JP6280478B2 - Thermal head - Google Patents

Description

  The present invention relates to a thermal head used in a thermal printer or the like.

  The thermal head generates heat on the heating portions of a plurality of heating resistors arranged in a direction (main scanning direction) orthogonal to the direction in which the printing medium such as thermal recording paper is conveyed, and the heat causes characters on the printing medium. This is an output device for forming images such as images and figures. This thermal head is widely used in recording devices such as a barcode printer, a digital plate making machine, a video printer, an imager, and a seal printer.

  A general thermal head includes a heat radiating plate, a heat generating plate attached to the heat radiating plate, and a circuit board attached to the heat radiating plate on the same side as the heat generating plate. Heat generating resistors are linearly arranged at predetermined intervals in a heat generating region extending in a band shape on the surface opposite to the surface of the heat generating plate opposite to the heat radiating plate. Also, a drive IC (Integrated Circuit) that is a part of a drive circuit that drives the heating resistor is mounted on, for example, a circuit board (see, for example, Patent Document 1).

JP 2012-66476 A

  In such a thermal head, it is desired to make the print density uniform from one end to the other end of the heat generating area in the main scanning direction, thereby improving the print quality.

  Accordingly, an object of the present invention is to improve the printing quality of a thermal head.

  In order to solve the above-mentioned problems, the present invention provides a thermal head, a heat sink, a circuit board placed on the top surface of the heat sink, and a top surface of the heat sink adjacent to the circuit board. A heat insulating layer formed on the upper surface of the insulating substrate, and a plurality of heating resistors formed on the upper surface of the heat insulating layer and arranged in a row in the main scanning direction. A folded electrode connecting the first ends of the heating resistors, an individual electrode formed on one of the second ends of the pair of heating resistors, and a common formed on the other of the second ends of the heating resistors An insulating substrate having a common electrode bus connected along the main scanning direction at a position closer to the circuit board than the individual electrodes connected to the electrode lines, and an upper surface of the common electrode bus along the main scanning direction Reinforced bumps that reduce the resistance of the current path A power supply terminal disposed at an end of the common electrode bus in the main scanning direction and supplied with power; a protective layer formed above the heat retaining layer; and driving the heating resistor mounted on the circuit board And a bonding wire for connecting the individual electrode and the driving IC.

  According to the present invention, the print quality of the thermal head can be improved.

It is a partially cutaway top view in an embodiment of a thermal head according to the present invention. It is a figure for demonstrating one Embodiment of the thermal head which concerns on this invention, Comprising: It is YY 'arrow sectional drawing of FIG. It is a partial top view of the thermal head according to the present invention. FIG. 4 is a view for explaining one embodiment of a thermal head according to the present invention, and is a cross-sectional view taken along the line XX ′ of FIG. 3. It is a figure for demonstrating the conventional thermal head, Comprising: (a) is a partial top view, (b) is the XX 'arrow sectional drawing.

  An embodiment of a thermal head according to the present invention will be described with reference to the drawings. This embodiment is merely an example, and the present invention is not limited to this.

  1 to 5, the direction of the arrow ds represents the direction (sub-scanning direction) in which the printing medium is conveyed, and the direction of the arrow dm is orthogonal to the direction in which the printing medium is conveyed and the heating resistor 23a. Represents a direction (main scanning direction) in which a plurality of are arranged at intervals and the heat generating region 24 extends.

  As shown in FIGS. 1, 2, 3, and 4, the thermal head 10 according to the present embodiment includes, for example, a heating plate 20, a circuit board 40, and a heat radiating plate 30. The heat generating plate 20 is placed on the heat dissipation plate 30 adjacent to the circuit board 40 on the downstream side in the transport direction in the direction in which the printing medium is transported. The heat sink 30 is a plate formed of a metal such as aluminum.

  A heat generating region 24 extending in a strip shape is formed in the heat generating plate 20. A control signal and driving power for forming a predetermined heat generation pattern in the heat generation region 24 are input to the circuit board 40 and further to the heating element plate 20 electrically connected to the circuit board 40 via the bonding wires 44. Entered.

  The heating element plate 20 includes a support substrate 22, a heating resistor layer 23, an electrode 28, a reinforcing bump group 70, and a protective layer 29.

The support substrate 22 includes a ceramic insulating plate 22a such as alumina (Al ₂ O ₃ ), for example, and a heat insulating layer 22b called a glaze layer formed in layers on the upper surface of the insulating plate 22a. The heat insulating layer 22b is formed of, for example, silicon oxide (SiO ₂ ).

The heating resistor layer 23 is formed in a layer on a part of the upper surface of the heat insulating layer 22b, for example, with a cermet such as TaSiO ₂ . In the heating resistor layer 23, a plurality of heating resistors 23a are arranged at intervals in the main scanning direction dm.

  The electrode 28 includes a common electrode 28a, an individual electrode 28b, and a folded electrode 28c made of, for example, aluminum (Al). The electrode 28 and the heating resistor layer 23 are covered with a protective layer 29 made of, for example, silicon oxynitride (SiON).

  The common electrode lines 34 and the individual electrodes 28b of the common electrode 28a are alternately formed in a layered manner on the upper surface of the heating resistor 23a in the main scanning direction dm. The plurality of common electrode lines 34 of the common electrode 28a are common extending from one end side to the other end side in the main scanning direction dm of the heating element plate 20 in the vicinity of the end portion of the heating element plate 20 near the circuit board 40. The electrode bus 32 is connected to each other. The common electrode bus 32 is formed such that the common portion width W1 which is the width in the sub scanning direction ds direction is about 300 μm and the thickness is about 0.8 μm.

  The folded electrode 28c has a U-shape, and is formed on the upper surface of the heating resistor layer 23 in the form of a layer in the vicinity of the end portion of the heating plate 20 that is separated from the circuit board 40.

  An end of the common electrode 28a on the downstream side in the transport direction of the common electrode wire 34 (the other end of the second end of the heating resistor 23a) and an end on the upstream side in the transport direction of the folded electrode 28c (the first end of the heating resistor 23a). And the other) are arranged so as to face each other with a gap of a predetermined length as the length of the heating resistor sandwiched from the sub-scanning direction ds.

  Similarly, the other end of the folded electrode 28c on the upstream side in the transport direction (one of the first ends of the heating resistors 23a) and the end of the individual electrode 28b on the downstream side in the transport direction (one of the second ends of the heating resistors 23a). Are arranged so as to face each other with a gap having a predetermined length from the sub-scanning direction ds. Thus, the folded electrode 28c is electrically connected to a pair of heating resistors 23a adjacent in the main scanning direction dm.

  The current that has flowed through the common electrode 28a is located in the gap between the common electrode 28a and the folded electrode 28c and the heating resistor 23a located in the gap between the folded electrode 28c and the individual electrode 28b and the folded electrode 28c. Since it passes through the heat generating resistor 23a, the heat generating portion 23b generates heat when the thermal head 10 prints on the printing medium. The heat generating portions 23b are arranged at intervals in the main scanning direction dm to form a heat generating region 24 extending in the main scanning direction dm.

  One end of a bonding wire 44 having a diameter of 20 to 30 μm formed of, for example, gold (Au) is connected to the individual electrode bonding pad 26 which is a bonding pad of the individual electrode 28b, and the other end is connected to the driving IC 42 on the circuit board 40. Connected. The common electrode 28a is connected to a common electrode bonding pad 27 provided at one end and the other end of the common electrode bus 32 in the main scanning direction dm via a bonding wire (not shown) provided on the circuit board 40. Drive power is supplied from. The bonding wire connected to the common electrode bonding pad 27 is connected to the power supply unit so as not to contact the bonding wire 44 connected to the individual electrode bonding pad 26 of the individual electrode 28b. The drive IC 42 and the bonding wire 44 are sealed with a resin 48.

  On the common electrode bus 32 of the common electrode 28a, a reinforcing bump group 70 is formed as a reinforcing protrusion group that reinforces the common electrode bus 32 so as to lower the electric resistance value. The reinforcing bump group 70 is configured by arranging two rows of reinforcing bumps 74 in which a plurality of reinforcing bumps 72 are arranged in a line at predetermined intervals in the sub-scanning direction ds. For example, about 120 reinforcing bump rows 74 are arranged in a straight line from one end to the other end in the main scanning direction dm of the common electrode bus 32 along the main scanning direction dm while the reinforcing bumps 72 are in contact with each other at the root portion. It is installed. Further, the reinforcing bump rows 74 are regularly arranged such that a plurality of reinforcing bumps 72 having substantially the same size have a constant distance between the centers of adjacent reinforcing bumps 72 along the main scanning direction dm. . The upper surface of the reinforcing bump group 70 is covered with the resin 48 but is not covered with the protective layer 29.

  The reinforcing bump 72 is a substantially frustoconical bump having a diameter (bump diameter A1) of about 70 μm formed of gold similarly to the bonding wire 44, and the upper end of the reinforcing bump 72 with respect to the upper surface of the common electrode bus 32. The bump height H1, which is the height, is about 35 μm. Here, the sub-scanning direction bump interval D1, which is the distance between the reinforcing bump rows 74 adjacent in the sub-scanning direction ds, is about 100 μm.

  When a current flows from the common electrode bonding pad 27 toward the center of the common electrode bus 32 in the main scanning direction dm, the current is once divided into the common electrode bus 32 and the reinforcing bump row 74 and then merges. In this way, the reinforcing bump group 70 jumps the current flowing from the common electrode bonding pad 27 toward the center in the main scanning direction dm. For this reason, the thermal head 10 can reduce the resistance value of the current path when the current flows from the common electrode bonding pad 27 toward the center in the main scanning direction dm, and can suppress the attenuation of the current. Further, since the reinforcing bumps 72 are regularly bonded and extended along the main scanning direction dm, the thermal head 10 substantially equalizes the voltage at the common electrode bus bar 32 along the main scanning direction dm. Can do.

  Here, a manufacturing method of the thermal head 10 in the present embodiment will be described.

  In the method of manufacturing the thermal head 10 in the present embodiment, first, the heat insulating layer 22b made of silicon oxide or the like is fixed to the upper surface of the insulating plate 22a made of alumina or the like.

Next, the heating resistor layer 23 made of cermet such as TaSiO ₂ is fixed to the upper surface of the heat insulating layer 22b by sputtering or the like. Thereafter, a conductive material such as aluminum is fixed to the entire surface by sputtering or the like.

  Next, the heating resistor layer 23 and the conductive material are patterned by etching so that the heating resistors 23 a are arranged on the lower surface of the electrode 28.

  Thereafter, while covering the electrode 28, the heat generating portion 23b, and the heat insulating layer 22b, the common electrode bonding pad 27 portion of the common electrode 28a, the reinforcing bump group 70, and the individual electrode bonding pad 26 portion of the individual electrode 28b are excluded. A protective layer 29 such as silicon oxynitride is fixed to the entire surface by sputtering or the like.

  Next, a plurality of reinforcing bumps 72 are bonded to the upper surface of the common electrode bus 32 of the common electrode 28a by ultrasonic bonding, thereby forming the reinforcing bump group 70. Specifically, this ultrasonic bonding is a process in which the gold wire is bonded to the common electrode bus bar 32 by ultrasonic vibration and then the gold wire is cut to form a bump that is a conductive protrusion.

  The heating plate 20 thus formed is placed on the heat sink 30 together with the circuit board 40. Further, the thermal head 10 is manufactured by connecting the heating element plate 20 and the circuit board 40 with the bonding wires 44, and further sealing the connection portion with the bonding wires 44 with the resin 48.

  By the way, when the driving IC 42 is mounted on the circuit board 40 instead of the heating element plate 20 and the common electrode 28a formed so as to extend in the main scanning direction dm is used on the heating element plate 20 as in the thermal head 10, driving is performed. Since the IC 42 is not placed on the heating element plate 20, the width of the heating element plate 20 in the sub-scanning direction ds can be shortened as compared with the case where the driving IC 42 is placed on the heating element plate 20. Like the heating plate 120 shown in FIG. 5, since the bonding wire 44 exists, the driving power is applied only to the common electrode bonding pads (not shown) at both ends in the main scanning direction dm of the common electrode 28a via the bonding wire. Could not supply.

  For this reason, in the conventional thermal head, the voltage applied to the common electrode bonding pad drops due to the resistance of the common electrode bus 32 toward the central portion of the common electrode bus 32 of the common electrode 28a in the main scanning direction dm. As a result, the current flowing through the heating resistor is reduced. Therefore, in the conventional thermal head, the print density at the center in the main scanning direction dm is thinner than at both ends, and the print density may not be uniform.

  As described above, in the conventional thermal head, a voltage drop occurs in the main scanning direction dm, and the print density does not become uniform. Therefore, the print density is increased from one end to the other end of the heat generating region 24 in the main scan direction dm. It was difficult to make uniform.

  On the other hand, in the thermal head 10, in the common electrode bus 32 in the common electrode 28a, the reinforcing bump rows 74 formed of the reinforcing bumps 72 arranged in parallel in the main scanning direction dm are arranged at predetermined intervals along the sub scanning direction ds. The reinforced bump group 70 is provided.

  Therefore, the thermal head 10 jumps the current flowing from the common electrode bonding pad 27 toward the center in the main scanning direction dm by the reinforcing bump group 70 and shunts it in parallel to reinforce the power source along the main scanning direction dm. By preventing the voltage drop, the potential can be stabilized from one end to the other end in the main scanning direction dm of the common electrode bus 32 of the common electrode 28a, and the current flowing through all the heating resistors 23a can be made almost uniform. it can.

  As a result, the thermal head 10 can make the print density uniform from one end to the other end of the heat generating region 24 in the main scanning direction dm, thereby improving the print quality.

  Further, since the thermal head 10 is configured to connect the reinforcing bump 72 formed of gold, which is a material having higher conductivity than aluminum, to the common electrode bus 32, the reinforcing bump 72 is formed of the same aluminum as the common electrode bus 32. Compared with the case, it is possible to make the current flow more easily from the common electrode bonding pad 27 toward the central portion in the main scanning direction dm.

  Furthermore, since the thermal head 10 is arranged so that two rows of reinforcing bumps 74 extending along the main scanning direction dm are arranged in the sub scanning direction ds with a sub scanning direction bump interval D1 therebetween, only one row of reinforcing bumps is arranged. Compared with the case where 74 is formed, the current can be more easily passed.

  Further, since the thermal head 10 extends the reinforcing bump row 74 from one end to the other end of the common electrode bus 32 in the main scanning direction dm, the thermal head 10 starts from one end of the common electrode bus 32 in the main scanning direction dm. The potential can be stabilized up to the other end.

  The common electrode bus 32 is very narrow because the common portion width W1 is formed to be about 300 μm. However, the reinforcing bump 72 is a bump having a bump diameter A1 of about 70 μm. Even with the narrow common electrode bus 32, two rows of reinforcing bumps 74 can be arranged on the upper surface.

  Further, since the thermal head 10 is sandwiched between the individual electrode bonding pad 26 and the circuit board 40 and the bonding wire 44 passes above, the width in the sub-scanning direction ds installed on the upper surface of the insulating plate 22a is limited. For this reason, since the thermal head 10 has a configuration in which the common electrode bus 32 is provided closer to the circuit board 40 than the individual electrode 28b, the common portion width W1 is as narrow as about 300 μm, and the thickness of the common electrode bus 32 is further reduced. Since the common electrode bus 32 is formed as thin as about 0.8 μm, the resistance value of the current path is high. In the thermal head 10 having such a configuration, it is difficult in manufacturing to lower the resistance value of the current path by adding a conductive layer on the upper surface of the common electrode bus bar 32. The thermal head 10 of the present embodiment is useful because it can reduce the resistance value of the current path of the common electrode bus 32 even in such a case.

  By the way, as a configuration for stabilizing the potential from one end to the other end of the common electrode bus 32 in the main scanning direction dm, one end is connected to the common electrode bus 32 by ultrasonic bonding, and the common electrode is connected along the main scanning direction dm. It is also conceivable to use a reinforcing bonding wire that floats upward from the bus bar 32 and whose other end is reconnected to the common electrode bus bar 32 by ultrasonic bonding. However, in the case of such a thermal head, the height of the upper end portion of the reinforcing bonding wire with respect to the common electrode bus bar 32 is required to be about 50 μm at maximum, so that the reinforcing bonding wire and the bonding wire 44 may come into contact with each other. When the reinforcing bonding wire and the bonding wire 44 come into contact with each other, the common electrode bus bar 32 and the individual electrode 28b are short-circuited.

  On the other hand, in the thermal head 10 of the present embodiment, the reinforcing bumps 72 that are bumps are used instead of wires, so that the bump height H1 can be suppressed to about 35 μm. The possibility of contact with can be reduced.

  In the case of a reinforced bonding wire, since one end and the other end of the wire are connected to the common electrode bus 32 by ultrasonic bonding, a certain distance is required from one end to the other end along the main scanning direction dm. On the other hand, in the thermal head 10 according to the present embodiment, the reinforcing bumps 72 which are bumps instead of wires are used, so that the reinforcing bumps 72 can be finely arranged along the main scanning direction dm while being in contact with each other.

  As described above, in the thermal head 10 of the present embodiment, the circuit board 40 placed on the upper surface of the heat radiating plate 30 and the circuit board 40 placed on the upper surface of the heat radiating plate 30 adjacent to the sub-scanning direction ds. An insulating plate 22a, a heat insulating layer 22b formed on the upper surface of the insulating plate 22a, a heating resistor 23a formed on the upper surface of the heat insulating layer 22b and arranged in a plurality at intervals in the main scanning direction dm, A folded electrode 28c that connects the first ends of a pair of adjacent heating resistors 23a, a gap between one end of the folded electrodes 28c, and an individual electrode 28b that is formed on one of the second ends of the pair of heating resistors 23a; In the main scanning direction dm, a gap is provided between the other end of the folded electrode 28c and connected to the common electrode line 34 formed on the other end of the second end of the heating resistor 23a and closer to the circuit board 40 than the individual electrode 28b. Formed along The common electrode bus 32 of the common electrode 28a to which power is supplied to the end in the scanning direction, and the reinforcement formed on the upper surface of the common electrode bus 32 of the common electrode 28a along the main scanning direction dm to lower the resistance value of the current path. A bump group 70; a common electrode bonding pad 27 that is arranged at the end of the common electrode bus 32 of the common electrode 28a in the main scanning direction dm and is supplied with power; a protective layer 29 formed on the upper surface of the heat retaining layer 22b; A drive IC 42 that is mounted on the circuit board 40 and drives the heating resistor 23a, and a bonding wire 44 that connects the individual electrode 28b and the drive IC 42 are provided.

  In the thermal head 10 described above, the reinforcing bumps 72 are made of gold. However, the invention is not limited to this. For example, the common electrode 28a made of aluminum such as silver (Ag), copper (Cu), or aluminum is used. It may be connected to the common electrode bus bar 32 by bonding and may be made of various conductive materials. However, in the thermal head 10, since the bonding wire 44 is already used, when a wire similar to the bonding wire 44 is used as the reinforcing bump 72, it is not necessary to prepare a new wire.

  Further, in the thermal head 10 described above, the reinforcing bump group 70 includes two rows of reinforcing bumps 74 extending in the main scanning direction dm with an interval in the sub-scanning direction ds. The reinforcing bump rows 74 may be arranged in the number of rows of three or more at intervals in the sub-scanning direction ds, or only one row may be arranged.

  Furthermore, in the thermal head 10 described above, the reinforcing bump row 74 has a plurality of reinforcing bumps 72 arranged in a straight line along the main scanning direction dm. However, the present invention is not limited to this, and a plurality of straight lines are bent in a Z shape. The reinforcing bumps 72 may be arranged in various ways substantially along the main scanning direction dm, such as a so-called zigzag shape.

  Further, in the thermal head 10 described above, the reinforcing bump row 74 is arranged such that the plurality of reinforcing bumps 72 are in contact with each other along the main scanning direction dm. The reinforcing bumps 72 adjacent to dm may be arranged at intervals so as not to contact each other.

  Furthermore, in the thermal head 10 described above, the reinforcing bump row 74 has the reinforcing bumps 72 arranged along the main scanning direction dm so that the intervals between the centers of the plurality of reinforcing bumps 72 are constant. For example, the density along the main scanning direction dm is made sparse at the end of the common electrode bus 32 in the main scanning direction dm, and the density along the main scanning direction dm is made dense at the center of the main scanning direction dm. The reinforcing bumps 72 may be arranged at various densities depending on the position in the scanning direction dm.

  In the thermal head 10 described above, the reinforcing bump 72 has a substantially truncated cone shape. However, the shape is not limited to this, and may be various shapes such as a cylindrical shape and a spherical shape.

  As described above, the diameter, height, shape, and arrangement of the reinforcing bumps 72 in the reinforcing bump group 70, the length, the number of lines, and the arrangement of the reinforcing bump rows 74 may vary, but the main bump direction 74 is along the main scanning direction dm. In order to make the print density uniform, it is desirable to arrange them regularly.

  Furthermore, it is desirable to set the diameter, height, shape, and arrangement of the reinforcing bumps 72 in the reinforcing bump group 70, the length, the number of lines, and the arrangement of the reinforcing bump rows 74 in accordance with the material of the reinforcing bumps 72.

  In short, the reinforcing bump group 70 only needs to be able to shunt the current flowing from the common electrode bonding pad 27 toward the center in the main scanning direction dm in the common electrode bus 32.

  Further, each of the reinforcing bumps 72 according to the position in the common electrode bus 32 so as to cancel the assumed voltage effect in accordance with the resistance value measured in advance along the main scanning direction dm in the common electrode bus 32 of the common electrode 28a. The diameter, height, shape, arrangement, and material of the reinforcing bumps 72 may be changed, or the number and arrangement of the reinforcing bumps 72 may be changed.

  Further, in the thermal head 10 described above, the reinforcing bump group 70 is formed by the two reinforcing bump arrays 74. However, the present invention is not limited to this, and one reinforcing bump array 74 and the above-described reinforcing bonding wire are arranged in the main scanning direction. A plurality of reinforcing bonding wire rows arranged in parallel along dm may be formed. In that case, in the reinforcing bonding wire row, the reinforcing bonding wires may be formed only in the central portion without forming the reinforcing bonding wires at both ends of the common electrode bus 32 in the main scanning direction dm.

  Further, in the thermal head 10 described above, the present invention is applied to the configuration in which the individual electrode bonding pads 26 are arranged in a line in the main scanning direction dm. However, the present invention is not limited to this, and the position is regularly changed in the sub scanning direction ds. The present invention may be applied to a configuration in which individual electrode bonding pads are arranged in the main scanning direction dm.

DESCRIPTION OF SYMBOLS 10 ... Thermal head, 20, 120 ... Heat generating body plate, 22 ... Support substrate, 22a ... Insulating plate, 22b ... Thermal insulation layer, 23 ... Heat generating resistor layer, 23a ... Heat generating resistor, 23b ... ... Exothermic part, 24... Exothermic region, 26... Individual electrode bonding pad, 27... Common electrode bonding pad, 28 .. electrode, 28 a. ...... Protective layer, 30 ... Heat sink, 32 ... Common electrode bus bar, 34 ... Common electrode child wire, 40 ... Circuit board, 42 ... Drive IC, 44 ... Bonding wire, 48 ... Resin, 70 ... Reinforcing bump group 72 ... Reinforcing bumps, 74 ... Reinforcing bump rows, dm ... Main scanning direction, ds ... Sub scanning direction

Claims (7)

A heat sink,
A circuit board placed on the upper surface of the heat sink;
An insulating substrate placed on the upper surface of the heat sink adjacent to the circuit board,
A heat insulating layer formed on the upper surface of the insulating substrate;
A plurality of heating resistors formed on the top surface of the heat retaining layer and arranged at intervals in the main scanning direction;
A folded electrode connecting the first ends of a pair of adjacent heating resistors;
An individual electrode formed on one of the second ends of the pair of heating resistors;
Insulation having a common electrode bus line formed along the main scanning direction at a position closer to the circuit board than the individual electrode and connected to a common electrode line formed on the other second end of the heating resistor A substrate,
Reinforcing bump group formed along the main scanning direction on the upper surface of the common electrode bus, and lowering the resistance value of the current path;
A power supply terminal that is arranged at an end of the common electrode bus in the main scanning direction and is supplied with power;
A protective layer formed above the heat retaining layer;
A driving IC mounted on the circuit board for driving the heating resistor;
A bonding wire connecting the individual electrode and the driving IC;
A thermal head comprising:   The reinforcing bump group is a conductive protrusion, and the reinforcing bump connected to the common electrode bus is constituted by a reinforcing bump row arranged substantially along the main scanning direction. The thermal head described.   The thermal head according to claim 2, wherein the reinforcing bump group includes a plurality of the reinforcing bumps arranged regularly along a main scanning direction.   The thermal head according to claim 3, wherein the reinforcement bump row includes a plurality of reinforcement bumps arranged in contact with each other substantially along the main scanning direction.   3. The thermal head according to claim 2, wherein the reinforcing bump group includes a plurality of reinforcing bump rows arranged at a predetermined interval in a sub-scanning direction orthogonal to the main scanning direction.   The thermal head according to claim 2, wherein the reinforcing bump is the same as the bonding wire.   The thermal head according to claim 2, wherein the common electrode bus bar is made of aluminum, and the reinforcing bump is made of gold.

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