Patent Publication Number: US-2012026248-A1

Title: Inkjet head assembly and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2010-0074146 filed on Jul. 30, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inkjet head assembly, and more particularly, an inkjet head assembly in which a connection structure of a flexible printed circuit board (FPCB) applying voltage to a piezoelectric actuator for driving an inkjet head is improved to reduce a width of the inkjet head such that the productivity of the inkjet head is improved, and a method for manufacturing the same. 
     2. Description of the Related Art 
     Generally, an inkjet head converts an electrical signal into physical power to discharge ink in droplet form through a small nozzle. The inkjet head may be divided into two main types according to an ink discharging method. One type is a thermal inkjet head generating bubbles in ink using a heat source to discharge the ink by the expansive force of the bubbles, and the other type is a piezoelectric inkjet head using a piezoelectric element to discharge ink by pressure applied to the ink due to the deformation of the piezoelectric element. 
     In order to drive the piezoelectric inkjet head, an electrical signal should be applied to an actuator thereof. Generally, voltage is applied to the actuator by connecting a flexible printed circuit board (FPCB) to the actuator and connecting the FPCB to an inkjet head driving driver. 
     Generally, since an ink tank for supplying the ink to the inkjet head is disposed at an outer side of the actuator, when the FPCB is connected to the actuator, a space for bending the FPCB from a connection portion between the FPCB and the actuator to an upper portion of the ink tank is required. As a result, a width of the inkjet head is increased, and the number of the inkjet heads capable of being manufactured on a single wafer in the case of an inkjet head manufactured at a wafer level is reduced, which causes a deterioration in productivity such as a decrease in processing yield, an increase in a manufacturing costs, and the like. 
     In addition, physical stress applied to the FPCB is increased due to warp deformation of the FPCB, and connection defects such as electrical short-circuits at a bonding portion between the FPCB and the actuator due to elasticity of the FPCB, or the like, are generated. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides an inkjet head assembly in a connection structure between an inkjet head and a FPCB is improved to reduce the entire width of the inkjet head and increase the number of inkjet heads capable of being manufactured on a single wafer such that productivity is improved, for example, an increase in processing yield, a decrease in manufacturing costs, and the like, and a method for manufacturing the same. 
     Another aspect of the present invention also provides an inkjet head assembly, capable of reducing physical stress applied to a FPCB and improving bonding characteristics of the FPCB when the FPCB is connected to an inkjet head, and a method for manufacturing the same. 
     According to an aspect of the present invention, there is provided an inkjet head assembly, including: an inkjet head plate having an ink flow passage formed therein and having an actuator formed thereon, the actuator providing driving force for discharging ink; a flexible printed circuit board (FPCB) applying voltage to the actuator; and an intermediate substrate provided so as to electrically connect the actuator to the flexible printed circuit board and having a second bonding portion bonded to the flexible printed circuit board formed inwardly of a first bonding portion, bonded to the actuator, in a width direction of the inkjet head plate. 
     A conductor pattern connecting the first bonding portion to the second bonding portion may be formed in the intermediate substrate. 
     Each of a first terminal electrode and a second terminal electrode may be formed at positions corresponding to the first and second bonding portions of the conductor pattern. 
     The intermediate substrate may include: a wiring pattern formed on one surface of the intermediate substrate; and a via conductor formed to penetrate through the intermediate substrate from one of the first bonding portion and the second bonding portion and connected to the wiring pattern. 
     A cavity may be formed on a lower portion of the intermediate substrate so as to secure a vibration space of the actuator. 
     The first and second bonding portions may be made of an anisotropic conductive film (ACF). 
     The intermediate substrate may be a FR-4 (glass epoxy) substrate. 
     According to another aspect of the present invention, there is provided a method for manufacturing an inkjet head assembly, including: preparing an inkjet head plate having an ink flow passage formed therein and having an actuator formed thereon, the actuator providing driving force for discharging ink; preparing a flexible printed circuit board (FPCB) applying voltage to the actuator; forming a conductor pattern in an intermediate substrate so as to electrically connect the actuator to the flexible printed circuit board; forming a first bonding portion on an upper portion of the actuator and bonding the first bonding portion to a lower portion of the intermediate substrate; forming a second bonding portion at an inner side in a width direction of the inkjet head plate than a first bonding portion on an upper portion of the intermediate substrate; and bonding the flexible printed circuit board to the second bonding portion. 
     The forming of the conductor pattern in the intermediate substrate may include: forming a via to penetrate through the intermediate substrate at a position corresponding to one of the first bonding portion and the second bonding portion; forming a via conductor by filling the via with a conductive material; and forming a wiring pattern on one surface of the intermediate substrate, the wiring pattern connecting one end of the via conductor to the other of the first bonding portion and the second bonding portion. 
     The method for manufacturing an inkjet head assembly may further include forming a cavity on a lower portion of the intermediate substrate so as to secure a vibration space of the actuator. 
     The forming of the cavity may be performed by an etching method. 
     The first and second bonding portions may be made of an anisotropic conductive film (ACF). 
     The intermediate substrate may be a FR-4 (glass epoxy) substrate. 
     The forming of the conductor pattern in the intermediate substrate may include forming each of a first terminal electrode and a second terminal electrode at positions corresponding to the first and second bonding portions of the conductor pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view schematically showing an inkjet head assembly according to an exemplary embodiment of the present invention; 
         FIG. 2  is an cut-away perspective view schematically showing the inkjet head assembly according to an exemplary embodiment of the present invention; 
         FIG. 3  is a cross-sectional view schematically showing the inkjet head assembly according to an exemplary embodiment of the present invention; 
         FIG. 4  is an enlarged cross-sectional view of an intermediate substrate in the inkjet head assembly according to an exemplary embodiment of the present invention; 
         FIGS. 5A and 5B  are process views showing a method for manufacturing an inkjet head plate of the inkjet head assembly according to an exemplary embodiment of the present invention; 
         FIGS. 6A to 6C  are process views showing a method for manufacturing an intermediate substrate of the inkjet head assembly according to an exemplary embodiment of the present invention; and 
         FIGS. 7A to 7D  are process views showing a method for assembling the inkjet head assembly according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, it should be noted that the spirit of the present invention is not limited to the exemplary embodiments set forth herein and those skilled in the art and understanding the present invention could easily accomplish retrogressive inventions or other exemplary embodiments included in the spirit of the present invention by the addition, modification, and removal of components within the same spirit, but those are to be construed as being included in the spirit of the present invention. 
     In addition, components having like functions are denoted by like reference numerals throughout the drawings of each exemplary embodiment. 
       FIGS. 1 through 3  are respectively, an exploded perspective view, a cut-away perspective view, and a cross-sectional view schematically showing an inkjet head assembly according to an exemplary embodiment of the present invention.  FIG. 4  is an enlarged cross-sectional view of an intermediate substrate in the inkjet head assembly according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 to 3 , an inkjet head assembly  100  according to an exemplary embodiment of the present invention may include an inkjet head plate  110  having an ink flow passage formed therein, a piezoelectric actuator  120  providing driving force for discharging ink to the inkjet head assembly  110 , an ink tank  130  supplying the ink to the ink flow passage of the inkjet head plate  110 , a flexible printed circuit board  140  applying voltage to the piezoelectric actuator  120 , and an intermediate substrate  150  electrically connecting the piezoelectric actuator  120  and the flexible printed circuit board  140 . 
     In the inkjet head assembly  100 , an inkjet head is configured to have a plurality of head cells including nozzles, in an amount such as ninety six nozzles, two hundred and fifty six nozzles, or the like, according to the performance of the inkjet head. In the exemplary embodiment, the inkjet head assembly  100  has a structure in which two sets of inkjet heads are arranged in a width direction of the inkjet head plate  110 . 
     Herein, directions of the inkjet head plate  110  are defined as follows. A length direction thereof indicates a direction from one head cell toward another head cell, among the plurality of head cells, and the width direction indicates a direction perpendicular to the length direction in a plane of the inkjet head plate  110 . 
     The inkjet head plate  110  may include ink inlet  111  into which ink is introduced, manifolds  112  transporting the ink introduced into the ink inlets  111  to the ink flow passages of individual head cells, a plurality of pressure chambers  114  provided on a lower portion of a position in which the piezoelectric actuator  120  is mounted, and a plurality of nozzles  116  discharging the ink. A plurality of restrictors  113  may be formed between the manifold  112  and the pressure chambers  114  in order to restrain the ink in the pressure chamber  114  from flowing backward to the manifold  112  when the ink is discharged. In addition, the pressure chambers  114  and the nozzles  116  may be interconnected by a plurality of dampers  115 . 
     The inkjet head plate  110  may be formed by appropriately forming the above-mentioned components configuring the ink flow passage on upper and lower substrates, and bonding the upper and lower substrates each other using a method such as silicon direct bonding (SDB) method or the like. At this time, the upper substrate may be a single crystal silicon substrate or a SOI substrate, and the lower substrate may be a SOI substrate. In addition, the inkjet head plate  110  is not limited thereto but may configure the ink flow passage using more substrates. In some cases, the ink flow passage may be implemented on a single substrate. The components configuring the ink flow passage are also only examples, and an ink flow passage having various configurations may be provided according to requirements and design specifications. 
     The piezoelectric actuators  120  are formed on an upper portion of the inkjet head plate  110  so as to correspond to the pressure chambers  114  of the inkjet head plate  110 , and provide the driving force for discharging the ink introduced into the pressure chambers  114  to the nozzles  116 . For example, the piezoelectric actuator  120  may be configured to include a lower electrode serving as a common electrode, a piezoelectric film deformed according to the application of voltage, and an upper electrode serving as a driving electrode. 
     The lower electrode may be formed on the entire surface of the inkjet head plate  110  and may be made of one conductive metal material; however, it may be preferably formed of two metal thin film layers made of titanium (Ti) and platinum (Pt). The lower electrode serves as a diffusion prevention layer preventing interdiffusion between the piezoelectric film and the inkjet head plate  110  as well as serving as the common electrode. The piezoelectric film is formed on the lower electrode, and is disposed on the upper portion of each of the plurality of pressure chamber  114 . The piezoelectric film may be made of a piezoelectric material, preferably, a lead zirconate titanate (PZT) ceramic material. The upper electrode is formed on the piezoelectric film, and may be made of any one material selected from a group consisting of Pt, Au, Ag, Ni, Ti, Cu, and the like. 
     In the exemplary embodiment of the present invention, a configuration in which the ink is discharged by the piezoelectric driving method using the piezoelectric actuator  120  is exemplary described; however the present invention is not limited by an ink discharging method and may be configured so as to discharge the ink by various methods such as a thermally driven method, or the like. 
     The ink tank  130  is connected to the ink inlet  111  so as to supply the ink to the ink flow passage of the inkjet head plate  110 , and is disposed at an outer side of the piezoelectric actuator  120  in the width direction of the inkjet head plate  110 . 
     The intermediate substrate  150  for electrically interconnecting the piezoelectric actuator  120  and the flexible printed circuit board  140  is formed with a conductor pattern having a predetermined form. 
     Referring to  FIG. 4 , first bonding portions  151  for bonding the intermediate substrate  150  to the piezoelectric actuator  120  are formed on a lower surface of the intermediate substrate  150 , and second bonding portions  152  for bonding the intermediate substrate  150  to the flexible printed circuit board  140  are formed on an upper surface thereof. The second bonding portion  152  may be formed inwardly of the first bonding portion  152  in the width direction of the inkjet head plate  110 . 
     The intermediate substrate  150  may be configured as a printed circuit board having conductor patterns formed on one surface thereof, and be made of an epoxy resin based substrate, for example, a FR-4 (glass epoxy) substrate. 
     The conductor patterns formed in the intermediate substrate  150  may include a via conductor  154  filling a via  153  penetrating through the intermediate substrate  150  from the first bonding portion  151  and a wiring pattern  155  formed from the second bonding portion  152  on an upper surface of the intermediate substrate  150  to an upper end of the via conductor  154 . That is, a lower end of the via conductor  155  may be connected to the first bonding portion  151 , and the upper end thereof may be connected to the wiring pattern  155 . 
     The via  153  may be formed in the intermediate substrate  150  by applying a drilling process using mechanical drilling or laser drilling to the printed circuit board, and the via conductor  154  may be formed by plating a metal in the via  153  through an electroplating method. As the metal, any one selected from a group consisting of Pt, Au, Ag, Ni, Ti, Cu, and the like may be used. 
     At this time, the conductor patterns formed in the intermediate substrate  150  may include terminal electrodes in order to ensure electrical connections on portions connected to the first and second bonding portions  151  and  152 . That is, a first terminal electrode  156  may be formed on the lower end of the via conductor  154  connected to the first bonding portion  151 , and a second terminal electrode  157  may be formed on the portion of the wiring pattern  155  connected to the second bonding portion  152 . 
     The first and second bonding portions  151  and  152  may be made of a conductive medium having a bonding force of a level that is not electrically short circuited, for example, a protrusion-shaped connection member such as a solder ball, a solder bump, or the like, and an anisotropic conductive film (ACF). In addition to the above-mentioned medium, the first and second bonding portions  151  and  152  may also be made of various load applying conductive media. In the exemplary embodiment, a case in which the first and second bonding portions  151  and  152  are made of the ACF is assumed. 
     When the second bonding portion  152  is bonded to the intermediate substrate  150 , a polymer film (not shown) may be applied to an upper portion of the wiring pattern  155  in order to protect the wiring pattern  155  formed on the upper surface of the intermediate substrate  150 . 
     A cavity  158  may be formed on a lower portion of the intermediate substrate  150  so as to secure a vibration space of the piezoelectric actuator  120 . That is, the cavity  158  is configured such that when the piezoelectric actuator  120  is vibrated, the vibration is not disturbed by the intermediate substrate  150 . 
     The cavity  158  may be formed through an etching process. More specifically, a dry etching method such as a reactive ion etching (RIE) method using inductively coupled plasma (ICP) or a wet etching method using, for example, tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH) as etchant for silicon may be used. 
     Although the exemplary embodiment of the present invention has described a case in which the cavity  158  is formed on the lower portion of the intermediate substrate  150 , the present invention is not limited thereto and the cavity  158  may not be formed. This is because, in the vibration of the piezoelectric actuator  120 , ½ of the amplitude thereof does not exceed the sum of thicknesses of the first bonding portion  151  and the first terminal electrode  156 . 
     The FPCB  140  is coupled to the second bonding portions  152  to be bonded to the intermediate substrate  150 . At this time, since the second bonding portions  152  are disposed at the inner side, that is, in the vicinity of the center, in the width direction of the inkjet head plate  110  than the first bonding portions  151 , a warp deformation space from the second bonding portions  152  to the outer side of the piezoelectric actuator  120  may be secured. 
     Therefore, it is unnecessary to separately prepare a space for bending the FPCB  140  between the piezoelectric actuator  120  and the ink tank  130 , and the entire width of the inkjet head assembly may be reduced by about 25%. 
     In addition, since the intermediate substrate  150  is interposed between the FPCB  140  and the piezoelectric actuator  120 , a height at which the FPCB  140  is bent to an upper portion of the ink tank  130  is reduced by a thickness of the intermediate substrate  150 . 
     Accordingly, when the FPCB  140  is warped, deformed, it is bent to have a smooth curve, such that physical stress applied to the FPCB  140  is significantly reduced and the FPCB  140  is securely bonded to the intermediate substrate. Therefore, the occurrence of electrical short-circuits in the second bonding portion  152  may be prevented due to the characteristics of the FPCB  140  having elasticity. 
     Hereinafter, a method for manufacturing an inkjet head assembly according to an exemplary embodiment of the present invention having the above-mentioned configuration will be described. 
     First, schematically describing a method for manufacturing an inkjet head assembly according to an exemplary embodiment of the present invention, the ink flow passage is formed on a wafer to manufacture the inkjet head plate, the conductor patterns are formed in the substrate to manufacture the intermediate substrate, the intermediate substrate is stacked on and bonded to the inkjet head plate, and the flexible printed circuit board (FPCB) is bonded to the intermediate substrate, such that the inkjet head assembly according to an exemplary embodiment of the present invention is completed. Meanwhile, processes manufacturing the intermediate substrate and the inkjet head plate may be performed regardless of order. That is, any one of the intermediate substrate and the inkjet head plate may be first manufactured, and the intermediate substrate and the inkjet head plate may also be simultaneously manufactured. However, for convenience of explanation, the process of manufacturing the inkjet head plate will be first described below. In addition, the processes of manufacturing the inkjet head plate are generally the processes forming the ink flow passage in at least one wafer. Hereinafter, for convenience of explanation, a detailed description of the processes of manufacturing the inkjet head plate will be omitted. 
       FIGS. 5A and 5B  are process views showing a method for manufacturing the inkjet head plate of the inkjet head assembly according to an exemplary embodiment of the present invention,  FIGS. 6A to 6C  are process views showing a method for manufacturing the intermediate substrate of the inkjet head assembly according to an exemplary embodiment of the present invention, and  FIGS. 7A to 7D  are process views showing a method for assembling the inkjet head assembly according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 5A , the ink flow passage is first formed in the inkjet head plate  110 . As the components of the ink flow passage, there may be the ink inlet  111  into which ink is introduced, the manifold  112  transporting the ink introduced into the ink inlet  111  to the ink flow passage of individual head cells, the plurality of pressure chambers  114  provided on the lower portion of a position in which the piezoelectric actuator  120  is mounted, and the plurality of nozzles  116  discharging the ink. The plurality of restrictors  113  may be formed between the manifold  112  and the pressure chambers  114  in order to restrain the ink in the pressure chambers  114  from flowing backward to the manifold  112  when the ink is discharged, and the plurality of dampers  115  may be formed between the pressure chambers  114  and the nozzles  116 . 
     These components of the ink flow passage may be formed by performing an etching process on the inkjet head plate  110  composed of a single crystal silicon substrate or a SOI substrate. More specifically, the dry etching method such as the reactive ion etching (RIE) method using the ICP or the wet etching method using the TMAH or the KOH may be used. 
     As shown in  FIG. 5B , the piezoelectric actuator  120  may be formed on the upper portion of the inkjet head plate  110  in which the ink flow passage is formed. The piezoelectric actuator  120  may be formed at the position corresponding to the pressure chambers  114  and may include the lower electrode serving as the common electrode, the piezoelectric film deformed according to the application of the voltage, and the upper electrode serving as the driving electrode. 
     Next, as shown in  FIG. 6A , a substrate forming the intermediate substrate  150  is prepared. As the intermediate substrate  150 , the epoxy resin based substrate, for example, the FR-4 substrate may be used. 
     As shown in  FIG. 6B , a hole forming the via  153  and a groove forming the cavity  158  are formed in the intermediate substrate  150 . The hole and the groove may be formed by the etching process. More specifically, the dry etching method such as the reactive ion etching (RIE) method using the ICP or the wet etching method using the TMAH or the KOH may be used. 
     As shown in  FIG. 6C , the via conductor  154  is formed by filling the via  153  with the conductive material, and the wiring pattern  155  is formed on the upper surface of the intermediate substrate  150 . The via conductor  154  may be formed by plating a metal in the via  153  through the electroplating method. As the metal, any one material selected from a group consisting of Pt, Au, Ag, Ni, Ti, Cu, and the like may be used. In addition, the wiring pattern  155  may be formed by printing or sputtering the metal material. 
     The first terminal electrode  156  may be formed on the lower end of the via conductor  154  in order to securely bond the intermediate substrate to the piezoelectric actuator  120 , and the second terminal electrode  157  may be formed on the end of a FPCB side of the wiring pattern  155  in order to secure bond the intermediate substrate to the FPCB  140 . 
     In addition, in order to protect the wiring pattern  155 , the polymer film (not shown) may be applied to the upper surface of the intermediate substrate  150 , with the exception of the portions in which the second terminal electrodes  157  are formed. 
     Meanwhile, although the exemplary embodiment of the present invention has described a case in which the via conductor  154  is connected to the first bonding portion  151  and the wiring pattern  155  is connected to the second bonding portion  152 , the present invention is not limited thereto. The wiring pattern may be formed on the lower surface of the intermediate substrate  150  to be connected to the first bonding portion  151 , and the via conductor may be formed to be connected to the second bonding portion  152 . In addition, the present invention may be variously modified according to requirements and design specifications. 
     Next, a method for assembling the inkjet head assembly  100  according to an exemplary embodiment of the present invention will be described with reference to  FIGS. 7A to 7D . As shown in  FIG. 7A , the first bonding portion  151  is formed on the upper surface of the piezoelectric actuator  120 . The first bonding portion  151  may be formed at the outer side of the piezoelectric actuator  120  in the width direction of the inkjet head plate  110 , and may be formed on the first terminal electrode  156 . 
     As shown in  FIG. 7B , the intermediate substrate  150  is coupled to the inkjet head plate  110  by aligning the position of the first bonding portion  151  with the position at which the via conductor  154  of the intermediate substrate  150  is formed. At this time, the coupling through the first bonding portion  151  may be performed by conducting pre-bonding through thermal pressing and then conducting real-bonding using an ultrasonic wave. 
     As shown in  FIG. 7C , the second bonding portion  152  for the boding to the FPCB  140  is formed on one end of the wiring pattern  155  of the intermediate substrate  150 . That is, the first bonding portion  152  may be formed in the vicinity of the center in the width direction of the inkjet head plate  110 , and may be formed on the second terminal electrode  157  of the wiring pattern  155 . 
     As shown in  FIG. 7D , the FPCB is disposed on the intermediate substrate  150  in such a manner as to be aligned with the intermediate substrate  150 , and is bonded thereto through the second bonding portion  152 . At this time, the bonding may be performed by conducting pre-bonding through the thermal pressing and then conducting real-bonding using the thermal pressing. 
     As set forth above, according to the exemplary embodiments of the present invention, there are provided the inkjet head assembly and a method for manufacturing the same in which the entire width of the inkjet head is reduced to increase the number of the inkjet heads capable of being manufactured on a single wafer, thereby allowing for an improvement in productivity such as an increase in processing yield, a decrease in a manufacturing costs, and the like. 
     Furthermore, in the inkjet head assembly according to the exemplary embodiments of the present invention, the physical stress applied to the FPCB when the FPCB is connected to the inkjet head is reduced, thereby allowing for improving the bonding characteristics of the FPCB. 
     Although the exemplary embodiments of the present invention have been described in detail, they are only examples. It will be appreciated by those skilled in the art that various modifications and equivalent other embodiments are possible from the present invention. For example, the method for forming the via conductor and the wiring pattern in the intermediate substrate in the inkjet head assembly according to the exemplary embodiment of the present invention is only an example. Various methods may be used and the order of each process of the method for manufacturing the inkjet head assembly may also be different from the order as described above. Accordingly, the actual technical protection scope of the present invention must be determined by the spirit of the appended claims.