Abstract:
A method for manufacturing a light emitting diode includes steps: providing a base having leads formed thereon; fixing a light emitting die on the leads; disposing a glass encapsulant on the base; co-firing the encapsulant with the base to fix them together. The base is made of silicon or ceramic. The encapsulant has a cover covering the light emitting die received in a groove of the base and a positioning plate fittingly engaging into the groove in one embodiment. The encapsulant has a cavity receiving the light emitting die to cover the light emitting die fixed on a top face of the base in another embodiment. Various mechanisms are used to protect the light emitting die during co-firing of the encapsulant and the base.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a method for manufacturing a light emitting diode. 
         [0003]    2. Description of Related Art 
         [0004]    As new type light source, LEDs are widely used in various applications. An LED often includes a die to emit light, a substrate supporting the die, a pair of leads connected to the die to transfer power to the die, and an encapsulant covering the die to protect the die from the outside environment. In order to allow the light emitted from the die to transmit to the outside environment, the encapsulant is generally made of transparent epoxy. However, the epoxy is prone to become yellow when subjects to a high temperature or after a long period of use, affecting the color of the light output from the LED. Therefore, glass is introduced to make the encapsulant so as to substitute the epoxy. Different from the epoxy encapsulant which can be directly molded on the substrate, the glass encapsulant should be made firstly and then fixed to the substrate via adhesive. Nevertheless, the glass and the substrate generally are heterogeneous structures, stress variation between the glass encapsulant and the substrate cannot well-match each other when the glass encapsulant and the substrate subject to a high temperature. Furthermore, the adhesive is easy to deteriorate when subjects to the high temperature, which raises a risk of damage of the LED. 
         [0005]    What is needed, therefore, is a method for manufacturing a light emitting diode which can overcome the limitations described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the present disclosure 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 disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  shows a first step of a process for manufacturing an LED in accordance with a first embodiment of the present disclosure. 
           [0008]      FIG. 2  shows a second step of the process for manufacturing the LED in accordance with the first embodiment of the present disclosure. 
           [0009]      FIG. 3  shows a third step of the process for manufacturing the LED in accordance with the first embodiment of the present disclosure. 
           [0010]      FIG. 4  shows a forth step of the process for manufacturing the LED in accordance with the first embodiment of the present disclosure. 
           [0011]      FIG. 5  shows a fifth step of the process for manufacturing the LED in accordance with the first embodiment of the present disclosure. 
           [0012]      FIG. 6  shows an individual LED formed in accordance with the first embodiment, which has been manufactured after the step shown in  FIG. 5 . 
           [0013]      FIG. 7  is a view similar to  FIG. 5 , showing an LED to be manufactured in accordance with a second embodiment of the present disclosure. 
           [0014]      FIG. 8  is a view similar to  FIG. 5 , showing an LED to be manufactured in accordance with a third embodiment of the present disclosure. 
           [0015]      FIG. 9  is a view similar to  FIG. 3 , showing an LED to be manufactured in accordance with a forth embodiment of the present disclosure. 
           [0016]      FIG. 10  is a view similar to  FIG. 3 , showing an LED to be manufactured in accordance with a fifth embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0017]    Referring to  FIGS. 1-6 , steps of a process for manufacturing an LED (light emitting diode) in accordance with a first embodiment of the present disclosure are disclosed. 
         [0018]    Firstly, a base  10  having a plurality of pairs of leads  30  is provided as shown in  FIG. 1 . The base  10  may be made of Si or ceramic such as Al 2 O 3  or AlN. The base  10  has a plurality of grooves  12  defined in a top face thereof. Each groove  12  has an inner diameter gradually increasing from a bottom towards a top of the base  10 . Each pair of leads  30  are formed within the base  10  corresponding to each groove  12 . Each lead  30  is made of electrically conductive materials such as copper, silver or gold. Each lead  30  includes a first conductive portion  32 , a second conductive portion  36  parallel to the first conductive portion  32  and a connecting portion  34  connecting the first conductive portion  32  with the second conductive portion  36  (see  FIG. 6 ). The first conductive portion  32  of the lead  30  is located at a bottom of a corresponding groove  12  and has a top face exposed within the groove  12 . The second conductive portion  36  of the lead  30  is located at a bottom of the base  10  and has a bottom face exposed. The connecting portion  34  is perpendicular to the first and second conductive portions  32 ,  36  and substantially received within the base  10 . 
         [0019]    Then a plurality of light emitting dies  20  are fixed on the leads  30  as shown in  FIG. 2 , respectively. The light emitting dies  20  are preferably mounted on the leads  30  by flip chip bonding for increasing a light extracting efficiency of the LED. Each light emitting die  20  may be made of GaN, AlGaN, AlInGaN or other suitable light emitting materials. The light emitting die  20  can emit light by driven of current conducted from the leads  30 . Each light emitting die  20  is received in a corresponding groove  12  and connected to the two first conductive portions  32  of one corresponding pair of leads  30  via electrically conductive interconnection  50  (see  FIG. 6 ). The electrically conductive interconnection  50  can be electrically conductive adhesive or solder balls. The electrically conductive adhesive may be epoxy doped with silver particulates for providing good electrical conduction between the light emitting die  20  and the leads  30 . 
         [0020]    An encapsulant  40  is further disposed on the base  10  to seal the light emitting dies  20  within the grooves  12  as shown in  FIG. 3 . The encapsulant  40  is made of transparent glass composed of SiO 2 , Na 2 O.SiO 2  or other suitable materials. The encapsulant  40  includes a cover  42  and a plurality of positioning plates  44  formed on a bottom face of the cover  42 . The cover  42  may be made integrally with the positioning plates  44  by casting or machining of an individual stock, or made separately from the positioning plates  44  and fixed with the positioning plates  44  via co-firing or adhering. The cover  42  has a size similar to that of the base  10  so that the cover  42  can substantially overlay an entire area of the top face of the base  10 . Each positioning plate  44  has a thickness smaller than that of the cover  42  and a width gradually decreasing along a top-to-bottom direction. Each positioning plate  44  is fittingly received in a top of the groove  12  to thereby position the cover  42  on the base  10 . 
         [0021]    The base  10  and the encapsulant  40  are securely fixed to each other by co-firing as shown in  FIG. 4 . A temperature during co-firing is preferably selected between 300 and 500 for promoting joint of the encapsulant  40  to the base  10 . Furthermore, in order to lower the temperature of co-firing for protecting the light emitting dies  20 , a liquid glass (i.e., sodium silicate, not shown) can be smeared between the encapsulant  40  and the base  10  before the co-firing. In addition, noble gas can be filled within the grooves  12  so as to protect the light emitting dies  20  from destroy due to outside dust or moisture entering the grooves  12 . The connection between the base  10  and the encapsulant  40  under co-firing is reliable, secure and firm, whereby the LED can have a stable structure to resist a high working temperature. 
         [0022]    Finally, the base  10  and the encapsulant  40  are diced into a plurality of individual LEDs along areas between adjacent grooves  12  as shown in  FIG. 5 . The above process of firstly packing and then dicing can simplify manufacturing processes of the LEDs, thereby facilitating rapid mass production of the LEDs. 
         [0023]    Since the light emitting die  20  is easily to be damaged under a high temperature, in order to further reduce possibility of damage to the light emitting die  20  during co-firing, a transparent protective layer  60  can be formed around the light emitting die  20  before co-firing. As shown in  FIG. 7 , the protective layer  60  substantially covers the light emitting die  20  and coupled with the leads  30  and the base  10 . The protective layer  60  may be liquid epoxy dispensed on the light emitting die  20  and then baked to harden. A thickness of the protective layer  60  should be controlled within a range so that the protective layer  60  would not block the positioning plate  44  received in the groove  12 . Preferably, the protective layer  60  is spaced a gap from a bottom face of the positioning plate  44  of the encapsulant  40 . Alternatively, the protective layer  60  can have phosphors doped therein for changing color of the light emitted from the light emitting die  20 . The phosphors may be made of garnet compound, silicate, nitride or other suitable materials, depending on the actual requirement of the color. The light excited from the phosphors mixes with the light directly emitted from the light emitting die  20  to have a desirable color. 
         [0024]    The phosphors can also be placed on other locations of the LED. For example, the phosphors may be doped within one or both of the cover  42  and the positioning plate  44 , or in the form of a single layer adhered on a top face of the cover  42  or a bottom face of the positioning plate  44 .  FIG. 8  shows the phosphors being dispersed in a layer (not labeled) secured to the top face of the cover  42  as an example. The location of the phosphors remote from the light emitting die  20  can prevent chromatic dispersion from occurring when the mixed light transmits through the encapsulant  40 . 
         [0025]    For meeting thickness requirements of thin products, the structure of the LED can be varied to have a small thickness as shown in  FIG. 9 . The differences between the LEDs of this embodiment and the previous embodiments are the base  10   a  and the encapsulant  40   a . The base  10   a  has a flat top face without grooves  12  defined therein, and the light emitting dies  20   a  are mounted on the top face of the base  10   a . The encapsulant  40   a  defines a plurality of cavities  46   a  in a bottom face thereof corresponding to the light emitting dies  20 , respectively. The light emitting dies  20   a  are received in the cavities  46   a  of the encapsulant  40   a  to be protected by the encapsulant  40   a . It is noted that the encapsulant  40   a  and the base  10   a  are also fixed to each other by co-firing in this embodiment. 
         [0026]    Referring to  FIG. 10 , in order to realize convenient position between the encapsulant  40   a  and the base  10   a  before co-firing, the encapsulant  40   a  can form a plurality of protrusions  44   a  on the bottom face of a cover  42   a  thereof, and the base  10   a  can form a plurality of holes  14   a  in the top face thereof corresponding to the protrusions  44   a , respectively. The protrusions  44   a  are retained in the holes  14   a , respectively, whereby the encapsulant  40   a  is able to accurately cover the light emitting dies  20   a  by the guidance of the protrusions  44   a . The protrusions  44   a  can further enhance joint strength between the encapsulant  40   a  and the base  10   a  by engagement into the holes  14   a . The protrusions  44   a  may be made integrally with or separately from the cover  42   a  in a manner as that of the positioning plates  44  disclosed in accordance with the first embodiment. 
         [0027]    It is believed that the present disclosure and its 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 present disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments.