Abstract:
A heat dissipation structure for a liquid crystal television is disclosed. The liquid crystal television includes a front plate and a rear plate. The front plate has a screen and a metal backboard. The heat dissipation structure includes a printed circuit board (PCB) mounted to the metal backboard; a television integrated circuit (IC) chip for controlling operations of the liquid crystal television being attached on the PCB; and one or more heat dissipating posts provided between the PCB and the metal backboard. The heat generated by the television IC chip is dispersed to the metal backboard via the heat dissipating post or posts.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to heat dissipation, more particularly, to a heat dissipation structure for a liquid crystal television. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a low price liquid crystal television, printed circuit broads (PCBs) are implemented with PCBs having only two copper sheets to reduce the cost. However, such PCBs have poor heat dispersing performance. In order to maintain a television IC (integrated circuit) chip operating normally, a heat sink is usually used to disperse the heat from the television IC chip. 
         [0003]      FIG. 1  is a schematic diagram showing a sectional view of a general liquid crystal television  1  with a conventional heat sink  40 . As shown, the liquid crystal television  1  includes a front plate  10  having a television screen  12  mounted on a front side thereof and a metal backboard  14  mounted on a rear side thereof. The liquid crystal television  1  further includes a rear plate  18 , which is assembled with the front plate  10  to constitute the liquid crystal television  1 . 
         [0004]    A main printed circuit board (PCB)  20  is mounted on a rear side of the metal backboard  14  by means of pillars  25 . A television IC chip  30 , which controls operations of the liquid crystal television  1 , is installed on the main PCB  20 .  FIG. 2  is a schematic diagram showing an EP-LQFP (Exposed Pad Low-profile Quad Flat Package) type of television IC chip  30  mounted on the PCB  20 . As shown in the drawing, the PCB  20  has metal portions  202 ,  204 ,  206 ,  208 . The television IC chip  30  has a die  32  disposed on a metal pad  38  and leads  34  electrically connected with the die  32  by wires (not shown). The die  32  is packed by package material  36 . The bottom of the metal pad  38  is exposed from the package material  36  and is mounted on the metal portion  204  of the PCB  20  by means of solder  29 . As shown, the metal portion  204  at the top side of the PCB  20  is connected with the metal portion  208  at the bottom side of the PCB  20  by VIAs  210 . These VIAs  210  are through holes penetrating the PCB  20  and having metal (e.g. copper) plated on inner surfaces thereof. 
         [0005]    The PCB  20  has only two copper sheets for the sake of low cost. Accordingly, heat dispersion for the television IC chip  30  is poor. As the television IC chip  30  operates functions, a temperature thereof will be increased. Once the television IC chip  30  is overheated, it may operate abnormally. 
         [0006]    To avoid such a problem, a heat sink  40  is attached to the television IC chip  30  to assist the television IC chip  30  to dissipate the heat, as shown in  FIG. 3 . However, the heat sink  40  with multiple fins is thick and occupies a considerable space, and thereby hindering the liquid crystal television  1  from being further thinned. In addition, the heat sink  40  is expensive. 
         [0007]    It will be highly satisfactory if a low cost solution to the above problems is provided. 
       SUMMARY OF THE INVENTION 
       [0008]    An objective of the present invention is to provide a heat dissipation structure for a liquid crystal television. The liquid crystal television includes a front plate and a rear plate. The front plate has a screen installed at a front side and a metal backboard mounted at a back side thereof. The front plate and the rear plate are assembled to form the liquid crystal television. By using the heat dissipation structure, the heat generated by the television IC chip can be effectively dispersed with a low cost. 
         [0009]    In accordance with the present invention, the heat dissipation structure comprises a printed circuit board (PCB) mounted to the metal backboard; a television integrated circuit (IC) chip for controlling operations of the liquid crystal television being attached on the PCB; and one or more heat dissipating posts provided between the PCB and the metal backboard. At least one of the heat dissipating posts is located at a position corresponding to the television IC chip. Preferably, the heat dissipating post is located at a position aligning with a die embedded within the television IC chip. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be described in detail in conjunction with the appending drawings, in which: 
           [0011]      FIG. 1  is a schematic diagram showing a sectional view of a general liquid crystal television with a conventional heat sink; 
           [0012]      FIG. 2  is a schematic diagram showing an EP-LQFP chip mounted on a PCB; 
           [0013]      FIG. 3  is a schematic diagram showing an EP-LQFP chip with a conventional heat sink, which is mounted on a PCB; 
           [0014]      FIG. 4  is a schematic diagram showing a heat dissipation structure in accordance with an embodiment of the present invention; 
           [0015]      FIG. 5  is a schematic diagram showing a section view of a liquid crystal television provided with the heat dissipation structure of  FIG. 4 ; 
           [0016]      FIG. 6  is a schematic diagram showing a section view of a liquid crystal television provided with a heat dissipation structure in accordance with another embodiment of the present invention; and 
           [0017]      FIG. 7  is a schematic diagram showing a section view of a liquid crystal television provided with a heat dissipation structure in accordance with a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 4  is a schematic diagram showing a heat dissipation structure in accordance with an embodiment of the present invention.  FIG. 5  is a schematic diagram showing a section view of a liquid crystal television  2  provided with the heat dissipation structure of  FIG. 4 . The same reference numbers of these drawing and other drawings indicate the same components, and the relevant descriptions will be omitted to avoid repetition and redundancy. 
         [0019]    Similar to  FIGS. 1-3 , an EP-LQFP type of television IC chip  20  is disposed on a PCB  20 . The PCB  20  is mounted on a metal backboard  14  of a front plate  10  of the liquid crystal television  2  by means of pillars  25 . In the present invention, no convention heat sink is used. As shown, a heat dissipating post  50  is provided between the PCB  20  and the metal backboard  14 . The dissipating post  50  is made of heat conductive material such as metal (e.g. aluminum). The position where the dissipating post  50  is located is corresponding to the television IC chip  30 . Preferably, the dissipating post  50  is positioned to align with a die  32  embedded in the television IC chip  30  so as to effectively transfer the heat from the die  32  to the metal backboard  14 . As known, the die  32  is usually embedded in the center of the television IC chip  30 . By doing so, heat dispersion is achieved. As known, the metal backboard  14  has a great area, and therefore the effect of heat dispersion is good. 
         [0020]    The cost of the heat dissipating post  50  is quite low as compared to a heat sink. In addition, setting up the heat dissipating post  50  is easy. The heat dissipating post  50  can be provided along with the pillars  25 , which are used to mount the PCB  20  to the metal backboard  14  as mentioned above. 
         [0021]    To avoid formation of a gap between the dissipating post  50  and the PCB  20 , thermal conductive paste  52  is applied on an end of the heat dissipating post  50 , which is connected with a metal portion  208  on the bottom side of the PCB  20 . The thinner the thermal conductive paste  52  is, the better the heat dispersion performance can be achieved, but the higher the temperature of the metal backboard  14  will be. In practice, the thickness of the thermal conductive paste  52  is about 1 mm, for example. 
         [0022]    As can be seen in  FIG. 5 , in the absence of the heat sink (e.g. the heat sink  40  in  FIG. 1 ), a front plate  10  and a rear plate  18  of the liquid crystal television  2  can be closer to each other, and therefore the whole thickness of the liquid crystal television  2  can be reduced. 
         [0023]    To manifest the effect of the present invention, the inventor carried out an experiment by software, in which the temperatures of the television IC chip  30  in the conditions shown in  FIGS. 2 ,  3  and  4  were measured. The ambient temperature was 25° C. The television IC chip  30  operated at its full power of 3.6 watts. For each condition of  FIG. 2 ,  FIG. 3  and  FIG. 4 , the temperature T c  at a point C was measured, and the temperature T J  at a point J was estimated, as shown in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Temperatures of the chip and die 
               
             
          
           
               
                   
                   
                   
                 With heat 
               
               
                   
                 No heat dispersion 
                 With heat sink 
                 dissipating post 
               
               
                   
                 means (FIG. 2) 
                 (FIG. 3) 
                 (FIG. 4) 
               
               
                   
                   
               
             
          
           
               
                 T C  (° C.) 
                 85.9 
                 55.2 
                 67.2 
               
               
                 Ψ JC  (° C./Watt) 
                 0.08 
                 3.69 
                 0.08 
               
               
                 T J  (° C.) 
                 86.2 
                 68.5 
                 67.5 
               
               
                   
               
             
          
         
       
     
         [0024]    Where Ψ JC  is the thermal resistivity between the point C and the point J. In  FIG. 2  or  FIG. 4 , the temperature T C  at the point C is the temperature measured from the top surface of the television IC chip  30 . It is noted that the temperature at the top surface of the television IC chip  30  in  FIG. 3  is not possible to be measured. Accordingly, in  FIG. 3 , the point C is at a base of the heat sink  40 , and the temperature T C  is the temperature of the base of the heat sink  40 . This temperature should be close to the actual temperature at the surface of the television IC chip  30 . 
         [0025]    As can be seen from the table, for the chip surface, the heat dissipation efficiency of the present invention, in which the heat dissipating post  50  is used, is about 61% as compared to the situation where the heat sink  40  is used. However, for the heat dissipation of the die  32 , the present invention is superior to the prior art. In this case, the temperature of the metal backboard  14  is increased by 6.2° C. Such a temperature rise will not noticeably influence the screen  12 , and therefore is acceptable. 
         [0026]    The heat dissipation structure of the present invention is particularly effective for an exposed pad type of IC chip such as EP-LQFP or EP-TQFP ((Exposed Pad thin-profile Quad Flat Package) type of IC chip. However, such a structure can also be used to other types of IC chips. For example, a PBGA (plastic ball grid array) type of IC chip can also be applied with the present invention. 
         [0027]      FIG. 6  is a schematic diagram showing a section view of a liquid crystal television  3  provided with a heat dissipation structure in accordance with another embodiment of the present invention. In the present embodiment, a television IC chip  30  is mounted on a PCB  20  as the previous embodiment. However, the PCB  20  is reversely mounted to a metal backboard  14  of the liquid crystal television  3 , so that the television IC chip  30  is positioned on a surface of the PCB  20  facing the metal backboard  14 . A heat dissipating post  60  is provided between the television IC chip  30  and the metal backboard  14 . Thermal conductive paste  62  is applied to an end of the heat dissipating post  60  toward the television IC chip  30  to prevent any gap from being formed therebetween. 
         [0028]      FIG. 7  is a schematic diagram showing a section view of a liquid crystal television  4  provided with a heat dissipation structure in accordance with a further embodiment of the present invention. As compared to the embodiment shown in  FIG. 5 , in the present embodiment, several heat dissipating posts  70  are provided. One of the heat dissipating posts  70  (e.g. the middle one in this drawing) is disposed to correspond to the center of a television IC chip  30 . In general, a die (not shown in this drawing) is embedded in the center of the television IC chip  30 . Accordingly, the middle heat dissipating post  70  substantially aligns with the die. The other heat dissipating posts  70  are disposed in the vicinity of the middle one. Thermal conductive paste  72  is applied to an end of each heat dissipating post  70  connected with the television IC chip  30  to prevent any gap from being formed therebetween. 
         [0029]    While the preferred embodiments of the present invention have been illustrated and described in detail, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present invention is therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present invention are within the scope as defined in the appended claims.