Abstract:
A light emitting module includes a circuit board, a reflective layer, at least one light emitting chip and at least one metal wire. The circuit board has at least one connecting pad. The reflective layer is disposed on the circuit board and has at least one first opening exposing the connecting pad and at least one second opening exposing the circuit board. The light emitting chip is located in the second opening. The metal wire has a first end portion connecting to the connecting pad and a second end portion extending from the first end portion and crossing above the reflective layer and electrically connecting to the light emitting chip in the second opening. Consequently, the reflective layer can extend close to the light emitting chip and maximize the covered area of the reflective layer, and thus increase the light emitting efficiency of the light emitting module.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of invention 
         [0002]    The invention relates to a light emitting module, and in particular to a light emitting module with light emitting chips directly disposed on a circuit board. 
         [0003]    2. Related art 
         [0004]    Light emitting diode (LED) has an advantage of energy conservation. LED may become a new generation of light source by replacing traditional light bulbs or fluorescent lamps for indoor and outdoor lighting application. Typically, multiple LED elements are assembled to form a light emitting module providing sufficient light intensity depended on a specific occasion because a single LED element may only provide a finite light intensity. 
         [0005]    A conventional LED element includes a light emitting chip disposed on an insulating base; an encapsulating material for encapsulating the light emitting chip, the encapsulating material fitting to the insulating base; and a leadframe with at least one metal wire for electrically connecting with an external power source. Accordingly, the light emitting chip can emit light. A conventional LED module includes a circuit board and a plurality of assembled LED elements disposed on the circuit board, and the metal wire of each LED element electrically connect to an interconnection layer of the circuit board respectively. 
         [0006]      FIG. 1  shows a conventional light emitting module. The light emitting chip  11  is disposed directly on a circuit board  12  to form “chip on board (COB).” The circuit board  12  includes a metal substrate  121 , an insulating layer  122  disposed on the metal substrate  121  and an interconnection layer  123  disposed on the insulating layer  122 . Since the LED chip  11  is in direct contact with the metal substrate  121 , the heat produced by lighting the LED chip  11  can be dissipated by high thermal conductivity of the metal substrate  121 . The LED chip has two electrodes with metal wires  15  bonded to the interconnection layer  123 . The power source is supplied to the LED chip  11  by connecting the interconnection layer  123  with the external power source. 
         [0007]    A reflective layer  13  is formed on the interconnection layer  123  to improve the reflection of the light emitted from the LED chip  11  away from the direction of circuit substrate. Also, an encapsulating material  14  is used to encapsulate the LED chip  11 . The LED module shown in  FIG. 1  obviously has advantages of the simplified structure and processes of manufacturing the LED module. 
         [0008]    However, the metal wires  15  are required for electrically connecting the light emitting chip  11  with the interconnection layer  123 . An end  124  of the interconnection layer  123  adjacent the light emitting chip  11  has to be exposed out of the reflective layer  13  for electrically connecting the end  124  with the light emitting chip  11  by the metal wire  15 . Accordingly, at least one specific distance L is provided between the light emitting chip  11  and the reflective layer  13 , and thus the reflective layer  13  may not further extend to an edge of the light emitting chip  11 . The part of light emitted from the light emitting chip may not be reflected outwards by the reflective layer  13  and thus the light emitting efficiency of the whole light emitting module may be decreased. 
       SUMMARY OF THE INVENTION 
       [0009]    It is a primary object of the present invention to provide a light emitting module having a maximized area of a reflective layer to improve the reflectivity of light emitted from the light emitting chip. 
         [0010]    In order to achieve the forementioned object, the present invention provides a light emitting module comprising a circuit board, a reflective layer, at least one light emitting chip and at least one metal wire. The circuit board has at least one connecting pad. The reflective layer is disposed on the circuit board, and has at least one first opening to expose the connecting pad and has at least one second opening to expose a portion of the circuit board. The light emitting chip is disposed in the second opening. The metal wire has a first end portion connecting with the connecting pad in the first opening and a second end portion extending from the first end portion and above the reflective layer, the second end portion electrically connecting with the light emitting chip in the second opening. 
         [0011]    Moreover, the present invention provides another light emitting module comprising a circuit board, a reflective layer and at least one light emitting chip. The circuit board has at least one connecting pad. The reflective layer is disposed on the circuit board, and has at least one first opening to expose the connecting pad. The light emitting chip is disposed in the first opening, and has at least one electrode disposed on the lower surface thereof directly connecting to the connecting pad. 
         [0012]    The reflective layer of the invention can be extended to an edge of the light emitting chip as possible so that a covering area of the reflective layer can be maximized to improve the reflectivity of light emitted from the light emitting chip and to enhance the light emitting efficiency of the whole light emitting module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic cross-sectional view showing a conventional light emitting module; 
           [0014]      FIG. 2  is a schematic cross-sectional view showing a light emitting module of a first embodiment according to the present invention; 
           [0015]      FIG. 3  is a schematic top view showing a light emitting module of the first embodiment according to the present invention; 
           [0016]      FIG. 4  is a schematic illustration showing a light emitting module of the first embodiment according to the present invention; 
           [0017]      FIG. 5  is a schematic cross-sectional view showing a light emitting module of a second embodiment according to the present invention; 
           [0018]      FIG. 6A  is a schematic cross-sectional view showing a light emitting module of a third embodiment according to the present invention and  FIG. 6B  is a variation of  FIG. 6A ; 
           [0019]      FIG. 7A  is a schematic cross-sectional view showing a light emitting module of a fourth embodiment according to the present invention and  FIG. 7B  is a variation of  FIG. 7A ; 
           [0020]      FIG. 8  is a schematic cross-sectional view showing a light emitting module of a fifth embodiment according to the present invention; and 
           [0021]      FIG. 9  is a schematic top view showing a light emitting module of the fifth embodiment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
         [0023]      FIG. 2  is a schematic cross-sectional view showing a light emitting module of a first embodiment according to the present invention. As shown in  FIG. 2 , the light emitting module comprises a circuit board  21 , a reflective layer  22 , a plurality of light emitting chips  23  and a plurality of metal wires  24 . 
         [0024]    In the embodiment, the circuit board  21  comprises a metal substrate  211  having excellent thermal conductivity, an insulating layer  212  disposed on the metal substrate  211  and an interconnection layer  213  disposed on the insulating layer  212 . The interconnection layer  213  comprises at least one connecting pad  214 . The material of the metal substrate  211  can be aluminum, copper, Cu—Al alloy and the like having high thermal conductivity. 
         [0025]    The reflective layer  22  is disposed on the circuit board  21 , and has at least one first opening  221  to expose the connecting pad  214  of the interconnection layer  213 . In addition, reflective layer  22  further has at least one second opening  222  to expose a portion of the circuit board  21 . The reflective layer  22  can be formed with the material of white and high reflectivity, for example a mixture of silica gel and titanium dioxide particles, having reflectivity more than 60%, in particular more than 80%. 
         [0026]    The light emitting chip  23  is disposed in the second opening  222  and is electrically connected with the metal substrate  211  of the circuit board  21 . In the embodiment, the light emitting chip  23  has two electrodes formed on the upper surface. Two metal wires  24  are bonded to the upper surface of the light emitting chip  23 . The light emitting chip  23  can be LED chip or laser diode chip. 
         [0027]    The metal wire  24  is formed by wire bonding, above the reflective layer  22 , and electrically connected the light emitting chip  23  and the interconnection layer  213  of the circuit board  21 . Specifically, the metal wire  24  has a first end portion  241  and a second end portion  242  opposite to the first end portion  241 . The first end portion  241  is connected with the connecting pad  214  in the first opening  221 . The second end portion  242  is extended from the first end portion  241  and above the reflective layer  22 , and electrically connected with the light emitting chip  23  in the second opening  222 . 
         [0028]    Moreover, the light emitting module further includes an annular protruded structure  25  disposed on the reflective layer  22 . In the embodiment, after the reflective layer  22  is formed, the annular protruded structure  25  is formed thereon. Alternatively, the reflective layer  22  and the annular protruded structure  25  can be formed integrally by using the same material in the same step of the process. The light emitting module can further include a transparent protective layer  26  formed on the light emitting chip  23  with an edge of the annular protruded structure  25  serving as a boundary. The protective layer  26  can be material of silica gel, epoxy or a mixture of epoxy, and used for protecting the light emitting chip  23  and the metal wire  24 . 
         [0029]    Also, phosphor material can be added into the transparent protective layer  26  so that the protective layer  26  acts as a wave length conversion layer for converting the wave length of the light emitted from the light emitting chip  23 . The phosphor material can be YAG phosphor, silicate phosphor, nitride phosphor, oxide phosphor and aluminum oxide phosphor. 
         [0030]      FIG. 3  is a schematic top view showing a light emitting module of the first embodiment according to the present invention. As shown in  FIGS. 2 and 3 , the annular protruded structure  25  is substantially a circle around all the perimeters of the first opening  221  and the second opening  222 . The annular protruded structure  25  has a profile of cylinder, semi-cylinder, cylinder-like, triangle, triangle-like, trapezoid, trapezoid-like, rectangle, rectangle-like or the other shapes with a closed section. 
         [0031]    In another word, the annular protruded structure  25  is disposed to surround all the light emitting chips  23  and the metal wires  24 . In order to maximize a reflective layer covering area, the second opening  222  has a shape in accordance with a shape of the light emitting chip  23 . In the embodiment, the light emitting module includes a plurality of light emitting chip  23  correspondent with a plurality of second opening  222  in number. Also, the light emitting chip  23  are arranged in an array, and every two adjacent light emitting chips  23  are separated with a first predetermined distance L1. For example, the first predetermined distance L1 is greater than or equal to 0.5 mm, preferred greater than or equal to 0.6 mm. In addition, the reflective layer  22  and each of the light emitting chips  23  separated with a second predetermined distance L2. For example, the second predetermined distance L2 is less than or equal to 0.5 mm, preferred less than or equal to 0.1 mm. The reflective layer  22  and the first end portion  241  of the metal wire  24  connecting to the connecting pad  214  are separated with a third predetermined distance L3. For example, the third predetermined distance L3 is less than or equal to 0.5 mm, preferred less than or equal to 0.1 mm.  FIG. 4  is a schematic illustration showing a light emitting module of the first embodiment according to the present invention. 
         [0032]    Accordingly, since the metal wire  24  is above the reflective layer  22 , and the metal wire  24  is electrically connected to the light emitting chip  23  with the interconnection layer  213  of the circuit board  21 , the metal wire  24  do not occupy the area between the light emitting chip  23  and the reflective layer  22  so that the reflective layer  22  can extend to an edge of the light emitting chip  23  as near as possible. Therefore, a covering area of the reflective layer  22  can be maximized to raise the reflectivity of light emitted from the light emitting chip  23  and to improve the light emitting efficiency of the whole light emitting module. Referring to  FIG. 3 , a ratio of the area not covered by the reflective layer  22  to the area surrounded by the annular protruded structure  25  with deducting the area occupied by the light emitting chip  23  and ends of the metal wires  24 , as an opening ratio, is less than or equal to 20%, preferred less than or equal to 10%. 
         [0033]      FIG. 5  is a schematic cross-sectional view showing a light emitting module of a second embodiment according to the present invention. As shown in  FIG. 5 , the structure of the light emitting module is similar to that of the first embodiment according to the present invention. The difference is that the embodiment shown in  FIG. 5  further includes a heat dissipation layer  216  disposed between the circuit board  21  and the light emitting chip  23 . Specifically, the heat dissipation layer  216  is disposed between the metal substrate  211  and the light emitting chip  23 . The heat dissipation layer  216  is made of insulating material with excellent thermal conductive property. Accordingly, the light emitting chip  23  can be prevented from directly contacting to the metal substrate  211  so as to reduce the risk of the high voltage puncture to the light emitting chip  23 . Alternatively, the heat dissipation layer  216  can be made of the same material to the interconnection layer  213  of the circuit board  21  so as to improve the heat dissipation effect and enhance the electro-optical conversion properties of the light emitting chip  23 . 
         [0034]      FIG. 6A  is a schematic cross-sectional view showing a light emitting module of a third embodiment according to the present invention. As shown in  FIG. 6A , the structure of the light emitting module is similar to that of the first embodiment according to the present invention. The difference is that the circuit board  31  includes a ceramic substrate  311  and an interconnection layer  313  disposed on the ceramic substrate  311 , the interconnection layer  313  having a connecting pad  214 . Since the ceramic substrate  311  has excellent thermal conductive property and insulating property, it also can reduce the risk of the high voltage puncture to the light emitting chip  23 . 
         [0035]    The embodiment shown in  FIG. 6B  is a variation of that shown in  FIG. 6A . As shown in  FIG. 6B , the structure of the light emitting module is similar to that of  FIG. 6A . The difference is that the connecting pads  214  on the two sides respectively extend under the reflective layers  22  and cover all the exposed lower area of the first opening  221  in the embodiment. Accordingly, the ceramic substrate  311  having poor reflectivity can be covered as possible by the reflective layer  22  in order to improve the light emitting efficiency of the whole light emitting module. 
         [0036]      FIG. 7A  is a schematic cross-sectional view showing a light emitting module of a fourth embodiment according to the present invention. As shown in the drawing, the structure of the light emitting module is generally similar to that of the first embodiment as shown in  FIG. 2 . The difference is that the light emitting chip  23  shown in  FIG. 7A  has two electrodes disposed on two opposite surfaces, the upper surface and the lower surface. The electrode on the upper surface of the light emitting chip  23  connected to the interconnection layer  213  is the same as that of the first embodiment by the metal wire  24 . The electrode  231  on the lower surface of the light emitting chip  23  is directly connected to the interconnection layer  213  of the circuit board  21 . 
         [0037]    The embodiment shown in  FIG. 7B  is a variation of that shown in  FIG. 7A . As shown in  FIG. 7B , the structure of the light emitting module is similar to that of  FIG. 7A . The difference is that the reflective layer  22  and the annular protruded structure  25  are formed integrally by using the same material. Therefore, the steps of the process and the cost can be reduced. 
         [0038]      FIG. 8  is a schematic cross-sectional view showing a light emitting module of a fifth embodiment according to the present invention. As shown in the drawing, the structure of the light emitting module is generally similar to that of the first embodiment shown in  FIG. 2 . The difference is that the light emitting chip  23  shown in  FIG. 8  has two electrodes  331  both disposed on the lower surface. Specifically, the circuit board  31  has two connecting pads  313 . The reflective layer  32  is disposed on the circuit board  31 , and has at least one first opening  222  so that the connecting pads  313  can be exposed therein. The light emitting chip  23  is disposed in the first opening  222 , and has two electrodes  331  on the lower surface thereof. The electrodes  331  are directly connected to the connecting pads  313 , respectively.  FIG. 9  is a schematic top view of the fifth embodiment showing a plurality of light emitting chips  33  connected each other by the interconnection layer  312 . 
         [0039]    Accordingly, the connection of the light emitting chip  23  and the interconnection layer  313  can be simplified without wires. Therefore, the reflective layer  32  can be extended to an edge of the light emitting chip  23  as possible so that a covering area of the reflective layer  32  can be maximized to raise the reflectivity of light outputted from the light emitting chip  23  and to enhance the light emitting efficiency of the whole light emitting module. 
         [0040]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.