Abstract:
A light emitting diode (LED) package including a chip carrier, an adhesive layer, a light emitting diode (LED) chip and an anti-aging layer is provided. The adhesive is disposed on the chip carrier. The LED chip having a light emitting layer is adhered on the chip carrier by the adhesive layer, and is electrically connected with the chip carrier. The anti-aging layer is disposed between the adhesive and the chip carrier. In the LED package described above, the light emitted from the LED being illuminated on the adhesive layer is reduced or prevented by the anti-aging layer. Therefore, the aging phenomenon of the LED package is retarded, and the lifetime of the LED package is further enhanced.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority benefit of Taiwan application serial no. 93137153, filed on Dec. 2, 2004.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to a package structure of light emitting diode (LED). More particularly, the present invention relates to an LED package structure with an anti-aging layer.  
         [0004]     2. Description of Related Art  
         [0005]     In recent years, since the light emitting efficiency of LED is continuously increasing, the application of LED in some field has gradually replaced the usual light bubble or fluorescent light, such as the scanning light source with need of highly reaction speed, the back light source for the LCD (liquid crystal display), the front light source in car for the monitoring panel, the traffic light, or the usual illumination light source. The usual LED is also a semiconductor device, wherein the material in use usually includes the III-V group elements, such as GaP and GaAs. The mechanism for emitting the light in the LED is transforming the electric energy into the light. In other words, by applying a current through the foregoing semiconductor compound material, due to the recombination of electrons and holes, the energy is released by the energy form of light, so that the light emitting effect can be achieved. Since the light emitting phenomenon of LED is not by thermal mechanism or discharging mechanism, it is called electrolumnescent (EL) light, and the lifetime of LED can last for more than hundred thousand hours without idling time. In addition, the LED has advantages of fast response speed (about 10-9 seconds), small volume, low power consumption, low contamination, high reliability, suitable for massive production, so that the applications of LED is very wide.  
         [0006]      FIG. 1  is a cross-section view, schematically illustrating a conventional packaging structure of LED. In  FIG. 1 , the conventional LED structure  100  includes a lead frame structure  102 , an adhesive layer  104 , an LED chip  106 , two bonding wires  108   a  and  108   b , and a packaging structure body  110 . Wherein, the lead frame structure  102  has two conductive leads  102   a ,  102   b , and a chip seat  102   c  disposed on the conductive lead  102   a . The adhesive layer  104  is disposed on the chips pad  102   c  at the conductive lead  102   a . The LED chip  106  is adhered to the chips pad  102   c  via the adhesive layer  104 , and the bonding wires  108   a ,  108   b  are respectively electrically coupled to the conductive leads  102   a ,  102   b.    
         [0007]      FIG. 2  is a perspective view, schematically illustrating the LED structure in use. In  FIG. 2 , the conventional LED chip  106  is formed from a substrate  106   a , an N-type semiconductor layer  106   b , a light emitting layer  106   c , a P-type semiconductor layer  106   d , an N-type contact pad  106   e , and a P-type contact pad  106   f . Wherein, the N-type semiconductor layer  106   b  is formed on the substrate  106   a , the light emitting layer  106   c  is formed on the N-type semiconductor layer  106   b , and the P-type semiconductor layer  106   d  is formed on the light emitting layer  106   c . In addition, a portion of the N-type semiconductor layer  106   b  is not covered by the light emitting layer  106   c  and the P-type semiconductor layer  106   d.    
         [0008]     In  FIG. 1  and  FIG. 2 , the foregoing N-type contact pad  106   e  is disposed on the exposed portion of the N-type semiconductor layer  106   b , not being covered by the light emitting layer  106   c  and the P-type semiconductor layer  106   d . The P-type contact pad  106   f  is disposed on the P-type semiconductor layer  106   d . Usually, a well ohmic contact is formed between the N-type contact pad  106   e  and the N-type semiconductor layer  106   b , and another well ohmic contact is also formed between the P-type contact pad  106   f  and the P-type semiconductor layer  106   d . In other words, the bonding wires  108   a  is electrically coupled to the N-type semiconductor layer  106   b  via the N-type contact pad  106   e , and the bonding wires  108   b  is electrically coupled to the P-type semiconductor layer  106   d  via the P-type contact pad  106   f.    
         [0009]     It should be noted in the conventional LED packaging structure that the adhesive layer  104  usually is the silver paste. However, after the silver paste is illuminated by the light which is emitted from light emitting layer  106   c , the silver paste is easily aging, causing a poor adhesive capability, and further causing the lifetime of the LED packaging structure to be largely reduced.  
       SUMMARY OF THE INVENTION  
       [0010]     The invention provides an LED packaging structure with anti-aging layer, so that the aging speed of the LED packaging structure is effectively reduced.  
         [0011]     The invention provides an LED packaging structure, including chip carrier, an adhesive layer, an LED chip, and an anti-aging layer. The adhesive layer is disposed on the chip carrier. The LED chip is adhered to the chips carrier by the adhesive layer, and is electrically coupled with chip carrier. In addition, the LED chip has a light emitting layer to emit a light. The anti-aging layer is disposed between the adhesive layer and the light emitting layer.  
         [0012]     In an embodiment of the invention, the chip carrier includes a lead frame structure or a circuit board. In the foregoing descriptions, the lead frame structure can include several conductive leads and a chip pad. The chip seat is disposed on one of the conductive leads for holding the LED chip.  
         [0013]     In an embodiment of the invention, the adhesive layer includes, for example, silver paste or other adhesive material with good adhesive capability and thermal conductivity.  
         [0014]     In an embodiment of the invention, the LED chip includes, for example, a substrate, a patterned semiconductor layer, and two contact pads. The substrate has a first surface and a second surface, and the patterned semiconductor layer is disposed over the first surface, and the contact pads are disposed on the patterned semiconductor layer.  
         [0015]     In an embodiment of the invention, the anti-aging layer is, for example, disposed over the second surface. In other words, the anti-aging layer and the patterned semiconductor layer can also be for example respectively disposed on the two opposite surfaces of the substrate. As known by the ordinary skilled artisans, the anti-aging layer can also be disposed between the substrate and the patterned semiconductor layer. In addition, material for the anti-aging layer can be metal, semiconductor, oxide, or polymer.  
         [0016]     In an embodiment of the invention, the anti-aging layer can be, for example, an optical absorption layer, a light guiding structure, a filtering layer, or a combination of these layers, so as to reducing the aging effect of the adhesive layer. In addition, the light guiding structure includes, for example, a light guiding layer and a reflection layer, wherein the reflection layer is disposed between the light guiding layer and the adhesive layer.  
         [0017]     In an embodiment of the invention, the LED packaging structure further includes a packaging structure body. The packaging structure body is, for example, enclosing the adhesive layer, the LED chip, the anti-aging layer, and a portion of the chip carrier.  
         [0018]     In an embodiment of the invention, the LED packaging structure further includes several bonding wires. The bonding wires are connected between the LED chip and the chip carrier.  
         [0019]     In the LED packaging structure, since the anti-aging layer, such as optical absorption layer, light guiding structure, or filtering layer, is used in design, the aging of the LED packaging structure can be effectively retarded, and the lifetime of the LED packaging structure can be prolonged. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0021]      FIG. 1  is a cross-section view, schematically illustrating a conventional packaging structure of LED.  
         [0022]      FIG. 2  is a perspective view, schematically illustrating the LED structure in use.  
         [0023]      FIG. 3  is a cross-section view, schematically illustrating a packaging structure of LED, according to a first preferred embodiment of the invention.  
         [0024]      FIG. 4  is a perspective view, schematically illustrating the LED chip in  FIG. 3 .  
         [0025]      FIG. 5  is a cross-sectional view, schematically illustrating the anti-aging layer in  FIG. 3 .  
         [0026]      FIG. 6  is a cross-section view, schematically illustrating a packaging structure of LED, according to a second preferred embodiment of the invention.  
         [0027]      FIG. 7  is a perspective view, schematically illustrating the LED chip in  FIG. 6 .  
         [0028]      FIG. 8A  and  FIG. 8B  are perspective views, schematically illustrating a packaging structure of LED, according to a third preferred embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Firs Embodiment  
       [0029]      FIG. 3  is a cross-section view, schematically illustrating a packaging structure of LED, according to a preferred embodiment of the invention. In  FIG. 3 , the LED packaging structure  200  of the embodiment includes a chip carrier  202 , an adhesive layer  204 , an LED chip  206  and an anti-aging layer  212 . Wherein, the adhesive layer  204  is disposed over the chip carrier  202 . The LED chip  206  is adhered to the chip carrier  202  by the adhesive layer  204 , and is electrically coupled with the chip carrier  202 . In addition, the LED chip  206  has a light emitting layer  206   c  to emit a light. The anti-aging layer  212  is disposed between the adhesive layer  204  and the light emitting layer  206   c , so as to prevent the light emitted from the light emitting layer  206   c  from illuminating on the adhesive layer  204 .  
         [0030]     In accordance with the foregoing descriptions, the LED packaging structure  200  further includes, for example, the bonding wire  208   a  and the bonding wire  208   b . The bonding wire  208   a  and the bonding wire  208   b  are for example coupled between the LED chip  206  and the chip carrier  202 . In addition, the LED packaging structure  200  further includes a packaging structure body  210 . This packaging structure body  210  can for example enclose the forgoing adhesive layer  204 , the LED chip  206 , the anti-aging layer  212  and a portion of the chip carrier  202 .  
         [0031]     The forgoing structures are described in more detail as follows. However, the descriptions are just the examples for descriptions, and the invention is not only limited to the descriptions. The ordinary skilled artisans can base on the descriptions of the invention to have the proper modification without beyond the scope of the invention.  
         [0032]     The chip carrier  202  used in the embodiment is for example a lead structure, which includes a conductive lead  202   a , a conductive lead  202   b , and a chip seat  202   c . Wherein, the chip seat  202   c  is implemented on the conductive lead  202   a  for holding the LED chip  206 .  
         [0033]     In order to allow the LED chip  206  to be easily adhered to the chip seat  202   c , the foregoing adhesive layer  204  usually needs the good properties of adhesive capability and thermal conductivity. In the embodiment, the adhesive layer  204  can be for example the silver paste or other material with good adhesive capability and thermal conductivity.  
         [0034]      FIG. 4  is a perspective view, schematically illustrating the LED chip in  FIG. 3 . In  FIG. 3  and  FIG. 4 , the LED chip  206  used in the embodiment includes for example a substrate  206   a , an N-type semiconductor layer  206   b , a light emitting layer  206   c , a P-type semiconductor layer  206   d , an N-type contact pad  206   e , and a P-type contact pad  206   f . Wherein, the substrate  206   a  has a first surface A and a second surface B. The N-type semiconductor layer  206   b  is formed over the first surface A of the substrate  206   a , and the light emitting layer  206   c  is formed over the N-type semiconductor layer  206   b . The P-type semiconductor layer  206   d  is formed over the light emitting layer  206   c . In addition, a portion of the N-type semiconductor layer  206   b  is not covered by the light emitting layer  206   c  and the P-type semiconductor layer  206   d . As described above, the N-type semiconductor layer  206   b , the light emitting layer  206   c , and the P-type semiconductor layer  206   d  are generally called together as a patterned semiconductor layer.  
         [0035]     In  FIG. 3  and  FIG. 4 , it can be clearly seen that the N-type contact pad  206   e  is located on the exposed portion of the N-type semiconductor layer  206   b  without being covered by the light emitting layer  206   c , and the P-type semiconductor layer  206   d . In the embodiment, a well ohmic contact can be formed between the N-type contact pad  206   e  and the N-type semiconductor layer  206   b , and another well ohmic contact is also formed between the P-type contact pad  206   f  and the P-type semiconductor layer  206   d.    
         [0036]     It can be seen from  FIG. 3  and  FIG. 4  that the bonding wire  208   a  is electrically coupled to the N-type semiconductor layer  206   b  by the N-type contact pad  206   e , and the bonding wire  208   b  is electrically coupled to the P-type semiconductor layer  206   d  by the N-type contact pad  206   f . In the embodiment, the bonding wires  208   a ,  208   b  can be for example the gold wire with good tractility.  
         [0037]     Accordingly, since the adhesive capability of the adhesive layer  204  becomes worse after being illuminated by the light, it needs the anti-aging layer  212  to be disposed between the light emitting layer  206   c  and the adhesive layer  204  in the LED chip  206 . As a result, the light is effectively blocked and does not illuminate on the adhesive layer  204 . In  FIG. 4 , the anti-aging layer  212  of the embodiment is disposed on the second surface B of the substrate, so as to prevent the adhesive layer  204  from being directly illuminated by the light emitted from the light emitting layer  206   c  and causing the poor quality. In other words, the anti-aging layer  212  and the patterned semiconductor layer, which includes the N-type semiconductor layer  206   b , the light emitting layer  206   c , and the P-type semiconductor layer  206   d , are respectively disposed on the opposite surfaces of the substrate  206   a.    
         [0038]     In order to prevent the aging of the adhesive layer  204 , the embodiment proposes several designs of the anti-aging layer  212 , such as an optical absorption layer, a light guiding structure, a filtering layer, or a combination of these layers. The aging effect is reduced by absorbing, guiding or filtering the light. In more detail, the optical absorption layer used in the embodiment can be, for example, the material of metal or polymer. The ordinary skilled artisans can change the material according to the different wavelength of the emitting light. The light guiding structure used in the embodiment can, for example, guide the light emitted from the light emitting layer  206   c  to the side of the LED chip  206 , so that the light illuminating onto the adhesive layer  204  is greatly reduced. The filtering layer used in the embodiment can be, for example, a stacked structure by multiple films with different refractive index, and can filter the light from the light emitting layer  206   c , so as to prevent the adhesive layer  2054  form getting worse. Accordingly, the embodiment takes the light guiding structure as the example for descriptions, as shown in  FIG. 5 .  
         [0039]      FIG. 5  is a cross-sectional view, schematically illustrating the anti-aging layer in  FIG. 3 . In  FIG. 5 , the light guiding structure  300  includes for example a light guiding layer  302  and a reflection layer  304 . The reflection layer  304  is disposed between light guiding layer  302  and the adhesive layer  204 . When the light emitted from the emitting layer  206   c  of the LED chip  206  is illuminating on the light guiding structure, that is, the anti-aging layer  300 , the light is reflected by the reflection layer  304 . Wherein, a portion of the light being reflected by the reflection layer  304  emits out from the front surface of the LED chip  206 , and the other portion of the light can be guided to the side of the LED chip  206 .  
         [0040]     Accordingly, the light guiding structure  300  with both capabilities of reflecting the light and guiding the light can effectively prevent the light from directly illuminating on the adhesive layer  204 , so that the lifetime and the reliability of the LED package can be effectively improved.  
       Second Embodiment  
       [0041]      FIG. 6  is a cross-section view, schematically illustrating a packaging structure of LED, according to a second preferred embodiment of the invention.  FIG. 7  is a perspective view, schematically illustrating the LED chip in  FIG. 6 . In  FIG. 6  and  FIG. 7 , the LED packaging structure  200 ′ of this embodiment is similar to the LED packaging structure  200  of the first embodiment. The difference is that the anti-aging layer  212 ′ is disposed on the first surface A of the substrate  206  in the LED packaging structure  200 ′ of this embodiment. This also means that the anti-aging layer  212 ′ is disposed between the substrate  206   a  and the N-type semiconductor layer  206   b.    
       Third Embodiment  
       [0042]      FIG. 8A  and  FIG. 8B  are perspective views, schematically illustrating a packaging structure of LED, according to a third preferred embodiment of the invention. Referring to  FIG. 8A , in the LED packaging structure  500   a  of this embodiment, the LED chip  206  (see  FIG. 4 ) is disposed on a circuit board  400 , and the LED chip  206  is adhered to the circuit board  400  by the adhesive layer  204 .  
         [0043]     Referring to  FIG. 8B , in the LED packaging structure  500   b  of this embodiment, the LED chip  206 ′ (see  FIG. 7 ) is disposed on a circuit board  400 , and the LED chip  206 ′ is adhered to the circuit board  400  by the adhesive layer  204 . In the foregoing packaging structures, the anti-aging layers  212  and  212 ′ disposed between the adhesive layer  204  and the light emitting layer  206   c  can effectively prevent the light emitted by the light emitting layer  206   c  from directly illuminating on the adhesive layer  204 , so as to improve the lifetime and the reliability of the LED packaging structures  500   a  and  500   b.    
         [0044]     In summary, the LED packaging structures of the invention at least has the advantages as follows.  
         [0045]     The LED packaging structures of the invention can effectively retard the aging speed of the LED packaging structures, and further improve the lifetime and the reliability of the LED packaging structures.  
         [0046]     The LED packaging structures of the invention can be easily integrated into the current fabrication process without causing much additional fabrication cost.  
         [0047]     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.