Thermal print head

Abstract

To provide a thermal print head capable of preventing a print medium from being damaged during printing.SOLUTION: The thermal print head 1 includes a substrate 10, a wiring layer 20, a heating resistor 30, and a protective layer 33. The wiring layer 20 includes gold wiring portions (the plurality of strip portions 22 and the first individual wiring portions 26) and silver wiring portions (the coupling portion 23, the detour portion 24, and the second individual wiring portion 27). The protective layer 33 includes a first layer 34 constituting the outermost surface of the protective layer 33. The first layer 34 contains glass and boron nitride particles dispersed in the glass. In the plan view of the main surface 10a, the first layer 34 overlaps the heating resistor 30 and is shifted from the silver wire portion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open Publication No. 2023-176504 (Patent Document 1) discloses a thermal printhead including a substrate, a resistor layer disposed on the substrate, a wiring layer electrically connected to the resistor layer, and a protective layer covering the resistor layer. The protective layer contains glass and additive particles. The additive particles include boron nitride particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-176504

[0004] [overview] An object of the present disclosure is to provide a thermal printhead that can prevent damage to a print medium during printing.

[0005] The thermal printhead of the present disclosure includes a substrate having a main surface, a wiring layer disposed on the main surface, a heating resistor, and a protective layer covering the wiring layer and the heating resistor. The wiring layer includes a gold wiring portion connected to the heating resistor and a silver wiring portion connected to the gold wiring portion. The protective layer includes a first layer constituting the outermost surface of the protective layer. The first layer includes glass and boron nitride particles dispersed in the glass. In a plan view of the main surface, the first layer overlaps the heating resistor and is offset from the silver wiring portion. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic plan view of a thermal printhead according to an embodiment. [Figure 2] FIG. 2 is a schematic enlarged cross-sectional view of the thermal printhead according to the embodiment taken along the cross-sectional line II-II shown in FIG. [Figure 3] FIG. 3 is a schematic partially enlarged plan view of the thermal printhead according to the embodiment. [Figure 4] FIG. 4 is a flowchart illustrating an example of a method for manufacturing a thermal printhead according to an embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view of a thermal printer including a thermal printhead according to an embodiment. [Figure 6] FIG. 6 is a schematic plan view of a thermal printhead of a comparative example. [Figure 7] FIG. 7 is a schematic enlarged cross-sectional view of the thermal printhead of the comparative example taken along the cross-sectional line VI-VI shown in FIG. [Figure 8] FIG. 8 is a partial enlarged photograph of the outermost surface of the protective layer on the connecting portion of the heating resistor and the common wiring in the thermal printhead of the comparative example. [Figure 9] FIG. 9 is a partial enlarged photograph of the outermost surface of the protective layer on the first planarizing layer in the thermal printhead of the comparative example. [Figure 10] FIG. 10 is a partially enlarged photograph of the outermost surface of the protective layer on the connecting portion of the heating resistor and the common wiring in the thermal printhead of the example. [Figure 11] FIG. 11 is a partial enlarged photograph of the outermost surface of the protective layer on the first planarizing layer in the thermal printhead of the example.

[0007] [Detailed explanation] The 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 designated by the same reference numerals, and the description thereof will not be repeated. At least some of the configurations of the embodiments described below may be combined in any manner.

[0008] A thermal printhead 1 according to an embodiment will be described with reference to Figures 1 to 3. The thermal printhead 1 mainly comprises a substrate 10, a glaze 11, a planarizing layer 15, a wiring layer 20, a heating resistor 30, a protective layer 33, a driving IC 40, and a sealing member 43.

[0009] 1 and 2, the substrate 10 is a ceramic substrate such as an alumina substrate. The substrate 10 has a main surface 10a. In a plan view of the main surface 10a (hereinafter simply referred to as "plan view"), the longitudinal direction of the substrate 10 is the main scanning direction X, the lateral direction of the substrate 10 is the sub-scanning direction Y, and the thickness direction of the substrate 10 is the plate thickness direction Z. The plate thickness direction Z is perpendicular to the main scanning direction X and the sub-scanning direction Y. In the plan view, the sub-scanning direction Y is the transport direction of a print medium 47 (see FIG. 5) such as thermal recording paper.

[0010] 1 to 3, glaze 11 is disposed on main surface 10a of substrate 10. Glaze 11 is formed of, for example, a glass material such as amorphous glass. The thermal conductivity of glaze 11 may be lower than that of substrate 10. The softening point of glaze 11 is, for example, not lower than 800°C and not higher than 850°C. Glaze 11 is provided on a portion of main surface 10a of substrate 10. In other words, glaze 11 is a so-called partial glaze. Glaze 11 includes heater glaze 12 and die bonding glaze 13.

[0011] 1 to 3, the heater glaze 12 extends in the main scanning direction X in a plan view of the main surface 10a and has a band shape. The heater glaze 12 is disposed between the heating resistor 30 and the substrate 10. The heater glaze 12 prevents heat from the heating resistor 30 from dissipating to the substrate 10. The heater glaze 12 is a heat storage layer. The heater glaze 12 protrudes from a portion of the main surface 10a. The heater glaze 12 is provided to increase the height of the heating resistor 30 from the main surface 10a and press the heating resistor 30 against the print medium 47 (see FIG. 5).

[0012] 1 and 2, the die bonding glaze 13 is disposed upstream of and spaced apart from the heater glaze 12 in the sub-scanning direction Y. In a plan view of the main surface 10a, the die bonding glaze 13 extends in the main scanning direction X and has a band shape. The die bonding glaze 13 supports a part of the wiring layer 20 and the driving IC 40.

[0013] 1 to 3, the planarization layer 15 is disposed on the main surface 10a of the substrate 10. The thickness of the planarization layer 15 is smaller than the thickness of the glaze 11. The planarization layer 15 can prevent disconnections in the wiring layer 20 due to roughness of the main surface 10a of the substrate 10 and steps between the main surface 10a and the glaze 11. The planarization layer 15 is formed of, for example, glass. The planarization layer 15 includes a first planarization layer 16 and a second planarization layer 17. The first planarization layer 16 is disposed between the heater glaze 12 and the die bonding glaze 13 in a plan view of the main surface 10a. The second planarization layer 17 is disposed on the opposite side of the heater glaze 12 from the first planarization layer 16 in the sub-scanning direction Y.

[0014] 1 to 3, the wiring layer 20 is disposed on the main surface 10a of the substrate 10. Specifically, the wiring layer 20 is disposed on the glaze 11 and the planarization layer 15. The wiring layer 20 forms a conductive path for supplying current to the heating resistor 30. The wiring layer 20 includes gold wiring portions (e.g., a plurality of strip portions 22 and a first individual wiring portion 26) connected to the heating resistor 30, and silver wiring portions (e.g., a connecting portion 23, a detour portion 24, and a second individual wiring portion 27) connected to the gold wiring portions. The wiring layer 20 includes a common wiring 21 and a plurality of individual wirings 25.

[0015] The common wiring 21 is disposed on the glaze 11 and the planarization layer 15. The common wiring 21 includes a plurality of strip-shaped portions 22, a connecting portion 23, and a detour portion 24.

[0016] The plurality of strip-shaped portions 22 are connected to the heating resistor 30. The plurality of strip-shaped portions 22 are arranged on the heater glaze 12 and the second planarizing layer 17. Each of the plurality of strip-shaped portions 22 extends in the sub-scanning direction Y. The plurality of strip-shaped portions 22 are arranged at equal pitches in the main scanning direction X. The plurality of strip-shaped portions 22 are gold (Au) wiring and are formed from a gold particle sintered body.

[0017] The connecting portions 23 are disposed on the second planarizing layer 17. The connecting portions 23 extend in the main scanning direction X. The connecting portions 23 are connected to the plurality of strip-shaped portions 22 and connect the plurality of strip-shaped portions 22. The connecting portions 23 are silver (Ag) wiring and are formed from a silver particle sintered body.

[0018] The detour portion 24 is disposed on the planarizing layer 15, the heater glaze 12, and the die bonding glaze 13. The detour portion 24 is connected to the connecting portion 23. The detour portion 24 extends from both ends of the connecting portion 23 in the main scanning direction X to the upstream side in the sub-scanning direction Y so as to detour around the multiple individual wirings 25. The detour portion 24 is, for example, a silver (Ag) wiring and is formed from a silver particle sintered body. Because the connecting portion 23 and the detour portion 24 contain silver (Ag) rather than gold (Au) as the main component, the cost of the thermal printhead 1 can be reduced.

[0019] The plurality of individual wirings 25 are disposed on the glaze 11 and the first planarization layer 16. Each of the plurality of individual wirings 25 includes a first individual wiring portion 26 and a second individual wiring portion 27.

[0020] The first individual wiring portion 26 is connected to the heating resistor 30. The first individual wiring portion 26 is disposed on the heater glaze 12 and the first planarizing layer 16. The first individual wiring portion 26 is a gold (Au) wiring and is formed from a gold particle sintered body.

[0021] The second individual wiring portion 27 is connected to the first individual wiring portion 26. The second individual wiring portion 27 is disposed on the heater glaze 12, the die bonding glaze 13, and the first planarizing layer 16. The second individual wiring portion 27 is a silver (Ag) wiring and is formed of a silver particle sintered body.

[0022] 1 to 3, the heating resistor 30 is disposed on the heater glaze 12 (more specifically, on the top of the heater glaze 12). The heating resistor 30 extends in the main scanning direction X and has a strip shape in plan view. The heating resistor 30 protrudes from the glaze 11 (more specifically, the heater glaze 12) on the side opposite to the substrate 10.

[0023] The heating resistor 30 is connected to the wiring layer 20. Specifically, the heating resistor 30 is connected to the plurality of strip portions 22 and the plurality of first individual wiring portions 26. In a plan view, the heating resistor 30 is arranged so as to intersect with the plurality of strip portions 22 and the first individual wiring portions 26. The heating resistor 30 is formed so as to straddle the plurality of strip portions 22 and the plurality of first individual wiring portions 26. With reference to FIG. 3 , the portion of the heating resistor 30 sandwiched between the strip portions 22 and the first individual wiring portions 26 in the main scanning direction X is a heating portion 31. The heating portion 31 is a portion that generates heat when the heating resistor 30 is partially energized. Heat generated by the heating portion 31 causes printing on a print medium 47 (see FIG. 5 ).

[0024] 1 and 2, the protective layer 33 covers the heating resistor 30 and protects the heating resistor 30. The protective layer 33 covers the wiring layer 20 and protects the wiring layer 20. The protective layer 33 includes a first layer 34. The first layer 34 constitutes the outermost surface of the protective layer 33. During printing using the thermal printhead 1, the outermost surface of the first layer 34 may come into contact with the print medium 47 (see FIG. 5). The protective layer 33 may further include a second layer 35. The protective layer 33 may be a laminate of the first layer 34 and the second layer 35.

[0025] The second layer 35 is an insulating layer. The second layer 35 includes glass, such as amorphous glass. The second layer 35 does not include boron nitride particles. The second layer 35 may include additives, such as alumina particles. The softening point of the second layer 35 is higher than that of the first layer 34 and lower than that of the glaze 11. The softening point of the second layer 35 is, for example, approximately 780 degrees Celsius.

[0026] The second layer 35 is formed on the heating resistor 30 and covers the heating resistor 30. The second layer 35 is formed on the common wiring 21 and the plurality of individual wirings 25 and covers the common wiring 21 and the plurality of individual wirings 25. Specifically, the second layer 35 is formed on the plurality of strip-shaped portions 22, the connecting portion 23, the detour portion 24, the plurality of first individual wiring portions 26, and the plurality of second individual wiring portions 27 and covers the plurality of strip-shaped portions 22, the connecting portion 23, the detour portion 24, the plurality of first individual wiring portions 26, and the plurality of second individual wiring portions 27. In a plan view of the main surface 10a of the substrate 10, the second layer 35 overlaps the plurality of strip-shaped portions 22, the connecting portion 23, the detour portion 24, the plurality of first individual wiring portions 26, and the plurality of second individual wiring portions 27. The second layer 35 is disposed between the heating resistor 30 and the first layer 34.

[0027] The second layer 35 may be a laminate of an insulating layer and a conductive layer. The insulating layer covers the heating resistor 30 and is disposed between the heating resistor 30 and the conductive layer. The conductive layer is formed on the insulating layer. The conductive layer includes glass and conductive particles dispersed in the glass. The conductive particles may be, for example, ruthenium oxide (RuO2) particles. When the second layer 35 includes a conductive layer, the second layer 35 can be prevented from being charged due to static electricity generated by contact between the print medium 47 and the first layer 34. This can prevent deterioration of the heating resistor 30 and electrical breakdown of the drive IC 40 due to charging of the second layer 35.

[0028] The first layer 34 is, for example, an insulating layer. The first layer 34 includes glass, such as amorphous glass, and boron nitride particles dispersed in the glass. The first layer 34 may further include alumina particles dispersed in the glass. The glass is, for example, lead-free glass (i.e., glass that does not contain lead oxide). The content of the boron nitride particles in the first layer 34 is, for example, 5% by weight or more and 70% by weight or less. The particle diameter of the boron nitride particles is equal to or less than the thickness of the first layer 34. The particle diameter of the boron nitride particles is, for example, 4 μm or less. The content of the alumina particles in the first layer 34 is, for example, 70% by weight or less. The softening point of the first layer 34 is, for example, approximately 700 degrees Celsius.

[0029] The first layer 34 may further include conductive particles such as ruthenium oxide (RuO2), and the first layer 34 may be a conductive layer. When the first layer 34 is a conductive layer, the first layer 34 can be prevented from being charged due to static electricity generated by contact between the print medium 47 and the first layer 34. This can prevent deterioration of the heating resistor 30 and electrical breakdown of the drive IC 40 due to charging of the first layer 34.

[0030] The first layer 34 is formed on the second layer 35. In a plan view of the main surface 10a, the outer edge of the first layer 34 is surrounded by the outer edge of the second layer 35. The thickness of the first layer 34 is smaller than the thickness of the second layer 35. In a plan view of the main surface 10a, the first layer 34 overlaps the heating resistor 30 and is offset from the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the plurality of second individual wiring portions 27). In other words, in a plan view of the main surface 10a, the entire first layer 34 does not overlap the silver wiring portions. In a plan view of the main surface 10a, the first layer 34 may overlap the gold wiring portions (e.g., the plurality of strip portions 22 and the plurality of first individual wiring portions 26).

[0031] 1 and 2, the driving IC 40 selectively energizes the plurality of individual wirings 25. The driving IC 40 is disposed on the die bonding glaze 13. The driving IC 40 is electrically connected to the plurality of second individual wiring portions 27.

[0032] 1 and 2, the sealing member 43 seals the driving IC 40. The sealing member 43 has electrical insulating properties and is made of an insulating resin material such as epoxy resin.

[0033] 1 to 3, the thermal printhead 1 includes a protrusion 45 formed on the main surface 10a. The protrusion 45 includes a heater glaze 12, a wiring layer 20 (more specifically, a plurality of strip portions 22 and a plurality of first individual wiring portions 26), a heating resistor 30, and a protective layer 33.

[0034] An example of a method for manufacturing the thermal printhead 1 of this embodiment will be described with reference to FIG.

[0035] A glaze 11 is formed on the main surface 10a of the substrate 10 (step S1). For example, a glass paste is printed on the main surface 10a of the substrate 10. The glass paste is fired. In this way, the glaze 11 is formed. The glaze 11 includes, for example, a heater glaze 12 and a die bonding glaze 13.

[0036] A planarization layer 15 is formed on the area of ​​the main surface 10a of the substrate 10 that is exposed from the glaze 11 (step S2). For example, a glass paste is printed on the area of ​​the main surface 10a that is exposed from the glaze 11. The glass paste is fired. In this way, the planarization layer 15 is formed. The planarization layer 15 includes, for example, a first planarization layer 16 and a second planarization layer 17.

[0037] The wiring layer 20 is formed (step S3). For example, a conductive paste containing gold (Au) particles is printed on the heater glaze 12 and the planarization layer 15. The conductive paste is patterned by photolithography and then fired. In this way, the gold wiring portions of the wiring layer 20 (e.g., the multiple strip portions 22 of the common wiring 21 and the first individual wiring portions 26 of the multiple individual wirings 25) are formed. A conductive paste containing silver (Ag) particles is printed on the planarization layer 15, the heater glaze 12, and the die bonding glaze 13. The conductive paste is patterned by photolithography and then fired. In this way, the silver wiring portions of the wiring layer 20 (e.g., the connecting portion 23 and the detour portion 24 of the common wiring 21 and the second individual wiring portions 27 of the multiple individual wirings 25) are formed.

[0038] The heating resistor 30 is formed (step S4). For example, a resistor paste is applied onto the heater glaze 12, the strip portions 22, and the first individual wiring portions 26. The resistor paste contains a conductive material, such as ruthenium oxide, tantalum nitride, tantalum, or silver vanadium, and glass. The resistor paste is then fired. In this way, the heating resistor 30 is formed.

[0039] A protective layer 33 is formed (step S5). Specifically, a glass paste that does not contain boron nitride particles is printed on the glaze 11, the planarizing layer 15, the wiring layer 20, and the heating resistor 30. This glass paste may contain alumina particles. This glass paste is fired. In this way, a second layer 35 is formed. Then, a glass paste that contains boron nitride particles is printed on the second layer 35. This glass paste may contain alumina particles. This glass paste is fired. In this way, a first layer 34 is formed.

[0040] The laminate of the substrate 10, glaze 11, planarizing layer 15, wiring layer 20, heating resistor 30, and protective layer 33 is divided (step S6). For example, a cutting groove is formed in the substrate 10 by laser scribing. The laminate is cut along the cutting groove. In this way, the laminate is divided into individual pieces.

[0041] The driving IC 40 is mounted on the die bonding glaze 13 (step S7). For example, the driving IC 40 is fixed to the die bonding glaze 13 using a bonding material (not shown) such as a resin adhesive or solder. The driving IC 40 is electrically connected to the plurality of second individual wiring portions 27.

[0042] The driving IC 40 is sealed with the sealing member 43 (step S8). For example, a sealing resin material is potted onto the driving IC 40. The sealing resin material is cured to form the sealing member 43. In this way, the thermal printhead 1 is obtained.

[0043] The operation of the thermal printhead 1 of this embodiment will be described with reference to FIG.

[0044] The thermal printer 2 includes the thermal printhead 1 of this embodiment and a platen roller 46. The protrusion 45 faces the platen roller 46. As the platen roller 46 rotates, it feeds the print medium 47 toward the thermal printhead 1. The print medium 47 is fed from the downstream side in the sub-scanning direction Y to the upstream side in the sub-scanning direction Y. The print medium 47 is supplied between the protrusion 45 and the platen roller 46.

[0045] The driving IC 40 applies current individually to the plurality of heat generating elements 31 (see FIG. 2) through the plurality of individual wirings 25. The heat generating elements 31 to which the current is applied selectively generate heat. The heat generated by the heat generating elements 31 is transferred to the print medium 47. In this way, printing is performed on the print medium 47 using the thermal printhead 1.

[0046] The operation of the thermal printhead 1 of this embodiment will be described below in comparison with a thermal printhead 1b of a comparative example shown in Figures 6 and 7. The thermal printhead 1b of the comparative example has a similar configuration to the thermal printhead 1 of this embodiment, but differs from the thermal printhead 1 of this embodiment in that the first layer 34 is formed more widely on the second layer 35. Specifically, in the thermal printhead 1b of the comparative example, in a plan view of the main surface 10a of the substrate 10, the first layer 34 also overlaps the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the plurality of second individual wiring portions 27).

[0047] During printing using the thermal printhead 1b of the comparative example, scratches were produced on the print medium 47 (see FIG. 5). This is because, as shown in FIGS. 8 and 9, microprotrusions were formed on the outermost surface of the first layer 34, with which the print medium 47 may come into contact during printing, in areas that overlap with silver wiring portions (e.g., the connecting portions 23, the detour portions 24, and the plurality of second individual wiring portions 27) in a planar view of the main surface 10a of the substrate 10. The black dots shown in FIGS. 8 and 9 are the microprotrusions. These microprotrusions are formed when air bubbles are generated in the areas of the first layer 34 that overlap with silver wiring portions (e.g., the connecting portions 23, the detour portions 24, and the plurality of second individual wiring portions 27) in a planar view of the main surface 10a of the substrate 10, causing a portion of the outermost surface of the first layer 34 to bulge. The bubbles are thought to be generated when silver atoms in the silver wiring portion diffuse into the first layer 34 of the protective layer 33, and because the first layer 34 contains boron nitride particles, it is difficult for the bubbles to escape from the first layer 34, and the bubbles remain in the first layer 34.

[0048] In contrast, no scratches were observed on the print medium 47 (see FIG. 5) during printing using the thermal printhead 1 of this embodiment. This is because, as shown in FIGS. 10 and 11, almost no microprotrusions are formed on the outermost surface of the first layer 34, which may come into contact with the print medium 47 during printing. The absence of black dots like those shown in FIGS. 8 and 9 in FIGS. 10 and 11 indicates that no microprotrusions are formed on the thermal printhead 1 of this embodiment. In this embodiment, in a plan view of the main surface 10a of the substrate 10, the first layer 34 of the protective layer 33 containing boron nitride particles is offset from the silver wiring portions (e.g., the connecting portions 23, the detour portions 24, and the second individual wiring portions 27). This prevents silver atoms in the silver wiring portions from diffusing into the first layer 34. Air bubbles are prevented from being generated in the first layer 34, preventing microprotrusions from being formed on the outermost surface of the first layer 34.

[0049] The effects of the thermal printhead 1 of this embodiment will be described.

[0050] The thermal printhead 1 of this embodiment includes a substrate 10 having a principal surface 10a, a wiring layer 20 disposed on the principal surface 10a, a heating resistor 30, and a protective layer 33 covering the wiring layer 20 and the heating resistor 30. The wiring layer 20 includes gold wiring portions (e.g., multiple strip portions 22 and first individual wiring portions 26) connected to the heating resistor 30 and silver wiring portions (e.g., connecting portions 23, detour portions 24, and second individual wiring portions 27) connected to the gold wiring portions. The protective layer 33 includes a first layer 34 constituting the outermost surface of the protective layer 33. The first layer 34 includes glass and boron nitride particles dispersed in the glass. In a plan view of the principal surface 10a, the first layer 34 overlaps the heating resistor 30 but is offset from the silver wiring portions.

[0051] This prevents air bubbles from forming in the first layer 34. This prevents minute protrusions from forming on the outermost surface of the first layer 34. This can prevent the first layer 34 from scratching the print medium 47 during printing. Furthermore, because the outermost surface of the protective layer 33 is formed by the first layer 34 containing boron nitride particles, the abrasion resistance of the protective layer 33 is improved. Furthermore, because the wiring layer 20 includes silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second individual wiring portion 27), the cost of the thermal printhead 1 is reduced.

[0052] In the thermal printhead 1 of this embodiment, the first layer 34 overlaps the gold wiring portions (for example, the strip portions 22 and the first individual wiring portions 26) in a plan view of the main surface 10a.

[0053] Therefore, the gold wiring portions (for example, the plurality of strip portions 22 and the first individual wiring portions 26) can be protected by the first layer 34. The reliability of the thermal printhead 1 is improved.

[0054] In the thermal printhead 1 of this embodiment, the blending ratio of boron nitride particles in the first layer 34 is 5% by weight or more and 70% by weight or less.

[0055] The blending ratio of boron nitride particles in the first layer 34 is 5 wt % or more, which improves the abrasion resistance of the protective layer 33. The blending ratio of boron nitride particles in the first layer 34 is 70 wt % or less, which allows the boron nitride particles to be dispersed more uniformly in the first layer 34. The abrasion resistance of the protective layer 33 is improved.

[0056] In the thermal printhead 1 of this embodiment, the particle size of the boron nitride particles is equal to or smaller than the thickness of the first layer .

[0057] This can prevent the outlines of the boron nitride particles from appearing on the outermost surface of the protective layer 33. This makes the outermost surface of the protective layer 33 smooth. This can prevent the first layer 34 from damaging the print medium 47 during printing.

[0058] In the thermal printhead 1 of this embodiment, the particle size of the boron nitride particles is 4 μm or less.

[0059] Therefore, the boron nitride particles can be dispersed more uniformly in the first layer 34. The abrasion resistance of the protective layer 33 is improved.

[0060] In the thermal printhead 1 of this embodiment, the glass is lead-free glass.

[0061] This prevents air bubbles from being generated in the first layer 34. It also prevents minute protrusions from being formed on the outermost surface of the first layer 34. It is possible to prevent the first layer 34 from damaging the print medium 47 during printing.

[0062] In the thermal printhead 1 of this embodiment, the protective layer 33 contains alumina particles dispersed in glass. The compounding ratio of the alumina particles in the first layer 34 is 70% by weight or less.

[0063] Therefore, the boron nitride particles and alumina particles can be more uniformly dispersed in the first layer 34. The wear resistance of the protective layer 33 is improved.

[0064] In the thermal printhead 1 of this embodiment, the protective layer 33 further includes a second layer 35. The second layer 35 does not contain boron nitride particles and is disposed between the heating resistor 30 and the first layer 34. In a plan view of the main surface 10a, the second layer 35 overlaps the silver wiring portions (e.g., the connecting portions 23, the detour portions 24, and the second individual wiring portions 27).

[0065] This prevents minute protrusions from being formed on the outermost surface of the first layer 34. This can prevent the first layer 34 from damaging the print medium 47 during printing. The silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second individual wiring portion 27) can be protected by the second layer 35. This prevents the silver wiring portions from being oxidized. This improves the reliability of the thermal printhead 1.

[0066] In the thermal printhead 1 of this embodiment, the thickness of the first layer is smaller than the thickness of the second layer .

[0067] Therefore, the amount of boron nitride particles used in the first layer 34 can be reduced, thereby reducing the cost of the thermal printhead 1.

[0068] In the thermal printhead 1 of this embodiment, the softening point of the second layer 35 is higher than the softening point of the first layer 34.

[0069] Therefore, even if the temperature of the protective layer 33 rises during use of the thermal printhead 1 and the first layer 34 softens, the second layer 35 can remain hard. The boron nitride particles contained in the first layer 34 are prevented from settling into the second layer 35. Air bubbles are prevented from being generated in the protective layer 33, and minute protrusions are prevented from being formed on the outermost surface of the protective layer 33. The first layer 34 can be prevented from damaging the print medium 47 during printing.

[0070] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) a substrate having a major surface; a wiring layer disposed on the main surface; A heating resistor; a protective layer that covers the wiring layer and the heating resistor; the wiring layer includes a gold wiring portion connected to the heating resistor and a silver wiring portion connected to the gold wiring portion, the protective layer includes a first layer that constitutes an outermost surface of the protective layer, the first layer includes glass and boron nitride particles dispersed in the glass; In a plan view of the main surface, the first layer overlaps the heating resistor and is offset from the silver wiring portion. (Appendix 2) 2. A thermal printhead as described in Appendix 1, wherein, in the planar view of the main surface, the first layer overlaps the gold wiring portion. (Appendix 3) 3. The thermal printhead according to claim 1, wherein the content of the boron nitride particles in the first layer is 5% by weight or more and 70% by weight or less. (Appendix 4) 4. The thermal printhead of claim 1, wherein the particle size of the boron nitride particles is equal to or less than the thickness of the first layer. (Appendix 5) 5. The thermal printhead of claim 4, wherein the particle size of the boron nitride particles is 4 μm or less. (Appendix 6) 6. The thermal printhead of claim 1, wherein the glass is lead-free glass. (Appendix 7) the first layer includes alumina particles dispersed in the glass; 7. The thermal printhead according to claim 1, wherein the alumina particles have a mixing ratio of 70% by weight or less in the first layer. (Appendix 8) the protective layer further comprises a second layer; the second layer does not contain the boron nitride particles and is disposed between the heating resistor and the first layer; 8. A thermal printhead according to any one of claims 1 to 7, wherein, in the plan view of the main surface, the second layer overlaps the silver wiring portion. (Appendix 9) 9. The thermal printhead of claim 8, wherein the thickness of the first layer is less than the thickness of the second layer. (Appendix 10) 10. The thermal printhead of claim 8 or 9, wherein the softening point of the second layer is higher than the softening point of the first layer.

[0071] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0072] 1, 1b thermal print head, 2 thermal printer, 10 substrate, 10a main surface, 11 glaze, 12 heater glaze, 13 die bonding glaze, 15 planarization layer, 16 first planarization layer, 17 second planarization layer, 20 wiring layer, 21 common wiring, 22 strip portion, 23 connecting portion, 24 detouring portion, 25 individual wiring, 26 first individual wiring portion, 27 second individual wiring portion, 30 heating resistor, 31 heating portion, 33 protective layer, 34 first layer, 35 second layer, 40 driving IC, 43 sealing member, 45 protrusion, 46 platen roller, 47 printing medium.

Claims

1. a substrate having a major surface; a wiring layer disposed on the main surface; A heating resistor; a protective layer that covers the wiring layer and the heating resistor; the wiring layer includes a gold wiring portion connected to the heating resistor and a silver wiring portion connected to the gold wiring portion, the protective layer includes a first layer constituting an outermost surface of the protective layer, the first layer includes glass and boron nitride particles dispersed in the glass; In a plan view of the main surface, the first layer overlaps the heating resistor and is offset from the silver wiring portion.

2. The thermal printhead according to claim 1 , wherein the first layer overlaps the gold wiring portion in the plan view of the main surface.

3. 3. The thermal printhead according to claim 1, wherein the content of the boron nitride particles in the first layer is 5% by weight or more and 70% by weight or less.

4. 3. The thermal printhead according to claim 1, wherein the particle size of the boron nitride particles is equal to or smaller than the thickness of the first layer.

5. The thermal printhead of claim 4 , wherein the particle size of the boron nitride particles is 4 μm or less.

6. 3. The thermal printhead according to claim 1, wherein the glass is lead-free glass.

7. the first layer includes alumina particles dispersed in the glass; 3. The thermal printhead according to claim 1, wherein the alumina particles in the first layer have a content of 70% by weight or less.

8. the protective layer further comprises a second layer; the second layer does not contain the boron nitride particles and is disposed between the heating resistor and the first layer; 3. The thermal printhead according to claim 1, wherein the second layer overlaps the silver wiring portion in the plan view of the main surface.

9. The thermal printhead of claim 8 , wherein the thickness of the first layer is less than the thickness of the second layer.

10. 10. The thermal printhead according to claim 8, wherein the softening point of the second layer is higher than the softening point of the first layer.

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