Patent Publication Number: US-2013248906-A1

Title: Light emitting diode package structure and method for fabricating the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan Patent Application No. 101110295, filed on Mar. 26, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light emitting diode package structure, and in particular relates to a light emitting diode package structure having a hydrophobic rib layer. 
     2. Description of the Related Art 
     Because light emitting diodes (LED) have several advantages over conventional lamps, such as a small size, a long lifespan, low power consumption, high response speed, etc., considerable research attention has been recently focused on development thereof. 
       FIG. 1  shows a cross-sectional schematic representation of a light emitting diode package structure  10  in prior art by a molding process. The light emitting diode package structure  10  includes a substrate  12 , a light emitting diode chip  14 , a conductive wire  16  and an encapsulant  18 . The light emitting diode chip  14  is formed on the substrate  12 . The light emitting diode chip  14  is electrically connected to a conductive pads (not shown in  FIG. 1 ) on the substrate  12  by the conductive wire  16 . The light emitting diode chip  14  is covered by the encapsulant  18 . 
     In a conventional molding process, a release film is formed on a mold for stripping step. However, the material of the release film is unique and the cost of the mold equipment is high. Additionally, a certain thickness is required between the adjacent light emitting diode chips  14 , and thus the light emitting diode chips  14  are separated into individual die only by a dicing process. Due to the thickness limitation, a relatively simpler breaker machine can not be used. 
     U.S. Pat. No. 7,732,233 discloses a light emitting diode package structure. The reliability of the light emitting diode is improved by the material characteristic of an Si-substrate and the arrangement of the connectors, the photo-electronic devices, the depressions and the solder bumps. The depressions are firstly formed, and then the light emitting diode chip is formed in the depressions. Next, a planar layer and an encapsulant layer are sequentially formed on the light emitting diode chip. However, the package structure is complex and the fabrication method is tedious. 
     Therefore, there is a need to develop a light emitting diode package structure with a fabrication method which is simpler than that of prior art, wherein the light emitting diode chip is separated into individual die by a less complex breaker machine. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a light emitting diode package structure, including: a substrate; a light emitting diode chip formed on a substrate; a first hydrophobic rib layer formed on the substrate and surrounding the light emitting diode; and a first cover layer formed on the substrate and covering the light emitting diode, wherein the first hydrophobic rib layer is used as a border of the first cover layer and an angle between the facet of the first cover layer and the substrate is about 60-90 degrees. 
     The invention provides a method for fabricating a light emitting diode package structure, including: providing a substrate; forming a first hydrophobic rib layer on the substrate; forming a light emitting diode chip on the substrate, wherein the light emitting diode chip is disposed in a region surrounded by the first hydrophobic rib layer; and forming a first cover layer on the substrate and covering the light emitting diode, wherein the first hydrophobic rib layer is used as a border of the first cover layer and an angle between the facet of the first cover layer and the substrate is about 60-90 degrees. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a cross-sectional schematic representation of a light emitting diode package structure in prior art; 
         FIG. 2A  shows a cross-sectional schematic representation of a light emitting diode package structure in accordance with an embodiment of the present invention; 
         FIG. 2B  shows a top-view schematic representation of a light emitting diode package structure in accordance with an embodiment of the present invention; 
         FIGS. 3A-3C  show a series of top-view schematic representations of the first hydrophobic rib layer in accordance with various embodiments of the present invention; 
         FIG. 4  shows a top-view schematic representation of the first cover layer in accordance with an embodiment of the present invention; 
         FIG. 5  shows a cross-sectional schematic representation of a light emitting diode package structure in accordance with a second embodiment of the present invention; 
         FIG. 6  shows a cross-sectional schematic representation of a light emitting diode package structure in accordance with a third embodiment of the present invention; 
         FIG. 7  shows a cross-sectional schematic representation of a light emitting diode package structure in accordance with a fourth embodiment of the present invention; and 
         FIG. 8  shows a cross-sectional schematic representation of a light emitting diode package structure having a plurality of light emitting diode chips in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 2A  shows a light emitting diode package structure  100 . The light emitting diode package structure  100  includes a substrate  102 , a light emitting diode chip  104 , a first hydrophobic rib layer  106  and a first cover layer  108 . The light emitting diode chip  104  is formed on a substrate; the first hydrophobic rib layer  106  is formed on the substrate  102  and surrounds the light emitting diode  104 , and a first cover layer  108  is formed on the substrate  102  and covers the light emitting diode  104 . 
     Additionally, the light emitting diode package structure  100  of the invention further includes a plurality of through holes  112  formed in the substrate, a plurality of first conductive pads  114  formed on the through holes  112 , a plurality of second conductive pads  116  formed below the through holes  112 , and a plurality of conductive lines  120  formed on the light emitting diode chip  104 , wherein the light emitting diode chip  104  is electrically connected to the second conductive pads  116  by the conductive lines  120 , the first conductive pads  114  and the through holes  112 . 
     Note that the electrical connection between the first conductive pads  114  and the second conductive pads  116  is shortened by the help of the through holes  112 . Thus, the electrically transmission distance is shortened. 
     The substrate  102  includes Al 2 O 3 , AlN, silicon, SiC, copper, copper alloy, aluminum, aluminum alloy, metal core printed circuit board (MCPCB), direct bond copper (DBC), FR4 or FR5. 
     The first hydrophobic rib layer  106  includes fluorine-based materials or silane-based materials, such as Teflon or tetraethoxy-silane nanocrystalline structure. The first hydrophobic rib layer  106  includes transparent materials or non-transparent materials. 
     The first cover layer  108  includes silicone, epoxy, glass or combinations thereof. 
       FIG. 2B  shows a top-view of  FIG. 2A . The pattern of the first hydrophobic rib layer  106  is circular and has a thickness of about 10-500 μm. The light emitting diode chip  104  is surrounded by the first hydrophobic rib layer  106 . 
     Note that the first hydrophobic rib layer  106  is used as a border of the first cover layer  108  to inhibit the overflow problem of the first cover layer  108 . Additionally, the first cover layer  108  has a convex structure due to the hydrophobic properties of the surface of the first hydrophobic rib layer  106 . The light extraction efficiency of the light emitting diode chip  104  is improved due to the convex structure of the first cover layer  108 . An angle θ 1  between the facet ff′ of the first cover layer  108  and the substrate  102  is about 60-90 degrees. 
       FIGS. 3A-3C  show a series of top-views of the first hydrophobic rib layer  106  in various embodiments. 
     In  FIG. 3A , the pattern of the first hydrophobic rib layer  106  is rectangular. In  FIG. 3B , the pattern of the first hydrophobic rib layer  106  is elliptic. In  FIG. 3C , the pattern of the first hydrophobic rib layer  106  is triangular. Furthermore, other regular or irregular shapes are all included in the scope of the invention, wherein only the light emitting diode chip  104  is surrounded by the first hydrophobic rib layer  106 . 
       FIG. 4  shows another embodiment of the first hydrophobic rib layer  106 . The  FIG. 4  is similar to  FIG. 1 . The difference between  FIG. 4  and  FIG. 1  is that the first hydrophobic rib layer  106  in  FIG. 1  is a continuous block and the first hydrophobic rib layer  106  in  FIG. 4  is a non-continuous block. 
       FIG. 5  shows a second embodiment of a light emitting diode package structure, wherein like elements are identified by the same reference numbers as in  FIG. 2A , and thus omitted for brevity. 
     In  FIG. 5 , the first cover layer  108  further includes a dopant  110 . The dopant  110  includes the light diffusion particles or the light wavelength conversion particles. The function of dopant  110  is to improve the uniformity of the spatial light color of the light emitting diode chip  104  and to produce a different light color from that of the light emitting diode chip  104 . 
     The light diffusion particles include SiO 2 , Al 2 O 3 , TiO 2 , CaF 2 , CaCO 3 , BaSO 4  or combinations thereof. 
     The light wavelength conversion particles include Yttrium aluminum garnet (YAG) phosphor, silicate phosphor, Terbium aluminum garnet (TAG) phosphor, oxide phosphor, nitride phosphor, aluminum oxide phosphor or combinations thereof. 
       FIG. 6  shows a third embodiment of a light emitting diode package structure. In  FIG. 6 , a dopant layer  110   a  is formed on a surface of the light emitting diode chip  104 . The dopant layer  110   a  includes the light diffusion layer or the light wavelength conversion layer. The function of dopant  110   a  is to improve the uniformity of the spatial light color of the light emitting diode chip  104  and to produce a different light from that of the light emitting diode chip  104 . 
       FIG. 7  shows a fourth embodiment of a light emitting diode package structure, wherein like elements are identified by the same reference numbers as in  FIG. 2A , and thus omitted for brevity. 
     The difference between  FIG. 7A  and  FIG. 2  is that a second hydrophobic rib layer  206  and a second cover layer  208  is added in  FIG. 7 . The second hydrophobic rib layer  206  is formed on the substrate  102  and surrounds the first hydrophobic rib layer  106 , and the second cover layer  208  is formed on the substrate  102  and the first cover layer  108 , wherein the second hydrophobic rib layer  206  is used as a border of the second cover layer  208  and an angle θ 2  between the facet ff′ of the second cover layer  208  and the substrate  102  is about 60-90 degrees. 
     Additionally, in other embodiments, the second cover layer  208  further includes a dopant (not shown in  FIG. 7 ). The dopant includes the light diffusion particles or the light wavelength conversion particles. The function of dopant is to improve the uniformity of the spatial light color of the light emitting diode chip  104  and to produce a different light from that of the light emitting diode chip  104 . 
       FIG. 8  shows a light emitting diode package structure of the invention having a plurality of light emitting diode chips. There are three light emitting diode chips in  FIG. 8 . The number of the light emitting diode chips is merely exemplary and not meant to limit the invention. The number of light emitting diode chips may be adjusted according to actual applications. 
     Note that the first hydrophobic rib layer  106  is used as a border of the first cover layer  108 , and thus the overflow problem of the first cover layer  108  between the adjacent light emitting diode chips is inhibited. 
     In prior art, referring to  FIG. 1 , the light emitting diode chips are separated into individual die only by a dicing process. By the design of the first hydrophobic rib layer  106 , the light emitting diode chips  104  of the invention are separated into individual die by a laser cutting process, a blade cutting process or a breaker machine (along a cutting line  150 , referring to  FIG. 8 ). 
     Additionally, referring to  FIG. 2A , the invention provides a method for fabricating a light emitting diode package structure, including the following steps. A substrate  102  is firstly provided. Then, a first hydrophobic rib layer  106  is formed on the substrate  102 . The first hydrophobic rib layer  106  is formed by a dispensing process, screening process, laminate adhesive process, lithography process, printing process or deposition process. 
     Next, a light emitting diode chip  104  is formed on the substrate, wherein the light emitting diode chip  104  is disposed in a region surrounded by the first hydrophobic rib layer  106 . 
     Then, a first cover layer  108  is formed on the substrate and covers the light emitting diode  104 , wherein the first hydrophobic rib layer  106  is used as a border of the first cover layer  108  and an angle between the facet ff′ of the first cover layer  108  and the substrate  102  is about 60-90 degrees. The first cover layer  108  is formed by a dispensing process, screening process, molding process or laminate adhesive process. 
     Note that in prior art, a convex structure of the encapsulant is formed by a molding process with a mold. The convex structure of the first cover layer  108  of the invention is easily formed by using a less complex dispensing process for the first hydrophobic rib layer  106 . 
     Besides the above-mentioned steps, a dopant  110  is further formed in the first cover layer  108  to form the package structure of  FIG. 5 , wherein the dopant  110  includes the light diffusion particles or the light wavelength conversion particles. 
     Besides the above-mentioned steps, before forming the first cover layer  108 , a dopant layer  110   a  is further formed on a surface of the light emitting diode chip  104  to form the package structure of  FIG. 6 . The dopant layer  110   a  includes the light diffusion layer or the light wavelength conversion layer. 
     The package structure of  FIG. 7  is formed by the following steps. A second hydrophobic rib layer  206  is formed on the substrate  102  and surrounds the first hydrophobic rib layer  106 . A second cover layer  208  is formed on the substrate  102  and the first cover layer  108 , wherein the second hydrophobic rib layer  206  is used as a border of the second cover layer  208  and an angle θ 2  between the facet f 1 f 1 ′ of the second cover layer  208  and the substrate  102  is about 60-90 degrees. 
     From the above descriptions, the light emitting diode package structure and method for fabricating the same has the following advantages: 
     (1) The first hydrophobic rib layer  106  is used as a border of the first cover layer  108  to inhibit the overflow problem of the first cover layer  108 . 
     (2) The first cover layer  108  has a convex structure due to the hydrophobic properties of the surface of the first hydrophobic rib layer  106 . The light extraction efficiency of the light emitting diode chip  104  is improved due to the convex structure of the first cover layer  108 . 
     (3) By the design of the first hydrophobic rib layer  106 , the light emitting diode chips  104  of the invention are separated into individual die by a laser cutting process, a blade cutting process or a breaker machine (along a cutting line  150 , referring to  FIG. 8 ). 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.