Abstract:
A light emitting diode (LED) package and a method of manufacturing a LED package is provided. The LED package includes a case having first and second lead frames disposed through the case; an LED chip disposed on the case, the LED chip having first and second electrodes directly connected to the first and second lead frames through a eutectic bond, respectively; and a lens disposed over the case covering the LED chip.

Description:
The present application claims the benefit of Korean Patent Application No. 10-2009-0127788, filed in Korea on Dec. 21, 2009, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light emitting diode (LED) package, and more particularly, to an LED package being capable of preventing problems during a bonding process and a method of fabricating the LED package. 
     2. Discussion of the Related Art 
     Recently, LEDs are widely used because their characteristic of small size, low power consumption and high reliability. For example, LEDs are used for electric illumination and light sources in display devices. Particularly, to replace fluorescent lamps, LEDs that emits white light can be used. LEDs that emit white light are also being introduced for backlight units in liquid crystal display (LCD) devices. 
       FIG. 1  is a cross-sectional view of a related art LED package. As shown in  FIG. 1 , the LED package  10  includes an LED chip  20  for emitting light, a case  30  as a housing, fluorescent particles  40 , first and second electrode leads  50   a  and  50   b , a heat-transfer body  60 , a pair of wires  70  and a lens  80 . The lens  80  covers the LED chip  20  and the fluorescent particle  40 . 
     The LED chip  20  is disposed on the heat-transfer body  60 . The heat-transfer body  60  has a space. The space of the heat-transfer body  60  is covered with the case  30  and is packed with the fluorescent particles  40 . The first and second electrode leads  50   a  and  50   b  are disposed through the heat-transfer body  60 , and one end of each of the first and second electrode leads  50   a  and  50   b  protrudes from the case  30  to be electrically connected to an exterior current supplying unit (not shown) to receive a driving current for the LED chip  20 . The other end of each of the first and second electrode leads  50   a  and  50   b  is respectively electrically connected to the LED chip  20  through the wires  70 . The lens  80  covers the LED chip  20 , the fluorescent particles  40 , the heat-transfer body  60  and the wires  70 , and controls an angle of light from the LED chip  20 . 
     When the driving current is applied to the LED chip  20 , the LED chip  20  emits light. The light from the LED chip  20  mixes with light from the fluorescent particles  40  to produce white light. Thus, white light is emitted through the lens  80 . 
     The LED package  10  requires the wires  70  to provide the driving current from the exterior current supplying unit to the LED chip  20 . Unfortunately, there can be an open defect on the wires  70 . In addition, since the wires  70  are positioned at a path of the light from the LED chip  20 , luminescent efficiency of the LED package  10  is decreased. Furthermore, a bonding process, for example, a soldering process, is required for connecting the wires  70  to the LED chip  20 . The bonding process is very complicated such that processing yield is also decreased. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an LED package and a method of fabricating the LED package that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to improve lamination efficiency of an LED package. 
     Another object of the present invention is to prevent problems during a bonding process for an LED package. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a light emitting diode (LED) package comprises a case having first and second lead frames disposed through the case; an LED chip disposed on the case, the LED chip having first and second electrodes directly connected to the first and second lead frames through a eutectic bond, respectively; and a lens disposed over the case covering the LED chip. 
     In another aspect, a method of fabricating a light emitting diode (LED) package comprises forming a case having first and second lead frames on a surface thereof; forming a LED chip having a transparent substrate, a LED structure, a first electrode and a second electrode; positioning the LED chip on the case such that the first and second electrodes directly contact the first and second lead frames; irradiating electromagnetic radiation onto the contact portion between the first electrode and the first lead frame as well as the second electrode and the second lead frame to generate eutectic bonding. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a cross-sectional view of a related art LED package; 
         FIG. 2  is a schematic cross-sectional view of an LED chip according to an exemplary embodiment of the present invention; 
         FIG. 3  is a schematic cross-sectional view of an LED package according to an exemplary embodiment of the present invention; 
         FIG. 4  is a schematic cross-sectional view showing a bonding feature of an LED chip to an LED package according to an exemplary embodiment of the present invention; and 
         FIGS. 5A to 5E  are cross-sectional view illustrating a bonding process for an LED chip according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings. 
       FIG. 2  is a schematic cross-sectional view of an LED chip according to an exemplary embodiment of the present invention. As shown in  FIG. 2 , an LED chip  100  includes a substrate  101 , an n-type semiconductor layer  120 , an active layer  130 , a p-type semiconductor layer  140 , first and second reflection plates  170   a  and  170   b , a first electrode  150  and a second electrode  160 . The p-type semiconductor layer  140  and the n-type semiconductor layer  120  form a forward-biased junction. The substrate  101  may be formed of a transparent material, such as sapphire. Alternatively, zinc oxide (ZnO), gallium nitride (GaN), silicon carbide (SiC) or aluminum nitride (AlN) may be used for the substrate  101 . 
     The n-type semiconductor layer  120  is formed on the substrate  101 . To improve a lattice junction property, a buffer layer (not shown) may be formed between the substrate  101  and the n-type semiconductor layer  120 . The buffer layer may be formed of GaN or AlN/GaN. The n-type semiconductor layer  120  may be formed of GaN or GaN/AlGaN where an n-type conductive dopant is doped. For example, the n-type conductive dopant may be silicon (Si), germanium (Ga) or tin (Sn). Here, Si is generally used. 
     The active layer  130  is formed on the n-type semiconductor layer  120 . The active layer  130  is formed of a GaN-based material such that the active layer  130  has a single quantum well structure, a multi-quantum well structure, or their super lattice structure. For example, at least one of AlGaN, AlNGaN, InGaN may be used for the active layer  130 . 
     The p-type semiconductor layer  140  is formed on the active layer  130 . The p-type semiconductor layer  140  may be formed of GaN or GaN/AlGaN where a p-type conductive dopant is doped. For example, the p-type conductive dopant may be magnesium (Mg), zinc (Zn) or beryllium (Be). Here, Mg is used. 
     The p-type semiconductor layer  140  and the active layer  130  are mesa-etched to expose one portion of the n-type semiconductor layer  120 . Namely, each of the p-type semiconductor layer  140  and the active layer  130  overlaps the other portion of the n-type semiconductor layer  120 . 
     The first electrode  150  is formed over one portion of the n-type semiconductor layer  120 , and the second electrode  160  is formed over the p-type semiconductor layer  140 . The first and second electrodes  150  and  160  have substantially the same height from the substrate  101 . This may be referred to as a top-top type arrangement. The LED chip  100  may be referred to as a horizontal type. 
     When voltages are applied to the second electrode  160  and the first electrode  150 , holes and electrons are injected into the p-type semiconductor layer  140  and the n-type semiconductor layer  120 , respectively. The holes and the electrons recombine in the active layer  130  so that light is emitted through the substrate  101 . 
     In the LED chip  100  according to an exemplary embodiment of the present invention, the first reflection plate  170   a  is disposed on the n-type semiconductor layer  120  and under the first electrode  150 , and the second reflection plate  170   b  is disposed on the p-type semiconductor layer  140  and under the second electrode  160 . By using the first and second reflection plates  170   a  and  170   b , light efficiency of the LED chip  100  is improved. 
     Each of the first and second reflection plates  170   a  and  170   b  is formed of a high reflective property material having a reflectivity above about 70% in a visible ray wavelength, an infrared wavelength, and an ultraviolet wavelength. Also, each of the first and second refection plates  170   a  and  170   b  should be electrically conductive if the first and second electrodes  150  and  160  are connected through the first and second reflective plates  170   a  and  170   b . For example, silver (Ag), aluminum (Al), molybdenum (No) or chromium (Cr) may be used for the first and second reflection plates  170   a  and  170   b . Here, the material for the first and second reflective plates  170   a  and  170   b  may be deposited as a film. 
       FIG. 3  is a schematic cross-sectional view of an LED package according to an exemplary embodiment of the present invention, and  FIG. 4  is a schematic cross-sectional view showing a bonding feature of an LED chip to an LED package according to an exemplary embodiment of the present invention. 
     As shown in  FIGS. 3 and 4 , the LED package  200  includes a lead frame  250  including first and second lead frames  250   a  and  250   b , a heat-transfer body  260 , the LED chip  100 , a case  230  as a housing and a lens  280  covering the LED chip  100 . 
     The LED chip  100  is a horizontal type and includes the first electrode  150  (of  FIG. 2 ) and the second electrode  160  (of  FIG. 2 ). The LED chip  100  is disposed over the lead frame  250  in an inverted orientation as compared to the orientation of  FIG. 3 . The first electrode  150  and the second electrode  160  are electrically connected to the first and second lead frames  250   a  and  250   b  such that a power is provided into the LED chip  100 . As a result, the LED chip  100  emits light. 
     Heat from the LED chip  100  is transferred to the outside through the heat-transfer body  260 . The heat-transfer body  260  is formed of a thermally conductive material, such as metallic material. The heat-transfer body  260  has a space. The space of the heat-transfer body  260  is covered with the case  230  and is packed with the fluorescent particles  240 . However, heat-transfer body  260  can be omitted. In this case, the fluorescent particles  240  are disposed in the case  230 . 
     The first and second lead frames  250   a  and  250   b  may be disposed through the case  230  or the heat-transfer body  260 , and one end of each of the first and second lead frames  250   a  and  250   b  protrudes from the case  230 . If the heat-transfer body is used, the first and second lead frames  250   a  and  250  may be in contact with the heat-transfer body  260 . One end of each of the first and second lead frames  250   a  and  250   b  are electrically connected to an external current supply unit to receive a driving current for the LED chip  100 . 
     The lens  280  covers the LED chip  100 , the fluorescent particles  240  and the heat-transfer body  260  and controls an angle of light from the LED chip  100 . The lens controls a radiation angle of the light from each LED chip  100 . The lens  280  may be classified as a high-dome emitter type, a low-dome emitter type or a side emitter type depending on their shape. The high-dome emitter type lens has a radiation angle of about 140 degrees. The low-dome emitter type lens has a radiation angle of about 110 degrees and a lower dome shape than the high-dome emitter type. The side emitter type lens has a crown shape and a radiation angle of about 200 degrees. 
     When the LED chip  100  emits blue light, the fluorescent particle  240  is a yellow type. For example, the yellow type fluorescent particle may be a cerium doped yttrium-aluminum-garnet T 3 Al 5 O 12 :Ce (YAG:Ce)-based material. 
     When the LED chip  100  emits UV light, the fluorescent particles  240  includes red, green and blue color fluorescent particles. By controlling a relative ratio of the red, green and blue color fluorescent particles, a color of light from the LED package  200  can be controlled. 
     For example, the red fluorescent particles may be a Y 2 O 3 :EU (YOX)-based material as a compound of yttrium oxide (Y 2 O 3 ) and europium (EU). Yttrium oxide (Y 2 O 3 ) has a main wavelength of 611 nm. The green fluorescent particles may be a LaPO 4 :Ce,Tb (LAP)-based material as a compound of phosphoric acid (PO 4 ), lanthanum (La), terbium (Tb). Phosphoric acid has a main wavelength of 544 nm. The blue fluorescent particles may be a BaMgAl 10 O 17 :EU (BAM)-based material as a compound of barium (Ba), magnesium (Mg), a aluminum oxide-based material, and europium (EU). Barium has a main wavelength of 450 nm. The main wavelength is defined as a wavelength for generating highest luminance. 
     When electrical power is provided to the LED chip  100  through the lead frame  250 , the LED chip  100  emits light. The fluorescent particles  240  are excited by the light from the LED chip  100  such that the light from the LED chip  100  and the light from the fluorescent particles  240  are mixed. As a result, white light is emitted through the lens  280 . 
     In the LED package  200  according to an exemplary embodiment of  FIG. 3 , the LED chip  100  is electrically connected to the lead frame  250  by a eutectic bonding. Namely, the LED chip  100  is electrically connected to the lead frame  250  by a thermally pressing under a high temperature of about 200 to 700° C. to obtain strength and reliability in the bonding. 
     For the eutectic bonding, the lead frame  250  may be formed of one of Au/Sn, Au/Ni, Au/Ge, Au, Sn and Ni. Preferably, the lead frame  250  may be formed of a plating with one of the above materials. In addition, each of the first electrode  150  and the second electrode  160 , which are eutectically bonded with the lead frame  250 , may be formed of one of Au/Sn, Au/Ni, Au/Ge, Au, Sn and Ni. Preferably, each of the first electrode  150  and the second electrode  160  may be formed of a plating of one of the above material. For example, each of the first electrode  150  and the second electrode  160  may be formed of Au/Sn, and the lead frame  250  may be formed of Au. In this case, a weight ratio of Au to Sn may be 8:2. Alternatively, each of the first electrode  150  and the second electrode  160  may be formed of Au, and the lead frame  250  may be formed of Au/Sn. 
     When thermal pressing is performed by contacting each of the first and second electrodes  150  and  160  with the lead frame  250 , a contact portion of the first electrode  150  and the lead frame  250  and a contact portion of the second electrode  160  and the lead frame  250  are melted such that a eutectic alloy is formed at an interface between the first electrode  150  and the lead frame  250  and an interface between the second electrode  160  and the lead frame  250 . As a result, the first electrode  150  and the second electrode  160  are electrically connected to the first and second lead frames  250   a  and  250   b  of the lead frame  250 . 
     The eutectic alloy has a predetermined composition ratio of Au to Sn and serves as first and second conductive adhesive films  310   a  and  310   b . Namely, the LED chip  100  is electrically connected to the first and second lead frames  250   a  and  250   b  by the first and second conductive adhesive films  310   a  and  310   b  as the eutectic alloy. 
     The eutectic bonding has an excellent bonding strength and dose not require a step of coating an adhesive material. As mentioned above, the first and second electrodes  150  and  160  of the LED chip  100  are electrically connected by the eutectic bonding to the first and second lead frames  250   a  and  250   b . Namely, the LED chip  100  has a flip-chip bonding structure on the lead frame  250 . 
     Since the LED chip  100  receives power from an exterior current supplying unit through the lead frame  250  without the wire  70  (of  FIG. 1 ), the open defect on the wire is avoided. In addition, a decrease in luminance efficiency caused by the wire is also avoided. Furthermore, since a bonding process, for example, a soldering process, for connecting the wires to the LED chip is not required, processing yield is improved. Moreover, since the material having a high heat-transfer property, e.g., Au/Sn, is used for the first and second electrodes, a thermal damage on the LED package is further decreased. 
     The LED package  200  further includes an insulating pattern  320  between the first and second lead frame  250   a  and  250   b . The insulating pattern  320  has a thickness greater than the first and second lead frame  250   a  and  250   b  such that an electrical short between the first and second electrodes  150  and  160  is prevented. Namely, an end of the insulating pattern  320  is disposed between the first and second electrodes  150  and  160  to serve as a wall. For example, the insulating pattern  320  may be formed of at least one of SiO 2 , Si 3 N 4 , Al 2 O 3 , TiO 2 , HfO 2 , T 2 O 3 , MgO and AlN. 
       FIGS. 5A to 5E  are cross-sectional views illustrating a bonding process for an LED chip according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 5A , first and second lead frame patterns  270   a  and  270   b  and the insulating pattern  320  are formed on the heat-transfer body  260 . Without the heat-transfer body  260 , first and second lead frame patterns  270   a  and  270   b  and the insulating pattern  320  may be formed on the case  230 . Each of the first and second lead frame patterns  270   a  and  270   b  may be formed of one of Au/Sn, Au/Ni, Au/Ge, Au, Sn and Ni. The first and second lead frame patterns  270   a  and  270   b  are spaced apart from each other to expose a portion of the heat-transfer body  260 . The insulating pattern  320  is disposed in a space  272  between the first and second lead frame patterns  270   a  and  270   b . For example, after forming the first and second lead frame patterns  270   a  and  270   b  on the heat-transfer body  260 , the insulating pattern  320  is formed in the space. Alternatively, after forming the insulating pattern  320  on the heat-transfer body  260 , the first and second lead frame patterns  270   a  and  270   b  are formed at both sides of the insulating pattern  320 , respectively. The insulating pattern  320  has substantially the same thickness as each of the first and second lead frame patterns  270   a  and  270   b  to form a flat top surface. 
     Next, as shown in  FIG. 5B , the LED chip  100  is disposed over the heat-transfer body  260  such that the first and second electrodes  150  and  160  respectively contact the first and second lead frame patterns  270   a  and  270   b  and the insulating pattern  320  is positioned between the first and second electrodes  150  and  160 . The LED chip  100  may be moved using a vacuum chuck, e.g., a collet chuck. As mentioned above, each of the first and second electrodes  150  and  160  may be formed of one of Au/Sn, Au/Ni, Au/Ge, Au, Sn and Ni. A width of the insulating pattern  320  is equal to or smaller than a distance between the first and second electrodes  150  and  160 . 
     Next, as shown in  FIG. 5C , to fix the LED chip  100  on the first and second lead frame patterns  270   a  and  270   b , the LED chip  100  is pressed using a pressing apparatus, e.g., a capillary. 
     Next, as shown in  FIG. 5D , by irradiating a laser beams LB onto a front side and a rear side of the LED chip such that a contact portion between the first lead frame pattern  270   a  and the first electrode  150  and a contact portion between the second lead frame pattern  270   b  and the second electrode  160  are heated. Alternatively, one laser beam LB may be employed onto one of the front side and rear side of the LED chip. 
     As a result, eutectic bonding is generated between the first lead frame pattern  270   a  and the first electrode  150  and the second lead frame pattern  170   b  and the second electrode  160 . A thickness of each of the first and second lead frame patterns  270   a  and  270   b  is reduced by the eutectic bonding reaction to form the first and second lead frame  250   a  and  250   b , as shown in  FIG. 5E . In addition, since the thickness of each of the first and second lead frame patterns  270   a  and  270   b  is reduced by the eutectic bonding reaction, the insulating pattern  320  has a thickness greater than each of the first and second lead frames  250   a  and  250   b  and is disposed between the first and second electrodes  150  and  160  to serve as a wall. Through the eutectic bonding reaction, the first and second conductive adhesive films  310   a  and  310   b  are formed between the first lead frame pattern  270   a  and the first electrode  150  and between the second lead frame pattern  270   b  and the second electrode  160 , respectively. Due to the first and second conductive adhesive films  310   a  and  310   b , the first and second electrodes  150  and  160  of the LED chip  100  are electrically connected to the first and second lead frames  250   a  and  250   b , respectively. 
     The pressing step and the laser beam irradiation step may be simultaneously performed. 
     The laser beams LB may be an infra-red laser beam. For example, a YAG type laser source having a wavelength of 1064 nm may be used. The laser beams are irradiated during about 0.01 to about 1 sec. A temperature at a contact portion between the first lead frame pattern  270   a  and the first electrode  150  and a contact portion of the second lead frame pattern  270   b  and the second electrode  160  may be about 200 to 700° C. during the heating process. 
     In accordance with exemplary embodiments of the present invention, since a contact portion between the first lead frame pattern  270   a  and the first electrode  150  and a contact portion of the second lead frame pattern  270   b  and the second electrode  160  is momentarily and locally heated by the laser beam LB, thermal damage on the LED chip is minimized. Since the LED chip  100  receives power from the exterior current supplying unit (not shown) through the lead frame  250  without the use of the wire  70  (of  FIG. 1 ), the open defect on the wire is avoided. In addition, a decrease in luminance efficiency caused by the wire is also avoided. Furthermore, since a bonding process, for example, a soldering process, for connecting the wires to the LED chip is not required, processing yield is improved. Moreover, since the material having a high heat-transfer property, e.g., Au/Sn, is used for the first and second electrodes, a thermal damage on the LED package is further decreased. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.