EP3047973A2

EP3047973A2 - Inkjet head, method of producing inkjet head, and inkjet recording device

Info

Publication number: EP3047973A2
Application number: EP16150184.6A
Authority: EP
Inventors: Hikaru Hamano
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2015-01-23
Filing date: 2016-01-05
Publication date: 2016-07-27
Also published as: EP3047973A3

Abstract

An inkjet head includes a head chip and a wiring substrate. The head chip includes channels, driving electrodes disposed in the respective channels, and connecting electrodes disposed on a surface of the head chip. The connecting electrodes are electrically connected to the respective driving electrodes. The wiring substrate includes wiring electrodes arranged on a surface of the wiring substrate. The wiring electrodes are electrically connected to the respective connecting electrodes. The wiring substrate is bonded to a face, on which the connecting electrodes are disposed, of the head chip with an adhesive containing conductive particles, thereby allowing electrical connections to be established between the connecting electrodes and the respective wiring electrodes. The adhesive further contains non-conductive particles.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet head, a method of producing an inkjet head, and an inkjet recording device.

2. Description of Related Art

A typical inkjet head for recording various images through ejection of inks from channels includes a shear-mode inkjet head. The shear-mode inkjet head includes drivable walls that are composed of piezoelectric elements and that separate multiple arranged channels. Two faces of each drivable wall are provided with driving electrodes. Applying driving signals having a predetermined voltage to such pairs of driving electrodes generates shearing force in the drivable walls. The shearing force varies the volume and thus pressure in the channels. Such a variation in pressure causes ink in the channels to be ejected from nozzles.
An example head chip of such an inkjet head is a so-called harmonica-shaped head chip. The harmonica-shaped head chip usually has a hexahedral shape. Two opposing faces of the hexahedron are provided with openings that serve as an inlet and an outlet of ink of a straight channel that extends between these openings. In a head chip having such straight channels, the driving electrodes on two faces of each drivable wall are disposed inside the channels and not exposed to the outside. This precludes ready application of voltage to the driving electrodes.
A solution to such a disadvantage is found in Japanese Unexamined Patent Application Publication No. 2002-178509 that discloses an inkjet head including a head chip provided with connecting electrodes, which are electrically connected to driving electrodes, on the rear face of the head chip for respective channels; and a wiring substrate bonded to the rear face of the head chip, the wiring substrate including wiring electrodes arranged to be electrically connected to the respective connecting electrodes. The driving electrodes are electrically led to the exterior of the head chip through the wiring substrate so that a voltage can be readily applied to the driving electrodes. The wiring substrate has through-holes for supplying ink at positions corresponding to the channels. The ink in a manifold bonded to the rear face of the wiring substrate is fed to the channels through the respective through-holes.
The bonding of the head chip and the wiring substrate causes the connecting electrodes to overlap the wiring electrodes. This provides a gap between the head chip and the wiring substrate having a thickness equal to the thicknesses of both electrodes. The adhesive used for bonding is disposed in this gap and flows through the gap due to a capillary force generated immediately after bonding while the adhesive is still in a state of low viscosity. The fluid adhesive spreads substantially throughout the space between the head chip and the wiring substrate. The adhesive then cures to bond together the head chip and the wiring substrate.
The adhesive may contain conductive particles. The conductive particles in the adhesive disposed between the connecting electrodes and the wiring electrodes establish a reliable electrical connection between the connecting electrodes and the wiring electrodes. The fluidity of the adhesive during bonding may cause the conductive particles in the adhesive to agglomerate between the head chip and the wiring substrate.
In particular, agglomeration of the conductive particles is often observed near the openings of the channels. Such agglomeration could short-circuit adjacent electrodes between the head chip and the wiring substrate.
The applicant of the present application has also proposed a technique for preventing such short-circuiting that would be caused by agglomeration of conductive particles between electrodes of a head chip and electrodes of a wiring substrate through specific conditions, such as the pitch of channels, the arrangement of the wiring electrodes, the thickness of the wiring substrate, and the Young's modulus in Japanese Unexamined Patent Application Publication No. 2012-16848 .
The applicant of the present application confirmed that short-circuiting between electrodes caused by agglomeration of conductive particles in the adhesive occurs not only between the electrodes of the head chip and the electrodes of the wiring substrate but also between adjacent wiring electrodes in the array of wiring electrodes on the surface of the wiring substrate.
An example of the agglomeration of conductive particles will now be described with reference to Figs. 12A and 12B. Fig 12A is a plan view illustrating a wiring substrate 1003c of a head chip of a conventional inkjet head after bonding. Fig. 12B is a photograph illustrating the wiring substrate 1003c of the head chip of the conventional inkjet head after boding.
With reference to Fig. 12A, a wiring substrate 1003c is bonded to a head chip, which is disposed below the dashed line in the drawing, with an adhesive containing conductive particles P1. The conductive particles P1 aggregate between adjacent wiring electrodes 1033Ac and 1033Bc on the wiring substrate 1003c.
Fig. 12B illustrates an example photograph of a wiring substrate bonded to a head chip with an adhesive containing conductive particles P1. The dark areas in the photograph correspond to wiring electrodes on the wiring substrate, and the multiple substantial circles correspond to the conductive particles P1. In Fig. 12B, the head chip is disposed below the dashed line in the drawing, and adhesive fillets are formed inside the areas defined by the dotted lines. The conductive particles P1 agglomerate in the adhesive fillets illustrated in Fig. 12B.
Unsatisfactory bonding of the head chip and the wiring substrate is usually prevented through the application of slightly excess adhesive. As a result, some of the adhesive flows outward from between the head chip and the wiring substrate to the exterior of the head chip and forms adhesive fillets at the periphery of the head chip. The adhesive fillets are disposed across the side faces of the head chip and the surface of the wiring substrate. As the adhesive flows, many conducive particles agglomerate in the adhesive fillet and may cause short-circuiting between wiring electrodes passing under the adhesive fillet.
An example of the inkjet heads is a shear-mode inkjet head. The shear-mode inkjet head includes a head chip that has drivable walls separating channels supplied with ink and that is composed of piezoelectric elements, and driving electrodes disposed on the surfaces of the drivable walls. The driving electrodes receive a predetermined voltage to cause shearing of the drivable walls, which leads to a variation in the volume of the channels. This generates pressure that causes the ink inside the channels to be ejected from nozzles.
An example of the head chips for such an inkjet head is a harmonica-shaped head chip. A harmonica-shaped head chip has a hexahedral shape and straight channels. The driving electrodes on the surfaces of the drivable walls face the interiors of the channels and are not exposed to the exterior. This precludes direct application of a voltage to the driving electrodes. Thus, connecting electrodes, which are electrically connected to the driving electrodes through the openings of the channels formed in a face of the head chip, are provided on the same face as the openings to promote ready application of a voltage to the driving electrodes.
A conventional inkjet head, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2014-128941 , includes a head chip that has a face provided with openings and connecting electrodes and a wiring substrate that is provided with wiring electrodes corresponding to the connecting electrodes, the head chip and the wiring substrate being bonded together with an adhesive containing conductive spherical particles that establish an electrical connection between the connecting electrodes and the respective wiring electrodes.
Unfortunately, bonding of the head chip and the wiring substrate with an adhesive containing conductive spherical particles requires application of high pressure to establish a sufficient electrical connection.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inkjet head, a method of producing an inkjet head, and an inkjet recording device that prevent short-circuiting of wiring electrodes of a wiring substrate due to agglomeration of conductive particles in an adhesive applied to bond a head chip and the wiring substrate.
An object of the present invention is to provide an inkjet head that establishes a reliable electrical connection between electrodes of a head chip and electrodes of a wiring substrate without application of high pressure during bonding of the head chip and the wiring substrate.
An object of the present invention is to provide a method of producing an inkjet head that establishes a reliable electrical connection between electrodes of a head chip and electrodes of a wiring substrate without application of high pressure during bonding of the head chip and the wiring substrate.
An object of the present invention is to provide an inkjet recording device that includes an inkjet head that establishes a reliable electrical connection between electrodes of a head chip and electrodes of a wiring substrate without application of high pressure during bonding of the head chip and the wiring substrate, and can carry out high-quality image recording.
Other objects of the present invention will be apparent through the following description.
In order to achieve one or more of the above-described objects, an inkjet head reflecting an aspect of a preferred embodiment of the present invention comprises: a head chip comprising: a plurality of channels, a plurality of driving electrodes disposed in the respective channels, and a plurality of connecting electrodes disposed on a surface of the head chip, the connecting electrodes being electrically connected to the respective driving electrodes; and a wiring substrate comprising a plurality of wiring electrodes arranged on a surface of the wiring substrate, the wiring electrodes being electrically connected to the respective connecting electrodes, wherein the wiring substrate is bonded to a face, on which the connecting electrodes are disposed, of the head chip with an adhesive containing conductive particles, thereby allowing electrical connections to be established between the connecting electrodes and the respective wiring electrodes; and the adhesive further contains non-conductive particles.
Preferably, in the above-described inkjet head, a size of the conductive particles is larger than or equal to a size of the non-conductive particles.
Preferably, in the above-described inkjet head, a volume mixing ratio of the non-conductive particles to the adhesive is at least twice a volume mixing ratio of the conductive particles to the adhesive.
Preferably, in the above-described inkjet head, a Young's modulus of the conductive particles is larger than a Young's modulus of the non-conductive particles.
Preferably, in the above-described inkjet head, the conductive particles comprise conductive particles having protrusions.
Preferably, in the above-described inkjet head, a size of the non-conductive particles is smaller than a height of the protrusions.
In order to achieve one or more of the above-described objects, an inkjet head reflecting another aspect of a preferred embodiment of the present invention comprises: a head chip comprising: a plurality of channels, a plurality of driving electrodes disposed in the respective channels, and a plurality of connecting electrodes disposed on a surface of the head chip, the connecting electrodes being electrically connected to the respective driving electrodes; and a wiring substrate comprising a plurality of wiring electrodes disposed on a surface of the wiring substrate, the wiring electrodes corresponding to the respective connecting electrodes, wherein the head chip and the wiring substrate are bonded to each other with an adhesive containing conductive particles having protrusions, thereby allowing electrical connections to be established between the connecting electrodes and the respective wiring electrodes.
Preferably, in the above-described inkjet head, the conductive particles comprise core-shell particles, each of the core-shell particles comprising an organic core and a shell that is made of a metal film having the protrusions and that is disposed on a surface of the organic core.
Preferably, in the above-described inkjet head, in each of the conductive particles, a Young's modulus of the shell is larger than a Young's modulus of the organic core.
Preferably, in the above-described inkjet head, the shell of each of the conductive particles comprises an outermost layer made of gold and an inner layer made of a metal having a Young's modulus larger than a Young's modulus of gold, and the inner layer forms the protrusions.
Preferably, in the above-described inkjet head, at least one of each connecting electrode and each wiring electrode has an oxide film on a surface thereof.
Preferably, in the above-described inkjet head, a height of the protrusions of the conductive particles is larger than a thickness of the oxide film.
Preferably, in the above-described inkjet head, the adhesive is a thermosetting adhesive.
Preferably, in the above-described inkjet head, openings of the channels and the connecting electrodes are disposed on a same face of the head chip.
Preferably, in the above-described inkjet head, the wiring substrate is disposed parallel to the face, on which the openings and the connecting electrodes are disposed, of the head chip.
Preferably, in the above-described inkjet head, the connecting electrodes are connected to the respective driving electrodes through the openings of the respective channels.
Preferably, in the above-described inkjet head, the driving electrodes are disposed on respective drivable walls facing interiors of the respective channels.
Preferably, in the above-described inkjet head, the wiring electrodes are electrically connected to the respective connecting electrodes, and the wiring electrodes are disposed on a surface of an area of the wiring substrate, the area extending outside of a bonding area where the wiring substrate and the head chip are bonded to each other.
In order to achieve one or more of the above-described objects, a method of producing an inkjet head reflecting another aspect of a preferred embodiment of the present invention comprises: bonding the head chip and the wiring substrate to each other with the adhesive; and electrically connecting the connecting electrodes and the respective wiring electrodes to each other by curing the adhesive.
In order to achieve one or more of the above-described objects, an inkjet recording device reflecting another aspect of a preferred embodiment of the present invention comprises: any one of the above-described inkjet heads, and the inkjet recording device applies a voltage to the driving electrodes via the wiring electrodes and the connecting electrodes of the inkjet head and ejects ink in ink-ejecting channels of the channels from nozzles disposed at the ink-ejecting channels, thereby recording an image on a recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention.

Fig. 1 is a schematic view illustrating an inkjet recording device according to a first embodiment of the present invention.
Fig. 2 is an exploded perspective view illustrating an inkjet head.
Fig. 3 is partial rear view illustrating a head chip of the inkjet head.
Fig. 4 is a view, from a wiring substrate, illustrating the bonded state of the head chip and the wiring substrate.
Fig. 5 is a partial cross-sectional view illustrating the head chip and the wiring substrate, taken along line V-V in Fig. 4.
Fig. 6A is a cross-sectional view illustrating the head chip and the wiring substrate, taken along line Via-Via in Fig. 5.
Fig. 6B is a cross-sectional view illustrating the head chip and the wiring substrate, taken along line Vib-Vib in Fig. 5.
Fig. 7A is a plan view illustrating the wiring substrate after being bonded to the head chip of the inkjet head.
Fig. 7B is a photograph illustrating the wiring substrate after being bonded to the head chip of the inkjet head.
Fig. 8 is a graph illustrating the number of particles versus the size (diameter) of the particles.
Fig. 9 is a plan view illustrating the surface of the wiring substrate prepared through the method of producing an inkjet head.
Fig. 10 is a cross-sectional view illustrating the head chip and the wiring substrate clamped by a pair of pressure plates.
Fig. 11 illustrates the thermally expanded state of the gas inside dummy channels.
Fig. 12A is a plan view illustrating a wiring substrate after being bonded to a head chip of a conventional inkjet head.
Fig. 12B is a photograph illustrating the wiring substrate after being bonded to the head chip of the conventional inkjet head.
Fig. 13 is a schematic view of an inkjet recording device according to a second embodiment of the present invention.
Fig. 14 is an exploded perspective view illustrating an example inkjet head.
Fig. 15 is a partial rear view illustrating a head chip of the inkjet head in Fig. 14.
Fig. 16 illustrates the bonded state of a head chip and a wiring substrate.
Fig. 17 is a cross-sectional view taken along line (v)-(v) in Fig. 16.
Fig. 18 is a partially cutaway conceptual diagram illustrating a conductive particle.
Fig. 19 is a cross-sectional view illustrating a connecting electrode and a wiring electrode electrically connected via an adhesive containing a conductive particle. Fig. 20 is graph illustrating the number of conductive particles versus the size (diameter) of conductive particles.
Fig. 21 is a plan view illustrating the surface of a wiring substrate prepared through the method of producing an inkjet head.
Fig. 22 is a cross-sectional view illustrating the head chip and the wiring substrate clamped by a pair of pressure plates.
Fig. 23 illustrates the thermally expanded state of the gas inside dummy channels.
Fig. 24 is a cross-sectional view illustrating a head chip and a wiring substrate according to a third embodiment in a bonded state.
Fig. 25 is a cross-sectional view of a connecting electrode and a wiring electrode electrically connected via an adhesive containing a conductive particle and non-conductive particles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Details of the embodiments according to the present invention will now be described with reference to the accompanying drawings. The examples illustrated in the drawings should not be construed to limit the present invention. In the description below, components that have identical functions and configurations will be denoted by the same reference signs, and redundant description will be omitted.

[First Embodiment]

An inkjet recording device according to a first embodiment of the present invention will now be described. The configuration of the device according to this embodiment will be described with reference to Figs. 1 to 7B. With reference to Fig. 1, the overall configuration of an inkjet recording device 1000 according this embodiment will now be described. Fig. 1 is a schematic view of the inkjet recording device 1000. The inkjet recording device will be exemplified with a line head inkjet printer. Any other inkjet recording device may also be applied to the present invention. For example, the inkjet recording device may be a scanning inkjet recording device that performs scanning with the inkjet head in the direction orthogonal to the recording medium conveying direction to form an image. The inkjet recording device includes ink of the colors yellow (Y), magenta (M), cyan (C), and black (K). Alternatively, the ink may be any single color. For example, black (K) ink may be used alone.
The inkjet recording device 1000 includes a conveying unit 1200, an image forming unit 1300, an ink supply unit 1400, and a controller 1500. In the inkjet recording device 1000, an image is formed on a recording medium P conveyed by the conveying unit 1200 at the image forming unit 1300 with ink supplied from the ink supply unit 1400 under the control of the controller 1500.
The conveying unit 1200 holds the recording medium P on which an image is to be formed and sends the recording medium P to the image forming unit 1300. The conveying unit 1200 includes a feeding roller 1210, rollers 1220 and 1230, and a reeling roller 1240. A long roll of the recording medium P is fed from the feeding roller 1210, supported by the rollers 1220 and 1230, and reeled at the reeling roller 1240.
The image forming unit 1300 ejects ink onto the recording medium P to form an image. The image forming unit 1300 includes multiple line heads 1310 and a carriage 1330 that supports the multiple line heads 1310. An irradiating unit 1320 should be provided for use of ink that is curable by active energy beams.
The line heads 1310 eject ink onto the recording medium P conveyed by the conveying unit 1200 to form an image. The line heads 1310 are provided for the respective colors yellow (Y), magenta (M), cyan (c), and black (K). Fig. 1 illustrates the line heads 1310 for the colors Y, M, C, and K disposed in this order from upstream to downstream in the conveying direction of the recording medium P by the conveying unit 1200.
The line heads 1310 according to this embodiment are attached to the carriage 1330 and have a length (width) that covers the entire length of the recording medium P in the direction substantially orthogonal to the recording medium P conveying direction (width direction). Specifically, the inkjet recording device 1000 is a line head inkjet recording device that carries out single-pass printing. The line heads 1310 each includes arrays of inkjet heads 1100 (see Fig. 2). With reference to Fig. 1, the carriage 1330 may include a carriage heater 1330a for heating the ink.
The irradiating unit 1320 emits active energy beams to cure ink ejected from the inkjet recording device 1000 onto the recording medium P. The irradiating unit 1320 includes a fluorescent tube, such as a low-pressure mercury lamp, which is energized to emit active energy beams, such as ultraviolet (UV) rays. The irradiating unit 1320 is disposed further downstream of the line heads 1310 in the conveying direction of the recording medium P. The irradiating unit 1320 emits active energy beams on the recording medium P after image formation to cure the ink ejected onto the recording medium P.
Examples of the fluorescent tube generating UV light other than the low-pressure mercury lamp include a mercury lamp having an operational pressure in the range of several hundred pascals (Pa) to one million pascals (Pa), a light source that functions as a sterilizing lamp, a cold-cathode tube, an UV laser source, a metal halide lamp, and a light-emitting diode. Among such tubes, a light source that emits high-intensity UV light at low power is preferred (for example, the light-emitting diode). In addition to UV light, any other active energy beam may be selected for curing the ink depending on the properties of the ink. The light source may also be selected depending on the wavelength of the active energy beam.
The ink supply unit 1400 includes an ink tank 1410, a pump 1420, an ink tube 1430, a sub-tank 1440, an ink tube 1450, and a heater 1460. The ink supply unit 1400 stores ink and supplies the ink to the line heads 1310 of the image forming unit 1300 such that ink of different colors can be ejected from the respective nozzles of the line heads 1310. The ink in the ink tank 1410 is fed to the sub-tank 1440 that adjusts the back-pressure of the ink in the inkjet head 1100 via the ink tube 1430 by the pump 1420. The sub-tank 1440 is provided with a float sensor 1440a. The controller 1500 operates the pump 1420 in response to the fluid level detected by the float sensor 1440a so as to store a predetermined amount of ink in the sub-tank 1440. The ink in the sub-tank 1440 is supplied to the inkjet head 1100 through the ink tube 1450. This embodiment is exemplified by a configuration including the ink tank 1410, the pump 1420, the ink tube 1430, the sub-tank 1440, the ink tube 1450, and the heater 1460. Alternatively, this embodiment may be applied to any other configuration that can supply ink to the inkjet head 1100.
The heater 1460 provided for the ink supply unit 1400 heats the ink from outside the inkjet head 1100. With reference to Fig. 1, the heater 1460 covers the entire ink supply unit 1400. Alternatively, separate heaters for heating different components of the ink supply unit 1400 may be provided. The heater 1460 heats the ink inside the ink supply unit 1400 to a predetermined temperature or higher and maintains this temperature. Typically, the heater 1460 is composed of heating wires and heat-transferring members and covers the components of the ink supply unit 1400 or is bonded to the exterior of the components of the ink supply unit 1400.
Any ink may be used for the inkjet recording device 1000 according to this embodiment. Examples of such ink include UV curable ink, phase-transition ink that reversibly transitions between a gel phase and a sol phase at a phase-transition temperature, and phase-transition ink that reversibly transitions between a solid phase and a liquid phase at a phase-transition temperature.
The controller 1500 comprehensively controls the operation of the inkjet recording device 1000 through operational control of the units of the inkjet recording device 1000. The controller 1500 includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). In the controller 1500, various processing programs, such as a system program stored in the ROM, are read from the ROM and loaded to the RAM. The programs loaded to the RAM are executed by the CPU to carry out various control processes, such as the image forming process and the ink supplying process described above.
The configuration of the inkjet head 1100 will now be described with reference to Figs. 2 to 7B. Fig. 2 is an exploded perspective view illustrating the inkjet head 1100 according to this embodiment. Fig. 3 is a partial rear view illustrating a head chip 1001 of the inkjet head 1100. Fig. 4 illustrates the bonded state of the head chip 1001 and a wiring substrate 1003 viewed from the wiring substrate 1003. Fig. 5 is a partial cross-sectional view illustrating the head chip 1001 and the wiring substrate 1003, taken along line V-V in Fig. 4. Fig. 6A is a cross-sectional view illustrating the head chip 1001 and the wiring substrate 1003, taken along line Via-Via in Fig. 5. Fig. 6B is a cross-sectional view illustrating the head chip 1001 and the wiring substrate 1003, taken along line Vib-Vib in Fig. 5. Fig. 7A is a plan view illustrating the wiring substrate 1003 after being bonded to the head chip 1001 of the inkjet head 1100. Fig. 7B is a photograph illustrating the wiring substrate 1003 after being bonded to the head chip 1001 of the inkjet head 1100. An adhesive 1005 applied between the head chip 1001 and the wiring substrate 1003 is not shown in Figs. 2 to 5.
With reference to Fig. 2, the inkjet head 1100 includes a head chip 1001, a nozzle plate 1002 that is bonded to the front face 1001a of the head chip 1001, a wiring substrate 1003 that is bonded to the rear face 1001b of the head chip 1001, a flexible printed circuit board (FPC) 1004 connected to an edge 1003a of the wiring substrate 1003, and an ink manifold (common ink chamber) (not shown) bonded to the rear face of the wiring substrate 1003.
The head chip 1001 has a hexahedral shape and includes two channel rows A and B. With reference to Fig. 3, the channel row on the bottom of the drawing is referred to as row A, and channel row on the top as row B. The channel rows each include alternating driving channels 1011A (1011B) and dummy channels 1012A (1012B). The walls between the adjacent driving channels 1011A (1011B) and dummy channels 1012A (1012B) constitute drivable walls 1013 composed of piezoelectric elements.
The driving channels 1011A and 1011B and the dummy channels 1012A and 1012B have openings in the front face 1001a and the rear face 1001b of the head chip 1001 and are straight channels extending from the front face 1001a to the rear face 1001b. Driving electrodes 1014 are provided on the surfaces of at least the drivable walls 1013, among the surfaces of the walls facing the interiors of the driving channels 1011A and 1011B and the dummy channels 1012A and 1012B.
The head chip 1001 is an independently-driven head chip including the driving channels 1011A and 1011B and the dummy channels 1012A and 1012B alternately disposed in the corresponding channel row. Driving signals having a predetermined voltage are applied to the driving electrodes 1014 to deform the drivable wall 1013 disposed between the adjacent driving electrodes 1014 with a shearing force. The deformation by the shearing force varies the pressure for ejection of the ink in the driving channels 1011A and 1011B and causes the ink to be ejected as ink droplets from nozzles 1021 of the nozzle plate 1002 bonded to the front face 1001a of the head chip 1001.
In this embodiment, the ink-ejecting face of the head chip 1001 including the nozzles 1021 is referred to as "front face," whereas the opposite face is referred to as "rear face." The direction parallel to the front face 1001a and the rear face 1001b of the head chip 1001 and away from the head chip 1001 is defined as "lateral direction."
The driving channel ejects ink in accordance with image data during image recording, whereas the dummy channel does not eject ink regardless of the image data. The dummy channels 1012A and 1012B not ejecting ink are usually not filled with ink, or the nozzles 1021 are not provided at the positions corresponding to the dummy channels 1012A and 1012B in the nozzle plate 1002. The nozzle plate 1002 according to this embodiment has these nozzles 1021 only at positions corresponding to the driving channels 1011A and 1011B.
The rear face 1001b of the head chip 1001 is provided with connecting electrodes 1015A and 1015B corresponding to the driving channels 1011A and 1011B, respectively, and the dummy channels 1012A and 1012B, respectively. One end of each of the connecting electrodes 1015A and 1015B is electrically connected to the corresponding driving electrode 1014 of the corresponding driving channel 1011A or 1011B or the corresponding dummy channel 1012A or 1012B.
The other end of each of the connecting electrodes 1015A corresponding to the driving channels 1011A and the dummy channels 1012A in the row A extends from the inside of the channel 1011A or 1012A toward an edge 1001c of the rear face 1001b of the head chip 1001 to a distance of approximately 200 µm from the edge 1001c. The other end of each of the connecting electrodes 1015B corresponding to the driving channels 1011B and the dummy channels 1012B in the row B extends from the inside of the channel 1011B or 1012B toward the row A to a distance of approximately 200 µm from the channel row A. Both connecting electrodes 1015A and 1015B extend in the same direction from the channels 1011A, 1011B, 1012A, and 1012B.
The wiring substrate 1003 is preferably a flat substrate having an area larger than that of the rear face 1001b of the head chip 1001, in consideration of defining a bonding area 1031. The wiring substrate 1003 is bonded to the rear face 1001b of the head chip 1001 with the adhesive 1005. At least one edge 1003a of the bonded wiring substrate 1003 preferably extends outside the bonding area 1031 (which is indicated by the dash-dot line in Fig. 2), which is bonded to the head chip 1001 and considerably protrudes in the lateral direction parallel to the direction in which the channel rows of the head chip 1001 are arranged.
The bonding area 1031 on the surface of the wiring substrate 1003 is covered by the bonded head chip 1001 and is defined by a profile projecting from the periphery of the rear face 1001b of the head chip 1001 onto the wiring substrate 1003.
The wiring substrate 1003 may be composed of any material, such as glass, ceramic, silicon, and plastic. Among these materials, glass is preferred for its appropriate rigidity, inexpensiveness, and machinability.
The wiring substrate 1003 is bonded to the rear face 1001b of the head chip 1001 and covers all the channels. The wiring substrate 1003 has through- holes 1032A and 1032B, which are for supplying ink from the rear face of the wiring substrate 1003 to the driving channels 1011A and 1011B, at positions corresponding to the driving channels 1011A and 1011B of the head chip 1001 in the bonding area 1031 for bonding the head chip 1001. The openings of the through- holes 1032A and 1032B facing the head chip 1001 have shapes identical to the openings of the driving channels 1011A and 1011B on the rear face 1001b.
The wiring substrate 1003 does not have through-holes at positions corresponding to the dummy channels 1012A and 1012B. In other words, the dummy channels 1012A and 1012B are covered with the wiring substrate 1003. The head chip according to this embodiment includes dummy channels. Any other head chip may also be applied to the present invention. For example, through-holes and connecting electrodes (not shown) may be disposed at positions corresponding to the dummy channels 1012A and 1012B, and electrical power may be supplied to the connecting electrodes to eject ink from the nozzles.
The surface of the wiring substrate 1003 to be bonded to the head chip 1001 is provided with wiring electrodes 1033A and 1033B at positions corresponding to the respective connecting electrodes 1015A and 1015B aligned on the rear face 1001b of the head chip 1001. The wiring electrodes 1033A correspond to the connecting electrodes 1015A in the channel row A, and the wiring electrodes 1033B correspond to the connecting electrodes 1015B in the channel row B.
With reference to Fig. 4, one end of each wiring electrode 1033A is disposed near the corresponding driving channel 1011A or dummy channel 1012A and overlaps with the corresponding connecting electrode 1015A. The other end extends toward a common edge 1003a of the wiring substrate 1003 protruding in the lateral direction of the head chip 1001. One end of each wiring electrode 1033B is disposed near the corresponding driving channel 1011B or dummy channel 1012B and overlaps with the corresponding connecting electrode 1015B. The other end passes through the area between adjacent driving channels 1011A in the channel row A across the row A, and extends toward the edge 1003a of the wiring substrate 1003, like the wiring electrodes 1033A. Thus, the wiring electrodes 1033A and 1033B are alternately arranged on the surface of the wiring substrate 1003 protruding in the lateral direction of the head chip 1001, and extend from the inside of the bonding area 1031 to near the edge 1003a.
The edge 1003a of the wiring substrate 1003 is connected to an FPC 1004, which exemplifies an external wiring material, for example, via an anisotropic conductive film (ACF), to establish an electrical connection with a driver circuit (not shown). In this way, driving signals having a predetermined voltage are applied from the driver circuit to the driving electrodes 1014 in the channels 1011A, 1011B, 1012A, and 1012B via the FPC 1004, the respective wiring electrodes 1033A and 1033B of the wiring substrate 1003, and the respective connecting electrodes 1015A and 1015B of the head chip 1001.
The adhesive 1005 applied for the bonding of the head chip 1001 and the wiring substrate 1003 is a conductive adhesive containing conductive particles P1 and non-conductive particles P2. Examples of the adhesive 1005 include a cold-setting adhesive that is curable at room temperature, a thermosetting adhesive that is curable through polymerization promoted by heat, and a radiation curable adhesive that is curable through polymerization promoted by irradiation with active energy beams, such as UV light. Hereinafter, a conductive state refers to a state of having electrical resistivity of 10⁷ Ω·cm or less.
In particular, heating of the thermosetting adhesive to a predetermined temperature for curing after bonding temporarily lowers the viscosity and increases the fluidity of the adhesive. This also causes an increase in the fluidity of the conductive particles in the adhesive, which facilitates agglomeration of the conductive particles P1 in an adhesive fillet F formed of the adhesive that flowed outside the head chip 1001 (agglomeration refers to the formation of groups of several particles to several tens of particles). Thus, the present invention can be suitably applied to the bonding with such a thermosetting adhesive. A preferred example of a thermosetting adhesive is an epoxy adhesive. Any other thermosetting adhesive may also be applied to the present invention.
Examples of the conductive particles P1 include metal particles composed of gold or nickel or resin particles composed of, for example, divinylbenzene plated with metal, such as gold or nickel. Either type of conductive particles may be used in the present invention. The non-conductive particles P2 may be composed of resin, such as divinylbenzene, silica, alumina, or zirconia, for example.
Fig. 6A, which is a cross-sectional view taken along line Via-Via in Fig. 5, illustrates an adhesive fillet F formed of the adhesive 1005 that flowed outside from between the head chip 1001 and the wiring substrate 1003 onto a flat area between the wiring electrodes 1033A and 1033B during bonding of the head chip 1001 and the wiring substrate 1003 with the adhesive 1005. The adhesive fillet F is disposed outside the bonding area 1031 of the wiring substrate 1003 around the periphery of the head chip 1001, along a side face of the head chip 1001 and a face of the wiring substrate 1003. The reference sign Fa in the drawing denotes the area in which the adhesive fillet F is formed.
The wiring electrodes 1033A and 1033B extending outside the bonding area 1031 pass under the adhesive fillet F and extend to the edge 1003a of the wiring substrate 1003.
Portions of the wiring electrodes 1033A and 1033B passing under the adhesive fillet F in an area near the bonding area 1031 may come into direct contact with the agglomerated conductive particles P1. In order to avoid such a risk, the adhesive 1005 contains the non-conductive particles P2.
Fig. 7A is a plan view illustrating an agglomerate of the particles in the adhesive 1005 formed in an area corresponding to the cross-sectional view in Fig. 6A. The head chip 1001 is disposed below the dashed line in the drawing. An agglomerate of particles formed between adjacent wiring electrodes 1033A and 1033B consists of a mixture of the conductive particles P1 and the non-conductive particles P2, rather than only the conductive particles P1. Thus, this can prevent short-circuiting between the wiring electrodes 1033A and 1033B that would be caused by the conductive particles P1 in the adhesive fillet F.
Fig. 7B is an example photograph illustrating the wiring substrate 1003 bonded to the head chip 1001 with the adhesive 1005 containing the conductive particles P1 and the non-conductive particles P2. The black area represents the wiring electrodes 1033A and 1033B on the wiring substrate 1003, the multiple substantial circles represent the conductive particles P1, and the white blur represents the non-conductive particles P2.
In Fig. 7B, the head chip 1001 is disposed below the dashed line, and adhesive fillets F are disposed inside the areas defined by dotted lines. In the adhesive fillets F in Fig. 7B, the non-conductive particles P2 are disposed between wiring electrodes 1033A and 1033B, i.e. , the areas between the wiring electrodes 1033A and 1033B are not filled with agglomerates of only conductive particles P1. With reference to Fig. 7B, it can be confirmed by visual observation that the short-circuiting between the wiring electrodes 1033A and 1033B due to the agglomeration of only conductive particles P1 does not occur.
Fig. 6B, which is a cross-sectional view taken along line Vib-Vib in Fig. 5, illustrates an adhesive fillet F formed of the adhesive 1005 that flowed outside from between the head chip 1001 and the wiring substrate 1003 onto a flat area of a wiring electrode 1033A during bonding of the head chip 1001 and the wiring substrate 1003 with the adhesive 1005. The adhesive 1005 containing the conductive particles P1 and the non-conductive particles P2 flows into the area between the connecting electrodes 1015A and the wiring electrodes 1033A. This establishes a reliable electrical connection between the connecting electrodes 1015A and the wiring electrodes 1033A via the conductive particles P1.
With reference to Fig. 8, preferred conditions for the inkjet head 1100 will now be described. Fig. 8 is a graph illustrating the number of particles versus the size (diameter) of the particles.
With reference to Fig. 6B, the conductive particles P1 and the non-conductive particles P2 enter between the connecting electrodes 1015A and the wiring electrodes 1033A. Therefore, the conductive particles P1 should mediate an electrical connection between the connecting electrodes 1015A and the wiring electrodes 1033A, to establish a reliable electrical connection between the connecting electrodes 1015A and the wiring electrodes 1033A. Thus, it is preferred that the size of the conductive particles P1 be larger than or equal to that of the non-conductive particles P2.
The particles have a distribution of the number of particles versus the size (diameter) of the particles in Fig. 8. In the distribution curve, the average size of particles corresponds to the peak of the number of particles. Thus, it is preferred that the size of the conductive particles P1 corresponding to the peak of the distribution curve be larger than or equal to the size of the non-conductive particles P2 corresponding to the peak of the distribution curve.
A reliable electrical connection can be established between the connecting electrodes 1015A and the wiring electrodes 1033A by using readily deformable non-conductive particles P2 composed of a material softer than the material of the conductive particles P1. Thus, it is preferred that the Young's modulus of the conductive particles P1 be larger than that of the non-conductive particles P2. The Young's modulus of the non-conductive particles P2 is 5 to 10 GPa, for example.
Although the adhesive 1005 may have any degree of viscosity, it is preferred that the adhesive 1005 have high viscosity during bonding of the wiring substrate 1003 and the head chip 1001 to avoid the intrusion of the adhesive 1005 into the openings of the driving channels 1011A and 1011B of the head chip 1001 and thus prevent short-circuiting. In consideration of defoaming of the adhesive 1005 if air bubbles enter the adhesive 1005, it is preferred that the adhesive 1005 has low viscosity. In consideration of prevention of the intrusion of the adhesive 1005 into the openings of the driving channels 1011A and 1011B and ready defoaming of the adhesive 1005 including air bubbles, it is preferred that the adhesive 1005 have viscosity of 5 to 15 Pa.s, for example.
With reference to Fig. 9 to 11, an example method of producing the inkjet head 1100 will now be described.
Fig. 9 is a plan view illustrating a surface of the wiring substrate 1003 prepared through the method of producing the inkjet head 1100. Strips of the adhesive 1005 are applied to the surface of the wiring substrate 1003, which is provided with the through- holes 1032A and 1032B and the wiring electrodes 1033A and 1033B, over the areas where the connecting electrodes 1015A and 1015B of the head chip 1001 are to overlap with the wiring electrodes 1033A and 1033B. The head chip 1001 is then positioned and bonded to the bonding area 1031.
The head chip 1001 and the wiring substrate 1003 are clamped by a pair of pressure plates to hermetically seal the dummy channels 1012A and 1012B having openings in the front face 1001a of the head chip 1001 remote from the bonding surface of the wiring substrate 1003.
Fig. 10 is a cross-sectional view illustrating the head chip 1001 and the wiring substrate 1003 clamped by a pair of pressure plates 1006a and 1006b. The head chip 1001 and the wiring substrate 1003 bonded together are disposed between the pressure plates 1006a and 1006b to apply predetermined pressure to the head chip 1001 and the wiring substrate 1003 in the vertical direction. This causes the adhesive 1005 applied in strips to flow between the head chip 1001 and the wiring substrate 1003 due to a capillary force. In Fig. 10, the adhesive 1005 is not shown.
During bonding of the wiring substrate 1003 and the head chip 1001, a force of 50 kgf is applied to the entire head chip 1001, for example. For example, for a head chip 1001 with dimensions of 82 mm by 4.6 mm, the pressure applied is 1.3 Mpa.
Some of the adhesive 1005 reaching the dummy channels 1012A and 1012B flows along the wiring substrate 1003 and enters the dummy channels 1012A and 1012B. This is because the openings of the dummy channels 1012A and 1012B are covered by the wiring substrate 1003.
Among the faces of the pressure plates 1006a and 1006b, the face of the pressure plate 1006a adjacent to the front face 1001a of the head chip 1001 is provided with a seal 1007 composed of a sheet of elastic material. The seal 1007 is in contact with the front face 1001a of the head chip 1001. A typical example of the elastic material is rubber, preferably, silicone rubber.
The seal 1007 is provided for the following reason. Typically, the head chip 1001 is prepared through full-cut dicing of ceramics with a dicing blade, for example. Thus, the full-cut faces (front face 1001a and rear face 1001b) may have minute asperities due to the dicing. Such asperities prevent the dummy channels 1012A and 1012B from being hermetically sealed with the mere flat pressure plate 1006a. This drawback may be solved by polishing the full-cut faces. Alternatively, as illustrated in the drawing, the seal 1007 composed of an elastic material and disposed between the head chip 1001 and the pressure plate 1006a can provide an effective hermetic seal for the openings in the asperous front face 1001a of the head chip 1001, without polishing.
The openings of the dummy channels 1012A and 1012B adjacent to the wiring substrate 1003 are hermetically sealed by the adhesive 1005 flowing to the periphery of the openings and the wiring substrate 1003. Thus, the seal 1007 is not necessarily required for the pressure plate 1006b adjacent to the wiring substrate 1003. The dummy channels 1012A and 1012B of the head chip 1001 are hermetically sealed between the seal 1007 on the pressure plate 1006a and the wiring substrate 1003 and retain gas (air) inside the channels.
Heating of the head chip 1001 and the wiring substrate 1003 in this state causes expansion of the gas sealed inside the dummy channels 1012A and 1012B.
For a thermosetting adhesive 1005, the heat applied for thermal curing can also contribute to such thermal expansion. If the adhesive 1005 is not a thermosetting adhesive, an appropriate heating device, such as an oven, may be used to heat the head chip 1001 and the wiring substrate 1003 clamped with the pressure plates 1006a and 1006b. With reference to Fig. 11, a case where the adhesive 1005 is a thermosetting adhesive and the heat applied for curing is used for heating the head chip 1001 and the wiring substrate 1003 will now be described. Fig. 11 illustrates the thermally expanded state of the gas inside the dummy channels 1012A and 1012B.
As illustrated in Fig. 11, the expansion of the gas inside the dummy channels 1012A and 1012B due to heating of the head chip 1001 causes the adhesive 1005 inside the dummy channels 1012A and 1012B to intrude between the rear face 1001b of the head chip 1001 and the wiring substrate 1003 from the dummy channels 1012A and 1012B. Curing of the adhesive 1005 in this state forms independent adhesive fillets 1051 from the adhesive 1005 remaining inside the openings of the dummy channels 1012A and 1012B at the four corners of the openings. In this way, the peripheries of the openings of the dummy channels 1012A and 1012B are surrounded and sealed by the adhesive fillets 1051. At the same time, clogging of the adhesive 1005 does not occur in the interiors of the dummy channels 1012A and 1012B.
The adhesive 1005 protruding from the dummy channels 1012A and 1012B due to thermal expansion spreads between the head chip 1001 and the wiring substrate 1003. The adhesive 1005 that flows out the head chip 1001 forms adhesive fillets F as illustrated in Figs. 6A and 6B. The protrusion of the adhesive 1005 from the dummy channels 1012A and 1012B generates a flow that readily conveys many conductive particles P1 to the adhesive fillets F, where the conductive particles P1 agglomerate. Such agglomerates increase the risk of short-circuiting between the wiring electrodes 1033A and 1033B. In this embodiment, the non-conductive particles P2 effectively prevents short-circuiting between the wiring electrodes 1033A and 1033B that would be caused by the agglomerated conductive particles P1 in the adhesive fillets F. Thus, highly advantageous effects are achieved through application of this embodiment to the method of production described above.
Since the heating temperature and time for thermal expansion of the gas should be determined such that the gas inside the dummy channels 1012A and 1012B appropriately expand before the temperature of the adhesive reaches the curing temperature, the fluidity of the adhesive 1005 should be maintained without an excess increase in the viscosity of the adhesive 1005, and the adhesive 1005 should lose flow characteristics after some extent of flow for a certain time. Specific temperature and time are appropriately determined depending on the type (curing temperature and viscosity) of the adhesive 1005, the volume of the dummy channels 1012A and 1012B, and the dimensions and the thermal conductivity of the head chip 1001.
After bonding of the head chip 1001 and the wiring substrate 1003, the nozzle plate 1002 is bonded to the front face 1001a of the head chip 1001, and a manifold (not shown) is bonded to the rear face of the wiring substrate 1003. Furthermore, the FPC 1004 may be connected to the edge 1003a of the wiring substrate 1003 to externally lead the wiring electrodes from the inkjet head 1100.
A protective film, such as a parylene film, may be deposited on the surface of the driving electrodes 1014 after the bonding of the head chip 1001 and the wiring substrate 1003 and before the bonding of the nozzle plate 1002. If a protective film is not provided, the wiring substrate 1003 may be bonded to the head chip 1001 after the nozzle plate 1002 is bonded to the head chip 1001. In such a case, the seal 1007 may be omitted because the nozzle plate 1002 hermetically seals the openings of the dummy channels 1012B in the front face 1001a of the head chip 1001.
According to this embodiment, the inkjet head 1100 includes the head chip 1001 and the wiring substrate 1003. The head chip 1001 includes a plurality of channels 1011A, 1012A, 1011B, and 1012B; a plurality of driving electrodes 1014 disposed in the respective channels 1011A, 1012A, 1011B, and 1012B; and a plurality of connecting electrodes 1015A and 1015B disposed on the surface of the head chip 1001. The connecting electrodes 1015A and 1015B are electrically connected to the respective driving electrodes 1014. The wiring substrate 1003 includes a plurality of wiring electrodes 1033A and 1033B arranged on the surface of the wiring substrate 1003. The wiring electrodes 1033A and 1033B are electrically connected to the respective connecting electrodes 1015A and 1015B. The wiring substrate 1003 is bonded to the face, on which the connecting electrodes 1015A and 1015B are disposed, of the head chip 1001 with the adhesive 1005 containing conductive particles P1, thereby allowing electrical connections to be established between the connecting electrodes 1015A and 1015B and the respective wiring electrodes 1033A and 1033B. The adhesive 1005 contains a mixture of the conductive particles P1 and the non-conductive particles P2.
In the bonding step of the head chip 1001 and the wiring substrate 1003 with the adhesive 1005 containing the conductive particles P1, the non-conductive particles P2 in the adhesive 1005 can prevent short-circuiting of the wiring electrodes 1033A and 1033B of the wiring substrate 1003 that would be caused by the agglomerated conductive particles P1 in the adhesive 1005.
The average size of the conductive particles P1 is larger than or equal to that of the non-conductive particles P2. Such a particle size profile can ensure a reliable electrical connection between the connecting electrodes 1015A and 1015B of the head chip 1001 and the respective wiring electrodes 1033A and 1033B of the wiring substrate 1003 without disconnection.
The Young's modulus of the conductive particles P1 is larger than that of the non-conductive particles P2. Thus, the non-conductive particles P2 can be composed of a material softer than the material of the conductive particles P1. This combination of materials establishes a reliable electrical connection between the connecting electrodes 1015A and 1015B of the head chip 1001 and the respective wiring electrodes 1033A and 1033B of the wiring substrate 1003 without disconnection.
The openings of the channels 1011A, 1012A, 1011B, and 1012B and the connecting electrodes 1015A and 1015B are provided on the same face of the head chip 1001. Thus, the head chip 1001 and the wiring substrate 1003 can be easily bonded together.
The wiring substrate 1003 is disposed parallel to the face, on which the openings and the connecting electrodes 1015A and 1015B are disposed, of the head chip 1001. Although this configuration increases the fluidity of the adhesive 1005 and the conductive particles P1 between the head chip 1001 and the wiring substrate 1003, the non-conductive particles P2 in the adhesive 1005 can effectively prevent short-circuiting between the wiring electrodes 1033A and 1033B of the wiring substrate 1003 that would be caused by the agglomerated conductive particles P1 in the adhesive 1005.
The connecting electrodes 1015A and 1015B are connected to the respective driving electrodes 1014 through the openings of the channels 1011A, 1012A, 1011B, and 1012B. This readily establishes an electrical connection between the connecting electrodes 1015A and 1015B and the driving electrodes 1014.
The driving electrodes 1014 are provide on the drivable walls 1013 facing the interiors of the channels 1011A, 1012A, 1011B, and 1012B. In this way, driving signals can be applied to the driving electrodes 1014 to generate a shearing force that deforms the drivable walls 1013 to vary the pressure applied to the ink in the driving channels 1011A and 1011B, thereby causing the ink to be ejected from the nozzles 1021 of the driving channels 1011A and 1011B.
The wiring electrodes 1033A and 1033B are electrically connected to the respective connecting electrodes 1015A and 1015B and provided on the surface of the area of the wiring substrate 1003 which area extends outside of the bonding area 1031 where the wiring substrate 1003 and the head chip 1001 are bonded to each other. This can readily establish an electrical connection between the wiring substrate 1003 and the FPC 1004. The adhesive fillets F are formed on the wiring substrate 1003 extending outside of the bonding area 1031. The non-conductive particles P2 in the adhesive 1005 can effectively prevent short-circuiting between the wiring electrodes 1033A and 1033B that would be caused by the agglomerated conductive particles P1 in the adhesive fillets F.
In the method of producing the inkjet head 1100 according to this embodiment, the head chip 1001 and the wiring substrate 1003 are bonded together with the adhesive 1005, and the adhesive 1005 is cured to electrically connect the connecting electrodes 1015A and 1015B to the respective wiring electrodes 1033A and 1033B. This readily establishes an appropriate electrical connection between the head chip 1001 and the wiring substrate 1003 to produce the inkjet head 1100.
The inkjet recording device 1000 including the inkjet head 1100 achieves the advantageous effects described above.

[Example 1]

An example of the inkjet head 1100 will now be described. The inkjet head 1100 was produced under several conditions and then evaluated. The head chip 1001 selected was a harmonica-shaped double-row independent-drive chip having 1024 driving channels. The conductive particles P1 were resin particles composed of divinylbenzene plated with Ni-Au and had a standard particle size ±0.5 µm. Here, the phrase "standard particle size ±0.5 µm indicates that the curve in Fig. 8 resides within the range of ±0.5 5 µm of the average or standard particle size.
The non-conductive particles P2 were resin particles composed of divinylbenzene having a standard particle size ±0.5 µm. The wiring electrodes 1033A and 1033B were composed of aluminum and had a thickness of 3 µm.

Table 1 shows the conditions and evaluation involving the inkjet head 1100 for 13 examples including a comparative example and inventive examples.

Table 1

No.	CONDUCTIVE PARTICLES P1		NON-CONDUCTIVE PARTICLES P2		DEFECT RATE
No.	PARTICLE SIZE	MIXING RATIO	PARTICLE SIZE	MIXING RATIO	DISCONNECTION	SHORT-CIRCUITING
0	3 µ m	1%	NONE		A	C
1	3 µ m	1%	1 µm	0.50%	A	B
2	3 µ m	1%	1 µ m	1%	A	B
3	3 µ m	1%	1 µm	2%	A	A
4	3 µ m	1%	1 µm	5%	A	A
5	3 µ m	1%	3 µm	0.50%	A	B
6	3 µ m	1%	3 µ m	1%	A	B
7	3 µ m	1%	3 µm	2%	A	A
8	3 µm	1%	3 µm	5%	A	A
9	3 µ m	1%	5 µm	0.50%	B	B
10	3 µ m	1%	5 µ m	1%	B	B
11	3 µ m	1%	5 µm	2%	B	A
12	3 µ m	1%	5 µm	5%	B	A

In Table 1, "No." refers to the identification numerals of the comparative example and the inventive examples. No. 0 represents a comparative example of an inkjet head 1100 including an adhesive 1005 without non-conductive particles P2. Nos. 1 to 12 represent inkjet heads 1100 according to examples including adhesives 1005 containing conductive particles P1 and non-conductive particles P2.
"Particle size" refers to the average size (diameter) of a predetermined number of particles. "Mixing ratio" refers to the ratio of the volume of the particles to the volume of the adhesive 1005. "Defect rate" refers to the number of head chips 1001 that have disconnection or short-circuiting for ten head chips 1001. "Disconnection" refers to information indicating an increase in the rate of defects or disconnection between the wiring electrodes 1033A and 1033B and the respective connecting electrodes 1015A and 1015B in comparison with the comparative example No. 0. In column "Disconnection," rank A indicates no increase in the rate of disconnection, and rank B indicates a slight increase. "Short-circuiting" refers to information indicating a decrease in the frequency of short-circuiting between adjacent wiring electrodes 1033A and 1033B in comparison with the comparative example No. 0. In column "short-circuiting," rank C indicates no decrease in frequency, rank B indicates a slight decrease in frequency, and rank A indicates a significant decrease in frequency.
With reference to Table 1, an adhesive 1005 containing the conductive particles P1 and the non-conductive particles P2 is an inevitable component for reducing the frequency of short-circuiting. The results on "Particle size" demonstrate that the conductive particles P1 having an average size larger than or equal to that of the non-conductive particles P2 (Nos. 1 to 8) can establish a stable connection without an increase in the frequency of disconnection.
The results on "mixing ratio" demonstrate that an adhesive 1005 containing non-conductive particles P2 having a volume mixing ratio that is half or more of the volume mixing ratio of conductive particles P1 (Nos. 1 to 12) is preferred because of the reduced frequency of short-circuiting, and that an adhesive 1005 containing non-conductive particles P2 having a volume mixing ratio that is at least twice the volume mixing ratio of conductive particles P1 (Nos. 3, 4, 7, 8, 11, and 12) is more preferred because of the significantly reduced frequency of short-circuiting. The inkjet heads 1100 of Nos. 3, 4, 7, and 8 are particularly preferred in view of reduced disconnection and short-circuiting.
These results conclude that the volume mixing ratio of the non-conductive particles P2 to the adhesive 1005 is preferably half or more of the volume mixing ratio of the conductive particles P1 to the adhesive 1005, more preferably twice or more. An adhesive 1005 having such a volume mixing ratio can prevent short-circuiting between adjacent wiring electrodes 1033A and 1033B of the wiring substrate 1003.

[Second Embodiment]

An inkjet recording device according to a second embodiment of the present invention will now be described.

(Inkjet Recording Device)

Fig. 13 is a schematic view of an inkjet recording device according to the present invention.
In the inkjet recording device 2000, a recording medium P is held between a pair of conveying rollers 2101a of a conveying mechanism 2101 and is conveyed in the Y direction (sub-scanning direction) in the drawing on a rotating conveying roller 2101b driven by a conveying motor 2101c.
An inkjet head 2010 is disposed between the conveying roller 2101b and the conveying rollers 2101a such that the inkjet head 2010 faces the recording face PS of the recording medium P. The inkjet head 2010 is placed on a carriage 2102 such that the nozzle face faces the recording face PS of the recording medium P and is electrically connected to a controller (not shown) via a flexible cable 2103. The carriage 2102 is driven by a driving unit (not shown) in a reciprocating manner along guiding rails 2104 suspended across the width direction of the recording medium P in the X-X' direction (main scanning direction), which is substantially orthogonal to the recording medium P conveying direction (sub-scanning direction) in the drawing.
The inkjet head 2010 moves along the recording face PS of the recording medium P in the X-X' direction in the drawing as the carriage 2102 moves in the main scanning direction. During the motion, the inkjet head 2010 ejects ink in the channels (driving channels) of the inkjet head 2010 from nozzles in communication with the channels, to record a predetermined inkjet image on the recording face PS of the recording medium P.

(Inkjet Head)

The configuration of the inkjet head 2010 will now be described with reference to the drawings.
Fig. 14 is an exploded perspective view illustrating an example inkjet head. Fig. 15 is a partial rear view illustrating a head chip of the inkjet head in Fig. 14. Fig. 16 illustrates the bonded state of a head chip and a wiring substrate. Fig. 17 is a cross-sectional view taken along line (v)-(v) in Fig. 16.
The inkjet head 2010 includes a head chip 2001, a nozzle plate 2002 bonded to the front face 2001a of the head chip 2001, a wiring substrate 2003 bonded to the rear face 2001b of the head chip 2001, and a flexible printed circuit board (FPC) 2004 connected to the edge 2003a of the wiring substrate 2003.
The head chip 2001 has a hexahedral shape and includes two channel rows A and B. With reference to Fig. 15, the channel row on the bottom of the drawing is referred to as row A, and channel row on the top as row B. The channel rows each include alternating driving channels 2011A (2011B) and dummy channels 2012A (2012B). The walls between the adjacent driving channels 2011A (2011B) and dummy channels 2012A (2012B) constitute drivable walls 2013A (2013B) composed of piezoelectric elements.
The driving channels 2011A and 2011B and the dummy channels 2012A and 2012B are straight channels extending from the front face 2001a to the rear face 2001b of the head chip 2001 and have openings in the front face 2001a and the rear face 2001b of the head chip 2001. The reference signs 2011A, 2011B, 2012a, and 2012b in Fig. 15 denote openings of channels arrayed on the rear face 2001b of the head chip 2001. Driving electrodes 2014 are provided on the surfaces of at least the drivable walls 2013A and 2013B, among the surfaces of the walls facing the interiors of the driving channels 2011A and 2011B and the dummy channels 2012A and 2012B.
The head chip 2001 is an independently-driven head chip including the driving channels 2011A and 2011B and the dummy channels 2012A and 2012B alternately disposed in the corresponding channel row. Driving signals having a predetermined voltage are applied to the driving electrodes 2014 to deform the drivable walls 2013A and 2013B disposed between the adjacent driving electrodes 2014 with a shearing force. The deformation by the shearing force varies the pressure for ejection of the ink in the driving channels 2011A and 2011B and causes the ink to be ejected as ink droplets from nozzles 2021 of the nozzle plate 2002 bonded to the front face 2001a of the head chip 2001.
In this embodiment, the ink-ejecting face of the head chip 2001 including the nozzles 2021 is referred to as "front face," whereas the opposite face is referred to as "rear face." The direction parallel to the front face 2001a and the rear face 2001b of the head chip 2001 and away from the head chip 2001 is defined as "lateral direction."
The driving channel ejects ink in accordance with image data during image recording, whereas the dummy channel does not eject ink regardless of the image data. The dummy channels 2012A and 2012B not ejecting ink are usually not filled with ink, or the nozzles 2021 are not provided at the positions corresponding to the dummy channels 2012A and 2012B in the nozzle plate 2002. The nozzle plate 2002 according to this embodiment has these nozzles 2021 only at positions corresponding to the driving channels 2011A and 2011B.
The rear face 2001b of the head chip 2001 is provided with connecting electrodes 2015A and 2015B corresponding to the driving channels 2011A and 2011B, respectively, and the dummy channels 2012A and 2012B, respectively. One end of each of the connecting electrodes 2015A and 2015B is electrically connected to the corresponding driving electrode 2014 through the opening 2011a or 2011b of the corresponding driving channel 2011A or 2011B or the opening 2012a or 2012b of the corresponding dummy channel 2012A or 2012B.
With reference to Fig. 15, the other end of each of the connecting electrodes 2015A corresponding to the driving channels 2011A and the dummy channels 2012A in the row A extends from the opening 2011a or 2012a of the channel 2011A or 2012A, toward an edge 2001c of the rear face 2001b of the head chip 2001. The other end of each of the connecting electrodes 2015B corresponding to the driving channels 2011B and the dummy channels 2012B in the row B extends from the opening 2011b or 2012b of the channel 2011B or 2012B toward the row A with a gap between the row A and the end. Both connecting electrodes 2015A and 2015B extend in the same direction from the openings 2011a, 2011b, 2012a, and 2012b.
The wiring substrate 2003 is bonded to the rear face 2001b of the head chip 2001 with an adhesive 2005 (for example, see Fig. 17). The wiring substrate 2003 is preferably a flat substrate having an area larger than that of the rear face 2001b of the head chip 2001, in consideration of defining a bonding area 2031 (which is indicated by the dash-dot line in Fig. 14) for the head chip 2001. Specifically, at least one edge 2003a of the wiring substrate 2003 bonded to the head chip 2001 preferably extends outside the bonding area 2031, as illustrated in Fig. 14, which considerably protrudes in the lateral direction parallel to the direction in which the channel rows of the head chip 2001 are arranged. The protruding edge 2003a provides a large connecting space for the FPC 2004.
The bonding area 2031 on the surface of the wiring substrate 2003 is covered by the rear face 2001b of the head chip 2001 and is defined by a profile projecting from the periphery of the rear face 2001b of the head chip 2001 onto the wiring substrate 2003.
The wiring substrate 2003 may be composed of any material, such as glass, ceramic, silicon, and plastic. Among these materials, glass is preferred for its appropriate rigidity, inexpensiveness, and machinability.
The wiring substrate 2003 is bonded to the head chip 2001 to cover the openings 2011a, 2011b, 2012a, and 2012b of all channels on the rear face 2001b of the head chip 2001. Specifically, the wiring substrate 2003 is disposed parallel to the rear face 2001b of the head chip 2001 provided with the openings 2011a, 2011b, 2012a, and 2012b and the connecting electrodes 2015A and 2015B and is bonded to the head chip 2001 with the adhesive 2005.
The wiring substrate 2003 has through- holes 2032A and 2032B in the bonding area 2031 for the head chip 2001 of the wiring substrate 2003 for supplying ink from the rear face of the wiring substrate 2003 to the driving channels 2011A and 2011B. The through- holes 2032A and 2032B are formed at positions corresponding to only the driving channels 2011A and 2011B in the head chip 2001. The openings of the through- holes 2032A and 2032B adjacent to the head chip 2001 have shapes identical to those of the openings 2011a and 2011b of the respective driving channels 2011A and 2011B.
The wiring substrate 2003 does not have through-holes at positions corresponding to the dummy channels 2012A and 2012B. In other words, the dummy channels 2012A and 2012B are covered with the wiring substrate 2003.
The surface, of the wiring substrate 2003, to be bonded to the head chip 2001 is provided with wiring electrodes 2033A and 2033B at positions corresponding to the respective connecting electrodes 2015A and 2015B aligned on the rear face 2001b of the head chip 2001. The wiring electrodes 2033A correspond to the connecting electrodes 2015A in the channel row A, and the wiring electrodes 2033B correspond to the connecting electrodes 2015B in the channel row B.
With reference to Fig. 16, one end of each wiring electrode 2033A is disposed near the corresponding driving channel 2011A or dummy channel 2012A and overlaps with the corresponding connecting electrode 2015A. The other end extends toward a common edge 2003a of the wiring substrate 2003 protruding in the lateral direction of the head chip 2001. One end of each wiring electrode 2033B is disposed near the corresponding driving channel 2011B or dummy channel 2012B and overlaps with the corresponding connecting electrode 2015B. The other end of each wiring electrode 2033B passes through the area between adjacent driving channels 2011A in the channel row A across the row A, and extends toward the edge 2003a of the wiring substrate 2003, like the wiring electrodes 2033A. Thus, the wiring electrodes 2033A and 2033B are alternately arranged on the surface of the wiring substrate 2003 protruding in the lateral direction of the head chip 2001, and extend from the inside of the bonding area 2031 to near the edge 2003a.
The edge 2003a of the wiring substrate 2003 is connected to an FPC 2004, which exemplifies an external wiring material, for example, via an anisotropic conductive film (ACF), to establish an electrical connection with a driver circuit (not shown). In this way, driving signals having a predetermined voltage are applied from the driver circuit to the driving electrodes 2014 in the channels 2011A, 2011B, 2012A, and 2012B via the FPC 2004, the respective wiring electrodes 2033A and 2033B of the wiring substrate 2003, and the respective connecting electrodes 2015A and 2015B of the head chip 2001.

(Adhesive Containing Conductive Particles)

Examples of the adhesive 2005 for bonding the head chip 2001 and the wiring substrate 2003 include a cold-setting adhesive that is curable at room temperature, a thermosetting adhesive that is curable through polymerization promoted by heat, and a radiation curable adhesive that is curable through polymerization promoted by irradiation with active energy beams, such as UV light.
The adhesive 2005 according to the present invention is a conductive adhesive containing conductive particles 2006 having protrusions. The head chip 2001 and the wiring substrate 2003 are bonded together with the adhesive 2005 to establish an electrical connection between the connecting electrodes 2015A and 2015B on the rear face 2001b of the head chip 2001 and the respective wiring electrodes 2033A and 2033B on the wiring substrate 2003.
Fig. 18 is a partially cutaway schematic view of one of the conductive particles 2006. Fig. 19 is a cross-sectional view illustrating a connecting electrode 2015A (2015B) and a wiring electrode 2033A (2033B) electrically connected via the adhesive 2005 containing conductive particles 2006.
Each of the conductive particles 2006 has multiple protrusions 2006a on its surface. The conductive particles 2006 disposed between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B after bonding of the head chip 2001 and the wiring substrate 2003 come into contact with the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B at the tips of the protrusions 2006a.
This causes the load applied during pressure bonding of the head chip 2001 and the wiring substrate 2003 to concentrate at the small contact surfaces at the tips of the protrusions 2006a. As a result, high pressure per unit area is applied to the conductive particles 2006 and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. This causes the conductive particles 2006 to stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B to provide a sufficient contact area, achieve a reliable contact state, and establish a reliable electrical connection between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B.
Even if the head chip 2001 and the wiring substrate 2003 have warp and undulation, a sufficient contact state can be achieved between the conductive particles 2006 and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B, and a reliable electrical connection can be established between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B, without the application of significantly high pressure during pressure bonding.
The application of pressure causes the protrusions 2006a of the conductive particles 2006 to stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. Thus, a variation can be reduced in the resistance between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B, and a stable electrical connection can be established.
The conductive particles 2006 having the protrusions 2006a on their surfaces do not readily move in the adhesive 2005 and are barely agglomerated between the head chip 2001 and the wiring substrate 2003. In particular, heating of a thermosetting adhesive 2005 to a predetermined temperature for curing temporarily lowers the viscosity and increases the fluidity of the adhesive. This causes an increase in the fluidity of the conductive particles in the adhesive, which facilitates agglomeration of the conductive particles. The conductive particles 2006 having the protrusions 2006a on their surfaces do not significantly flow even if the adhesive 2005 has reduced viscosity during heating. This prevents agglomeration of the conductive particles 2006. In this way, short-circuiting that would be caused by agglomeration can be effectively prevented between electrodes.
Agglomeration due to the flow of conductive particles 2006 may occur in adhesives other than thermosetting adhesives. The decreased viscosity of thermosetting adhesives 2005 due to heating increases the fluidity of the adhesive, thereby causing rotational migration of the conductive particles 2006. It is preferred that the adhesive 2005 according to the present invention be a thermosetting adhesive that can effectively prevent agglomeration, as described above. A preferred example of a thermosetting adhesive is an epoxy adhesive. Any other thermosetting adhesive may also be applied to the present invention.
According to the present invention, an adhesive 2005 containing such conductive particles 2006 is preferred in the case where either or both of the connecting electrodes 2015A (2015B) and the wiring electrodes 2033A (2033B) are electrodes having oxide films on their surfaces, such as the ones made of aluminum. Although electrodes coated with oxide films typically have high connection resistance, the protrusions 2006a of the conductive particles 2006 readily stick out of the oxide films and come into contact with the metal surfaces beneath. The conductive particles 2006 come into direct contact with the metal surfaces beneath the oxide films on the electrodes 2015A, 2015B, 2033A, and 2033B to establish an electrical connection, without application of significantly high pressure during pressure bonding. Thus, highly advantageous effects are achieved in the present invention. To ensure such advantages, it is preferred that the minimum height of the protrusions 2006a be greater than the maximum thickness of the oxide films on the surfaces of the connecting electrodes 2015A (2015B) and the wiring electrodes 2033A (2033B).
The conductive particles 2006 according to the present invention may be of any type having electric conductivity and having protrusions 2006a on their surfaces. Particles not coated with oxide films are preferred to establish a reliable electrical connection between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B. With reference to Fig. 18, preferred example of the conductive particles 2006 includes core-shell particles each composed of an organic core 2061 coated with a metal film or shell 2062 having protrusions 2006a. During pressure bonding, the organic cores 2061 of the conductive particles 2006 disposed between the electrodes deform to absorb the fluctuation in the pressure distribution and equalize the pressure applied to the conductive particles 2006 and the electrodes 2015A, 2015B, 2033A, and 2033B.
The organic cores 2061 may be of any type and may be, for example, resin particles composed of divinylbenzene as a main constituent monomer.
The shells 2062 are each made of a metal film covering the surface of the organic core 2061. The shells 2062 may be composed of any metal, such as nickel and gold. It is preferred that the Young' s modulus of the shells 2062 be larger than the Young' s modulus of the organic cores 2061 so that the protrusions 2006a on the surfaces of the shells 2062 of the conductive particles 2006 can stick into the surfaces of the electrodes and establish a stable electrical connection. In this way, the protrusions 2006a are less likely to deform compared to the organic cores 2061 when the conductive particles 2006 are disposed between the electrodes during pressure bonding. The protrusions 2006a of the conductive particles 2006 maintain their shape as they stick into the surfaces of the electrodes and thus establish a stable electrical connection.
With reference to Fig. 18, a core-shell particle serving as a conductive particle 2006 includes a shell 2062 including an outermost layer 2621 composed of gold and an inner layer 2622 composed of a metal having a Young's modulus larger than that of gold. It is preferred that the inner layer 2622 form the protrusions 2006a. Fig. 18 illustrates the conductive particle 2006 including the organic core 2061, the inner layer 2622 having the protrusions 2006a prepared by plating the surface of the organic core 2061 with nickel (which has a Young's modulus of 200 GPa), and the outermost layer 2621 prepared by plating the surface of the inner layer 2622 with gold (which has a Young's modulus of 79 GPa).
The outermost layer 2621 composed of gold, which has high electrical conductivity, can establish a satisfactory electrical connection between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B. The deformation of gold to a certain degree during pressure bonding increases the contact area between the protrusions 2006a and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. The inner layer 2622, which has a larger Young's modulus, does not deform as much as the outermost layer 2621. Thus, deformation of the protrusions 2006a formed by the inner layer 2622 is prevented. In this way, the establishment of a satisfactory electrical connection between the electrodes by the protrusions 2006a is compatible with the prevention of deformation of the protrusions 2006a during pressure bonding.
The conductive particles 2006 may have any size. A preferred size is smaller than the sum of the thickness of the connecting electrodes 2015A (2015B) and the thickness of the wiring electrodes 2033A (2033B), specifically within the range of 1 to 5 µm. A particle size within this range establishes a reliable electrical connection between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B.
The size of particles is defined by the average size (diameter) of the particles. The sizes of the particles have a distribution of the number of particles versus the size of the particles in Fig. 20. In the distribution curve, the average size of the particles corresponds to the peak of the number of particles. The size of a particle is determined by measuring the diameter, from a protrusion tip to a protrusion tip, of the particle and captured in an electron microgram.
The protrusions 2006a may have any height within the range of the particle size mentioned above. It is preferred that the protrusions 2006a have a height larger than the thickness of the oxide film, specifically 15 nm or more, in consideration of reduction of the connection resistance by the protrusions 2006a sticking out of the oxide films, which are disposed on the surfaces of the electrodes and have a thickness within the range of about 5 to 10 nm, into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B due to the applied pressure. The appropriate upper limit of the height of the protrusions 2006a is approximately 300 nm.
The protrusions 2006a protruding from the surfaces of the conductive particles 2006 may have any shape. It is preferred that the protrusions 2006a are tapered in consideration of effective penetration to the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B due to the pressure applied during bonding of the head chip 2001 and the wiring substrate 2003.
Any number of protrusions 2006a may be provided. The preferred number is twenty to two hundred protrusions 2006a per particle in consideration of the establishment of a contact state approximating point contact between the protrusions 2006a and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B and effective penetration of the surfaces by the protrusions 2006a due to pressure.
The conductive particles 2006 having such protrusions 2006a may be any commercially available conductive particles.
The preferred content of the conductive particles 2006 in the adhesive 2005 is 0.1% to 5% in a volume mixing ratio of the conductive particles 2006 to the adhesive 2005 in consideration of dispersion.

[Method of Producing Inkjet Head]

An example method of producing the inkjet head 2010 described above will now be described with reference to Figs. 21 to 23.
Fig. 21 is a plan view illustrating the surface of a wiring substrate 2003 before being bonded to a head chip 2001. Strips of the adhesive 2005 containing the conductive particles 2006 are applied to the surface of the wiring substrate 2003, which is provided with the through- holes 2032A and 2032B and the wiring electrodes 2033A and 2033B, over the areas where the connecting electrodes 2015A and 2015B of the head chip 2001 are to overlap with the wiring electrodes 2033A and 2033B. The head chip 2001 is then positioned and bonded to the bonding area 2031 through pressure bonding.
Fig. 22 is a cross-sectional view illustrating the head chip 2001 and the wiring substrate 2003 bonded together through pressure bonding. The head chip 2001 and the wiring substrate 2003 bonded together are disposed between pressure plates 2007a and 2007b to apply a predetermined pressure to the head chip 2001 and the wiring substrate 2003 in the vertical direction. This causes the adhesive 2005 applied in strips to flow between the head chip 2001 and the wiring substrate 2003 due to a capillary force. In Fig. 22, the adhesive 2005 is not shown.
Some of the adhesive 2005 reaching the dummy channels 2012A and 2012B flows along the wiring substrate 2003 and enters the dummy channels 2012A and 2012B. This is because the openings 2012a and 2012b of the dummy channels 2012A and 2012B are covered by the wiring substrate 2003.
The pressure applied to the head chip 2001 and the wiring substrate 2003 causes some of the conductive particles 2006 in the flowing adhesive 2005 to be disposed between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B, as illustrated in Fig. 19. The conductive particles 2006 are compressed by the pressure applied to the head chip 2001 and the wiring substrate 2003 by the pressure plates 2007a and 2007b. This causes the protrusions 2006a at the surfaces of the conductive particles 2006 to stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. This establishes a reliable electrical connection between the connecting electrodes 2015A and 2015B of the head chip 2001 and the respective wiring electrodes 2033A and 2033B of the wiring substrate 2003.
The contact state of the protrusions 2006a of the conductive particles 2006 and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B approximates point contact having small contact areas. A sufficient contact state can be achieved between the conductive particles 2006 and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B, without the application of significantly high pressure during bonding of the head chip 2001 and the wiring substrate 2003, compared to the pressure applied to spherical conductive particles without the protrusions 2006a.
Among the faces of the pressure plates 2007a and 2007b, the face of the pressure plate 2007a adjacent to the front face 2001a of the head chip 2001 is provided with a seal 2008 composed of a sheet of elastic material. The seal 2008 comes into contact with the front face 2001a of the head chip 2001 while pressure is applied. A typical example of the elastic material is rubber, preferably, silicone rubber.
The seal 2008 is provided for the following reason. Typically, the head chip 2001 is prepared through full-cut dicing of ceramics, which is the material of the head chip, with a dicing blade, for example. Thus, the full-cut faces (front face 2001a and rear face 2001b) may have minute asperities due to the dicing. Such asperities prevent the dummy channels 2012A and 2012B from being hermetically sealed with the mere flat pressure plate 2007a. This drawback may be solved by polishing the full-cut faces. Alternatively, as illustrated in the drawing, the seal 2008 disposed between the head chip 2001 and the pressure plate 2007a can provide an effective hermetic seal for the openings in the asperous front face 2001a of the head chip 2001, without polishing.
The openings 2012a and 2012b of the dummy channels 2012A and 2012B adjacent to the wiring substrate 2003 are hermetically sealed by the adhesive 2005 flowing to the periphery of the openings and the wiring substrate 2003. Thus, the seal 2008 is not necessarily required for the pressure plate 2007b adjacent to the wiring substrate 2003. The dummy channels 2012A and 2012B of the head chip 2001 are hermetically sealed between the seal 2008 on the pressure plate 2007a and the wiring substrate 2003 and retain gas (air) inside the channels.
Heating of the head chip 2001 and the wiring substrate 2003 in this state causes expansion of the gas sealed inside the dummy channels 2012A and 2012B.
For a thermosetting adhesive 2005, the heat applied for thermally curing the adhesive 2005 can also contribute to such thermal expansion. If the adhesive 2005 is not a thermosetting adhesive, an appropriate heating device, such as an oven, may be used to heat the head chip 2001 and the wiring substrate 2003 clamped with the pressure plates 2007a and 2007b. With reference to Fig. 23, a case where the adhesive 2005 is a thermosetting adhesive and the heat applied for curing is used for heating the head chip 2001 and the wiring substrate 2003 will now be described. Fig. 23 illustrates the thermally expanded state of the gas inside the dummy channels 2012A and 2012B.
As illustrated in Fig. 23, the expansion of the gas inside the dummy channels 2012A and 2012B due to heating of the head chip 2001 causes the adhesive 2005 inside the dummy channels 2012A and 2012B to intrude between the rear face 2001b of the head chip 2001 and the wiring substrate 2003 from the openings 2012a and 2012b of the dummy channels 2012A and 2012B. Curing of the adhesive 2005 in this state prevents clogging of the adhesive 2005 in the interiors of the dummy channels 2012A and 2012B.
The conductive particles 2006 in the adhesive 2005 that were not caught between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B during thermal expansion flow together with the adhesive 2005 that has an increased fluidity due to a decrease in viscosity caused by the heating. However, the conductive particles 2006 have low fluidity because the protrusions 2006a on the surfaces prevent rotational movement of the conductive particles 2006 and thus prevent agglomeration. The adhesive 2005 cured with little agglomeration of the conductive particles 2006 prevents occurrence of short-circuiting between the electrodes.
In the inkjet head 2010 according to this embodiment, the wiring substrate 2003 is bonded to the rear face 2001b of a head chip 2001, with the wiring substrate 2003 and the rear face 2001b parallel to each other, the rear face 2001b being provided with the openings 2011a, 2011b, 2012a, and 2012b and the connecting electrodes 2015A and 2015B. Such a configuration causes the adhesive 2005 to flow over a large area between the head chip 2001 and the wiring substrate 2003. However, the fluidity of the conductive particles 2006 is reduced by the protrusions 2006a, leading to prevention of agglomeration. So, the present invention has especially highly advantageous effects when applied to such a configuration.
The inkjet head 2010 described above includes a head chip 2001 that is an independently-driven head chip including the driving channels 2011A and 2011B and the dummy channels 2012A and 2012B. The inkjet head 2010 may include any other head chip. Alternatively, all the channels of the head chip 2001 may be ink-ejecting channels that eject ink. The number of channel rows and the number of channels in each row are not limited to those illustrated in the drawings.

[Example 2]

The advantageous effects of the present invention are exemplified through the second example described below.
A shear-mode head chip including drivable walls composed of PZT was produced. The rear face of the head chip was provided with connecting electrodes electrically connected to internal driving electrodes through openings of channels disposed on the rear face, as illustrated in Fig. 15. The surfaces of the connecting electrodes were coated with oxide films having a thickness within the range of 5 to 10 nm. The head chip had the following specification.

Number of channel rows: 2
Number of channels in each row: 512
Dimensions of each channel: depth 360 µm × width 82 µm × length 3.0 mm
Connecting electrodes: composed of aluminum and have a thickness of 3 µm

The wiring substrate was prepared by forming through-holes by blasting on a transparent glass substrate only at positions corresponding to the channels on the head chip and by forming wiring electrodes corresponding to the connecting electrodes of the head chip on a one-to-one basis, as illustrated in Fig. 16. The wiring electrodes were composed of aluminum and had a thickness of 1 µm. The surfaces of the wiring electrodes were coated with oxide films having a thickness within the range of 5 to 10 nm.
The head chip and the wiring substrate were bonded with a thermosetting adhesive (product number 353ND manufactured by Epoxy Technology Inc. (EPO-TEK®) having a final curing temperature of 100°C). Strips of the adhesive were applied to the wiring substrate in the same manner as illustrated in Fig. 21.
An adhesive containing conductive particles without protrusions and an adhesive containing conductive particles having protrusions were used to produce inkjet heads through pressure bonding with an identical pressure. The content of the conductive particles in each adhesive was 1% in a volume mixing ratio of the conductive particles to the adhesive. The size of the conductive particles and the height of the protrusions of the conductive particles are listed in Table 2.

[Evaluation]

Connection resistance: for each prepared inkjet head, the resistance of the conductive particles and the connection resistance between the conductive particles and the electrodes with the wiring resistance eliminated were measured with a digital multimeter and evaluated in accordance with the following ranks. The results are shown in Table 2.

[Evaluation Criteria]

A: less than 1 Ω
B: 1 Ω or more and less than 10 Ω
C: 10 Ω or more

Agglomeration of conductive particles: the dispersed state of the conductive particles in the adhesive before application to the wiring substrate and the dispersed state of the conductive particles in the adhesive after bonding together the head chip and the wiring substrate were observed with a microscope and evaluated in accordance with the following ranks. The results are shown in Table 2.

[Evaluation Criteria]

A: no agglomeration of 10 or more conductive particles was observed
B: agglomeration of 10 or more conductive particles was observed
* The initial rank of the adhesive is rank A.

Table 2

No.	CONDUCTIVE PARTICLES		OXIDE FIRM	CONNECTION RESISTANCE	AGGLOMERATION OF CONDUCTIVE PARTICLES
No.	PARTICLE SIZE	PROTRUSION	OXIDE FIRM	CONNECTION RESISTANCE	AGGLOMERATION OF CONDUCTIVE PARTICLES
1	2 µm	NONE	5∼10nm	C	B
2	2 µm	5∼10nm	5∼10nm	B	A
3	2 µm	30∼50nm	5∼10nm	A	A
4	2 µm	70∼100nm	5∼10nm	A	A
5	2 µm	100∼200nm	5∼10nm	A	A
6	2 µm	200∼300nm	5∼10nm	A	A
7	3 µm	NONE	5∼10nm	C	B
8	3 µm	5∼10nm	5∼10nm	B	A
9	3 µm	30∼50nm	5∼10nm	A	A
10	3 µm	70∼100m	5∼10nm	A	A
11	3 µm	100∼200m	5∼10nm	A	A
12	3 µm	200∼30nm	5∼10nm	A	A

The inkjet heads (Nos. 2 to 6 and 8 to 12) produced with adhesives containing conductive particles having protrusions on the surfaces were superior to the inkjet heads (Nos. 1 and 7) produced with adhesives containing conductive particles without protrusions, in terms of both connection resistance and agglomeration of conductive particles.
According to this embodiment, the inkjet head 2010 includes the head chip 2001 and the wiring substrate 2003. The head chip 2001 includes a plurality of channels 2011A, 2011B, 2012A, and 2012B; a plurality of driving electrodes 2014 disposed in the respective channels 2011A, 2011B, 2012A, and 2012B; and a plurality of connecting electrodes 2015A and 2015B disposed on the surface of the head chip 2001. The connecting electrodes 2015A and 2015B are electrically connected to the respective driving electrodes 2014. The wiring substrate 2003 includes a plurality of wiring electrodes 2033A and 2033B disposed on the surface of the wiring substrate 2003. The wiring electrodes 2033A and 2033B correspond to the respective connecting electrodes 2015A and 2015B. The head chip 2001 and the wiring substrate 2003 are bonded to each other with the adhesive 2005 containing conductive particles 2006 having protrusions 2006a, thereby allowing electrical connections to be established between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B.
A conventional adhesive containing spherical conductive particles applied to the surfaces of wiring electrodes and/or connecting electrodes coated with oxide films requires high pressure to achieve direct contact of the conductive particles disposed between the electrodes and the surfaces of the electrodes. Although long-size harmonica-shaped head chips can be readily fabricated, such chips often have warp and undulation. Thus, even if uniform pressure is applied to establish an electrical connection, unequal pressure may be applied to the electrodes. Such biased pressure is also applied to the conductive particles in the adhesive. This may cause some of the conductive particles disposed between the electrodes to be sufficiently pressed to establish a satisfactory electrical connection, and some other conductive particles disposed between the electrodes to be insufficiently pressed to establish an insufficient electrical connection. Thus, application of high pressure is required during bonding of the head chip and the wiring substrate to establish a satisfactory electrical connection among all electrodes. The application of high pressure during bonding of the head chip and the wiring substrate may damage the head chip and the wiring substrate. In particular, a harmonica-shaped head chip directly receives pressure on the piezoelectric components during bonding. Application of excess pressure lowers the piezoelectric characteristics and may accordingly worsen the ejection characteristics of the inkjet head.
In contrast, with the configuration according to this embodiment, the load applied to the head chip 2001 and the wiring substrate 2003 during pressure bonding is concentrated on small contact areas at the tips of the protrusions 2006a of the conductive particles 2006. This causes the tips of the protrusions 2006a to come into contact with the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B at high pressure. Thus, the conductive particles 2006 stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B to provide sufficient contact areas, and establish a reliable electrical connection between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B. The application of pressure causes the protrusions 2006a of the conductive particles 2006 to stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. This reduces variation in the resistance between the connecting electrodes 2015A and 2015B and the wiring electrodes 2033A and 2033B and establishes a stable electrical connection. The conductive particles 2006 having the protrusions 2006a on their surfaces do not readily move in the adhesive 2005 and are barely agglomerated between the head chip 2001 and the wiring substrate 2003. This effectively prevents short-circuiting between the electrodes due to agglomeration.
The conductive particles 2006 are core-shell particles having organic cores 2061 coated with shells 2062 made of metal films having protrusions 2006a. Due to such configuration, the organic cores 2061 of the conductive particles 2006 disposed between the electrodes deform during pressure bonding of the head chip 2001 and the wiring substrate 2003 to absorb the fluctuation in the pressure distribution and equalize the pressure applied to the conductive particles 2006 and the electrodes 2015A, 2015B, 2033A, and 2033B.
In each conductive particle 2006, the Young's modulus of the shells 2062 is larger than the Young's modulus of the organic core 2061. In this way, the protrusions 2006a do not deform as easily as the organic core 2061 when the conductive particle 2006 are disposed between the electrodes during pressure bonding. The protrusions 2006a of the conductive particles 2006 maintain their shape as they stick into the surfaces of the electrodes and thus establish a stable electrical connection.
The shell 2062 of the conductive particle 2006 includes an outermost layer 2621 composed of gold and an inner layer 2622 composed of a metal having a Young's modulus larger than that of gold. The inner layer 2622 forms the protrusions 2006a. The outermost layer 2621 composed of gold, which has high electrical conductivity, can establish a satisfactory electrical connection between the connecting electrodes 2015A and 2015B and the respective wiring electrodes 2033A and 2033B. The deformation of gold to a certain degree during pressure bonding increases the contact area between the protrusions 2006a and the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B. The inner layer 2622, which has a larger Young's modulus, does not deform as much as the outermost layer 2621. Thus, deformation of the protrusions 2006a formed by the inner layer 2622 is prevented. In this way, the establishment of a satisfactory electrical connection between the electrodes by the protrusions 2006a is compatible with the prevention of deformation of the protrusions 2006a during pressure bonding.
At least one of each connecting electrode 2015A (2015B) and each wiring electrode 2033A (2033B) has an oxide film on the surface thereof. Although electrodes coated with oxide films typically have high connection resistance, the protrusions 2006a of the conductive particles 2006 readily stick out of the oxide films and come into contact with the metal surfaces beneath. The conductive particles 2006 come into direct contact with surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B to establish an electrical connection, without application of significantly high pressure during pressure bonding. This achieves the highly advantageous effects of the present invention.
The height of the protrusions 2006a of the conductive particles 2006 is larger than the thickness of the oxide film. In this way, the application of pressure causes the protrusions 2006a to penetrate the oxide films and stick into the surfaces of the electrodes 2015A, 2015B, 2033A, and 2033B to reduce the connection resistance of the electrical connection between the electrodes.
The adhesive 2005 is a thermosetting adhesive. Heating of the thermosetting adhesive 2005 to a predetermined temperature for curing temporarily lowers the viscosity and increases the fluidity of the adhesive. This causes an increase in the fluidity of the conductive particles in the adhesive, which facilitates agglomeration of the conductive particles. The increase in fluidity of the conductive particles 2006 due to reduced viscosity of the adhesive 2005 during heating can be prevented by the use of the conductive particles 2006 having the protrusions 2006a on their surfaces. This prevents agglomeration of the conductive particles 2006. In this way, short-circuiting that would be caused by agglomeration can be effectively prevented between electrodes.

[Third Embodiment]

An inkjet recording device according to a third embodiment of the present invention will now be described. The third embodiment is the combination of the first and second embodiments. That is, the adhesive 2005 according to the third embodiment differs from the adhesive 2005 according to the second embodiment in that the adhesive contains non-conductive particles in addition to conductive particles 2006 having protrusions 2006a. The difference from the second embodiment will now be described.
Fig. 24 is a cross-sectional view illustrating a head chip and a wiring substrate according to the third embodiment in a bonded state. With reference to Fig. 24, an adhesive 2005 contains conductive particles 2006 and non-conductive particles 2009. The conductive particles 2006 have a size larger than the size of the non-conductive particles 2009. The conductive particles 2006 disposed between connecting electrodes 2015A (2015B) and wiring electrodes 2033A (2033B) establish an electrical connection between the connecting electrodes 2015A (2015B) and the respective wiring electrodes 2033A (2033B).
Fig. 25 is a cross-sectional view of the connecting electrode 2015A (2015B) and the wiring electrode 2033A (2033B) electrically connected via the adhesive 2005 containing a conductive particle 2006 and non-conductive particles 2009. With reference to Fig. 25, the size of the non-conductive particles 2009 is smaller than the height of the protrusions 2006a of the conductive particle 2006. Through such a configuration, the protrusions 2006a of the conductive particles 2006 come into contact with the electrodes even if the non-conductive particles 2009 are disposed between the conductive particles 2006 and the connecting electrodes 2015A (2015B) or between the conductive particles 2006 and the wiring electrodes 2033A (2033B). Thus, connection failure can be prevented between the connecting electrodes 2015A (2015B) and the wiring electrodes 2033A (2033B).
The size of the non-conductive particles 2009 may be larger than or equal to the height of the protrusions 2006a. In such a case, it is preferred that the size of the non-conductive particles 2009 be smaller than or equal to the size of the conductive particles 2006, like the first embodiment.

[Example 3]

The advantageous effects of the present invention are exemplified through the third example described below. The inkjet head in this example is identical to the inkjet head in Example 1 according to the first embodiment, except for the configuration of the adhesive.
The conductive particles in the adhesive were resin particles composed of divinylbenzene plated with Ni-Au and had an average particle size of 3 µm.The mixing ratio of the conductive particles was 1%. The conductive particles included ones without protrusions and ones having protrusions having a height of the protrusions within the range of 70 to 100 nm.
The non-conductive particles in the adhesive were resin particles composed of divinylbenzene. The mixing ratio of the non-conductive particles was 5%. Non-conductive particles having average particle sizes of 40 nm, 100 nm, 500 nm, and 1 µm were used.

Table 3 shows the conditions and evaluation of eight examples.

Table 3

No.	CONDUCTIVE PARTICLES			NON-CONDUCTIVE PARTICLES		DEFECT RATE
No.	PARTICLE SIZE	MIXING RATIO	PROTRUSION	PARTICLE SIZE	MIXING RATIO	DISCONNECTION	SHORT-CIRCUITING
1	3 µ m	1%	NONE	40nm	5%	B	A
2	3 µ m	1%	NONE	100nm	5%	B	A
3	3 µ m	1%	NONE	500nm	5%	A	A
4	3 µ m	1%	NONE		1 µm	5%	A	A
5	3 µ m	1%	70∼00nm	40nm	5%	A	A
6	3 µ m	1%	70∼100nm	100nm	5%	A	A
7	3 µ m	1%	70∼100nm	500nm	5%	A	A
8	3 µ m	1%	70∼100nm	1 µm	5%	A	A

The evaluation criteria for "disconnection" and "short-circuiting" in Table 3 are the same as those in Example 1 according to the first embodiment.
With reference to Table 3, in the case in which conductive particles without protrusions were used (Nos. 1 to 4), an increase in the frequency of disconnections was observed when the size of the non-conductive particles was 100 nm or less (Nos. 1 and 2).
In the case in which conductive particles having protrusions were used (Nos. 5 to 8), no increase in the frequency of disconnections was observed regardless of the size of the non-conductive particles.
The inkjet head according to this embodiment includes an adhesive 2005 containing conductive particles 2006 and non-conductive particles 2009. At least some of the conductive particles 2006 have protrusions 2006a on their surfaces. The conductive particles 2006 having the protrusions 2006a in the adhesive 2005 establish a reliable electrical connection between the connecting electrodes 2015A (2015B) and the wiring electrodes 2033A (2033B), and the non-conductive particles 2009 in the adhesive 2005 prevent short-circuiting between the wiring electrodes 2033A and 2033B. The protrusions 2006a of the conductive particles 2006 decrease the fluidity of the conductive particles 2006 in the adhesive 2005 to prevent agglomeration of the conductive particles 2006. As a result, short-circuiting between the wiring electrodes 2033A and 2033B can be effectively prevented.
The size of the non-conductive particles 2009 may be smaller than the height of the protrusions 2006a. The adhesive 2005 containing such non-conductive particles 2009 having a significantly small particle size exhibits thixotropy. As a result, the viscosity of the non-pressurized adhesive 2005 increases to prevent agglomeration of the conductive particles 2006. This effectively prevents short-circuiting between the wiring electrodes 2033A and 2033B. The significantly small non-conductive particles 2009 can be disposed between the conductive particles 2006 and the connecting electrodes 2015A (2015B) and/or between the conductive particles 2006 and the wiring electrodes 2033A (2033B). The use of the conductive particles 2006 with the protrusions 2006a having the height of the protrusions mentioned above in combination with the non-conductive particles 2009 prevents an increase in the connection resistance between the connecting electrodes 2015A (2015B) and the wiring electrodes 2033A (2033B) because the protrusions 2006a come into contact with the electrodes even if the non-conductive particles 2009 are disposed between the conductive particles 2006 and the electrodes.
The inkjet head and the inkjet recording device according to the embodiments of the present invention described above are mere examples and should not be construed to limit the present invention.
For example, in the embodiments described above, a wiring substrate larger than a head chip is bonded to cover the rear face of the head chip. Alternatively, any other configuration may be applied.
For example, the connecting electrodes may be provided on a side face (a face connecting the front and rear faces) of the head chip, and the wiring substrate may be bonded to the side face of the head chip to establish an electrical connection between the wiring electrodes of the wiring substrate and the connecting electrodes via the adhesive containing conductive particles. In such a case, the wiring electrodes can be led out from the face of the wiring substrate bonded to the side face of the head chip to the opposite face of the wiring substrate through the end face of the wiring substrate to establish an electrical connection between the wiring electrodes and a driver circuit on the opposite face.
Alternatively, a cuboid ink manifold (ink storage section) may be bonded to the rear face of the head chip, the ink manifold having a profile that is the same size as the profile of the rear face of the head chip in a direction orthogonal to the rear face or a profile that overlaps with the rear face. The ink manifold may have a wiring substrate integrated with the face bonded to the head chip (bonding face) and the side face (a face adjacent to the bonding face) such that wiring electrodes are led from the bonding face across the side face of the wiring substrate. Through such a configuration, the connecting electrodes on the rear face of the head chip and the wiring electrodes provided on the wiring substrate on the bonding face of the manifold are electrically connected with an adhesive containing conductive particles. Alternatively, the wiring electrodes may be led from a face of the wiring substrate bonded to the head chip to the opposite face via through-holes.
The present invention can be applied to an inkjet recording device having such a configuration to prevent short-circuiting between the connecting electrodes.
The detailed configuration and detailed operation of the components constituting the inkjet recording device according to the embodiments described above may be modified in various ways without departing from the scope of the invention.

Claims

An inkjet head comprising:
a head chip comprising:
a plurality of channels,

a plurality of driving electrodes disposed in the respective channels, and

a plurality of connecting electrodes disposed on a surface of the head chip, the connecting electrodes being electrically connected to the respective driving electrodes; and

a wiring substrate comprising a plurality of wiring electrodes arranged on a surface of the wiring substrate, the wiring electrodes being electrically connected to the respective connecting electrodes, wherein

the wiring substrate is bonded to a face, on which the connecting electrodes are disposed, of the head chip with an adhesive containing conductive particles, thereby allowing electrical connections to be established between the connecting electrodes and the respective wiring electrodes; and

the adhesive further contains non-conductive particles.
The inkjet head according to claim 1, wherein a size of the conductive particles is larger than or equal to a size of the non-conductive particles.
The inkjet head according to claim 1 or 2, wherein a volume mixing ratio of the non-conductive particles to the adhesive is at least twice a volume mixing ratio of the conductive particles to the adhesive.
The inkjet head according to any one of claims 1 to 3, wherein a Young's modulus of the conductive particles is larger than a Young's modulus of the non-conductive particles.
The inkjet head according to any one of claims 1 to 4, wherein the conductive particles comprise conductive particles having protrusions.
The inkjet head according to claim 5, wherein a size of the non-conductive particles is smaller than a height of the protrusions.
An inkjet head comprising:
a head chip comprising:
a plurality of channels,

a plurality of driving electrodes disposed in the respective channels, and

a plurality of connecting electrodes disposed on a surface of the head chip, the connecting electrodes being electrically connected to the respective driving electrodes; and

a wiring substrate comprising a plurality of wiring electrodes disposed on a surface of the wiring substrate, the wiring electrodes corresponding to the respective connecting electrodes, wherein

the head chip and the wiring substrate are bonded to each other with an adhesive containing conductive particles having protrusions, thereby allowing electrical connections to be established between the connecting electrodes and the respective wiring electrodes.
The inkjet head according to claim 7, wherein the conductive particles comprise core-shell particles, each of the core-shell particles comprising an organic core and a shell that is made of a metal film having the protrusions and that is disposed on a surface of the organic core.
The inkjet head according to claim 8, wherein, in each of the conductive particles, a Young's modulus of the shell is larger than a Young's modulus of the organic core.
The inkjet head according to claim 8 or 9, wherein the shell of each of the conductive particles comprises an outermost layer made of gold and an inner layer made of a metal having a Young's modulus larger than a Young's modulus of gold, and wherein the inner layer forms the protrusions.
The inkjet head according to any one of claims 7 to 10, wherein at least one of each connecting electrode and each wiring electrode has an oxide film on a surface thereof.
The inkjet head according to claim 11, wherein a height of the protrusions of the conductive particles is larger than a thickness of the oxide film.
The inkjet head according to any one of claims 7 to 12, wherein the adhesive is a thermosetting adhesive.
The inkjet head according to any one of claims 1 to 13, wherein openings of the channels and the connecting electrodes are disposed on a same face of the head chip.
The inkjet head according to claim 14, wherein the wiring substrate is disposed parallel to the face, on which the openings and the connecting electrodes are disposed, of the head chip.
The inkjet head according to any one of claims 1 to 15, wherein the connecting electrodes are connected to the respective driving electrodes through the openings of the respective channels.
The inkjet head according to any one of claims 1 to 16, wherein the driving electrodes are disposed on respective drivable walls facing interiors of the respective channels.
The inkjet head according to any one of claims 1 to 17, wherein the wiring electrodes are electrically connected to the respective connecting electrodes, and wherein the wiring electrodes are disposed on a surface of an area of the wiring substrate, the area extending outside of a bonding area where the wiring substrate and the head chip are bonded to each other.
A method of producing the inkjet head according to any one of claims 1 to 18, the method comprising:
bonding the head chip and the wiring substrate to each other with the adhesive; and

electrically connecting the connecting electrodes and the respective wiring electrodes to each other by curing the adhesive.
An inkjet recording device comprising the inkjet head according to any one of claims 1 to 18, wherein
the inkjet recording device applies a voltage to the driving electrodes via the wiring electrodes and the connecting electrodes of the inkjet head and ejects ink in ink-ejecting channels of the channels from nozzles disposed at the ink-ejecting channels, thereby recording an image on a recording medium.