Patent Publication Number: US-8537301-B2

Title: Method of fabricating bottom chassis, bottom chassis fabricated by the method of fabricating the same, method of fabricating liquid crystal display, and liquid crystal display fabricated by the method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0001945 filed on Jan. 8, 2010, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary embodiments of the present invention relates to a bottom chassis, and is a method of fabricating a bottom chassis of a liquid crystal display (LCD). 
     2. Description of the Background 
     Liquid crystal displays (LCDs) have been adopted as one of the most widely used flat panel displays applicable to various electronics devices due to their low power consumption, low weight, thin structure, and high resolution. 
     An LCD typically includes a liquid crystal panel having two substrates and a liquid crystal layer interposed between the two substrates and displaying an image, a backlight unit irradiating light onto the liquid crystal panel, and a bottom chassis that can be disposed below the liquid crystal panel and the backlight unit to receive the liquid crystal panel and the backlight unit. The bottom chassis also dissipates heat from a light source, acts as a ground, and intercepts electromagnetic waves. 
     However, a conventional steel plate used to manufacture a bottom chassis may not have sufficient strength if the bottom chassis is too thin. To increase the strength of a bottom chassis, a steel plate that is thicker than 1 mm has mostly been used, which makes the bottom chassis bulky and thick as compared to other components of the LCD. Thus, there is a limited ability to reduce the overall thickness and weight of an LCD having a conventional thick bottom chassis. The above conventional bottom chassis may have a number of drawbacks. For example, it may be vulnerable to contamination from operator&#39;s fingerprints or affected by contaminants during an assembling process of manufacturing an LCD. 
     Thus, there is a need for an approach to make a thin, a high strength bottom chassis that can be suitable to achieve a slim, lightweight LCD and while also being a contaminant proof chassis. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a method of fabricating a bottom chassis formed using a new steel plate having a high contamination resistance while having a strength even with a small thickness, and providing a high-yield assembly by determining optimum factors affecting a tapping torque during a process and forming a burring part into which a screw can be inserted for engaging an object to the steel plate. 
     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. 
     Exemplary embodiments of the present invention disclose a method for fabricating a bottom chassis. The method includes forming a chassis using a steel plate having a thickness in the range of about 0.5 mm to 0.9 mm. The steel plate has a stack structure comprising an inner layer, an electro-galvanized layer formed on the inner layer, and a polymer chromium (Cr)-free contamination resistant layer formed on the electro-galvanized layer. The inner layer comprises approximately 0.001 to 0.1 weight percent (wt. %) carbon (C), approximately 0.002 to 0.05 wt. % silicon (Si), approximately 0.28 to 2.0 wt. % manganese (Mn), iron (Fe), and other impurities. The method also includes providing a burring part by performing a burring process and a tapping process on the chassis for inserting a bolt for an engagement. 
     Exemplary embodiments of the present invention disclose a chassis. The chassis includes a steel plate having a thickness in the range of approximately 0.5 mm to 0.9 mm. The steel plate has a stack structure comprising an inner layer containing approximately 0.001 to 0.1 is weight percent (wt. %) carbon (C), approximately 0.002 to 0.05 wt. % silicon (Si), approximately 0.28 to 2.0 wt. % manganese (Mn), balance iron (Fe), and other impurities. An electro-galvanized layer is formed on the inner layer, and a polymer chromium (Cr)-free contamination resistant layer is formed on the electro-galvanized layer. The chassis comprises a burring part formed to receive a bolt for an engagement. 
     Exemplary embodiments of the present invention disclose a method of fabricating a liquid crystal display (LCD). The method includes providing a bottom chassis having a thickness in the range of about 0.5 mm to 0.9 mm. The bottom chassis has a stack structure comprising an inner layer containing about 0.001 to 0.1 weight percent (wt. %) carbon (C), about 0.002 to 0.05 wt. % silicon (Si), about 0.28 to 2.0 wt. % manganese (Mn), balance iron (Fe), and other impurities. An electro-galvanized layer is disposed on the inner layer, and a polymer chromium (Cr)-free contamination resistant layer is disposed on the electro-galvanized layer. A burring part is provided to receive a bolt to engage an object with the burring part via a hole formed in the object. 
     Exemplary embodiments of the present invention disclose a liquid crystal display. The liquid crystal display includes a bottom chassis having a thickness in the range of about 0.5 mm to 0.9 mm. The bottom chassis has a stack structure comprising an inner layer containing about 0.001 to 0.1 weight percent (wt. %) carbon (C), about 0.002 to 0.05 wt. % silicon (Si), about 0.28 to 2.0 wt. % manganese (Mn), balance iron (Fe), and other impurities. An electro-galvanized layer is disposed on the inner layer, and a polymer chromium (Cr)-free contamination resistant layer disposed on the electro-galvanized layer. The bottom chassis comprises a burring part formed to engage an object with the burring part via a hole formed in the object. 
     It is to be understood that both the foregoing general description and the following is detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a perspective view of a liquid crystal display (LCD) according to exemplary embodiments of the present invention. 
         FIG. 2  is a cross-sectional view of a steel plate used as a bottom chassis shown in  FIG. 1  in a vertical direction. 
         FIG. 3  is a perspective view of a bottom chassis fabricated according to exemplary embodiments of the present invention. 
         FIG. 4  is an enlarged cross-sectional view taken along line A-A′ of  FIG. 3 . 
         FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9  are cross-sectional views for illustrating a method of fabricating the bottom chassis shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Advantages and features of the present invention can be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, is these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. Accordingly, in some specific embodiments, well known processing steps, devices or methods or redundant parts can be omitted in order to avoid unnecessarily obscuring the invention. 
     It is understood that when an element or layer is referred to as being “on,” or “connected to” another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It is understood that, although the terms of a numerical term such as a first, second, third, they may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these numerical terms. These terms are merely used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, an element, a component, a region, a layer or a section designated as a “first” discussed below could be interpreted as an element, a component, a region, a layer or a section designated as a “second” without departing from the teachings of the present invention. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context is clearly indicates otherwise. It is also understood that the terms “comprises” and/or “comprising,” when used in this specification, can specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It is also noted that terms related to spatially relative terms, such as “below,” “beneath,” “lower,” “above,” “upper”—these terms may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It is understood that the spatially relative terms are intended to show different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” or “on” with respect to the other elements or features. Thus, the term “under” can be interpreted to encompass both an orientation of above and below. The device may be otherwise oriented and the spatially relative descriptors used herein can be interpreted accordingly. 
     Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings. 
       FIG. 1  is a perspective view of a liquid crystal display (LCD)  100  according to exemplary embodiments of the present invention.  FIG. 2  is a cross-sectional view of a steel plate used as a bottom chassis shown in  FIG. 1  in a vertical direction. The bottom chassis in  FIG. 1  can be fabricated by a molding process of a steel plate which has a cross-section view as seen in  FIG. 2 . 
     Referring to  FIG. 1 , the LCD  100  may include a liquid crystal panel  110 , a backlight unit  120 , a bottom chassis  130 , and a top chassis  140 . 
     The liquid crystal panel  110  can display an image and may have a liquid crystal layer (not shown) interposed between a pair of substrates (not shown). One of the pair of substrates has thin-film-transistors (TFTs) to control liquid crystals and pixels that can be the smallest units of a screen. The other substrate may have a color filter with three, i.e., red (R), green (G), and blue (B) pixels coated onto a glass plate and realizing an image. 
     The backlight unit  120  can be disposed behind the liquid crystal panel  110  and can provide light to the liquid crystal panel  110 . Although not shown in  FIG. 1  and  FIG. 2 , the backlight unit  120  may include a light source, a reflection sheet, an optical plate such as a light guide plate or a diffusion sheet, and other optical sheets. 
     In some examples, the bottom chassis  130  can be disposed below the liquid crystal panel  110  and the backlight unit  120  and may receive the liquid crystal panel  110  and the backlight unit  120 . To provide a space for receiving the liquid crystal panel  110  and the backlight unit  120 , the bottom chassis  130  may comprise a bottom surface and side walls. 
     The top chassis  140  can be combined with the bottom chassis  130  and may define an effective display area of the liquid crystal panel  110 . 
     As described above, the bottom chassis  130  can be fabricated using the steel plate of  FIG. 2 . The steel plate has a resistance against contaminations and a high strength even though it is thin. The steel plate is described in detail below with reference to  FIG. 2 . 
     Referring to  FIG. 2 , the steel plate can be used for making the bottom chassis  130  having a stack structure in which an inner layer  210 , an electro-galvanized layer  220 , and a polymer chromium (Cr)-free contamination resistant layer  230  (to be referred to as a “contamination resistant layer”) can be stacked. 
     Upon the fabrication of the bottom chassis  130  using the steel plate, the inner is layer  210  on one side of the steel plate can be disposed in a direction to which the backlight unit  120  is received while the contamination resistant layer  230  on the other side can be disposed to an opposite direction to which the backlight unit  120  is received. Thus, the bottom chassis  130  may have the inner layer  210  at an inside surface, the contamination resistant layer  230  at an outside surface, and the electro-galvanized layer  220  interposed between the inner layer  210  and the contamination resistant layer  230 . 
     It is contemplated that the inner layer  210  may contain about 0.001 to 0.1 weight percent (wt. %) carbon (C), about 0.002 to 0.05 wt. % silicon (Si), about 0.28 to 2.0 wt. % manganese (Mn), balance iron (Fe), and other impurities. 
     For example, C can be added to provide a sufficient strength of the inner layer  210 . The C content may be in the range of about 0.001 to 0.1 wt. %. If the C content is less than about 0.001 wt. %, the inner layer  210  may not have a sufficient strength. If the C content is greater than about 0.1 wt. %, the inner layer  210  has a limited weldability and a low toughness. 
     Si can be added to obtain a sufficient strength due to solid-solution strengthening. The Si content may be in the range of about 0.002 to 0.05 wt. %. If the Si content is less than about 0.002 wt. %, a solid-solution strengthening effect of the inner layer  210  can be reduced. If the Si content is greater than about 0.05 wt. %, an interface oxide layer can be formed to degrade a surface quality. 
     The Mn can be added to obtain a sufficient strength and a high processibility of the inner layer  210 . The Mn content may be in the range of about 0.28 to 2.0 wt. %. If the Mn content is less than about 0.28 wt. %, it may be difficult to obtain a sufficient strength and high processibility. If the Mn content is greater than about 2.0 wt. %, heterogeneity may occur due to Mn segregation. 
     Other impurities in the inner layer  210 , for example, may include less than about 0.1 wt. % phosphorous (P), less than about 0.008 wt. % sulfur(S), about 0.01 to 0.03 wt. % chromium (Cr), about 0.007 to 0.015 wt. % nickel (Ni), about 0.001 to 0.004 wt. % molybdenum (Mo), about 0.043 to 0.045 wt. % aluminum (Al), about 0.02 to 0.04 wt. % copper (Cu), about 0.0017 to 0.0018 wt. % tin (Sn), less than about 0.004 wt. % oxygen (O), and less than about 0.003 wt. % nitrogen (N). If necessary, the impurities may further contain about 0.0075 to 0.0083 wt. % niobium (Nb) and about 0.0306 to 0.0310 wt. % titanium (Ti). 
     Referring to  FIG. 2 , the electro-galvanized layer  220  can be formed on the inner layer  210  by plating coatings of about 10 to 30 g/m 2  thereon. For example, electro-galvanization may be performed by plating coatings of about 20 g/m 2  using a sulfate bath. 
     The contamination resistant layer  230  can be formed on the electro-galvanized layer  220  by coating a polymer Cr-free composition. In some examples, the contamination resistant layer  230  can be based on polymer resin and may not contain Cr. 
     The contamination resistant layer  230  may contain about 10 to 30 wt. % amine based resin, about 10 to 50 wt. % silica compound, about 1 to 10 wt. % inorganic sol, and epoxy resin as remaining binder resin. 
     The amine based resin can provide sufficient adhesive strength to the contamination resistant layer  230  due to cross-linking. The content of the amine-based resin in the contamination resistant layer  230  may be about 10 to 30 wt. %. If the content of the amine based resin is less than about 10 wt. %, it cannot provide a sufficient adhesion strength due to cross-linking. If the content of the amine based resin is greater than about 30 wt. %, the processibility may be degraded. 
     The silica compound can be added to improve storage stability, adhesion, corrosion resistance, and processibility. The content of silica compound in the contamination resistant layer  230  may be about 10 to 50 wt. %. If the content of silica compound is less than about 10 wt. %, it may result in reduced conductivity. If the content exceeds about 50 wt. %, the processibility may be degraded. 
     The silica compound can be made with a mixture containing silica and silane at a ratio. For example, the silica compound may contain silica and silane mixed in a weight ratio of about 1:0.2 to 1:0.8. The silica can be selected from a humed silica or a colloidal silica, and the silane can be selected from glycidoxypropylethoxysilane, aminopropylethoxysilane, or methoxypropyltrimethoxysilane. If the silica and the silane are mixed in a weight ratio less than about 1:0.2, the contamination resistant layer  230  may exhibit a low degree of cross-linking. If the silica and the silane are mixed in a weight ratio greater than about 1:0.8, the contamination resistant layer  230  may have low processibility. 
     The contamination resistant layer  230  may also contain the inorganic sol in order to improve adhesion and corrosion resistance. The inorganic sol may be zircornia sol, alumina sol, titan sol, or a mixture of at least two of these materials. The content of inorganic sol in the contamination resistant layer  230  may be about 1 to 10 wt. %. If the content of inorganic sol is less than about 1 wt. %, the addition of the inorganic sol may have little effect on improving adhesion and corrosion resistance. If the content exceeds about 10 wt. %, corrosion resistance may increase while decreasing conductivity and processibility, thus, film formation may be difficult. 
     The epoxy resin can act as a binder resin and may form a dense barrier film. In addition, the epoxy resin can resist corrosive factors such as salt or oxygen and may have an excellent corrosion resistance as well as a chemical resistance. 
     The contamination resistant layer  230  may be formed by applying coatings of about 0.8 to 1.3 g/m 2 . If a coating weight is less than about 0.8 g/m 2 , it may be difficult to form into a bottom chassis having a desired shape. If the coating weight is greater than about 1.3 g/m 2 , an electrical conductivity can be degraded such that the bottom chassis  130  may not be served as a ground for a circuit in a device or a light source in the backlight unit  120 . The contamination resistant layer  230  may have a coating thickness of about 1 μm. 
     It is contemplated that a formation process of coatings on the contamination resistant layer  230  may include applying a solution which contains a solvent and materials discussed above on the electro-galvanized layer  220  to have a composition by utilizing the following process: one-coating-one-baking method, performing a baking-drying process, and performing water cooling or air cooling process. 
     The baking-drying process may be performed at a temperature in the range of about 140° C. to 220° C. If the baking-drying process is performed below about 140° C., the resin may not properly be cured, thereby degrading corrosion resistance and other physical properties of the coating layer. On the other hand, if the baking-drying process is performed above about 220° C., over-baking occurs. Consequently, the coating layer may crack or turn yellow in color. 
     The bottom chassis  130  may have a thickness of about 0.5 mm to 0.9 mm. If the bottom chassis  130  has a thickness greater than about 0.9 mm, it may not have a light weight, and thus may not achieve a slim design. If the bottom chassis  130  has a thickness less than about 0.5 mm, the electro-galvanized layer  220  and the contamination resistant layer  230  may become too thin, thereby degrading corrosion resistance or contamination resistance. Otherwise, the electro-galvanized layer  220  or the contamination resistant layer  230  may become thicker and the is inner layer  210  may become thinner, thereby reducing a mechanical strength of the bottom chassis  130 . 
     The steel plate can be a high tensile steel plate with a tensile strength (TS) of about 300 MPa to 500 MPa and elongation of about 30% to 45%. 
     The fabrication and characteristics of the steel plate described above are described with a detailed explanation with reference to Examples discussed below, however, aspects of the present invention may not be limited to the Examples. 
     In some examples, exemplary steel plates can be illustrated. Steel plates can be processed to become a bottom chassis after conducting a molding process. In this example, inner layers may have the same compositions as in Example 1, Example 2, and Comparative Example seen in TABLE 1 and TABLE 2. An Electro-galvanization may be conducted by applying coatings of about 20 g/m 2  in a sulfate bath to form electro-galvanized layers. Thereafter, polymer Cr-free contamination resistant layers can be formed by applying coatings of about 1.0 g/m 2  over the electro-galvanized layers using one-coating-one-baking method, subsequent to a baking-drying process at temperature of about 180° C. and cooling. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
               
            
           
           
               
               
               
               
            
               
                   
                 Example 1 
                 Example 2 
                 Comparative Example 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Elements 
                 C 
                 0.0013 
                 0.0548 
                 0.0168 
               
               
                 added 
                 Si 
                 0.0029 
                 0.0062 
                 0.0058 
               
               
                   
                 Mn 
                 0.3600 
                 0.2810 
                 0.1430 
               
               
                   
                 P 
                 0.0678 
                 0.0141 
                 0.0178 
               
               
                   
                 S 
                 0.0073 
                 0.0046 
                 0.0044 
               
               
                   
                 Cr 
                 0.0297 
                 0.0112 
                 0.0101 
               
               
                   
                 Ni 
                 0.0144 
                 0.0073 
                 0.0096 
               
               
                   
                 Mo 
                 0.0032 
                 0.0017 
                 0.0022 
               
               
                   
                 Al 
                 0.0432 
                 0.0450 
                 0.0375 
               
               
                   
                 Cu 
                 0.0351 
                 0.0242 
                 0.0111 
               
               
                   
                 Nb 
                 0.0079 
                 — 
                 — 
               
               
                   
                 Ti 
                 0.0308 
                 — 
                 — 
               
               
                   
                 Sn 
                 0.0017 
                 0.0018 
                 0.0014 
               
               
                   
                 O 
                 0.0032 
                 0.0038 
                 0.0040 
               
               
                   
                 N 
                 0.0015 
                 0.0028 
                 0.0019 
               
               
                   
               
            
           
         
       
     
     TABLE 2 shows mechanical properties of the steel plates fabricated according to Example 1, Example 2, and Comparative Example. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Mechanical 
                 Thickness 
                 YP 
                 TS 
                 El 
                   
                 r 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Properties 
                 (mm) 
                 (MPa) 
                 (MPa) 
                 (%) 
                 n 
                 r-bar 
                 Δr 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 0.810 
                 215.5 
                 374.3 
                 40.75 
                 0.241 
                 1.76 
                 0.01 
               
               
                 Example 2 
                 0.802 
                 221.4 
                 355.4 
                 42.51 
                 0.235 
                 1.67 
                 −0.51 
               
               
                 Comparative 
                 1.002 
                 208.1 
                 327.7 
                 43.26 
                 0.199 
                 1.61 
                 0.80 
               
               
                 Example 
               
               
                   
               
            
           
         
       
     
     As evident from TABLE 2, the steel plates fabricated according to the Example 1 and the Example 2 may have a thickness of about 0.8 mm, which is about 80 percent of the thickness (1.0 mm) of the conventional steel plate fabricated according to the Comparative Example and may show slightly higher yield points (YP) and tensile strengths (TS) than those of the conventional steel plate. 
     Thus, the bottom chassis according to exemplary embodiments of the present invention, which can be formed using a steel plate, having the above-described physical properties, may be thinner than a conventional bottom chassis, yet maintain similar mechanical properties to the values of the conventional one, thereby achieving a lightweight, slim design. Accordingly, the overall thickness and weight of an LCD can be reduced. Further, the bottom is chassis may have a polymer Cr-free contamination resistant layer at an outside surface thereof, thereby preventing contamination during assembly. 
     In some examples, a bottom chassis may have a burring part for inserting a bolt formed on a bottom surface so as to engage various objects such as an inverter substrate or a shield case. The burring part may be formed by performing a burring process and a tapping process. 
     Since a bottom chassis fabricated using the above steel plate may be thinner than a conventional bottom chassis, it may be difficult to achieve a desired tapping torque during the tapping process. To achieve the desired tapping torque, it may be necessary to determine several factors to achieve optimum values that can affect a tapping torque during the burring process. 
     Thus, a method of fabricating a bottom chassis according to exemplary embodiments of the present invention may include factors possibly affecting an optimum value of a tapping torque during a process of forming a burring part on a bottom surface of the thin bottom chassis, thereby achieving a desired tapping torque during a subsequent tapping process. In this way, high assembling quality can be ensured. 
     A bottom chassis including a burring part and a method of fabricating the bottom chassis is described in detail with reference to  FIG. 3  and  FIG. 4 . Hereinafter, a ‘steel plate’ can is refer to a steel plate having the same physical properties as described with reference to  FIG. 2 . A ‘bottom chassis’ can refer to a bottom chassis fabricated using the steel plate. 
       FIG. 3  is a perspective view of a bottom chassis  300  fabricated according to exemplary embodiments of the present invention and  FIG. 4  is an enlarged cross-sectional view taken along line A-A′ of  FIG. 3 .  FIG. 3  shows the bottom chassis  300  with from the perspective that its rear surface facing up. 
     Referring to  FIG. 3  and  FIG. 4 , the bottom chassis  300  may have a bottom surface and sidewalls to provide a receiving space. The bottom chassis  300  may have at least one engaging portion  310  formed on the bottom surface so as to engage with a predetermined object  400  such as an inverter substrate or shield case disposed on the rear surface thereof. 
     In some examples, the engaging portion  310  can guide a position at which the object  400  can be fastened to the bottom surface  300 . As illustrated in  FIG. 4 , the engaging portion  310  may have a protrusion projecting from the bottom surface toward the rear surface having a height h 1 , but the present invention is not limited thereto. For example, the engaging portion  310  may be a flat portion with a zero height h 1 . A number, a position, and a planar shape of the engaging portion  310  may not be limited to those illustrated in  FIG. 3  and  FIG. 4 . The engaging portion  310  may have other various configurations for engaging the object  400 . 
     The engaging portion  310  may have has a burring part  320  for inserting a bolt. The formation of the burring part  320  will be described below with reference to  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9 . 
     In some examples, the object  400  fixed to a rear surface of the bottom chassis  300  has a throughhole  420  corresponding to the burring part  320  on the bottom chassis  300 . 
     The bolt M can pass through the throughhole  420  in the object  400  and can join with the burring part  320  so that the object  400  can be fastened to the bottom chassis  300 . 
     A method of fabricating a bottom chassis  300  according to exemplary embodiments of the present invention is described in detailed explanation with reference to  FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9 .  FIG. 5 ,  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9  are cross-sectional views for explaining the method of fabricating the bottom chassis  300  shown in  FIG. 3 . The cross-sectional views can be based on an enlarged cross-sectional view taken along line A-A′ of  FIG. 3 . 
     Referring to  FIG. 5 , the bottom chassis  300  may have a bottom surface and side walls for providing a receiving space. 
     An engaging portion  310  can be formed on the bottom surface of the bottom chassis  300  so as to guide a position at which the object  400  is fastened to the bottom chassis  300 . For example, a pressure can be applied to a region of the bottom surface in which the engaging portion  310  can be formed so that the engaging portion  310  can protrude towards the rear surface of the bottom chassis  300  with a height h 1 . The projecting engaging portion  310  may have a thickness that can be varied with a position. For example, the engaging portion  310  can be tapered toward a top surface thereof. 
     However, aspects of the present invention are not limited thereto, and for example, engaging portion  310  may have a flat shape. In this example, the engaging portion  310  may have the same uniform thickness as thickness t 1  of the bottom surface of the bottom chassis  300 , i.e., the thickness of the steel plate. 
     Referring to  FIG. 6 ,  FIG. 7 ,  FIG. 8  and  FIG. 9 , a process of forming a burring part can subsequently be performed.  FIG. 6 ,  FIG. 7 ,  FIG. 8  are cross-sectional views for explaining a burring process and  FIG. 9  is a cross-sectional view for explaining a tapping is process. 
     For example, piercing can be performed to punch a hole in a part of the engaging portion  310  and can form a piercing hole  312 . The piercing hole  312  may be an initial hole for forming a burring part. When the engaging portion  310  has a projecting shape as an example, the piercing hole  312  can be formed on a flat part, i.e., a top surface of the engaging portion  310 . 
     Referring to  FIG. 7 , a burning die  314  can be disposed on a front surface of the bottom chassis  300  and has an opening  314   a  with a diameter greater than that of the piercing hole  312  and a burring punch which will be described below. In this example, the burring die  314  can come into to contact with the engaging portion  310  so that the opening  314   a  and the piercing hole  312  can overlap each other. The piercing hole  312  may overlap a central portion of the opening  314   a.    
     Referring to  FIG. 8 , a burring tool, i.e., a burring punch (not shown) having a diameter greater than that of the piercing hole  312  can be pushed into the piercing hole  312  towards the front surface of the bottom chassis  300  to produce an initial burring part  318  having a shape as indicated by the dotted line. The initial burring part  318  can be referred to as a burring part formed before being subjected to a tapping process. 
     Referring to  FIG. 9 , a tapping process can be performed to form a screw tap  319  along an inner circumference of the initial burring part  318 , thereby completing a burring part  320 . The tapping process can be conducted using a tapping tool (not shown) that can be inserted into the initial burring part  318  for a rotation. For example, the tapping process can be performed using a rolling tap in order to prevent from loss of the cross-sectional area of the burring part  320 . 
     Factors that can affect a tapping torque during the tapping process may include a is thickness of a steel plate, i.e., the thickness t 1  of the bottom surface, sidewalls of the bottom chassis  300 , diameter r 1  of the piercing hole  312 , diameter r 2  of the opening  314   a  of the burring die  314 , and a height h 2  of the initial burring part  318 . In this example, the initial burring part  318  may have substantially the same height h 2  as the burring part  320 . 
     In some examples, the thickness of the steel plate can be in the range of about 5 mm to 9 mm, preferably about 6 mm. 
     For example, with respect to a thickness t 1  of the steel plate, and if the burring part  320  is provided for inserting an 3 mm diameter M3 bolt the piercing hole  312  may have about 1.0 mm to 1.4 mm diameter r 1  and the opening  314   a  may have about 3.2 mm to 3.6 mm diameter r 2 . For example, if the height h 1  of the engaging portion  310  is 0 which means the engaging portion  310  has a flat shape, the height h 2  of the initial burring part  318  may be in the range of about 0.9 mm to 1.3 mm. If the height h 1  of the engaging portion  310  exceeds 0, the height h 2  of the initial burring part  318  may decrease compared to when the height h 1  is 0. 
     In some examples, if the burring part  320  is provided for inserting a 4 mm diameter M4 bolt, the piercing hole  312  may have about 1.4 mm to 1.8 mm diameter r 1  and the opening  314   a  may have about 4.2 mm to 4.6 mm diameter r 2 . Furthermore, if the height h 1  of the engaging portion  310  is 0, the height h 2  of the initial burring part  318  may be in the range of about 1.2 mm to 1.6 mm. If the height h 1  of the engaging portion  310  exceeds 0, the height h 2  of the initial burring part  318  may decrease compared to when the height h 1  is 0. 
     By determining optimum values for the thickness t 1 , the diameters r 1  and r 2 , and the height h 2 , a desired tapping torque can be obtained for the tapping process, which is shown in Examples seen in TABLE 3 below. However, aspects of the present invention are not limited to the Examples. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Factors 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Steel Plate 
                 0.6 
                 0.6 
                 0.6 
               
               
                   
                 Thickness (mm) 
               
               
                   
                 Piercing Hole 
                 1.2 
                 1.6 
                 1.6 
               
               
                   
                 Diameter (mm) 
               
               
                   
                 Opening Diameter 
                 3.4 
                 4.4 
                 4.4 
               
               
                   
                 (mm) 
               
               
                   
                 Burring Part Height 
                 1.1 
                 1.4 
                 0.83 
               
               
                   
                 (mm) 
               
               
                   
                 Tapping Torque 
                 7 
                 13 
                 13 
               
               
                   
                 (Kgf · cm) 
               
               
                   
                 Number of Tapping 
                 20 
                 20 
                 20 
               
               
                   
                 (times) 
               
               
                   
                   
               
            
           
         
       
     
     Example 1 shows conditions for forming a burring part when an M3 bolt is to be inserted into the 0.6 mm thick steel plate. As evident from Example 1, if the diameter r 1  of the piercing hole  312 , the diameter r 2  of the opening  314   a  on the burring die  314 , and the height h 2  of the initial burring part  318  (if the height h 1  of the engaging portion  310  is 0) are 1.2 mm, 3.4 mm, and 1.1 mm, respectively, a tapping tool can repeatedly be engaged 20 times with a tapping torque 7 Kgf cm during the tapping process. 
     Example 2 shows conditions for forming a burring part when an M4 bolt is inserted into the 0.6 mm thick steel plate. As evident from Example 2, if the diameter r 1 , the diameter r 2 , and the height h 2  (if the h 1  is 0) are 1.6 mm, 4.4 mm, and 1.4 mm, respectively, a tapping tool can repeatedly be engaged 20 times with a tapping torque 13 Kgf cm during the tapping process. 
     Example 3 shows conditions for forming a burring part when an M4 bolt is inserted into the 0.6 mm thick steel plate and the height h 1  of the engaging portion  310  is 8 mm. As evident from Example 3, if the diameter r 1 , the diameter r 2 , and the height h 2  (if the h 1  is 8 mm) are 1.6 mm, 4.4 mm, and 0.83 mm, respectively, a tapping tool can repeatedly be engaged 20 times with a tapping torque 13 Kgf cm during the tapping process. 
     As described above, exemplary embodiments of the present invention can provide the optimum values of a steel plate in terms of a thickness and other factors used for a burring process and thus can achieve a desired tapping torque for a tapping process, thereby ensuring a high assembling quality between the bottom chassis and another object. Accordingly, a high throughput of LCDs can be achieved. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.