JP2010125765A - Liquid jetting head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid jetting head capable of preventing a short circuit of an electric circuit caused by the migration of a conductive bump. <P>SOLUTION: The inkjet head 10 includes individual electrodes 66, a common electrode 68, a piezoelectric sheet 60, a plurality of individual electrode terminals 70a and 70b electrically communicating with the individual electrodes 66, respectively, and an actuator unit 16 having a common electrode terminal 72 electrically communicating with the common electrode 68. The individual electrode terminals 70a and 70b and the common electrode terminal 72 are arranged on the surface of the actuator unit 16. The conductive bump 74 is formed on the surface of each electrode terminal 70a and 70b. A migration-preventing part 82 composed of a material more hardly causing the migration than the conductive bump 74 and electrically communicating with the conductive bump 74 is arranged between the common electrode terminal, and the conductive bump 74 formed in the individual electrode terminal 70a in the vicinity of the common electrode terminal 72. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid discharge head that applies a discharge pressure to a liquid in a pressure chamber by causing a volume change in a pressure chamber of a flow path unit, thereby discharging the liquid from a nozzle communicating with the pressure chamber. .

  As one of conventional liquid discharge heads, an ink jet head of an ink jet printer is well known, and Patent Document 1 discloses an example of an ink jet head.

  The inkjet head of Patent Document 1 is configured by stacking a flow path unit having a nozzle that discharges ink (liquid) and an actuator unit that applies discharge pressure to the ink (liquid) in the flow path unit. On the surface of the actuator unit, flexible printed circuit boards (hereinafter referred to as “FPC”) for applying a driving voltage to the actuator unit are joined.

The actuator unit is provided corresponding to each of the pressure chambers formed in the flow path unit, and is provided in common with the plurality of individual electrodes to which the drive voltage is individually applied, and the plurality of pressure chambers, and It has a common electrode held at a ground potential, and a piezoelectric sheet sandwiched between the individual electrode and the common electrode. A plurality of electrode terminals that are electrically connected to the individual electrodes and the common electrode are formed on the surface of the actuator unit. The surface of the electrode terminals is made of a metal material containing Ag (silver). Conductive bumps are formed. The corresponding electrode of the FPC is electrically connected to each conductive bump.
JP 2005-305847 A

  According to the above-described conventional technique (Patent Document 1), since the conductive bump is formed using a metal material containing Ag with low contact resistance, the electrical connection between the actuator unit and the FPC can be reliably performed. Connection failure can be prevented.

  However, Ag contained in the conductive bumps is most likely to undergo migration due to a potential difference among metal materials (Ag, Pd, Cu, Sn, Au) used in electric circuits. There was a risk that the electrical circuit would grow and short circuit. For example, in order to maintain the common electrode at the ground potential, a common electrode terminal that is electrically connected to the common electrode is disposed on the surface of the actuator unit, and the common electrode terminal is grounded to the ground potential. In this case, however, the migration of the conductive bumps occurs due to the potential difference generated between the conductive bumps formed on the surface of the individual electrode terminals and the common electrode terminals, and Ag dentlite crystals grow. This may cause a short circuit between the individual electrode terminal and the common electrode terminal.

  In the actuator unit of the inkjet head, in order to achieve “multi-channel” or “miniaturization” of the inkjet printer, it is necessary to arrange a plurality of individual electrodes at a high density, but as the density of the individual electrodes increases, Since the distance between the individual electrode terminal and the common electrode terminal becomes narrow, when migration of conductive bumps occurs, short circuit of the electric circuit due to the dentrite crystal of Ag is likely to occur, and failures frequently occur. . For this reason, conventionally, the distance between the individual electrode terminal and the common electrode terminal must be sufficiently ensured so that the dentite crystal of Ag does not reach, and this is “multi-channel” or “miniaturization”. It was an obstacle.

  SUMMARY An advantage of some aspects of the invention is to provide a liquid discharge head that can prevent a short circuit of an electric circuit due to migration of conductive bumps.

  In order to solve the above-described problems, a liquid discharge head according to the present invention includes a plurality of nozzles that discharge liquid, a flow path unit having a plurality of pressure chambers individually connected to each of the nozzles, and each of the pressure chambers. And a plurality of individual electrodes to which drive voltages are individually applied, a common electrode that is provided in common to each of the pressure chambers and that is held at a constant potential, and the individual electrodes and the common A piezoelectric sheet sandwiched between electrodes, a plurality of individual electrode terminals electrically connected to each of the individual electrodes, and a common electrode terminal electrically connected to the common electrode, and the drive voltage And an actuator unit that applies a discharge pressure to the liquid in the pressure chamber, wherein the individual electrode terminal and the common electrode terminal are the actuators. A conductive bump is formed on the surface of the individual electrode terminal, and the common electrode terminal and the individual electrode terminal disposed in the vicinity thereof are formed on the surface of the individual electrode terminal. Between the conductive bumps, a migration preventing portion made of a material that is less likely to cause migration than the conductive bumps and electrically connected to the conductive bumps is provided.

In this configuration, since the conductive bump and the migration preventing portion are electrically connected, there is no potential difference between them. Therefore, metal ions (for example, Ag ⁺ ) of the conductive bumps are not attracted to the migration preventing unit, and the metal ions can be prevented from getting over the migration preventing unit and reaching the common electrode terminal. Even if the metal ions of the conductive bump can bypass the migration prevention unit, the migration prevention unit can secure a long bypass path for the metal ion, so that the metal ions reach the common electrode terminal. Can be prevented. Furthermore, since it is not necessary to separate the individual electrode terminals on which the conductive bumps are formed from the common electrode terminals more than necessary, a plurality of individual electrode terminals and a plurality of individual electrodes that are electrically connected to them are arranged at high density. can do.

  The individual electrode terminal has a terminal portion main body on which the conductive bump is formed, and the migration prevention portion is disposed around the terminal portion main body as a part of the individual electrode terminal. It may be a configuration.

  In this configuration, since the conductive bump can be surrounded by the migration preventing portion, it is possible to prevent the metal ions of the conductive bump from bypassing the migration preventing portion, and the metal ions reach the common electrode terminal. Can be reliably prevented.

  In the standby state, a potential difference may be generated between the individual electrode and the common electrode, and when the liquid is ejected from the nozzle, the potential difference may be eliminated instantaneously.

  In this configuration, in a standby state in which liquid is not discharged, a potential difference occurs between the conductive bump and the common electrode terminal over a long period of time. However, as described above, the migration prevention unit prevents migration of the conductive bump. Since prevention or progress can be prevented, a short circuit of the electric circuit can be prevented.

  In the standby state, a reference voltage is applied to the common electrode, and a standby voltage having an absolute value larger than the reference voltage is applied to the individual electrodes, thereby reducing the volume of the pressure chamber from a natural state. When the liquid is ejected from the nozzle, the volume of the pressure chamber is instantaneously expanded by applying a driving voltage having an absolute value smaller than the standby voltage to the individual electrode. May be.

  This configuration relates to a mode in which a potential difference is generated between the conductive bump and the common electrode terminal in the standby state.

  In the standby state, a reference voltage is applied to the common electrode, and a standby voltage substantially equal to the reference voltage is applied to the individual electrodes, so that the volume of the pressure chamber is maintained in a natural state. When discharging the liquid from the nozzle, the volume of the pressure chamber is instantaneously reduced by applying a driving voltage having an absolute value larger than the standby voltage to the individual electrode. Also good.

  In this configuration, when a drive voltage is applied to the individual electrodes, a constant potential difference is generated between the individual electrodes and the common electrode. Therefore, the higher the liquid discharge frequency, the longer the potential difference occurs. However, as described above, since the migration prevention unit can prevent or prevent the migration of the conductive bumps, the electrical circuit can be prevented from being short-circuited.

  The conductive bump may be made of a metal material containing Ag.

  In this configuration, since the conductive bump is formed of a metal material containing Ag having a small contact resistance, the electrical connection between the actuator unit and the FPC can be prevented while preventing a short circuit of the electric circuit due to the migration of the conductive bump. It can be done reliably.

The present invention is configured as described above, and the migration prevention unit can prevent or prevent the migration of the migration of the conductive bumps. Therefore, the metal ions (for example, Ag ⁺ ) of the conductive bumps can be prevented. A short circuit of the electric circuit due to reaching the common electrode terminal can be prevented.

  Preferred embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the present invention is applied to an inkjet head of an inkjet printer. However, the present invention is similar to a colored liquid discharge head of a color filter manufacturing apparatus and a conductive liquid discharge head of an electrical wiring apparatus. The present invention can also be applied to other liquid discharge heads.

(First embodiment)
[Overall configuration of inkjet head]
FIG. 1 is an exploded perspective view showing an inkjet head 10 as a “liquid ejection head” according to the first embodiment of the present invention and an FPC 12 joined thereto, and FIG. 2 is a plan view showing the inkjet head 10. FIG. 3 is a partially enlarged cross-sectional view showing the inkjet head 10 and the FPC 12 bonded thereto.

  The ink jet head 10 is mounted on a carriage (not shown) provided in a reciprocating manner in the ink jet printer, and is orthogonal to the paper transport direction (ie, sub-scanning direction) Y (ie, main scanning direction) X. In addition, ink supplied from an ink cartridge (not shown) (four colors of black (BK), magenta (M), yellow (Y), and cyan (C) in this embodiment) is applied from the FPC 12. As shown in FIG. 1 and FIG. 3, a flow path unit 14 and an actuator unit 16 are provided.

[Configuration of channel unit]
As shown in FIG. 3, the flow path unit 14 includes a pressure chamber plate 18, an aperture plate 20, a connection flow path plate 22, a first manifold plate 24, a second manifold plate 26, a damper plate 28, a cover plate 30, and a nozzle plate. 32 eight plates are stacked in this order from the top. These plates 18 to 32 are formed with “recesses” or “through holes” by electrolytic etching, laser processing, or the like, and these “recesses” or “through holes” communicate with each other. As shown in FIG. 2, four ink flow paths N1 to N4 corresponding to four colors of ink of black (BK), magenta (M), yellow (Y), and cyan (C) are configured. .

  Note that “lower” or “lower” used in the description of the present embodiment means a direction of ejecting ink, and “upper” or “upper” means the opposite side (others). The same applies to the embodiment of FIG.

  As shown in FIG. 2, the ink flow paths N <b> 1 to N <b> 4 are built into four rectangular areas S <b> 1 to S <b> 4 arranged side by side from one end side to the other end side in the main scanning direction X in the flow path unit 14. The ink flow path N1 for black (BK) ink that is rarely used and is most frequently used is designed to be larger than the other ink flow paths N2 to N4.

  The ink channel N1 for black (BK) ink has one ink introduction channel 34 (FIG. 2) and a plurality (three in this embodiment) of common ink chambers 36 (three in the present embodiment) communicated with the ink introduction channel 34. 2) and a plurality (68 in this embodiment) of individual ink flow paths 38 (FIG. 3) communicated with each of the common ink chambers 36, and these are arranged from the upstream side of the ink flow. It communicates in order.

  The ink introduction flow path 34 (FIG. 2) is an introduction flow path for introducing ink from an ink cartridge (not shown) into the common ink chamber 36, and at one end of the flow path unit 14 in the sub-scanning direction Y. Through holes (not shown) formed in each of the pressure chamber plate 18, the aperture plate 20, and the connection flow path plate 22 are configured to communicate with each other in the thickness direction of these plates 18 to 22.

  As shown in FIG. 3, the common ink chamber 36 is formed by the through holes 24 a and 26 a formed in the first manifold plate 24 and the second manifold plate 26 in the thickness direction, and thereby. The upper end opening of the space is closed by the connection flow path plate 22, and the lower end opening is closed by the damper plate 28. 2 is designed to be a rectangle that extends long in the sub-scanning direction Y, as shown in FIG. One end portion of the common ink chamber 36 in the sub-scanning direction Y communicates with the ink introduction channel 34 and the other end portion is closed. Further, as shown in FIG. 3, a concave portion 28a is formed on the bottom surface of the damper plate 28 at the bottom of the common ink chamber 36, which is a portion that closes the through hole 26a, so that a plate-like damper 40 that can be elastically deformed. The pressure wave acting on the ink in the common ink chamber 36 is attenuated by elastically deforming the damper 40. As shown in FIG. 1, a plurality of individual ink channels 38 (FIG. 3) are arranged in two rows in a staggered manner on both sides of the common ink chamber 36 in the width direction. Each of 38 communicates with the common ink chamber 36.

  As shown in FIG. 3, each individual ink flow path 38 is a flow path for discharging ink in the common ink chamber 36 from the nozzle 50 to the outside based on the “drive signal”. 44, the pressure chamber 46, the discharge flow path 48, and the nozzle 50 are communicated in this order from the upstream side.

  The connection flow path 42 is configured by a through hole 22a formed in the connection flow path plate 22. The upstream end of the connection flow path 42 is in communication with the common ink chamber 36, and the downstream end is the aperture. 44 is communicated with the upstream end of 44. The aperture 44 is configured such that the lower opening of the recess 20a formed on the lower surface of the aperture plate 20 is covered with the connection flow path plate 22, and the downstream end of the aperture 44 is pressurized via the through hole 20c. It communicates with the upstream end of the chamber 46.

  The pressure chamber 46 is configured by closing the upper end opening of the through hole 18 a formed in the pressure chamber plate 18 with the actuator unit 16 and closing the lower end opening with the aperture plate 20. The upper surface 46 a is constituted by the lower surface of the actuator unit 16. The plan view shape of the pressure chamber 46 (that is, the plan view shape of the through-hole 18a) is designed to be a substantially rectangular shape extending long in the main scanning direction X. In the ink flow path N1, a plurality of individual ink flow paths 38 are formed. Are arranged side by side in a staggered manner in the sub-scanning direction Y.

  The discharge flow path 48 is a through hole 20b, 22b, 24b, 26b formed in each of the aperture plate 20, the connection flow path plate 22, the first manifold plate 24, the second manifold plate 26, the damper plate 28, and the cover plate 30. , 28b, 30a, and the upstream end of the discharge channel 48 communicates with the downstream end of the pressure chamber 46.

  The nozzle 50 has a tapered shape with an inner diameter reduced toward the downstream end (that is, the discharge port) by a tapered through-hole 32 a formed in the nozzle plate 32. The side end portion communicates with the downstream end portion of the discharge channel 48. In the ink flow path N1, a plurality of nozzles 50 constituting each of the plurality of individual ink flow paths 38 are arranged side by side in a staggered manner in the sub-scanning direction Y corresponding to the pressure chambers 46. Yes.

  Therefore, in the ink flow path N1, black (BK) ink is introduced from one ink introduction flow path 34 to each of the three common ink chambers 36 (FIG. 2), and the ink is staggered from each common ink chamber 36. Are provided to a plurality of pressure chambers 46 arranged side by side in a row, and discharged from the plurality of nozzles 50 communicated with each of the pressure chambers 46 to the outside.

  On the other hand, the ink flow paths N2 to N4 through which inks other than black (BK) ink flow are one ink introduction flow path 52 (FIGS. 1 and 2) and a plurality (this embodiment) communicated with the ink introduction flow path 52. In FIG. 2, two common ink chambers 54 (FIG. 2) and a plurality (68 in this embodiment) of individual ink channels 56 (FIG. 1) communicated with each of the common ink chambers 54 are provided.

  The ink introduction channel 52 (FIGS. 1 and 2) is similar to the ink introduction channel 34 except that the volume is smaller than the ink introduction channel 34 (FIGS. 1 and 2) of the ink channel N1. The common ink chamber 54 (FIG. 2) and the individual ink channel 56 (FIG. 1) are configured in comparison with the common ink chamber 36 (FIG. 2) and the individual ink channel 38 (FIG. 1) of the ink channel N1. Except that the total number is small. As a result, the uniformity of the “ink ejection performance” is maintained in all of the ink flow paths N1 to N4, and the “balance of ink ejection amounts” is achieved. That is, since the “ink ejection performance” required for the ink flow paths N2 to N4 is in common with the “ink ejection performance” required for the ink flow path N1, the ink introduction flow path 52 (FIGS. 1 and 2). ), The common ink chamber 54 (FIG. 2) and the individual ink flow path 56 (FIG. 1) are composed of the ink introduction flow path 34 (FIGS. 1 and 2), the common ink chamber 36 (FIG. 2) and the individual ink flow path. It is designed to be the same as the configuration of FIG. 38 (FIG. 1). Further, since the “usage frequency” of the ink flowing through the ink flow paths N2 to N4 is less than the “usage frequency” of the black (BK) ink flowing through the ink flow path N1, the common ink chamber 54 (FIG. 2) and individual The total number of ink channels 56 (FIG. 1) is designed to be smaller than the total number of common ink chambers 36 (FIG. 2) and individual ink channels 38 (FIG. 1).

  As shown in FIGS. 1 and 2, a filter 58 that traps foreign matter mixed in the ink is used in an area where the ink introduction channels 34 and 52 are formed on the upper surface of the channel unit 14. The actuator unit 16 is joined to other regions using an adhesive or the like.

[Configuration of actuator unit]
As shown in FIG. 3, the actuator unit 16 constitutes an inner upper surface 46 a of the pressure chamber 46 in the flow path unit 14, and selectively applies ejection pressure to the ink in the plurality of pressure chambers 46. The first piezoelectric sheet 60, the second piezoelectric sheet 62, and the third piezoelectric sheet 64 are stacked in this order from the top.

  Each of the piezoelectric sheets 60, 62 and 64 is a sheet member made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity and having a thickness of about 15 to 30 μm. A plurality of individual electrodes 66 individually corresponding to each of the plurality of pressure chambers 46 are formed on the upper surface of the first piezoelectric sheet 60 to be opposed to the pressure chambers 46, and the second piezoelectric layer serving as an intermediate layer is formed. A common electrode 68 corresponding to each of the pressure chambers 46 is formed on the upper surface of the sheet 62 so as to straddle each of the pressure chambers 46. Therefore, in the actuator unit 16, the first piezoelectric sheet 60 is an “active layer”, and the second piezoelectric sheet 62 and the third piezoelectric sheet 64 are “inactive layers”. A portion sandwiched between the individual electrode 66 and the common electrode 68 is an “active portion 60a”.

  Further, as shown in FIG. 4, a plurality of individual electrode terminals 70 a and 70 b that are electrically connected to the individual electrodes 66 are formed on the upper surface of the first piezoelectric sheet 60 that is the uppermost layer, A common electrode terminal 72 is formed, one conductive bump 74 is formed on the surface of the individual electrode terminals 70a and 70b, and a plurality (in this embodiment, five) are formed on the surface of the common electrode terminal 72. ) Conductive bumps 76 are formed. As shown in FIG. 3, the first piezoelectric sheet 60 is formed with a through hole 60b penetrating in the thickness direction, and a conductive connecting material 78 is disposed inside the through hole 60b. The common electrode 68 and the common electrode terminal 72 are electrically connected through the connecting material 78.

  In addition, although it does not specifically limit as a method of manufacturing the laminated body of piezoelectric sheet 60,62,64, In this embodiment, each of the individual electrode 66, individual electrode terminal 70a, 70b, and the common electrode terminal 72 is each. A first green sheet having a conductive pattern constituting the upper surface formed thereon, a second green sheet having the conductive pattern constituting the common electrode 68 formed on the upper surface, and a third green sheet having no conductive pattern; The “green sheet method” is used in which the two are fired. Further, as a method of forming the “conductive pattern” of the individual electrode 66, the individual electrode terminals 70a and 70b, the common electrode 68, and the common electrode terminal 72, a conductive paste made of a metal material containing Ag—Pd or the like is used as a green sheet. A “screen printing method” is used in which screen printing is performed on the upper surface.

  Hereinafter, the common electrode terminal 72, the individual electrode 66, and the individual electrode terminals 70a and 70b will be described in more detail.

  As shown in FIG. 2, the common electrode terminal 72 is a band-like shape formed to extend in the sub-scanning direction Y at both ends in the main scanning direction X on the upper surface of the first piezoelectric sheet 60 (that is, the surface of the actuator unit 16). In this embodiment, three common electrode terminals 72 made of a metal material including Ag—Pd and the like are arranged side by side in the sub-scanning direction Y at intervals. A substantially hemispherical conductive bump 76 made of a metal material containing Ag is formed on the surface of the common electrode terminal 72.

  The number of common electrode terminals 72 is not particularly limited. For example, one common electrode terminal 72 may be disposed at both ends in the main scanning direction X on the upper surface of the first piezoelectric sheet 60. In addition, one or a plurality of common electrode terminals 72 may be provided only at one end in the main scanning direction X. Further, the number of conductive bumps 76 formed on the surface of the common electrode terminal 72 may be appropriately increased or decreased.

  As shown in FIG. 4, the individual electrodes 66 are island-shaped conductive layers formed on the upper surface of the first piezoelectric sheet 60. In the present embodiment, the number of the individual electrodes 66 is the same as the number of the individual ink flow paths 38 (FIG. 1). The individual electrodes 66 are formed in a zigzag pattern in two rows on both sides in the width direction of the common ink chambers 36 (FIG. 4) and 54 (FIG. 2) using a metal material containing Ag—Pd or the like. The planar view shape of the individual electrode 66 is designed to be substantially the same shape as the planar view shape of the pressure chamber 46 (substantially rectangular in this embodiment), and the area when the individual electrode 66 is viewed in plan (hereinafter referred to as “plane”). The viewing area ") is designed to be approximately the same size as the planar viewing area of the pressure chamber 46.

  The individual electrode terminals 70a and 70b are made of a material that is difficult to cause migration (a metal material including Ag-Pd or the like), and is formed on the upper surface of the first piezoelectric sheet 60 so as to extend from each of the individual electrodes 66. The conductive layer is disposed at a position deviated laterally from the region where the pressure chamber 46 is disposed so as not to hinder the volume change of the pressure chamber. A substantially hemispherical conductive bump 74 made of a metal material containing Ag is formed on the surfaces of the individual electrode terminals 70a and 70b.

  The planar shape and planar area of the individual electrode terminals 70a and 70b depend on the position of the individual electrode terminals 70a and 70b on the upper surface of the first piezoelectric sheet 60 (that is, the surface of the actuator unit 16), as shown in FIG. Are designed in two ways.

  That is, the planar view shape of the individual electrode terminal 70 a disposed in the vicinity of the common electrode terminal 72 is designed in a substantially sector shape, and the narrow portion of the substantially sector shape is connected to the individual electrode 66. The area of the individual electrode terminal 70a in plan view is designed to be larger than the bottom area of the conductive bump 74 formed on the surface thereof, and the conductive bump 74 is formed at the center of the surface of the individual electrode terminal 70a. Has been. Accordingly, in the individual electrode terminal 70 a, the circular portion where the conductive bump 74 is formed is the terminal portion main body 80, and the annular portion around the terminal portion main body 80 is more migrated than the conductive bump 74. The migration prevention portion 82 is made of a difficult material (a metal material including Ag—Pd or the like) and is electrically connected to the conductive bump 74. That is, the migration preventing unit 82 is disposed around the terminal unit main body 80 as a part of the individual electrode terminal 70a.

  Therefore, as compared with the case where the migration prevention unit 82 is not present, the distance between the individual electrode terminal 70a and the common electrode terminal 72 can be shortened, and the actuator unit 16 can be reduced in size. 10 can be reduced in size.

  The shape of the individual electrode terminal 70a in plan view is not particularly limited as long as the annular migration preventing portion 82 can be secured, and may be a circle, a square, a hexagon, or the like. Further, the material of the migration preventing portion 82 is not particularly limited as long as migration is less likely to occur than the conductive bump 74. For example, when the conductive bump 74 is formed of a metal material containing Ag. Alternatively, the migration prevention unit 82 may be formed of a metal material including Au, Ag—Cu, or the like. The material of the conductive bump 74 is not limited to “a metal material containing Ag”, but may be “a material containing Ag and a resin”.

  On the other hand, the planar view shape of the individual electrode terminal 70b disposed away from the common electrode terminal 72 is designed to be a substantially rectangular shape having one end in the longitudinal direction rounded in an arc shape, and the length of the individual electrode terminal 70b is long. The other end in the direction is connected to the individual electrode 66. The width of the individual electrode terminal 70b is designed to be smaller than the width or diameter of the bottom surface of the conductive bump 74, and a part of the conductive bump 74 formed on the surface of the individual electrode terminal 70b is separated from the individual electrode terminal 70b. It protrudes and is in contact with the upper surface of the first piezoelectric sheet 60.

Therefore, the individual electrode terminal 70b does not hinder the individual electrode 66 from being arranged at a high density, and can be downsized by the high density arrangement. In addition, since the individual electrode terminal 70b is necessary and sufficiently separated from the common electrode terminal 72, even if migration occurs in the conductive bump 74 formed on the surface of the individual electrode terminal 70b, the individual electrode terminal 70b is electrically conductive. The Ag ⁺ ions of the conductive bump 74 do not reach the common electrode terminal 72, and the electric circuit is not short-circuited.

  In the present embodiment, the individual electrode terminal 70a having the migration preventing portion 82 is disposed only in the vicinity of the common electrode terminal 72. However, by arranging the individual electrode terminal 70a in other regions, The migration of the conductive bumps 74 between the two individual electrodes 66 in which the potential difference occurs may be prevented.

[Configuration of FPC]
As shown in FIG. 3, the FPC 12 is composed of a base material 86 made of a flexible synthetic resin material (polyimide resin, polyester resin, polyamide resin, etc.), a conductive metal material (copper foil, etc.), and A plurality of wirings (not shown) formed on the bottom surface of the base material 86, a plurality of terminals 88 provided at respective ends of the plurality of wirings, and a bottom surface of the base material 86 so as to cover the plurality of wirings A driving device 92 (FIG. 1) that is electrically connected to each of the wirings is mounted at a predetermined position on the upper surface of the base material 86.

  When connecting the FPC 12 to the actuator unit 16, first, uncured insulating synthetic resin (solder resist or the like) is applied to the lower surface of the base member 86 so as to cover the wiring (not shown). Subsequently, each of the plurality of terminals 88 in the FPC 12 is pressed against the conductive bumps 74 formed on the individual electrode terminals 70 a and 70 b of the actuator unit 16 and the conductive bumps 76 formed on the common electrode terminal 72. Then, the conductive bumps 74 and 76 penetrate the uncured synthetic resin and come into contact with the terminal 88, and the conductive bumps 74 and 76 and the uncured synthetic resin are brought into contact with each other over a wide area. Therefore, in the next step, the uncured synthetic resin is heated and cured to change it to the insulating layer 90 to ensure the bonding between the conductive bumps 74 and 76 and the insulating layer 90, and the conductive bump 74. 76 and the terminal 88 are electrically and mechanically connected. Accordingly, each of the individual electrode terminals 70a and 70b is electrically connected to a corresponding output terminal (not shown) of the driving device 92, and each of the common electrode terminals 72 is a ground terminal (not shown) of the driving device 92. Is electrically connected.

[Operation of inkjet head]
When the ink jet head 10 is used, the ink jet head 10 is mounted on a carriage (not shown) of the ink jet printer, and the ink introduction channels 34 and 52 (FIGS. 1 and 2) of the ink jet head 10 and the printer main body. A built-in ink tank (not shown) is connected via an ink tube. The input side end of the FPC 12 is connected to a control board (not shown) incorporated in the printer body.

  In a state where the power of the ink jet printer is turned on and the ink jet head 10 is in a standby state (hereinafter referred to as “standby state”), the control board (not shown) waits for the driving device 92 (FIG. 1) of the FPC 12. As shown in FIG. 5, a constant “reference voltage (ground potential 0 V in this embodiment)” corresponding to the standby signal is applied from the driving device 92 to the common electrode 68 as shown in FIG. Thus, a fixed “standby voltage (28 V in this embodiment)” having an absolute value larger than the “reference voltage” is applied to the individual electrode 66. Then, the active portion 60a (FIG. 3) of the first piezoelectric sheet 60 is contracted in a direction orthogonal to the thickness direction (that is, the polarization direction), and the entire piezoelectric sheets 60, 62, and 64 protrude downward. It is transformed to become. At this time, since the lower surface of the third piezoelectric sheet 64 which is the lowermost layer constitutes the inner upper surface 46a of the pressure chamber 46, the lower surface is deformed so as to protrude to the inside of the pressure chamber 46. Is reduced more than the natural state.

  When ink (liquid) is ejected from the nozzles 50, an ejection request signal is given from the control board (not shown) to the driving device 92 of the FPC 12, and as shown in FIG. A constant “drive voltage (0 V in this embodiment)” having an absolute value smaller than the “standby voltage” is instantaneously applied. At this time, the common electrode 68 is held at a constant “reference voltage”. Accordingly, at the moment when the “driving voltage” is applied, the potential difference between the individual electrode 66 and the common electrode 68 is eliminated, and the volume of the pressure chamber 46 is expanded to a natural state by restoring the active portion 60a. Ink in the common ink chamber 36 is sucked into the pressure chamber 46. Then, after the moment when the potential difference is eliminated, the “standby voltage” is applied to the individual electrode 66 again, the active portion 60a is contracted again, and the volume of the pressure chamber 46 is reduced from the natural state. Therefore, a discharge pressure is applied to the ink in the pressure chamber 46 at a timing according to the discharge request signal, and the ink is discharged from the nozzle 50 by the discharge pressure.

  In this embodiment, since the individual electrode 66 and the individual electrode terminals 70a and 70b are electrically connected and the common electrode 68 and the common electrode terminal 72 are electrically connected, printing is performed. In a non-standby state, a potential difference (28 V in this embodiment) corresponding to the “standby voltage” is also generated between the individual electrode terminals 70 a and 70 b and the common electrode terminal 72. However, in this embodiment, as described above, since the individual electrode terminal 70a on which the conductive bump 74 is formed has the migration preventing portion 82 (FIG. 4), migration of the conductive bump 74 occurs. The electrical circuit is not short-circuited by the migration.

That is, since the migration prevention unit 82 and the conductive bump 74 are electrically connected to each other, there is no potential difference between them, and Ag ⁺ ions of the conductive bump 74 move to the migration prevention unit 82 side. There is nothing. Therefore, as a matter of course, the Ag ⁺ ions do not reach the common electrode terminal 72 over the migration preventing unit 82. Moreover, since the migration prevention unit 82 is formed of a material (a metal material containing Ag—Pd, Au, Ag—Cu, or the like) that is less likely to cause migration than the conductive bump 74, the migration prevention unit 82 is electrically There is no short circuit.

  In the operation mode shown in FIG. 5, the “standby voltage” is 28 V and the “drive voltage” is 0 V. However, the “drive voltage” may be a voltage having an absolute value smaller than the “standby voltage”. These voltage values may be appropriately changed as long as the conditions are satisfied.

[Other operations of inkjet head]
Note that the operation mode of the inkjet head 10 can be appropriately changed according to a signal given from the control board (not shown) to the driving device 92, and the operation mode shown in FIG. 6 is changed to the operation mode shown in FIG. May be adopted.

  In the operation mode shown in FIG. 6, in the standby state, a standby signal is given from the control board (not shown) to the driving device 92 (FIG. 1) of the FPC 12, and the driving device 92 supplies the standby signal to the common electrode 68. A constant “reference voltage (ground potential of 0 V in this embodiment)” corresponding to the signal is applied, and a “standby voltage” (this embodiment) having almost the same magnitude as the “reference voltage” is applied from the driving device 92 to the individual electrode 66. In this case, 0V) "is applied. Accordingly, the potential difference between the individual electrode 66 and the common electrode 68 is substantially “0 (zero)”, and the volume of the pressure chamber 46 is not reduced and remains in a natural state. When ink (liquid) is ejected from the nozzles 50, an ejection request signal is given from the control board (not shown) to the drive device 92 of the FPC 12, and the individual electrodes 66 are shown in FIG. As described above, a “drive voltage (28 V in this embodiment)” having an absolute value larger than the “standby voltage” is instantaneously applied. Then, a constant potential difference (28 V in this embodiment) is instantaneously generated between the individual electrode 66 and the common electrode 68 so that the entire piezoelectric sheets 60, 62, and 64 are convex downward. Transformed. At this time, since the lower surface of the third piezoelectric sheet 64 which is the lowest layer constitutes the inner upper surface 46a of the pressure chamber 46, the lower surface is deformed so as to protrude inside the pressure chamber 46, and the volume of the pressure chamber 46 is increased. Is reduced. Thereby, a discharge pressure is applied to the ink in the pressure chamber 46 at a predetermined timing according to the discharge request signal, and the ink is discharged from the nozzle 50 by the discharge pressure.

  In this operation mode (FIG. 6), when a “drive voltage” is applied to the individual electrode 66, a constant potential difference (28 V in the present embodiment) is generated between the individual electrode 66 and the common electrode 68. As the use frequency of ink increases, the potential difference is generated over a longer time, and the migration prevention unit 82 functions more effectively. In the operation mode shown in FIG. 6, the “standby voltage” is set to 0 V and the “drive voltage” is set to 28 V. However, the “drive voltage” may be a voltage having an absolute value larger than the “standby voltage”. These voltage values may be appropriately changed as long as the conditions are satisfied.

(Second Embodiment)
FIG. 7 is a partially enlarged plan view showing the main part of the inkjet head 100 according to the second embodiment of the present invention. The inkjet head 100 according to the second embodiment is obtained by changing the individual electrode terminal 70a having the migration preventing unit 82 in the inkjet head 10 according to the first embodiment to another individual electrode terminal 102a.

  The individual electrode terminal 102a is an island-shaped conductive layer formed on the upper surface of the first piezoelectric sheet 60 with a metal material including Ag—Pd, Au, Ag—Cu, or the like. The planar view shape of the individual electrode terminal 102a is designed to be substantially T-shaped, and the vertical bar portion 104a constituting the substantially T-shape is connected to the individual electrode 66, and the horizontal bar portion constituting the substantially T-shape. 104 b is disposed substantially parallel to the common electrode terminal 72 between the vertical bar portion 104 a and the common electrode terminal 72. A substantially hemispherical conductive bump 106 made of a metal material containing Ag and electrically connected to the horizontal bar portion 104b is formed on the surface of the vertical bar portion 104a. As shown in FIG. 7, the width of the vertical bar portion 104 a is designed to be smaller than the width or diameter of the bottom surface of the conductive bump 106, and a part of the conductive bump 106 contacts the upper surface of the first piezoelectric sheet 60. is doing.

  In the second embodiment, since a part of the conductive bump 106 is in contact with the upper surface of the first piezoelectric sheet 60, migration of the conductive bump 106 may occur. 72 can function as a “migration prevention unit”, so that the migration can be prevented from progressing.

That is, since the conductive bump 106 and the horizontal bar portion (migration preventing portion) 104b are electrically connected to each other, there is no potential difference between them, and Ag ⁺ ions of the conductive bump 106 are generated by the horizontal bar portion. (Migration prevention unit) 104b is not attracted. Therefore, the cross-bar (migration-preventing portion) 104b, can function as a wall to prevent the progression of Ag ⁺ ions, it is possible to ensure a long detour path of Ag ⁺ ions. Thereby, a short circuit of the electric circuit due to the Ag ⁺ ions reaching the common electrode terminal 72 can be prevented.

(Third embodiment)
FIG. 8 is a partially enlarged cross-sectional view showing the inkjet head 110 and the FPC 12 bonded thereto according to the third embodiment of the present invention, and FIG. 9 is a partially enlarged plan view showing the inkjet head 110. An inkjet head 110 according to the third embodiment is obtained by changing the actuator unit 16 in the inkjet head 10 according to the first embodiment to another actuator unit 112.

  As shown in FIG. 8, the actuator unit 112 includes an insulating top sheet 114, first piezoelectric sheet 116, second piezoelectric sheet 118, third piezoelectric sheet 120, fourth piezoelectric sheet 122, fifth piezoelectric sheet 124, and The sixth piezoelectric sheet 126 is configured to be laminated in this order from the upper side, and the individual surface electrode 128, the individual electrode terminals 130a and 130b (FIG. 9), and the common electrode terminal 132 are formed on the upper surface of the top sheet 114. ing. A plurality of individual electrodes 134 individually corresponding to the pressure chambers 46 are formed on the upper surfaces of the third piezoelectric sheet 120 and the fifth piezoelectric sheet 124 at positions facing the pressure chambers 46, respectively. The individual electrodes 134 and the individual electrode terminals 130 a and 130 b are electrically connected via a conductive connecting member 138 disposed in the through hole 136. A common electrode 140 corresponding to each of the pressure chambers 46 is formed across the pressure chambers 46 on the upper surfaces of the second piezoelectric sheet 118, the fourth piezoelectric sheet 122, and the sixth piezoelectric sheet 126. The common electrode 140 and the common electrode terminal 132 are electrically connected to each other through a conductive connecting member 144 disposed inside the through hole 142.

  In this inkjet head 110, as shown in FIG. 9, the individual surface electrode 128 having substantially the same configuration as the individual electrode 66 of the first embodiment and the individual electrode having substantially the same configuration as the individual electrode terminals 70a and 70b of the first embodiment. The terminals 130a and 130b and the common electrode terminal 132 having substantially the same configuration as the common electrode terminal 72 of the first embodiment are formed on the surface of the actuator unit 112, and the individual electrode 134 that directly contributes to the ink ejection operation is as follows. As shown in FIG. 8, the actuator unit 112 is disposed inside. Therefore, the individual surface electrode 128 is different from the individual electrode 66 that directly contributes in that it does not directly contribute to the ink ejection operation. However, the configuration when the actuator unit 112 is viewed in plan is the same as that when the actuator unit 16 is viewed in plan. It is almost the same as the configuration.

  That is, the planar view shape of the individual electrode terminal 130 a disposed in the vicinity of the common electrode terminal 132 is designed in a substantially sector shape, and the narrow portion of the substantially sector shape is connected to the individual surface electrode 128. In addition, the area of the individual electrode terminal 130a in plan view is designed to be larger than the bottom area of the conductive bump 146 formed on the surface thereof, and the conductive bump 146 is formed at the center of the surface of the individual electrode terminal 130a. Yes. Therefore, in the individual electrode terminal 130 a, the circular portion where the conductive bump 146 is formed is the terminal portion main body 148, and the annular portion around the terminal portion main body 148 is less likely to migrate than the conductive bump 146. The migration preventing unit 150 is made of a material (a metal material including Ag—Pd or the like) and is electrically connected to the conductive bump 146.

  Therefore, also in the third embodiment, the migration of the conductive bump 146 can be prevented by the migration preventing unit 150, and a short circuit of the electric circuit can be prevented.

  In the third embodiment, various “configuration changes” and “operation mode changes (FIG. 6)” described in the description of the first embodiment are possible, and the individual electrode terminals 130a (FIG. 9) are also possible. It is also possible to use the individual electrode terminal 102a (FIG. 7) in the second embodiment instead of the above.

It is a disassembled perspective view which shows the inkjet head which concerns on 1st Embodiment, and FPC joined to this. It is a top view which shows the inkjet head which concerns on 1st Embodiment. It is a partial expanded sectional view which shows the inkjet head which concerns on 1st Embodiment, and FPC joined to this. It is a partial enlarged plan view showing an ink jet head concerning a 1st embodiment. It is a graph which shows operation | movement of the inkjet head which concerns on 1st Embodiment. It is a graph which shows other operation | movement of the inkjet head which concerns on 1st Embodiment. It is a partial enlarged plan view showing an ink jet head concerning a 2nd embodiment. It is a partial expanded sectional view which shows the inkjet head which concerns on 3rd Embodiment, and FPC joined to this. It is a partial enlarged plan view showing an ink jet head concerning a 3rd embodiment.

Explanation of symbols

10 ... Inkjet head 12 ... FPC
14 ... Flow path unit 16 ... Actuator unit 46 ... Pressure chamber 60a ... Active part 60, 62, 64 ... Piezoelectric sheet 66 ... Individual electrode 68 ... Common electrode 70a, 70b ... Individual electrode terminal 72 ... Common electrode terminal 74, 76 ... Conductivity Bump 80 ... Terminal part body 82 ... Migration prevention part 92 ... Drive device 100 ... Inkjet head 102a ... Individual electrode terminal 104a ... Vertical bar part 104b ... Horizontal bar part (migration prevention part)
106 ... conductive bump 110 ... inkjet head 112 ... actuator unit 114 ... top sheet 128 ... individual surface electrode 130a, 130b ... individual electrode terminal 132 ... common electrode terminal 134 ... individual electrode 140 ... common electrode 146 ... conductive bump 148 ... terminal Main body 150 ... Migration prevention unit

Claims (6)

A flow path unit having a plurality of nozzles for discharging liquid and a plurality of pressure chambers individually connected to the nozzles;
A plurality of individual electrodes provided corresponding to each of the pressure chambers and individually applied with a driving voltage; a common electrode provided in common to each of the pressure chambers and held at a constant potential; A piezoelectric sheet sandwiched between the individual electrode and the common electrode, a plurality of individual electrode terminals electrically connected to each of the individual electrodes, and a common electrode terminal electrically connected to the common electrode. And an actuator unit that applies a discharge pressure to the liquid in the pressure chamber based on the drive voltage,
The individual electrode terminal and the common electrode terminal are disposed on the surface of the actuator unit, and conductive bumps are formed on the surface of the individual electrode terminal,
Between the common electrode terminal and the conductive bump formed on the individual electrode terminal disposed in the vicinity thereof, the conductive bump is made of a material that is less likely to cause migration than the conductive bump. A liquid discharge head in which a migration preventing portion that is electrically connected to the liquid discharge head is disposed. The individual electrode terminal has a terminal portion main body on which the conductive bump is formed,
The liquid ejection head according to claim 1, wherein the migration prevention unit is disposed around the terminal unit main body as a part of the individual electrode terminal. In the standby state, there is a potential difference between the individual electrode and the common electrode,
The liquid discharge head according to claim 1, wherein the potential difference is eliminated instantaneously when discharging the liquid from the nozzle. In the standby state, a reference voltage is applied to the common electrode, and a standby voltage having an absolute value larger than the reference voltage is applied to the individual electrodes, thereby reducing the volume of the pressure chamber from a natural state. And
The volume of the pressure chamber is instantaneously expanded by applying a driving voltage having an absolute value smaller than the standby voltage to the individual electrode when liquid is ejected from the nozzle. The liquid discharge head described. In the standby state, a reference voltage is applied to the common electrode, and a standby voltage substantially equal to the reference voltage is applied to the individual electrodes, so that the volume of the pressure chamber is maintained in a natural state. ,
The volume of the pressure chamber is instantaneously reduced by applying a driving voltage having an absolute value larger than the standby voltage to the individual electrode when discharging the liquid from the nozzle. The liquid discharge head according to 2.   The liquid discharge head according to claim 1, wherein the conductive bump is formed of a metal material containing Ag.

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