Abstract:
A packaging structure and a related fabrication method for high-power LED chip are provided herein, which mainly contains a base made of a metallic material and an electrically insulating material integrated into a single object. The metallic material forms a heat sinking seat in the middle of the base, which is exposed from the top surface of the base, and from the bottom surface or a side surface of the base. The metallic material also forms a plurality of electrodes surrounding the heat sinking seat, which are exposed from the top surface of the base, and from the bottom surface or a side surface of the base, respectively. The electrically insulating material is interposed between the electrodes and the heat sinking seat so that they are adhere together, and so that the heat sinking seat and any one of the electrodes, and any two electrodes are electrically insulated. The packaging structure achieves superior heat dissipation efficiency by separating the electricity and heat dissipation channels and, in another way, is applicable in mass production for a significantly reduced production cost.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to light emitting diodes, and more particularly to a packaging structure for a high-power light emitting diode chip and a related fabrication method thereof.  
         [0003]     2. The Prior Arts  
         [0004]     Spirited research activities have been focused on high-power light emitting diodes (LEDs) in the relevant industries in recent years. One of the most important considerations for the package of a high-power LED chip is about the appropriate handling of the high temperature and the heat produced by the high-power LED chip, so that the functionality, performance, and operational life of the LED chip is not compromised.  
         [0005]      FIG. 1   a  is a schematic sectional view showing a conventional packaging structure of a LED chip. As illustrated, the LED chip (or, some people refer to it as a LED die)  16  is positioned on top of a substrate  19  made of Bismaleimide Triazine (BT) resin. The electrodes (not shown) of the LED chip  16  are connected, by bonding wires (or, some people refer to them as gold wires)  13 , to the copper foil  15  previously configured on the substrate  19  for establishing electrical connection to external circuitry. The LED chip  16  is surrounded by a reflection mirror  14 . A resin  17  is filled to seal and protect the LED chip  16  and the bonding wires  13  inside. This conventional packaging structure is applicable in mass production and, therefore, contributes to a lower production cost. However, in this conventional structure, the heat produced by the LED chip  16  could only be dissipated through the thin copper foil  15  as resin is not an acceptable thermal conductor. In other words, the copper foil  15  functions as a conduction channel for both electricity and heat for the LED chip  16 , and, if the LED chip  16  is a high-power one, such an arrangement is not appropriate for handling the high-volume heat produced by the high-power LED chip  16 .  
         [0006]     U.S. Pat. No. 6,274,924 discloses a packaging structure which offers separate conduction channels for electricity and heat. To facilitate the explanation, the reference diagram of U.S. Pat. No. 6,274,924 is included here as the accompanied drawing  FIG. 1   b . As shown in  FIG. 1   b , the disclosed packaging structure molds a metallic lead frame  12  in an electrically insulating plastic body that can withstand high temperature. The LED chip  16  is positioned on top of a thermally conductive but electrically insulating submount  18 . The LED chip  16  and the submount  18  are then positioned on top of a metallic heat sinking element  10  which is usually made of copper. Also on top of the heat sinking element  10 , there could be an optional reflection mirror  14  under the LED chip  16  and the submount  18 . The heat sinking element  10 , along with the LED chip  16  and the submount  18 , is then positioned inside a preserved space of the lead frame  12 &#39;s plastic body. The electrodes (not shown) of the LED chip  16  are connected to the lead frame  12  also by bonding wires (not shown). At last, the LED chip  16  and the bonding wires is covered and protected by a previously prepared transparent protection lens  20  filled with resin (not shown).  
         [0007]     The packaging structure provided by the U.S. Pat. No. 6,274,924 offers satisfactory heat dissipation by separating the conduction channels for electricity and heat. However, the production process as described above is rather complex and a higher production cost is therefore inevitable. In addition, the lead frame  12  and the protection lens  20  have to be prepared in advance by molding, leading to a very inflexible production process, let alone the cost involved for the molds. For example, if the packaging structure depicted in  FIG. 1   b  is to be used to package two or more LED chips  16 , the lead frame  12  and the protection lens  20  have to be re-designed and manufactured.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, the major objective of the present invention is to provide a packaging structure and a related fabrication method for packaging a high-power LED chip which, in one way, achieve superior heat dissipation efficiency and, in another way, are applicable in mass production for a significantly reduced production cost.  
         [0009]     The packaging structure provided by the present invention mainly contains a base, a reflection plate, the LED chip being packaged, bonding wires for connecting the electrodes of the LED chip, and a transparent filler or lens for sealing and protecting the LED chip and the bonding wires. The base, having a flat form factor, is made of a metallic material and an electrically insulating material integrated into a single object. The metallic material forms a heat sinking seat in the middle of the base having appropriate distances to the edges of the base. The heat sinking seat is exposed from the top surface of the base, and from the bottom surface or a side surface of the base. The metallic material also forms a plurality of electrodes surrounding the heat sinking seat. The electrodes are exposed from the top surface of the base, and from the bottom surface or a side surface of the base. The electrically insulating material is interposed between the electrodes and the heat sinking seat so that they are adhere together, and so that the heat sinking seat and any one of the electrodes, and any two electrodes are electrically insulated.  
         [0010]     The LED chip being packaged is adhered to the exposed top surface of the heat sinking seat. The positive and negative electrodes of the LED chip are connected separately to the exposed top surfaces of the base&#39;s electrodes respectively. The reflection plate is fixedly attached to the base via an appropriate means so that a vertical through hole of the reflection plate exposes the LED chip on top of the heat sinking seat of the base. The light emitted from the LED chip, as a result, is able to radiate outward. The reflection plate is made of a metallic material having high reflectivity, or of a non-metallic material in which the wall of the through hole is coated with a film or a layer of high reflectivity material. The filler or the protection lens is made of a transparent material such as resin, and is placed inside the through hole so as to seal and protect the LED chip and the bonding wires.  
         [0011]     The base of the packaging structure has a simplified structure and, therefore, is very suitable for mass production. The fabrication method provided by the present invention use a single metallic plate to produce the bases for a large number of units of the packaging structure simultaneously. The heat sinking seats and the electrodes of the bases are formed by etching the metallic plate in a single operation or by etching the two major surfaces of the metallic plate in separate operations. Then, the insulating material is filled between the heat sinking seats and the electrodes. Subsequently, the reflection plate is adhered to the base; the LED chip is fixed to the top of the heat sinking seat; bonding wires are connected between the electrodes of the LED chip and the exposed top surfaces of the base&#39;s electrodes; the filler is stuffed inside the through hole of the reflection plate; and, at last, the units of the packing structure are separated by cutting.  
         [0012]     The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1   a  is a schematic sectional view showing a conventional packaging structure of a LED chip.  
         [0014]      FIG. 1   b  is the reference diagram of U.S. Pat. No. 6,274,924.  
         [0015]      FIG. 2   a  is a schematic sectional view showing the packaging structure according to a first embodiment of the present invention.  
         [0016]      FIG. 2   b  is a blown-up view showing the packaging structure of  FIG. 2   a.    
         [0017]      FIG. 2   c  is a schematic sectional view showing the packaging structure according to a second embodiment of the present invention.  
         [0018]      FIG. 2   d  is a schematic sectional view showing the packaging structure according to a third embodiment of the present invention.  
         [0019]      FIG. 2   e  is a schematic sectional view showing the packaging structure according to a fourth embodiment of the present invention.  
         [0020]      FIG. 2   f  is a schematic sectional view showing the packaging structure according to a fifth embodiment of the present invention.  
         [0021]      FIG. 3   a  is a perspective view showing the base and the packaging structure for two LED chips according to an embodiment of the present invention.  
         [0022]      FIG. 3   b  is a perspective view showing the base and the packaging structure for three LED chips according to an embodiment of the present invention.  
         [0023]      FIGS. 4   a - 4   g  show the results of the processing steps of a fabrication method according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.  
         [0025]      FIGS. 2   a  and  2   b  are schematic sectional view and blown-up view of the packaging structure according to a first embodiment of the present invention. As illustrated, the packaging structure provided by the present embodiment contains at least a base  100 , a reflection plate  110 , the LED chip being packaged  150 , a plurality of the bonding wires  120 , and a transparent filler  130 . The base  100 , having a flat form factor, is composed of a heat sinking seat  102 , a plurality of electrodes  104 , and an insulator  106 , integrated together into a single solid object. The heat sinking seat  102  and the electrodes  104  are made of a metallic material having high electrical and thermal conductivities. The insulator  106 , on the other hand, is made of an insulating material such as resin or the like.  
         [0026]     The heat sinking seat  102  is positioned in the middle of the flat base  100  with appropriate distances to the edges of the base  100 . The heat sinking seat  102  is exposed both from the top surface of the base  100 , and from at least one of the bottom surface and a side surface of the base  100 . In the present embodiment, the heat sinking seat  102  has multiple exposures on the top surface of the base  100  so as to enhance the heat dissipation by increasing its contact area with air. Please note that the shape of the heat sinking seat  102  as shown in  FIGS. 2   a  and  2   b  is only exemplary; other appropriate shapes could also be adopted by the heat sinking seat  102 . The electrodes  104  are positioned at appropriate locations around the heat sinking seat  102 . Similarly, the electrodes  104  are exposed both from the top surface of the base  100 , and from at least one of the bottom surface and a side surface of the base  100 , respectively. Please also note that the shapes of the electrodes  104  as shown in FIGS.  2   a  and  2   b  are only exemplary. Generally, for the single-chip packaging of the present embodiment, there are two electrodes  104  for connecting to the positive and negative electrodes of the chip  150  respectively. In alternative embodiments which provide multiple-chip packaging, the number of the electrodes  104  is twice the number of the chips  150 . The insulator  106  makes up the rest of the base  100 . The insulator  106  therefore is located between the heat sinking seat  102  and the electrodes  104  so as to, for one thing, adhere the heat sinking seat  102  and the electrodes  104  together and, for another thing, form the insulation between the heat sinking seat  102  and any one of the electrodes  104 , and between any two electrodes  104 . The fabrication of the base  100  will be described in details later.  
         [0027]     The reflection plate  110  also has a flat form factor with a vertical through hole (not numbered) at an appropriate location in the middle. The reflection plate  110  is made of a metallic material having high reflectivity (e.g., aluminum), or it could be made of an insulating material such as resin but the wall of the through hole has a white coating, or is coated with a film made of highly reflective material such as silver. The reflection plate  110  is adhered to the base  100  with a layer of an appropriate adhesive  160 . When the reflection plate  110  is made of a metallic material, the adhesive  160  also provides the insulation between the reflection plate  110  and the base  110 &#39;s heat sinking seat  102  and electrodes  104 . The location and aperture of the through hole are properly configured so that, after the reflection plate  110  is joined with the base  100 , the top surface of the heat sinking seat  102  and at least some portion of the top surface of the electrodes  104  are exposed for the fixation of the LED chip  150  and the connection of the bonding wires  120  respectively. As such, when the LED chip  150  is fixed on the exposed top surface of the heat sinking seat  102 , the light emitted from the LED chip  150  is able to radiate out of the packaging structure via the through hole. The through hole in the present embodiment has a circular aperture and the diameter of the aperture is larger as it is closer to the top. Please note that the geometric properties of the through hole here is only exemplary.  
         [0028]     The LED chip  150  is fixedly adhered to the top surface of the heat sinking seat  102  as mentioned earlier. The positive and negative electrodes (not shown) of the LED chip  150  are connected to separate electrodes  104  of the base  100  respectively via the bonding wires  120 . As such, the heat produced by the LED chip is dissipated through the heat sinking seat  102  (i.e., the heat dissipation channel) while the bonding wires  120  and the electrodes  104  jointly provide access to the electricity (i.e., the electricity channel). With this separation of the electricity and heat dissipation channels, superior heat dissipation efficiency is thereby achieved. The through hole of the reflection plate  160  is filled with the filler  130  made of a transparent material such as resin so as to seal and protect the LED chip  150  and the bonding wires  120 . In the present embodiment, the filler  130  completely fills up the through hole of the reflection plate  110 . In a second embodiment as shown in  FIG. 2   c , a transparent protection lens  170  (such as a dome-shaped lens commonly used for LEDs) is used to cover the LED chip  150  and the bonding wires  120 .  
         [0029]      FIGS. 2   d - 2   f  are schematic sectional views showing the packaging structure according to a third, fourth, and fifth embodiments of the present invention respectively. For the third embodiment shown in  FIG. 2   d , a concaved reflection mirror  103  is formed on the top surface of the heat sinking seat  102  and beneath the LED chip  150 . The reflection mirror  103  could be made of a metal or a metallic oxide having high thermal conductivity such as silver, aluminum, or aluminum oxide. The reflection mirror  103  could also be a coating of highly reflective material, regardless of its thermal conductivity. The purpose of having this reflection mirror  103  is to enhance the brightness of the LED chip  150  after it is packaged. The fourth embodiment shown in  FIG. 2   e  is to demonstrate that the present invention could also be applied in producing white light from various colored LEDs and appropriate phosphors. In this embodiment, a blue-light LED chip  150  is buried inside a yellow phosphor  105  before they are sealed by the filler  130 . The yellow phosphor  105  would produce yellow light as it is excited by the blue light from the LED chip  150 , and the yellow light is mixed with the exciting blue light to produce two-wavelength white light. In another embodiment, an UV (ultra-violet) LED chip  150  is buried in red, green, and blue phosphors  105 , and the red, green, and blue lights from the excitation of the red, green, and blue phosphors  105  by the UV light from the LED chip  150  are mixed to produce three-wavelength white light. A fifth embodiment shown in  FIG. 2   f  is actually a combination of the third and fourth embodiments. A large number of research results about the reflection mirror  103  and the phosphors  105  have already been disclosed in the related arts, and their implementations are not limited to those exemplified in the afore-mentioned embodiments.  
         [0030]      FIGS. 3   a  and  3   b  demonstrate how the present invention is applied in the packaging of two and three LED chips respectively, by showing their bases and packaging structures. As should be obvious from the illustrations, the present invention could be easily adapted to package an even larger number of the LED chips. The only difference between these multiple-chip packaging structures lies only in the formation of an appropriate number of electrodes  104  at appropriate positions in the base  100 . The multiple-chip packaging structure is also very suitable for color-mixing various colored LEDs. Using the three-chip packaging structure shown in  FIG. 3   b  as an example, the three LED chips  150  could be a red-light one, a green-light one, and blue-light one respectively. Then, by packaging them together in the illustrated packaging structure, the three colored lights would mix with each other to form white light. As a brief summary, the present invention could be applied in the packaging of various colored LED chips, various numbers of LED chips, and in the production of various mono-colored and full-colored lights.  
         [0031]      FIGS. 4   a ˜ 4   g  show the results of the processing steps of a fabrication method according to an embodiment of the present invention. Initially, a large metallic plate  190  having high electrical and thermal conductivities is provided, as shown in  FIG. 4   a . The metallic plate  190  is used for the subsequent formation of the bases  100  of multiple packaging units  200  simultaneously. The bases  100  of the packaging units  200  are arranged in an array, adjacent to each other or to the boarder  180  of the metallic plate  190 . The bases  100  are formed mainly by appropriate means of etching and machinery to remove the part of the bases  100  for the subsequent filling of the insulator  106  and, after that, the heat sinking seats  102  and the electrodes  104  of the bases  100  are left behind, as shown in  FIG. 4   b . Then, the part of the bases  100  etched away is filled with the insulator  106  and the result is shown in  FIG. 4   c.    
         [0032]     Depending on the complexity of the shapes of the heat sinking seat  102  and the electrodes  104 , the foregoing etching and machinery process could be conducted to the two major surfaces of the metallic plate  190  simultaneously, producing the patterns of the heat sinking seats  102  and the electrodes  104  for all packaging units  200  in a single run. The filling of the insulator  106  is then performed subsequently. However, if the shapes of the heat sinking seat  102  and the electrodes  104  are rather complex, the etching and the filling of the insulator  106  could be conducted to a major surface of the metallic plate  190  in a first run, and then conducted to the other major surface in a second run. The formation of the bases  100  of all packaging units  200  is then completed.  
         [0033]     Next, as shown in  FIG. 4   d , a previously prepared plate member  210  composed of multiple reflection plates  110  is adhered to the processed metallic plate  190  of  FIG. 4   c  by an appropriate adhesive. Then, for each packaging unit  200 , the fixation and wire bonding of the LED chip  150  is conducted, whose result is shown in  FIG. 4   e . The transparent filler  130  is then injected into the through holes of the reflection plates  110  to seal the packaging units  200 , as shown in  FIG. 4   f . At last, as illustrated in  FIG. 4   g , the packaging units  200  are separated by cutting.  
         [0034]     Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.