Patent Publication Number: US-2005140297-A1

Title: Tubeless plasma display panel and manufacture of plasma display panel

Description:
FIELD OF THE INVENTION  
      The present invention generally relates to plasma display panels, and more particularly, to a system and method for manufacturing a plasma display panel.  
     DESCRIPTION OF THE RELATED ART  
      Generally, plasma display panels are used as large screen displays. Typically, plasma display panels are flat and provide better image quality compared to cathode ray tube displays. Plasma display panels include display cells filled with a discharge gas. Each display cell is coated with a light-emitting layer typically made of a phosphorous-based material. To produce an image in the plasma display panel, an electric bias is applied to select one or more display cells. Upon receiving the electrical bias, the discharge gas in the selected display cell emits ultraviolet rays. When ultraviolet rays strike the light-emitting layer of the selected display cell, the light-emitting layer produces a visible color light. The color of the visible light depends upon the composition of the phosphorous-based material of the light-emitting layer.  
       FIGS. 1A-1E  illustrate a known conventional process of manufacturing a plasma display panel  100 . Referring to  FIG. 1A , a plasma display panel  100  comprises two glass substrates, a front substrate  110  and a rear substrate  112  joined together to form a gap  120 . A tube  134  is mounted on the rear substrate  112  using beads of a sealing material  144   a . A vacuum nozzle  132  is coupled to the tube  134 . The vacuum nozzle  132  is configured to pump impurities out of the gap  120  and fill a discharge gas into the gap  120 . Referring to  FIG. 1B , display cells  114  are formed within the gap  120 . The display cells  114  are separated by partition walls  116 . Each display cell  114  includes a light-emitting layer  118  made from a phosphorus-based material. The layer  118  corresponds to a specific color of light emission.  
      The rear substrate  112  includes an opening  115  under the tube  134 . The front substrate  110  and the rear substrate  112  are joined together using a bead of sealing material  142   a . Typically, the sealing materials  142   a  and  144   a  comprises a mixture of glass frit and organic resin. The sealing materials  142   a  and  144   a  are heated to melt the glass frit and bum-off the organic resin. After the heating, the beads of sealing materials  142   a  and  144   a  convert into impermeable seals  142   b  and  144   b  respectively as shown in  FIG. 1C .  
      Referring to  FIG. 1D , unwanted gaseous impurities are initially removed from the gap  120  via the tube  134  using a vacuum pump (not shown) because for an efficient emission of ultraviolet rays from the discharge gas, the discharge gas must be clear of all impurities. Referring to  FIG. 1E , after removing gaseous impurities from the gap  120 , the discharge gas is filled into the gap  120  via the tube  134 . Referring to FIGURE IF, once the gap  120  is filled with a desired amount of discharge gas, the tube  134  is sealed to block discharge gas leakage. Typically, the tube  134  is cut using a melting process to sever the tube  134  from the vacuum nozzle  132  while sealing the tube  134 . Therefore, the plasma display panel  100  typically includes a protruding tip  136  over the rear substrate  112 . The protruding tip  136  is a remaining portion of the cut tube  134 .  
       FIG. 1G  is a temperature graph illustrating a change of temperature during the process of manufacturing the plasma display panel  100 . Initially, the temperature of the plasma display panel  100  is raised to a temperature T 1  during the time t 1  to form the impermeable sealing  144   b  between the front substrate  110  and the rear substrate  112 . After the impermeable sealing  144   b  is formed, the temperature of the plasma display panel  100  is lowered to a temperature T 2 . The gas pumping is then performed to remove impurities from the gap  120  during the time t 2 . The processing temperature is then reduced to fill the discharge gas in the gap  120 .  
      The plasma display panel  100  includes protruding tube tip  136 , which can be damaged during the transportation of the plasma display panel  100 . Further, the time required for evacuating the gaseous impurities from the gap  120  is typically long and non-uniform because the gaseous impurities must exit from the opening  115 . Therefore, there is a need for a system and method of manufacturing plasma display panels that can overcome the disadvantages of the conventional manufacturing process.  
     SUMMARY OF THE INVENTION  
      The present application describes a system and method for manufacturing a plasma display panel with substantially flat surfaces without tubular protrusions. The plasma display panel includes display cells formed between a front substrate and a rear substrate. Each display cell includes a light-emitting layer. The display cells are filled with a discharge gas before the front and rear substrates are sealed together. According to an embodiment, the display cells are filed with the discharge gas by placing the plasma display panel assembly including the front and rear substrates in an inner cavity of a processing chamber. The processing chamber is sealed after the assembly is placed into the inner cavity. The inner cavity of the processing chamber is then filled with the discharge gas and the discharge gas flows into the display cells through the lateral sides of the plasma display panel assembly. After the display cells are filed with the discharge gas, the front and rear substrates are sealed inside the inner cavity of the processing chamber and then removed from the processing chamber.  
      According to one embodiment, the processing chamber includes a base plate and a gas distribution plate. The base plate and the gas distribution plate are coupled together to form the inner cavity. After the plasma display panel assembly is placed inside the inner cavity, the base and gas distribution plates are sealed together before the inner cavity is filled with the discharge gas. The gas distribution plate includes an inlet hole for dispensing the discharge gas inside the inner cavity of the processing chamber. According to one embodiment, the base and gas distribution plates are made of a glass material.  
      The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A-1F  illustrate a conventional process of manufacturing a plasma display panel;  
       FIG. 1G  is a temperature graph illustrating a change of temperature during the conventional process of manufacturing the plasma display panel;  
       FIG. 2A  illustrates a processing chamber for manufacturing a plasma display panel;  
       FIG. 2B  shows an impermeable sealing formed between two plates of the processing chamber for manufacturing the plasma display panel;  
       FIG. 2C  illustrates a process of evacuating gaseous impurities from display cells formed between two substrates of the plasma display panel;  
       FIG. 2D  illustrates a process of filling a discharge gas inside the display cells of the plasma display panel;  
       FIG. 2E  illustrates a process of forming a sealing between two substrates of the plasma display panel;  
       FIG. 2F  illustrates a plasma display panel manufactured without protruding tube tips;  
       FIG. 2G  is a temperature graph illustrating the temperature of the processing chamber during the manufacturing of the plasma display panel;  
       FIG. 2H  is a pressure graph illustrating the internal pressure of the processing chamber during manufacturing of a plasma display panel;  
       FIG. 3  illustrates a processing chamber for manufacturing a plasma display panel using alternate sealing means between two plates of the processing chamber; and  
       FIG. 4  is a flowchart illustrating an exemplary sequence of steps performed during a process of manufacturing a plasma display panel. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S)  
       FIG. 2A  illustrates a processing chamber  200  for manufacturing a plasma display panel  270 . The processing chamber  200  includes a base plate  210  and a gas distribution plate  220 . The base plate  210  and the gas distribution plate  220  can be made from glass. The gas distribution plate  220  includes an opening  215 . The base plate  210  and the gas distribution plate  220  are coupled together via a sealing  225   a  to form a cavity  213 . The sealing  225   a  is initially deposited as a bead of a sealing material. In the present example, the sealing  225   a  comprises a crystallizing sealing material, which is heated to a sealing temperature to make the sealing impermeable. A gas flow tube  230  is mounted on the opening  215  of the gas distribution plate  220 . The gas flow tube  230  can be made from glass. A vacuum nozzle  240  is coupled to the gas flow tube  230 . The vacuum nozzle  240  can be connected to a gas supply unit (not shown) to provide the discharge gas and a gas-pumping unit (not shown) for removing gaseous impurities from the processing chamber  200 .  
      An assembly of a plasma display panel  270  is placed inside the cavity  213 . The assembly of the plasma display unit  270  includes a rear substrate  250  and a front substrate  260 . The rear substrate  250  and the front substrate  260  are coupled together with a sealing  252   a . The sealing  252   a  is initially deposited as a bead of a sealing material. In the present example, the sealing  252   a  comprises a crystallizing sealing material, which is heated to a sealing temperature to make the sealing impermeable. The sealing temperature of the sealing material  252   a  is higher than the sealing temperature of the sealing material  225   a . Display cells  255  are formed between the rear substrate  250  and the front substrate  260 . The display cells  255  are separated by rib barriers  256 . Each display cell  255  includes a light-emitting layer  257  made of a phosphorous-based material. The sealing material  252   a  is placed at the periphery of an area enclosing the display cells  255 . The sealing material  252   a  is heated to a sealing temperature to make the sealing between the two plates impermeable.  
       FIG. 2B  shows a sealing formed between two plates of the processing chamber  200 . Initially, the bead of sealing material  225   a  joining the base plate  210  and the gas distribution plate  220  is heated to its sealing temperature to make an impermeable seal  225   b . The impermeable seal  225   b  hermetically seals the cavity  213 . Because the sealing temperature of the sealing material  252   a  is higher than the sealing temperature of the sealing material  225   a , the sealing material  252   a  remains unchanged.  
       FIG. 2C  illustrates a process of evacuating gaseous impurities from display cells formed between two substrates of the plasma display panel  270 . A gas pump (not shown) removes gaseous impurities from the display cells  255  via the glass tube  230 . Because the rear substrate  250  and the front substrate  260  of the plasma display panel  270  are not sealed together, more gaseous impurities can evacuate from the lateral sides of the plasma display panel  270 , which results in an enhanced emission of light from the light-emitting layers  257 . The evacuation of gaseous impurities is accomplished more efficiently and faster than the conventional manufacturing process.  
       FIG. 2D  illustrates a process of filling discharge gas in display cells of the plasma display panel  270 . The discharge gas can be a gaseous mixture of inert gases including Xenon (Xe), Neon (Ne), or Helium (He). After gaseous impurities have been removed from the display cells  255 , the discharge gas is filled into the display cells  255  through the gas tube  230 . Because the rear substrate  250  and the front substrate  260  of the plasma display panel  270  are not sealed together, the discharge gas flows into the display cells  255  from the lateral sides of the plasma display panel  270  within the processing chamber  200 . The display cells  255  are filled with the discharge gas faster and more efficiently than the conventional plasma display manufacturing process.  
       FIG. 2E  illustrates a process of forming a sealing between the rear substrate  250  and the front substrate  260  of the plasma display panel  270 . After the display cells  255  are filed with the discharge gas, the processing chamber  200  is heated to a sealing temperature of the sealing material  252   a  to seal the substrates of the plasma display panel  270 .  
       FIG. 2F  illustrates the plasma display panel  270  manufactured without a protruding tube tip. When the temperature inside the processing chamber  200  reaches the sealing temperature of the sealing material  252   a , the sealing material  252   a  is converted into an impermeable seal  252   b , which hermetically confines the discharge gas within the display cells  255 . After the front and rear substrates of the plasma display panel  270  are sealed together, the plasma display panel  270  can be removed from the processing chamber  200 . The substrates  250  and  260  are free of tubes, tubular portions, gas channel, or equivalent structures. The plasma display panel  270  has a substantially flat rear surface, which is free of tubular protrusions.  
       FIG. 2G  is a temperature graph illustrating the temperature of the processing chamber  200  during the manufacturing of the plasma display panel  270 . Initially, the processing chamber is heated during the time t 1  to a temperature T AS , which is the sealing temperature of the sealing material  225   a  of the processing chamber  200 . The temperature T AS  can be determined by the manufacturer of the sealing material  225   a  based on the composition of the sealing material. After the sealing material  225   a  is converted into an impermeable seal  225   b , the temperature of the processing chamber is reduced to a filling temperature T E  during the time t 2 .  
      When the temperature of the processing chamber reaches the filling temperature T E , gaseous impurities are removed from the processing chamber  200  and the discharge gas is filled into the display cells  255 . The filling temperature T E  can be determined according to the properties of the discharge gas mixture used for the display cells. After the display cells are filled with the discharge gas, the processing chamber  200  is heated during the time t 3  to a temperature T BS , which is the sealing temperature of the sealing material  252   a . The sealing material  252   a  is used to seal the rear substrate  250  with the front substrate  260  of the plasma display panel  270 . The sealing temperature T BS  can be determined by the manufacturer of the sealing material  252   a  based on the composition of the sealing material  252   a . After the sealing material  252   a  is converted into an impermeable seal  252   b , the temperature of the processing chamber is reduced to an ambient temperature RT and the plasma display panel  270  is removed from the processing chamber  200 .  
       FIG. 2H  is a pressure graph illustrating the internal pressure of the processing chamber  200  during the manufacturing of the plasma display panel  270 . When the display cells  255  are substantially filled with the discharge gas, the internal pressure of the processing chamber  200  reaches a predetermined pressure P gas . After the sealing material  252   a  is converted into an impermeable seal  252   b  and the temperature of the processing chamber  200  reaches the ambient temperature RT, the internal pressure of the processing chamber normalizes at pressure P 2 . The pressure P gas  can be determined according to various factors such as, for example, a size of the plasma display panel  270 , a number of display cells  255  within the plasma display panel  270 , a type of gaseous mixture used for the discharge gas, and the like.  
       FIG. 3  illustrates a processing chamber for manufacturing a plasma display panel using alternate sealing means between two plates of a processing chamber  300 . The processing chamber  300  includes a base plate  310  and a gas distribution plate  312 . The base plate  310  and the gas distribution plate  312  can be made from glass. The gas distribution plate  312  includes an opening  315 . The base plate  310  and the gas distribution plate  312  are coupled together via a sealing  314  to form a cavity  316 . A plasma display panel  370  is placed inside the cavity  316 . The plasma display panel  370  includes a front substrate  330  and a rear substrate  320  joined together with a sealing  325 . The front substrate  330  and the rear substrate  320  form display cells  355 . Each display cell includes a light-emitting layer  357 .  
      In the present example, the sealing  314  is an O-ring type fastener that can be desirably fastened and detached from the base plate  310  and the gas discharge plate  312 . The sealing  314  is reusable. The reusable sealing  314  results in a simple and economical manufacturing process because the deposition and heating of the sealing material  314  is not required during the gas-filling process for each plasma display panel.  
       FIG. 4  is a flowchart illustrating an exemplary sequence of steps performed during a process of manufacturing a plasma display panel. For purposes of illustration, various steps are described in particular order, however, when supported by accompanying system elements, these steps can be performed in any order, serially or in parallel. Initially, a plasma display panel assembly is placed in a processing chamber ( 410 ). The processing chamber can include various types of sealing means for the base plate and the gas distribution plate as described previously herein. Next, it is determined whether the plates of the processing chamber require sealing ( 420 ). If plates of the processing chamber require sealing, then plates are sealed ( 430 ) for example, by increasing the internal temperature of the processing chamber to a sealing temperature of the sealing material used to join plates.  
      If plates of the processing chamber do not require sealing, then gaseous impurities from the plasma display panel are evacuated ( 440 ). A discharge gas is then filed into the plasma display panel ( 450 ). The plasma display panel is then sealed ( 460 ). The plasma display panel can be sealed, for example, by increasing the internal temperature of the processing chamber to a sealing temperature of the sealing material used to join the front substrate and the rear substrate of the plasma display panel. The plasma display panel is then removed from the processing chamber ( 470 ). The plasma display panels manufactured using the process described herein have a substantially flat rear surface, which is free of tubular protrusions.  
      Realizations in accordance with the present invention have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of claims that follow. Finally, structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow.  
      The section headings in this application are provided for consistency with the parts of an application suggested under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any patent claims that may issue from this application. Specifically and by way of example, although the headings refer to a “Field of the Invention,” the claims should not be limited by the language chosen under this heading to describe the so-called field of the invention. Further, a description of a technology in the “Description of Related Art” is not be construed as an admission that technology is prior art to the present application. Neither is the “Summary of the Invention” to be considered as a characterization of the invention(s) set forth in the claims to this application. Further, the reference in these headings to “Invention” in the singular should not be used to argue that there is a single point of novelty claimed in this application. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this patent specification, and the claims accordingly define the invention(s) that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification but should not be constrained by the headings included in this application.