wiring layer 20 and the resistor 40. However, the end 21b is exposed from the protective layer 50. The main component of the material constituting the protective layer 50 is, for example, glass. The protective layer 60 is disposed on the substrate 10 so as to cover the embedded wiring 30. The material constituting the protective layer 60 is, for example, a resin material.

[0020] (Operation of thermal print head 100) The operation of the thermal printhead 100 will now be described.

[0021] In the thermal printhead 100, a predetermined potential is applied to the embedded wiring 30 and the multiple second wirings 22. In the thermal printhead 100, a potential is individually supplied to each of the multiple first wirings 21 at the end 21b of each of the multiple first wirings 21 from a driver IC (Integrated Circuit). As a result, a current flows through a portion of the resistor 40 connecting one end 21a to which the individual potential is applied and an end 22a facing the one end 21a, the portion generates heat, and the heat is transferred to the paper in contact with the protective layer 50 above the portion. In this manner, the thermal printhead 100 prints on the paper.

[0022] (Modification) Modifications will be described below.

[0023] The thermal printhead according to the modified example is referred to as thermal printhead 100A. Fig. 3 is a plan view of thermal printhead 100A. Note that protective layers 50 and 60 are omitted from Fig. 3. As shown in Fig. 3, thermal printhead 100A has a substrate 10, a wiring layer 20, embedded wiring 30, a resistor 40, and protective layers 50 and 60. In this respect, the configuration of thermal printhead 100A is common to the configuration of thermal printhead 100.

[0024] In the thermal printhead 100A, the ends 21a and 22a are arranged alternately in the first direction DR1. That is, in the thermal printhead 100A, the ends 21a and 22a face each other with a gap therebetween in the first direction DR1. In this respect, the configuration of the thermal printhead 100A differs from the configuration of the thermal printhead 100.

[0025] (Method of manufacturing the thermal printhead 100) A method for manufacturing the thermal printhead 100 will now be described.

[0026] Fig. 4 is a process diagram showing a manufacturing method of the thermal printhead 100. As shown in Fig. 4, the manufacturing method of the thermal printhead 100 includes a preparation step S1, a ceramic layer forming step S2, a glaze layer forming step S3, a wiring layer forming step S4, a resistor forming step S5, a first protective layer forming step S6, a buried wiring forming step S7, a second protective layer forming step S8, and a singulation step S9.

[0027] In the preparation step S1, a ceramic substrate 11 is prepared. After the preparation step S1, a ceramic layer forming step S2 is performed.

[0028] 5 is a cross-sectional view illustrating the ceramic layer forming step S2. As shown in FIG. 5, in the ceramic layer forming step S2, a ceramic layer 12 is formed on a ceramic substrate 11. In the ceramic layer forming step S2, first, a paste containing ceramic particles is applied onto the ceramic substrate 11. At this time, the paste is not applied to the positions that will become the recesses 10c. Second, the applied paste is fired. After the ceramic layer forming step S2, a glaze layer forming step S3 is performed.

[0029] FIG. 6 is a cross-sectional view illustrating the glaze layer forming step S3. In the glaze layer forming step S3, as shown in FIG. 6, a glaze layer 13 is formed on the ceramic layer 12. In the glaze layer forming step S3, first, a paste containing glass particles is applied onto the ceramic layer 12. Second, the applied paste is fired. The portion where the paste is not applied becomes a recess 10c. In this manner, the substrate 10 is formed. After the glaze layer forming step S3, the wiring layer forming step S4 is performed.

[0030] FIG. 7 is a cross-sectional view for explaining the wiring layer forming step S4. As shown in FIG. 7, in the wiring layer forming step S4, the wiring layer 20 is formed on the substrate 10 (main surface 10a). In the wiring layer forming step S4, first, a paste containing metal particles is applied onto the main surface 10a. Second, the applied paste is fired to form a metal layer. Third, the metal layer is patterned to form the wiring layer 20. The patterning is performed by etching using a resist pattern formed on the metal layer as a mask. The resist pattern is formed by applying a photoresist onto the metal layer and exposing and exposing the applied photoresist to light. After the wiring layer forming step S4, the resistor forming step S5 is performed.

[0031] Fig. 8 is a cross-sectional view for explaining the resistor forming step S5. As shown in Fig. 8, in the resistor forming step S5, the resistor 40 is formed on the glaze layer 13 so as to extend along the first direction DR1 while overlapping the end 21a and the end 22a. In the resistor forming step S5, first, a paste containing conductive particles is applied onto the glaze layer 13 along the first direction DR1 so as to overlap the end 21a and the end 22a. Second, the applied paste is fired to form the resistor 40. After the resistor forming step S5, the first protective layer forming step S6 is performed.

[0032] Fig. 9 is a cross-sectional view illustrating the first protective layer forming step S6. In the first protective layer forming step S6, as shown in Fig. 9, a protective layer 50 is formed on the substrate 10 (principal surface 10a) so as to cover the wiring layer 20 and the resistor 40. In the first protective layer forming step S6, first, a paste containing glass particles is applied onto the principal surface 10a so as to cover the wiring layer 20 and the resistor 40. Second, the applied paste is fired to form the protective layer 50. After the first protective layer forming step S6, an embedded wiring forming step S7 is performed.

[0033] Fig. 10 is a cross-sectional view illustrating the embedded wiring forming step S7. As shown in Fig. 10, in the embedded wiring forming step S7, the embedded wiring 30 is formed in the recess 10c. In the embedded wiring forming step S7, first, a paste containing metal particles is embedded in the recess 10c. Second, the above paste embedded in the recess 10c is fired to form the embedded wiring 30. After the embedded wiring forming step S7, a second protective layer forming step S8 is performed.

[0034] FIG. 11 is a cross-sectional view for explaining the second protective layer forming step S8. As shown in FIG. 11, in the second protective layer forming step S8, a protective layer 60 is formed on the substrate 10 so as to cover the embedded wiring 30. In the second protective layer forming step S8, first, a constituent material of the protective layer 60 is applied onto the substrate 10 so as to cover the embedded wiring 30. Second, the constituent material of the applied protective layer 60 is heated and cured to form the protective layer 60. After the second protective layer forming step S8, a singulation step S9 is performed. In the singulation step S9, the substrate 10, the protective layer 50, and the protective layer 60 are cut along the boundary of the thermal printhead 100. In the above manner, the structure of the thermal printhead 100 shown in FIG. 1 and FIG. 2 is formed.

[0035] (Effects of Thermal Print Head 100) The effects of the thermal printhead 100 will be described below in comparison with a comparative example. The thermal printhead according to the comparative example is referred to as a thermal printhead 200.

[0036] Fig. 12 is a plan view of the thermal printhead 200. Note that the protective layer 50 is omitted in Fig. 12. Fig. 13 is a cross-sectional view taken along line XIII-XIII in Fig. 12. As shown in Figs. 12 and 13, the thermal printhead 200 has a substrate 10, a wiring layer 20, a resistor 40, and a protective layer 50. In this regard, the configuration of the thermal printhead 200 is common to the configuration of the thermal printhead 100.

[0037] In the thermal printhead 200, the substrate 10 has a ceramic base material 11 and a glaze layer 14 disposed on the ceramic base material 11, and the main surface 10a is formed by the surface of the glaze layer 14. In the thermal printhead 200, the wiring layer 20 further has a third wiring 23. The third wiring 23 extends along the first direction DR1 and is connected to an end 22b. In the thermal printhead 200, the end 21a and the end 22a face each other with a gap therebetween in the first direction DR1.

[0038] The thermal printhead 200 does not have the recess 10c, the embedded wiring 30, or the protective layer 60, but does have a conductive layer 70. The conductive layer 70 is disposed on the third wiring 23. The multiple second wirings 22, the third wirings 23, and the conductive layer 70 form a common electrode of the thermal printhead 200. In the thermal printhead 200, the protective layer 50 further covers the conductive layer 70. In these respects, the configuration of the thermal printhead 200 differs from the configuration of the thermal printhead 100.

[0039] In the thermal printhead 200, the electrical resistance value of the common electrode is reduced by the conductive layer 70. However, as a result of arranging the conductive layer 70 on the wiring layer 20 (third wiring 23), the height difference between the common electrode and the resistor 40 becomes small, or the surface of the common electrode becomes higher than the surface of the resistor 40. Therefore, when attempting to bring the paper to be printed into contact with the protective layer 50 above the resistor 40, the paper may come into contact with the protective layer 50 above the common electrode.

[0040] On the other hand, in the thermal printhead 100, a recess 10c is formed in the main surface 10a, and the embedded wiring 30 that forms part of the common electrode is arranged in the recess 10c, so that it is possible to reduce the electrical resistance value of the common electrode (for example, to make the electrical resistance value of the common electrode 100 mΩ or less) without reducing the height difference between the common electrode (embedded wiring 30) and the resistor 40 (i.e., without the distance DIS becoming a positive value and the surface of the embedded wiring 30 becoming higher than the surface of the resistor 40).

[0041] In the thermal printhead 100, the recesses 10c can be made deeper by increasing the thickness T. For example, when the thickness T is 30 μm or more, it is possible to sufficiently reduce the electrical resistance value of the common electrode while ensuring the height difference between the common electrode and the resistor 40. When the raised portion 10d is further formed on the main surface 10a, the position of the resistor 40 becomes higher by the amount of the raised portion 10d, so that the height difference between the common electrode and the resistor 40 can be further ensured.

[0042] (Additional Note) The above embodiment includes the following configurations.

[0043] <Appendix 1> A substrate; A wiring layer; Buried wiring and and a resistor. The substrate has a main surface, A recess is formed in the main surface, The recess extends along a first direction in a plan view, the wiring layer includes a plurality of first wirings and a plurality of second wirings; one end of each of the first wirings and one end of each of the second wirings face each other in the first direction or in a second direction perpendicular to the first direction in a plan view; the buried wiring is buried in the recess and is electrically connected to the other end of each of the plurality of second wirings; A thermal printhead, wherein the resistor is arranged on the main surface so as to extend along the first direction while overlapping one end of each of the plurality of first wirings and one end of each of the plurality of second wirings.

[0044] <Appendix 2> The main surface further includes a raised portion. The raised portion extends along the first direction, A thermal printhead as described in Appendix 1, wherein one end of each of the multiple first wirings and one end of each of the multiple second wirings are located on the raised portion.

[0045] <Appendix 3> The substrate includes a ceramic substrate, a ceramic layer disposed on the ceramic substrate, and a glaze layer disposed on the ceramic layer; The main surface is composed of a surface of the ceramic layer and a surface of the glaze layer, The recess is provided in the ceramic layer, 3. The thermal printhead of claim 2, wherein the raised portion is composed of the glaze layer.

[0046] <Appendix 4> 4. The thermal printhead of claim 3, wherein the ceramic layer has a thickness of 30 μm or more.

[0047] <Appendix 5> 5. The thermal printhead of claim 1, wherein a surface of the embedded wiring is lower than a surface of the resistor.

[0048] <Appendix 6> the plurality of second wirings and the embedded wiring form a common electrode, 6. The thermal printhead according to claim 1, wherein the common electrode has an electrical resistance of 100 mΩ or less.

[0049] 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]

[0050] 10 substrate, 10a main surface, 10b main surface, 10c recess, 10d protrusion, 11 ceramic base material, 12 ceramic layer, 13 glaze layer, 14 glaze layer, 20 wiring layer, 21 first wiring, 21a, 21b end, 22 second wiring, 22a, 22b end, 23 third wiring, 30 wiring, 40 resistor, 50, 60 protective layer, 70 conductive layer, 100, 100A, 200 thermal print head, DIS distance, DR1 first direction, DR2 second direction, S1 preparation step, S2 ceramic layer forming step, S3 glaze layer forming step, S4 wiring layer forming step, S5 resistor forming step, S6 first protective layer forming step, S7 buried wiring forming step, S8 second protective layer forming step, S9 singulation step, T thickness.

Claims

1. A substrate; A wiring layer; Buried wiring and and a resistor. The substrate has a main surface, A recess is formed in the main surface, The recess extends along a first direction in a plan view, the wiring layer includes a plurality of first wirings and a plurality of second wirings; one end of each of the first wirings and one end of each of the second wirings face each other in the first direction or in a second direction perpendicular to the first direction in a plan view; the buried wiring is buried in the recess and is electrically connected to the other end of each of the plurality of second wirings; A thermal printhead, wherein the resistor is arranged on the main surface so as to extend along the first direction while overlapping one end of each of the plurality of first wirings and one end of each of the plurality of second wirings.

2. The main surface further includes a raised portion. The raised portion extends along the first direction, The thermal printhead of claim 1 , wherein one end of each of the plurality of first wirings and one end of each of the plurality of second wirings are on the raised portion.

3. The substrate includes a ceramic substrate, a ceramic layer disposed on the ceramic substrate, and a glaze layer disposed on the ceramic layer; The main surface is composed of a surface of the ceramic layer and a surface of the glaze layer, The recess is provided in the ceramic layer, The thermal printhead of claim 2 , wherein the raised portion is comprised of the glaze layer.

4. The thermal printhead of claim 3 , wherein the ceramic layer has a thickness of 30 μm or more.

5. 5. The thermal printhead according to claim 1, wherein a surface of the buried wiring is lower than a surface of the resistor.

6. The plurality of second wirings and the embedded wiring f form a common electrode, 5. The thermal printhead according to claim 1, wherein the common electrode has an electrical resistance value of 100 m[Omega] or less.

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