Patent Publication Number: US-2003231275-A1

Title: Liquid crystal display device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Technical Field  
       [0002] The present invention relates to a liquid crystal display device.  
       [0003] 2. Background Art  
       [0004] Previously, COG (Chip on Glass) modules and COG stick modules have been known as liquid crystal display devices.  
       [0005]FIG. 13 shows a perspective view of a COG stick module, and hereinafter, a method for fabricating a COG stick module as shown in FIG. 13 will be described.  
       [0006] As shown in FIG. 1, electrical conductive lines of a transparent electrical conductive line electrodes  2  are formed on a transparent substrate  3  by photolithography, and on the obtained transparent substrate  3  with transparent electrodes  2 , LSI input/output electrical conductive lines  4  are formed to obtain a COG stick substrate  1 , and moreover, on this COG stick substrate  1 , an LSI  5  is mounted by an ACF (Anisotropic Conductive Film) method as shown in FIG. 2, whereby a circuit board portion (a COG stick)  6  is fabricated. Then, FPC (Flexible Printed Circuits)  7  for connection to a liquid crystal display element  11  is connected to an output terminal of the LSI  5  of the circuit board portion  6 .  
       [0007] In addition, a liquid crystal display portion  11 , as shown in FIG. 13, in which a front glass substrate  9  with transparent pixel electrodes (unillustrated) and a rear glass substrate  10  with transparent counter pixel electrodes (unillustrated) are overlapped with each other so that both electrodes are arranged in an opposed manner and liquid crystals are sealed in respective pixel regions between the front glass substrate  9  and rear glass substrate  10 , respectively, is fabricated in advance, its electrode terminals and the FPC  7  are connected, whereby a liquid crystal display device  15  is obtained.  
       [0008] Moreover, it is desirable to arrange a sheet polarizer on the front surface of the front surface  9 , and a flexible cable  8  for a connection to a power-source side is connected to the input electrical conductive lines  4  on the side opposite to the output electrical conductive lines  4  on the LSI  5  side of the circuit board  6 .  
       [0009] As the transparent substrate  3  of the circuit board portion  6 , a transparent glass substrate is used, and furthermore, transparent electrical conductive line electrodes  2  are formed on this glass substrate, whereby after the LSI  5  is mounted by an ACF method on the circuit board portion  6 , it becomes possible to inspect, from the transparent substrate  3  surface on the side opposite to the LSI  5   a  attaching portion, through a microscope or the like, a connection state between the LSI  5  and transparent electrical conductive line electrode  2  visually or by use of an image recognition device.  
       [0010] For the above-described front and rear transparent substrates  9  and  10 , a transparent resin and transparent glass are used, however, since glass is used in most cases, the region where the LSI  5  is connected exists on a glass substrate, and therefore, a liquid crystal display device composed of the above-described liquid crystal display portion  11  and circuit board portion  6  is sometimes referred to as a Chip on Glass (COG) stick module.  
       [0011] In addition, FIG. 14 shows a configuration view according to a prior art in a case where electric components  13  and a connector  17  are set in the above-described COG stick module, wherein the liquid crystal display portion  11  is attached on a backlight  23 , and the electric components  13  and connector  17  are also attached on a printed circuit board  24  with a COG stick module attached, separately from the COG stick module.  
       [0012] No electric components other than the LSI  5  can be mounted on the COG stick substrate  1  of the prior-art COG stick module as shown in FIG. 13 or FIG. 14. This is because an ITO transparent electrode was used for electrical conductive lines on the COG stick substrate  1 , and no soldering components including capacitors, resistors, a ZIF connector could be mounted.  
       [0013] In addition, when electric components such as power-stabilizing capacitors and step-up capacitors are mounted on the printed circuit board  24 , terminals for a connection of said electric components including capacitors are required, and therefore, a large number of input pins are required on the transparent substrate  3 .  
       SUMMARY OF THE INVENTION  
       [0014] It is an object of the present invention to provide a liquid crystal display device, of which the final outside dimensions is reduced as much as possible, which is often determined depending on the printed circuit substrate  24  shown in FIG. 14.  
       [0015] In addition, it is an object of the present invention to provide a liquid crystal display device in which an LSI can be mounted in a reduced space and in which, after the LSI is mounted, the mounted condition (an electrically connected condition) and lighting of an image display portion can be visually confirmed.  
       [0016] The above-described objects of the present invention are achieved by the following construction.  
       [0017] According to an embodiment of the invention, a liquid crystal display device comprises: a liquid crystal display portion in which a first substrate with transparent pixel electrodes and a second substrate with transparent counter pixel electrodes are overlapped with each other so that both electrodes are arranged in an opposed manner and liquid crystals are sealed in pixel regions between the first substrate and second substrate; a circuit board portion in which, on the surface of a hard substrate with electrical conductive lines connected to the transparent pixel electrodes of the liquid crystal display portion, an integrated circuit chip to control conduction of the electrical conductive line is mounted; and a first flexible connecting means which unites either first or second substrate of the liquid crystal display portion and the hard substrate of the circuit board portion into one substrate, covers a region of the circuit board portion including an electrical conductive line installing region other than an integrated circuit chip mounting part, and is loaded with electric components electrically connected to the integrated circuit chip.  
       [0018] According to another embodiment of the invention, in the liquid crystal display device, the liquid crystal display portion and the circuit substrate portion are separate, and the transparent pixel electrodes of the liquid crystal display portion and the electrical conductive lines of the circuit substrate portion are electrically connected via a second soft connecting means.  
       [0019] According to another embodiment of the invention, in the liquid crystal display device, the first substrate and the second substrate of said liquid crystal display portion, and the hard substrate of said circuit substrate portion are transparent substrates.  
       [0020] According to another embodiment of the invention, in the liquid crystal display, the transparent substrates are glass substrates.  
       [0021] According to another embodiment of the invention, in the liquid crystal display device, the glass substrates are the same kind of glass and the same thickness. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a perspective view of a COG stick substrate on which LSI input/output electrical conductive lines have been formed, according to an embodiment of the present invention.  
     [0023]FIG. 2 is a perspective view showing a circuit board portion (a COG stick) obtained by mounting an LSI on the COG stick substrate of FIG. 1.  
     [0024]FIG. 3 is a perspective view showing an FPC assembly in which electric components including condensers, resistors, and a connector have been mounted on FPC, according to an embodiment of the present invention.  
     [0025]FIG. 4 is a perspective view showing a COG stick assembly in which the FPC assembly of FIG. 3 has been connected to the circuit board portion (COG stick) of FIG. 2.  
     [0026]FIG. 5 is a perspective view of a liquid crystal display device according to an embodiment of the present invention.  
     [0027]FIG. 6 is a partial view of a section along the A-A line of FIG. 5.  
     [0028]FIG. 7 is a perspective view of a liquid crystal display device according to an embodiment of the present invention.  
     [0029]FIG. 8 is a perspective view showing an FPC assembly in which electric components including condensers, resistors, and a connector have been mounted on FPC, according to an embodiment of the present invention.  
     [0030]FIG. 9 is a perspective view of a liquid crystal display device according to an embodiment of the present invention.  
     [0031]FIG. 10 is a perspective view of a liquid crystal display device according to an embodiment of the present invention.  
     [0032]FIG. 11 is a perspective view of a liquid crystal display device according to an embodiment of the present invention.  
     [0033]FIG. 12 is a plan view showing a main part of the liquid crystal display device according to an embodiment of the present invention shown in FIG. 10.  
     [0034]FIG. 13 is a perspective view of a liquid crystal display device according to a prior art.  
     [0035]FIG. 14 is a perspective view of a liquid crystal display device according to a prior art. 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS  
     [0036] Embodiments of the present invention will be described with reference to the drawings.  
     [0037] In the present embodiment, as shown in the perspective view of FIG. 5, electric components including capacitors, resistors, and a connector are mounted on a flexible connecting means such as a bilayered (or multilayered) FPC. By connecting the above-described flexible connecting means mounted with electric components, such as FPC, to a COG stick, a component mounted area is reduced compared to that of a prior-art article, therefore, a liquid crystal display device which occupies a reduced space and allows simple assembly can be provided.  
     [0038] Hereinafter, a method for fabricating a liquid crystal display device according to the present embodiment will be described with reference to the drawings. As shown in FIG. 1, electrical conductive lines of a transparent electrical conductive line electrodes  2  and LSI input/output electrical conductive line  4  are formed on a hardened substrate  3  (not necessarily transparent) such as a glass plate by photolithography to obtain a COG stick substrate  1  as shown in FIG. 1, and on this COG stick substrate  1 , an LSI  5  is mounted by an ACF method, whereby a circuit board portion (a COG stick)  6  is fabricated (FIG. 2).  
     [0039] Next, as shown in FIG. 3, a bilayered (or multilayered) FPC (Flexible Printed Circuits)  8  is fabricated, and on this FPC  8 , electric components  13  including capacitors, resistors, and a connector are mounted so as to provide an FPC assembly  14  (FIG. 3). The FPC  8  is of such outside dimensions as not to protrude from the external form of the COG stick substrate  1  and not to overlap the LSI  5 , which is mounted on the COG stick substrate  1 .  
     [0040] The FPC assembly  14  of FIG. 3 is connected to the COG stick  6  as shown in FIG. 2 by a widely-known method via an ACF or the like, whereby a COG stick assembly  16  as shown in FIG. 4 is fabricated.  
     [0041] By connecting the COG stick assembly  16  and a crystal display element  11  by the FPC  7  as a flexible cable, a liquid crystal display device as shown in FIG. 5 can be obtained.  
     [0042]FIG. 6 shows a main part of a section along the A-A line of FIG. 5, wherein electrical conductive lines such as a transparent electrical conductive line electrodes  2  made of ITO and electrical conductive lines  4  made of ITO exists on a substrate  3 , and on the substrate  3 , via an anisotropic conductive film (ACF)  25  which is formed by plating the front surfaces of particles  21  with gold and embedding the same in a resin  19 , an LSI  5  is connected to the transparent electrical conductive line electrodes  2  and the LSI input/output electrical conductive lines  4 . Moreover, electric components  13  including capacitors and resistors are arranged on FPC  8 . These electric components  13  are connected to the above-described transparent electrical conductive line electrodes  2  and LSI input/output electrical conductive lines  4  via electrical conductive line  18  (copper electrical conductive line formed by etching) and an external power-supply unit of the anisotropic conductive film (ACF), etc. The FPC  8  is connected to the substrate  3  via the ACF  25 . In addition, electrical conductive lines  20  (copper electrical conductive line formed by etching) of the FPC  7  for connecting electrically to the liquid crystal display element  11  are also connected to the ITO transparent electrical conductive line electrodes  2  and the LSI input/output electrical conductive lines  4  via the ACF  25 .  
     [0043] In the liquid crystal device  15  shown in FIG. 5, the FPC  7 , which connects the circuit board portion  6  and the liquid crystal display element  11 , can be bent, therefore, if the circuit board portion  6  as a mounting portion of the LSI  5  and the liquid crystal display portion  11  are overlapped with each other with the front glass substrate  9  having the liquid crystal display portion  11  exposed outside as shown in FIG. 7, a compact liquid crystal display device  15  can be obtained.  
     [0044] The FPC  7 , which connects the COG stick assembly  16  and the liquid crystal display element  11 , can be bent, therefore, if a board-to-board connector  17  is attached to the FPC stick assembly  14  in advance, which is formed by loading electric components  13  and connectors on the FPC  7  as shown in FIG. 8, the FPC stick assembly  14  can be attached to an external power-supply unit or the like through one-touch operation (FIG. 8 and FIG. 9). A heat seal, a flexible flat cable (FFC), an anisotropic conductive rubber connector or the like may be used in place of the FPCs  7  and  8 .  
     [0045] Although the FPC assembly  14  as shown in FIG. 3 has been connected to the COG stick  6  as shown FIG. 2 in the above-described embodiment, it may be possible to, as shown in FIG. 10 and FIG. 11, directly form ITO transparent electrodes  2  and LSI input/output electrical conductive lines  4  on one substrate  10  of transparent substrates  9  and  10 , further mount an LSI  5  on the substrate  10 , and attach, thereon, a FPC assembly  14  composed of FPC  8  mounted with electric components  13  and a connector  17 , so as to form a liquid crystal display device. FIG. 10 shows a case where no connector  17  is attached, while FIG. 11 shows a case where a connector  17  is provided.  
     [0046]FIG. 12 shows an enlarged plan view of an FPC assembly  14  installing part of FIG. 10. The electric components  13  (capacitors  13   a  and resistors  13   b ) and connector  17  are connected by metal (copper) electrodes on the surface of the flexible connecting means  8  or in through holes.  
     [0047] As is clearly understood by a comparison between the constructions of the liquid crystal display devices of FIG. 9 through FIG. 11 and the construction of the prior-art liquid crystal display device as shown in FIG. 14, the installing space of the electronic components  13  and connector  17 , etc., is compact in the cases of the present embodiment.  
     [0048] Although the substrate  3  is not necessarily transparent, by providing this substrate  3  as a transparent plate such as glass, an advantage is provided such that a connected condition between the FPCs  7  and  8  and LSI  5  and the transparent electrical conductive line electrodes  2  and LSI input/output electrical conductive lines  4  can be easily confirmed.  
     [0049] The adhesion between the transparent electrical conductive electrodes  2  and the substrate  3  can be improved in comparison with the adhesion between the transparent electrical conductive electrode  2  and an organic resin board such as an epoxy resin board and a polyester resin board.  
     [0050] As a result, there is an advantage that the reliability of the liquid crystal display device  11  of this invention in the environment of high temperature and high humidity can be especially raised.  
     [0051] In addition, there is merit on the production process that those substrates  3  can be obtained from one original glass plate at the same time by the cutting separation of the glass plate, because the substrates  3  have the same chemical composition and thickness as substrates  9  and substrates  10 .  
     [0052] In this case, the merit is caused that transparent pixel electrodes of liquid crystal display portion (a liquid crystal display element  11 ) and transparent electrical conductive lines of circuit substrate portion  6  can be processed at the same time (the coating of the transparent conductive film and the patterning processing can be manufactured at the same process).  
     [0053] The simplification of these processes becomes practicable merit from an industrial production viewpoint in economically manufacturing the liquid crystal display devices of this invention.  
     [0054] The glass such as soda lime silicate, alumino silicate, alumino borosilicate, non alkali silicate can be used as the glass which can be used for the glass substrate.  
     [0055] In addition, by covering the transparent electrical conductive line electrodes  2  and the LSI input/output electrical conductive line  4  with the FPCs  7  and  8 , electrolytic corrosion of the transparent electrical conductive line electrode  2  and LSI input/output electrical conductive line  4  made of ITO, etc., due to moisture can be prevented, whereby disconnection due to electrolytic corrosion of the transparent electrical conductive line electrodes  2  and the LSI input/output electrical conductive lines  4  can be prevented.  
     [0056] In addition, as is clearly understood by a comparison between FIG. 14 showing a prior art and FIG. 5 and FIG. 9 through FIG. 11 showing the present embodiment, the liquid crystal display device according to the present invention has a great space-saving effect.  
     [0057] In addition, in the present embodiment, since the electric components  13  including capacitors and resistors to be connected to the LSI  5  are mounted on the flexible connecting means  8 , there exists an advantage such that the number of input terminals can be greatly reduced compared to that of the prior art. As a description thereof based on the example of FIG. 12, one input terminal is used in common among five capacitors  13   a,  and the capacitors  13   a  are provided with five output terminals and form a closed circuit with the LSI  5 . In addition, one input terminal is provided in common among three resistors  13   b,  and the resistors  13   b  form a closed circuit in which output terminals from the respective resistors  13   b  are lead out to the LSI  5 . Namely, if input and output terminals were respectively provided for the five capacitors  13   a  and three resistors  13   b,  16 lines of electrical conductive line would be required, while 10 lines are sufficient in the construction as shown in FIG. 12, therein exists an advantage.  
     [0058] Industrial Applicability  
     [0059] According to an embodiment of the invention, since the first flexible connecting means (FPC  8 ), which covers a region of the circuit board portion (substrate portion  6 ) including electrical conductive lines installing region other than the integrated circuit chip (LSI  5 ) mounting part and is loaded with electric components electrically connected to the integrated circuit chip, is provided and the electrical conductive lines (transparent electrical conductive line electrode  2  and LSI input/output electrical conductive lines  4 ) of the circuit board portion are covered by the first flexible connecting means, the electrical conductive lines, which are made of ITO, etc., are prevented from corroding due to moisture, whereby disconnection due to electrolytic corrosion of the electrical conductive lines are eliminated.  
     [0060] Moreover, according to an embodiment of the invention, since the electric components are loaded on the circuit substrate portion, a compact construction can be provided as a whole, whereby a great space-saving effect is provided.  
     [0061] Moreover, according to an embodiment of the invention, since electric components including capacitors and resistors are loaded on the circuit substrate portion, the integrated circuit chip (LSI  5 ) and the electric components can form closed circuits, whereby the number of input terminals of the electric components can be greatly reduced compared to that of the prior art, therein exists an advantage.  
     [0062] Moreover, according to an embodiment of the invention, in addition to the effects of the first aspect of the invention, the liquid crystal display portion and the circuit board portion can be overlapped with each other by bending the first flexible connecting means (FPC  7 ), whereby a liquid crystal display portion which occupies a reduced space as a whole can be obtained.  
     [0063] Moreover, according to an embodiment of the invention, since the hard substrate (hard substrate  3 ) is transparent, an advantage is provided such that a connected condition between the first and second flexible connecting means (FPC  8  and FPC  7 ) and integrated circuit chip (LSI  5 ) and the electrical conductive line (transparent electrical conductive line electrode  2  and LSI input/output electrical conductive line  4 ) of the circuit board portion (substrate  3 ) can be easily confirmed.  
     [0064] Moreover, according to an embodiment of the invention, the adhesion between the transparent electrical conductive electrodes  2  and the substrate  3  can be improved in compared with the adhesion between the transparent electrical conductive electrode  2  and a synthetic resin board, and the reliability of this invention in the environment of high temperature and high humidity can be raised.  
     [0065] Moreover, according to an embodiment of the invention, there is a merit on the production process that those substrates  3  can be obtained from one original glass plate at the same time by the cutting separation of the glass plate, because substrates  3  have the same chemical composition and thickness as substrates  9  and substrates  10 .