Abstract:
A LED package structure is disclosed. The LED package structure includes a substrate, a light emitting diode, a plasma chemical vapor deposition layer and a transparent material layer, wherein the substrate has a plurality of contacts. The light emitting diode is disposed on the substrate and electrically contacted to the contacts. The plasma chemical vapor deposition layer is disposed on the light emitting diode and the refractive index of the plasma chemical vapor deposition layer is smaller than that of the light emitting diode. The transparent material layer is disposed on the plasma chemical vapor deposition layer and the refractive index of the transparent material layer is smaller than that of the plasma chemical vapor deposition layer.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a LED package structure, and more particularly, to a LED package structure which can enhance the light extraction efficiency.  
       BACKGROUND OF THE INVENTION  
       [0002]     A LED (Light Emitting Diode) is a solid-state semiconductor device and a refractive index of its substrate is about 2.3 or near. In general, a LED package structure includes a LED chip with a refractive index about 2.5 on which p-electrode and n-electrode are connected to the substrate by using the method of wire bond or flip chip, and then a packaging resin made of transparent material with a refractive index of about 1.58 is used to package the LED chip. With regard to this type of LED package structure, because the difference between the refractive index of the substrate (about 2.5) and that of the transparent packaging resin (about 1.58) is too big, the light extraction efficiency of the LED package structure is merely about 5%, wherein most of the light is retained inside the LED chip, thus resulting in illumination loss and heat generation causes the degradation of LED performance.  
         [0003]     For improving the above-mentioned problems, some conventional technologies are developed to implement various regular or irregular microstructures on the surface of the LED chip for roughening, thereby destroying the total internal reflection. However, with the application of these conventional methods, since the rough structure on the surface of the LED chip is difficult to be controlled, the efficiency and quality differences among the respective LED chips are quite a lot.  
       SUMMARY OF THE INVENTION  
       [0004]     Therefore, there is a need to develop an improved LED package structure and a method thereof for substantially resolving the problem that the light extraction efficiency of the conventional LED chip is too low.  
         [0005]     Accordingly, one aspect of the present invention is to provide a LED package structure, which includes a plasma chemical vapor deposition layer with a single-layer or multiple-layer structure so as to substantially reduce the total internal reflection within the LED chip, thereby resolving the problem of the LED chip having too low light extraction efficiency.  
         [0006]     The other aspect of the present invention is to provide a method for manufacturing the LED package structure, wherein a plasma chemical vapor deposition method is used to manufacture the LED package structure having plasma chemical vapor deposition layers with the single-layer or multiple-layer for enhancing the light extraction efficiency of the LED chip, thus promoting the performance of the LED chip.  
         [0007]     According to an preferred embodiment of the present invention, the present invention provides a LED package structure comprising a substrate having a plurality of contacts, a LED disposed on the substrate, a plasma chemical vapor deposition layer disposed on the LED, and a transparent material layer disposed on the plasma chemical vapor deposition layer, wherein the LED is electrically connected to the contacts, and the refractive index of the plasma chemical vapor deposition layer is smaller than that of the LED, and the refractive index of the transparent material layer is smaller than that of the plasma chemical vapor deposition layer.  
         [0008]     According to the other preferred embodiment of the present invention, the present invention provides a LED package structure comprising a substrate having a plurality of contacts, a plurality of LED chips disposed on the substrate, a plasma chemical vapor deposition layer disposed on the LED chips, and a transparent material layer disposed on the plasma chemical vapor deposition layer, wherein the LED chips are electrically connected to the contacts, and the refractive index of the plasma chemical vapor deposition layer is smaller than that of the LED chips, and the refractive index of the transparent material layer is smaller than that of the plasma chemical vapor deposition layer.  
         [0009]     According to the preferred embodiment of the present invention, the aforementioned plasma chemical vapor deposition layer can be such as a transition metal oxide which has the refractive index in the range of about 1.7 to 2.6.  
         [0010]     According to the preferred embodiment of the present invention, the aforementioned plasma chemical vapor deposition layer can be such as titanium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), zirconium oxide (ZrO 2 ) or niobium oxide (Nb 2 O 5 ).  
         [0011]     With the application of the aforementioned LED package structure and the manufacturing method thereof, a single layer or multiple layers of plasma chemical vapor deposition layers with a gradually-decreasing refractive index is deposited on the LED chip by the plasma chemical vapor deposition method, so that the total internal reflection can be reduced for enhancing the light extraction efficiency of the LED chip. In comparison with the conventional structure and the manufacturing method thereof, the package structure and the manufacturing method thereof of the present invention not only are relative brief and more efficient, but also can precisely control the deposition of a single layer or multiple layers of the gradient-index plasma chemical vapor deposition layer on the LED chip. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0013]      FIGS. 1A-1C  are a series of cross-sectional schematic diagrams showing the process for manufacturing a LED package structure according to a preferred embodiment of the present invention; and  
         [0014]      FIGS. 2A-2E  are a series of cross-sectional schematic diagrams showing the process for manufacturing the other LED package structure according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]     Referring  FIG. 1A  to  FIG. 1C ,  FIG. 1A  to  FIG. 1C  are a series of cross-sectional schematic diagrams showing the process for manufacturing a LED package structure according to a preferred embodiment of the present invention. At first, such as shown in  FIG. 1A , a LED chip  120  with a refractive index between about 2.3 and about 4 is provided. In this embodiment, the LED chip  120  is a gallium nitride (GaN) with the refractive index of about 2.5. An anode electrode and a cathode electrode (not shown) located on the LED chip  120  are electrically connected to a substrate (e.g. a printed circuit board  100 ) having a plurality of contacts via solder bumps  110  by using a flip chip method. Alternatively, the LED chip  120  can be electrically connected to the printed circuit board  100  by wire bonding. Then, such as shown in  FIG. 1B , a plasma chemical vapor deposition layer  130  is conformally formed on the LED chip  120 , wherein the refractive index of the plasma chemical vapor deposition layer  130  is smaller than that of the LED chip  120 . In this embodiment, the plasma chemical vapor deposition layer  130  is a single-layer structure, and its thickness is larger than about 20 nm. The refractive index of the plasma chemical vapor deposition layer  130  is between about 1.7 and about 2.6. In this embodiment, the refractive index of the plasma chemical vapor deposition layer  130  is about 2.1. Further, the plasma chemical vapor deposition layer  130  is formed by a plasma chemical vapor deposition method, and is made of a transition metal oxide such as titanium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), zirconium oxide (ZrO 2 ) and niobium oxide (Nb 2 O 5 ). The plasma chemical vapor deposition method is a true surface deposition process that can deposit the plasma chemical vapor deposition layer  130  with a thickness from few Å up to few μm onto the LED chip  120 . In the plasma chemical vapor deposition method, monomer of high refractive index precursor is polyermized onto the surface of the LED chip  120 . The monomer is activated by plasma into a gaseous complex, composed of electrons, ions, gas atoms, free radicals and molecules in an excited state, such state also known as the plasma state. The plasma state generates highly reactive free radicals, which can be uniformly diffused and deposited on the surface of the LED chip  120 . As the LED chip  120  is exposed to the plasma, high refractive index precursor reacts with the mixing reactive gases and forms free radicals that are combined and form a high refractive index thin film coating on the surface of the LED chip  120 . The thin film has uniform, highly crosslinked, stand for high temperature and amorphous in nature. Each individual layer thickness and the refractive index of the thin film can be calculated and controlled. Thereafter, such as shown in  FIG. 1C , a transparent material layer  140  is formed on the plasma chemical vapor deposition layer  130  for forming the LED package structure, wherein the refractive index of the transparent material layer  140  is smaller than that of the plasma chemical vapor deposition layer  130 . The refractive index of the transparent material layer  140  is between about 1.4 and about 1.7, and is made of UV curable heat-resistant resin, silicone or epoxy. In this embodiment, the refractive index of the transparent material layer  140  is about 1.58. According to this LED package structure of the present invention, the difference between the refractive index of the LED chip  120  and that of the plasma chemical vapor deposition layer  130  is about 0.4, and the difference between the refractive index of the plasma chemical vapor deposition layer  130  and that of the transparent material layer  140  is about 0.5. Because the difference between the refractive index of the LED chip  120  and that of the transparent material layer  140  can be lowered by adding the plasma chemical vapor deposition layer  130 , the light extraction efficiency of the LED package structure can achieve about 11%, which is larger than the double of the light extraction efficiency of the conventional LED package structure (about 5%) without the plasma chemical vapor deposition layer  130 . The LED package structure of the present invention is characterized in adding the plasma chemical vapor deposition layer  130  between the LED chip  120  and the transparent material layer  140 , and because the refractive index of the plasma chemical vapor deposition layer  130  is between that of the LED chip  120  and that of the transparent material layer  140 , the problem of the LED chip  120  having too low light extraction efficiency caused by the large difference between the refractive index of the LED chip  120  and that of the transparent material layer  140  can be prevented.  
         [0016]     Referring to  FIG. 2A  to  FIG. 2E ,  FIG. 2A  to  FIG. 2E  are a series of cross-sectional schematic diagrams showing the process for manufacturing a LED package structure according to the other preferred embodiment of the present invention. At first, such as shown in  FIG. 2A , a LED chip  220  with a refractive index between about 2.3 and about 4 is provided. In this embodiment, the LED chip  220  is a GaAs with the refractive index of about 3.6. An anode electrode and a cathode electrode (not shown) on the LED chip  220  are electrically connected to a printed circuit board  200  having a plurality of contacts via solder bumps  210  by using a flip chip method. Alternatively, the LED chip  220  is electrically connected to the printed circuit board  200  by wire bonding. Then, a process of forming a plasma chemical vapor deposition layer with a multiple-layers structure is performed. In this embodiment, such as shown in  FIG. 2B , a first refractive index layer  230  is first conformally formed on the LED chip  220 , wherein the refractive index of the first refractive index layer  230  is smaller than that of the LED chip  220 . In this embodiment, the refractive index of the first refractive index layer  230  is between about 2.1 and about 2.6 and its thickness is larger than about 20 nm. Further, the first refractive index layer  230  is formed by a plasma chemical vapor deposition method and is made of a transition metal oxide such as TiO 2 , Ta 2 O 5 , ZrO 2  and Nb 2 O 5 . Thereafter, such as shown in  FIG. 2C , a second refractive index layer  232  is conformally formed on the first refractive index layer  230 , wherein the refractive index of the second refractive index layer  232  is smaller than that of the first refractive index layer  230 . In this embodiment, the refractive index of the second refractive index layer  232  is between about 1.7 and about 2.1, and its thickness is larger than about 20 nm. Additionally, the second refractive index layer  232  is formed by a plasma chemical vapor deposition method and is made of a transition metal oxide such as TiO 2 , Ta 2 O 5 , ZrO 2  and Nb 2 O 5 . Then, such as shown in  FIG. 2D , a third refractive index layer  234  is conformally formed on the second refractive index layer  232 , wherein the refractive index of the third refractive index layer  234  is smaller than that of the second refractive index layer  232 . In this embodiment, the refractive index of the third refractive index layer  234  is about 1.8 or 1.7 and its thickness is larger than about 20 nm. Further, the third refractive index layer  234  is formed by a plasma chemical vapor deposition method and, is made of a transition metal oxide, such as TiO 2 , Ta 2 O 5 , ZrO 2  and Nb 2 O 5 . Thereafter, such as shown in  FIG. 2E , a transparent material layer  240  is formed on the third refractive index layer  234  for forming the LED package structure, wherein a refractive index of the transparent material layer  240  is smaller than that of the third refractive index layer  234 . In the embodiment, the refractive index of the transparent material layer  240  is between about 1.4 and about 1.7, and is made of UV curable heat-resistant resin, silicone or epoxy. The difference between the refractive index of the second refractive index layer  232  and that of the first refractive index layer  230  is between about 0.2 and about 0.6. The difference between the refractive index of the third refractive index layer  234  and that of the second refractive index layer  232  is between about 0.1 and about 0.4. Additionally, the first refractive index layer  230 , the second refractive index layer  232  and the third refractive index layer  234  are formed by using the plasma chemical vapor deposition method, and their respective materials and thickness are similar to one another. Thus, in the present embodiment, the first refractive index layer  230 , the second refractive index layer  232  and the third refractive index layer  234  can be regarded as one gradient-index plasma chemical vapor deposition layer, wherein the refractive index is gradually decreasing from the LED chip  220  to the transparent material layer  240 . The LED package structure is characterized in adding the gradient-index plasma chemical vapor deposition layer between the LED chip  220  and the transparent material layer  240 . Because the large difference between the refractive index of the LED chip  120  and that of the transparent material layer  140  is avoided, the problem of the LED chip  220  having too low light extraction efficiency is resolved. Besides, the gradient-index plasma chemical vapor deposition layer is formed by using the plasma chemical vapor deposition method, so that the plasma chemical vapor deposition layers with various refractive indices can be formed directly within the same working environment, wherein the plasma chemical vapor deposition method can precisely control the composition and thickness of the plasma chemical vapor deposition layer. Therefore, the manufacturing method of the present invention can not only simplify the process of depositing the plasma chemical vapor deposition layer, but also achieve much better efficacy of manufacturing the plasma chemical vapor deposition layer.  
         [0017]     It is worthy to be noted that, in one process of manufacturing the LED package structure of the present invention, a wafer with a plurality of LED chips is first diced into individually separate chips, and then the chip is connected to a substrate by a wire bonding or flip chip method, and thereafter a plasma chemical vapor deposition layer is deposited on the LED chip by a plasma chemical vapor deposition method and a transparent material layer is deposited on the plasma chemical vapor deposition layer above the LED chip; and, alternatively, in another process of manufacturing the LED package structure of the present invention, a wafer with a plurality of LED chips is first electrically connected to the substrate by a wire bonding or flip chip method, and then the plasma chemical vapor deposition layer is deposited on the wafer by the plasma chemical vapor deposition method and the transparent material layer is deposited on the plasma chemical vapor deposition layer above the wafer, and thereafter the wafer can be diced into individual separate chips or just be kept as a whole without dicing. Similarly, in further another process of manufacturing the LED package structure of the present invention, the LED chips with different colors, such as with three primary colors of red, green and blue, can be first assembled to form a LED chip set, and then the LED chip set is electrically connected to a substrate by a wire bonding or flip chip method, and thereafter the plasma chemical vapor deposition layer is deposited on the LED chip set by the plasma chemical vapor deposition method and the transparent material layer is deposited on the plasma chemical vapor deposition layer above the LED chip set.  
         [0018]     In general, the LED package structure of the present invention is featured in first depositing a single-layered or multiple-layered gradient-index plasma chemical vapor deposition layer on the LED chip; and then depositing the transparent material layer on the plasma chemical vapor deposition layer, thereby reducing the loss caused by the total internal reflection and increasing the light extraction efficiency of the LED chip. In comparison with the conventional structure and manufacturing method, the package structure and the manufacturing method thereof according to the present invention are briefer, and the plasma chemical vapor deposition method can precisely control the thickness and composition of the single-layered or multiple-layered plasma chemical vapor deposition layer on the LED chip.  
         [0019]     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.