Patent Publication Number: US-6661169-B2

Title: Rear plate of a plasma display panel and method for forming plasma display panel ribs

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a plasma display panel (PDP). In particular, the present invention relates to a rear plate of a PDP and the method for forming ribs thereon. 
     2. Description of the Related Art 
     Recently, a variety of flat panel displays, such as a liquid crystal display (LCD) and a plasma display panel (PDP) have been intensively developed to replace cathode ray tube (CRT) displays. In PDP technololgy, an ultraviolet light is emitted to excite the RBG phosphors to produce visible lights. The advantages of the PDP include a large display area, wide viewing angle, and intense brightness. 
     The PDP has a front plate and a rear plate spaced apart to each other with the peripheries thereof sealed. In general, the PDP includes barrier ribs for partitioning the discharge spaces. The barrier ribs prevent discharge coupling and color cross-talk between adjacent cells. The traditional method for forming the ribs is described hereafter with FIGS. 1A and 1B. 
     As shown in FIG. 1A, the address electrodes  12  are formed on the glass substrate  10 . The dielectric layer  14  is formed to protect the address electrodes  12  after sintering. The rib material layer  16  is formed on the dielectric layer  14 . The dry film is laminated on the rib material layer  16 . After exposing and developing, the dry film  18  is patterned as shown in FIG.  1 A. 
     Referring to  1 B, the rib material layer  16  is patterned by sandblasting to form the ribs  16   a.    
     In the above-mentioned traditional processes, the dielectric layer  14  under the ribs  16   a  is used to protect the address electrodes  12  from damage in the sandblasting step. A sintering step is needed after forming the dielectric layer  14 , the manufacturing time is longer and the manufacturing cost is increased. Moreover, the height of the ribs  16   a  is about 100˜200 μm, therefore the sandblasting time is too long to keep the uniformity of the bottom width and the profiles of the ribs  16   a . If the lateral action between the sands and the rib material is strong in the sandblasting step, the bottom area of the ribs  16   a  will be small. The size of the ribs  16   a  affects the size of the discharging cell and the strength of the ribs  16   a . If the width of the ribs  16   a  is narrowed, the space of the discharging cell is increased so that the coating yield of the phosphors is enhanced. Therefore, the brightness is enhanced and the consumption of power is reduced. When the width the ribs  16   a  is too smaller, the strength of the ribs  16   a  is also reduced. The height of the ribs  16   a  is very high now, if the width of the ribs  16   a  is further reduced or the height is further increased, the stability of the ribs  16   a  is damaged and these ribs  16   a  may collapse. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for fabricating ribs of a PDP. In this method, one sintering step can be eliminated, the width of the rib and the profile of the ribs can all be effectively controlled, and the space of the discharging cell can be increased without damaging the stability of the rib. 
     The present invention provides a method for forming PDP ribs. First, a plurality of address electrodes and base plates are formed on the glass substrate. The address electrodes and the base plates alternate with each other, and a predetermined distance is formed between each address electrode and each base plate. A rib material layer is formed above the address electrodes, the base plates and the glass substrate. A patterned mask layer is formed on the rib material layer. The rib material layer is sandblasted to form a plurality of ribs accord to the pattern of the base plates. The shape of the base plates can be changed on demand so the structure of the ribs can be changed. Alternatively, a passivative film can be formed on the address electrodes to prevent from damage in the sandblasting step. 
     The present invention also provides a rear plate of the plasma display panel (PDP). The rear plate includes a glass substrate, a plurality of address electrodes, a plurality of base plates, and a plurality of ribs. The address electrodes and the base plates alternate with each other and are parallel to each other. There is a predetermined distance between each address electrode and each base plate. The ribs are disposed on the base plates, and the bottom width of each rib is the same as that of each base plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given herein and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the present invention. 
     FIGS.  1 A˜ 1 B depict the method for fabricating the ribs of the PDP in the prior art; 
     FIGS.  2 A˜ 2 D depict the method for forming the ribs of PDP according to the present invention; and 
     FIG. 3 depicts the top view of a rib in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the present invention, the rear plate of the PDP includes the glass substrate  100 , the address electrodes  102   a , the base plates  102   b , and the ribs  106   a , as shown in FIG.  2 D. The address electrodes  102   a  and the base plates  102   b  are formed in the same process, and arranged in parallel and alternate with each other. A predetermined distance is defined between each address electrode  102   a  and each base plate  102   b . The ribs  106   a  are disposed above the base plates  102   b . Each rib has a bottom width and each base plate has a base width, and the bottom width of each rib  106   a  is the same as the base width of the base plate  102   b . Alternatively, the passivative film  104   a  can be formed on the address electrodes  102   a.    
     A detailed description of the method for forming the above-mentioned ribs of PDP is given hereafter with reference to FIGS.  2 A˜ 2 D. 
     Referring to FIG. 2A, the address electrodes  102   a  and the base plates  102   b  are formed on the glass substrate  100 . The address electrodes  102   a  and the base plates  102   b  can be made by the same process and the same material. Specifically, the material used to form the address electrodes  102   a  or the base plates  102   b  includes conductive material, such as silver (Ag), photosensitive polymer, and glass frit for forming the rib. The address electrodes  102   a  and the base plates  102   b  can be patterned by exposing once or twice, then developing and sintering. The temperature of the sintering step is about 500˜550° C. The predetermined distance d between each address electrode  102   a  and each base plate  102   b  is about 20˜50 μm. The base width of each base plate  102   b  is about 140˜150 μm. 
     Note that the base plates  102   b  are floating although the base plates  102   b  are formed by the conductive material. 
     With Reference to FIG. 2B, passivative film  104  is laminated on the glass substrate  100 , address electrodes  102   a  and base plates  102   b  with a thickness of 5˜15 μm. The material used to form the passivative film  104  incldues a photosensitive material and a dielectric material. 
     With Reference to FIG. 2C, after the passivative film  104  is exposed and developed, the passivative films  104   a  only cover the address electrodes  102   a . Alternatively, the passivative film  104   a  can be formed by directly screen-printing the organic binder on the address electrodes  102   a . Moreover, if the sandblasting process is controlled well, the passivative film  104   a  can be omitted. 
     The rib material layer  106  having a predetermined thickness is further formed on the glass substrate  100 , the passivative film  104   a  and the base plates  102   b . The patterned mask layer  108  is formed on the rib material layer  106 . The thickness of the patterned mask layer  108  is about 30˜100 μm. For example, the patterned mask layer  108  can be formed by laminating the photosensitive dry film on the rib material layer  106 , then the photosensitive dry film is patterned by exposing and developing. 
     The sandblasting process is conducted to pattern the rib material layer  106  and removes the parts of the rib material  106  uncovered by the patterned mask layer  108  to form the ribs  106   a . The patterned mask layer  108  is then removed. The rear plate of the PDP is thus formed. 
     It should be noted that the bottom width of the bottom  106 ″ of the rib  106   a  is decided by the base width of each base plate  102   b . The roughness of the base plate surface is larger than the roughness of the glass substrate surface because the base plates  102   b  is composed of conductive materials. The adhesion between the rib material layer  106  and the base plates  102   b  is better than the adhesion between the rib material layer  106  and the glass substrate  100 . The part of the rib material layer  106  located on the glass substrate  100  is easily removed in the sandblasting process. Therefore, the bottom width of the bottom  106 ″ of the rib  106   a  equals the base width of each base plate  102   b . The top width of the top  106 ′ of the rib  106   a  is decided by the patterned mask layer  108 . Therefore, the top width of the top  106 ′ and the bottom  106 ″ of each rib  106   a  can be adjusted on demand. 
     Moreover, the bottom width of the bottom  106 ″ of the rib  106   a  can be altered by the shape of the base plate  102   b . The base plate  102   b  can be the traditional straight shape or the zigzag shape, as shown in FIG.  3 . In FIG. 3, the central width of the base plate  102   a  is reduced, the discharging space of each discharging cell  110  is then increased, thus the luminescent efficiency is enhanced. The brightness of the PDP is further enhanced and electric power is saved. 
     According to the present invention, no dielectric material is needed above the address electrodes. Instead, the passivative film on the address electrodes is just a dry film, no sintering process is needed. Therefore, the sintering step for sintering the dielectric layer on the address electrodes can be eliminated, resulting in a decrease in costs and enhancement of the performance of the PDP. 
     Further, the ribs can be shaped by adjusting the base plates under the rib material layer. 
     Furthermore, the discharging space of each discharging cell can be increased by shaping the base plates. Parts of the rib are narrowed to increase discharging space, thereby enhancing the brightness of the PDP and conserving electric power without sacrificing the stability of the ribs. 
     Moreover, the bottom width of each rib is adjusted by each base plate, and the top width of each rib is adjusted by the patterned mask layer. Therefore, it is easy to alter the shape of the ribs, and the processes are flexible. 
     While the present invention is described by preferred embodiments, it should be understood that the invention is not limited to these embodiments in any way. On the contrary, it is intended to cover all the modifications and arrangements as they would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be interpreted in the broadest sense so as to encompass all the modifications and arrangements.