Abstract:
Disclosed is a method of manufacturing a light-emitting diode (LED) device, which is advantageous in terms of easy formation of metal material reflective surfaces using a lead frame, thereby improving the luminance characteristics by a simple manufacturing process. The current method includes forming the lead frame having a first pattern part mounted with an LED chip, a second pattern part electrically connected to the first pattern part to be used as an electrode, a third pattern part spaced from the first pattern part to be electrically insulated from the first pattern part and used as another electrode, a fourth pattern part and a fifth pattern part integrated with both sides of the first pattern part, forming a layer plated with a metal having high reflectivity on the fourth and fifth pattern parts, and upwardly folding the fourth and fifth pattern parts to be perpendicular to the first pattern part to form the reflective surfaces. Accordingly, the reflective surfaces of a surface mountable LED device, regardless of a mold type or a pre-mold type, can be readily formed from the lead frame with excellent heat releasing performance, whereby the LED device exhibits high heat releasing effects, therefore preventing the deterioration of luminance characteristics.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates, in general, to surface mountable light-emitting diode devices. More specifically, the present invention is directed to a method of manufacturing a light-emitting diode device, capable of simply forming reflective surfaces made of a metal material by use of a lead frame.  
           [0003]    2. Description of the Related Art  
           [0004]    As well known to those skilled in the art, a light-emitting diode (hereinafter, referred to as ‘LED’) composed of a compound semiconductor, such as GaAs, AlGaAs, GaN, InGaN or AlGaInP, as a light-emitting source, is a semiconductor device capable of emitting light of various colors.  
           [0005]    With great advances in semiconductor techniques, LED devices have recently been produced to have high luminance and quality characteristics, in place of commercially available LED products with low luminance. In addition, fabrication of blue and white diodes has been practically realized, whereby the LEDs are widely applicable to displays, next-generation lighting sources and the like. For instance, a surface mountable LED device is available.  
           [0006]    [0006]FIG. 1 schematically shows the surface mountable LED device, comprising a package molded with an epoxy resin. A certain surface of the package  2  is formed to an open window  4  so as to easily emit light, and the other surfaces are attached with electrodes  5  so as to be mounted in a printed circuit board  1 . In the package  2 , a light-emitting surface of an LED chip is disposed to face to the light-emitting window  4 , and the electrodes  5  are connected with the LED chip by a wire.  
           [0007]    Factors determining the characteristics of the LED device include color, luminance, strength of luminance, etc. While the characteristics of such an LED device mainly depend on a compound semiconductor material used for the LED chip, they are further affected by a structure of the package for use in mounting the LED chip. The LED package structure has an influence on luminance and luminance angle distributions.  
           [0008]    The surface mountable LED package suffers from low luminance due to a broad luminance distribution.  
           [0009]    [0009]FIG. 2 shows a structure of a conventional surface mountable LED device. As shown in FIG. 2, the LED device comprises a lead frame  21 , a package  22  formed by a pre-molding process to contain a portion of the lead frame  21 , an LED chip  23  mounted on the lead frame  21  in the package  22 , and a molding material  25  filled in the package  22  to protect the LED chip  23 .  
           [0010]    With reference to FIGS. 3 a  through  3   e,  there is shown a process of manufacturing such a conventional LED device, comprising forming a lead frame (FIG. 3 a ), plating (FIG. 3 b ), pre-molding (FIG. 3 c ), mounting a chip and wire-bonding (FIG. 3 d ), and filling epoxy (FIG. 3 e ). In such a case, the lead frame  31  includes a first pattern part  31   a  for use in mounting an LED chip thereon, a second pattern part  31   b  integrated with the first pattern part  31   a  for use in an electrode, and a third pattern part  31   c  spaced from the first pattern part  31   a  so as to be electrically insulated from the first pattern part  31   a.  On a front surface of the lead frame  31 , a metal-plated layer having high adhesion and conductivity is formed to easily perform a wire-bonding process. In FIG. 3 c  illustrating the pre-molded state, a hexahedron-shaped package  33  having an inner cavity is formed to surround the other portions of the lead frame  31  with the exception of electrode portions of the second and third pattern parts  31   b  and  31   c  of the lead frame  31  to be used as external electrodes. An LED chip  34  is mounted on the first pattern part  31   a  of the lead frame  31  in the package  33 , and the LED chip  34  is wire-bonded to each of the second and third pattern parts  31   b  and  31   c  in the package  33  to form wire-bonded portions. As shown in FIG. 3 e,  the package  33  is filled with transparent epoxy  36  to protect the LED chip  34  and the wire-bonded portions.  
           [0011]    However, such an LED device is disadvantageous in terms of characteristic deterioration and decreased functions, resulting from defects of crystals caused by artificial growth in the compound semiconductor, serving as the emitting source. Further, packaging and transparent molding materials may be degraded in characteristics thereof, too.  
           [0012]    As seen in FIG. 2 and FIGS. 3 a  through  3   e,  the conventional LED device is low in reflection efficiency, since a plastic material is used at the pre-molding process. Also, upon use of such a device for extended periods, deterioration of the pre-molded package takes place as in molding materials, thus significantly lowering luminance characteristics.  
           [0013]    Moreover, the pre-molded package has low thermal conductivity, and is restricted for use in products with high luminance. Additionally, upon emission of light from the LED chip, inner surfaces of the package useful as a light-emission passage are non-uniform, thus lowering reflection efficiency.  
         SUMMARY OF THE INVENTION  
         [0014]    Accordingly, the object of the present invention is to alleviate the problems encountered in the related art and to provide a method of manufacturing a light-emitting diode device, characterized by simply forming metal material reflective surfaces by use of a lead frame, therefore resulting in improving the luminance characteristics by a simple manufacturing process.  
           [0015]    To achieve the above object, there is provided a method of manufacturing an LED device according to a primary embodiment of the present invention, comprising the steps of forming a lead frame including a first pattern part mounted with an LED chip, a second pattern part electrically connected to the first pattern part to be used as an electrode, a third pattern part spaced from the first pattern part to be electrically insulated from the first pattern part and used as another electrode, a fourth pattern part and a fifth pattern part integrated with both sides of the first pattern part; forming a metal-plated layer having high adhesion and conductivity on the first pattern part through the third pattern part of the lead frame; forming another metal-plated layer having high reflectivity on the fourth and fifth pattern parts; mounting the LED chip on the plated first pattern part to emit light upward; connecting the mounted LED chip to the second and third pattern parts by means of a wire; molding the mounted LED chip and the portions connected by the wire for protection thereof; upwardly folding the fourth and fifth pattern parts to be perpendicular to the first pattern part of the lead frame to allow plated surfaces of the fourth and fifth pattern parts to face each other; and forming externally exposed portions of the second and third pattern parts to make external electrodes. Thereby, reflective surfaces can be easily formed with a desired metal-plated layer, and thus the luminance characteristics of the LED device can be further improved.  
           [0016]    According to a secondary embodiment of the present invention, there is provided a method of manufacturing an LED device, comprising the steps of: forming a lead frame including a first pattern part mounted with an LED chip, a second pattern part electrically connected to the first pattern part to be used as an electrode, a third pattern part spaced from the first pattern part to be electrically insulated from the first pattern part and used as another electrode, a fourth pattern part and a fifth pattern part integrated with both sides of the first pattern part; forming a metal-plated layer having high adhesion and conductivity on the first pattern part through the third pattern part of the lead frame; forming another metal-plated layer having high reflectivity on the fourth pattern part and the fifth pattern part of the lead frame; upwardly folding the plated fourth pattern part and the plated fifth pattern part to be perpendicular to the first pattern part of the lead frame to allow plated surfaces of the fourth and fifth pattern parts to face each other; pre-molding the lead frame to surround all the other parts of the lead frame with the exception of electrode portions of the second and third pattern parts, to form a hexahedron-shaped package having an inner cavity; mounting the LED chip on the plated first pattern part of the lead frame surrounded by the package so as to emit light upward; wire-bonding the mounted LED chip to each of the second pattern part and the third pattern part in the package to form wire-bonded portions; molding the inside of the package to protect the LED chip and the wire-bonded portions; and forming the electrode portions of the second and third pattern parts to make leads. As a result, reflective surfaces can be easily formed with a desired metal-plated layer, and the luminance characteristics can be further improved.  
           [0017]    As for the manufacturing method of the LED device, the plated layer of each of the fourth pattern part and the fifth pattern part of the lead frame is composed of Ag, Ni, Pd or Cr, and the plated layer of each of the first pattern part through the third pattern part of the lead frame is composed of Ag, Au or Pd.  
           [0018]    In addition, as for the manufacturing method of the LED device, the upwardly folding step further comprises the step of controlling reflection angles by adjusting angles between the first pattern part and the fourth pattern part and between the first pattern part and the fifth pattern part, thereby obtaining a desired reflection angle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The above and other objects, features and other advantages of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 is a schematic view illustrating a general light-emitting diode device;  
         [0021]    [0021]FIG. 2 is a sectional view illustrating a structure of a conventional light-emitting diode device;  
         [0022]    [0022]FIGS. 3 a  through  3   e  are views illustrating a manufacturing process of such a conventional light-emitting diode device;  
         [0023]    [0023]FIGS. 4 a  through  4   f  are views illustrating a manufacturing process of a light-emitting diode device, according to a primary embodiment of the present invention;  
         [0024]    [0024]FIGS. 5 a  through  5   f  are views illustrating a manufacturing process of a light-emitting diode device, according to a secondary embodiment of the present invention; and  
         [0025]    [0025]FIGS. 6 a  through  6   b  are views illustrating a modification of the manufacturing process of the light-emitting diode device according to the secondary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Based on the present invention, a method of manufacturing an LED device according to a mold type or a pre-mold type is provided, to easily and simply form reflective surfaces by use of a lead frame, in which a manufacturing method of a mold type LED device differs in procedures thereof from that of a pre-mold type LED device.  
         [0027]    Referring to FIG. 4, there is sequentially shown a process of manufacturing the mold type LED device, according to a primary embodiment of the present invention.  
         [0028]    The mold type LED device forms a package structure by a molding process directly without a pre-molding process, and is fabricated by the following procedures.  
         [0029]    As shown in FIG. 4 a,  a lead frame  41  is formed for supporting an LED chip and forming electrodes for electric signal applications. As such, the lead frame  41  comprises a first pattern part  41   a  for use in mounting an LED chip thereon, a second pattern part  41   b  electrically connected to the first pattern part  41   a  to be used as an external lead electrode, a third pattern part  41   c  spaced from the first pattern part  41   a  to be electrically insulated from the first pattern part  41   a  and used as another external lead electrode, a fourth pattern part  41   d  and a fifth pattern part  41   e  integrated with both sides of the first pattern part  41   a.    
         [0030]    The fourth and fifth pattern parts  41   d  and  41   e  of the lead frame  41  are folded upward to be perpendicular to the first pattern part  41   a,  and function to concentrate rays of light emitted from the LED chip to a predetermined direction.  
         [0031]    With the aim of maximizing the reflection effects of light in a desired direction, the fourth and fifth pattern parts  41   d  and  41   e  are disposed to face each other at both sides of the first pattern part  41   a,  and, preferably, have a size suitable for reflecting the light emitted from the LED chip to be mounted onto the first pattern part  41   a.    
         [0032]    Further, such pattern parts for reflection of light may be formed to be coincident with lengths of both sides of the first pattern part  41   a,  and the other sides of the first pattern part  41   a  are formed with electrode parts, thus easily mounting the LED chip on the first pattern part  41   a.    
         [0033]    After such a lead frame  41  is formed, a front surface thereof is plated. FIG. 4 b  shows the plated lead frame  41 , in which each pattern part of the lead frame  41  may be plated with different metals according to functions of each pattern part. In the present invention, the first pattern part  41   a  through the third pattern part  41   c,  which are mounted with the LED chip and subjected to a wire-bonding process, are plated with a metal having high conductivity and adhesion, such as Ag, Au, Pd and so on. Meanwhile, the fourth and fifth pattern parts  41   d  and  41   e,  serving as a reflective surface, are plated with a metal that is glossy and has high reflectivity, such as Ag, Ni, Pd, Cr, etc.  
         [0034]    Since a pre-molding process is unnecessary for the mold type LED device, the plated lead frame  41  is directly mounted with the LED chip  42  at a plated surface thereof. Electrodes of the LED chip  42  are bonded to the second and third pattern parts  41   b  and  41   c  of the plated lead frame  41  by means of a wire  43 , to form wire-bonded portions. FIG. 4 c  shows the mounted LED chip  42  and the wire-bonded lead frame  41 .  
         [0035]    Then, a circumference of the LED chip  42  and the bonded wire  43  mounted on the lead frame  41  is molded to a predetermined shape for protection thereof. As shown in FIG. 4 d,  a hexahedron-shaped molding part  44  having parallel surfaces is formed so that the LED device is easily mounted. In addition, such a molding part  44  may be formed to other shapes.  
         [0036]    A constituent material of the molding part  44  comprises transparent epoxy with high light transmittance so that light emitted from the LED chip  42  is almost completely transmitted. Alternatively, other materials may be used so long as satisfying the above requirements of the molding material.  
         [0037]    In the state of the LED chip  42  and the wire-bonded portions being protected by the molding part  44 , the fourth and fifth pattern parts  41   d  and  41   e  of the plated lead frame  41  are folded upward to be perpendicular to the first pattern part  41   a  of the lead frame  41 . Thereby, the plated surfaces of the fourth pattern part  41   d  and the fifth pattern part  41   e  are disposed to be opposite, each of which is plated with a metal having high reflectivity.  
         [0038]    Hence, light emitted from the LED chip  42  is reflected on the plated surfaces of the fourth and fifth patterns parts  41   d  and  41   e,  and concentrated to a predetermined direction while not being externally transmitted, and then radiated. Thus, luminance characteristics of light emitted from the complete LED device can be improved.  
         [0039]    Such characteristics can be applied to a pre-mold type LED device.  
         [0040]    Turning now to FIGS. 5 a  through  5   f,  there is sequentially shown a process of manufacturing the pre-mold type LED device according to the secondary embodiment of the present invention.  
         [0041]    Likewise, a lead frame  51  is formed for supporting an LED chip and forming electrodes for electric signal applications. Such a lead frame  51  includes a first pattern part  51   a  for use in mounting an LED chip thereon, a second pattern part  51   b  electrically connected to the first pattern part  51   a  to be used as an external lead electrode, a third pattern part  51   c  spaced from the first pattern part  51   a  to be electrically insulated from the first pattern part  51   a  and used as another external lead electrode, a fourth pattern part  51   d  and a fifth pattern part  51   e  integrated with both sides of the first pattern part  51   a.  At this time, the first pattern part  51   a  through the third pattern part  51   c  are plated with a metal having high conductivity and adhesion, and the fourth and fifth pattern parts  51   d  and  51   e  are plated with another metal that is glossy and has high reflectivity.  
         [0042]    [0042]FIG. 5 a  shows a plated lead frame  51  having the above pattern parts.  
         [0043]    The fourth and fifth pattern parts  51   d  and  51   e  of the lead frame  51  are folded upward to be perpendicular to the first pattern part  51   a,  and function to concentrate rays of light emitted from an LED chip  53  in a predetermined direction. As such, in order to maximally obtain the reflection effects of light in a desired direction, the fourth and fifth pattern parts  51   d  and  51   e  are disposed to face each other at both sides of the first pattern part  51   a,  and have a size suitable for reflecting light emitted from the LED chip  53  to be mounted onto the first pattern part  51   a.    
         [0044]    In case of the pre-mold type, the fourth pattern part  51   d  and the fifth pattern part  51   e  of the plated lead frame  51  are folded upward to be perpendicular to the first pattern part  51   a  of the lead frame  51 , as shown in FIG. 5 b.  That is, reflective surfaces are formed before performing a molding process.  
         [0045]    Thereafter, a package structure  52  is formed to surround all the other portions of the reflective surfaces-formed lead frame  51  with the exception of only electrode portions of the second and third pattern parts  51   b  and  51   c  to be used as the external lead electrodes, for example, the first pattern part  51   a,  the wire-bonded portions of the second and third pattern parts  51   b  and  51   c,  and the fourth and fifth pattern parts  51   d  and  51   e  perpendicularly folded upward relative to the first pattern part  51   a,  by means of a pre-molding process. As such, the package structure  52  formed by the pre-molding process is in the form of hexahedron having an inner cavity to easily mount a desirable target therein, in which a surface facing to the first pattern part  51   a  is opened. FIG. 5 c  shows the pre-molded package  52 .  
         [0046]    As shown in FIG. 5 d,  an LED chip  53  is mounted onto the plated surface of the first pattern part  51   a  in the package  52 , and the LED chip  53  is connected to each of the second and third pattern parts  51   b  and  51   c  by means of a wire  54  in the package  52 .  
         [0047]    Then, the package  52  is filled with transparent epoxy  55  (FIG. 5 e ) as in a conventional pre-molding process. The externally exposed electrode portions of the second and third pattern parts  51   b  and  51   c  of the lead frame  51  are vertically folded to make mountable electrode structures, thereby manufacturing a pre-mold type LED device (FIG. 5 f ).  
         [0048]    To the conventional manufacturing process of the pre-mold type LED, the process of forming reflective surfaces after the lead frame is changed in only a shape thereof is further added according to the secondary embodiment. Thereby, it is possible to simply form the reflective surfaces plated with the metal having high reflectivity within the pre-molded package  52 . Eventually, the luminance of the LED device can be increased.  
         [0049]    Upon manufacturing the LED devices according to the primary and secondary embodiments of the present invention, the angles between the first pattern parts  41   a  and  51   a,  and the fourth pattern parts  41   d  and  51   d  and the fifth pattern parts  41   e  and  51   e  are controlled, thus obtaining the desired reflection angles.  
         [0050]    Alternatively, the shape of the above lead frame is changed, and thus the reflective surfaces may be formed to all four surfaces surrounding the LED chip.  
         [0051]    [0051]FIG. 6 a  shows a lead frame having a shape different from the lead frame of FIG. 5 a.  In such a case, the lead frame  61  comprises a first pattern part  61   a  for use in mounting an LED chip thereon, a second pattern part  61   b  electrically connected to the first pattern part  61   a  to be used as an external lead electrode, a third pattern part  61   c  spaced from the first pattern part  61   a  to be electrically insulated from the first pattern part  61   a  and used as another external lead electrode, a fourth pattern part  61   d  and a fifth pattern part  61   e  integrated with both sides of the first pattern part  51   a.  In addition, the lead frame  61  further includes a sixth pattern part  61   f  positioned between the first pattern part  61   a  and the second pattern part  61   b  to electrically connect the two pattern parts  61   a  and  61   b,  and a seventh pattern part  61   g  positioned between the first pattern part  61   a  and the third pattern part  61   c.    
         [0052]    The seventh pattern part  61   g  is electrically connected to either the first pattern part  61   a  or the third pattern part  61   c,  or to neither the first pattern part  61   a  nor the third pattern part  61   c.    
         [0053]    The sixth and seventh pattern parts  61   f  and  61   g  are plated with a metal having high reflectivity as in the fourth and fifth pattern parts  61   d  and  61   e,  and the second and third pattern parts  61   b  and  61   c  used for LED chip mounting and wire bonding are plated with a metal having good soldering characteristics.  
         [0054]    [0054]FIG. 6 b  shows reflective surfaces formed by the lead frame shown in FIG. 6 a.    
         [0055]    That is, the fourth pattern part  61   d  through the seventh pattern part  61   g  are perpendicularly folded upward relative to the first pattern part  61   a,  thus forming two pairs of opposite surfaces. In addition, the second and third pattern parts  61   b  and  61   c  are folded to be perpendicular to the sixth and seventh pattern parts  61   f  and  61   g,  and positioned parallel to the first pattern part  61   a.    
         [0056]    As such, on the plated surface of the first pattern part  61   a  surrounded by the fourth pattern part  61   d  through the seventh pattern part  61   g,  the LED chip is mountable. Thereby, light emitted from the LED chip is reflected on four reflective surfaces formed by the fourth pattern part  61   d  through the seventh pattern part  61   g,  and then radiated in a predetermined direction.  
         [0057]    The more the reflective surfaces, the higher the reflection effects.  
         [0058]    The LED device is manufactured by use of the lead frame having the shape of FIG. 6 a,  according to the same manufacturing procedures of the primary and secondary embodiments of the present invention.  
         [0059]    As described above, the present invention provides a method of manufacturing the LED device having reflective surfaces made of a metal material by use of the lead frame, in which the metal material can be freely selected from among metals having high reflectivity. In particular, portions of the lead frame functioning as a “heat sink” are used to form reflective surfaces, which increases the release of heat, thereby preventing the deterioration of the luminance characteristics. Further, in the lead frame, angles between the pattern parts are adjusted, whereby reflection angles are controllable, thus easily controlling the angles of the light to be emitted. Furthermore, uniform reflective films can be formed on the reflective surfaces.  
         [0060]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.