Patent Publication Number: US-6034475-A

Title: Plasma display with specific thermal expansion coefficients for substrate ribs and dielectric layer

Description:
BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to a composition of and method of manufacturing a plasma display panel. 
     B. Description of Prior Art 
     The prior art will be described with reference to FIGS. 1 and 2. The conventional printing technique, used for the manufacture of a plasma display panel, controls the ratio of temperature rise/drop only, having no consideration for thermal expansion coefficients of paste materials used therefor, which takes time and entails cracks in materials forming the interior of the panel because of sudden variation of temperature. After firing the barrier ribs, the bottom parts of the barrier ribs 3 on a dielectric layer 4 are broken into scale-like pieces, or the barrier ribs 3 are broken off at the middle part. 
     Since the manufacture of the lower panel of a plasma display requires a lot of firing steps, the optimum thermal expansion coefficient for each material should be taken into account from production yield aspect. 
     The conventional art will be described in greater detail. A glass 1 is first cleanly washed by a wet-cleaning equipment, and address electrodes 2 are formed on the glass 1 by a printing technique by the use of Ag paste and a screen mask. After that, drying and firing are performed with respect thereto. The thermal expansion coefficient of the glass 1 equals 76×10 -7  /° C. In the formation of the barrier ribs 3, a thermal expansion coefficient of the material forming the barrier ribs 3 equals 86×10 -7  /° C. The barrier ribs 3 are formed to a height of 150 μm by repeatedly performing printing and drying processes about 10 times, and, as shown in FIG. 2, the resultant material is fired for 60 minutes at 580° C. It takes four hours and fifty minutes to make the temperature rise, and that is, the temperature rises by 2° C. a minute. Making the temperature drop takes nine hours and thirty minutes, and the temperature drops by 1° C. a minute. The overall time required for the firing is 15 hours and twenty minutes, thus lowering the production yield. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a composition of and method of manufacturing a plasma display panel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     It is an object of the present invention to provide a composition of a plasma display panel which can eliminate defects such as cracks and reduce the time required for firing, with selection of an optimum thermal expansion coefficient for each material of the composition and optimum arrangement of those materials. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a plasma display panel including a glass substrate having a first thermal expansion coefficient; a dielectric layer over the glass substrate, wherein the dielectric layer has a second thermal expansion coefficient less than the first thermal expansion coefficient; and one or more barrier ribs over the dielectric layer, wherein the barrier ribs have a third thermal expansion coefficient greater than the second thermal expansion coefficient. 
     The invention further comprises a method of manufacturing a plasma display panel, including forming a glass substrate having a first thermal expansion coefficient; forming a dielectric layer over the glass substrate, wherein the dielectric layer has a second thermal expansion coefficient less than the first thermal expansion coefficient. The method further includes forming one or more barrier ribs over the dielectric layer, wherein the barrier ribs have a third thermal expansion coefficient greater than the second thermal expansion coefficient. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     FIG. 1 depicts a conventional plasma display panel with defects. 
     FIG. 2 is a firing profile of a conventional barrier rib. 
     FIG. 3 is a firing profile of a barrier rib in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     In the manufacture of a plasma display panel, the present invention reduces the time required for firing by finding out the interaction of materials through selection of an optimum thermal expansion coefficient for each material and several tests, thus having an advantageous yield aspect. 
     A window glass 1 is thoroughly washed by a wet-cleaning equipment, and printing is performed with respect to the window glass 1. In printing after drying and firing, the first test employs a glass with a thermal expansion coefficient of 85×10 -7  /° C., as shown in Table 1 (showing the result of thermal expansion coefficient test). A dielectric layer with a thermal expansion coefficient of 81×10 -7  /° C., is formed over the electrodes to a thickness of 20 to 30 μm, and goes under drying and firing, and then the barrier ribs are formed. 
     The glass, the dielectric layer and the barrier ribs of the prior art and of the present invention are of a generic glass type, and have SiO 2 , Al 2  O and PbO as main ingredients. In addition, materials such as CaCo 3  and TiO 2  are added to these main ingredients to impart varying thermal expansion coefficients. The materials used in the embodiment of the present invention were obtained from Japanese glass manufacturers, such as Noritake and Ashai Glass. 
     It is quite difficult and complicated to manufacture the barrier ribs, and a 10-time deposition printing must be carried out to form a thick layer of 150 μm. A thermal expansion coefficient of the material forming the barrier ribs is 85×10 -7  /° C., and is the same as that of the glass. 
     
                       TABLE 1                                                     
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Test for Thermal Expansion Coefficient of Each Material                   
                            Thermal                                       
Test Number                                                               
          Material                                                        
                       *TEC      expansion                                
                                     Result                               
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1       Glass    85 × 10.sup.-7 /° C.                        
                            large   No defect                             
                    81 × 10.sup.-7 /° C.                     
                              small                                       
                           85 × 10.sup.-7 /° C.              
                              large                                       
2                        75 × 10.sup.-7 /° C.                
                              small            Defect occurs              
                    85 × 10.sup.-7 /° C.                     
                              large                                       
                           85 × 10.sup.-7 /° C.              
                              large                                       
3                        85 × 10.sup.-7 /° C.                
                              large            Defect occurs              
                    80 × 10.sup.-7 /° C.                     
                              medium                                      
                           75 × 10.sup.-7 /° C.              
                              small                                       
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 *TEC: Thermal expansion coefficient                                      
 
    
     FIG. 3 shows a firing temperature profile during drying and firing after printing of the barrier ribs 3. The starting temperature is about 20° C., and the rate of temperatures rise/temperature drop is approximately 7° C./min, and the temperature is maintained at about 580° C. for about 60 minutes, thus reducing the time required for firing to about three hours and thirty minutes. As a result, no defect is found in the panel, and, particularly, there is no minute crack between the barrier ribs 3 and the dielectric layer 4. According to the trend of the thermal expansion coefficients of the materials, the printing is carried out so as to deposit materials on the glass substrate in the order of large, small and large thermal expansion coefficients. 
     In the second test shown in Table 1, a lower panel is manufactured in the same manner as in the first test, and the materials to be deposited have different thermal expansion coefficients. According to the trend of the thermal expansion coefficients of the materials, the printing is carried out to deposit materials on the substrate in the order of small, large and large thermal expansion coefficients, and after the firing work is performed for three hours and thirty minutes, significant defects occur, thus failing to manufacture a defect-free lower panel. 
     In the third test, deposition printing is carried out in the same manner as in the second test, and, as shown in Table 1, materials with different thermal expansion coefficients are used. That is, a thermal expansion coefficient of the glass is 85×10 -7  /° C., while that of the dielectric layer is 80×10 -7  /° C. The thermal expansion coefficient of the material used for the barrier ribs is 75×10 -7  /° C. The firing temperature is the same as that of the respective first and second tests, and a lower panel is not properly manufactured under the condition of the third test. Materials are deposited in the order of large, medium and small thermal expansion coefficients. 
     In conclusion, the present invention employs the optimum thermal expansion coefficient for each material during deposition printing for the manufacture of a lower panel of a plasma display, thus reducing the time required for the firing (fifteen hours, conventionally) to about three hours. According to the present invention, the deposition mechanism which may eliminate occurrence of cracks is shown in Table 2. 
     
                       TABLE 2                                                     
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Arrangement of Material of Thermal Expansion Coefficients                 
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Barrier rib   84˜87 × 10.sup.-7 /° C.                  
Dielectric layer                                                          
                   80˜83 × 10.sup.-7 /° C.             
Glass                         84˜87 × 10.sup.-7 /°     
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              C.                                                          
 
    
     It will be apparent to those skilled in the art that various modifications and variations can be made in the composition of a plasma display panel of the present invention without departing from the spirit or scope of the invention. Thus, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.