Thermal head

Abstract

A thermal head according to the present invention comprises a head base body and a flexible wiring board. The head base body has a first terminal. The flexible wiring board faces the head base body, and has a second terminal ultrasonically welded to the first terminal. The first terminal has a base layer and a surface layer that is positioned between the base layer and the second terminal.

Description

Thermal head

[0001] The disclosed embodiment relates to a thermal head.

[0002] Conventionally, various thermal heads have been proposed as printing devices such as facsimiles or video printers. For example, a thermal head in which terminals respectively provided on a head substrate and an FPC (flexible printed wiring board) are soldered and electrically connected is known.

[0003] Japanese Patent Application Laid-Open No. 2001-10096, Japanese Patent Application Laid-Open No. 2012-146353

[0004] The thermal head according to one aspect of the embodiment includes a head base and a flexible wiring board. The head base has a first terminal. The flexible wiring board has a second terminal ultrasonically bonded to the first terminal and faces the head base. The first terminal has an underlying layer and a surface layer located between the underlying layer and the second terminal.

[0005] FIG. 1 is a plan view showing an example of a thermal head according to an embodiment. FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1. FIG. 3 is an enlarged cross-sectional view of a main part of the thermal head according to the embodiment. FIG. 4 is a schematic view showing an example of a thermal printer according to the embodiment.

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

[0007] [Embodiment] (Thermal head) FIG. 1 is a plan view showing an example of a thermal head according to an embodiment.

[0008] As shown in FIG. 1, the thermal head 1 according to the embodiment includes a head base 10 and a flexible wiring board 30. The head base 10 further includes a substrate 11, a heat generating portion 12, a heat storage layer 13, a plurality of individual electrodes 14, a common electrode 15, a drive IC 20, and a first electrode 21.

[0009] The head base 10 has a roughly rectangular parallelepiped shape with a wide width in the direction of the arrangement of the heating elements 12, and each component constituting the thermal head 1 is provided on the first surface 111, which is the front surface of the substrate 11. The head base 10 prints on the recording medium P (see Figure 4) according to an electrical signal supplied from the outside.

[0010] The substrate 11 is substantially rectangular in shape. The substrate 11 is made of an electrically insulating material such as alumina ceramics, or a semiconductor material such as single-crystal silicon. The substrate 11 may have a glaze layer covering the first surface 111.

[0011] The heat storage layer 13 is located on the first surface 111 of the substrate 11, along the longitudinal direction of the substrate 11 (hereinafter sometimes referred to as the "first direction" or "main scanning direction"). The heat storage layer 13 is made of a material such as glass with low thermal conductivity, and can temporarily store a portion of the heat generated in the heat-generating section 12. Therefore, the time required to raise the temperature of the heat-generating section 12 can be shortened, and the thermal response characteristics of the thermal head 1 can be improved. The heat storage layer 13 may be formed, for example, by applying a predetermined glass paste obtained by mixing glass powder with a suitable organic solvent to the first surface 111 of the substrate 11 by conventionally known screen printing or the like, and then firing it.

[0012] The heating element 12 is located on the heat storage layer 13. The multiple elements constituting the heating element 12 are arranged along the longitudinal direction of the substrate 11. The heating element 12 has the function of generating heat in accordance with an electrical signal supplied from the outside and printing onto the recording medium P (see Figure 4). The multiple elements constituting the heating element 12 may be arranged at a density such as 100 dpi to 2400 dpi (dots per inch).

[0013] The heating element 12 has an electrical resistance layer with relatively high electrical resistance, such as a TaN-based, TaSiO-based, TaSiNO-based, TiSiO-based, TiSiCO-based, or NbSiO-based material. When a voltage is applied to the electrical resistance layer located between the individual electrodes 14 and the common electrode 15, this electrical resistance layer generates heat through Joule heating.

[0014] Multiple individual electrodes 14 are positioned on the first surface 111 side of the substrate 11, aligned on one side relative to the heating element 12. Each of the multiple individual electrodes 14 is individually connected to each element of the heating element 12. One end of each individual electrode 14 is electrically connected to an element of the heating element 12, and the other end is electrically connected to the drive IC 20.

[0015] The common electrode 15 electrically connects each element of the heating element 12 to the connection terminals 32 of the flexible wiring board 30. The common electrode 15 has a main wiring section 15a, a sub-wiring section 15b, and a lead section 15c. The main wiring section 15a extends along one of the two long sides 11a of the substrate 11. The sub-wiring section 15b extends along one of the two short sides 11b and the other short side 11c of the substrate 11. The lead sections 15c extend individually from the main wiring section 15a toward each element of the heating element 12. The common electrode 15 is electrically connected to the connection terminals 32 of the flexible wiring board 30 via a terminal section 15d located at the end of the substrate 11 on the long side 11d. The common electrode 15 has individual electrodes 14 arranged on it and is positioned to surround the remaining three sides of the heating element 12, excluding the other long side 11d of the substrate 11. The individual electrodes 14 and the common electrode 15 are made of a metal such as Cu, Al, Au, or Ag.

[0016] The first electrode 21 electrically connects the drive IC 20 to the connection terminal 32 of the flexible wiring board 30. The first electrode 21 is located on the first surface 111 of the substrate 11. The first electrode 21 is electrically connected to the connection terminal 32 of the flexible wiring board 30 via a terminal portion 21a located at the end of the long side 11d of the substrate 11.

[0017] The flexible printed circuit board 30 has a wide board shape in the direction of the arrangement of the heating elements 12. The flexible printed circuit board 30 is, for example, an FPC (flexible printed circuit board). The head base 10 and the flexible printed circuit board 30 are ultrasonically bonded. This electrically connects the terminals of the head base 10 and the flexible printed circuit board 30, respectively.

[0018] Next, the joining of the head base 10 and the flexible wiring board 30 will be further explained using Figures 1 and 2. Figure 2 is a cross-sectional view taken along line A-A in Figure 1.

[0019] As shown in Figures 1 and 2, the flexible wiring board 30 has a base material 31 and a wiring region 33 located on the back surface of the base material 31. The wiring region 33 is the region to which the head base 10 and the flexible wiring board 30 are joined, and is positioned to extend in a first direction. Multiple connection terminals 32 are located in the wiring region 33. The multiple connection terminals 32 are ultrasonically bonded to terminal portions 21a and terminal portions 15d. Terminal portions 21a and 15d are examples of first terminals. The connection terminals 32 are examples of second terminals.

[0020] As shown in Figure 2, the head base 10 has a terminal portion 21a as a first terminal. The terminal portion 21a has a base layer 21a1 and a surface layer 21a2. The base layer 21a1 is located on the substrate 11. The surface layer 21a2 is located between the base layer 21a1 and the connection terminal 32.

[0021] Thus, because the terminal portion 21a has a base layer 21a1 and a surface layer 21a2, it becomes possible to electrically connect the terminal portion 21a and / or the connecting terminal 32 by ultrasonic bonding without plating and / or soldering the surface of the terminal portion 21a and / or the connecting terminal 32. This reduces manufacturing costs, for example.

[0022] Furthermore, as shown in Figure 1, the terminal portions 21a and 15d, which serve as first terminals, are arranged in multiple locations along the longitudinal direction of the head base 10 in the bonding region where ultrasonic bonding is performed. The area of ​​the first terminals located at the ends in the longitudinal direction may be larger than the area of ​​the first terminals located in the central part in the longitudinal direction. In this embodiment, the area of ​​the terminal portion 15d located at the ends in the longitudinal direction is larger than the area of ​​the terminal portion 21a located in the central part in the longitudinal direction. Note that the areas of the terminal portions 15d and 21a represent the areas that are bonded to the flexible wiring board 30, and as an example, the area shown is the area when viewed from above.

[0023] The bonding area between the head base 10 and the flexible wiring board 30 is most prone to delamination at both ends in the longitudinal direction of the head base 10 due to thermal expansion and contraction of the flexible wiring board 30. In this case, it is preferable to make the area of ​​the first terminal located at the end of the head base 10, for example, terminal portion 15d, larger than the area of ​​the first terminal located in the center of the head base 10, for example, terminal portion 21a. This improves the bonding strength, for example, by ultrasonic bonding, and makes it less likely for the flexible wiring board 30 to delaminate from the head base 10.

[0024] Here, the ends of the head base 10 in the longitudinal direction refer to the 25% area from both ends of the head base 10 in the longitudinal direction. The central part of the head base 10 in the longitudinal direction refers to the part of the head base 10 excluding the ends of the head base 10 in the longitudinal direction, that is, the 50% area including the center of the head base 10 in the longitudinal direction.

[0025] The length of a first terminal located at the end of the head base 10, for example, terminal portion 15d, along the longitudinal direction of the head base 10 may be greater than the length of a first terminal located in the central part of the head base 10, for example, terminal portion 21a, along the longitudinal direction of the head base 10. The length of a first terminal located at the end of the head base 10, for example, terminal portion 15d, along the short direction of the head base 10 may be greater than the length of a first terminal located in the central part of the head base 10, for example, terminal portion 21a, along the short direction of the head base 10. Furthermore, the area of ​​terminal portion 15d located at the end of the head base 10 may be greater than the area of ​​terminal portion 21a located in the central part of the head base 10.

[0026] Figure 3 is an enlarged cross-sectional view of the main part of the thermal head according to the embodiment. Figure 3 is an enlarged view of region B shown in Figure 2. As shown in Figure 3, the base layer 21a1 may have a recess 23 and a protrusion 24 facing the connection terminal 32 as the second terminal. The surface layer 21a2 may be positioned so as to be in contact with at least the recess 23. This improves the adhesion between the base layer 21a1 and the surface layer 21a2, and improves the reliability of the bond. Here, "recess 23" refers to the portion that is further from the connection terminal 32 than the boundary portion 22 between the base layer 21a1 and the surface layer 21a2, which is defined based on the average thickness of the base layer 21a1. Also, "protrusion 24" refers to the portion that is closer to the connection terminal 32 than the boundary portion 22, which is set based on the average thickness of the base layer 21a1. The average thickness of the base layer 21a1 can be calculated, for example, by taking a cross-sectional photograph so that the boundary portion 22 between the base layer 21a1 and the surface layer 21a2 is visible, as shown in Figure 3, and then processing the boundary portion 22 using image processing.

[0027] Furthermore, the thickness of the base layer 21a1 may be greater than the thickness of the surface layer 21a2. This ensures a sufficient deformation area of ​​the base layer 21a1 due to ultrasonic bonding, improving the adhesion between the terminal portion 21a and the connecting terminal 32 due to ultrasonic bonding, and improving bonding reliability.

[0028] Furthermore, the base layer 21a1 may contain Ag or Cu. The surface layer 21a2 may contain Al. As a result, the base layer 21a1 deforms well by ultrasonic bonding, and the surface layer 21a2 functions well as an adhesion layer with the connection terminal 32, further improving the adhesion between the terminal portion 21a and the connection terminal 32 by ultrasonic bonding, and further improving the bonding reliability.

[0029] Furthermore, the connection terminal 32 as the second terminal may be a single layer made of Cu or a laminate made of Au, Ni, and Cu in that order from the terminal portion 21a side. The connection terminal 32 may include, for example, a first layer 32a made of Au and a second layer 32b made of Ni. As a result, the first layer 32a suppresses surface oxidation of the second layer 32b and functions well as an adhesion layer with the terminal portion 21a, further improving the adhesion between the terminal portion 21a and the connection terminal 32 by ultrasonic bonding, and further improving bonding reliability.

[0030] Note that the arrangement of the components of the head base 10 and flexible wiring board 30 shown in Figure 1 is a schematic representation of one example and does not necessarily correspond to the actual shape.

[0031] Furthermore, although Figures 2 and 3 illustrate the joining of terminal portion 21a and connection terminal 32, the joining of terminal portion 15d and connection terminal 32 may be similar. In addition, it is also possible to apply this to ultrasonic bonding of other first terminals on the head base 10 and other second terminals on the flexible wiring board 30.

[0032] (Manufacturing method for thermal heads) Next, an example of a manufacturing method for thermal head 1 will be described.

[0033] First, the base layer 21a1 material is applied to the first surface 111 of the substrate 11. For example, screen printing can be applied to apply the base layer 21a1 material. The thickness of the base layer 21a1 can be, for example, 10 μm or more and 20 μm or less.

[0034] Next, the material for the surface layer 21a2 is deposited on the surface of the underlayer 21a1. For example, sputtering can be applied to deposit the material for the surface layer 21a2. The thickness of the surface layer 21a2 can be, for example, 0.2 μm or more and 2 μm or less.

[0035] Next, the surface layer 21a2 and the connection terminal 32 are pressed together and ultrasonic bonding is performed. At this time, the load can be, for example, 500 N to 3000 N. The frequency can be, for example, 10 kHz to 100 kHz. The ultrasonic output can be, for example, 40 W to 300 W. The bonding time can be, for example, 100 ms to 5000 ms. The amount of indentation of the flexible wiring board 30 into the head base 10 can be, for example, 40 μm to 300 μm. The bonding area may be heated during ultrasonic bonding. This can further improve the bonding strength.

[0036] Furthermore, when the terminal portion 21a and the connecting terminal 32 are ultrasonically bonded, the thermal head 1 may have a recess at the joint. These recesses may also be arranged in a multi-layered, uniform shape. Moreover, when the terminal portion 21a and the connecting terminal 32 are ultrasonically bonded, the joint may be formed by diffusion bonding between the metal constituting the terminal portion 21a and the metal constituting the connecting terminal 32. Additionally, when the terminal portion 21a and the connecting terminal 32 are ultrasonically bonded, it is not necessary to provide solder, anisotropic conductive film (ACF), anisotropic conductive paste (ACP), etc., around the joint.

[0037] (Thermal Printer) Next, a thermal printer having a thermal head 1 will be described with reference to Figure 4. Figure 4 is a schematic diagram showing an example of a thermal printer according to the embodiment.

[0038] The thermal printer 100 according to this embodiment includes the thermal head 1 described above, a transport mechanism 40, a platen roller 50, a power supply unit 60, and a control device 70. The thermal head 1 is mounted on the mounting surface 80a of a mounting member 80 located on the housing (not shown) of the thermal printer 100. The thermal head 1 is mounted on the mounting member 80 such that the longitudinal direction of the substrate 11 and the direction in which the heat-generating part 12 extends are aligned with the main scanning direction, which is perpendicular to the transport direction S. A heat sink (not shown) may also be placed between the thermal head 1 and the mounting member 80.

[0039] The transport mechanism 40 includes a drive unit (not shown) and transport rollers 43, 45, 47, and 49. The transport mechanism 40 transports the recording medium P, such as thermal paper or image receiving paper on which ink is transferred, onto the heating element 12 of the thermal head 1 along the transport direction S indicated by the arrow. The drive unit includes, for example, a motor (not shown) and drives the transport rollers 43, 45, 47, and 49. The transport rollers 43, 45, 47, and 49 may be cylindrical shafts 43a, 45a, 47a, and 49a made of a metal such as stainless steel, covered with elastic members 43b, 45b, 47b, and 49b made of butadiene rubber or the like. When the recording medium P is image receiving paper on which ink is transferred, an ink film (not shown) is transported together with the recording medium P between the recording medium P and the thermal head 1.

[0040] The platen roller 50 presses the recording medium P onto the heating element 12 of the thermal head 1. The platen roller 50 is arranged to extend in a direction perpendicular to the transport direction S, i.e., along the main scanning direction, and both ends are supported and fixed so that it can rotate while pressing the recording medium P onto the heating element 12. The platen roller 50 can be constructed, for example, by covering a cylindrical shaft 50a made of metal such as stainless steel with an elastic member 50b made of butadiene rubber or the like.

[0041] As described above, the power supply unit 60 supplies current to generate heat in the heating element 12 of the thermal head 1 and current to operate the drive IC 20 of the thermal head 1. As described above, the control device 70 supplies a control signal to the drive IC 20 to control the operation of the drive IC 20 in order to selectively generate heat in the heating element 12 of the thermal head 1.

[0042] The thermal printer 100 performs a predetermined printing on the recording medium P by selectively heating the heating portion 12 by the power supply device 60 and the control device 70 while pressing the recording medium P against the heating portion 12 of the thermal head 1 by the platen roller 50 and transporting the recording medium P onto the heating portion 12 by the transport mechanism 40. When the recording medium P is a receiving paper or the like, printing on the recording medium P is performed by thermally transferring the ink of an ink film (not shown) transported together with the recording medium P to the recording medium P.

[0043] As described above, the embodiments of the present disclosure have been described. However, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit thereof.

[0044] In one embodiment, (1) the thermal head includes a head base having a first terminal, a second terminal ultrasonically bonded to the first terminal, and a flexible wiring board facing the head base, and the first terminal has an underlying layer and a surface layer located between the underlying layer and the second terminal.

[0045] (2) In the thermal head of (1) above, the underlying layer has recesses and protrusions facing the second terminal, and the surface layer may be located so as to contact at least the recesses.

[0046] (3) In the thermal head of (1) or (2) above, the thickness of the underlying layer may be greater than the thickness of the surface layer.

[0047] (4) In any one of the thermal heads of (1) to (3) above, the underlying layer contains Ag or Cu, and the surface layer may contain Al.

[0048] (5) In any one of the thermal heads of (1) to (4) above, the second terminal may be a single layer made of Cu or a laminate made of Au, Ni, and Cu in this order from the first terminal side.

[0049] (6) In any one of the thermal heads described in (1) to (5) above, the first terminals are arranged in a plurality along the longitudinal direction of the head base in the bonding region to be ultrasonically bonded, and the area of ​​the first terminals located at the ends in the longitudinal direction may be larger than the area of ​​the first terminals located in the central part in the longitudinal direction.

[0050] Further effects and modifications can be readily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents.

[0051] 1 Thermal head 10 Head base 11 Substrate 12 Heat-generating section 13 Heat storage layer 14 Individual electrodes 15 Common electrode 20 Drive IC 21 First electrode 21a Terminal section 21a1 Underlayer 21a2 Surface layer 30 Flexible wiring board 31 Base material 32 Connection terminal 100 Thermal printer

Claims

1. A thermal head comprising a head base having a first terminal, and a flexible wiring board facing the head base, having a second terminal ultrasonically bonded to the first terminal, wherein the first terminal has a base layer and a surface layer located between the base layer and the second terminal.

2. The thermal head according to claim 1, wherein the base layer has recesses and protrusions facing the second terminal, and the surface layer is positioned to be in contact with at least the recesses.

3. The thermal head according to claim 1 or 2, wherein the thickness of the underlayment is greater than the thickness of the surface layer.

4. The thermal head according to any one of claims 1 to 3, wherein the base layer contains Ag or Cu, and the surface layer contains Al.

5. The thermal head according to any one of claims 1 to 4, wherein the second terminal is a single layer made of Cu or a laminate made of Au, Ni, and Cu in that order from the first terminal side.

6. The thermal head according to any one of claims 1 to 5, wherein the first terminals are arranged in a plurality along the longitudinal direction of the head base in the bonding region to be ultrasonically bonded, and the area of ​​the first terminals located at the ends in the longitudinal direction is larger than the area of ​​the first terminals located in the central part in the longitudinal direction.

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