Patent Publication Number: US-2007108464-A1

Title: Led package with improved heat dissipation and led assembly incorporating the same

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of Korean Patent Application No. 10-2005-0110474 filed on Nov. 17, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a Light Emitting Diode (LED) and, more particularly, to an LED package having a package base made of a thermally conductive polymer to improve heat dissipation performance and an LED assembly incorporating the same.  
      2. Description of the Related Art  
      To date, LEDs are being adopted as a light source of backlight units for use with lighting devices and Liquid Crystal Displays (LCDs).  
      Such LEDs are semiconductor devices that are activated in response to electric current to generate various colors of light. The color of light generated by an LED is mainly determined by chemical components of LED semiconductor. Such LEDs have several merits such as longer lifetime, lower driving voltage, better initial activation characteristics, higher vibration resistance and higher tolerance on repetitive power switching over conventional lighting devices using filaments, and thus demand for them is gradually on the rise.  
      However, an LED chip does not perfectly convert current into light and thus generates heat at a considerable amount. The heat if not dissipated or radiated properly may give stress to internal elements of the LED thereby to shorten the lifetime of the LED. To solve this problem, the LED dissipates or radiates heat to the outside by using a heat dissipation or radiation structure having metal lead frames.  
      An example of such a heat dissipating structure is shown in  FIGS. 1 and 2 .  
      Referring to  FIG. 1  first, an LED package  10  includes a thermal conducting member  14  with an LED chip  12  seated thereon. The thermal connecting member  14  also functions as heat guide means. The LED chip  12  is powered via a pair of wires  16  and a pair of leads  18 . An encapsulant  20  of typically silicone is arranged to encapsulate the LED chip  12 , and a lens  22  is capped on the encapsulant  20 . A housing  24  is arranged around the thermal connecting member  14  to support the thermal connecting member  14  and the leads  18 .  
      The LED package  10  shown in  FIG. 1  is mounted on a metal board  30  acting as a heat sink as shown in  FIG. 2  thereby to constitute an LED assembly. A thermally conductive pad  36  such as solder is interposed between the heat conducting member  14  of the LED package  10  and a metal body  32  of the main board  30  to promote heat conduction between them. In addition, the leads  18  are also stably connected to a circuit pattern  34  on the metal body  32  of the metal board  30 .  
      However, this type of heat dissipation structure has drawbacks as follows. First, it is too complicated to be automated and has a number of parts to be assembled together, which inevitably raise manufacturing cost. Moreover, this structure can be hardly reduced in size owing to its complicity and the large number of parts.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide an LED package with improved heat dissipation performance owing to a package base formed of a thermally conductive polymer and an LED assembly incorporating the same.  
      Another aspect of the invention is to improve the reflectivity of the LED package by providing a reflector around an LED chip.  
      Further another aspect of the invention is to insert the LED package at least partially into a metal board in order to further enhance heat dissipation efficiency.  
      According to an aspect of the invention, an LED package includes a base made of a thermally conductive polymer; a pair of terminals formed on an upper side of the base; a LED chip electrically connected to the terminals; and a transparent encapsulant arranged on the upper side of the base to encapsulate the LED chip.  
      The LED package may further include a wall extended from a periphery of the upper side of the base beyond the LED chip to form a recess surrounding the LED chip, where the transparent encapsulant is filled.  
      The LED package may further include a reflector applied on an inner surface of the wall of the base.  
      Preferably, the reflector comprises metal. More preferably, the reflector comprises at least one selected from the group consisting of Ag, Al, Au, Cu, Pd, Pt, Rd and alloys thereof. The reflector may comprise a deposit. The LED package may further include an insulating layer formed on a predetermined area in an upper side of the terminals to insulate the reflector from the terminals.  
      Preferably, the reflector comprises a metal film bonded to an inner surface of the wall of the base.  
      The wall may be integral with the base or comprise a separate body bonded to the base.  
      According to another aspect of the invention, an LED assembly includes a metal board having a circuit pattern formed on an upper side thereof and an LED package as described above, mounted on the upper side of the metal board. The terminals of the light emitting diode package are electrically connected to the circuit pattern.  
      Preferably, the metal board has a recess for receiving at least a part of the light emitting diode package.  
      The LED assembly may further include an upper board attached to the upper side of the metal board, the upper board receiving at least a part of the light emitting diode package to expose the transparent encapsulant.  
      Preferably, the metal board may be at least a part of a board of a backlight unit on which the light emitting diode assembly is mounted as a light source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a cross-sectional perspective view illustrating an LED package of the related art;  
       FIG. 2  is a cross-sectional view illustrating the LED package of  FIG. 1  mounted on a metal board;  
       FIG. 3  is a perspective view illustrating an LED package of the invention;  
       FIG. 4  is a cross-sectional view illustrating the LED package of  FIG. 3  taken along the line  4 - 4  of  FIG. 3 , mounted on a metal board;  
       FIG. 5  is a cross-sectional view illustrating the LED package of  FIG. 3  taken along the line  5 - 5  of  FIG. 3 , received in a recess of a metal board;  
       FIG. 6  is a cross-sectional view illustrating an LED package according to another embodiment of the invention;  
       FIG. 7  is a cross-sectional view illustrating a variation to the LED package shown in  FIG. 6 ;  
       FIG. 8  is an exploded cross-sectional view of the LED package shown in  FIG. 7 ;  
       FIG. 9  is an exploded cross-sectional view illustrating another variation to the LED package shown in  FIG. 6 ;  
       FIG. 10  is a perspective view illustrating an LED assembly of the invention;  
       FIG. 11  is a perspective view illustrating an LED assembly according to another embodiment of the invention;  
       FIG. 12  is an exploded cross-sectional view illustrating an LED assembly according to further another embodiment of the invention;  
       FIG. 13  is an assembled cross-sectional view of the LED assembly shown in  FIG. 13 ; and  
       FIG. 14  is a side elevation view illustrating an LED assembly according to still another embodiment of the invention, shown partially in cross-section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  
       FIG. 3  is a perspective view illustrating an LED package  100  of the invention, and  FIG. 4  is a cross-sectional view illustrating the LED package  100  taken along the line  4 - 4  of  FIG. 3 , mounted on a metal board  130 .  
      Referring to  FIGS. 3 and 4 , the LED package  100  of this embodiment includes a base  102  made of a thermally conductive polymer, a pair of terminals  104  formed on an upper side of the base  102 , an LED chip  106  attached to one of the terminals  104  and electrically connected to both of the terminals  104  via wires W, and a transparent encapsulant  108  arranged on the upper side of the base  102  to encapsulate the LED chip  106 .  
      The LED package  100  has an external appearance similar to a common surface mounted LED package. However, unlike the common LED package, the LED package  100  of this embodiment has the base  102  made of a thermally conductive polymer.  
      The term “thermally conductive polymer” indicates a polymer that is specially fabricated to have an excellent thermal conductivity. It is generally known that the thermally conductive polymer has a thermal conductivity of 1 W/mK or more.  
      Representative examples of the thermally conductive polymer include Coolpoly® available from Cool Polymer Inc of the United States and LUCON 9000™ available from LG Chem, Ltd. of Korea.  
      Coolpoly® has a thermal conductivity in the range from 10 W/mK to 100 W/mK, which is a very high thermal conductivity in view of Al having a thermal conductivity of about 200 W/mK and common plastics have a thermal conductivity of about 0.2 W/mK. Coolpoly® also has relatively good workability such as formability.  
      LUCON 9000™ has a thermal conductivity in the range from 1 W/mK to 50 W/mK which is relatively lower than that of Coolpoly® but still shows a performance about 50 times or more with respect to common plastics. It is also known that LUCON 9000™ has better formability than Coolpoly®.  
      Considering desired thermal conductivity and formability, it is preferable that the thermally conductive polymer has a thermal conductivity of 10 or more.  
      With the base  102  made of the thermally conductive polymer, heat generated from the LED chip  106  is conducted effectively to the outside also via the base  102 .  
      As shown in  FIG. 4 , the LED package  10  of this embodiment is mounted on a metal board  130  acting as a heat sink thereby to constitute an LED assembly. The metal board  130  includes a board body  132  made of metal and a circuit pattern  134  formed on the board body  132  with an insulating pattern (not shown) interposed between the board body  132  and the circuit pattern  134 .  
      The terminals  104  are connected to the circuit pattern  134  to conduct heat to the board body  132  through the pattern  134  in a similar manner as in the prior art. In the meantime, the heat conducted through the terminals  104  to the package base  102  is conducted to the board body  132  of the metal board  132  through the contact between the base  102  and the metal board body  132 . That is, as shown in FIG.  4 , a thermally conductive pad  136  may be interposed between the underside of the LED package base  102  and the top surface of the metal board body  132  to ensure heat conduction between the package base  102  and the board body  132 . In this manner, the LED package base  102  having excellent thermal conductivity can completely conduct heat from the terminals  104  to the metal board body  132  so that the LED chip  106  can maintain a suitable temperature.  
      Comparing  FIG. 4  with  FIG. 2 , the heat dissipation structure of this embodiment is simplified but can obtain a heat dissipation performance substantially the same as that of the prior art. This results from excellent thermal conductivity of the LED package base  102  as described above.  
      Heat dissipation effect through direct contact between the LED package base  102  and the metal board  130 - 1  will now be described with reference to  FIG. 5  that is a cross-sectional view illustrating the LED package  100  of  FIG. 3  taken along the line  5 - 5  of  FIG. 3 , received in a recess of a metal board  130 - 1 . A circuit pattern  138  connected with the terminals  106  of the LED package  100  is arranged on the recess of the metal board  130 - 1  with an insulating layer (not shown) interposed between the circuit pattern  138  and a body of the metal board  130 - 1 .  
      Alternatively, the circuit pattern  138  may be arranged on the sidewall of the recess or the top surface of the metal board  130 - 1  to be connected with the terminals  106  of the LED package  100 .  
      This allows the LED package base  102  to be in direct contact with the metal board  150 . With the LED package  100  received in the recess of the metal board  130 - 1 , any heat generated from the LED chip  102  is conducted through the LED package base  102  to the metal board  150  as described above. Such heat conduction is easily carried out owing to high thermal conductivity of the LED package base  102  as described above, and thus the LED chip  106  can maintain a suitable temperature.  
      Effective heat dissipation performance like this through direct contact between the LED package base  102  and the metal base  150  cannot be realized by the prior art.  
      While it has been illustrated in  FIG. 5  that only the base  102  of the LED package  100  is received in the metal board  130 - 1 , it is not intended to limit the invention. Rather, the LED package  100  may be received in the metal board  130 - 1  to the extent that the LED chip  106  is positioned under the top surface of the metal board  130 - 1 . With this arrangement, the sidewall of the recess of the metal board  130 - 1  can act as a reflector so that light of the LED chip  106  can be guided upward more effectively.  
       FIG. 6  is a cross-sectional view illustrating an LED package  200  according to another embodiment of the invention.  
      Referring to  FIG. 6 , the LED package  100  of this embodiment includes a base  202  made of a thermally conductive polymer, first and second terminals  210  and  212  formed on a portion of the base  202 , an LED chip  220  attached to the first terminal  210  and electrically connected to both of the terminals  210  and  212  via wires W, and a transparent encapsulant  230  arranged on the upper side of the base  202  to encapsulate the LED chip  220 .  
      The package base  202  is divided into an upper base part  202   a  and a lower base part  202   b  across the terminals  210  and  212 . The upper base part  202   a  is in the form of a wall with a recess  206  formed therein. The wall has an inner surface  204  acting as a reflector to guide light of the LED chip  220  in the direction of arrow A.  
      The LED package  200  of this structure is configured suitable to project light from LED chip  220  in a specific direction. Since the LED package  200  of this structure is generally required of high power, the LED chip  200  generates a large amount of heat. Thus, the package base  202  made of a thermally conductive polymer as described above is particularly advantageous to radiate or dissipate the heat to the outside.  
      The LED package  200  of this embodiment can be also applied in the form of  FIG. 4  or  5  to conduct heat more effectively to the metal board.  
      Alternatively, the LED package of  FIG. 6  may be configured to be flat in a vertical direction of the paper as shown in  FIG. 14 . Such an LED package  200  (see  FIG. 14 ) is also referred to as a side-view LED package which also can effectively dissipate or radiate heat to a metal board carrying the LED package  200 .  
       FIG. 7  is a cross-sectional view illustrating an LED package  200 - 1  that is a variation to the LED package  200  shown in  FIG. 6 , and  FIG. 8  is an exploded cross-sectional view of the LED package  200 - 1  shown in  FIG. 7 .  
      Referring to  FIGS. 7 and 8 , the LED package  200 - 1  is substantially the same as the LED package  200  shown in  FIG. 6  except for a reflector  230  applied to an inner surface  204  of the LED package  200 . Accordingly, the like reference signs are used to designate the like components, and the detailed description thereof will be omitted.  
      The reflector  230  made of metal is configured to cover substantially the entire inner surface  204  of the wall of the LED package base  202 , and at the bottom end thereof, contacts the terminals  210  and  212 . The reflector  230  is divided into two reflector parts  230   a  and  230   b  with a predetermined gap G so that the reflector part  230   a  contacts the terminal  210  and the reflector part  230   b  contacts the terminal  212 . With this arrangement, the terminals  210  and  212  in contact with the reflector  230  may be protected from short-circuit. Of course, it is also possible to make the reflector  230  not to contact the terminals  210  and  212 , that is, the reflector  230  to be separated from the terminals  210  and  212  at a predetermined interval. In such a case, it is not required to divide the reflector  230  into the reflector parts  230   a  and  230   b  with the gap G.  
      In this embodiment, the reflector  230  is manufactured of a high reflectivity metal, and preferably, of at least one selected from the group consisting of Ag, Al, Au, Cu, Pd, Pt, Rd and alloys thereof.  
      In addition, the reflector  230  is provided in the form of a sheet metal or metal film, and attached to the inside wall  204  of the LED package base  202  via adhesive and the like. Alternatively, the reflector  230  may be attached to the inside wall  204  of the LED package base  202  via interference fit.  
      With this arrangement, the reflector  230  can reflect light of the LED chip  220  in an upward direction as designated with arrow A, thereby improving light efficiency of the LED package  200 - 1 . In addition, the reflector  230  reflects light so as not to be absorbed by the inside wall  204 , thereby to insulate heat that otherwise may be applied to the interior of the LED package  200 - 1 .  
      Alternatively, the reflector  230  may be provided by deposition. That is, the reflector  230  may be formed by bonding high reflectivity metal particles to the inner surface  204  of the upper base part  202   a  of the LED package base  202  through sputtering or electron beam process.  
      In this case, the reflector  230  is formed in the form of a film, and possibly, to a thickness of several Å to several μm. However, the thickness of the reflector  230  is not specifically limited but may be set to any value that can effectively reflect light from the LED chip  220  in the direction of arrow A.  
      In this case, it is preferable to previously form an insulating layer (not shown) on regions where the inner surface  204  contacts the terminals  210  and  212  so that the reflector  230  does not contact the terminals  210  and  212 .  
      With this arrangement, the reflector  230  can reflect light from the LED chip  220  in the upward direction as indicated with arrow A, thereby improving light efficiency of the LED package  200 - 1 . The reflector  230  also reflects light not to be absorbed into the inner surface  204 , thereby to insulate heat that may otherwise be applied to the interior of the LED package  200 - 1 . Furthermore, the reflector  230  can be arranged continuously on the entire inner surface  204  of the upper base part  202   a  of the base  202 , thereby to improve reflection efficiency over the embodiment shown in  FIG. 6 .  
      As another alternative, the reflector  230  may be made of a high reflectivity polymer. That is, the reflector  230  may be provided for example by applying the high reflectivity polymer on the inner surface  204  of the upper base part  202   a . In this case, it is not required to separate the reflector  230  into the reflector parts  230   a  and  230   b  as in  FIG. 8 .  
       FIG. 9  is an exploded cross-sectional view illustrating another variation to the LED package  200 - 2  shown in  FIG. 6 . The LED package  200 - 2  shown in  FIG. 9  has a base made by attaching an upper base part  203  to a lower base part  202 .  
      In this arrangement, the lower base part  202  is made of a thermally conductive polymer as described above, but the upper base part  203  is made of a common polymer. The upper base part  203  integrally bonded to the lower base part  202  via for example adhesive makes a structure that is substantially the same as the LED package  200  shown in FIG.  6 . Since the upper base part  203  is made of a common polymer, the LED package  200 - 2  also has a merit in that the inner surface  204  of the upper base part  203  has a higher reflectivity than that of  FIG. 6 .  
      Alternatively, it is possible to realize more excellent reflection efficiency by making the upper base part  203  of a high reflectivity polymer. Also, further excellent reflection efficiency can be obtained by providing the reflector  230  of  FIG. 7  to the inner surface  204  of the upper base part  203 .  
       FIG. 10  is a perspective view illustrating an LED assembly of the invention.  
      The LED assembly shown in  FIG. 10  is used particularly for lighting, and includes a plurality of LED packages  100  and a metal board  130 . Each LED package  100  has a structure the same as that illustrated in FIGS.  3  to  5 , and the metal board  130  has a structure basically the same as that illustrated in  FIG. 4 . A circuit pattern (see the reference sign  134  in  FIG. 4 ) is formed on the surface of the metal board  130  to be connected with the terminals (see the reference sign  104  in  FIG. 4 ) of the LED packages  100 .  
      With this arrangement, heat generated from the LED package  100  can be efficiently conducted to metal board  130  through the LED package base (see the reference sign in FIG.  4 ), thereby preventing heat stress that otherwise may be applied to the LED package  100 .  
       FIG. 11  is a perspective view illustrating an LED assembly according to another embodiment of the invention.  
      The LED assembly shown in  FIG. 11  is used particularly for lighting, and includes a plurality of LED packages  100  (only one is shown) and a metal board  130 - 1  having a plurality of recesses  136  corresponding to the LED packages  100 . Each LED package  100  has a structure the same as that illustrated in FIGS.  3  to  5 , and the metal board  130 - 1  has a structure basically the same as that illustrated in  FIG. 5 . A circuit pattern (see the reference sign  138  in  FIG. 5 ) is formed on the surface of the metal board  130 - 1  or the recesses  136  to be connected with the terminals (see the reference sign  104  in  FIG. 5 ) of the LED packages  100 .  
       FIGS. 12 and 13  are cross-sectional views illustrating an LED assembly according to further another embodiment of the invention.  
      Referring to  FIGS. 12 and 13 , the LED assembly includes a plurality of LED packages  100 , a metal board  130  mounted with the LED packages  100  and an upper board  140  having holes H corresponding to the LED packages  100 . Here, the LED packages  100  and the metal board  130  are structured substantially the same as those shown in  FIG. 10 .  
      With this arrangement, the holes H of the upper board  140  act as reflectors that guide light from the LED chips  106  to emit upward. Accordingly, the LED assembly of this embodiment has substantially the same function as that illustrated in  FIG. 11 . The upper board  140  is preferably made of a high reflectivity material. For example, the upper board  140  may be made of one selected from high reflectivity polymers and various metals.  
       FIG. 14  is a side elevation view illustrating an LED assembly according to other embodiment of the invention, shown partially in cross-section.  
      The LED assembly shown in  FIG. 14  is applied to a backlight unit  170 . In  FIG. 14 , an LED package  200  is shown in a cross-section taken along the line  14 - 14  of  FIG. 6 , and corresponds to a side view LED package.  
      The LED assembly of this embodiment is realized by mounting the LED package  200  in plural numbers on the metal board  130  to be arrayed in a direction vertical to the paper of  FIG. 14 . The metal board  130  of the LED assembly  200  also serves as a circuit board of the backlight unit  170 , and the LED packages  200  serve as a light source of the backlight unit  170 .  
      A light guide plate  150  is placed on the board  130 , and a scattering pattern  152  such as microstructural features is formed on the underside of the light guide plate  150 . With this arrangement, light beams L introduced into the light guide plate  150  from the LED package  200  propagate inside the light guide plate  150 , and when scattered upward at the scattering pattern  152 , exit the light guide plate  150 , thereby backlighting an LCD panel  160  placed above the light guide plate  150 .  
      In this arrangement also, the base  202  of the LED package  200  has excellent thermal conductivity to efficiently conduct heat from the LED chip  220  to the metal board  130 , and thus the LED package  200  and the LED chip  220  therein can maintain a suitable temperature.  
      As described above, the LED package and the LED assembly according to the exemplary embodiments of the invention are provided with the package base made of a thermally conductive polymer, which can improve heat dissipation performance remarkably. Optionally, the reflector arranged around the LED chip can improve the reflecting efficiency of the LED package. Moreover, the LED package may be received at least partially in the metal board to further improve the heat dissipation efficiency.  
      While the present invention has been described with reference to the particular illustrative embodiments and the accompanying drawings, it is not to be limited thereto but will be defined by the appended claims. It is to be appreciated that those skilled in the art can substitute, change or modify the embodiments into various forms without departing from the scope and spirit of the present invention.