Abstract:
A light-emitting diode (LED) assembly and a method for fabrication thereof are disclosed. The LED assembly includes a heat-absorbing member in which a working fluid is provided, an LED die ( 60 ) directly attached to the heat-absorbing member, and a heat-dissipating member thermally attached to the heat-absorbing member. The heat-absorbing member absorbs heat via the working fluid from the LED die and transfers the heat to the heat-dissipating member for dissipation. The method involves directly attaching the LED die to the heat-absorbing member.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to light-emitting diode (LED) assemblies, and more particularly to an LED assembly with improved heat dissipation ability so that heat generated by the LEDs of the assembly can be effectively removed. The present invention relates also to a method of packaging the LEDs.  
       DESCRIPTION OF RELATED ART  
       [0002]     Light-emitting diode (LED) is a highly efficient light source currently used widely in such field as automobile, screen display, and traffic light indication. When the LED operates to give off light, heat is accordingly produced. If not rapidly and efficiently removed, the heat produced may significantly reduce the lifespan of the LED.  
         [0003]      FIG. 7  shows an LED module  10  mounted to a circuit board  18  in accordance with related art. The LED module  10  includes an LED die  11 , a packaging layer  12 , and a pair of conductive pins  14 ,  15 . The LED die  11 , which is placed in a recess defined in the conductive pin  15 , is protectively packaged via the packaging layer  12 . Heat produced by the LED die  11  during its operation is transferred by the conductive pin  15  to the circuit board  18  through which the heat is dissipated into ambient air. In this embodiment, heat dissipation efficiency for the LED die  11  is not satisfactory since the heat is conducted only through the conductive pin  15 , and the circuit board  18  has a relatively low heat removal ability.  
         [0004]      FIG. 8A  and  FIG. 8B  show another kind of LED module  20  with improved heat conduction capability compared with the LED module  10  illustrated in  FIG. 7 . The LED module  20  includes an LED die  21 , a packaging layer  22  and a metal block  23 . Protected by the packaging layer  22 , the LED die  21  is accommodated in a recess defined at a top portion of the metal block  23 . The LED module  20  is mounted within a through hole  281  defined in a circuit board  28 , and a bottom surface of the metal block  23  of the LED module  20  is maintained in thermal contact with a metal plate  29  placed under the circuit board  28 , whereby heat generated by the LED die  21  is capable of being conducted via the metal block  23  to the metal plate  29  for dissipation. In this particular embodiment, the metal plate  29  functions as a heat dissipation device and the metal block  23  has a relatively large contacting surface with the metal plate  29 , thus increasing the heat dissipation efficiency for the LED module  20 . However, before being conducted to the metal plate  29 , the heat generated by the LED die  21  has to travel a long distance through the metal block  23 . Furthermore, if the heat transferred to the metal plate  29  is not dispersed entirely and rapidly over the metal plate  29 , a hot spot may exist at the contacting surfaces between the metal block  23  and the metal plate  29 .  
         [0005]     As an energy-efficient light source, currently LED has a trend of substituting for the well-known fluorescent lamps for indoor lighting purpose. In order to increase the overall lighting brightness, a plurality of LEDs are often incorporated into a single lamp, in which case how to efficiently dissipate heat generated by these LEDs becomes a challenge.  
         [0006]     Therefore, it is desirable to provide an LED assembly wherein one or more of the foregoing disadvantages may be overcome or at least alleviated.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention relates, in one aspect, to a light-emitting diode (LED) assembly. The LED assembly includes a heat-absorbing member in which a working fluid is provided, an LED die directly attached to the heat-absorbing member, and a heat-dissipating member thermally attached to the heat-absorbing member. The heat-absorbing member absorbs heat via the working fluid from the LED die and transfers the heat to the heat-dissipating member for dissipation.  
         [0008]     The present invention relates, in another aspect, to a method of packaging a light-emitting diode (LED). The method includes steps of: (A) providing a heat-absorbing member wherein a working fluid is provided in the heat-absorbing member; (B) attaching an LED die directly to the heat-absorbing member; and (C) thermally attaching a heat-dissipating member to the heat-absorbing member.  
         [0009]     Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an isometric view of an LED assembly in accordance with a first embodiment of the present invention;  
         [0011]      FIG. 2  is a cross-sectional view of the LED assembly of  FIG. 1 ;  
         [0012]      FIG. 3  is a cross-sectional view of an LED assembly in accordance with a second embodiment of the present invention;  
         [0013]      FIG. 4  is a cross-sectional view of an LED assembly in accordance with a third embodiment of the present invention;  
         [0014]      FIG. 5  is a cross-sectional view of an LED assembly in accordance with a fourth embodiment of the present invention;  
         [0015]      FIG. 6  is an isometric view of an LED assembly in accordance with a fifth embodiment of the present invention;  
         [0016]      FIG. 7  is a cross-sectional view of an LED module in accordance with related art;  
         [0017]      FIG. 8A  is an isometric view of an LED assembly in accordance with related art; and  
         [0018]      FIG. 8B  is a cross-sectional view of the LED assembly of  FIG. 8A . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1  illustrates an LED assembly in accordance with a first embodiment of the present invention. The LED assembly includes a heat sink  30 , a heat pipe  40 , a circuit board  50 , and a plurality of LED dies  60 .  
         [0020]     The heat sink  30  is made of highly thermally conductive material such as copper, aluminum, or their alloys. The heat sink  30  as shown in this embodiment is an extruded aluminum heat sink, including a chassis  31  and a plurality of pin fins  32  extending upwardly from the chassis  31 . The chassis  31  defines an elongated groove  311  at a bottom surface thereof for receiving the heat pipe  40  therein. The groove  311  has a substantially rectangular shape.  
         [0021]     The heat pipe  40  is a heat transfer device having a relatively high heat transfer capability due to a phase change mechanism it adopts. The heat pipe  40  has the advantage of low thermal resistance and is capable of transferring a large amount of heat while maintaining a low temperature gradient between different sections thereof. In this particular embodiment, the heat pipe  40  has an elongated, substantially rectangular shaped configuration conforming to the shape of the groove  311  of the heat sink  30 . The heat pipe  40  has a flat bottom surface  41 . The heat pipe  40  is generally made of copper or copper alloy.  
         [0022]     The circuit board  50  defines a plurality of through holes  51  for respectively receiving the LED dies  60  therein. The through holes  51  are arranged in a single row and are spaced from each other. The LED dies  60  are electrically mounted on the circuit board  50  via a plurality of wires (not labeled).  
         [0023]     With reference to  FIG. 2 , in assembly, the heat pipe  40  is placed in the groove  311  of the heat sink  30 , and is thermally and mechanically connected to the heat sink  30 . Preferably, the heat pipe  40  is connected to the heat sink  30  via a layer of thermal interface material (TIM) such as thermal grease or tape. Alternatively, the heat pipe  40  is soldered to the heat sink  30  via a soldering material such as tin. The circuit board  50  is attached to the bottom surface of the chassis  31  of the heat sink  30  in such a manner that the through holes  51  in the circuit board  50  correspond to the flat bottom surface  41  of the heat pipe  40 . A layer of dielectric material (not shown) such as a thin layer of rubber may be arranged between the heat sink  30  and the circuit board  50  so as to electrically insulate the circuit board  50  from the heat sink  30 . The LED dies  60  are respectively received in the through holes  51  of the circuit board  50 , and are maintained in thermal and physical contact with the bottom surface  41  of the heat pipe  40 . Preferably, a thin layer of TIM  70  is arranged between the bottom surface  41  of the heat pipe  40  and a top surface (not labeled) of each of the LED dies  60 . Each of the LED dies  60  is electrically connected to the circuit board  50  via a pair of wires (not labeled). In order to protect these LED dies  60 , a packaging layer  80  is provided to encapsulate each of the LED dies  60 . The packaging layer  80  is light penetrable and is generally made of polymeric material such as resin. The packaging layer  80  also functions to firmly secure the LED dies  60  in place.  
         [0024]     In operation, the LED dies  60  give off light and at the same time generate a large amount of heat. The heat then is directly transferred to the heat pipe  40 . As is best shown in  FIG. 2 , the heat pipe  40  has a hollow pipe body and contains a working fluid (not labeled) such as water therein. The heat pipe  40  generally is vacuumed. Against an inner surface of the pipe body is a wick structure  42 , which is typically in the form of a plurality of fine grooves, a mesh screen or sintered powder, as is well known in the art by those skilled persons. As the heat is transferred to the heat pipe  40 , the working fluid contained therein absorbs the heat and evaporates into vapor. Since the spreading resistance with regard to the vapor is negligible, the vapor which carries the heat then runs quickly to be full of an interior of the heat pipe  40 , and whenever the vapor comes into contact with cooler walls (i.e., the top wall and the side walls) of the heat pipe  40 , it releases the heat to the heat sink  30  which thermally contacts with the top and side walls. After the heat is released, the vapor condenses into liquid, which is then brought back by the wick structure  42  to the evaporating region, i.e., the contacting interface between the heat pipe  40  and each of the LED dies  60 . Since the heat pipe  40  transfers the heat employing a phase change mechanism of the working fluid, the heat transferred to the heat pipe  40  from the LED dies  60  is thus rapidly and evenly distributed over the entire pipe body and then is further conveyed to the heat sink  30  through which the heat is dissipated into ambient air.  
         [0025]     In the present LED assembly, the heat pipe  40  has a much higher heat transfer capability in comparison with the metal block  23  as shown in  FIGS. 8A and 8B , which helps to conduct the heat from the LED dies  60  to the heat sink  30  more quickly. Furthermore, since the heat pipe  40  employs the working fluid to transfer the heat, the heat is capable of being distributed quickly throughout the heat pipe  40  and accordingly the heat sink  30 , hot spot problem suffered by the related art is thus effectively avoided.  
         [0026]      FIG. 3  illustrates a second embodiment of the present LED assembly, in which a plurality of recesses  43  are defined at the bottom surface  41  of the heat pipe  40   a  whereby the LED dies  60  are respectively received in the recesses  43  when they are mounted to the heat pipe  40   a.  Due to the presence of the recesses  43 , the LED dies  60  and the heat pipe  40   a  are capable of being assembled in a more compact manner.  
         [0027]     Apparently, in order to increase the heat dissipation efficiency for the LED assembly, multiple heat pipes  40  can be used. For example, two or more heat pipes  40  can be thermally attached to the chassis  31  of the heat sink  30 .  
         [0028]      FIG. 4  illustrates a third embodiment of the present LED assembly, in which a vapor chamber-based heat spreader  100  is provided. The heat spreader  100  has a much larger size than the heat pipe  40  shown in the first embodiment. The heat spreader  100  has a top surface from which a plurality of fins  34  extend upwardly and a flat bottom surface to which a circuit board  50   a  is attached. In this embodiment, the circuit board  50   a  defines three rows of through holes  51  therein. The LED dies  60  are respectively located in the through holes  51  and are maintained in thermal and physical contact with the bottom surface of the heat spreader  100 , either directly or through a layer of TIM. The heat spreader  100  contains a working fluid therein and also employs a phase change mechanism to transfer heat. The heat from the LED dies  60  is directly transferred to the heat spreader  100  and then is transferred from the heat spreader  100  to the fins  32  for dissipation. As with the heat pipe  40   a  shown in  FIG. 3 , the heat spreader  100  may also define a plurality of recesses at the bottom surface thereof for accommodating the LED dies  60  therein. In this embodiment, more LED dies  60  can be provided to the assembly so as to increase the overall lighting brightness.  
         [0029]      FIG. 5  illustrates a fourth embodiment of the present LED assembly, which is similar to the third embodiment shown in  FIG. 4 . However, the vapor chamber-based heat spreader  100   a  in this embodiment has a plurality of protrusions  101  extending outwardly from the bottom surface thereof. These protrusions  101  correspond to the through holes  51  defined in the circuit board  50   b  and are positioned in these through holes  51 . The LED dies  60  are thermally and physically attached to these protrusions  101 , either directly or by a layer of TIM. The presence of these protrusions  101  facilitates the positioning and securing of the circuit board  50   b  to the heat spreader  100   a.    
         [0030]      FIG. 6  shows a fifth embodiment of the present LED assembly. The LED assembly in this embodiment employs a liquid cooling system to dissipate the heat generated by the LED dies  60 . The liquid cooling system includes a cold plate  200  through which a working fluid such as water (hereinafter as “coolant”) is circulated, a pump  210 , a heat exchanger  230  and a plurality of connecting pipes  220 . In this embodiment, the circuit board  50   c  defines a plurality of rows of through holes  51  therein. The cold plate  200  defines a flow channel  201  therein for passage of the coolant. The flow channel  201  is wave-shaped in order to increase heat exchange area between the coolant and the cold plate  200 . The LED dies  60  are respectively received in the through holes  51  of the circuit board  50   c  and are maintained in thermal and mechanical contact with a top surface of the cold plate  200 , either directly or via a layer of TIM. As the coolant passes through the flow channel  201 , it receives the heat generated by the LED dies  60 . The pump  210  drives the coolant to flow into the connecting pipe  220  through which the coolant is guided to the heat exchanger  230  where the heat carried in the coolant is released. Thereafter, the cooled coolant is sent back by the pump  210  to the cold plate  200  where it again available for absorbing heat from the LED dies  60 .  
         [0031]     According to the foregoing embodiments of the present LED assembly, the LED dies  60  are directly attached to the heat pipe  40  ( 40   a ), the vapor chamber-based heat spreader  100  ( 100   a ) or the cold plate  200 . The heat pipe  40  ( 40   a ), the heat spreader  100  ( 100   a ) or the cold plate  200  functions as a heat-absorbing member directly absorbing the heat from these LED dies  60 . Also, a working fluid is provided in the heat-absorbing member so as to effectively transfer the heat absorbed to a heat-dissipating member (i.e., the heat sink  30 , the fins  34  or the heat exchanger  230 ) which is thermally connected with the heat-absorbing member. In particular, the heat is rapidly transferred from the heat-absorbing member to the heat-dissipating member for dissipation via a phase change mechanism or a rapid circulation of the working fluid in the heat-absorbing member, whereby the heat generated by the LED dies  60  is efficiently and effectively removed.  
         [0032]     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.