Patent Publication Number: US-2010117113-A1

Title: Light emitting diode and light source module having same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following commonly-assigned copending applications: application Ser. No. 12/168,783, entitled “LIGHT EMITTING DIODE WITH AUXILIARY ELECTRIC COMPONENT”; and application Ser. No. 12/233,005, entitled “THERMOELECTRIC COOLER AND ILLUMINATION DEVICE USING SAME”. Disclosures of the above-identified applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to light emitting diodes (LEDs), and particularly to an LED having high heat transfer efficiency and a light source module using the LED. 
     2. Description of Related Art 
     In recent years, due to excellent light quality and high luminous efficiency, light emitting diodes (LED) have increasingly been used to substitute for cold cathode fluorescent lamps (CCFL) as a light source of an illumination device, referring to “Solid-State Lighting: Toward Superior Illumination” by Michael S. Shur, or others. on proceedings of the IEEE, Vol. 93, NO. 10 (October, 2005). 
     Referring to  FIG. 5 , a typical LED  100  includes a substrate  102 , an LED chip  104  disposed on the substrate  102 , and an encapsulant material  106  covering the LED chip  104 . In operation, the LED  100  is mounted to a circuit board  108 . The LED chip  104  emits light and generates heat therefrom. The light passes through the encapsulant material  106  to illuminate. The heat is transferred to the circuit board  108  by the substrate  102 , and dissipated in the air. However, a conventional material of the substrate  102 , such as fiberglass generally has high thermal resistance. Heat transfer efficiency of the LED  100  is limited due to the high thermal resistance of the substrate  102 . Thus, the heat from the LED  100  can not be dissipated quickly, and light intensity of the LED  10  may be attenuated gradually, shortening life thereof. 
     What is needed, therefore, is an LED having high heat transfer efficiency which can overcome the limitations described, and a light source module using the LED. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is cross-section of a LED, in accordance with a first embodiment. 
         FIG. 2  is cross-section of a LED, in accordance with a second embodiment. 
         FIG. 3  is cross-section of a LED, in accordance with a third embodiment. 
         FIG. 4  is cross-section of a light source module according to a fourth embodiment using a plurality of LEDs in  FIG. 1 . 
         FIG. 5  is a schematic view of a typical LED. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a LED  10  in accordance with a first embodiment is shown. The LED  10  includes a substrate  11 , an LED chip  12 , and an encapsulant material  15 . 
     The substrate  11  supports the LED chip  12  and the encapsulant material  15  thereon, and may be made of ceramic material, which has good electrical insulation property. The ceramic material can be comprised of a mixture of silicon oxide (SiO 2 ) and aluminum oxide (Al 2 O 3 ). The substrate  11  includes a first surface  110  and a second surface  112  surrounding the first surface  110 . The second surface  112  connects with the first surface  110  to cooperatively form an accommodating space  114  for receiving the LED chip  12 . The substrate  11  has at least one first through hole  116  defined in the first surface  110  to communicate with the accommodating space  114 . In the first embodiment, one first through hole  116  is defined and filled with a first thermally conductive material  1160 . The first thermally conductive material  1160  may be metal material, such as copper, silver, etc. 
     The LED chip  12  is mounted directly on the first surface  110  of the substrate  11  to contact the first thermally conductive material  1160  in the first through hole  116 . Thereby the first thermally conductive material  1160  in the first through hole  116 , together with the substrate  11  can transfer the heat generated by the LED chip  12  to the outside of the LED  10 . In this manner, the LED chip  12  may operate continually within an acceptable temperature range to achieve stable optical performance, and the brightness and the luminous efficiency of the LED  10  are stably maintained. The first thermally conductive material  1160  in this embodiment is silver, which has a high heat transfer coefficient of about 430 W/mk, and has anti-oxidation characteristic. To prevent the first thermally conductive material  1160  and the ceramic material of the substrate  11  expanding and crushing one another if unevenly heated, in the first embodiment, the ceramic material of the substrate  11  has a thermal expansivity in a range from about 5.8 ppm/° C. to about 6.2 ppm/° C., and the first thermally conductive material  1160  has a thermal expansivity in a range from about 7 ppm/° C. to about 10 ppm/° C., which is near to that of the ceramic material. 
     The LED  10  further includes a positive electrode  170  and a negative electrode  172  formed on the first surface  110 . The LED chip  12  is electrically connected to the positive electrode  170  and the negative electrode  172  each through a first wire  1700 , and each first wire  1700  is further connected to an exterior power supply (not shown) having an anode and a cathode through a second wire  1800  (encapsulated in the substrate  11  in  FIG. 1 ). Thereby, electric current can be applied to the LED chip  12 . 
     The encapsulant material  15  is disposed on the first surface  110  of the substrate  11  to fill the accommodating space  114  and cover the LED chip  12 , as well as the positive electrode  170  and the negative electrode  172 . The encapsulant material  15  is configured for optically adjusting (e.g., diverging or converging) a direction of the light emitted from the LED chip  12 , thus adjusting an illuminating scope of the LED  10 . In addition, the encapsulant material  15  protects the LED chip  12  from contaminants. The encapsulant material  15  is arc-shaped in this embodiment. 
     Referring to  FIG. 2 , an LED  20 , in accordance with a second embodiment, is shown. The LED  20  is similar to the LED  10  in the first embodiment except that a substrate  21  has four first through holes  216  defined in a first surface  210  thereof. The four first through holes  216  are parallel with one another, and each is filled with a first thermally conductive material  2160  contacting the LED chip  22 . 
       FIG. 3  illustrates an LED  30  according to a third embodiment. The LED  30  is similar to the LED  20  in the second embodiment except that the LED  30  includes two LED chips  32  disposed on a substrate  31  and adjacent to one another. The two LED chips  32  are each electrically connected to a positive electrode  370  and a negative electrode  372  through a first wire  3700 . In addition, the substrate  31  has six first through holes  316  defined in a first surface  310  thereof. Each LED chip  22  contacts a thermally conductive material  3160  through several of the first through holes  316 , for example, through three first through holes  316 . 
     Referring to  FIG. 4 , a light source module  40 , in accordance with a fourth embodiment, is shown. The light source module  40  includes a circuit board  41 , a plurality of LEDs  10  mounted on the circuit board  41 , and a heat dissipation plate  43  contacting the circuit board  41 . 
     The LEDs  10  according to the fourth embodiment all have a same structure as the LED  10  in the first embodiment. Therefore, for the purpose of brevity, the LEDs  10  in the fourth embodiment are not further described herein with the understanding that like reference numbers of the LED  10  in the first embodiment refer to like parts in the LEDs  10  in the fourth embodiment. The LEDs  10  in the fourth embodiment are used as a light source for illumination. In alternative embodiments, the LEDs in the fourth embodiment can be the LEDs  20  from the second embodiment and/or the LEDs  30  from the third embodiment. 
     The circuit board  41  can be a ceramic circuit board, or a fiberglass circuit board (FR4). The circuit board  41  includes a third surface  410  and an opposite fourth surface  412 . The LEDs  10  are arranged on the third surface  410  and electrically coupled to the circuit board  41  by connecting the second wires  1800  to the circuit board  41  (not shown). 
     The circuit board  41  has a plurality of second through holes  416  defined in the third surface  410  corresponding to the first through holes  116 . Each second through hole  416  is filled with a second thermally conductive material  4160  contacting the first thermally conductive material  1160  in the corresponding first through hole  116 . 
     The heat dissipation plate  43  is coupled to the circuit board  41  through a bonding sheet  42 . The bonding sheet  42  may be an insulated adhesive layer coated between the fourth surface  412  and the heat dissipation plate  43 , and has a surface  420  coinciding with the fourth surface  412 . The bonding sheet  42  has a plurality of third through holes  426  defined in the surface  420  corresponding to the second through holes  416 . Each third through hole  426  is filled with a third thermally conductive material  4260  contacting the second thermally conductive material  4160  in the corresponding second through hole  416 , and the heat dissipation plate  43 . The first, the second, and the third thermally conductive materials  1160 ,  4160  and  4260  each can be metal material with high thermal conductivity, such as silver, silver alloy, or others. The heat dissipation plate  43  can be made of metal, such as copper, aluminum, or others. In operation, heat from each LED  10  can be transferred in sequence from the first thermally conductive material  1160 , the corresponding second thermally conductive material  4160 , and the corresponding third thermally conductive material  4260  to the heat dissipation plate  43 . The heat then can be dissipated efficiently by the heat dissipation plate  43  to the air. It is noted, that a diameter of each second through hole  416  is larger than that of the corresponding first through hole  116 . Thereby ensuring a contacting surface of the first thermally conductive material  1160  in each first through hole  116  completely contacts the second thermally conductive material  4160  in the corresponding second through holes  416 . The heat may be fully transferred from the first thermally conductive material  1160  to the second thermally conductive material  4160 . Similarly, a diameter of each third through hole  426  is preferably larger than that of the corresponding second through hole  416 . Thus the heat may be fully transferred from the second thermally conductive material  4160  to the third thermally conductive material  4260 . 
     The light source module  40  can further include a heat dissipation device  45  to enhance heat dissipation efficiency. For example, the heat dissipation device  45  may include a base  450  contacting an opposite side of the heat dissipation plate  43  to bonding sheet  42 , and a plurality of fins  452  extending from the base  450 . Heat can be further transferred from the heat dissipation plate  43  to the fins  452  through the base  450 . The fins  452  increase surface area contacting the air. Thus, if there is a need, more heat can be dissipated to the air. 
     It is believed that the exemplary embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.