Patent Publication Number: US-2007103939-A1

Title: Sectional light emitting diode backlight unit

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a light emitting diode (LED) backlight unit, and more particularly to a sectional LED backlight unit.  
      2. Description of the Prior Art  
      Most of the light source generators in the traditional liquid crystal display (LCD) backlight units are cold cathode fluorescent lamps (CCFL) nowadays, but since the CCFL consists of mercury (Hg), the CCFL will be possibly superseded under the requirement for green merchandises in the future. The light emitting diode (LED) is being substituted for the CCFL stage by stage as the light source generators in the LCD, LCD TV, or other flat display panels with various sizes. In addition, the light intensity per watt of the LED is gradually becoming higher enough for application in the backlight unit due to the improvement in the LED technology.  
      In a conventional LED backlight unit, the LED package is positioned directly under the panel, and a reflector is positioned in the bottom of the backlight unit to reflect light by a flat reflecting structure. However, for a better optical performance, this conventional LED backlight unit will have the disadvantages of larger thickness and non-uniform luminance.  
      Please refer to  FIG. 1 .  FIG. 1  shows another conventional LED backlight unit  10  using dies positioned on the substrate to form a package structure. As shown in  FIG. 1 , the LED backlight unit  10  comprises a silicon substrate  11 , an array formed by LED dies  18  positioned on a surface  12  of the silicon substrate  11 , and a circuit layer  17  formed on the surface  12  of the silicon substrate  11  to electrically connect to the LED dies  18 . The circuit layer  17  is connected to a power supply device at two electrodes  16 . This kind of LED backlight unit has a fixed size when being assembled, and thus it is not able to match the flat display panels having different sizes.  
      Therefore, it is still necessary to develop a LED backlight unit that can be conveniently utilized in the flat display panel with large size.  
     SUMMARY OF THE INVENTION  
      An objective of the present invention is to provide a sectional light emitting diode backlight unit that can be combined as a direct light backlight unit with proper size according to the display panel size.  
      According to the present invention, the sectional light emitting diode backlight unit comprises a circuit board, a frame disposed on the circuit board, a plurality of light emitting diode dies disposed on the circuit board inside the frame, each light emitting diode die being electrically connected to a circuit on the circuit board, a plurality of connecting pads disposed on a first side of the circuit board outside the frame, the connecting pads being electrically connected to a circuit on the circuit board, and an encapsulating material positioned on the circuit board inside the frame to cover the light emitting diode dies; wherein at least one second side of the circuit board has a connection means for assembly with another sectional light emitting diode backlight unit.  
      The sectional light emitting diode backlight unit according to the present invention can be combined as a large-sized backlight unit for a large-sized display panel such as LCD TV. Therefore, the present invention has the advantages as follows. The backlight unit can be manufactured in a relatively smaller size with a simpler package process, and combined as a direct light backlight unit with proper size when applied to a large-sized flat display panel. Since the circuit of each backlight unit is independent, it is convenient to replace it when failed. A plurality of light emitting diode dies are directly disposed on the circuit board so that the resulting backlight unit thickness is thinner than using a plurality of mono-chip light emitting diode packages disposed on the circuit board. A desired luminance of the backlight unit can be maintained by a local adjustment in accordance with the decrease of light intensity sensed by a light sensor.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a schematic diagram of a conventional LED backlight unit.  
       FIG. 2  shows a sectional LED backlight unit according to an embodiment of the present invention.  
       FIG. 3  shows a schematic cross-sectional view of the sectional LED backlight unit shown in  FIG. 2 .  
       FIG. 4  shows a schematic cross-sectional diagram of another embodiment of the sectional LED backlight unit according to the present invention.  
       FIG. 5  shows a schematic diagram of still another embodiment of the sectional LED backlight unit according to the present invention.  
       FIG. 6  shows a schematic diagram of further another embodiment of the sectional LED backlight unit according to the present invention.  
       FIG. 7  shows a schematic diagram of an embodiment of a direct light LED backlight unit combined by the sectional LED backlight units according to the present invention. 
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 2  and  FIG. 3 .  FIG. 2  shows an embodiment of the sectional LED backlight unit according to the present invention, and  FIG. 3  is a schematic cross-sectional view of the sectional LED backlight unit shown in  FIG. 2 . The sectional LED backlight unit  20  comprises a circuit board  22 , a plurality of LED dies  24 , a frame  26 , a plurality of connecting pads  28 , and an encapsulating material  32 , wherein the circuit board  22  has one or more connection means  30  for assembly with one or more another sectional LED backlight units to form a larger backlight device.  
      The circuit board  22  has a circuit to electrically connect the LED dies or other components positioned on the circuit board with a control device or power supply device. Since the high power LED backlight unit produces relatively more heat, materials with better heat conduction are preferred to be the circuit board. The circuit can be designed as a single layer or multi-layer as desired. It is preferred that the circuit board has a reflecting layer on the surface in order to improve light efficiency of the whole sectional LED backlight unit. The frame  26  is disposed on the circuit board  22  to contain the follow-up encapsulating material  32 . Transparent material can be chosen for a transparent frame to avoid shadow on the display panel, but it is not limited. Other opaque materials also can be chosen for an opaque frame. A plurality of LED dies  24  are disposed on the circuit board  22  inside the frame  26 , and each LED die  24  is electrically connected to the circuit board  22  by using a flip chip method or a wiring bonding method. A plurality of connecting pads  28  are disposed on one side of the circuit board  22  outside the frame  26 , and the connecting pads  28  are electrically connected to the circuit on the circuit board  22  in order to be electrically connected with external devices. Each sectional LED backlight unit  20  has an independent circuit. The encapsulating material  32  is positioned on the circuit board  22  inside the frame  26  to cover the LED dies  24 , and the encapsulating material  32  may include, for example, an organic molding compound, a ceramic material permeable to light, a glass material permeable to light, an insulation fluid material permeable to light, or a composite material comprising at least two materials selected from a group consisting of the above-mentioned materials. The encapsulating material  32  may further include at least a wavelength converting material or a scatterer dispersed in the encapsulating material  32  or coated on the encapsulating material  32 . For example, the wavelength converting material can be fluorescent material (phosphor), or the like.  FIG. 4  is a diagram of another embodiment of the sectional LED backlight unit according to the present invention, wherein the encapsulating material  32  further includes the scatterers  33  dispersed in the encapsulating material  32 . The scatterer  33  may include a ceramic material permeable to light, a glass material permeable to light, or the like. The shape and size of the scatterer  33  is not limited.  
      In the sectional LED backlight unit according to the present invention, the plurality of LED dies are arranged in array form, and directly disposed on the circuit board, and thus the sectional LED backlight unit thickness is relatively thinner. Different color LED dies and wavelength converting materials are used according to the desired color of light from the sectional LED backlight unit. For example, red LED dies, green LED dies, and blue LED dies are used to generate a white light, or ultraviolet LED dies are used with red, green, and blue light-emitting wavelength converting materials together to generate a white light, or ultraviolet LED dies and blue LED dies are used with green and red light-emitting wavelength converting materials to generate a white light.  
      Please refer to  FIG. 5 .  FIG. 5  shows another embodiment of the sectional LED backlight unit according to the present invention. According to the present invention, the sectional LED backlight unit  20  may further comprise a diffuser plate  34  positioned over the LED dies  24  to diffuse light, such that the light emitted from the backlight unit is uniform and gentle. The sectional LED backlight unit  20  also may comprise a heat dissipation device  36  to dissipate heat, and the circuit board  22  is positioned on the heat dissipation device  36  for quick transmission of heat away from the backlight unit. For example, the heat dissipation device  36  can be a heat dissipating plate, a heat dissipating fin, a heat dissipating sink, or a heat dissipating pipe. In addition, a heat dissipating paste or gel can be filled between the circuit board  22  and the heat dissipation device  36 .  
      Please refer to  FIG. 6 .  FIG. 6  shows further another embodiment of the sectional LED backlight unit according to the present invention. According to the present invention, the sectional LED backlight unit  20  may further comprise a light sensor  38  positioned on the circuit board  22  to sense light intensity, and the light sensor  38  is electrically connected to a controller that controls light emission of the LED dies, so that the intensity of light emitted from the LED dies  24  can be adjusted through the controller according to the corresponding data of light intensity sensed by the light sensor  38 . Location of the light sensor  38  is not limited, but it is preferred that the light sensor  38  is positioned in the center of the circuit board  22  to obtain a representative light intensity. A plurality of light sensors also can be installed to monitor the light intensity of the LED dies  24  around, and the power for the LED dies  24  to emitting light can be adjusted by using the controllers accordingly. For the sectional LED backlight units, one light sensor is enough if the single LED backlight unit size is not large. The purpose of installing the light sensor  38  inside the sectional LED backlight unit  20  is to compensate the luminance immediately. After the sectional LED backlight unit  20  is used for a period of time, the light intensity sensed by the light sensor  38  might decline, and the controller can increase electric power to the LED dies  24  to increase the luminance in order to maintain a good light output of the sectional LED backlight unit  20 .  
      According to the present invention, at least one side of the circuit board  22  in the sectional LED backlight unit  20  has a connection means for connecting to another sectional LED backlight unit to be an assembled backlight unit having a size as desired.  FIG. 7  shows an embodiment of a direct light LED backlight unit combined by the sectional LED backlight units  20  according to the present invention, and the direct light LED backlight unit can be utilized in a large-sized display panel. In  FIG. 7 , four sectional LED backlight units  20  according to the present invention are connected to each other. For example, the two sectional LED backlight units  20  are connected to each other and fixed on the heat dissipation device by using screw holes and screws. The screw holes can be positioned on the circuit board edge, and the screw holes are, for example, semicircular for not occupying the circuit board area too much, so that when the two sectional LED backlight units  20  are connected to each other, a circular hole is formed. Then, the screws are used to fix the two sectional LED backlight units  20 , and it is convenient for assembly. In addition, the heat dissipation device can be a heat dissipating plate with larger size that is able to support and collocate to fix the sectional LED backlight units  20 . As the combination shown in  FIG. 7 , the length of the combination can be further increased to obtain a desired display panel size.  
      Furthermore, other connection means also can be utilized for the combination of the sectional LED backlight units  20 . For example, the sectional LED backlight units  20  can be connected by using tenons, or adhesion, or an indented edge of the circuit board for connecting with each other. It is preferred to avoid a joint black band occurring in the joint area.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.