Thermal head

Abstract

A thermal head according to the present invention comprises a substrate, an electrode, a first metal layer, and a second metal layer. The electrode is positioned on the substrate. The first metal layer is positioned on the substrate and the electrode, and covers the electrode. The second metal layer has a first portion that is positioned on the first metal layer, and a second portion that is positioned between the substrate and the first metal layer.

Description

Thermal head

[0001] The disclosed embodiments relate to a thermal head.

[0002] Conventionally, various thermal heads have been proposed as printing devices such as facsimiles or video printers. For example, a connection structure of electronic components plated on an electrode located on a substrate and joined via a conductive member is known.

[0003] Japanese Patent Application Laid-Open No. 2009-123719

[0004] The thermal head according to one aspect of the embodiment includes a substrate, an electrode, a first metal layer, and a second metal layer. The electrode is located on the substrate. The first metal layer is located on the substrate and the electrode and covers the electrode. The second metal layer has a first portion located on the first metal layer and a second portion located between the substrate and the first metal layer.

[0005] FIG. 1 is an exploded perspective view showing an outline of the thermal head according to the embodiment. FIG. 2 is a plan view showing an outline of the thermal head shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a plan view showing an example of a main part of the thermal head according to the embodiment. FIG. 5 is a cross-sectional view taken along line A-A in FIG. 4. FIG. 6 is a cross-sectional view taken along line B-B in FIG. 4. FIG. 7 is a schematic view showing an example of a thermal printer according to the embodiment.

[0006] Hereinafter, embodiments of the thermal head disclosed in the present application will be described with reference to the accompanying drawings. Note that this disclosure is not limited by the following embodiments.

[0007] In the conventional structure, there was room for improvement in bonding reliability.

[0008] One aspect of the embodiment aims to provide a thermal head with high bonding reliability.

[0009] <Embodiment> Figure 1 is an exploded perspective view showing a schematic of a thermal head according to an embodiment. As shown in Figure 1, the thermal head X1 according to the embodiment includes a head base 3, a connector 31, a sealing member 12, a heat sink 1, and an adhesive member 14. Note that the connector 31, sealing member 12, heat sink 1, and adhesive member 14 are not necessarily required.

[0010] The heat sink 1 dissipates excess heat from the head base 3. The head base 3 is placed on the heat sink 1 via an adhesive member 14. The head base 3 prints onto the recording medium P (see Figure 7) when an external voltage is applied. The adhesive member 14 bonds the head base 3 and the heat sink 1 together. The connector 31 electrically connects the head base 3 to the outside. The connector 31 has connector pins 8 and a housing 10. The sealing member 12 joins the connector 31 and the head base 3.

[0011] The heat sink 1 has a rectangular parallelepiped shape. The heat sink 1 is made of a metal material such as copper, iron, or aluminum, and dissipates the heat generated in the heat-generating part 9 of the head base 3 that does not contribute to printing.

[0012] The head base 3 is rectangular in shape when viewed from above, and the components constituting the thermal head X1 are arranged on the substrate 7. The head base 3 prints on the recording medium P (see Figure 7) according to electrical signals supplied from the outside.

[0013] Next, we will further explain each component that makes up the thermal head X1 using Figures 2 and 3. Figure 2 is a plan view showing a schematic of the thermal head shown in Figure 1. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. In Figure 2, the protective layer 25, the coating layer 27, and the sealing member 12 are shown by dashed lines, and the coating member 29 is shown by a broken line.

[0014] For the sake of clarity, Figures 2 and 3 illustrate a three-dimensional Cartesian coordinate system that includes the Z-axis extending along the thickness direction of the thermal head X1. This Cartesian coordinate system may also be shown in other drawings used in later explanations.

[0015] The head base 3 includes a substrate 7, a heat-generating resistor 15, a common electrode 17, individual electrodes 19, a first connecting electrode 22, a second connecting electrode 26, a ground electrode 4, a connection terminal 2, a conductive member 23, a drive IC 11, a bonding material 24, a covering member 29, a protective layer 25, and a covering layer 27. Note that not all of these components are necessarily included. Furthermore, the head base 3 may also include other components.

[0016] The substrate 7 is placed on the heat sink 1 and, in plan view, is rectangular. The substrate 7 has a first surface 7f, a second surface 7g, and a side surface 7e. The first surface 7f has a first long side 7a, a second long side 7b, a first short side 7c, and a second short side 7d. The components constituting the head base 3 are arranged on the first surface 7f. The second surface 7g is located on the opposite side from the first surface 7f. The second surface 7g is located on the heat sink 1 side and is joined to the heat sink 1 via an adhesive member 14. The side surface 7e connects the first surface 7f and the second surface 7g and is located on the second long side 7b side.

[0017] The substrate 7 is formed of, for example, an electrically insulating material such as alumina ceramics or a semiconductor material such as single-crystal silicon. For the sake of convenience in this explanation, the first surface 7f may be referred to as the "top surface" and the second surface 7g as the "bottom surface." Similarly, with respect to the side surface 7e, the side of the first surface 7f may be referred to as "up" or "upper," and the side of the second surface 7g may be referred to as "down" or "lower."

[0018] The substrate 7 may have a heat storage layer 13 located on the first surface 7f. The heat storage layer 13 may have a base portion 13a and a raised portion 13b. The base portion 13a is located across the entire surface of the first surface 7f. The raised portion 13b is raised from the base portion 13a in the thickness direction of the substrate 7. In other words, the raised portion 13b protrudes in a direction away from the first surface 7f.

[0019] The raised portion 13b is positioned adjacent to the first long side 7a of the substrate 7 and extends along the main scanning direction. The cross-section of the raised portion 13b may be approximately semi-elliptical. This allows the protective layer 25 located on the heat-generating portion 9 to make good contact with the recording medium P (see Figure 7) to be printed on. The height of the heat storage layer 13, including the base portion 13a and the raised portion 13b, from the first surface 7f of the substrate 7 can be, for example, 30 μm to 60 μm. The raised portion 13b is an example of a glaze.

[0020] The heat storage layer 13 is made of, for example, glass with low thermal conductivity, and temporarily stores a portion of the heat generated in the heat-generating section 9. Therefore, the time required to raise the temperature of the heat-generating section 9 can be shortened, and the thermal response characteristics of the thermal head X1 can be improved.

[0021] The heat storage layer 13 is formed, for example, by applying a predetermined glass paste obtained by mixing glass powder with a suitable organic solvent to the first surface 7f by screen printing or the like, firing it, etching it as needed, and then firing it again.

[0022] The heating resistor 15 is located on the upper surface of the heat storage layer 13. A common electrode 17 and individual electrodes 19 are located on top of the heating resistor 15. Between the common electrode 17 and the individual electrodes 19 is an exposed region of the heating resistor 15. As shown in Figure 2, the exposed regions of the heating resistor 15 are arranged in rows on the raised portion 13b of the heat storage layer 13, and each exposed region constitutes an element of the heating unit 9.

[0023] Furthermore, the heating resistor 15 does not necessarily have to be located between the various electrodes and the heat storage layer 13. For example, it may be located only between the common electrode 17 and the individual electrodes 19, so as to electrically connect the common electrode 17 and the individual electrodes 19. The heating resistor 15 may also be located between the first connecting electrode 22 and the second connecting electrode 26 and the heat storage layer 13, or between the ground electrode 4 and the heat storage layer 13.

[0024] Each element of the heating section 9, which is composed of multiple heating resistors 15, is shown in a simplified manner in Figure 2 for the sake of explanation, but is located at a density such as 100 dpi to 2400 dpi (dots per inch). The heating resistors 15 are formed from materials with relatively high electrical resistance, such as TaN-based, TaSiO-based, TaSiNO-based, TiSiO-based, TiSiCO-based, or NbSiO-based materials. Therefore, when a voltage is applied to the heating section 9, the heating section 9 generates heat through Joule heating.

[0025] The common electrode 17 comprises main wiring sections 17a and 17d, a sub-wiring section 17b, and a lead section 17c. The common electrode 17 electrically connects the multiple elements constituting the heating section 9 to the connector 31. The main wiring section 17a extends along the first long side 7a of the substrate 7. The sub-wiring section 17b extends along the first short side 7c and the second short side 7d of the substrate 7, respectively. The lead sections 17c extend individually from the main wiring section 17a toward each heating section 9. The main wiring section 17d extends along the second long side 7b of the substrate 7.

[0026] The individual electrodes 19 electrically connect the heating element 9 and the drive IC 11. The heating element 9 is composed of multiple elements divided into multiple groups, and the individual electrodes 19 electrically connect each element of the heating element 9 that constitutes each group to the corresponding drive IC 11. The individual electrodes 19 are electrically connected to the drive IC 11 by a bonding material 24.

[0027] The first connection electrode 22 electrically connects the drive IC 11 and the connector 31. Each of the multiple first connection electrodes 22 connected to each drive IC 11 is composed of multiple wires having different functions.

[0028] The second connecting electrode 26 electrically connects adjacent drive ICs 11. Multiple second connecting electrodes 26 are composed of multiple wires having different functions.

[0029] The common electrode 17, individual electrodes 19, first connecting electrode 22, and second connecting electrode 26 are made of a conductive material. The material of the common electrode 17, individual electrodes 19, first connecting electrode 22, and second connecting electrode 26 may be, for example, one of the metals Al, Au, Cu, or Ag, or an alloy thereof.

[0030] The ground electrode 4 is surrounded by individual electrodes 19, the first connecting electrode 22, and the main wiring portion 17d of the common electrode 17. The ground electrode 4 is maintained at a ground potential of 0 to 1V.

[0031] The thickness of the individual electrodes 19 is, for example, 0.5 μm or less, and may be, for example, around 0.1 μm to 0.5 μm. This makes it less likely for heat generated in the heat-generating section 9 to dissipate through the individual electrodes 19. In addition, by reducing the step difference with the substrate 7, for example, the protective layer 25 covering the heat-generating section 9 becomes less likely to peel off, improving the reliability of the thermal head X1.

[0032] Furthermore, the thickness of the various electrodes excluding the individual electrode 19 is, for example, about 0.1 μm to 10 μm, or for example, about 0.3 μm to 5 μm. Note that the thickness of the various electrodes excluding the individual electrode 19 may be the same as the thickness of the individual electrode 19.

[0033] The connection terminal 2 is located on the second long side 7b of the circuit board 7 and connects the common electrode 17, individual electrodes 19, first connection electrode 22, and ground electrode 4 to the connector 31. The connection terminal 2 is positioned to correspond to the connector pins 8, and when connecting the connector 31, the connector pins 8 and the connection terminal 2 are connected so that they are electrically independent of each other.

[0034] As shown in Figure 3, a conductive member 23 is positioned on each connection terminal 2. Examples of conductive members 23 include solder or ACP (Anisotropic Conductive Paste). A plating layer made of, for example, Ni, Au, or Pd may be positioned between the conductive member 23 and the connection terminal 2.

[0035] The various electrodes constituting the head base 3 described above can be formed, for example, by sequentially laminating material layers of metals such as Al, Au, Ag, Cu, or Ni onto the heat storage layer 13 using thin-film molding techniques such as sputtering, and then processing the laminate into a predetermined pattern using photoetching or the like. The various electrodes constituting the head base 3 can be formed simultaneously using the same process. Alternatively, the electrodes may be manufactured using methods such as screen printing, flexographic printing, gravure printing, or gravure offset printing.

[0036] The drive IC 11 is located, for example, on the first surface 7f side of the substrate 7. Furthermore, multiple drive ICs 11 are positioned along the arrangement direction of the heating unit 9 so as to correspond to each element of the heating unit 9 assigned to each drive IC 11. The drive IC 11 is connected to the individual electrodes 19 and the first connecting electrode 22. The drive IC 11 controls the energized state of the heating unit 9. The drive IC 11 supplies power to the heating unit 9 to individually heat each element of the heating unit 9 according to an electrical signal supplied from an external source. As the drive IC 11, for example, a switching IC having multiple switching elements internally can be used.

[0037] The bonding material 24 is located on the individual electrodes 19 and electrically connects the drive IC 11 and the individual electrodes 19. The bonding material 24 is conductive. The bonding material 24 may contain gold (Au) and / or tin (Sn). The material of the bonding material 24 may be, for example, AuSn, SnAg, SnAgCu, SnAgCuNi, Sn, or Au. Such a bonding material 24 has high mechanical strength, such as shear stress, and is less likely to peel off from the individual electrodes 19, thus providing high durability.

[0038] The protective layer 25 is located on the heat storage layer 13, which is located on the first surface 7f side of the substrate 7. The protective layer 25 covers the heat-generating resistor 15, which includes the heat-generating part 9, the common electrode 17, and the individual electrodes 19. More specifically, the protective layer 25 covers a portion of the individual electrodes 19 from the edges of the substrate 7, i.e., the first long side 7a, the first short side 7c, and the second short side 7d of the substrate 7. The protective layer 25 protects the covered area from corrosion due to the adhesion of moisture contained in the atmosphere, or from abrasion due to contact with the recording medium P (see Figure 7) to be printed on. Examples of materials for the protective layer 25 include SiN, SiO, and SiO. ２ SiO2, TiN, TiON, TiCrN, or TiAlON can be used.

[0039] The coating layer 27 is located on the first surface 7f side of the substrate 7. The coating layer 27 partially covers the common electrode 17, individual electrodes 19, first connecting electrode 22, and second connecting electrode 26. The coating layer 27 protects the covered area from oxidation due to contact with the atmosphere or corrosion due to the adhesion of moisture contained in the atmosphere. For example, a resin material such as epoxy resin, polyimide resin, or silicone resin can be used as the coating layer 27.

[0040] The covering member 29 seals the drive IC 11, the individual electrodes 19, the second connecting electrode 26, and the first connecting electrode 22 while they are connected. The covering member 29 is arranged to extend in the main scanning direction and integrally seals multiple drive ICs 11. For the covering member 29, a resin material such as epoxy resin or silicone resin can be used.

[0041] The connector 31 has a plurality of connector pins 8 and a housing 10 that houses the plurality of connector pins 8. The connector pins 8 have a first end and a second end and are electrically connected to various electrodes of the head base 3. The first end is exposed to the outside of the housing 10 and is electrically connected to the connection terminal 2 of the head base 3. The second end is housed inside the housing 10 and is brought out to the outside.

[0042] The sealing member 12 has a first sealing member 12a and a second sealing member 12b. The first sealing member 12a is located on the first surface 7f of the substrate 7. The first sealing member 12a seals the connector pins 8 and various electrodes. The second sealing member 12b is located on the second surface 7g of the substrate 7. The second sealing member 12b is positioned to seal the contact portion between the connector pins 8 and the substrate 7.

[0043] The sealing member 12 is positioned so that the connection terminals 2 and the connector pins 8 are not exposed to the outside. The sealing member 12 can be formed of, for example, an epoxy-based thermosetting resin, an ultraviolet curable resin, or a visible light curable resin. Note that the first sealing member 12a and the second sealing member 12b may be made of the same material. Also, the first sealing member 12a and the second sealing member 12b may be made of different materials.

[0044] The adhesive member 14 is located on the heat sink 1. The adhesive member 14 joins the second surface 7g of the head base 3 and the heat sink 1. Examples of the adhesive member 14 include a double-sided tape or a resinous adhesive.

[0045] Next, the main part of the thermal head X1 according to the embodiment will be further described with reference to FIGS. 4 to 6. FIG. 4 is a plan view showing an example of the main part of the thermal head according to the embodiment. FIG. 5 is a cross-sectional view taken along line A - A of FIG. 4. FIG. 6 is a cross-sectional view taken along line B - B of FIG. 4. Note that FIG. 5 corresponds to an enlarged cross-sectional view of the region V shown in FIG. 3. FIG. 6 corresponds to a cross-sectional view taken along line VI - VI of FIG. 5. Note that the covering member 29 is omitted in FIGS. 4 to 6.

[0046] As shown in FIGS. 4 to 6, the thermal head X1 according to the embodiment includes individual electrodes 19, a first metal layer 20, and a second metal layer 21.

[0047] The individual electrodes 19 are located on the substrate 7. The individual electrodes 19 may be located on the underlying portion 13a. The individual electrodes 19 have terminal portions 19a located at the ends. The individual electrodes 19 are an example of an electrode.

[0048] Each individual electrode 19 has a terminal portion 19a and a wiring portion 19b. The terminal portion 19a is located at the end of the individual electrode 19. The terminal portion 19a is located in the electrode region 30 on which the drive IC 11 (see Figure 3) is mounted. The wiring portion 19b is electrically connected to the terminal portion 19a.

[0049] The first metal layer 20 is located on the individual electrodes 19. Specifically, the first metal layer 20 is located so as to cover the terminal portion 19a of the individual electrodes 19. More specifically, the first metal layer 20 is located on the terminal portion 19a, with a portion of it located on the wiring portion 19b. In other words, the first metal layer 20 is located so as to be in contact with the terminal portion 19a, and is located on the wiring portion 19b at a distance from the wiring portion 19b.

[0050] The first metal layer 20 protects the individual electrodes 19, particularly the terminal portion 19a, from corrosion by covering the surface of the individual electrodes 19.

[0051] The second metal layer 21 has a first portion 21a and a second portion 21b. The first portion 21a is located on the first metal layer 20. More specifically, the first portion 21a is positioned to cover the portion of the first metal layer 20 that is in contact with the individual electrodes 19 and the interface between the first metal layer 20 and the substrate 7. The second portion 21b is located between the substrate 7 and the first metal layer 20. More specifically, the second portion 21b is positioned to cover the interface between the first metal layer 20 and the substrate 7. In other words, the first metal layer 20 is configured such that the portion that is not in contact with the individual electrodes 19 is covered by the first portion 21a and the second portion 21b.

[0052] The second metal layer 21 has a first portion 21a, which protects the surface of the first metal layer 20 from corrosion. This improves the durability of the first metal layer 20.

[0053] Furthermore, because the second metal layer 21 has a second portion 21b, moisture contained in the atmosphere is less likely to enter through the small gap between the first metal layer 20 and the substrate 7, thereby protecting the terminal portion 19a and / or the first metal layer 20 from corrosion.

[0054] Thus, according to the thermal head X1 of this embodiment, the durability of the first metal layer 20 is improved, thereby improving the bonding reliability between the individual electrodes 19 and the first metal layer 20, and between the first metal layer 20 and the second metal layer 21. In addition, the bonding performance between the second metal layer 21 and the drive IC 11 (see Figure 3) via the bonding material 24 is improved.

[0055] Furthermore, the thickness of the second metal layer 21 may be greater in the first portion 21a than in the second portion 21b. The second portion 21b is a small gap region sandwiched between the first metal layer 20 and the substrate 7, whereas the first portion 21a has a larger area facing the atmosphere. By increasing the thickness of the first portion 21a, even if moisture from the atmosphere enters, it becomes more difficult for it to reach the first metal layer 20, thus protecting it from corrosion. This further improves the durability of the first metal layer 20 and further improves the reliability of the bonding between the individual electrodes 19 and the first metal layer 20, and between the first metal layer 20 and the second metal layer 21.

[0056] The first metal layer 20 may contain Ni as a material. The first metal layer 20 may contain B, P, etc. as impurities. The first metal layer 20 may also contain Cu as a material.

[0057] The second metal layer 21 may contain Au as a material. The second metal layer 21 may be a single layer or a laminate. If the second metal layer 21 is a single layer, for example, it may be made of Au, Sn, SnAg, SnAgCu, or SnAgCuNi. If the second metal layer 21 is a laminate, for example, it may have a layer made of Pd and a layer made of Au, in that order from the first metal layer 20 side. This improves the bonding between the second metal layer 21 and the drive IC 11 (see Figure 3) via the bonding material 24.

[0058] The surface shape of the second metal layer 21 facing the bonding material 24 may be flat or curved.

[0059] The first metal layer 20 and the second metal layer 21 having the above configuration can be positioned, for example, by an electroless plating method.

[0060] The shape and composition of the first metal layer 20 and the second metal layer 21 can be determined by visual inspection or other means based on SEM (Scanning Electron Microscope) images taken of a cross-section of the thermal head X1 including the terminal portion 19a of the individual electrode 19, and EDS (Energy Dispersive X-ray Spectroscopy).

[0061] Furthermore, although not shown in the diagram, the connections between the ground electrode 4, the first connecting electrode 22, and the second connecting electrode 26 and the drive IC 11 may be the same as the connections to the drive IC 11 in the individual electrodes 19 described above.

[0062] Next, a thermal printer Z1 having a thermal head X1 will be described with reference to Figure 7. Figure 7 is a schematic diagram showing an example of a thermal printer according to the embodiment.

[0063] The thermal printer Z1 according to this embodiment includes the thermal head X1 described above, a transport mechanism 40, a platen roller 50, a power supply unit 60, and a control device 70. The thermal head X1 is mounted on the mounting surface 80a of a mounting member 80 located on the housing (not shown) of the thermal printer Z1. The thermal head X1 is mounted on the mounting member 80 so as to be aligned with the main scanning direction, which is perpendicular to the transport direction S.

[0064] The transport mechanism 40 includes a drive unit (not shown) and transport rollers 43, 45, 47, and 49. The transport mechanism 40 transports the recording medium P, such as thermal paper or image receiving paper onto which ink is transferred, along the transport direction S indicated by the arrow onto the protective layer 25 located on the multiple heating elements 9 of the thermal head X1. The drive unit has the function of driving the transport rollers 43, 45, 47, and 49, and can use a motor, for example. The transport rollers 43, 45, 47, and 49 may be cylindrical shafts 43a, 45a, 47a, and 49a made of a metal such as stainless steel, covered with elastic members 43b, 45b, 47b, and 49b made of butadiene rubber or the like. When the recording medium P is image receiving paper onto which ink is transferred, an ink film (not shown) is transported together with the recording medium P between the recording medium P and the heating elements 9 of the thermal head X1.

[0065] The platen roller 50 has the function of pressing the recording medium P onto the protective layer 25 located on the heating element 9 of the thermal head X1. The platen roller 50 is arranged to extend in a direction perpendicular to the transport direction S, and both ends are supported and fixed so that it can rotate while pressing the recording medium P onto the heating element 9. The platen roller 50 can be constructed, for example, by covering a cylindrical shaft 50a made of metal such as stainless steel with an elastic member 50b made of butadiene rubber or the like.

[0066] The power supply unit 60 has the function of supplying current to generate heat in the heat-generating part 9 of the thermal head X1 and current to operate the drive IC 11, as described above. The control device 70 has the function of supplying a control signal to the drive IC 11 to control the operation of the drive IC 11 in order to selectively generate heat in the heat-generating part 9 of the thermal head X1, as described above.

[0067] The thermal printer Z1 presses the recording medium P onto the heating element 9 of the thermal head X1 using the platen roller 50, and transports the recording medium P onto the heating element 9 using the transport mechanism 40, while selectively heating the heating element 9 with the power supply unit 60 and the control unit 70 to print a predetermined image on the recording medium P. If the recording medium P is image receiving paper or the like, the ink from an ink film (not shown) transported together with the recording medium P is thermally transferred to the recording medium P to print an image on the recording medium P.

[0068] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit thereof. For example, although a planar head in which the heating element 9 is located on the main surface of the substrate 7 has been described as an example, an end-face head in which the heating element 9 is located on the end face of the substrate 7 may also be used.

[0069] Furthermore, although the explanation used a so-called thin-film head in which the heat-generating resistor 15 is formed by sputtering, the invention is not limited to a thin-film head. A so-called thick-film head in which the heat-generating resistor 15 is formed by printing or the like may also be used.

[0070] Alternatively, the portion covering the joint material 24 and the terminal portion 19a may be covered with an underfill material instead of the covering member 29. Such an underfill material can be made of, for example, an insulating resin such as epoxy resin.

[0071] Alternatively, a common electrode 17 and individual electrodes 19 may be formed on the heat storage layer 13, and a heating resistor 15 may be formed only in the region between the common electrode 17 and the individual electrodes 19 to form the heating section 9.

[0072] Furthermore, although an example was shown in which the connector 31 is directly connected to the circuit board 7, a flexible printed circuit board (FPC) may also be connected to the circuit board 7.

[0073] Furthermore, although a thermal head X1 having a coating layer 27 has been illustrated, the coating layer 27 is not necessarily required. In that case, the protective layer 25 may be positioned up to the area where the coating layer 27 was provided. Alternatively, the coating layer 27 may be provided in areas other than those shown in the illustration.

[0074] In one embodiment, (1) the thermal head comprises a substrate, an electrode located on the substrate, a first metal layer located on the substrate and the electrode and covering the electrode, and a second metal layer having a first portion located on the first metal layer and a second portion located between the substrate and the first metal layer.

[0075] (2) In the thermal head described in (1) above, the thickness of the second metal layer may be greater in the first portion than in the second portion.

[0076] (3) In the thermal head of (1) or (2) above, the first metal layer contains Ni as a material, the second metal layer is a single layer or a laminate, the single layer is made of Au, Sn, SnAg, SnAgCu or SnAgCuNi as a material, and the laminate may have a first layer made of Pd and a second layer made of Au, in order from the first metal layer side.

[0077] (4) In any one of the thermal heads described in (1) to (3) above, the electrode may be made of Al, Au, Cu, or Ag.

[0078] Further effects and modifications can be readily derived by those skilled in the art. Therefore, broader aspects of this disclosure are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents.

[0079] X1 Thermal head Z1 Thermal printer 1 Heat sink 3 Head base 4 Ground electrode 7 Substrate 9 Heat-generating part 11 Drive IC 15 Heat-generating resistor 17 Common electrode 19 Individual electrode 19a Terminal part 20 First metal layer 21 Second metal layer 22 First connection electrode 24 Bonding material 25 Protective layer 26 Second connection electrode 27 Covering layer 29 Covering member

Claims

1. A thermal head comprising a substrate, an electrode located on the substrate, a first metal layer located on the substrate and the electrode and covering the electrode, and a second metal layer having a first portion located on the first metal layer and a second portion located between the substrate and the first metal layer.

2. The thermal head according to claim 1, wherein the thickness of the second metal layer is greater in the first portion than in the second portion.

3. The thermal head according to claim 1 or 2, wherein the first metal layer contains Ni as a material, the second metal layer is a single layer or a laminate, the single layer is made of Au, Sn, SnAg, SnAgCu, or SnAgCuNi as a material, and the laminate comprises, in order from the first metal layer side, a first layer made of Pd and a second layer made of Au.

4. The thermal head according to any one of claims 1 to 3, wherein the electrode is made of Al, Au, Cu, or Ag.

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