Abstract:
A plasma display apparatus is provided that enables stable operation of a plasma display panel by accelerating heat dissipation from at least one interior circuit device and preventing degradation of the circuit device. The plasma display apparatus includes a plasma display panel on which an image is displayed, a chassis base facing the plasma display panel, a plurality of circuit devices operating the plasma display panel, a cabinet housing the plasma display panel, the chassis base, and a heat dissipation means interposed between the at least one circuit device and the cabinet to contact the circuit device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 2003-70279 filed on Oct. 9, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a plasma display apparatus, and more particularly, to a plasma display apparatus with a structure that facilitates heat dissipation from a circuit device.  
         [0004]     2. Description of the Related Art  
         [0005]     A plasma display apparatus is a flat panel display device that displays pictures by using a gas discharge effect. Because of its very good performance and characteristics such as high display capacity, high brightness, high contrast, clear latent image, and large viewing angle, the plasma display apparatus is considered to be a next generation display device to replace the is CRT.  
         [0006]     A plasma display apparatus includes a plasma display panel on which an image is displayed, a chassis base facing the plasma display panel, and a circuit section for driving the panel which is located on the back of the chassis base. A cabinet of the plasma display apparatus houses the plasma display panel and the chassis base.  
         [0007]     The plasma display panel includes a first and a second substrate, separated by a gap and facing each other to form a discharge space. A plurality of pairs of discharge sustain electrodes is formed on the first substrate, a plurality of address electrodes is formed on the second substrate, and barrier ribs that are interposed between the substrates separate the discharge space into a plurality of discharge cells.  
         [0008]     Such a plasma display apparatus can display an image by selectively discharging various discharge cells, thereby enabling a color display. For this purpose, a driving device connected to the address electrodes provides sequentially controlled signals to the address electrodes.  
         [0009]     However, the driving device generates much heat. Therefore, if the heat generated by the driving device is not properly dissipated, proper operation of the plasma display apparatus cannot be achieved.  
         [0010]     As the size of the discharge cells decreases, the driving device becomes denser. Therefore, better heat dissipation from the circuit device is required.  
         [0011]     According to a technique for improving the heat dissipation of the driving device disclosed in Japanese Patent Laid-Open publication 2000-268735, a conductive pattern is formed on a glass substrate and the driving device is mounted on the conductive pattern, and the is conductive pattern and a chassis base are connected by a metal clip. According to the disclosed technique, heat generated by the driving device is transferred to the chassis base via the conductive pattern.  
         [0012]     Generally, the chassis base performs as a heat sink that dissipates heat from the plasma display panel and the circuit section, and thus the heat gathers in the chassis base. The heat gathered in the chassis base is transferred to inside air by convection in a closed space. However, due to a low heat transfer rate, much heat accumulates in the chassis base, which is maintained at a high temperature.  
         [0013]     Therefore, according to the conventional art, because the heat generated by the driving device is not effectively dissipated, a malfunction may occur due to a degradation of a device or, in a severe case, the normal operation of the plasma display apparatus may be disturbed by thermal destruction caused by thermal stress.  
         [0014]     Also, when the heat generated by the driving device is transferred to the chassis base, there are some harmful effects to the plasma display panel and other circuit sections, the heat of which is dissipated through the chassis base.  
       SUMMARY OF THE INVENTION  
       [0015]     To solve the above and/or other problems, the present invention provides an improved plasma display apparatus that accelerates heat dissipation from one or more circuit devices.  
         [0016]     The present invention also provides a plasma display apparatus that can protect a plasma display panel and the circuit devices more effectively.  
         [0017]     According to an embodiment of the present invention, there is provided a plasma display apparatus that includes a plasma display panel on which an image is displayed. A chassis base supports the plasma display panel, and a plurality of circuit devices operates the plasma display panel. A cabinet houses the plasma display panel, the chassis base, and the plurality of circuit devices; and a heat dissipation means is interposed between at least one circuit device and the cabinet to contact the circuit device  
         [0018]     The heat dissipation means may include at least two different heat transfer media that are stacked. One of the heat transfer media may be a metal plate selected from the group consisting of aluminum plate, copper plate, silver plate, and nickel plate. One of the heat transfer media can be deformed easily by an external force. One of the heat transfer media may be a thermal conductive container filled with a liquid heat dissipation material. The liquid heat dissipation material may be a thermal grease.  
         [0019]     One of the heat transfer media is a thermal conductive container filled with a thermal conductive powder. The thermal conductive powder may be a powder selected from the group consisting of an aluminum powder, a graphite powder, a copper powder, a silver powder, and a nickel powder.  
         [0020]     One of the heat transfer media may be a matrix resin containing a heat transfer filler. The heat transfer filler is a metal powder selected from the group consisting of an aluminum powder, a graphite powder, a copper powder, a silver powder, and a nickel powder. One of the heat transfer media is a carbon fiber fabric.  
         [0021]     The heat dissipation means may be a heat pipe, or may include cooling fins.  
         [0022]     According to another embodiment of the present invention, there is provided a plasma display apparatus that includes a plasma display panel on which an image is displayed. A chassis base supports the plasma display panel. A plurality of circuit devices operates the plasma display panel. A heat dissipation means contacts at least one circuit device. A cabinet houses the plasma display panel, the chassis base, the plurality of circuit devices. Additionally, the heat dissipation means, includes at least a protrusion hole through which at least a portion of the heat dissipation means protrudes to the outside of the plasma display apparatus.  
         [0023]     The heat dissipation means may include at least two different heat transfer media that are stacked. One of the heat transfer media may be a metal plate selected from the group consisting of aluminum plate, copper plate, silver plate, and nickel plate. One of the heat transfer media can be deformed easily by an external force.  
         [0024]     One of the heat transfer media may be a thermal conductive container filled with a liquid heat dissipation material. The liquid heat dissipation material may be a thermal grease.  
         [0025]     One of the heat transfer media is a thermal conductive container filled with a thermal conductive powder. The thermal conductive powder is a powder selected from the group consisting of an aluminum powder, a graphite powder, a copper powder, a silver powder, and a nickel powder.  
         [0026]     One of the heat transfer media is a matrix resin containing a heat transfer filler. The heat transfer filler is a metal powder selected from the group consisting of an aluminum powder, a graphite powder, a copper powder, a silver powder, and a nickel powder.  
         [0027]     One of the heat transfer media may be a carbon fiber fabric.  
         [0028]     The heat dissipation means may be a heat pipe, or may include cooling fins. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to is the attached drawings.  
         [0030]      FIG. 1  is an exploded perspective view of a plasma display apparatus, according to a first embodiment of the present invention.  
         [0031]      FIG. 2  is a partial perspective view of the plasma display apparatus of  FIG. 1 .  
         [0032]      FIG. 3  is a cross-sectional view of the plasma display apparatus of  FIG. 1 .  
         [0033]      FIGS. 4A, 4B , and  4 C are schematic drawings of structure of the heat dissipation means which can be applied to the present invention.  
         [0034]      FIG. 5  is a cross-sectional view of a plasma display apparatus, according to a second embodiment of the present invention.  
         [0035]      FIG. 6  is a partial sectional views of plasma display apparatus, according to a third embodiment of the present invention.  
         [0036]      FIGS. 7 and 8  are partial sectional views of plasma display apparatus, according to modified embodiments of the third embodiment.  
         [0037]      FIG. 9  is a cross-sectional view of plasma display apparatus, according to a fourth embodiment of the present invention.  
         [0038]      FIG. 10  is cross-sectional view of plasma display apparatus, according to a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. Throughout the drawings, like reference numerals refer to like elements.  
         [0040]      FIG. 1  is an exploded perspective view of a plasma display apparatus according to a first embodiment of the present invention.  FIG. 2  is a partial perspective view of the plasma display apparatus of  FIG. 1 , and  FIG. 3  is a cross-sectional view of the plasma display apparatus of  FIG. 1 .  
         [0041]     Referring to  FIG. 1 , a plasma display apparatus includes a PDP  40 , a chassis base  50 , a circuit section  60 , and a cabinet  90 . Referring to  FIG. 2 , the PDP  40  includes a first panel  20  and a second panel  30  combined together.  
         [0042]     The first panel  20  on which an image will be displayed includes a first substrate  21 , discharge sustain electrodes  22 , bus electrodes  23 , a first dielectric layer  24 , and a protective layer  25 .  
         [0043]     The discharge sustain electrodes  22  are arranged in a predetermined pattern, such as a stripe pattern under the first substrate  21 .  
         [0044]     The discharge sustain electrode  22  may be composed of a transparent material such as indium tin oxide (ITO) for transmitting discharged visible light from a fluorescent layer  35 . Because the discharge sustain electrode  22  composed of ITO has low electric conductivity, overall impedance is reduced by including the bus electrode  23 .  
         [0045]     The bus electrode  23  is combined with the discharge sustain electrode  22 , and may be arranged in a predetermined pattern such as a stripe pattern. The bus electrode  23  may include a single metal layer composed of a metal having high electric conductivity such as aluminum, copper or silver, or a stacked metal layer such as a triple-layer of chrome-copper-chrome.  
         [0046]     As shown in  FIG. 2 , a first dielectric layer  24  is disposed under the first substrate  21  to cover the discharge sustain electrodes  22  and the bus electrodes  23 . A protective layer  25 , disposed under the first dielectric layer  24  protects the first dielectric layer  24  from ions or electrons when discharge occurs.  
         [0047]     The second panel  30  includes a second substrate  31 , address electrodes  32 , a second dielectric layer  33 , barrier ribs  34 , and fluorescent layers  35 .  
         [0048]     The second substrate  31  may also be composed of glass like the first substrate  21 . The address electrodes  32  are arranged in a predetermined pattern, such as a stripe pattern, on the second substrate  31 . The address electrodes  32  are arranged approximately orthogonal to the discharge sustain electrodes  22 .  
         [0049]     The second dielectric layer  33  is formed on the second substrate  31  to cover the address electrodes  32 . Barrier ribs  34  are formed on the second dielectric layer  33  parallel to the address electrodes  32 .  
         [0050]     The fluorescent layers  35  may be formed on the second dielectric layer  33  and the barrier ribs  34 . They include a red fluorescent layer, a green fluorescent layer, and a blue fluorescent layer.  
         [0051]      91  The first panel  20  and the second panel  30  may be combined using frit glass, and each of the cells is filled with a discharge gas.  
         [0052]     Driving devices  61   a  ( FIG. 1 ) are connected to terminals of the address electrodes  32  to sequentially apply scan signals to the address electrodes  32 . By applying a controlled signal to each of the address electrodes  32 , a selective discharge can be performed in each discharge cell, thereby enabling the display of a variety of colors with a range of gray scales.  
         [0053]     Referring to  FIG. 1 , the chassis base  50  accelerates the dissipation of heat from the PDP  40  and the circuit section  60 , and is composed of a material having high thermal conductivity such as aluminum. The chassis base  50  can be manufactured by die casting or press processing.  
         [0054]     The circuit section  60  for driving the PDP  40  is disposed on a back surface of the chassis base  50 . The circuit section  60  includes circuit devices  61  such as driving devices  61   a  that apply control signals to the PDP  40 , a circuit substrate  63  on which a plurality of circuit devices  61  are mounted, and cable  62 . A flexible printed circuit (FPC) may be used for the cable  62  and the driving devices  61   a  can be mounted on a film of the FPC (Chip On Film, COF).  
         [0055]     As shown in  FIG. 1 , cabinet  90  houses, the PDP  40  and the chassis base  50  on which the circuit section  60  are mounted, and the cabinet  90  includes a front cover  10  and a back cover  80 . The front cover  10  and the back cover  80  constitute an external appearance of the plasma display apparatus  100 , and protect parts therebetween.  
         [0056]     The front cover  10  includes a rim  11  and a filter  12 . The filter  12  can include tempered glass (not shown) fixed on the rim  11  and an electromagnetic interference (EMI) shielding layer (not shown). The rim  11  of the front cover  10  and the back cover  80  may be composed of a thermal conductive material.  
         [0057]     A heat dissipation means  70  is interposed between the driving devices  61   a  and the cabinet  90 . The heat dissipation means  70  as depicted in  FIGS. 1 and 3  includes a first heat transfer medium  71  and a second heat transfer medium  72 . The first heat transfer medium  71  contacts the driving devices  61   a  and the second heat transfer medium  72  contacts the back cover  80 .  
         [0058]     Also, as depicted in  FIG. 3 , the heat dissipation means  70  may be attached to the driving device  61   a  by a thermal conductive adhesive  75 . Additionally, the first heat transfer medium  71  and the second heat transfer medium  72  may be combined by a thermal conductive adhesive  75 .  
         [0059]     In one embodiment, the first heat transfer medium  71  is formed to have a thermal conductivity over 0.1 W/mk and high flexibility. The first heat transfer medium  71  may have a variety of shapes such as a matrix resin containing a heat transfer filler. The matrix resin may be an epoxy resin, and the heat transfer filler may be a powder that has high thermal conductivity such as aluminum powder, graphite powder, or copper powder.  
         [0060]     Also, the first heat transfer medium  71  may be formed by sealing a liquid heat dissipation material such as a heat radiation grease in a thermal conductive container. The thermal conductive container may be formed of an aluminum foil. In the first heat transfer medium  71  a high thermal conductive powder properly agglomerated may replace a liquid heat dissipation material in the thermal conductive container.  
         [0061]     A carbon fiber texture or a stack of carbon fibers may be used as the first heat transfer medium  71  since carbon fiber has high thermal conductivity and flexibility.  
         [0062]     In one embodiment the flexibility of the first heat transfer medium  71  protects the driving device  61   a  by absorbing and mitigating a compression force that can be generated while assembling the front cover  10  and the back cover  80 .  
         [0063]     The second heat transfer medium  72  may be a plate composed of a high thermal conductivity material such as aluminum, copper, silver, or nickel. By interposing the second heat transfer medium  72  with high thermal conductivity, the heat generated by the driving device  61   a  can be effectively transferred to the back cover  80 , and distributed in a plane of the second heat transfer medium  72 , thereby improving heat dissipation efficiency of the driving device  61 a.  
         [0064]     In use, heat generated by the driving devices  61   a  is transferred to the back cover  80  via the first and the second heat transfer mediums  71  and  72 , and then dissipated into the air by convection from the back cover  80 .  
         [0065]     The driving devices  61   a  extend horizontally and a structure of the heat dissipation means of the driving devices  61   a  can be formed to a variety of shapes as depicted in  FIGS. 4A, 4B  and  4 C.  
         [0066]     That is, the heat dissipation means  70  may be formed in a single body type, as depicted in  FIG. 4A , in a group type, as depicted in  FIG. 4B , or in an individual type, as depicted in  FIG. 4C . In a single body type, a heat dissipation means  70  dissipates the heat generated by all of the driving devices  61   a.  In a group type, a heat dissipation means  70  dissipates heat from a group of the driving devices  61   a.  In an individual type, a heat dissipation means  70  dissipates heat from each individual driving device  61   a.    
         [0067]     The single body type may rapidly diffuse the heat generated by the driving devices  61   a  to a wide area since it is formed as a single body. The individual type improves workability when maintenance work since the heat dissipation means can be individually attached and detached, thereby reducing maintenance costs. The group type has both of the advantages of the one body type and the individual type.  
         [0068]      FIG. 5  is a cross-sectional view of a plasma display apparatus according to second embodiment of the present invention. Referring to  FIG. 5 , a heat dissipation means  70  includes a first heat transfer medium  71 , a second heat transfer medium  72 , and a third heat transfer medium  73 , and is interposed between driving devices  61   a  and back cover  80 . The first and the third heat transfer mediums  71  and  73  are formed to have high flexibility and thermal conductivity, and the second heat transfer medium  72  is formed to have high thermal conductivity.  
         [0069]     The first and the third heat transfer mediums  71  and  73  can be formed in a variety of types. That is, a matrix resin that contains a heat transfer filler, a thermal conductive container in which a liquid heat dissipation material or a thermal conductive powder is filled, or a stacked layer of carbon fibers.  
         [0070]     The second heat transfer medium  72  can be a plate formed of aluminum, silver, copper, or nickel.  
         [0071]      81  By disposing the first and the third heat transfer mediums  71  and  73 , which have flexibility, on both sides of the second heat transfer medium  72 , which has high thermal conductivity, the driving devices  61   a  are protected more effectively than in the conventional manner. Also, because of the added flexibility, and a tolerance margin of the parts constituting the plasma display apparatus  100  can be increased.  
         [0072]      FIG. 6  is a partial sectioned view of a plasma display apparatus according to a third embodiment of the present invention. Referring to  FIG. 6 , a heat dissipation means  70  of the driving device  61   a  includes first and second heat transfer mediums  71  and  72 . The first heat transfer medium  71  has high flexibility and thermal conductivity and contacts the driving device  61   a,  and the second heat transfer medium  72  has high thermal conductivity and is interposed between the back cover  80  and the first heat transfer medium  71 . The heat dissipation means  70  may be attached to the chassis base  50  by a thermal conductive adhesive  75 .  
         [0073]     As shown in  FIG. 6 , air holes  80   a  for improved air flow are formed on the back cover  80 . When low temperature air from the outside enters the plasma display apparatus  100  through the air holes  80 a, the temperature of the heat dissipation means  70  and the temperature of the chassis base  50  are reduced. Therefore, heat generated by the driving device  61   a  can be rapidly transferred to the heat dissipation means  70  and the chassis base  50 . Particularly, since the second heat transfer medium  72  contacts the back cover  80  in which the air holes  80   a  are formed, the second heat transfer medium  72  may be air-cooled by direct contact with the outside air.  
         [0074]     As depicted in  FIG. 7 , a plurality of cooling fins  72   a  may be included on the back surface of the second heat transfer medium  72  to increase heat transfer efficiency. If the cooling fins  72   a  are formed, the heat dissipation of the driving device  61   a  is improved by increasing a surface area in contact with the air entering through the air holes  80   a  and the second heat transfer medium  72 .  
         [0075]     The heat dissipation means  70  may be attached to the chassis base  50  by a combining means  76 .  
         [0076]     When there are a sufficient number of the air holes  80   a,  the heat generated by the driving device  61   a  may be sufficiently removed by the air entering through the air holes  80   a.  In this case, the second heat transfer medium  72  and the back cover  80  may be mounted with a space interposed therebetween.  
         [0077]     Referring to  FIG. 8 , a heat dissipation means  70  of the driving device  61   a  includes a first and a second heat transfer mediums  71  and  72 . The first heat transfer medium  71  contacts the driving device  61   a.  A plurality of heat cooling fins  72   a  are formed on a back surface of the second heat transfer medium  72 , which contacts the first heat transfer medium  71 .  
         [0078]     In this embodiment, protrusion hole  80   b  is formed in the back cover  80 , and the heat cooling fins  72   a  formed on the second heat transfer medium  72  protrude from the plasma display apparatus  100  through the protrusion hole  80   b.  The heat dissipation means  70  may be fixed on a back side of the chassis base  50  by a combining means  76 .  
         [0079]     Since the cooling fins  72   a  formed on the second heat transfer medium  72  protrude outside of the plasma display apparatus  100  through the protrusion hole  80   b,  the heat generated by the driving device  61   a  may be directly transferred outside by convection, thereby promoting dissipation of heat from the driving device  61   a.    
         [0080]     Also, relatively low temperature outside air can enter the plasma display apparatus  100  through the protrusion hole  80   b,  and may reduce the temperature of the chassis base  50 . In this manner, the heat generated by the driving device  61   a  may be effectively dissipated via the chassis base  50 .  
         [0081]      FIG. 9  is a cross-sectional view of a plasma display apparatus  100  according to a fourth embodiment of the present invention. Referring to  FIG. 9 , the chassis base  50  has bent parts  50   a,  and the driving device  61   a  is installed on the bent part  50   a.  Also, a heat dissipation means  70  is interposed between the driving device  61   a  and an upper surface of the back cover  80 . The heat dissipation means  70  includes first and second heat transfer mediums  71  and  72 .  
         [0082]     The first heat transfer medium  71  has high thermal conductivity and flexibility and contacts the driving device  61   a.  The second heat transfer medium  72  also has high thermal conductivity and contacts an upper surface of the back cover  80 . The front cover  10  and the back cover  80  contact each other, and a rim part  11  of the front cover  10  and the back cover  80  may be composed of a high thermal conductive material such as aluminum.  
         [0083]     In use, heat generated by the driving device  61   a  is transferred to the back cover  80  by the first and second heat transfer mediums  71  and  72 , and dissipated outside through the front cover  10  and the back cover  80  by convection.  
         [0084]     By mounting the driving device  61   a  on the bent part  50   a  of the chassis base  50 , the utilization of back surface of the chassis base  50  on which various circuit devices are mounted can be improved. Also, since the heat dissipation means  70  is connected to both the front cover  10  and the back cover  80 , thermal capacity may be increased, and both the front cover  10  and the back cover  80  may be used for heat cooling, thereby improving heat dissipation of the driving device  61   a.    
         [0085]      FIG. 10  is a cross-sectional view of a plasma display apparatus  100  according to a fifth embodiment of the present invention. Referring to  FIG. 10 , the chassis base  50  in this embodiment is wider than the plasma display panel  40 , and the driving device  61   a  is mounted on the edge of the chassis base  50 . A heat dissipation means  70  of the driving device  61   a  includes first and second heat transfer mediums  71  and  72 , and a rim part of the front cover  10  can be formed of a high thermally conductive material such as but not limited to aluminum.  
         [0086]     The heat generated by the driving device  61   a  is conducted to the front cover  10  through the first and second heat transfer mediums  71  and  72 , and then dissipated outside of the plasma display apparatus  100  by convection.  
         [0087]     The front cover  10  can provide a heat cooling surface and therefore, heat dissipation through the chassis base  50  and the back cover  80  of the various circuit devices  61  may be improved.  
         [0088]     Also, the utilization of the back surface of the chassis base  50  on which various circuit devices are mounted may be improved by mounting the driving device  61   a  on a front surface of the chassis base  50 .  
         [0089]     Though is not shown, a heat pipe may be used as a heat dissipation means of the driving device. The heat pipe, which is widely used for cooling a high density electronic circuit or an electronic chip, is a heat transfer apparatus through which a coolant flows such that the coolant evaporates in a heat absorption section and condenses at a heat dissipation section.  
         [0090]     When the heat pipe is used as the heat dissipation means of the driving device, the heat absorption section contacts the driving device and the heat dissipation section contacts the back cover. The driving device can further be cooled by low temperature outside air if the heat dissipation section of the heat pipe is exposed to the outside through hole formed in the cabinet.  
         [0091]     In the drawings of embodiments of the present invention, the driving device is depicted as example of heat source for convenience of explanation; however, it will be understood by those skilled in the art that the present invention is not limited to the driving device but can be applied to various circuit devices such as a field effect transistor (FET).  
         [0092]     According to an embodiment of the present invention, heat generated by a driving device is conducted to a cabinet by a heat dissipation means interposed between a circuit device and the cabinet, and then is dissipated outside by convection at a surface of the cabinet.  
         [0093]     By using a cabinet having a wide surface for heat transfer, high heat transfer efficiency and thermal capacity can be achieved. Also, by reducing the amount of heat transferred to the chassis base from the driving device, the plasma display panel and other circuit sections, the heat of which is dissipated through the chassis base, can be effectively protected.  
         [0094]     Also, since the cabinet is in contact with the outside air which has a relatively low temperature, the efficiency of heat transfer through the cabinet is better than in the case when heat generated by the circuit device is transferred to a relatively high temperature inside air by a heat sink on a back surface of the circuit device.  
         [0095]     Therefore, according to embodiments of the present invention, overheating and degradation of the circuit device can be prevented, thereby enabling stable operation of the plasma display apparatus. Accordingly, a plasma display apparatus with a high resolution can be provided since heat generated by the circuit device is effectively exhausted and the plurality of circuit devices can be mounted in a dense arrangement.  
         [0096]     According to embodiments of the present invention, since the heat dissipation means in contact with the circuit device protrudes outside of the plasma display apparatus through a protrusion hole formed in the cabinet, heat generated by the driving device can be directly dissipated into the air by convection. Thus, heat transfer efficiency of the driving device is improved, and the plasma display panel and other driving devices are also effectively cooled by the low temperature air entering through the protrusion hole.  
         [0097]     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.