Thermal print head and manufacturing method of thermal print head
By adding the wiring material, such as silver or copper, to the glaze and protective layers in thermal print heads, the thermal print heads effectively reduce wiring defects and disconnections, addressing the diffusion issues in existing technologies.
Patent Information
- Application Number
- JP2023206385
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-12-06
- Publication Date
- 2025-06-18
AI Technical Summary
Existing thermal print heads face defects and disconnection issues in the wiring due to diffusion of metal materials from the wiring into the glaze and protective layers during manufacturing, especially when the wiring thickness is reduced or when using silver as the metal material.
Incorporating the constituent material of the wiring layer, such as silver or copper, into the glaze and protective layers, either as dispersed particles or dissolved in the glass, to create a concentration gradient that suppresses diffusion and reduces the likelihood of wiring defects.
This approach effectively suppresses the diffusion of metal materials from the wiring into the glaze and protective layers, reducing defects and disconnections in the wiring, even at thinner thicknesses and with cost-effective metal materials like silver.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a thermal print head and a method for manufacturing the thermal print head.
Background Art
[0002] Japanese Patent Application Laid-Open No. 2023-115544 (Patent Document 1) describes a thermal print head. The thermal print head described in Patent Document 1 includes a substrate, a glaze layer, wirings, and a protective film. The substrate has a main surface. The glaze layer is disposed on the main surface of the substrate. The wirings are disposed on the glaze layer. The protective film is disposed on the glaze layer so as to cover the wirings. The constituent material of the glaze layer and the constituent material of the protective film contain glass. The constituent material of the wirings is a metal material.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
[0004] The thermal print head of the present disclosure includes a substrate, a glaze layer disposed on the substrate, a wiring layer disposed on the glaze layer, and a protective layer disposed on the glaze layer so as to cover the wirings. At least one of the constituent material of the protective layer and the constituent material of the glaze layer is glass added with the constituent material of the wiring layer.
Brief Description of the Drawings
[0005]
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[0006] [Detailed Description] Details of the embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions will not be repeated. The thermal print head according to the embodiment is referred to as the thermal print head 100.
[0007] (Configuration of Thermal Print Head 100) The configuration of the thermal print head 100 will be described below.
[0008] FIG. 1 is a plan view of the thermal print head 100. In FIG. 1, the illustration of 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 print head 100 includes a substrate 10, a glaze layer 20, a wiring layer 30, a heating element 40, and a protective layer 50.
[0009] The substrate 10 has a main surface 10a and a main surface 10b. The main surface 10b is the opposite surface of the main surface 10a. The main surface 10a and the main surface 10b are end faces in the thickness direction of the substrate 10. The main component of the constituent material of the substrate 10 is a ceramic such as alumina (Al2O3), for example. The main component is a component that occupies more than 50 mass percent in the constituent material.
[0010] The glaze layer 20 is disposed on the substrate 10. 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. 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.
[0011] The common electrode 31 has a strip portion 31a and a plurality of protruding portions 31b. The strip portion 31a extends along the first direction DR1 in a plan view. The plan view refers to the case of viewing the thermal print head 100 along the normal direction of the main surface 10a. The protruding portion 31b protrudes from the strip portion 31a along the second direction DR2 in a plan view. The second direction DR2 is a direction perpendicular to the first direction DR1. More specifically, the protruding portion 31b protrudes from the side of the strip portion 31a extending along the first direction DR1. The plurality of protruding portions 31b are arranged at intervals along the first direction DR1.
[0012] The plurality of individual electrodes 32 are arranged at intervals along the first direction DR1 in a plan view. The individual electrode 32 has a tip portion 32a at one end and a bonding pad 32b at the other end. The tip portion 32a extends along the second direction DR2 in a plan view. The protruding portion 31b and the tip portion 32a are alternately arranged at intervals along the first direction DR1 in a plan view.
[0013] The main component of the constituent material of the wiring layer 30 is a metal material. Specific examples of the metal material constituting the wiring layer 30 include silver (Ag). The wiring layer 30 is formed of, for example, a sintered body containing a plurality of silver particles. However, the constituent material of the wiring layer 30 is not limited to this. The main component of the constituent material of the wiring layer 30 may be copper (Cu) or gold (Au).
[0014] Let the thickness of the wiring layer 30 be thickness T. The thickness T is preferably 1.5 μm or less. The portion of the wiring layer 30 covered by the protective layer 50 with the narrowest width is defined as the narrowest portion. The width of the wiring layer 30 at the narrowest portion is, for example, 20 μm or less. The width of the wiring layer 30 at the narrowest portion may be 15 μm or less. Note that the narrowest portion is, for example, at the tip portion 32a.
[0015] The heating element 40 extends along the first direction DR1 in a plan view. The heating element 40 is disposed on the glaze layer 20 while overlapping the protruding portion 31b and the tip portion 32a. Thereby, the adjacent protruding portion 31b and the tip portion 32a in the first direction DR1 are electrically connected to each other. The heating element 40 is formed of, for example, a sintered body containing ruthenium oxide (RuO2) particles.
[0016] The protective layer 50 is disposed on the glaze layer 20 so as to cover the wiring layer 30 and the heating element 40. However, the bonding pad 32b is exposed from the protective layer 50. The main component of the constituent material of the protective layer 50 is glass. The constituent material of the wiring layer 30 (silver in the above example) is added to the constituent material of the protective layer 50. For example, particles containing the constituent material of the wiring layer 30 are dispersed in the protective layer 50. Further, the constituent material of the wiring layer 30 may be dissolved in the glass contained in the protective layer 50.
[0017] When the constituent material of the wiring layer 30 is dissolved in the glass contained in the protective layer 50, the content of the constituent material of the wiring layer 30 in the glass is preferably 4 mass percent or more and preferably 25 mass percent or less. The content of the constituent material of the wiring layer 30 in the glass contained in the protective layer 50 is measured using an elemental analyzer (SEM-EDX) at a position where the distance from the interface between the wiring layer 30 and the protective layer 50 in the thickness direction of the protective layer 50 becomes a predetermined value. This predetermined value is, for example, 2 μm when the thickness of the protective layer 50 is 4 μm, and 5 μm when the thickness of the protective layer 50 is 8 μm.
[0018] <Modification example> In the above, an example in which the constituent material of the wiring layer 30 is added to the protective layer 50 has been described. However, the constituent material of the wiring layer 30 may be added to the glaze layer 20 or may be added to both the protective layer 50 and the glaze layer 20. When the constituent material of the wiring layer 30 is added to the glaze layer 20, the constituent material of the wiring layer 30 may be added as particles dispersed in the glaze layer 20 or may be added in a form dissolved in the glass constituting the glaze layer 20. When the constituent material of the wiring layer 30 is added to the glaze layer 20 in a form dissolved in the glass, the content of the constituent material of the wiring layer 30 in the glass is preferably 4 mass percent or more and preferably 25 mass percent or less. The content of the constituent material of the wiring layer 30 in the glass contained in the glaze layer 20 is measured using an elemental analyzer at a position where the distance from the interface between the wiring layer 30 and the glaze layer 20 in the thickness direction of the glaze layer 20 becomes a predetermined value. Note that this predetermined value is, for example, 50 μm when the thickness of the glaze layer 20 is 100 μm, and 100 μm when the thickness of the glaze layer 20 is 200 μm.
[0019] (Method for manufacturing the thermal print head 100) Hereinafter, a method for manufacturing the thermal print head 100 will be described.
[0020] FIG. 4 is a process diagram showing a method for manufacturing the thermal print head 100. As shown in FIG. 4, the method for manufacturing the thermal print head 100 includes a preparation step S1, a glaze layer formation step S2, a metal layer formation step S3, a patterning step S4, a heating element formation step S5, a protective layer formation step S6, and a singulation step S7.
[0021] The glaze layer formation step S2 is performed after the preparation step S1. The metal layer formation step S3 is performed after the glaze layer formation step S2. The patterning step S4 is performed after the metal layer formation step S3. The heating element formation step S5 is performed after the patterning step S4. The protective layer formation step S6 is performed after the heating element formation step S5. The singulation step S7 is performed after the protective layer formation step S6.
[0022] In the preparation step S1, the substrate 10 is prepared. FIG. 5 is a cross-sectional view for explaining the glaze layer formation step S2. As shown in FIG. 5, in the glaze layer formation step S2, the glaze layer 20 is formed on the main surface 10a. The glaze layer 20 is formed by applying a paste containing glass to the main surface 10a and firing the applied paste. When the constituent material of the wiring layer 30 is added as particles to the glaze layer 20, the particles formed of the constituent material of the wiring layer 30 are mixed into the above paste. When the constituent material of the wiring layer 30 is added in a form dissolved in glass to the glaze layer 20, the constituent material of the wiring layer 30 is previously dissolved in the glass contained in the above paste.
[0023] FIG. 6 is a cross-sectional view for explaining the metal layer forming step S3. As shown in FIG. 6, in the metal layer forming step S3, a metal layer 33 is formed on the glaze layer 20. The metal layer 33 is formed by applying a paste containing particles formed of the constituent material of the wiring layer 30 onto the glaze layer 20 and firing the applied paste. FIG. 7 is a cross-sectional view for explaining the patterning step S4. As shown in FIG. 7, in the patterning step S4, the wiring layer 30 is formed by patterning the metal layer 33. The metal layer 33 is patterned by etching using a resist pattern formed on the metal layer 33 as a mask. The resist pattern is formed by applying a photoresist onto the metal layer 33 and exposing and developing the applied photoresist.
[0024] FIG. 8 is a cross-sectional view for explaining the heating element forming step S5. As shown in FIG. 8, in the heating element forming step S5, a heating element 40 is formed on the glaze layer 20 so as to overlap the protruding portion 31b and the tip portion 32a and extend along the first direction DR1 in a plan view. The heating element 40 is formed by applying a paste containing ruthenium oxide particles and firing the applied paste.
[0025] FIG. 9 is a cross-sectional view for explaining the protective layer forming step S6. As shown in FIG. 9, in the protective layer forming step S6, a protective layer 50 is formed. The protective layer 50 is formed by applying a paste containing glass onto the glaze layer 20 so as to cover the wiring layer 30 and the heating element 40 and firing the applied paste. When adding the constituent material of the wiring layer 30 as particles to the protective layer 50, the particles formed of the constituent material of the wiring layer 30 are mixed into the above paste. When adding the constituent material of the wiring layer 30 in a form dissolved in the glass to the protective layer 50, the constituent material of the wiring layer 30 is previously dissolved in the glass contained in the above paste.
[0026] In the individual piece separation process S7, the substrate 10, the glaze layer 20, and the protective layer 50 are cut, whereby a plurality of thermal print heads 100 are obtained. Thus, the structure of the thermal print head 100 shown in FIGS. 1 to 3 is formed.
[0027] (Effect of Thermal Print Head 100) The effects of the thermal print head 100 will be described below.
[0028] The thermal print head according to the comparative example is designated as thermal print head 200. FIG. 10 is a cross-sectional view of the thermal print head 200. As shown in FIG. 10, the thermal print head 200 has a glaze layer 21 instead of the glaze layer 20 and a protective layer 51 instead of the protective layer 50. The constituent materials of the wiring layer 30 are not added to the glaze layer 21 and the protective layer 51. Except for these points, the configuration of the thermal print head 200 is common to the configuration of the thermal print head 100.
[0029] When the paste containing glass is fired to form the protective layer 51, the constituent materials of the wiring layer 30 diffuse into the protective layer 51. Similarly, due to the heating when forming the metal layer 33 and the heating when forming the protective layer 51, the constituent materials of the wiring layer 30 diffuse into the glaze layer 21. As a result of the above-mentioned diffusion, a defect may occur in the wiring layer 30 (see the portion surrounded by the dotted line in FIG. 10).
[0030] From the viewpoint of efficiently utilizing the heat generated in the heating element 40, the thickness T may be reduced. However, when the thickness T becomes small (for example, when the thickness T becomes 1.5 μm or less), the defect in the wiring layer 30 tends to progress, and the wiring layer 30 may be disconnected. Also, in order to reduce the manufacturing cost, the constituent material of the wiring layer 30 may be switched from gold to silver. However, since silver diffuses more easily into glass than gold, when silver is used as the constituent material of the wiring layer 30, the defect in the wiring layer 30 tends to progress.
[0031] Even in the thermal print head 100, heating is performed to form the protective layer 50. However, since the constituent material of the wiring layer 30 is added to the protective layer 50, the concentration gradient of the constituent material of the wiring layer 30 between the wiring layer 30 and the protective layer 50 becomes small, making it difficult for the constituent material of the wiring layer 30 to diffuse from the wiring layer 30 to the protective layer 50, and making it less likely for the wiring layer 30 to be damaged. Similarly, when the constituent material of the wiring layer 30 is added to the glaze layer 20 as well, the diffusion of the constituent material of the wiring layer 30 into the glaze layer 20 is also suppressed, resulting in the wiring layer 30 being even less likely to be damaged.
[0032] When the constituent material of the wiring layer 30 contains silver or copper, the manufacturing cost of the thermal print head 100 can be reduced compared to the case where the constituent material of the wiring layer 30 contains gold. When the constituent material of the wiring layer 30 is silver, the diffusion of the constituent material of the wiring layer 30 into the protective layer 50 and the glaze layer 20 becomes significant. However, in the thermal print head 100, even when the constituent material of the wiring layer 30 is silver, the diffusion into the protective layer 50 and the glaze layer 20 can be sufficiently suppressed. Also, when the thickness T is 1.5 μm or less, heat dissipation from the heating element 40 through the wiring layer 30 is suppressed, but the wiring layer 30 is likely to break. In the thermal print head 100, even when the thickness T is 1.5 μm or less, the occurrence of disconnection of the wiring layer 30 can be suppressed.
[0033] If the content of the constituent material of the wiring layer 30 in the glass contained in the protective layer 50 or the glaze layer 20 is too small, the effect of suppressing the diffusion of the constituent material of the wiring layer 30 becomes poor. Therefore, by setting the content of the constituent material of the wiring layer 30 in the glass contained in the protective layer 50 or the glaze layer 20 to 4 mass% or more, it is possible to more reliably suppress the diffusion of the constituent material of the wiring layer 30. If the content of the constituent material of the wiring layer 30 in the glass contained in the protective layer 50 or the glaze layer 20 is too large, the protective layer 50 and the glaze layer 20 may exhibit conductivity and may not be able to perform their original functions. Therefore, by setting it to 25 mass% or less, it is possible to more reliably ensure the electrical insulation of the protective layer 50 and the glaze layer 20.
[0034] (Supplementary Note) Embodiments of the present disclosure include the following configurations.
[0035] <Supplementary Note 1> A substrate, A glaze layer disposed on the substrate, A wiring layer disposed on the glaze layer, And a protective layer disposed on the glaze layer so as to cover the wiring layer, A thermal print head, wherein at least one of the constituent material of the protective layer and the constituent material of the glaze layer is glass to which the constituent material of the wiring layer is added.
[0036] <Supplementary Note 2> The thermal print head according to Supplementary Note 1, wherein the constituent material of the protective layer is glass to which the constituent material of the wiring layer is added.
[0037] <Supplementary Note 3> The thermal print head according to Supplementary Note 2, wherein particles containing the constituent material of the wiring layer are dispersed in the glass in the protective layer.
[0038] <Supplementary Note 4> The thermal print head according to Supplementary Note 2, wherein the constituent material of the wiring layer is dissolved in the glass in the protective layer, and the concentration of the constituent material of the wiring layer in the glass is 4 mass percent or more.
[0039] <Supplementary Note 5> The thermal print head according to any one of Supplementary Notes 1 to 4, wherein the thickness of the wiring layer is 1.5 μm or less.
[0040] <Supplementary Note 6> The thermal print head according to any one of Supplementary Notes 1 to 5, wherein the constituent material of the wiring layer is silver.
[0041] <Supplementary Note 7> The constituent material of the wiring layer is copper, the thermal print head according to any one of Appendices 1 to 5.
[0042] <Appendix 8> A step of preparing a substrate, A step of forming a glaze layer on the substrate, A step of forming a wiring layer on the glaze layer, A step of forming a protective layer on the glaze layer so as to cover the wiring layer, and A method of manufacturing a thermal print head, wherein at least one of the constituent material of the protective layer and the constituent material of the glaze layer is glass added with the constituent material of the wiring layer.
[0043] Although the embodiments of the present disclosure have been described as above, it is also possible to variously modify the above-described embodiments. Further, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.
Explanation of Reference Numerals
[0044] 10 Substrate, 10a Main surface, 10b Main surface, 20 Glaze layer, 21 Glaze layer, 30 Wiring layer, 31 Common electrode, 31a Strip portion, 31b Protrusion portion, 32 Individual electrode, 32a Tip portion, 32b Bonding pad, 33 Metal layer, 40 Heating element, 50, 51 Protective layer, 100, 200 Thermal print head, DR1 First direction, DR2 Second direction, S1 Preparation step, S2 Glaze layer formation step, S3 Metal layer formation step, S4 Patterning step, S5 Heating element formation step, S6 Protective layer formation step, S7 Singulation step, T Thickness.
Claims
1. A substrate, A glaze layer disposed on the substrate, A wiring layer disposed on the glaze layer, And a protective layer disposed on the glaze layer so as to cover the wiring layer, The thermal print head, wherein at least one of the constituent material of the protective layer and the constituent material of the glaze layer is glass added with the constituent material of the wiring layer.
2. The thermal print head according to claim 1, wherein the constituent material of the protective layer is glass added with the constituent material of the wiring layer.
3. The thermal print head according to claim 2, wherein in the protective layer, particles containing the constituent material of the wiring layer are dispersed in the glass.
4. The thermal print head according to claim 2, wherein in the protective layer, the constituent material of the wiring layer is dissolved in the glass, and the concentration of the constituent material of the wiring layer in the glass is 4 mass% or more.
5. The thermal print head according to claim 1, wherein the thickness of the wiring layer is 1.5 μm or less.
6. The thermal print head according to any one of claims 1 to 5, wherein the constituent material of the wiring layer is silver.
7. The thermal print head according to any one of claims 1 to 5, wherein the constituent material of the wiring layer is copper.
8. A step of preparing a substrate, A step of forming a glaze layer on the substrate, A step of forming a wiring layer on the glaze layer, And a step of forming a protective layer on the glaze layer so as to cover the wiring layer. A method for manufacturing a thermal print head, wherein at least one of the constituent materials of the protective layer and the constituent materials of the glaze layer is glass to which the constituent materials of the wiring layer are added.
Citation Information
Patent Citations
Thermal print head, thermal printer and manufacturing method of thermal print head
JP2023115544A