Thermal printhead and method of manufacturing the same

Abstract

A thermal printhead (1) of the present invention includes: an insulating substrate (10); an electrode (20) having a gold-containing solder pad (30) provided on a surface of the insulating substrate (10), and a silver-containing connecting portion (32) provided on a surface of the insulating substrate (10) opposite to the surface on which the solder pad (30) is provided; and a silver-containing film (70) having a different composition from the connecting portion (32) and provided on a surface of the solder pad (30) opposite to the surface of the insulating substrate (10). The connecting portion (32) covers the solder pad (30) in a manner sandwiching an edge portion.

Description

TECHNICAL FIELD

[0001] The present application relates to a thermal printhead and a manufacturing method thereof. BACKGROUND

[0002] A thermal printhead is a main component of a thermal printer which electrically connects a heating resistor between a pair of electrodes of a common electrode and an independent electrode formed on an insulating substrate, and performs printing on a thermal recording paper or the like using heat generated by passing current through the heating resistor. In the prior art, gold paste has been used in an electrode including a solder pad connecting the common electrode and the independent electrode of the thermal printhead and a connector.

[0003] However, gold contained in the gold paste is expensive, and therefore silver, which is less expensive than gold, has been proposed as a substitute for the gold paste. Patent Document 1 discloses a technique of forming a circuit on an insulating substrate using a conductor paste containing conductor particles in which a palladium coating film is formed on the surface of silver particles and the metal element composition is 80 to 99.5% by weight of silver and 0.5 to 20% by weight of palladium.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 6-132338 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, in the case of forming a silver electrode using the silver conductor paste, there are cases where the required characteristics of the thermal printhead cannot be sufficiently satisfied depending on the purpose of the formed electrode. On the other hand, if a gold electrode is formed at a specific site and a silver electrode is formed in contact with the gold electrode, over-etching of the silver conductor pattern occurs when the silver is etched using photolithography, and there are cases where the electrode is formed thinner than the target. Silver is easily aggregated, and pinholes are easily generated in the electrode, and therefore, for example, if heat is applied to the silver electrode as described above, the electrode can be broken.

[0009] The present application has been achieved in view of the problems in the prior art. Furthermore, an object of the present application is to provide a thermal printhead and a manufacturing method thereof capable of suppressing breakage of a silver electrode even when a gold electrode and a silver electrode are used.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] To solve the above problems, a thermal head of the present application includes an insulating substrate and an electrode having a gold-containing pad provided on a surface of the insulating substrate and a silver-containing connecting portion provided on the surface of the insulating substrate, the connecting portion being connected to a surface of the pad opposite to the insulating substrate. The thermal head includes a silver-containing film having a different composition from the connecting portion provided on the surface of the pad opposite to the insulating substrate. The connecting portion covers the pad in a manner sandwiching the edge portion.

[0012] A method of manufacturing a thermal head of another aspect of the present application includes a step of forming a silver-containing layer on a surface of an insulating substrate and a surface of a gold-containing pad provided on the surface of the insulating substrate in contact with the pad. The above method includes a step of forming a resist on at least a part of a surface of the layer in a manner covering an entire surface of the pad in a thickness direction and an edge portion as a whole. The above method includes a step of etching the silver-containing layer on which the resist is formed using an etching solution to form a silver-containing connecting portion connected to the pad. The above method includes a step of removing the resist on a surface of the connecting portion. The above method includes a step of forming a silver-containing film having a different composition from the connecting portion on the surface of the pad opposite to the insulating substrate.

[0013] Effects of the Invention

[0014] According to the present application, it is possible to provide a thermal head and a method of manufacturing the same, which can suppress disconnection of a silver electrode even when a gold electrode and a silver electrode are used. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a plan view showing a thermal head of the present embodiment.

[0016] Figure 2 is a cross-sectional view along the line II-II of Figure 1 .

[0017] Figure 3 is a cross-sectional view enlarging a region of a heat generating resistor of Figure 2 .

[0018] Figure 4 is a plan view enlarging a part of a region of an electrode of Figure 1 .

[0019] Figure 5 is a plan view showing a region of a gold pad.

[0020] Figure 6 is a cross-sectional view along the line VI-VI of Figure 5 .

[0021] Figure 7 is a cross-sectional view along the line VII-VII of Figure 6a sectional view of the line VII-VII of Fig. 7.

[0022] Figure 8 is a plan view showing a region of a gold bump of another embodiment.

[0023] Figure 9 is a plan view showing an example of forming a gold bump.

[0024] Figure 10 is a plan view showing an example of forming a silver layer in contact with the gold bump.

[0025] Figure 11 is a plan view showing an example of forming a resist at least on a part of a surface of a silver layer in a manner of covering an entire surface and an edge portion of the gold bump in a thickness direction.

[0026] Figure 12 is a plan view showing an example of forming a connecting portion by etching the silver layer with an etching solution on which the resist is formed.

[0027] Figure 13 is a plan view showing an example of a state after the resist remaining on a surface of a conductor pattern is removed.

[0028] Figure 14 is a plan view showing an example of forming a silver layer in a manner of covering an entire gold bump.

[0029] Figure 15 is a plan view showing an example of a state after the resist remaining on a surface of a conductor pattern is removed.

[0030] Figure 16 is a plan view showing a comparative example of forming a resist in a manner of exposing a gold bump in contact with a silver layer.

[0031] Figure 17 is a plan view showing a state of the comparative example after the resist remaining on a surface of a conductor pattern is removed.

[0032] Figure 18 is a plan view showing an example of forming a resist at least on a part of a surface of a layer containing silver in a manner of covering an entire surface and an edge portion of a first band portion in a thickness direction.

[0033] Figure 19 is a plan view showing an example of a state after the resist remaining on a surface of a conductor pattern is removed.

[0034] Figure 20is a plan view illustrating an example in which a resist is formed on at least a part of the surface of the silver layer in a manner so as to cover the entire surface and the edge portion of the first belt-shaped portion in contact with the second connecting portion and the second belt-shaped portion and the silver layer in the thickness direction.

[0035] Figure 21 is a plan view illustrating an example of a state after the resist remaining on the surface of the conductor pattern is removed.

[0036] Figure 22 is a plan view illustrating a comparative example in which a resist is formed in a manner so as to be exposed from the first belt-shaped portion in contact with the silver layer.

[0037] Figure 23 is a plan view illustrating a state of the comparative example after the resist remaining on the surface of the conductor pattern is removed.

[0038] Explanation of Reference Numerals

[0039] 1 thermal printhead

[0040] 10 insulating substrate

[0041] 11 ceramic layer

[0042] 12 glaze layer

[0043] 20 electrode

[0044] 21 independent electrode

[0045] 26 common electrode

[0046] 30 gold pad (pad containing gold)

[0047] 32 connecting portion

[0048] 33 covering portion

[0049] 35 edge portion

[0050] 40 heat-generating resistor

[0051] 51 drive IC

[0052] 53 connector

[0053] 70 silver film (film containing silver)

[0054] 110 gold conductor pattern

[0055] 120 silver layer (layer containing silver)

[0056] 130 resist

[0057] 140 silver conductor pattern DETAILED DESCRIPTION

[0058] The thermal printhead and its manufacturing method according to this embodiment will be described with reference to the accompanying drawings. In the drawings described below, the same or similar parts are labeled with the same or similar reference numerals. However, the drawings are schematic representations, and there may be differences between the actual dimensions and the thickness and planar dimensions of the constituent parts. Please be aware of this. Therefore, the specific thickness and dimensions should be determined with reference to the following description. Furthermore, the drawings naturally include parts where the dimensional relationships and ratios differ from each other.

[0059] [Thermal printhead]

[0060] use Figures 1-4 The thermal printhead 1 of this embodiment will be described. Figure 1 This is a top view showing the thermal printhead 1 of this embodiment. Figure 2 It is along Figure 1 A cross-sectional view of line II-II. Figure 3 It is Figure 2 A magnified cross-sectional view of the heating resistor 40 region. Figure 4 It is Figure 1 A magnified top view of a portion of electrode 20. In the figure, x, y, and z represent the main scanning direction x, the sub-scanning direction y, and the thickness direction z; these directions are orthogonal to each other. (Example) Figures 1-4 As shown, the thermal printhead 1 includes an insulating substrate 10, an electrode 20, a heating resistor 40, a protective layer 45, a heat sink 50, a driver IC 51, a sealing resin 52, a connector 53, and a silver-containing film (silver film 70). Furthermore, the protective layer 45 is omitted in the top view.

[0061] The insulating substrate 10 is a rectangular insulating substrate with the main scanning direction x as its long side and the secondary scanning direction y as its short side. The insulating substrate 10 only needs to be insulating, and may include, for example, a ceramic layer 11 and a glaze layer 12. As a result, a thermal printhead 1 with an excellent balance between heat storage and heat dissipation generated from the heating resistor 40 can be obtained.

[0062] The ceramic layer 11 contains, for example, ceramic with alumina as its main component. Furthermore, "main component" means that the ceramic content in the ceramic layer 11 is 50% by mass or more. The ceramic content in the ceramic layer 11 can be 70% by mass or more, 80% by mass or more, or 90% by mass or more. The thickness of the ceramic layer 11 is, for example, 0.6 mm to 1 mm.

[0063] The glaze layer 12 is provided on the ceramic layer 11. The glaze layer 12 covers one side of the surface of the ceramic layer 11. The glaze layer 12 stores heat generated by the heat generating resistor 40. The glaze layer 12 contains glass as a main component. Further, the so-called main component means that the content of glass in the glaze layer 12 is 50% by mass or more. The content of glass in the glaze layer 12 can be 70% by mass or more, 80% by mass or more, or 90% by mass or more. As the glass, for example, an amorphous glass of the SiO2-BaO-Al2O3-SnO-ZnO type can be exemplified. The thickness of the glaze layer 12 is, for example, 100 μm to 200 μm.

[0064] The electrode 20 is provided on the surface of the insulating substrate 10, and constitutes an electrically conductive path for passing current to the heat generating resistor 40. In addition, the electrode 20, as shown in Figs. 1 and 2, includes a plurality of individual electrodes 21, one common electrode 26, a plurality of gold-containing pads (a plurality of gold pads 30), and a plurality of connection portions 32. The thickness of the individual electrode 21 is, for example, 0.2 μm or more and 1.2 μm or less, and the thickness of the common electrode 26 is, for example, 0.2 μm or more and 1.2 μm or less. Figure 4 Figure 5 The electrode 20 is provided on the surface of the insulating substrate 10, and constitutes an electrically conductive path for passing current to the heat generating resistor 40. In addition, the electrode 20, as shown in Figs. 1 and 2, includes a plurality of individual electrodes 21, one common electrode 26, a plurality of gold-containing pads (a plurality of gold pads 30), and a plurality of connection portions 32. The thickness of the individual electrode 21 is, for example, 0.2 μm or more and 1.2 μm or less, and the thickness of the common electrode 26 is, for example, 0.2 μm or more and 1.2 μm or less.

[0065] The plurality of individual electrodes 21 is provided on the surface of the insulating substrate 10. The plurality of individual electrodes 21 is arranged at intervals in the main scanning direction x. The plurality of individual electrodes 21 is electrically connected to the drive IC 51, and is arranged in a bundle corresponding to each drive IC 51 on the insulating substrate 10. The plurality of individual electrodes 21 respectively extends from the drive IC 51 to the heat generating resistor 40 in the sub-scanning direction y. The plurality of individual electrodes 21 respectively has a pad 22, a first connecting portion 23, and a first band-shaped portion 24.

[0066] The plurality of pads 22 is respectively electrically connected to the drive IC 51. The plurality of pads 22 is respectively alternately shifted in the sub-scanning direction y, and is arranged along the main scanning direction x. The first connecting portion 23 extends along the sub-scanning direction y, and the first band-shaped portion 24 is connected to the pad 22. The first band-shaped portion 24 is arranged on the opposite side of the pad 22 with respect to the first connecting portion 23 in the sub-scanning direction y. The plurality of first band-shaped portions 24 respectively extends in a rectangular shape along the sub-scanning direction y. The plurality of first band-shaped portions 24 is arranged at intervals along the main scanning direction x in a comb-toothed manner.

[0067] ​A common electrode 26 is disposed between multiple independent electrodes 21. The common electrode 26 has a second connecting portion 27 and multiple second strip portions 28. The second connecting portion 27 is disposed on the opposite side of the heating resistor 40 from the drive IC 51. The second connecting portion 27 extends in a rectangular shape parallel to the heating resistor 40 along the main scanning direction x. Multiple second strip portions 28 are respectively connected to the second connecting portion 27 and extend in a rectangular shape from the second connecting portion 27 toward the heating resistor 40 along the sub-scanning direction y. Multiple second strip portions 28 are disposed between multiple independent electrodes 21. The multiple second strip portions 28 are arranged at equal intervals along the main scanning direction x in a comb-like manner. Multiple second strip portions 28 are respectively disposed between two adjacent first strip portions 24 in the main scanning direction x.

[0068] The heating resistor 40 is arranged across the surfaces of multiple individual electrodes 21 and the surface of a common electrode 26. Specifically, the heating resistor 40 is arranged across multiple first strips 24 and multiple second strips 28. The multiple individual electrodes 21 and the common electrode 26 are arranged in the thickness direction z between the insulating substrate 10 and the heating resistor 40. The resistivity of the heating resistor 40 is greater than that of the electrodes 20. Therefore, Joule heating is generated when current flows through the heating resistor 40 between a specific individual electrode 21 and the common electrode 26 adjacent to the individual electrode 21, and specific portions of the heating resistor 40 through which the current flows are selectively heated. The heating resistor 40 contains, for example, ruthenium oxide (RuO2) particles. The heating resistor 40 may contain glass frit to improve the adhesion between the glaze layer 12 and the protective layer 45. The thickness of the heating resistor 40 is, for example, 0.05 μm or more and 10 μm or less.

[0069] Protective layer 45 Figure 2 and Figure 3 The protective layer 45 is in contact with the surface of the insulating substrate 10. It covers a portion of the electrode 20 and the heating resistor 40 to protect them from foreign matter or other contaminants. The protective layer 45 can be formed from the same material as the glaze layer 12 described above.

[0070] Radiator 50 Figure 2 As shown, it is mounted on the insulating substrate 10 and has the function of dissipating heat from the insulating substrate 10. The heat sink 50 can be made of a metal with high thermal conductivity, such as aluminum.

[0071] The driving IC 51 is mounted on the insulating substrate 10 and connected to the plurality of independent electrodes 21. The driving IC 51 is connected to the electrodes 20 via a plurality of bumps by flip chip bonding, and any of the plurality of bumps can be connected to each of the plurality of independent electrodes 21. Alternatively, the driving IC 51 can be electrically connected to each of the plurality of connection portions 32 via a plurality of bumps by flip chip bonding. Further, the driving IC 51 can be connected to each of the plurality of independent electrodes 21 and each of the plurality of connection portions 32 via gold wiring by wire bonding. The driving IC 51 causes a specific portion of the heat generating resistor 40 to generate heat arbitrarily by selectively flowing current to the corresponding independent electrode 21. The driving IC 51 is covered with a sealing resin 52 for protection.

[0072] The connector 53 is provided on the insulating substrate 10 and is an external connection member used for supplying power to the thermal printhead 1 from an external connection device or controlling the driving IC 51. The connector 53 is electrically connected to the driving IC 51 via the gold pads 30 and the connection portions 32. Alternatively, as the external connection member, a flexible substrate can be used instead of the connector 53 to supply power to the thermal printhead 1 from the external connection device or control the driving IC 51.

[0073] As shown in FIG. 2, the plurality of connection portions 32 are arranged along the main scanning direction x. The connection portions 32 extend in the sub scanning direction y. The connection portions 32 are connected to bumps different from the bumps to which the plurality of independent electrodes 21 are connected among the plurality of bumps. One end of the connection portion 32 is connected to the driving IC 51, and the other end of the connection portion 32 is connected to the substantially rectangular gold pad 30. The shape of the gold pad 30 is not limited to a rectangle, and can be a circle or a polygon, or the like. Figure 5 As shown in FIG. 2, the plurality of connection portions 32 are arranged along the main scanning direction x. The connection portions 32 extend in the sub scanning direction y. The connection portions 32 are connected to bumps different from the bumps to which the plurality of independent electrodes 21 are connected among the plurality of bumps. One end of the connection portion 32 is connected to the driving IC 51, and the other end of the connection portion 32 is connected to the substantially rectangular gold pad 30. The shape of the gold pad 30 is not limited to a rectangle, and can be a circle or a polygon, or the like.

[0074] Figures 5-7 As shown in FIG. 2, the plurality of connection portions 32 are arranged along the main scanning direction x. The connection portions 32 extend in the sub scanning direction y. The connection portions 32 are connected to bumps different from the bumps to which the plurality of independent electrodes 21 are connected among the plurality of bumps. One end of the connection portion 32 is connected to the driving IC 51, and the other end of the connection portion 32 is connected to the substantially rectangular gold pad 30. The shape of the gold pad 30 is not limited to a rectangle, and can be a circle or a polygon, or the like.

[0075] ​The connecting portion 32 is provided on the surface of the insulating substrate 10, and is connected to the surface (upper surface of the gold bump 30) of the gold bump 30 on the side opposite to the insulating substrate 10. The connecting portion 32 contains silver. The connecting portion 32 can contain 50% by mass or more of silver, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. The thickness of the connecting portion 32 is, for example, 0.2 μm or more and 1.2 μm or less. The connecting portion 32 can be formed by printing and firing a silver paste. The connecting portion 32 is provided on the upper surface of the gold bump 30, and thus the connecting portion 32 is electrically connected to the gold bump 30. In addition, the connecting portion 32 is provided on the upper surface of the insulating substrate 10, and thus the current flowing through the gold bump 30 can flow, for example, to the drive IC 51.

[0076] The connecting portion 32 covers the gold bump 30 in a manner sandwiching the edge portion. The edge portion 35 of the covering portion 33 among the edge portions of the gold bump 30 can be entirely covered by the connecting portion 32. That is, the edge portion 35 of the covering portion 33 among the edge portions of the gold bump 30 is covered by the connecting portion 32 in a manner not exposed. In addition, one edge of the edge portion of the connecting portion 32 can have two intersection points with the edge portion of the gold bump 30. The connecting portion 32 covers the gold bump 30 in a manner sandwiching the edge portion, and thus the width of the connecting portion 32 is widened. Silver forming the connecting portion 32 is more likely to be aggregated by heat than gold, and thus a pinhole can be generated due to heat at the time of forming the protective layer 45 covering the surface of the connecting portion 32, Joule heat generated by passing current to the connecting portion 32, or the like, and the connecting portion 32 can be broken. However, since the width of the connecting portion 32 is widened, even if a pinhole is generated, the possibility of breakage can be reduced.

[0077] The electrode 20 includes a gold conductor pattern 110 and a silver conductor pattern 140, which will be described later. The gold conductor pattern 110 includes, for example, the first band portion 24, the second connecting portion 27, the second band portion 28, and the gold bump 30. The silver conductor pattern 140 includes, for example, a portion other than the above among the electrode 20. Specifically, the silver conductor pattern 140 includes the bump 22, the first connecting portion 23, and the connecting portion 32.

[0078] The silver film 70 is provided on the surface of the gold solder pad 30 on the side opposite the insulating substrate 10 (the upper surface of the gold solder pad 30). The silver film 70 is used for soldering, and is connected to the connector 53 or a flexible substrate or the like, for example, via solder. When the silver film 70 is connected to the connector 53 using solder, the gold solder pad 30 can be inhibited from dissolving into the solder. The thickness of the silver film 70 is, for example, 2 μm or more and 10 μm or less. When the thickness of the silver film 70 is within the above range, gold dissolving can be sufficiently inhibited at the time of soldering. The thickness of the silver film 70 can be 3 μm to 5 μm. The silver film 70 can also cover at least a portion of the surface of the non-covered portion 34, as long as gold dissolving can be inhibited. That is, the silver film 70 can also cover the entire surface of the non-covered portion 34, or can cover a portion of the surface. The silver film 70 can be provided in a manner smaller in area than the gold solder pad 30, as viewed in the thickness direction z.

[0079] The silver film 70 is different in composition from the connecting portion 32. In order to join solder to the surface of the silver film 70, the silver film 70 can be formed of a material having high solder wettability. The silver film 70 can contain silver, and in addition to silver, for example, can contain at least one element selected from platinum, palladium, and bismuth. Such a silver film 70 can improve solder wettability. The silver film 70 can be formed of, specifically, an alloy of silver and platinum, an alloy of silver and palladium, or silver containing bismuth oxide. The silver film 70 can also contain glass in order to improve adhesion to the protective layer 45. When the silver film 70 contains bismuth oxide, the bismuth oxide can inhibit glass from being precipitated to the surface of the silver film 70. As a result, the silver film 70 melts into the solder at the time of soldering, and thus the solder wettability of the silver film 70 is improved.

[0080] Further, in the manner of Figures 5-7 In the example in which a portion of the gold solder pad 30 is covered by the connecting portion 32, the gold solder pad 30 has the covered portion 33 and the non-covered portion 34, as shown in Figure 8 That is, the gold solder pad 30 can not have the non-covered portion 34. Thus, the entire surface of the gold solder pad 30 is surrounded by the insulating substrate 10 and the connecting portion 32.

[0081] As described above, the thermal printhead 1 of the present embodiment has the insulating substrate 10. The thermal printhead 1 has the electrode 20 including the gold-containing solder pad (gold solder pad 30) provided on the surface of the insulating substrate 10, and the silver-containing connecting portion 32 provided on the surface of the insulating substrate 10 and connected to the surface of the gold solder pad 30 on the side opposite the insulating substrate 10. The thermal printhead 1 has the silver-containing film (silver film 70) provided on the surface of the gold solder pad 30 on the side opposite the insulating substrate 10, and is different in composition from the connecting portion 32. The connecting portion 32 covers the gold solder pad 30 in a manner sandwiched from the edge portion.

[0082] In the thermal printhead 1 of this embodiment, since it has gold solder pads 30 and silver-containing connecting portions 32, the amount of expensive gold used can be reduced compared to the case where the electrode 20 is formed only by gold. Furthermore, since the connecting portion 32 covers the gold solder pads 30 by clamping them from the edges, the width of the connecting portion 32 is increased. Compared to gold, silver forming the connecting portion 32 tends to easily condense due to heat, but because the width of the connecting portion 32 is increased, the possibility of pinholes caused by silver condensation can be reduced. Therefore, according to the thermal printhead 1 of this embodiment, even when using gold solder pads 30 as gold electrodes and connecting portions 32 as silver electrodes 20, wire breakage of the silver electrode 20 can be suppressed.

[0083] Thermal printer

[0084] The thermal printer of this embodiment includes the thermal printhead 1 described above. As described above, since the breakage of the silver electrode 20 in the thermal printhead 1 can be suppressed, the thermal printer having the thermal printhead 1 can also suppress breakage. Therefore, a highly reliable thermal printer can be provided.

[0085] like Figure 2 As shown, the thermal printhead 1 is configured to face the paper pressure roller 72 of the thermal printer. The heating resistor 40 of the thermal printhead 1 faces the paper pressure roller 72 via a protective layer 45. A recording medium 71, such as thermal paper, is sandwiched between the protective layer 45 covering the heating resistor 40 and the paper pressure roller 72. When the thermal printer is operating, the paper pressure roller 72 rotates, and the recording medium 71 is conveyed at a certain speed between the heating resistor 40 and the paper pressure roller 72. Any part of the heating resistor 40 is heated, and this heat is transferred to the recording medium 71, thereby printing the recording medium 71.

[0086] [Manufacturing method of thermal printhead]

[0087] Next, the manufacturing method of the thermal printhead 1 according to this embodiment will be described. The manufacturing method of the thermal printhead 1 includes: a step of preparing an insulating substrate 10; a step of forming a gold-containing conductor pattern (gold conductor pattern 110); and a step of forming a silver-containing conductor pattern (silver conductor pattern 140).

[0088] (Preparation steps for insulating substrate)

[0089] In the preparation step of the insulating substrate 10, an insulating substrate 10 is prepared. The insulating substrate 10 may have a ceramic layer 11 and a glaze layer 12 disposed on the ceramic layer 11, as described above. The ceramic layer 11 can be the ceramic layer described above. The glaze layer 12 can be formed by a known method, for example, by printing and firing a glass paste onto the surface of the ceramic layer 11.

[0090] Next, a gold conductor pattern 110 and a silver conductor pattern 140 are formed on the surface of the insulating substrate 10. The method for forming the gold conductor pattern 110 and the silver conductor pattern 140 will be described later.

[0091] After the gold conductor pattern 110 and the silver conductor pattern 140 are formed, an auxiliary electrode electrically connected to the common electrode 26 can be formed on the surface of the second connecting portion 27 of the common electrode 26. Because the auxiliary electrode has a large area, it can expand the current path and suppress voltage drop. Therefore, even when the heating resistor 40 heats up over a wide area, sufficient current can flow, and the degradation of print quality can be suppressed. The auxiliary electrode can be formed, for example, by printing and firing a conductive paste containing silver particles onto the surface of the common electrode 26. The conductive paste may contain glass frit.

[0092] After forming the gold conductor pattern 110 and the silver conductor pattern 140, a silver film 70 can be formed on the surface of the gold conductor pattern 110 opposite to the insulating substrate 10. The silver film 70 is formed, for example, by printing and firing a conductive paste containing silver particles onto the surface of the gold pad 30. The conductive paste may contain glass frit.

[0093] The heating resistor 40 is formed by printing and firing a conductive paste in contact with the individual electrode 21 and the common electrode 26. The conductive paste may contain ruthenium oxide particles and glass frit with relatively high resistivity.

[0094] The protective layer 45 is formed by thick-film printing and firing of glass paste to cover the insulating substrate 10, the electrode 20 and the heating resistor 40.

[0095] The driver IC 51 is mounted on the surface of the insulating substrate 10. Specifically, the driver IC 51 is mounted on the surface of the insulating substrate 10 via flip-chip bonding, and is electrically connected to the independent electrode 21, thereby enabling the driver IC 51 to be mounted on the insulating substrate 10. Then, it is sealed with sealing resin 52 to cover the driver IC 51. Finally, by mounting the connector 53 and the heat sink 50 on the insulating substrate 10, the thermal printhead 1 is obtained.

[0096] Next, the steps for forming the gold conductor pattern 110 and the silver conductor pattern 140 will be explained.

[0097] (Steps for forming a gold conductor pattern)

[0098] In this embodiment, using Figures 9-13 This illustrates an example where the gold conductor pattern 110 is the gold solder pad 30. For example... Figure 9 As shown, in the gold conductor pattern forming step, a gold conductor pattern 110 is formed on the surface of the insulating substrate 10.

[0099] The gold conductor pattern 110 can also be directly printed using a printer, or can be formed by photolithography. In the case of direct printing, the printer uses a gravure printer, a screen printer, or an inkjet printer, or the like to print a gold resin paste, and the gold conductor pattern 110 can be formed.

[0100] In the case of using photolithography, the gold conductor pattern 110 can be formed by the steps of printing, firing, photoresist coating, masking, exposure, development, etching, and resist removal of a layer containing gold (gold layer).

[0101] The gold layer can be formed by printing a gold resin paste on the surface of the insulating substrate 10 using a printer such as a screen printer, and firing. The printing and firing steps can be performed only once, or the printing and firing steps can be repeated two or more times.

[0102] A photoresist is coated on the surface of the gold layer. The photoresist can be a positive resist or a negative resist. The coated photoresist can be stripped of solvent by heating or the like as needed. The method of coating the photoresist is not particularly limited, and a known coater such as a roll coater, a spray coater, or a spin coater can be used for coating.

[0103] The resist formed on the surface of the gold layer is masked using a photomask. The resist formed on the surface of the gold layer is irradiated with ultraviolet light by masking. The resist that has been deteriorated by the irradiation of ultraviolet light is dissolved by a developer, and the patterned resist is formed on the surface of the gold layer. As the developer, for example, an aqueous alkali solution such as an aqueous potassium hydroxide solution can be used.

[0104] After the gold layer on which the patterned resist is formed on the surface is etched by an etching solution, the gold conductor pattern 110 is formed. The etching method can use, for example, a known method such as a spray method or an immersion method.

[0105] The etching solution is not particularly limited as long as it can etch gold, and an iodine-based etching solution, an aqua regia-based etching solution, a cyanide-based etching solution, or the like can be used. As the iodine-based etching solution, for example, a mixture of iodine and potassium iodide can be exemplified. As the aqua regia-based etching solution, for example, a mixture of hydrochloric acid and nitric acid can be exemplified. As the cyanide-based etching solution, for example, a mixture of potassium cyanide and hydrogen peroxide can be exemplified. Of these, the etching solution is preferably an iodine-based etching solution in terms of ease of liquid handling and good etching speed.

[0106] The resist remaining on the surface of the gold conductor pattern 110 is dissolved and removed using a stripping solution such as an aqueous sodium hydroxide solution. Thus, the gold conductor pattern 110 is formed.

[0107] (Silver Conductor Pattern Formation Step)

[0108] Next, a silver conductor pattern 120 is formed on the surface of the gold conductor pattern 110.Figures 10-13 The method for forming a silver conductor pattern 140 is described. The steps for forming the silver conductor pattern 140 include forming a silver-containing layer (silver layer 120), forming a photoresist, performing an etching step, and removing the photoresist 130.

[0109] like Figure 10 As shown, in the step of forming the silver layer 120, the silver layer 120 is formed on the surface of the insulating substrate 10 and on the surface (upper surface) of the gold conductor pattern 110 opposite to the insulating substrate 10, in a manner that contacts the gold conductor pattern 110 disposed on the surface of the insulating substrate 10. In the method of this embodiment, as... Figure 10 As shown, the silver layer 120 is formed in such a way that it covers a portion of the gold solder pad 30.

[0110] The silver layer 120 contains silver and can be formed by printing silver paste onto the surface of the insulating substrate 10 using a printing machine such as a screen printing machine and then firing it. At this time, the silver layer 120 is formed in contact with the gold conductor pattern 110. The printing and firing steps can be performed only once, or the printing and firing steps can be performed repeatedly two or more times.

[0111] like Figure 11 As shown, in the step of forming the resist 130, the resist 130 is formed on at least a portion of the surface of the silver layer 120 in such a way that it covers the entire surface and edges of the gold conductor pattern 110 in contact with the silver layer 120 as viewed from the thickness direction z. That is, the resist 130 is formed on a portion of the silver layer 120, a portion of the insulating substrate 10, and the surface of the gold pad 30 in such a way that the gold conductor pattern 110 in contact with the silver layer 120 is not exposed. Specifically, the resist 130 is used to mask the exposed portion of the gold pad 30, which is the gold conductor pattern 110, in such a way that it is completely covered, and the silver layer 120 is masked with the resist 130 in such a way that it forms the connection portion 32, which is the silver conductor pattern 140. In order to prevent contact with the etching solution in the etching step described later, not only the upper surface of the gold conductor pattern 110 but also the entire edge of the gold conductor pattern 110 is masked with the resist 130.

[0112] The photoresist used in the formation of photoresist 130 can be either a positive or negative photoresist. The solvent in the coated photoresist can be removed by heating or other means as needed. There are no particular limitations on the coating method for the photoresist; for example, it can be applied using known coating machines such as roller coaters, spray coaters, or spin coaters.

[0113] A photoresist layer formed by coating a photoresist onto the surface of the silver layer 120 is masked by a photomask. The photoresist layer formed on the surface of the silver layer 120 is then exposed to ultraviolet light while being masked. The photoresist layer, which has deteriorated due to ultraviolet light exposure, is dissolved using a developer, thereby forming a patterned photoresist 130 on the surface of the silver layer 120. An alkaline aqueous solution, such as potassium hydroxide solution, can be used as the developer.

[0114] like Figure 12 As shown, in the step of forming the silver conductor pattern 140, the silver layer 120 with the resist 130 formed on its surface is etched using an etching solution to form the silver conductor pattern 140 connected to the gold conductor pattern 110. The silver layer 120 with the resist 130 is etched using an etching solution to form the silver conductor pattern 140. Etching can be performed using known methods such as spraying and immersion methods. The etching solution is not particularly limited as long as it can etch silver; a mixture of nitric acid, hydrochloric acid, and acetic acid can be used.

[0115] like Figure 13 As shown, in the step of removing the resist 130, the resist 130 on the surfaces of the gold conductor pattern 110 and the silver conductor pattern 140 is removed. Residual resist 130 on the surfaces of the gold conductor pattern 110 and the silver conductor pattern 140 can be removed by dissolving it with a stripping solution such as an aqueous sodium hydroxide solution. As described above, the gold pad 30 is covered by the resist 130 and does not come into contact with the etching solution, therefore, localized cell reactions are unlikely to occur between the gold pad 30 (gold conductor pattern 110) and the connection portion 32 (silver conductor pattern 140) during etching. Therefore, over-etching of the connection portion 32 formed by silver, which has a lower ionization tendency than gold, can be suppressed.

[0116] In the step of forming the silver film 70, a silver film 70 with a different composition than the connector 32 is formed on the surface of the gold solder pad 30 opposite to the insulating substrate 10 (the upper surface of the gold solder pad 30) for soldering. The silver film 70 can be formed by printing and firing silver paste. The silver paste may contain, for example, silver particles and resin components.

[0117] Next, the method for forming the silver conductor pattern 140 in another embodiment is described using... Figure 14 and Figure 15 Please provide an explanation. Figure 14 This is a top view illustrating an example of how the silver layer 120 is formed to cover the entire gold solder pad 30. Figure 15 This is a top view showing an example of the state after the resist 130 remaining on the surface of the conductor pattern has been removed. In the method of this embodiment, as... Figure 14 As shown, except that the silver layer 120 is formed in a manner that covers the entire gold solder pad 30, it is the same as the above embodiment.

[0118] Even when a silver layer 120 is formed as described above, a resist 130 is formed on a portion of the surface of the silver layer 120 in such a manner that it covers the entire surface and edges of the gold pads 30 in contact with the silver layer 120, viewed from the thickness direction z. With this masking, the gold pads 30 are covered by the resist 130 and do not come into contact with the etching solution. Therefore, as... Figure 15 As shown, the gold pads 30, which are gold conductor patterns 110, and the connection portion 32, which is silver conductor pattern 140, are less prone to localized cell reactions during etching. Therefore, it is possible to suppress over-etching of the connection portion 32 formed by silver, which has a lower ionization tendency than gold.

[0119] Next, use Figure 16 and Figure 17 The method for forming the silver conductor pattern 140 of the comparative example is explained. Figure 16 This is a top view illustrating a comparative example in which the resist 330 is formed by exposing the gold conductor pattern 310 in contact with the silver layer 320. Figure 17 This is a top view showing the state of a comparative example after the resist 330 remaining on the surface of the gold solder pad 230 (which is the gold conductor pattern 310) and the connection portion 232 (which is the silver conductor pattern 340) has been removed.

[0120] like Figure 16 As shown, the silver layer 320 is formed in such a way that it covers a portion of the gold pads 230 disposed on the surface of the insulating substrate 210. In the comparative example method, the silver layer 320 is masked with resist 330 in order to form the connection portion 232, but a portion of the gold pads 230, which is the gold conductor pattern 310, is not masked by the resist 330. In this masked case, the gold pads 230 come into contact with the etching solution during the etching step, and localized cell reactions easily occur between the gold pads 230, which is the gold conductor pattern 310, and the connection portion 232, which is the silver conductor pattern 340. Therefore, as Figure 17 As shown, the connection portion 232 is over-etched, making it easy to form a silver conductor pattern 340 with a smaller area than the resist 330.

[0121] Next, use Figure 18 and Figure 19 An example is given where the gold conductor pattern 110 consists of an independent electrode 21 and a shared electrode 26. Specifically, an example is given where the gold conductor pattern 110 consists of a first strip 24, a second connecting portion 27, and a second strip 28, and the silver conductor pattern 140 consists of a first connecting portion 23. In the method of this embodiment, as... Figure 18As shown, a silver layer 120 is formed on the surface of the insulating substrate 10 and the first strip portion 24 in contact with the first strip portion 24 provided on the surface of the insulating substrate 10. The silver layer 120 is formed in contact with one end of the first strip portion 24 on the side opposite to the second connecting portion 27. Next, a resist 130 is formed on at least a part of the surface of the silver layer 120 in a manner to cover the entire surface and the edge portion of the first strip portion 24 as viewed in the thickness direction z. Specifically, the resist 130 is formed on a part of the silver layer 120, a part of the insulating substrate 10, and the surface of the first strip portion 24. Next, the silver layer 120 on which the resist 130 is formed on the surface is etched with an etching solution, thereby forming the first connecting portion 23 connected to the first strip portion 24. In the case of masking as described above, the first strip portion 24 is covered with the resist 130 and does not come into contact with the etching solution. Therefore, as shown, the first strip portion 24 as a part of the gold conductor pattern 110 and the first connecting portion 23 as a part of the silver conductor pattern 140 do not easily undergo a local cell reaction at the time of etching. Thus, over-etching of the first connecting portion 23 formed of silver having a smaller ionization tendency than gold can be suppressed. Further, since the second connecting portion 27 and the plurality of second strip portions 28 as the gold conductor pattern 110 do not come into contact with the silver layer 120, they do not participate in the local cell reaction. Figure 19 As shown, the first strip portion 24 as a part of the gold conductor pattern 110 and the first connecting portion 23 as a part of the silver conductor pattern 140 do not easily undergo a local cell reaction at the time of etching. Thus, over-etching of the first connecting portion 23 formed of silver having a smaller ionization tendency than gold can be suppressed. Further, since the second connecting portion 27 and the plurality of second strip portions 28 as the gold conductor pattern 110 do not come into contact with the silver layer 120, they do not participate in the local cell reaction.

[0122] Next, a method of forming the silver conductor pattern 140 according to another embodiment will be described with reference to FIGS. 16A to 16D. Figure 20 and Figure 21 Next, a method of forming the silver conductor pattern 140 according to another embodiment will be described with reference to FIGS. 16A to 16D. Figure 20 is a plan view illustrating an example in which the resist 130 is formed on at least a part of the surface of the silver layer 120 in a manner to cover the entire surface and the edge portion of the first strip portion 24 as viewed in the thickness direction z. Figure 21 is a plan view illustrating an example of a state in which the resist 130 remaining on the surfaces of the gold conductor pattern 110 and the silver conductor pattern 140 is removed.

[0123] In the example shown in FIG. 17, the resist 130 is formed on not only the first strip portion 24 but also the surfaces of the second connecting portion 27 and the second strip portions 28. In the case of masking as described above, the first strip portion 24 is covered with the resist 130 and does not come into contact with the etching solution. Therefore, as shown, the first strip portion 24 as a part of the gold conductor pattern 110 and the first connecting portion 23 as a part of the silver conductor pattern 140 do not easily undergo a local cell reaction at the time of etching. Thus, over-etching of the first connecting portion 23 formed of silver having a smaller ionization tendency than gold can be suppressed. Figure 20 As shown, the first strip portion 24 as a part of the gold conductor pattern 110 and the first connecting portion 23 as a part of the silver conductor pattern 140 do not easily undergo a local cell reaction at the time of etching. Thus, over-etching of the first connecting portion 23 formed of silver having a smaller ionization tendency than gold can be suppressed. Further, since the second connecting portion 27 and the plurality of second strip portions 28 as the gold conductor pattern 110 do not come into contact with the silver layer 120, they do not participate in the local cell reaction. Figure 18 Figure 21 As shown, the first strip portion 24 as a part of the gold conductor pattern 110 and the first connecting portion 23 as a part of the silver conductor pattern 140 do not easily undergo a local cell reaction at the time of etching. Thus, over-etching of the first connecting portion 23 formed of silver having a smaller ionization tendency than gold can be suppressed. Further, since the second connecting portion 27 and the plurality of second strip portions 28 as the gold conductor pattern 110 do not come into contact with the silver layer 120, they do not participate in the local cell reaction.

[0124] Next, a method of forming the silver conductor pattern 140 according to another embodiment will be described with reference to FIGS. 16A to 16D. Figure 22 and​Figure 23 A method of forming the silver conductor pattern 340 of the comparative example will be described. Figure 22 is a plan view of a comparative example in which the resist 330 is formed so as to be exposed to the gold conductor pattern 310 in contact with the silver layer 320. Figure 23 is a plan view showing the state of the comparative example after the resist 330 remaining on the surfaces of the gold conductor pattern 310 and the silver conductor pattern 340 is removed.

[0125] As shown in Figure 22 , the silver layer 320 is formed so as to cover a part of the first strip portion 224. In the method of the comparative example, the silver layer 320 is masked with the resist 330 in a manner to form the first connecting portion 223 as the silver conductor pattern 340, but a part of the first strip portion 224 as the gold conductor pattern 310 is not masked with the resist 330. In the case where masking is performed like this, the first strip portion 224 is brought into contact with the etching solution in the etching step, and the first strip portion 224 as the gold conductor pattern 310 is likely to undergo a local battery reaction with the first connecting portion 223 as the silver conductor pattern 340. Therefore, as shown in Figure 23 , the first connecting portion 223 is likely to be over-etched. Further, since the second connecting portion 227 and the plurality of second strip portions 228 as the gold conductor pattern 310 are not in contact with the silver layer 320, they do not participate in the local battery reaction.

[0126] As described above, the method of manufacturing the thermal head 1 of the present embodiment includes the following steps. That is, the above-described method includes a step of forming a layer containing silver (silver layer 120) on the surface of the insulating substrate 10 and the surface of the gold conductor pattern 110 on the opposite side of the insulating substrate 10 in contact with the gold conductor pattern (gold conductor pattern 110) containing gold provided on the surface of the insulating substrate 10. The above-described method includes a step of forming a resist 130 on at least a part of the surface of the silver layer 120 in a manner to cover the entire surface and the edge portion as a whole of the gold conductor pattern 110 in contact with the silver layer 120 as viewed in the thickness direction z. The above-described method includes a step of etching the silver layer 120 on which the surface is formed with the resist 130 with an etching solution, thereby forming a conductor pattern containing silver (silver conductor pattern 140) connected to the gold conductor pattern 110. The above-described method includes a step of removing the resist 130 from the surface of the silver conductor pattern 140.

[0127] In the method of the present embodiment, the gold conductor pattern 110 and the silver conductor pattern 140 are formed. Thereby, among the conductor patterns necessary for the thermal head 1, since the portion replaceable with silver can be replaced from gold to silver, the amount of gold used can be reduced, and the cost of the thermal head 1 can be reduced.

[0128] However, if the silver conductor pattern 140 is formed in a manner to be electrically connected to the gold conductor pattern 110, over-etching in which silver is excessively etched occurs when silver is etched, and there is a case where the electrode 20 is formed thinner than a target. The reason is presumed to be that, due to contact of gold and silver which are different kinds of metals, a difference in potential occurs between these metals, a local cell reaction in which silver which has a larger ionization tendency is anode and gold which has a smaller ionization tendency is cathode occurs with an etching solution as an electrolyte. In a case where, for example, nitric acid is used as a silver etching solution, a reaction shown in the following reaction formula (1) occurs at the anode, and a reaction shown in the following reaction formula (2) occurs at the cathode.

[0129] Ag→ Ag + + e - (1)

[0130] HNO3+ 3H + + 3e - → 2H2O + NO↑ (2)

[0131] However, in the manufacturing method of the thermal head 1 of the present embodiment, a step of forming a resist 130 on at least a part of the surface of the silver layer 120 in a manner to cover the entire surface and the edge portion of the gold conductor pattern 110 as viewed in the thickness direction z is included. Therefore, even in a case where the edge portion of the silver conductor pattern 140 is in contact with the etching solution, the etching solution which becomes an electrolyte is not in contact with the gold conductor pattern 110, and thus a local cell is not formed. Therefore, a state in which only the edge portion of the silver conductor pattern 140 is in contact with the etching solution is formed, and electromotive force which occurs in a case where a local cell is formed does not occur, and thus over-ionization of silver and elution thereof are suppressed. Therefore, according to the manufacturing method of the thermal head 1 of the present embodiment, a case where the electrode 20 is formed thinner than a target is suppressed, and thus even in a case where a gold electrode 20 and a silver electrode 20 are used, disconnection of the silver electrode 20 is suppressed.

[0132] Further, in a case where the silver conductor pattern 140 is etched without being in contact with a different kind of metal like the gold conductor pattern 110, over-etching to the extent of a case where the gold conductor pattern 110 and the silver conductor pattern 140 are in contact does not easily occur. The reason is presumed to be that, as described above, since different kinds of metals are not in contact, a cathode and an anode are not formed in different kinds of metals, the entire surface of silver functions as an anode and a cathode, and the above reaction formula (1) and the above reaction formula (2) occur uniformly on the surface of silver. Further, since the anode and the cathode are the same kind of metal, there is almost no difference in potential between the anode and the cathode, and thus it is presumed that ionization of silver does not easily proceed at a too fast speed as in a case where different kinds of metals are in contact. Therefore, in a case where a single kind of metal is etched, over-etching as described above does not easily occur.

[0133] Further, the gold conductor pattern 110 is a gold pad 30, and the silver conductor pattern 140 can be a connection portion 32. In addition, the method of manufacturing the thermal printhead 1 can also include a step of forming a silver-containing film (silver film 70) having a different composition from the connection portion 32 on the surface of the gold pad 30 on the side opposite the insulating substrate 10. That is, the above-described method can also include a step of forming a silver-containing layer (silver layer 120) on the surface of the insulating substrate 10 and the surface of the gold pad 30 on the side opposite the insulating substrate 10 in contact with the gold pad 30 provided on the surface of the insulating substrate 10. The above-described method can also include a step of forming a resist 130 on at least a portion of the surface of the silver layer 120 in a manner so as to cover the entire surface and the edge portion of the gold pad 30 on the side opposite the insulating substrate 10 in contact with the silver layer 120. The above-described method can also include a step of etching the silver layer 120 on which the resist 130 is formed using an etching solution to form the silver-containing connection portion 32 connected to the gold pad 30. The above-described method can also include a step of removing the resist 130 from the surface of the connection portion 32. The above-described method can also include a step of forming a silver-containing film (silver film 70) having a different composition from the connection portion 32 on the surface of the gold pad 30 on the side opposite the insulating substrate 10. According to such a method, the above-described thermal printhead 1 can be manufactured.

[0134] [Other Embodiments]

[0135] As described above, several embodiments have been described, but the discussion and drawings constituting a part of the present application are illustrative and should not be construed as limiting. Those skilled in the art can conceive of alternative embodiments, examples, and applications of the present application. As such, the present embodiments include various embodiments and the like not described herein.

Claims

1. A thermal printhead, characterized by, include: Insulating substrate; An electrode having a gold-containing pad disposed on the surface of the insulating substrate and a silver-containing connecting portion disposed on the surface of the insulating substrate, the connecting portion being connected to the surface of the pad opposite to the insulating substrate. and A silver-containing film, with a different composition than the connecting portion, is disposed on the surface of the solder pad opposite to the insulating substrate. The connecting portion covers the solder pad in such a way that it clamps the solder pad from the edge of the solder pad. The electrode comprises a plurality of individual electrodes disposed on the surface of the insulating substrate and a common electrode disposed between the plurality of individual electrodes. The thermal printhead also includes a heating resistor disposed across the surfaces of the plurality of individual electrodes and the surface of the common electrode. The plurality of independent electrodes each have a first strip-shaped portion spanning the heating resistor and a first connecting portion connected to the end of the first strip-shaped portion. The end face of the first connector along the main scanning direction is the end face of a silver conductor pattern formed by printing. The end face of the first connector along the sub-scanning direction is the end face of a silver conductor pattern formed by etching.

2. The thermal printhead as described in claim 1, characterized in that: The solder pad has a covered portion that is covered by the connection portion when viewed in the thickness direction and a non-covered portion that is not covered by the connection portion.

3. The thermal printhead as described in claim 1, characterized in that: The solder pad is completely covered by the connecting portion when viewed in the thickness direction.

4. The thermal printhead as described in claim 1, characterized in that: The membrane also contains at least one element selected from platinum, palladium and bismuth.

5. The thermal printhead as described in claim 1, characterized in that: The membrane is formed from an alloy of silver and platinum, an alloy of silver and palladium, or silver containing bismuth oxide.

6. The thermal printhead as described in claim 1, characterized in that: The thickness of the solder pad is 0.2 μm or more and 1.2 μm or less, the thickness of the connector is 0.2 μm or more and 1.2 μm or less, and the thickness of the film is 2 μm or more and 10 μm or less.

7. The thermal printhead as described in claim 1, characterized in that: It also includes a driver IC mounted on the insulating substrate and connected to the plurality of independent electrodes.

8. The thermal printhead as described in claim 7, characterized in that: The driver IC is connected to the electrode via multiple bumps, and any one of the multiple bumps is connected to each of the multiple independent electrodes.

9. The thermal printhead as described in claim 8, characterized in that: The connecting portion is connected to a protrusion among the plurality of protrusions that is different from the protrusions connected to the plurality of independent electrodes.

10. The thermal printhead as described in claim 1, characterized in that: The membrane is arranged such that its area is smaller than that of the solder pad when viewed in the thickness direction.

11. The thermal printhead as described in claim 1, characterized in that: The membrane is connected to a connector or flexible substrate via solder.

12. The thermal printhead as described in claim 1, characterized in that: The insulating substrate comprises a ceramic layer and a glaze layer disposed on the ceramic layer.

13. A method for manufacturing a thermal printhead, characterized in that, include: The step of forming a silver-containing layer on the surface of the insulating substrate and the surface of the solder pad opposite to the insulating substrate in such a way as to contact the gold-containing solder pad disposed on the surface of the insulating substrate; The step of forming a resist on at least a portion of the surface of the layer in such a way that it covers the entire surface and edges of the pads in contact with the layer in the thickness direction; The step of using an etching solution to etch a silver-containing layer on the surface of which the resist is formed, to form a silver-containing connection portion that is connected to the solder pad; The step of removing the resist from the surface of the connection portion; and The step of forming a silver-containing film with a different composition from the connection portion on the surface of the solder pad opposite to the insulating substrate.

14. The method for manufacturing a thermal printhead as described in claim 13, characterized in that: The layer is formed in such a way that it covers a portion of the solder pad.

15. The method for manufacturing a thermal printhead as described in claim 13, characterized in that: The layer is formed in such a way that it covers the entire solder pad.

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