Abstract:
A light emitting device includes a light source, a light source carrier and a circuit board. The circuit board is configured to provide power to the light source via the light source carrier. The circuit board includes a metal substrate having an upper surface, the upper surface including a first electrode area, a second electrode area and a heat conduction area; a first metal electrode formed on the first electrode area; a first insulation layer formed between the first metal electrode and the metal substrate; a second metal electrode formed on the second electrode area; a second insulation layer formed between the second metal electrode and the metal substrate; and a solder resist layer covering the upper surface of the metal substrate; wherein the heat conduction area is exposed from the solder resist layer, and the heat conduction area is connected to the light source carrier.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a light emitting device, and more particularly, to a light emitting device capable of improving heat dissipation efficiency. 
         [0003]    2. Description of the Prior Art 
         [0004]    Since light emitting diodes (LEDs) have advantages of long service life, small size and low power consumption, the light emitting diodes are widely used in various kinds of illumination devices. Generally, when temperature of the light emitting diodes rises, light emitting efficiency of the light emitting diodes is significantly decreased and service life of the light emitting diodes is reduced as well. As the light emitting diodes are gradually used for various kinds of illumination devices, the heat dissipation problem of the light emitting diodes becomes more important. 
         [0005]    In the prior art, a substrate for carrying light emitting diodes is made of aluminum oxide (Al 2 O 3 ) or other materials with insulation and high heat-conductive characteristics, so as to dissipate heat of the light emitting diodes. However, thermal conductivity of the aluminum oxide is still lower than thermal conductivity of a metal material. Therefore, the prior art cannot further improve heat dissipation efficiency of a light emitting diode illumination device. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a light emitting device capable of improving heat dissipation efficiency, in order to solve the problems of the prior art. 
         [0007]    The light emitting device of the present invention comprises a light source, a light source carrier and a circuit board. The light source has a first electrode and a second electrode. The light source carrier comprises an insulation substrate, with a first through hole and a second through hole formed on the insulation substrate; a first upper metal pad arranged on an upper surface of the insulation substrate and electrically connected to the first electrode; a second upper metal pad arranged on the upper surface of the insulation substrate and electrically connected to the second electrode; a first conductor arranged in the first through hole; a second conductor arranged in the second through hole; a first lower metal pad arranged on a lower surface of the insulation substrate and electrically connected to the first upper metal pad through the first conductor; a second lower metal pad arranged on the lower surface of the insulation substrate and electrically connected to the second upper metal pad through the second conductor; and a third lower metal pad arranged on the lower surface of the insulation substrate and not electrically connected to the first lower metal pad and the second lower metal pad. The circuit board comprises a metal substrate having an upper surface and a lower surface, the upper surface comprising a first electrode area, a second electrode area and a heat conduction area; a first metal electrode formed on the first electrode area for providing a first voltage to the first lower metal pad; a first insulation layer formed between the first metal electrode and the metal substrate; a second metal electrode formed on the second electrode area for providing a second voltage different from the first voltage to the second lower metal pad; a second insulation layer formed between the second metal electrode and the metal substrate; and a solder resist layer covering the upper surface of the metal substrate; wherein the heat conduction area is exposed from the solder resist layer, and the heat conduction area is connected to the third lower metal pad. 
         [0008]    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 
         [0009]      FIG. 1  is a diagram showing a light emitting device of the present invention. 
           [0010]      FIG. 2  is a diagram showing a lower surface of a light source carrier in  FIG. 1 . 
           [0011]      FIG. 3  is a diagram showing an upper surface of a circuit board in  FIG. 1 . 
           [0012]      FIG. 4  is a diagram showing another embodiment of the lower surface of the light source carrier of the present invention. 
           [0013]      FIG. 5  is a diagram showing another embodiment of the upper surface of the circuit board of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Please refer to  FIG. 1  to  FIG. 3 .  FIG. 1  is a diagram showing a light emitting device of the present invention.  FIG. 2  is a diagram showing a lower surface of a light source carrier in  FIG. 1 .  FIG. 3  is a diagram showing an upper surface of a circuit board in  FIG. 1 . As shown in figures, the light emitting device  10  of the present invention comprises a light source  100 , a light source carrier  200  and a circuit board  300 . The light source  100  has a first electrode  110  and a second electrode  120 . The light source carrier  200  is configured to carry the light source  100 . The light source carrier  200  comprises an insulation substrate  205 , a first upper metal pad  240 , a second upper metal pad  250 , a first conductor  260 , a second conductor  270 , a first lower metal pad  210 , a second lower metal pad  220 , and a third lower metal pad  230 . A first through hole  206  and a second through hole  208  are formed on the insulation substrate  205 . The first upper metal pad  240  is arranged on an upper surface of the insulation substrate  205  and electrically connected to the first electrode  110 . The second upper metal pad  250  is arranged on the upper surface of the insulation substrate  205  and electrically connected to the second electrode  120 . The first conductor  260  is arranged in the first through hole  206 . The second conductor  270  is arranged in the second through hole  208 . The first lower metal pad  210  is arranged on a lower surface of the insulation substrate  205  and electrically connected to the first upper metal pad  240  through the first conductor  260 . The second lower metal pad  220  is arranged on the lower surface of the insulation substrate  205  and electrically connected to the second upper metal pad  250  through the second conductor  270 . The third lower metal pad  230  is arrange on the lower surface of the insulation substrate  205  and not electrically connected to the first lower metal pad  210  and the second lower metal pad  220 . 
         [0015]    The circuit board  300  comprises a metal substrate  310 , a first metal electrode  320 , a first insulation layer  330 , a second metal electrode  340 , a second insulation layer  350  and a solder resist layer  360 . The metal substrate  310  has an upper surface  370  and a lower surface  380 . The upper surface  370  comprises a first electrode area  372 , a second electrode area  374  and a heat conduction area  376 . The first electrode area  372  and the second electrode area  374  can be recessed areas formed by etching the upper surface  370 , but the present invention is not limited thereto. The first metal electrode  320  is formed on the first electrode area  372 . The first insulation layer  330  is formed between the first metal electrode  320  and the metal substrate  310 , in order to prevent conduction between the first metal electrode  320  and the metal substrate  310 . The second metal electrode  340  is formed on the second electrode area  374 . The second insulation layer  350  is formed between the second metal electrode  340  and the metal substrate  310 , in order to prevent conduction between the second metal electrode  340  and the metal substrate  310 . Due to the arrangement of the first insulation layer  330  and the second insulating layer  350 , the heat conduction area  376  is not electrically connected to the first metal electrode  320  and the second metal electrode  340 . The solder resist layer  360  is formed to cover the upper surface  370  of the metal substrate  310 . The solder resist layer  360  can prevent solder from flowing around, and has an insulation function. The heat conduction area  376  is exposed from the solder resist layer  360 , and the heat conduction area  376  can be directly or indirectly connected to the third lower metal pad  230 . For example, the heat conduction area  376  can be indirectly connected to the third lower metal pad  230  through a heat dissipation material (such as solder paste or heat dissipation paste), and thermal conductivity of the heat dissipation material is greater than 50 W/mk. In other embodiments of the present invention, the heat conduction area  376  can be directly connected to the third lower metal pad  230 , that is, the heat conduction area  376  can directly contact the third lower metal pad  230 . 
         [0016]    In addition, as shown in  FIG. 3 , the circuit board of the present invention can further comprise a first power electrode  392  and a second power electrode  394 . The first power electrode  392  can be electrically connected to the first metal electrode  320 , and is configured to receive a first voltage V 1  (such as a positive voltage). The second power electrode  394  can be electrically connected to the second metal electrode  340 , and is configured to receive a second voltage V 2  (such as a ground voltage) different from the first voltage V 1 . As such, the first metal electrode  320  can provide the first voltage V 1  to the first lower metal pad  210  for further transmitting the first voltage V 1  to the first electrode  110  of the light source  100 , and the second metal electrode  340  can provide the second voltage V 2  to the second lower metal pad  220  for further transmitting the second voltage V 2  to the second electrode  120  of the light source  100 , in order to drive the light source  100  to emit light. 
         [0017]    According to the above arrangement, when the light source  100  emits light, heat generated by the light source  100  can be transmitted to the light source carrier  200 , and the heat can be further transmitted to the heat conduction area  376  of the circuit board  300  through the third lower metal pad  230 . Therefore, the heat generated by the light source  100  when emitting light can be rapidly guided to the metal substrate  310  by the heat conduction area  376 , and the heat can be further dissipated by the metal substrate  310 . In one embodiment of the present invention, the metal substrate  310  can be a copper substrate. Since thermal conductivity of copper is higher than thermal conductivity of aluminum oxide, the circuit board  300  of the present invention can improve heat dissipation efficiency. Moreover, the light source  100 , the light source carrier  200  and the circuit board  300  are electrically connected with each other through the electrodes, thus the light emitting device  10  of the present invention does not need wire bonding for electrical connection. 
         [0018]    On the other hand, the solder resist layer  360  can be made of alight reflective material for reflecting light emitted by the light source  100 , such that light emitting efficiency of the light emitting device  10  can be improved. In one embodiment of the present invention, the light source  100  can be a flip-chip light emitting chip or an encapsulated light source, but the present invention is not limited thereto. Moreover, the circuit board  300  of the present invention can further comprise a first anti-oxidative metal layer  322  formed on the first metal electrode  320 , and a second anti-oxidative metal layer  342  formed on the second metal electrode  340 . The first anti-oxidative metal layer  322  and the second anti-oxidative metal layer  342  can be made of gold or silver, in order to prevent the first metal electrode  320  and the second metal electrode  340  from being oxidized. 
         [0019]    In the above embodiment, the light emitting device  10  of the present invention only comprises one light source  100 . However, in other embodiments of the present invention, the light emitting device of the present invention can comprise a plurality of light sources arranged on the light source carrier and electrically connected in series and/or in parallel. 
         [0020]    Please refer to  FIG. 4 .  FIG. 4  is a diagram showing another embodiment of the lower surface of the light source carrier of the present invention. As shown in  FIG. 4 , the light source carrier  200 ′ of the present invention can comprise a plurality of first lower metal pads  210 , a plurality of second lower metal pads  220 , and a plurality of third lower metal pads  230 . The plurality of first lower metal pads  210  can be electrically connected to the first upper metal pads through the plurality of first conductors respectively, in order to increase reliability of electrical connection between the first lower metal pads and the first upper metal pads. The plurality of second lower metal pads  220  can be electrically connected to the second upper metal pads through the plurality of second conductors respectively, in order to enhance reliability of electrical connection between the second lower metal pads and the second upper metal pads. The plurality of third lower metal pads  230  can be connected to the heat conduction area  376  of the circuit board  300  according to heat dissipation design. 
         [0021]    Please refer to  FIG. 5 .  FIG. 5  is a diagram showing another embodiment of the upper surface of the circuit board of the present invention. As shown in  FIG. 5 , the circuit board  300 ′ of the present invention can comprise a plurality of first metal electrodes  320  and a plurality of second metal electrodes  340 . The plurality of first metal electrode  320  can be electrically connected to the corresponding first lower metal pads respectively, in order to increase reliability of electrical connection between the first metal electrodes and the first lower metal pads. The plurality of second metal electrode  340  can be electrically connected to the corresponding second lower metal pads respectively, in order to increase reliability of electrical connection between the second metal electrodes and the second lower metal pads. 
         [0022]    In addition, layouts of the light source carrier and the circuit board of the present invention are not limited to the above embodiments. The layouts of the light source carrier and the circuit board of the present invention can vary according to design requirements. 
         [0023]    In contrast to the prior art, the present invention utilizes the metal substrate as a circuit substrate of the light emitting device, and the metal substrate has an exposed heat conduction area connected to the third lower metal pad of the light source carrier. The light emitting device of the present invention can use the light source carrier to rapidly guide the heat generated by the light source when emitting light to the metal substrate through the heat conduction area for further dissipating the heat by the metal substrate. Therefore, the light emitting device of the present invention has better heat dissipation efficiency. 
         [0024]    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.