Patent Publication Number: US-2012025240-A1

Title: Package of light emitting device and method of manufacturing the same

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to light emitting devices, and more particularly to a package of light emitting diode (LED) and a method of manufacturing the package. 
     2. Description of Related Art 
     LEDs are solid state light emitting devices formed of semiconductors, which are more stable and reliable than other conventional light sources such as incandescent bulbs. Such LEDs emit light close to approximately single color light, which is different from light having a wide light emitting spectrum from incandescent bulbs. Recently, LED packages capable of emitting white light have been developed. A type of such white LED package is encapsulating a blue LED chip with an encapsulant where yellow phosphors are scattered. When blue light is emitted from the blue LED chip, yellow light is emitted from the yellow phosphors absorbing part of the blue light from the blue LED chip, thereby outputting white light by mixing of the blue light and yellow light. The phosphors are often powder and mixed in liquid state encapsulant. The liquid encapsulant encapsulates the LED chip by an injection process and is then baked for solidification. During baking, the phosphors are prone to deposit irregularly due to gravity. Such a deposition of the phosphors negatively impacts an optical effect of the package. 
     In addition, epoxy resin is generally used as the material of the encapsulant. The epoxy resin is easy to deteriorate and cause etiolation under the high temperature, which shortens lifespan of the package. 
     What is needed therefore is a package of light emitting device and a method of manufacturing the same which can overcome the above mentioned limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the views. 
         FIG. 1  is a cross sectional view of a package of a light emitting device in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a flow chart of a method of manufacturing the package shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the package of light emitting device includes a light emitting element  10 , two electrodes  30 , a reflecting cup  40  and an encapsulant  50 . The light emitting element  10  is positioned at a bottom of a central recess (not labeled) defined by the reflecting cup  40  and electrically connected to the electrodes  30  by flip chip technology. The encapsulant  50  is positioned in the central recess of the reflecting cup  40  and encapsulates the light emitting element  10 . The encapsulant  50  can be transparent or translucent. 
     The light emitting element  10  can be a nitride gallium compound semiconductor which emits light with a peak wavelength at or above 430 nm, such as a blue LED chip. The light emitting element  10  can also be a nitride gallium compound semiconductor which emits light with a peak wavelength below 430 nm, such as an ultraviolet LED chip. Two pads  101  of the light emitting element  10  electrically connect the electrodes  30  respectively, to obtain power for the light emitting element  10 . 
     In the preferred embodiment, the light emitting element  10  is secured on a top surface of a base  20  by using flip chip technology. However, the connection is not limited thereto. The base  20  can be a mixture which includes titanium dioxide (TiO 2 ), hardener, and a compound of epoxy resin and silicone, and the titanium dioxide, the hardener and the compound of epoxy resin and silicone are mixed by a process of kneading. The hardener can be triethyl tetramine (TETA) or silica type hardener. The epoxy resin can be epichlorohydrin (CH 2 CHOCH 2 Cl), glycidol (CH 2 CHOCH 2 OH), etc. The silicone can be phenyl trimethylsilyl ((CH 3 O) 3 SiC 6 H 5 ), etc. 
     The electrodes  30  can extend from the top surface of the base  20  to a bottom surface of the base  20 , whereby the package is formed as a surface mounting type device. 
     The reflecting cup  40  can be a mixture which includes titanium dioxide (TiO 2 ), hardener, and a compound of epoxy resin and silicone, and the titanium dioxide, the hardener and the compound of epoxy resin and silicone are mixed by a process of kneading. The hardener can be triethyl tetramine (TETA) or silica type hardener. The epoxy resin can be epichlorohydrin (CH 2 CHOCH 2 Cl), glycidol (CH 2 CHOCH 2 OH), etc. The silicone can be phenyl trimethylsilyl ((CH 3 O) 3 SiC 6 H 5 ), etc. In this embodiment, the base  20  and the reflecting cup  40  are formed integrally from a same material as a single piece. 
     The encapsulant  50  includes phosphors and a compound of epoxy resin and silicone, and the phosphors and the compound of epoxy resin and silicone are mixed by a process of kneading. The compound of epoxy resin and silicone is a macromolecular compound or high polymer. The phosphors can be evenly scattered in the compound of epoxy resin and silicone by kneading. The process of kneading can homogenize the compound and the phosphors, and prevent deposition of the phosphors in the compound due to gravity. The epoxy resin can be epichlorohydrin (CH 2 CHOCH 2 Cl), glycidol (CH 2 CHOCH 2 OH), etc. The silicone can be phenyl trimethylsilyl ((CH 3 O) 3 SiC 6 H 5 ), etc. The phosphors can be silicon oxynitride phosphors, nitride phosphors, etc. The phosphors can be excited by absorbing light from the light emitting element  10  and emit a wavelength conversion light by converting a wavelength of the absorbed light to a light with a different wavelength. 
     In addition, at least one of the following can be added into the epoxy resin: hardener, accelerator, mold release agent, flame retardant, and reaction inhibitor. The hardener can be triethyl tetramine (TETA) or silica type hardener, etc. The accelerator can be platinum compounds. The mold release agent can be siloxane compounds. The flame retardant can be resins. The reaction inhibitor can be acetylene alcohol, etc. 
     Referring to  FIG. 2 , a method of manufacturing the package of light emitting device in accordance with an embodiment of the present invention includes the following steps: 
     First, a light emitting element  10  is provided. The light emitting element  10  can be an LED chip. 
     Then phosphors and a compound of epoxy resin and silicone are provided. The phosphors and the compound of epoxy resin and silicone are mixed to obtain a mixture by a process of kneading. 
     Finally, the mixture is brought to form the encapsulant  50  which encapsulates the light emitting element  10 . 
     Specifically, in the first step, the light emitting element  10  is mounted on the base  20 . The pads  101  of the light emitting element  10  connect the electrodes  30  formed on the base  20 . The base  20  can be a mixture which includes titanium dioxide (TiO 2 ), hardener, and a compound of epoxy resin and silicone, and the titanium dioxide, the hardener and the compound of epoxy resin and silicone are mixed by a process of kneading. After kneading, the base  20  is formed by a process of transfer molding or embedded shaping. 
     Further, the reflecting cup  40  can be formed on the base  20 . The light emitting element  10  is positioned at the bottom of the central recesses defined by the reflecting cup  40 . The encapsulant  50  is received in the reflecting cup  40 . The reflecting cup  40  can be a mixture which includes titanium dioxide (TiO 2 ), hardener, and a compound of epoxy resin and silicone, and the titanium dioxide, the hardener and the compound of epoxy resin and silicone are mixed by a process of kneading. After kneading, the reflecting cup  40  is formed by a process of transfer molding or embedded shaping. 
     Specifically, in the third step, the mixture after kneading can be liquefied directly in a mold under a high temperature, and formed the encapsulant  50  in the reflecting cup  40  by a process of transfer molding. The phosphors can be coated by the compound of epoxy resin and silicone and evenly scattered in the compound of epoxy resin and silicone during the kneading, whereby deposition of the phosphors is avoided when in the process of transfer molding. Meanwhile, the fluid mixture has a larger viscosity and sustains in a fluid status for a shorter time compared with other molding processes (i.e., injection molding), which is also advantageous for anti-deposition of the phosphors in the encapsulant  50 . The compound of epoxy resin and silicone as the material of the encapsulant  50  can also weaken etiolation of the encapsulant  50  under the high temperature. 
     In addition, at least one of the following components can also be added into the epoxy resin: hardener, accelerator, mold release agent, flame retardant, and reaction inhibitor. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.