Thermal print head

Abstract

To provide a thermal print head having improved heat accumulation performance.SOLUTION: A thermal print head 1 includes: an insulation substrate 10 having a major surface 11; a ground layer 12 disposed on the major surface 11; a glaze 15 disposed on the ground layer 12; and a heating resistor 30 disposed on the glaze 15. The ground layer 12 includes a first ceramic layer 13 containing a hollow ceramic filler.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] JP 2020-163654 A (Patent Document 1) discloses a thermal printhead including an insulating substrate, a heater glaze, a die bonding glaze, an intermediate glass layer, a heating resistor, an electrode layer, and a protective layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-163654 A [Summary]

[0004] It is an object of the present disclosure to provide a thermal printhead with improved heat storage.

[0005] The thermal printhead of the present disclosure includes an insulating substrate having a main surface, an underlayer disposed on the main surface, a glaze disposed on the underlayer, and a heating resistor disposed on the glaze. The underlayer includes a first ceramic layer containing hollow ceramic fillers. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic plan view of a thermal printhead according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the thermal printhead of the first embodiment taken along the cross-sectional line II-II shown in FIG. [Diagram 3] FIG. 3 is a schematic partial enlarged plan view of the thermal printhead according to the first embodiment. [Figure 4] FIG. 4 is a flowchart showing the method of manufacturing the thermal printheads according to the first to third embodiments. [Diagram 5] FIG. 5 is a schematic cross-sectional view of a thermal printhead according to the second embodiment. [Figure 6] 6 is a schematic cross-sectional view of a thermal printhead according to a third embodiment.

[0007] 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 given 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 arbitrarily combined.

[0008] (Embodiment 1)

[0009] A thermal printhead 1 according to a first embodiment will be described with reference to Figures 1 to 3. The thermal printhead 1 is mounted on a thermal printer (not shown). With reference to Figure 1, the thermal printhead 1 includes a head body 2 and connectors 3 and 4.

[0010] The head body 2 has, for example, a rectangular shape. In a plan view of the thermal printhead 1 (hereinafter simply referred to as "plan view"), the long side direction of the head body 2 is the main scanning direction X, the short side direction of the head body 2 is the sub-scanning direction Y, and the thickness direction of the insulating substrate 10 is the plate thickness direction Z. The plate thickness direction Z is a direction 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 the print medium (for example, thermal recording paper).

[0011] The connectors 3 and 4 are connected to a connector (not shown) on the thermal printer side when the thermal printhead 1 is incorporated into the thermal printer (not shown). The connectors 3 and 4 are connected to the upstream end of the head body 2 in the sub-scanning direction Y.

[0012] 1 to 3, the head body 2 includes an insulating substrate 10, an underlayer 12, a glaze 15, a wiring layer 20, pads 28, 29, a heating resistor 30, a protective layer 35, a supporting glass layer 38, a driving IC 41, conductive wires 43, 44, and a sealing member 50.

[0013] The insulating substrate 10 is, for example, a ceramic substrate formed of a ceramic material such as alumina. The insulating substrate 10 includes a main surface 11. The main surface 11 may have depressions (not shown) formed therein, or the main surface 11 may have a rough surface. The depressions are formed in the main surface 11, for example, during the manufacture of the insulating substrate 10. The depressions have a diameter of, for example, about 10 μm to about 30 μm.

[0014] The underlayer 12 is disposed on the main surface 11 of the insulating substrate 10. The depressions in the main surface 11 are filled with the underlayer 12. The underlayer 12 functions as a planarizing layer. The thickness of the underlayer 12 may be less than the thickness of the glaze 15.

[0015] The base layer 12 includes a first ceramic layer 13. In this embodiment, the base layer 12 is a single layer and is composed of the first ceramic layer 13. The first ceramic layer 13 includes a ceramic matrix and hollow ceramic fillers dispersed in the ceramic matrix. The ceramic matrix is ​​made of, for example, alumina. The hollow ceramic fillers are made of, for example, alumina. The hollow ceramic fillers have an average particle size of, for example, 100 μm or less. The hollow ceramic fillers may have an average particle size of, for example, 50 μm or less. The hollow ceramic fillers are, for example, E-SPHERES manufactured by Taiheiyo Cement Corporation.

[0016] The thermal conductivity of the hollow ceramic filler is lower than that of the ceramic matrix. The thermal conductivity of the hollow ceramic filler may be 0.5 times or less than that of the ceramic matrix, 0.2 times or less than that of the ceramic matrix, or 0.1 times or less than that of the ceramic matrix. The thermal conductivity of the hollow ceramic filler may be 5.0 W / (m·K) or less, 3.0 W / (m·K) or less, or 1.0 W / (m·K) or less. As an example, the thermal conductivity of the ceramic matrix is ​​about 29 W / (m·K), and the thermal conductivity of the hollow ceramic filler is 0.1 W / (m·K). Since the underlayer 12 includes the hollow ceramic filler, the thermal conductivity of the underlayer 12 is reduced. The thermal conductivity of the underlayer 12 may be lower than that of the insulating substrate 10.

[0017] The glaze 15 is disposed on the underlayer 12. The glaze 15 is formed of a glass material such as amorphous glass. The thermal conductivity of the glaze 15 may be lower than that of the insulating substrate 10. In this embodiment, the glaze 15 is a so-called partial glaze. That is, in a cross section including the sub-scanning direction Y and the plate thickness direction Z, the glaze 15 is provided on a part of the main surface 11 of the insulating substrate 10. The glaze 15 includes a heater glaze 16 and a die bonding glaze 17.

[0018] The heater glaze 16 extends in the main scanning direction X in a plan view of the main surface 11 of the insulating substrate 10 and has a band shape. The heater glaze 16 is disposed under the heating resistor 30. The heater glaze 16 suppresses heat from the heating resistor 30 from dissipating to the insulating substrate 10. The heater glaze 16 is a heat storage layer. The heater glaze 16 protrudes from a part of the main surface 11 of the insulating substrate 10. The heater glaze 16 is provided to increase the height of the heating resistor 30 from the main surface 11 of the insulating substrate 10 and press the heating resistor 30 against a printing medium (e.g., thermal recording paper). The heater glaze 16 has a thickness of, for example, 18 μm or more and 50 μm or less.

[0019] The die bonding glaze 17 is disposed at a distance from the heater glaze 16 on the upstream side in the sub-scanning direction Y. In a plan view of the main surface 11 of the insulating substrate 10, the die bonding glaze 17 extends in the main scanning direction X and has a band shape. The die bonding glaze 17 supports a part of the wiring layer 20 and the driving IC 41. The thickness of the die bonding glaze 17 is, for example, 30 μm or more and 50 μm or less. The die bonding glaze 17 may be omitted.

[0020] The wiring layer 20 is disposed on the glaze 15 and the underlayer 12. The wiring layer 20 constitutes a conductive path for passing electricity through the heating resistor 30. The wiring layer 20 is formed of a conductive material such as gold (Au), silver (Ag) or copper (Cu). The wiring layer 20 includes a common wiring 21 and a plurality of individual wirings 25.

[0021] The common wiring 21 is disposed on the glaze 15 and the underlayer 12. The common wiring 21 includes a plurality of first strip-shaped portions 22, a connecting portion 23, and a detour portion 24.

[0022] The multiple first band portions 22 are disposed on the glaze 15 and the underlayer 12. Each of the multiple first band portions 22 extends in the sub-scanning direction Y. The multiple first band portions 22 are arranged at equal pitches in the main scanning direction X. The connecting portion 23 is disposed on the underlayer 12. The connecting portion 23 extends in the main scanning direction X. The connecting portion 23 is connected to the multiple first band portions 22. The detour portion 24 extends from one end 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.

[0023] Each of the multiple individual wirings 25 partially energizes the heating resistor 30. The multiple individual wirings 25 are disposed on the glaze 15 and the underlayer 12. Each of the multiple individual wirings 25 includes a second strip portion 26 and a bonding portion 27.

[0024] The second band portions 26 are disposed on the glaze 15 (specifically, the heater glaze 16) and the underlayer 12 in the sub-scanning direction Y. The multiple second band portions 26 are arranged at equal pitches in the main scanning direction X. The second band portions 26 are disposed on the glaze 15 between a pair of first band portions 22 adjacent to each other in the main scanning direction X. The first band portions 22 and the second band portions 26 are disposed alternately in the main scanning direction X. The bonding portion 27 is an end portion on the upstream side in the sub-scanning direction Y of each of the multiple individual wirings 25.

[0025] The pads 28 and 29 are formed of the same material as the wiring layer 20. The pads 28 and 29 are arranged on the glaze 15 (specifically, the die bonding glaze 17). In the sub-scanning direction Y, the pad 28 is arranged between the multiple individual wirings 25 and the pad 29. In the sub-scanning direction Y, the pad 28 is arranged spaced apart from the multiple individual wirings 25 on the upstream side of the sub-scanning direction Y. The pad 29 is arranged spaced apart from the pad 28 on the upstream side of the sub-scanning direction Y.

[0026] The heating resistor 30 is disposed on the glaze 15 (specifically, the heater glaze 16). More specifically, the heating resistor 30 is disposed on the top of the heater glaze 16. The heating resistor 30 extends in the main scanning direction X and has a band shape in a plan view. The heating resistor 30 protrudes from the glaze 15 on the side opposite to the insulating substrate 10.

[0027] The heating resistor 30 is connected to the wiring layer 20. Specifically, the heating resistor 30 is connected to the plurality of first strip portions 22 of the common wiring 21 and the plurality of second strip portions 26 of the plurality of individual wirings 25. In a plan view, the heating resistor 30 is arranged so as to intersect with the plurality of first strip portions 22 and the plurality of second strip portions 26. The heating resistor 30 is formed so as to straddle the plurality of first strip portions 22 and the plurality of second strip portions 26. With reference to FIG. 3, the portion of the heating resistor 30 sandwiched between each of the first strip portions 22 and each of the second strip portions 26 in the main scanning direction X is a heating portion 31. The heating portion 31 is a portion that generates heat by partially passing electricity through the heating resistor 30. Heat generated by the heating portion 31 is printed on a print medium (for example, thermal recording paper).

[0028] 2, the protective layer 35 protects the heating resistor 30. The protective layer 35 may further protect the common wiring 21 and the individual wirings 25. The protective layer 35 includes a first protective layer 36 and a second protective layer 37.

[0029] The first protective layer 36 covers the heating resistor 30. The first protective layer 36 may further cover the multiple first strip-shaped portions 22 and the multiple second strip-shaped portions 26. The first protective layer 36 may further cover a portion of the base layer 12. The first protective layer 36 is formed of, for example, amorphous glass.

[0030] The second protective layer 37 is formed on the first protective layer 36. The second protective layer 37 is formed in an area where a print medium (e.g., thermal recording paper) may come into contact with the thermal printhead 1 when the print medium is transported. In a plan view, the length of the second protective layer 37 in the sub-scanning direction Y is shorter than the length of the first protective layer 36 in the sub-scanning direction Y. The second protective layer 37 is, for example, a coating film containing silicon carbide (SiC) or titanium (Ti). The thickness of the second protective layer 37 is thinner than the thickness of the first protective layer 36.

[0031] The support glass layer 38 is disposed on the pad 28. The support glass layer 38 is formed of, for example, amorphous glass. The support glass layer 38 may be formed of the same material as the first protective layer 36.

[0032] 1 and 2, the driving IC 41 selectively energizes the plurality of individual wirings 25. In this embodiment, the plurality of driving ICs 41 are arranged spaced apart from each other in the main scanning direction X. The driving IC 41 is arranged on the supporting glass layer 38.

[0033] The conductive wires 43 are bonded to the bonding portions 27 of the individual wirings 25 and the driving IC 41. The conductive wires 43 electrically connect the individual wirings 25 and the driving IC 41. The conductive wires 44 are bonded to the pads 29 and the driving IC 41. The conductive wires 44 electrically connect the pads 29 and the driving IC 41.

[0034] The sealing member 50 seals the driving IC 41. The sealing member 50 has electrical insulation properties and is made of an insulating resin material such as epoxy resin.

[0035] The thermal printhead 1 includes a protrusion 18 formed on an underlayer 12. The protrusion 18 includes a glaze 15 (specifically, a die bonding glaze 17), a wiring layer 20, a heating resistor 30, and a protective layer 35. In the protrusion 18, the glaze 15, the wiring layer 20, the heating resistor 30, a first protective layer 36, and a second protective layer 37 are laminated on the underlayer 12 in this order in the normal direction (Z direction) of the main surface 11.

[0036] A method for manufacturing the thermal printhead 1 of this embodiment will be described with reference to FIG.

[0037] The underlayer 12 is formed (step S1). For example, a ceramic paste containing ceramic powder, hollow ceramic filler, and a vehicle is applied onto the main surface 11 of the insulating substrate 10. The ceramic paste may be applied by printing such as screen printing, or may be applied by a dispenser. The ceramic paste is then fired. In this way, the underlayer 12 (first ceramic layer 13) is formed on the main surface 11 of the insulating substrate 10.

[0038] The method includes forming a glaze 15 (step S2). For example, a glass paste containing a glass powder and a vehicle is applied onto the underlayer 12. The glass paste may be applied by printing such as screen printing, or by application with a dispenser. The glass paste is then fired. In this manner, the glaze 15 is formed on the main surface 11 of the insulating substrate 10. The glaze 15 includes, for example, a heater glaze 16 and a die bonding glaze 17.

[0039] The wiring layer 20 and the pads 28, 29 are formed (step S3). The wiring layer 20 is formed on the glaze 15 and the underlayer 12. The pads 28, 29 are formed on the glaze 15 (specifically, the die bonding glaze 17).

[0040] Specifically, a conductive paste is applied onto the glaze 15 and the underlayer 12. The conductive paste includes a conductive material such as gold (Au), silver (Ag) or copper (Cu). The conductive paste may be applied by printing such as screen printing, or by application with a dispenser.

[0041] If necessary, the conductive paste is patterned. For example, the conductive paste is patterned by photolithography. Specifically, the conductive paste is dried. Photoresist is applied onto the conductive paste. The photoresist is covered with a photomask. The photoresist is exposed to ultraviolet light through the openings in the photomask. The portions of the photoresist that have been exposed to the ultraviolet light and have been altered are dissolved by a developer. In this way, the photoresist is patterned. The conductive paste is etched with an etchant through the patterned photoresist. In this way, the conductive paste is patterned. The resist is dissolved and removed by a stripper.

[0042] The conductive paste is then fired, thus forming the wiring layer 20 and the pads 28 and 29.

[0043] The heating resistor 30 is formed (step S4). For example, a resistor paste is applied onto the glaze 15 and the wiring layer 20. 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. Thus, the heating resistor 30 is formed.

[0044] The first protective layer 36 and the supporting glass layer 38 are formed (step S5). Specifically, a glass paste is applied onto the glaze 15, the underlayer 12, the wiring layer 20, the pads 28, and the heating resistor 30. The glass paste may be applied by printing such as screen printing, or may be applied by a dispenser. Then, the glass paste is fired. In this way, the first protective layer 36 and the supporting glass layer 38 are formed.

[0045] The second protective layer 37 is formed on the first protective layer 36 (step S6). The second protective layer 37 is formed by, for example, sputtering. In this manner, the protective layer 35 and the protrusions 18 are formed.

[0046] The laminate including the insulating substrate 10, the underlayer 12, the glaze 15, the wiring layer 20, the pads 28 and 29, the heating resistor 30, and the protective layer 35 is divided (step S7). For example, a cutting groove is formed in the insulating substrate 10 by a laser scribing method. The insulating substrate 10 is cut along the cutting groove. In this way, the laminate is divided into individual pieces.

[0047] The driving IC 41 is mounted on the supporting glass layer 38 (step S8). For example, the driving IC 41 is fixed to the supporting glass layer 38 using a joining material (not shown) such as a resin adhesive or solder.

[0048] The conductive wires 43 and 44 are bonded (step S9). The conductive wire 43 is bonded to the driving IC 41 and the bonding portion 27 of the individual wiring 25. The conductive wire 44 is bonded to the driving IC 41 and the pad 29.

[0049] The driving IC 41 is sealed (step S10). For example, a sealing resin material is potted on the driving IC 41. The sealing resin material is hardened. In this manner, the sealing member 50 is formed.

[0050] The connectors 3 and 4 are attached to the insulating substrate 10 (step S11). The connectors 3 and 4 are attached to the upstream end of the insulating substrate 10 in the sub-scanning direction Y. In this manner, the thermal printhead 1 is obtained.

[0051] The operation of thermal printhead 1 of the present embodiment will be described in comparison with thermal printheads of first and second comparative examples. The thermal printhead of the first comparative example has a similar configuration to thermal printhead 1 of the present embodiment, but differs from thermal printhead 1 of the present embodiment in that it does not have base layer 12. The thermal printhead of the second comparative example has a similar configuration to thermal printhead 1 of the present embodiment, but differs from thermal printhead 1 of the present embodiment in that base layer 12 is formed of a ceramic layer that does not contain hollow ceramic filler.

[0052] In the first comparative example, the thermal printhead does not include an underlayer 12, and the glaze 15 is in contact with the main surface 11 of the insulating substrate 10. Therefore, the heat from the heating resistor 30 is likely to dissipate to the insulating substrate 10. In the second comparative example, the thermal printhead includes an underlayer 12, but the underlayer 12 is a ceramic layer that does not include a hollow ceramic filler. The thermal conductivity of the ceramic layer that does not include a hollow ceramic filler is greater than that of the ceramic layer that includes a hollow ceramic filler. The heat from the heating resistor 30 is likely to dissipate to the insulating substrate 10. Therefore, the thermal storage capacity of the thermal printheads of the first and second comparative examples is insufficient. The power consumption of the thermal printheads of the first and second comparative examples increases.

[0053] Furthermore, in the first comparative example, if the thickness of the heater glaze 16 is increased to improve the heat storage of the thermal printhead, the size of the heater glaze 16 in the sub-scanning direction Y increases. This causes the thermal printhead to become larger. The printing density of the thermal printhead decreases, and the printing quality of the thermal printhead deteriorates.

[0054] Furthermore, in the first comparative example, a portion of the wiring layer 20 is in contact with the main surface 11 of the insulating substrate 10. When the insulating substrate 10 is a ceramic substrate, a depression (not shown) may be formed in the main surface 11 of the insulating substrate 10 during the manufacture of the ceramic substrate. Therefore, in the first comparative example, the wiring layer 20 may be broken.

[0055] In contrast, the thermal printhead 1 of the present embodiment includes an underlayer 12, which includes a first ceramic layer 13 containing hollow ceramic filler. The thermal conductivity of the ceramic layer containing hollow ceramic filler is smaller than that of the ceramic layer not containing hollow ceramic filler. Therefore, the thermal conductivity of the underlayer 12 is reduced. The underlayer 12 suppresses the dissipation of heat from the heating resistor 30 to the insulating substrate 10. Therefore, the heat storage capacity of the thermal printhead 1 can be improved. The power consumption of the thermal printhead 1 can be reduced.

[0056] Also, since there is no need to increase the thickness of the heater glaze 16 to improve the heat storage capacity of the thermal printhead 1, the size of the heater glaze 16 in the sub-scanning direction Y can be reduced. This allows the thermal printhead 1 to be miniaturized. The printing density of the thermal printhead 1 can be increased, and the printing quality of the thermal printhead 1 can be improved.

[0057] Furthermore, even if a depression is formed on main surface 11 of insulating substrate 10 during the manufacture of insulating substrate 10, this depression is filled with underlayer 12. Underlayer 12 functions as a planarizing layer. Therefore, disconnection of wiring layer 20 formed on underlayer 12 can be prevented.

[0058] The effects of the thermal printhead 1 of this embodiment will be described.

[0059] The thermal printhead 1 of the present embodiment comprises an insulating substrate 10 including a principal surface 11, an underlayer 12 disposed on the principal surface 11, a glaze 15 disposed on the underlayer 12, and a heating resistor 30 disposed on the glaze 15. The underlayer 12 includes a first ceramic layer 13 containing hollow ceramic filler.

[0060] Since the base layer 12 contains hollow ceramic filler, the thermal conductivity of the base layer 12 is reduced. The base layer 12 suppresses the heat from the heating resistor 30 from dissipating to the insulating substrate 10. This improves the heat storage capacity of the thermal printhead 1. The power consumption of the thermal printhead 1 can be reduced.

[0061] Also, since there is no need to increase the thickness of the glaze 15 (heater glaze 16) to improve the heat storage capacity of the thermal printhead 1, the size of the glaze 15 (heater glaze 16) can be reduced. Therefore, the thermal printhead 1 can be made smaller. The printing density of the thermal printhead 1 can be increased, and the printing quality of the thermal printhead 1 can be improved.

[0062] The thermal printhead 1 of this embodiment further includes a wiring layer 20 connected to the heating resistor 30. The wiring layer 20 is disposed on the glaze 15 and the underlayer 12.

[0063] Even if a depression is formed on the main surface 11 of the insulating substrate 10, the depression is filled with the underlayer 12. The underlayer 12 functions as a planarizing layer. Therefore, it is possible to prevent disconnection of the wiring layer 20 formed on the underlayer 12.

[0064] In the thermal printhead 1 of this embodiment, the insulating substrate 10 is a ceramic substrate.

[0065] Since the base layer 12 contains hollow ceramic fillers, the thermal conductivity of the base layer 12 is reduced. Therefore, a ceramic substrate having a higher thermal conductivity than a glass substrate can be used as the insulating substrate 10 while ensuring the heat storage capacity of the thermal printhead 1. The ceramic substrate is low in cost and has excellent heat resistance. Therefore, the productivity of the thermal printhead 1 is improved.

[0066] In the thermal printhead 1 of this embodiment, the hollow ceramic filler has an average particle size of 100 μm or less.

[0067] This can reduce the surface roughness of the underlayer 12. This can prevent the wiring layer 20 formed on the underlayer 12 from being broken.

[0068] In the thermal printhead 1 of this embodiment, the hollow ceramic filler has an average particle size of 50 μm or less.

[0069] This can reduce the surface roughness of the underlayer 12. This can prevent the wiring layer 20 formed on the underlayer 12 from being broken.

[0070] (Embodiment 2)

[0071] A thermal printhead 1 of the second embodiment will be described with reference to Fig. 5. The thermal printhead 1 of the present embodiment has a similar configuration to the thermal printhead 1 of the first embodiment, but differs from the thermal printhead 1 of the first embodiment in the base layer 12.

[0072] In this embodiment, the underlayer 12 includes a first ceramic layer 13 and a second ceramic layer 14. The first ceramic layer 13 is disposed between the insulating substrate 10 and the second ceramic layer 14. The second ceramic layer 14 is disposed between the glaze 15 and the first ceramic layer 13, and does not contain a hollow ceramic filler. The second ceramic layer 14 is, for example, an alumina layer. The wiring layer 20 is disposed on the second ceramic layer 14.

[0073] With reference to FIG. 4, the method for manufacturing thermal printhead 1 in this embodiment includes similar steps to the method for manufacturing thermal printhead 1 in embodiment 1, but differs from the method for manufacturing thermal printhead 1 in embodiment 1 in the step of forming base layer 12 (step S1).

[0074] The step of forming base layer 12 in the present embodiment includes forming first ceramic layer 13 and forming second ceramic layer 14. The step of forming first ceramic layer 13 in the present embodiment is similar to the step of forming base layer 12 (first ceramic layer 13) in the first embodiment.

[0075] Then, the second ceramic layer 14 is formed, for example, as follows. A ceramic paste containing a ceramic powder and a vehicle is applied onto the first ceramic layer 13. The ceramic paste may be applied by printing, such as screen printing, or by application with a dispenser. The ceramic paste is then fired. In this way, the second ceramic layer 14 is formed on the first ceramic layer 13.

[0076] The thermal printhead 1 of this embodiment has the following advantages in addition to the advantages of the thermal printhead 1 of the first embodiment.

[0077] In the thermal printhead 1 of this embodiment, the underlayer 12 includes a second ceramic layer 14 that does not contain hollow ceramic filler. The second ceramic layer 14 is disposed between the glaze 15 and the first ceramic layer 13. The wiring layer 20 is disposed on the second ceramic layer 14.

[0078] The surface of the base layer 12 is not the surface of the first ceramic layer 13 containing hollow ceramic filler, but the surface of the second ceramic layer 14 not containing hollow ceramic filler. Therefore, the surface of the base layer 12 is further flattened. Disconnection of the wiring layer 20 formed on the base layer 12 can be further prevented.

[0079] (Embodiment 3)

[0080] A thermal printhead 1 according to a third embodiment will be described with reference to Fig. 6. The thermal printhead 1 according to the present embodiment has a similar configuration to the thermal printhead 1 according to the second embodiment, but differs from the thermal printhead 1 according to the second embodiment mainly in the base layer 12.

[0081] In this embodiment, the main surface 11 of the insulating substrate 10 includes regions 11a, 11b, 11c, and 11d. The region 11a is a region of the main surface 11 that overlaps with the heater glaze 16 in a plan view of the main surface 11. The region 11a is located directly below the heater glaze 16 in the main surface 11. The region 11a is adjacent to the region 11c and the region 11d, and is between the region 11c and the region 11d. The region 11b is a region of the main surface 11 that overlaps with the die bonding glaze 17 in a plan view of the main surface 11. The region 11b is located directly below the die bonding glaze 17 in the main surface 11. The region 11c is adjacent to the region 11a and the region 11b, and is between the region 11a and the region 11b. The region 11d is adjacent to the region 11a, and is downstream of the region 11a in the sub-scanning direction Y.

[0082] In a plan view of the main surface 11 of the insulating substrate 10, the first ceramic layer 13 is disposed on the regions 11a and 11b. The regions 11c and 11d are exposed from the first ceramic layer 13. The second ceramic layer 14 is disposed on the first ceramic layer 13, as well as on the regions 11c and 11d.

[0083] With reference to FIG. 4, the method for manufacturing thermal printhead 1 in the present embodiment includes similar steps to the method for manufacturing thermal printhead 1 in embodiment 2, but differs from the method for manufacturing thermal printhead 1 in embodiment 2 in the step of forming base layer 12 (step S1).

[0084] The step of forming the underlayer 12 in this embodiment includes forming the first ceramic layer 13 and forming the second ceramic layer 14. In the step of forming the first ceramic layer 13 in this embodiment, the first ceramic layer 13 is formed on a part of the main surface 11 of the insulating substrate 10 (specifically, the regions 11a and 11b). For example, a ceramic paste containing ceramic powder, hollow ceramic filler, and a vehicle is applied onto the part of the main surface 11 of the insulating substrate 10 (specifically, the regions 11a and 11b). The regions 11c and 11d of the main surface 11 are exposed from the ceramic paste. Then, the ceramic paste is fired. In this manner, the first ceramic layer 13 is formed.

[0085] In the step of forming the second ceramic layer 14 in this embodiment, the second ceramic layer 14 is formed on the first ceramic layer 13 and on a portion of the main surface 11 of the insulating substrate 10 (specifically, the regions 11c and 11d). For example, a ceramic paste containing a ceramic powder and a vehicle is applied onto the first ceramic layer 13 and on the portion of the main surface 11 of the insulating substrate 10 (specifically, the regions 11c and 11d). Then, the ceramic paste is fired. In this manner, the second ceramic layer 14 is formed.

[0086] The thermal printhead 1 of this embodiment has the following advantages in addition to the advantages of the thermal printhead 1 of the second embodiment.

[0087] In the thermal printhead 1 of this embodiment, the glaze 15 includes a heater glaze 16 disposed under the heating resistor 30. In a plan view of the principal surface 11, the first ceramic layer 13 is disposed on a first region (region 11a) of the principal surface 11 that overlaps with the heater glaze 16. The second ceramic layer 14 is further disposed on a second region (regions 11b, 11d) of the principal surface 11 that is adjacent to the first region and is exposed from the first ceramic layer 13.

[0088] Since the area where the first ceramic layer 13 containing the hollow ceramic filler is formed is reduced, the cost of the thermal printhead 1 can be reduced.

[0089] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) an insulating substrate including a main surface; an underlayer disposed on the major surface; a glaze disposed on the underlayer; A heating resistor disposed on the glaze, The thermal printhead, wherein the underlayer includes a first ceramic layer containing hollow ceramic fillers. (Appendix 2) A wiring layer connected to the heating resistor is further provided. 2. The thermal printhead of claim 1, wherein the wiring layer is disposed on the glaze and the underlayer. (Appendix 3) the underlayer includes a second ceramic layer that does not contain the hollow ceramic filler; the second ceramic layer is disposed between the glaze and the first ceramic layer; 3. The thermal printhead of claim 2, wherein the wiring layer is disposed on the second ceramic layer. (Appendix 4) The glaze includes a heater glaze disposed under the heating resistor, In a plan view of the main surface, the first ceramic layer is disposed on a first region of the main surface that overlaps the heater glaze, A thermal printhead as described in Appendix 3, wherein the second ceramic layer is further disposed on a second region of the main surface adjacent to the first region and exposed from the first ceramic layer. (Appendix 5) 5. The thermal printhead according to claim 1, wherein the insulating substrate is a ceramic substrate. (Appendix 6) 6. The thermal printhead according to claim 1, wherein the hollow ceramic filler has an average particle size of 100 μm or less. (Appendix 7) 6. The thermal printhead according to claim 1, wherein the hollow ceramic filler has an average particle size of 50 μm or less.

[0090] The embodiments 1 to 3 disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0091] REFERENCE SIGNS LIST 1 thermal print head, 2 head body, 3, 4 connector, 10 insulating substrate, 11 main surface, 11a, 11b, 11c, 11d regions, 12 underlayer, 13 first ceramic layer, 14 second ceramic layer, 15 glaze, 16 heater glaze, 17 die bonding glaze, 18 protrusion, 20 wiring layer, 21 common wiring, 22 first strip portion, 23 connecting portion, 24 bypass portion, 25 individual wiring, 26 second strip portion, 27 bonding portion, 28, 29 pad, 30 heating resistor, 31 heating portion, 35 protective layer, 36 first protective layer, 37 second protective layer, 38 support glass layer, 41 driving IC, 43, 44 conductive wire, 50 sealing member.

Claims

1. an insulating substrate including a main surface; an underlayer disposed on the major surface; a glaze disposed on the underlayer; A heating resistor disposed on the glaze, The thermal printhead, wherein the underlayer comprises a first ceramic layer containing hollow ceramic fillers.

2. A wiring layer connected to the heating resistor is further provided. The thermal printhead of claim 1 , wherein the wiring layer is disposed on the glaze and the underlayer.

3. the underlayer includes a second ceramic layer that does not contain the hollow ceramic filler; the second ceramic layer is disposed between the glaze and the first ceramic layer; The thermal printhead of claim 2 , wherein the wiring layer is disposed on the second ceramic layer.

4. The glaze includes a heater glaze disposed under the heating resistor, In a plan view of the main surface, the first ceramic layer is disposed on a first region of the main surface that overlaps the heater glaze, The thermal printhead of claim 3 , wherein the second ceramic layer is further disposed on a second region of the main surface adjacent to the first region and exposed from the first ceramic layer.

5. The thermal printhead according to claim 1 , wherein the insulating substrate is a ceramic substrate.

6. 5. The thermal printhead according to claim 1, wherein the hollow ceramic filler has an average particle size of 100 [mu]m or less.

7. 5. The thermal printhead according to claim 1, wherein the hollow ceramic filler has an average particle size of 50 [mu]m or less.

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