Electrode structure for bump, bump structure, and thermal head

Abstract

This electrode structure for a bump includes an electrode pad, a protective film, and a conductive film. The protective film has an opening located on the electrode pad and covers the electrode pad. The conductive film is positioned on the electrode pad. The conductive film extends from the inside of the opening to between the electrode pad and the protective film.

Description

Bump electrode structure, bump structure and thermal head

[0001] The disclosed embodiments relate to a bump electrode structure, a bump structure, and a thermal head.

[0002] Various thermal heads have been proposed for use in printing devices such as facsimiles and video printers. For example, a bump structure for electronic components is known, in which aluminum wiring on a substrate is plated and then bonded with a bonding material.

[0003] JP 2016-213238 A JP 2009-44077 A

[0004] A bump electrode structure according to one aspect of the present invention includes an electrode pad, a protective film, and a conductive film. The protective film has an opening located above the electrode pad and covers the electrode pad. The conductive film is located above the electrode pad. The conductive film extends from inside the opening to between the electrode pad and the protective film.

[0005] Furthermore, a bump structure according to one aspect of the present invention includes the bump electrode structure described above, a seed layer located on the conductive film and the protective film, and a bump electrode located on the seed layer.

[0006] A thermal head according to one aspect of the present invention includes a substrate, an electronic component located on the substrate, and a bump structure electrically connecting the substrate and the electronic component, the bump structure having the bump electrode structure described above.

[0007] FIG. 1 is an exploded perspective view showing a schematic diagram of a thermal head according to an embodiment. FIG. 2 is a plan view showing a schematic diagram of the thermal head shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4A is an enlarged cross-sectional view showing an example of region A shown in FIG. 3. FIG. 4B is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5A is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5B is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5C is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5D is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5E is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 5F is an enlarged cross-sectional view showing another example of region A shown in FIG. 3. FIG. 6A is a plan view showing an example of a bump electrode structure according to an embodiment. FIG. 6B is a cross-sectional view taken along line B-B in FIG. 6A. FIG. 7 is a schematic diagram of a thermal printer according to an embodiment.

[0008] Hereinafter, embodiments of the bump electrode structure, bump structure, and thermal head disclosed in the present application will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments.

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

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

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

[0012] The head substrate 3 has a rectangular shape in a plan view, and the components that make up the thermal head X1 are arranged on a substrate 7. The head substrate 3 prints on a recording medium P (see FIG. 7) in accordance with an electrical signal supplied from the outside.

[0013] Next, the components constituting the thermal head X1 will be further described with reference to Figures 2 and 3. Figure 2 is a plan view showing an outline of the thermal head shown in Figure 1. Figure 3 is a cross-sectional view taken along line III-III shown in Figure 2. In Figure 2, the protective layer 25, the covering layer 27, and the sealing member 12 are indicated by dashed lines, and the covering member 29 is indicated by a broken line.

[0014] For ease of understanding, a three-dimensional Cartesian coordinate system including a Z axis extending along the thickness direction of the thermal head X1 is shown in Figures 2 and 3. This Cartesian coordinate system may also be shown in other drawings used in the following explanation.

[0015] The head substrate 3 includes a substrate 7, a heating resistor 15, a common electrode 17, individual electrodes 19, a first connection electrode 21, a second connection electrode 26, a ground electrode 4, a connection terminal 2, a conductive member 23, a driving IC 11 which is an electronic component, a bump structure 24, a covering member 29, a protective layer 25, and a covering layer 27. Note that it is not necessary to include all of these members. The head substrate 3 may also include members other than these.

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

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

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

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

[0020] The heat storage layer 13 is made of, for example, glass with low thermal conductivity, and temporarily stores a portion of the heat generated by the heat generating portion 9. This reduces the time required to increase the temperature of the heat generating portion 9, thereby improving the thermal response characteristics of the thermal head X1.

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

[0022] The heating resistor 15 is located on the upper surface of the heat storage layer 13. A common electrode 17 and an individual electrode 19 are located on the heating resistor 15. An exposed region of the heating resistor 15 is located between the common electrode 17 and the individual electrode 19. As shown in FIG. 2 , the exposed regions of the heating resistor 15 are located in a row on the raised portion 13b of the heat storage layer 13, and each exposed region constitutes an element of the heating section 9.

[0023] The heating resistor 15 does not necessarily have to be located between the various electrodes and the heat storage layer 13. The heating resistor may be located, for example, only between the common electrode 17 and the individual electrode 19 so as to electrically connect the common electrode 17 and the individual electrode 19. The heating resistor 15 may also be located between the first connection electrode 21 and the second connection electrode 26 and the heat storage layer 13, or between the ground electrode 4 and the heat storage layer 13.

[0024] 2 for ease of explanation, the elements of the heating unit 9, which is made up of a plurality of heating resistors 15, are positioned at a density of, for example, 100 dpi to 2400 dpi (dots per inch). The heating resistors 15 are formed from a material with a relatively high electrical resistance, such as a TaN-based material, a TaSiO-based material, a TaSiNO-based material, a TiSiO-based material, a TiSiCO-based material, or a NbSiO-based material. Therefore, when a voltage is applied to the heating unit 9, the heating unit 9 generates heat due to Joule heating.

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

[0026] The individual electrodes 19 electrically connect the heat generating section 9 and the driving IC 11. The multiple elements that make up the heat generating section 9 are divided into multiple groups. The individual electrodes 19 electrically connect each element of the heat generating section 9 that makes up each group to the driving IC 11 corresponding to that group. The individual electrodes 19 are electrically connected to the driving IC 11 by bump structures 24.

[0027] The first connection electrodes 21 electrically connect the driving ICs 11 and the connectors 31. The first connection electrodes 21 connected to each driving IC 11 are each made up of a plurality of wires having different functions.

[0028] The second connection electrodes 26 electrically connect adjacent driving ICs 11. The second connection electrodes 26 are made up of a plurality of wirings having different functions.

[0029] The common electrode 17, the individual electrodes 19, the first connection electrode 21, and the second connection electrode 26 are formed of a conductive material, and may be made of, for example, any one of metals selected from Al, Au, Ag, and Cu, or an alloy thereof.

[0030] The ground electrode 4 is surrounded by the individual electrodes 19, the first connection electrode 21, and the main wiring portion 17d of the common electrode 17. The ground electrode 4 is maintained at a ground potential of 0 to 1V.

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

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

[0033] The connection terminals 2 are located on the second long side 7b of the substrate 7, and connect the common electrode 17, the individual electrodes 19, the first connection electrode 21, and the ground electrode 4 to the connector 31. The connection terminals 2 are located to correspond to the connector pins 8, and when the connector 31 is connected, the connector pins 8 and the connection terminals 2 are connected so as to be electrically independent of each other.

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

[0035] The various electrodes constituting the head substrate 3 can be formed by, for example, sequentially stacking metal material layers such as Al, Au, Ag, Cu, or Ni on the heat storage layer 13 using a thin-film forming technique such as sputtering, and then processing the stack into a predetermined pattern using photoetching or the like. The various electrodes constituting the head substrate 3 can be formed simultaneously in the same process. Alternatively, the various electrodes may be produced by, for example, screen printing, flexographic printing, gravure printing, gravure offset printing, or the like.

[0036] The driving IC 11 is located, for example, on the first surface 7f side of the substrate 7. The multiple driving ICs 11 are located along the arrangement direction of the heat generating portion 9 so as to correspond to each element of the heat generating portion 9 assigned to each driving IC 11. The driving ICs 11 are connected to the individual electrodes 19 and the first connection electrodes 21. The driving ICs 11 control the electrical conduction state of the heat generating portion 9. The driving ICs 11 supply power to the heat generating portion 9 in accordance with an electrical signal supplied from the outside, causing each element of the heat generating portion 9 to individually generate heat. The driving ICs 11 can be, for example, a switching IC having multiple switching elements therein.

[0037] The bump structure 24 is located on the individual electrode 19 and electrically connects the driving IC 11 to the individual electrode 19. The bump structure 24 is conductive. Details of the bump structure 24 will be described later.

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

[0039] The covering layer 27 is located on the first surface 7f side of the substrate 7. The covering layer 27 partially covers the common electrode 17, the individual electrodes 19, the first connection electrode 21, and the second connection electrode 26. The covering layer 27 protects the covered area from oxidation due to contact with the atmosphere or corrosion due to adhesion of moisture contained in the atmosphere. The covering layer 27 can be made of a resin material such as an epoxy resin, a polyimide resin, or a silicone resin.

[0040] The covering member 29 seals the driving ICs 11 in a connected state with the individual electrodes 19, the second connection electrodes 26, and the first connection electrodes 21. The covering member 29 is arranged to extend in the main scanning direction, and integrally seals the multiple driving ICs 11. For example, a resin material such as epoxy resin or silicone resin can be used as the covering member 29.

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

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

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

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

[0045] Next, the main parts of the thermal head X1 according to the embodiment will be described in detail with reference to Fig. 4A. Fig. 4A is an enlarged cross-sectional view showing an example of region A shown in Fig. 3. Note that Fig. 4A does not show the covering member 29. For convenience, in the following description, the side closer to the individual electrodes 19 relative to the driving IC 11 may be referred to as "upper."

[0046] 4A, the bump structure 24 includes a bump electrode structure 240. The bump electrode structure 240 includes an electrode pad 241, a protective film 242, and a conductive film 243.

[0047] The electrode pads 241 are located on the driving IC 11. The electrode pads 241 are electrically connected to wiring (not shown) of the driving IC 11. The material of the electrode pads 241 may be, for example, Al.

[0048] The protective film 242 is located on the electrode pad 241. The protective film 242 is located so as to cover the electrode pad 241 and protects the electrode pad 241 from corrosion and wear. The protective film 242 is located on the electrode pad 241 and has an opening 244 penetrating in the thickness direction. The protective film 242 has insulating properties or low conductivity. The material of the protective film 242 is, for example, SiO ２ Alternatively, it may be SiN.

[0049] The protective film 242 may include, for example, a first protective film 242a and a second protective film 242b. The first protective film 242a is located on the electrode pad 241. The second protective film 242b is located on the second protective film 242b. The material of the first protective film 242a may be, for example, SiO ２ The material of the second protective film 242b may be, for example, SiN. The thickness of the first protective film 242a may be, for example, about 0.4 μm. The thickness of the second protective film 242b may be, for example, about 0.9 μm.

[0050] The conductive film 243 is located on the electrode pad 241. The conductive film 243 is conductive and is electrically connected to the electrode pad 241. The conductive film 243 is located inside the opening 244 and contributes to the conductivity of the bump electrode structure 240 in the thickness direction (Z-axis direction).

[0051] Furthermore, the conductive film 243 may include, for example, a Ni film 243a and an Au film 243b. The Ni film 243a is located on the electrode pad 241. The Au film 243b is located on the Ni film 243a. The Ni film 243a contains Ni. The material of the Ni film 243a may be, for example, Ni. The Ni film 243a may contain, for example, P or B. The thickness of the Ni film 243a may be, for example, approximately 0.1 μm to 5.0 μm.

[0052] The Au film 243b contains Au. The material of the Au film 243b may be, for example, Au. The thickness of the Au film 243b may be, for example, approximately 10 nm to 100 nm. The Ni film 243a and the Au film 243b may be formed by, for example, electroless plating.

[0053] In this way, since the conductive film 243 includes the Ni film 243a and the Au film 243b, the electrode pad 241 is less likely to be exposed, improving the durability of the electrode pad 241. Furthermore, since the Ni film 243a is covered with the Au film 243b, the Ni film 243a is less likely to corrode, improving the durability of the conductive film 243.

[0054] Furthermore, the conductive film 243 extends from the inside of the opening 244 to between the electrode pad 241 and the protective film 242. This increases the contact area between the electrode pad 241 and the protective film 242 and the conductive film 243, thereby improving the bonding strength between the electrode pad 241 and the protective film 242 and the conductive film 243. This improves the reliability of the bump structure 24.

[0055] Furthermore, the length L1 of the conductive film 243 extending between the electrode pad 241 and the protective film 242 from the edge of the opening 244 may be greater than the thickness t1 of the conductive film 243. Specifically, the length L1 is the length from the edge of the opening 244 to the tip of the conductive film 243 extending between the electrode pad 241 and the protective film 242. This further improves the bonding strength between the electrode pad 241 and the protective film 242 and the conductive film 243. This further improves the reliability of the bump structure 24. Here, the length L1 may be, for example, 2 μm or less. The thickness t1 may be, for example, 1.5 μm or less.

[0056] The bump structure 24 may also include a seed layer 245 , a bump electrode 246 , a first terminal portion 247 , and a second terminal portion 248 .

[0057] The seed layer 245 is located on the protective film 242 and the conductive film 243. The material of the seed layer 245 may be, for example, Ti. The thickness of the seed layer 245 may be, for example, about 10 nm to 500 nm. The seed layer 245 can be located by, for example, a sputtering method.

[0058] The bump electrode 246 is located on the seed layer 245. The material of the bump electrode 246 may be, for example, Cu. The thickness of the bump electrode 246 may be, for example, approximately 1 μm to 20 μm. The bump electrode 246 may be located by, for example, electrolytic plating. The bump electrode 246 may also include one located by, for example, sputtering.

[0059] The first terminal 247 is located on the bump electrode 246. The material of the first terminal 247 may be, for example, Ni. The thickness of the first terminal 247 may be, for example, approximately 0.1 μm to 5.0 μm. The first terminal 247 can be located by, for example, electrolytic plating.

[0060] The second terminal 248 is located between the first terminal 247 and the individual electrode 19, and is bonded to the individual electrode 19 by thermal interdiffusion. The material of the second terminal 248 may contain, for example, Au and / or Sn. The material of the second terminal 248 may be, for example, AuSn, SnAg, Sn, or Au. The thickness of the second terminal 248 may be, for example, approximately 1 μm to 10 μm. The second terminal 248 can be positioned by, for example, electrolytic plating or the like.

[0061] 4B is an enlarged cross-sectional view showing another example of region A shown in FIG. 4B. As shown in FIG. 4B, protective film 242 may be a laminated film obtained by laminating films having different diameters of openings 244. Specifically, protective film 242 may be obtained by laminating a first protective film 242a having openings 244a with a first diameter and a second protective film 242b having openings 244b with a second diameter larger than the first diameter.

[0062] 4B , the seed layer 245 may have a step that follows the step of the protective film 242. Specifically, the seed layer 245 may be concave in cross section so that the central portion that overlaps with the opening 244 when viewed from the driving IC 11 side is closer to the electrode pad 241 than the end portion that does not overlap with the opening 244 when viewed from the top. Furthermore, the surface of the bump electrode 246 facing the first terminal portion 247 may have a step that corresponds to the step of the seed layer 245. This makes the seed layer 245 stepped, further improving the reliability of the bump structure 24 in terms of shear strength.

[0063] 5A to 5F are enlarged cross-sectional views showing another example of region A shown in FIG. 3. As shown in FIGS. 5A and 5B, the conductive film 243 may extend from inside the opening 244 to above the protective film 242. That is, the conductive film 243 may extend on the inner wall of the opening 244 in the protective film 242 until it reaches the upper end of the inner wall. Alternatively, the conductive film 243 may cover the entire inner wall of the opening 244 in the protective film 242. The conductive film 243 may also extend to cover a portion of the upper surface of the protective film 242. In either case, the contact area between the electrode pad 241 and the protective film 242 and the conductive film 243 is further increased, thereby further improving the bonding strength between the electrode pad 241 and the protective film 242 and the conductive film 243. This further improves the reliability of the bump structure 24. Here, the length of the conductive film 243 covering the upper surface of the protective film 242 from the edge of the opening 244 may be, for example, 1 μm or more and 4 μm or less.

[0064] 5B , the protective film 242 has a structure in which a first protective film 242a having an opening 244a with a first diameter is stacked on a second protective film 242b having an opening 244b with a second diameter larger than the first diameter. This results in a stepped structure for the protective film 242. The conductive film 243 extends to cover a portion of the upper surface of the first protective film 242a, thereby improving the bonding strength between the protective film 242 and the conductive film 243. The conductive film 243 extends to cover a portion of the upper surface of the first protective film 242a so as to reach the inner wall of the opening 244b, thereby further improving the bonding strength between the protective film 242 and the conductive film 243. The conductive film 243 extends to reach the upper end of the inner wall of the opening 244b, thereby further improving the bonding strength between the protective film 242 and the conductive film 243. The conductive film 243 extends to cover a portion of the upper surface of the second protective film 242b, thereby further improving the bonding strength between the protective film 242b and the conductive film 243. In addition to simply improving the bonding strength, the above also improves the reliability of the shear strength of the bump structure 24.

[0065] 5C and 5D , the conductive film 243 located on the protective film 242 may have an arc-shaped end 243c in cross section, which improves the step coverage of the seed layer 245. This allows the surface shape of the bump electrode 246 to approach flatness, further improving the reliability of the bump structure 24.

[0066] 5E and 5F , when the bump structure 24 is viewed from above the driving IC 11, the areas of the bump electrodes 246 and the seed layer 245 may be smaller than the area of ​​the conductive film 243. This allows the bump structure 24 to be made smaller, and therefore, for example, the bump pitch can be made finer, enabling the bump structure 24 to be formed at a higher density.

[0067] Fig. 6A is a plan view showing an example of a bump electrode structure according to an embodiment. Fig. 6B is a cross-sectional view taken along line B-B shown in Fig. 6A. Note that some components of the bump structure 24 according to the embodiment are omitted from the illustration in Figs. 6A and 6B.

[0068] The electrode pad 241 may have a contact mark 241a on its surface. The contact mark 241a may be, for example, a probe mark created when the tip of a probe makes contact. The contact mark 241a may have a recessed portion 241b and a protruding portion 241c as shown in FIG. 6B . The recessed portion 241b may have, for example, a recessed or notched shape in the surface of the electrode pad 241. The protruding portion 241c may have, for example, a peeled or protruding shape in the surface of the electrode pad 241.

[0069] As described above, the bump structure 24 is formed on the driver IC 11, and the driver IC 11 with the bump structure 24 formed thereon is bonded to the substrate 7. Specifically, the bump structure 24 and the individual electrodes 19 are bonded by mutual diffusion due to heat. Note that, since the bump structure 24 is formed on the driver IC 11, the driver IC 11 with the bump structure 24 formed thereon may be considered as the driver IC.

[0070] The conductive film 243 may be positioned so as to cover the entire contact mark 241 a. This reduces the unevenness of the surface of the electrode pad 241 having the contact mark 241 a, thereby improving the step coverage of the seed layer 245. This allows the surface shape of the bump electrode 246 to be closer to flat, further improving the reliability of the bump structure 24.

[0071] Although not shown, the ground electrode 4, the first connection electrode 21, and the second connection electrode 26 may be connected to the driving IC 11 in the same manner as the connection of the driving IC 11 to the individual electrodes 19 described above.

[0072] Next, a thermal printer Z1 having a thermal head X1 will be described with reference to Fig. 7. Fig. 7 is a schematic diagram of a thermal printer according to an embodiment.

[0073] The thermal printer Z1 according to the embodiment includes the thermal head X1, a transport mechanism 40, a platen roller 50, a power supply unit 60, and a control unit 70. The thermal head X1 is attached to a mounting surface 80a of a mounting member 80 disposed in a housing (not shown) of the thermal printer Z1. The thermal head X1 is attached to the mounting member 80 so as to be aligned in the main scanning direction, which is perpendicular to the transport direction S.

[0074] The transport mechanism 40 includes a drive unit (not shown) and transport rollers 43, 45, 47, and 49. The transport mechanism 40 transports a recording medium P, such as thermal paper or image receiving paper onto which ink is transferred, along the transport direction S indicated by the arrow, onto the protective layer 25 located above the multiple heat generating elements 9 of the thermal head X1. The drive unit has a function of driving the transport rollers 43, 45, 47, and 49, and may be, for example, a motor. The transport rollers 43, 45, 47, and 49 may each have a cylindrical shaft 43a, 45a, 47a, and 49a made of a metal such as stainless steel, covered with elastic members 43b, 45b, 47b, and 49b made of a material such as butadiene rubber. When the recording medium P is an image receiving paper onto which ink is transferred, an ink film (not shown) is transported between the recording medium P and the heat generating elements 9 of the thermal head X1 along with the recording medium P.

[0075] The platen roller 50 has the function of pressing the recording medium P onto the protective layer 25 located above the heat generating portion 9 of the thermal head X1. The platen roller 50 is arranged to extend in a direction perpendicular to the transport direction S, and both ends are supported and fixed so that it can rotate while pressing the recording medium P onto the heat generating portion 9. The platen roller 50 can be configured, for example, by covering a cylindrical shaft 50a made of a metal such as stainless steel with an elastic member 50b made of butadiene rubber or the like.

[0076] As described above, the power supply device 60 has a function of supplying a current for generating heat from the heat generating portion 9 of the thermal head X1 and a current for operating the driving IC 11. The control device 70 has a function of supplying a control signal to the driving IC 11 for controlling the operation of the driving IC 11 in order to selectively generate heat from the heat generating portion 9 of the thermal head X1.

[0077] The thermal printer Z1 performs predetermined printing on the recording medium P by pressing the recording medium P onto the heat generating portion 9 of the thermal head X1 with the platen roller 50, while transporting the recording medium P onto the heat generating portion 9 with the transport mechanism 40, and selectively causing the heat generating portion 9 to generate heat with the power supply unit 60 and the control unit 70. When the recording medium P is image receiving paper or the like, printing on the recording medium P is performed by thermally transferring ink from an ink film (not shown) transported together with the recording medium P onto the recording medium P.

[0078] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present disclosure. For example, although a flat head in which the heat generating portion 9 is located on the first surface 7 f of the substrate 7 has been described as an example, an end face head in which the heat generating portion 9 is located on the end face of the substrate 7 may also be used.

[0079] Although the description has been given using a so-called thin film head in which the heating resistor 15 is formed by sputtering, the present invention is not limited to a thin film head. The thermal head X1 may be a so-called thick film head in which the heating resistor 15 is formed by printing or the like.

[0080] Furthermore, the portion covering the bump structure 24 may be covered with an underfill material instead of the covering member 29. Such an underfill material may be made of, for example, an insulating resin such as an epoxy resin.

[0081] In addition, the common electrode 17 and the individual electrodes 19 may be formed on the heat storage layer 13, and the heating resistor 15 may be formed only in the area between the common electrode 17 and the individual electrodes 19, thereby forming the heating portion 9.

[0082] Furthermore, although the example in which the connector 31 is directly connected to the substrate 7 has been shown, a flexible printed circuit (FPC) may be connected to the substrate 7 .

[0083] Although the thermal head X1 having the covering layer 27 has been exemplified, the thermal head X1 does not necessarily have to have the covering layer 27. In that case, the protective layer 25 may extend to the area where the covering layer 27 was provided. Furthermore, the covering layer 27 may be provided in an area other than that shown in the drawing.

[0084] The above-described embodiments disclose various techniques, the main techniques of which are listed below: (1) A bump electrode structure includes an electrode pad, a protective film having an opening located above the electrode pad and covering the electrode pad, and a conductive film located above the electrode pad, the conductive film extending from inside the opening to between the electrode pad and the protective film.

[0085] (2) In the bump electrode structure of (1) above, the length of the conductive film extending between the electrode pad and the protective film from the edge of the opening may be greater than the thickness of the conductive film.

[0086] (3) In the bump electrode structure of (1) or (2) above, the conductive film may extend from the inside of the opening to cover a part of the upper surface of the protective film.

[0087] (4) In the bump electrode structure of (3) above, the conductive film located on the protective film may have an arc-shaped end in cross section.

[0088] (5) In the bump electrode structure of any one of (1) to (4) above, the protective film may be a laminated film in which films having different diameters of the openings are laminated.

[0089] (6) In the bump electrode structure of any one of (1) to (5) above, the electrode pad may have a contact mark on its surface, and the conductive film may be positioned so as to cover the entire contact mark.

[0090] (7) The bump structure comprises any one of the bump electrode structures (1) to (6) above, a seed layer located on the conductive film and the protective film, and a bump electrode located on the seed layer.

[0091] (8) In the bump structure of (7) above, when the bump structure is viewed from above, the areas of the bump electrode and the seed layer may be smaller than the area of ​​the conductive film.

[0092] (9) In the bump structure of (7) or (8) above, the conductive film may have a Ni film facing the electrode pad and an Au film facing the seed layer.

[0093] (10) A thermal head includes a substrate, an electronic component located on the substrate, and a bump structure electrically connecting the substrate and the electronic component, wherein the bump structure has any one of the bump electrode structures (1) to (6) above.

[0094] Further advantages and modifications will readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0095] X1 Thermal head Z1 Thermal printer 1 Heat sink 3 Head base 4 Ground electrode 7 Substrate 9 Heat generating portion 11 Driver IC 15 Heat generating resistor 17 Common electrode 19 Individual electrode 21 First connection electrode 24 Bump structure 25 Protective layer 26 Second connection electrode 27 Covering layer 29 Covering member 240 Bump electrode structure 241 Electrode pad 242 Protective film 243 Conductive film 244 Opening 245 Seed layer 246 Bump electrode

Claims

1. A bump electrode structure comprising: an electrode pad; a protective film having an opening positioned above the electrode pad and covering the electrode pad; and a conductive film positioned above the electrode pad, wherein the conductive film extends from inside the opening to between the electrode pad and the protective film.

2. The bump electrode structure according to claim 1, wherein the length of the conductive film extending between the electrode pad and the protective film from the edge of the opening is greater than the thickness of the conductive film.

3. The bump electrode structure according to claim 1 or 2, wherein the conductive film extends from the inside of the opening to cover a portion of the upper surface of the protective film.

4. The bump electrode structure according to claim 3, wherein the conductive film located on the protective film has an arc-shaped end in cross section.

5. The bump electrode structure according to any one of claims 1 to 4, wherein the protective film is a laminated film in which films having openings with different diameters are laminated.

6. The bump electrode structure according to any one of claims 1 to 5, wherein the electrode pad has a contact mark on its surface, and the conductive film is positioned so as to cover the entire contact mark.

7. A bump structure comprising: a bump electrode structure according to any one of claims 1 to 6; a seed layer located on the conductive film and the protective film; and a bump electrode located on the seed layer.

8. The bump structure according to claim 7, wherein, when the bump structure is viewed from above, the areas of the bump electrode and the seed layer are smaller than the area of ​​the conductive film.

9. The bump structure according to claim 7 or 8, wherein the conductive film comprises a Ni film facing the electrode pad and a Au film facing the seed layer.

10. A thermal head comprising: a substrate; an electronic component located on said substrate; and a bump structure electrically connecting said substrate and said electronic component, said bump structure having a bump electrode structure according to any one of claims 1 to 6.

Images