Abstract:
Disclosed herein is a Plasma Display Panel (PDP) that adopts a moisture-proof structure to protect the adhesive portions of connection pads for driving electrodes. The PDP includes a front panel, a rear panel, a group of electrodes, and a plurality of conductive pads. The group of electrodes are each configured to have a predetermined first line width and are formed on at least one of the front panel and the rear panel. The conductive pads are configured to allow the group of electrodes to be electrically connected with the corresponding electrodes, and are each configured to have a second line width greater than the first line width. The structure of the PDP can effectively protect an overall panel pad from external moisture.

Description:
[0001]     This non-provisional application claims priority under 35 U.S.C. § 119 (a) on patent application Ser. No. 10-2005-0103716 filed in Korea on Nov. 1, 2005 the entire contents of which are hereby incorporated by reference.  
       BACKGROUND  
       [0002]     1. Field  
         [0003]     This application related generally to a plasma display panel that adopts a moisture-proof structure to protect the adhesive portions of connection pads for driving electrodes.  
         [0004]     2. Description of Related Art  
         [0005]      FIG. 1  is an exploded perspective view schematically showing the structure of a conventional Alternating Current (AC) three-electrode surface discharge Plasma Display Panel (PDP). Referring to  FIG. 1 , the PDP includes a front panel  10  configured to display information and a rear panel  20  disposed on a plane that is oriented parallel to a plane upon which the front panel  10  is disposed.  
         [0006]     The front panel  10  includes a plurality of pairs of display electrodes X and Y arranged with relative orientations parallel to each other on a glass substrate  11 , and the rear panel  20  includes a plurality of address electrodes A arranged with an orientation perpendicular to the display electrodes X and Y on a glass substrate  21 . In the front panel  10  and the rear panel  20 , the display electrodes X, Y and the address electrodes A are respective arranged in rows and columns.  
         [0007]     Generally, the display electrodes X, Y are composed of conductive films  13  that are transparent electrodes, such as indium tin oxide (ITO). In order to compensate for the high resistance characteristic of transparent conductive films  13 , bus electrodes  14 , which are made conductive metal material, are arranged along the edges of the transparent conductive films  13 . A dielectric layer  15 , which is made of a low-melting point glass material having a thickness of above 30 μm, is applied to the display electrodes X and Y, and a protecting layer  16 , such as a magnesium oxide layer, is deposited on the surface of the dielectric layer.  
         [0008]     The address electrodes A are made of conductive metal material, and are generally coated with a dielectric layer (not shown) to the thickness of about 10 μm. Barrier ribs  24  having a height of about 150 μm are arranged with an orientation parallel to the address electrodes A on the dielectric layer. Discharge spaces are defined for respective sub-pixels by these barrier ribs  24 . Red, green and blue phosphor layers  25  for displaying colors are disposed in the respective discharge spaces within the barrier ribs  24 , a pixel including a set of red, green, phosphor layers. The discharge spaces between the front panel  10  and the rear panel  20  are charged with a discharge gas for plasma discharge, and one pixel above the phosphor layers  25  includes three sub-pixels arranged parallel to each other in a row direction. The structure of each sub-pixel is generally referred to as a cell.  
         [0009]     The pairs of display electrodes X and Y and the address electrodes A are driven by an X driver, a Y driver and a Z driver, respectively.  
         [0010]      FIG. 2  is a plan view showing the conventional PDP. Referring to  FIG. 2 , the PDP is provided with a pixel area PA, which is formed of the sub-pixels described in conjunction with  FIG. 1 , in a sealed inner space formed through the bonding of the front panel  10  and the rear panel  20 , and a pad area (not identified by reference numeral in  FIG. 2 ) is formed in the peripheral region of the front and rear panels  10  and  20  of the PDP. In the pad area, a plurality of metal electrode pads P X , P Y  and P A  are formed for connecting a plurality of electrode groups, that is, a scan electrode group, a sustain electrode group and an address electrode group, which are formed in the pixel area PA, to respective driver circuits. The pads P X , P Y  and P A  are generally made of a low-resistance metal material containing Ag.  
         [0011]     In the PDP having a three-electrode surface discharge structure, described above in conjunction with  FIG. 1 , the scan electrode pads F Y , which are connected with the respective scan electrodes Y that are present in the pixel area PA, and the sustain electrode pads P X , which are connected with the respective sustain electrodes X that are present in the pixel area PA, are respectively formed on the left and right ends of the front panel  10  corresponding to the number of sub-pixels. Furthermore, the address electrode pads P A  are formed on the lower and/or upper end of the rear panel  20 . Although, for ease of description, the electrode pads are illustrated as being separately formed at the ends of corresponding electrodes in the present specification, it should be noted that the electrode pads may be formed as parts of corresponding electrodes and that the locations for forming the electrodes pads may also be changed in various ways according to the arrangement of the electrodes, which are formed on the front and rear panels  10  and  20  of the PDP, and according to the driving method thereof.  
         [0012]     Flexible Printed Circuits (FPCs) are attached to the pad area of the PDP. The FPC is used to connect the electrode groups of the pixel area PA to the driving circuits located outside the PDP.  
         [0013]      FIG. 3  is a diagram showing a section of the pad area of  FIG. 2  after the FPC is installed. In particular,  FIG. 3  shows a section taken along a line A-A′ ( FIG. 2 ) of an address electrode pad area in the pad area.  
         [0014]     As shown in  FIG. 3 , the FPC  40  includes a plurality of conductive pads  44  formed on a flexible resin film  42 . Each of the conductive pads  44  is formed of a single-layered or multi-layered film that is made of at least one of Cu, Sn, Ni and Au materials. The FPC  40  may be a Tape Carrier Package (TCP) or Chip On FPC (COF) on which Driving Integrated Circuits (ICs) (not shown) are mounted for supplying driving signals to the electrode pads P A , P X  or P Y  through the conductive pads  44 .  
         [0015]     The conductive pads  44  of FPC  40  come into electrical contact with respective address electrode pads P A . Such electrical contact is generally made with an Anisotropic Conduction Film (ACF)  46  interposed therebetween. The ACF  46  is made of adhesive material in which metal balls (not shown) are distributed, and the conductive pads  44  and the address electrode pads P A  are electrically connected through the balls (not shown) that are hardened and distributed by heating and pressing.  
         [0016]      FIG. 4  is a plan view showing a portion of the pad area in which the address electrode pads P A  and the conductive pads  44  are adhered to the FPC  40 .  
         [0017]     As shown in  FIG. 4 , the FPC  40  is aligned so that portions of the address electrode pads P A  of the pad area are covered therewith, and the remaining portions of the address electrode pads P A  are exposed outside the panel. In this case, when the conductive pads  44  have the same line width as the address electrode pads P A , exposed areas EAs, in which the portions of the address electrode pads P A  are not covered with the conductive pads  44 , are created due to misalignment.  
         [0018]     Accordingly, at the exposed areas EA, electromigration might cause an electric short to be generated between the remaining exposed portions of the address electrode pads P A , which are covered with the FPC  40 , and the conductive pads  44 . Furthermore, when the electrode pads P A  are made of a composition containing Ag, the above described phenomenon is intensified.  
         [0019]     First, when a potential difference exists between a pair of neighboring address electrode pads P A  and moisture is interposed therebetween, an aqueous colloid solution is created because the ionization of Ag occurs on an anode pad side. Thereafter, reactions through which Ag is oxidized, deoxidized, diffused and hydrolyzed in the colloidal solution and is then extracted after the movement thereof to a cathode, occur sequentially. These reactions can be represented by the following chemical formulas 1 to 5.  
         [0020]     The ionization of an Ag anode due to moisture 
 
Ag→Ag + +e − 
 
H 2 O→H++OH −   (1) 
 
         [0021]     The generation of AgOH colloid on an anode side 
 
Ag + +OH→AgOH   (2) 
 
         [0022]     Diffusion in the colloid after the generation of Ah 2 O 
 
2AgOH→AgO 2 +H 2 O   (3) 
 
         [0023]     Hydrolysis 
 
Ag 2 O+H 2 O→2AgOH→2Ag + +2OH −   (4) 
 
         [0024]     The extraction of Ag on the cathode 
 
Ag + +e − →Ag 
 
         [0025]     Ag extracted on the cathode through the above-described reactions grows gradually and, as a result, causes the neighboring pads to be short-circuited.  
         [0026]     Currently, as the line width and distance between address electrodes A are reduced to satisfy the trend toward a large-sized and high-definition panel, the probability of the occurrence of variation due to the tolerance in the manufacturing process increases, therefore the above-described problem may be more serious.  
         [0027]     To prevent the problem, the conventional technology, as shown in  FIG. 3 , uses a method of attaching the electrode pads P A  to the FPC  40  and forming a moisture-proof coating layer PL on the resultant product. However, even when using this method, defects due to an electric short between the electrode pads P A  continue to be generated in the PDP.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     Features of the subject technology will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0029]      FIG. 1  is an exploded perspective view schematically showing the structure of a conventional AC three-electrode surface discharge PDP;  
         [0030]      FIG. 2  is a plan view showing the conventional PDP;  
         [0031]      FIG. 3  is a diagram showing a section of the panel pad area of  FIG. 2  after the FPC is installed;  
         [0032]      FIG. 4  is a plan view showing a portion of a panel pad area in which address electrode pads and conductive pads are adhered to the FPC;  
         [0033]      FIG. 5  is a plan view showing the structure of a PDP;  
         [0034]      FIG. 6A  is a plan view showing an example in which the conductive pads of an FPC are aligned in the panel pad area, which is described in conjunction with  FIG. 5 ;  
         [0035]      FIG. 6B  is a sectional view showing a section taken along a line B-B′ of a contact portion between the conductive pad and the driving electrode of  FIG. 6A ;  
         [0036]      FIG. 7A  is a plan view showing another example in which the conductive pads of the FPC are aligned in the panel pad area, which is described in conjunction with  FIG. 5 ;  
         [0037]      FIG. 7B  is a sectional view showing a section of a contact portion between the conductive pad and driving electrode pad of  FIG. 7A ; and  
         [0038]      FIG. 7C  is a sectional view showing a section taken along a line D-D′ of a contact portion between the conductive pad and the driving electrode pad of  FIG. 7A . 
     
    
     DETAILED DESCRIPTION  
       [0039]     Referring to  FIG. 5 , a PDP may be configured with a front panel  110  and a rear panel  120 . A pixel area PA is formed in a sealed inner space between the front panel  110  and the rear panel  120 , which is defined by the bonding of the front panel  110  and the rear panel  120 . Although not shown, the pixel area PA includes a plurality of sub-pixels. A plurality of electrode groups and barrier ribs, which are formed on the front panel  110  and/or the rear panel  120 , divides a discharge space between the front and rear panels  110  and  120  into a plurality of sub-pixels, thus defining the pixel area PA.  
         [0040]     The electrode groups may include a sustain electrode group, a scan electrode group and an address electrode group, and may be appropriately disposed on the front panel  110  and/or the rear panel  120  according to the structure or driving method of the panel. The present implementation involves an application of concepts set forth herein to a PDP having a three-electrode surface discharge structure, which is described in conjunction with  FIG. 1 . Accordingly, a detailed description of the arrangement of driving electrodes is not reproduced here.  
         [0041]     The groups of electrodesPA are connected to external driving circuits through a plurality of electrode pads P A  exposed outside the inner space between the front panel  110  and the rear panel  120 . In  FIG. 5 , only the address electrode pads P A  among the plurality of electrode pads, which are formed on the rear panel  120 , are shown, and sustain electrodes and scan electrodes, which are formed on the front panel  120 , are omitted. However, since these concepts may be applied to electrode pads other than the address electrode pads, the address electrode pads P A  are referred to as driving electrode pads, which also or alternatively may include both the sustain electrode pads and the scan electrode pads, in the following description.  
         [0042]     The panel structure includes a moisture-proof dielectric layer  123  that exists outside the sealed inner space defined by the front panel  110  and the rear panel  120 . The moisture-proof dielectric layer  123  covers a portion of the driving electrode pads P A  exposed outside the sealed inner space of the panel. The moisture-proof dielectric layer  123  may be a white back dielectric layer, which enables the moisture-proof dielectric layer  123  to be provided without requiring a separate additional process if the white back dielectric layer is formed after the address electrodes are formed.  
         [0043]     The extended length D 1  of the moisture-proof dielectric layer  123  must be appropriately set such that portions of the driving electrode pads P A  having the minimum length can be exposed to allow the driving electrode pads P A  and the conductive pads  144  of an FPC  140  to realize excellent, electrical connection therebetween.  
         [0044]     Limitations may not be imposed upon the thickness of the moisture-proof dielectric layer  123 . Alternatively, the moisture-proof dielectric layer  123  may have a thickness of about 1-30 μm.  
         [0045]     Meanwhile, although  FIG. 5  shows the moisture-proof dielectric layer  123  formed on the address electrode pads PA, the moisture-proof dielectric layer  123  may also or alternatively be formed on the scan electrode pads (not shown) and/or sustain electrode pads (not shown) of the front panel  110 .  
         [0046]      FIG. 6A  is a plan view showing an example in which the conductive pads  144  of the FPC  140  are aligned in the panel pad area, which is described in conjunction with  FIG. 5 . For ease of illustration, only the FPC conductive pads  144  are shown.  
         [0047]     Referring to  FIG. 6A , the conductive pads  144  of the FPC are adhered to one end of the moisture-proof dielectric layer  123 . In the implementation shown, the conductive pads  144  of the FPC  140  are aligned to the respective exposed ends of the driving electrode pads P A  so that the FPC  140  and the moisture-proof dielectric layer  123  do not overlap each other. The line width of the conductive pads  144  of the FPC  140  is greater than that of the driving electrode pads P A . For instance, the line width W 1  of the conductive pads  144  may be greater than the line width W 2  of the driving electrode pads P A  by about 10 μm or more, or 20 μm or more, in at least one direction. As described above, the conductive pads  144  having a line width greater than that line width W 2  of the driving electrode pads are used, enabling the driving electrode pads P A  to be sufficiently covered by the conductive pads  144  of the FPC even when the conductive pads  144  of the FPC  140  and the driving electrode pads P A  are misaligned.  
         [0048]     As shown in  FIG. 6B , the driving electrode pads P A  are formed in the pad area of the rear panel  120 , and portions of the driving electrode pads P A  are covered with moisture-proof dielectric layer  123 .  
         [0049]     The FPC  140  is attached to exposed portions of the driving electrode pads P A , which are located beside the end of the moisture-proof dielectric layer  123 . The FPC  140  includes the plurality of conductive pads  144  that are formed on respective flexible resin films  142 . Each of the conductive pads  144  may be formed of a single-layered or multilayered film containing at least one of metal material made of Cu, Sn, Ni and/or Au, but which does not contain Ag. The FPC  140  may be a TCP or COF upon which driving ICs (not shown) are mounted for supplying driving signals to the driving electrode pads P A  through the conductive pads  144 . The FPC  140  and the driving electrode pads P A , as described above, are electrically connected with an intermediate layer, such as an ACF  146 , interposed therebetween.  
         [0050]     With reference to  FIG. 6A  again, in the pad structure, a mechanism for preventing electromigration caused by the driving electrode pads P A  is described below.  
         [0051]     First, portion A 1  of a driving electrode pad P A  protruding from the inner space of the panel to the outside is protected by the moisture-proof dielectric layer  123 . The moisture-proof dielectric layer  123  may be baked along with the baking of the dielectric layer formed on the address electrodes of the panel, and has a very compact and fine structure, which assists layer  123  insufficiently interrupting the penetration of moisture.  
         [0052]     Thereafter, Portion A 2  of the portions of the protruded driving electrode pad P A  is protected by the conductive pad  144  of the FPC, which is set to have a line width greater than that of the driving electrode pad P A . The electromigration caused by the driving electrode pad P A  occurs under a potential difference between neighboring driving electrode pads P A . Such potential differences are prevented or reduced by covering the driving electrode pad P A  completely with the conductive pads  144  of the FPC  140 , placing the conductive pads  144  into electrical contact with the driving electrode pad P A  to place the driving electrode pad P A  into an equipotential state relative to the conductive pad  144 . Accordingly, neighboring the driving electrode pads P A  do not undergo and potential difference, so that electromigration does not occur even when the penetration of moisture occurs.  
         [0053]     Finally, although a potential difference may occur between portions B of neighboring conductive pads  144 , the probability of the occurrence of electromigration is remarkably low in contrast to Ag or an Ag alloy because the conductive pads  144  are made of, for example, any of metal materials, such as Cu, Sn, Ni and Au, other than Ag, or an alloy containing one or more metal materials, or an alloy composed of a combination of the metal materials.  
         [0054]     As described above, the moisture-proof dielectric layer  123  is formed, or the line width of the conductive pads  144  is adjusted depending on the exposed portions of the pads, so that electromigration that might otherwise be caused by the portions of each pad protruding outside the panel can be restrained.  
         [0055]      FIG. 7A  is a plan view showing another example in which the conductive pads  144  of the FPC  140  are aligned in the panel pad area, which is described in conjunction with  FIG. 5 .  
         [0056]     Referring to  FIG. 7A , the conductive pads  144  of the FPC  140  are adhered to the end of the moisture-proof dielectric layer  123 . In this implementation, the FPC  140  is aligned and adhered so as to slightly overlap the moisture-proof dielectric layer  123 , unlike  FIG. 6A . The reason why the FPC is to be disposed so as to slightly overlap the moisture-proof dielectric layer is to prevent moisture from penetrating into a boundary surface between the conductive pads  144  and the moisture-proof dielectric layer  123 .  
         [0057]     The overlapping length of the conductive pads  144  of the FPC and the moisture-proof dielectric layer  123  can be greater then 0.5 mm. Furthermore, the overlapping range of the conductive pads  144  of the FPC  140  and the moisture-proof dielectric layer  123  may be appropriately designed in consideration of the loss of the drive voltage due to a parasite capacitance that occurs between the conductive pads  144  of the FPC  140  and the driving electrode pads P A  between which the moisture-proof dielectric layer  123  is interposed.  
         [0058]      FIG. 7B  is a sectional view showing a section of a contact portion between a conductive pad  144  and driving electrode pad P A  of  FIG. 7A . As shown in  FIG. 7B , the flexible resin film  142  and conductive pads  144  of the FPC  140  are formed such that a portion of the moisture-proof dielectric layer  123  formed on the driving electrode pad P A  is covered therewith. The ACP  146  described above is interposed between the conductive pads  144  of the FPC and the driving electrodes pad P A .  
         [0059]      FIG. 7C  is a sectional view showing a section taken along a line D-D′ of a contact portion of the conductive pad  144  and the driving electrode pad P A  of  FIG. 7A .  
         [0060]     Referring to  FIG. 7C , the driving electrode pad P A  formed on the rear panel  120  is electrically connected with the conductive pads  144 , and the ACF  146  is interposed therebetween. As shown in  FIG. 7C , an electrical connection between the two layers is made through metal balls distributed in the ACF  146 . Furthermore, it can be seen that the conductive pad  142  of the FPC  140  has a line width greater than that of the driving electrode pad P A  and thus surrounds the driving electrode pad P A .  
         [0061]     A method of implementing a PDP structure is described below, and method of manufacturing a PDP also is contemplated.  
         [0062]     First, when a front panel and a rear panel, each of which is formed of a transparent substrate, are provided, a pixel area, which is formed of a plurality of sub-pixels, and a sealed space, which surrounds the pixel area, are defined in the front panel and the rear panel. Thereafter, an electrode group, which is used to drive the sub-pixels, is formed on the front panel and/or the rear panel, and a plurality of driving electrode pads, which is used to supply power to the respective ends of electrodes constituting the electrode group, is formed outside the sealed space. Thereafter, a dielectric layer is formed such that the electrode group and the portions of the plurality of driving electrode pads are covered with the dielectric layer. In this case, the dielectric layer is formed such that the portions of the pads exposed outside the sealed space are covered with the dielectric layer. Thereafter, barrier ribs, which enable division into the plurality of sub-pixels, and phosphor layers are formed on the front panel or the rear panel, and the front panel and the rear panel are sealed by being bonded together. FPC pads are attached to respective driving electrode pads such that a portion of the dielectric layer is interposed between the plurality of driving electrode pads, which are exposed outside the sealed space, and the FPC pads in the pad area of the pane manufactured as described above.  
         [0063]     As described above, an effective panel structure for protecting the respective electrode pads of the exposed pad areas from external moisture can be achieved through the control of the extended length of the moisture-proof dielectric layer  123  and the line width of the conductive pads  144  of the FPC  140  with the division of the panel pad area, even if the size and resolution of the panel increase.  
         [0064]     In one implementation of the pane structure, the moisture-proof dielectric layer can be formed concurrent with (and integrated as part of the process of) the forming of the internal electrode dielectric layer of the panel, so that a separately added process is not required in order to form the moisture-proof dielectric layer. Furthermore, the moisture-proof dielectric layer formed as described above is just as compact as the electrode dielectric layer, so that it is suitable for protecting the electrode pads from moisture.  
         [0065]     Although various features have been disclosed for illustrative purposes, modifications, additions, and substitutions are possible.