Abstract:
A light emitting diode (LED) packaging structure includes a package body, a lead frame and a reflective wall. The package body includes a chip accommodating space for an LED chip, and a portion of the lead frame is exposed to the chip accommodating space. The reflective wall is connected with the lead frame and extendedly bends from the lead frame to cover a sidewall of the accommodating space so that rays of the LED chip can reflect from the reflective wall mostly.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Taiwan Application Serial Number 95102082, filed Jan. 19, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The invention relates to a packaging structure and the manufacturing method thereof. In particular, the invention relates to an LED packaging structure and the manufacturing method thereof.  
         [0004]     2. Related Art  
         [0005]     Light emitting diodes (LED) have the features of long lifetime, low power consumption, safety, and fast reactions. With technical progress, the brightness of the LED becomes higher, enlarging its applications. The conventional LED is fabricated using a metal lead frame along with plastic injection molding.  FIG. 1  shows a cross-sectional view of the conventional LED structure with a lead frame.  
         [0006]     Two lead frames  104 ,  106  are connected to the positive and negative electrodes of the LED chip  102 , respectively. In the prior art, the injection molding method is employed to wrap the packaging materials and to fix the lead frames, forming a body  108 . The body  108  is used as an auxiliary object for the LED chip  102  in the subsequent packaging. A concave region is formed in the body  108  for accommodating the LED chip  102 . The positive pole of the LED chip  102  is directly connected to a first lead frame  104  and via a wire  110  to a second lead frame  106 . A packaging glue  112  is a transparent material that fills the concave region during the packaging step, covering the LED chip  102 .  
         [0007]     In this conventional structure, the chip accommodating space is defined by the packaging body formed by injection. Only a light opening is left for the light from the chip to be emitted. The commonly used packaging body is made of an opaque and thermal resistant material, such as polyphthalamide (PPA). When the chip emits light, some indirectly emitted light hits the inside of the accommodating space. The incident light is absorbed, reflected, and scattered by the sidewall. Only very little indirectly emitted light leaves the light opening. Most of the light is wasted by the packaging material absorption during the multiple reflections and scatterings.  
         [0008]     Therefore, the output efficiency of the LED device is reduced by the optical absorption, resulting in considerable energy waste.  
       SUMMARY OF THE INVENTION  
       [0009]     One objective of the invention is to provide an LED packaging structure and the manufacturing method thereof for increasing the light output efficiency and reducing energy loss.  
         [0010]     Another objective of the invention is to provide an LED packaging structure and the manufacturing method thereof for obtaining a desired light output angle.  
         [0011]     A further objective of the invention is to provide an LED packaging structure and the manufacturing method thereof for increasing the heat dissipation of the light-emitting device.  
         [0012]     In accord with the above objectives, the disclosed LED packaging structure includes a packaging body, a lead frame and a reflective wall. The package body includes a chip accommodating space for an LED chip, and a portion of the lead frame is exposed to the chip accommodating space. The reflective wall is connected with the lead frame and extendedly bends from the lead frame to cover a sidewall of the accommodating space so that rays of the LED chip can reflect from the reflective wall mostly.  
         [0013]     The manufacturing method of the LED packaging structure includes the steps of: forming a first lead frame and a reflective wall connected to the first lead frame from a plate material; and using the packaging body to cover a portion of the first lead frame, a portion of a second lead frame, and the reflective wall by injection molding.  
         [0014]     According to a preferred embodiment of the invention, the manufacturing method of the LED packaging structure further includes the steps of: using a plate material to form a first lead frame and a reflective wall connected to the first lead frame, coating a highly reflective material on the reflective wall; using a packaging body to cover a portion of the first lead frame, a portion of a second lead frame, and the reflective wall using injection molding; employing a chip fixing step to fix the chip on any of the lead frames, using a bonding step to connect the LED chip with the other lead frame without an LED chip; and employing a gluing step to fill the chip accommodating space of the packaging body.  
         [0015]     The step of forming the first lead frame and the reflective wall include the steps of: reserving on the plate material the reflective wall connected to the first lead frame; and bending an interface between the reflective wall and the lead frame. Alternatively, one may form a cup-shaped recession in one portion of the plate material by stamping. The two adjacent surfaces of the recession are used as the lead frame and the reflective wall, respectively.  
         [0016]     In summary, the disclosed LED packaging structure provides a design that reduces optical energy loss and has high optical output efficiency. It further has the advantages of helping heat dissipation and controlling the light output angle. The manufacturing method does not require any additional special equipment. The reflective wall is formed concurrently in the same step as forming the lead frame. No additional material is needed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     These and other features, aspects and advantages of the invention will become apparent by reference to the following description and accompanying drawings which are given by way of illustration only, and thus are not limitative of the invention, and wherein:  
         [0018]      FIG. 1  shows a cross-sectional view of the conventional LED structure with a lead frame;  
         [0019]      FIG. 2A  is a three-dimensional view of the LED packaging structure in a preferred embodiment of the invention;  
         [0020]      FIG. 2B  is a schematic view of the initial lead frame plate material in the preferred embodiment;  
         [0021]      FIG. 3  is a flowchart illustrating the manufacturing method of the disclosed LED packaging structure; and  
         [0022]      FIG. 4  is a schematic view of the initial lead frame plate material in another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.  
         [0024]     The disclosed packaging structure uses the body of the lead frame to directly form external lead pins and the reflective wall inside the chip accommodating space. The manufacturing process is simple and convenient. No additional special equipment is required. The packaging structure thus made has the advantages of reducing energy loss and increasing light output efficiency.  
         [0025]     With reference to  FIG. 2A , the LED packaging structure includes a packaging body  202  with a chip accommodating space  204  defined by a recession structure inside the packaging body  202  for accommodating an LED chip; a lead frame  212  whose one portion is embedded in the packaging body  202  and exposed in the chip accommodating space  204 , and a reflective wall  214  connected to the lead frame  210  and extendedly bending from the lead frame  210  to cover a sidewall  216  of the accommodating space  204 .  
         [0026]     In a preferred embodiment, the LED packaging structure include the packaging body  202 , a first lead frame  210  (depicted in  FIG. 2B ) and a second lead frame  212  (depicted in  FIG. 2B ). The lead frames are embedded in the packaging body  202  by one portion, the embedded portions  210   a  and  212   a . The rest portions are exposed, the exposed portions  210   b  and  212   b . The embedded portions refer to the portions that are covered by the material of the packaging body  202  and the portions exposed in the chip accommodating space  204 .  
         [0027]     The material of the packaging body can be ordinary PPA, epitaxy, glass fiber, titanium oxide, calcium oxide, or their combinations.  
         [0028]     The LED chip  230  is directly disposed on the embedded portion  210   a  of the first lead frame. It is connected to the embedded portion  212   a  of the second lead frame via a wire  218  by bonding. The combination of the first lead frame  210  and the second lead frame  212  represents the combination of the positive and negative lead pins in the device for guiding an external current to illuminate the LED device.  
         [0029]     The drawing shows a side-view LED packaging structure. The light output direction  208  of the LED chip faces the light opening  206  of the packaging body  202           . The sidewall  216  of the packaging body  202  expands gradually toward the light opening  206 . This inclination design ensures that the light will emit via the light opening  206  after multiple internal reflections. It has the function of controlling the light output angle.  
         [0030]     When the LED chip  230  emits light via the light opening  206 , a portion of indirectly emitted light travels toward the sidewall  216  of the packaging body  202 . Since the sidewall  216  is already covered with a reflective wall  214 , most of the optical energy is stored. Even after many reflections, the energy loss is still far less than the energy waste in the conventional packaging body  202 .  
         [0031]     Since the reflective wall is connected to the lead frame, it helps dissipating the heat from the LED chip. Due to the metal with a high reflectivity, the light incident direction can be more easily and accurately predicted as the device emits light. By simulation or calculation, one can design an LED device with high reappearance, high reliability, and a specific light output angle.  
         [0032]      FIG. 2B  is a schematic view of the initial lead frame plate material. The manufacturing method of the disclosed reflective wall is the follows. A region by the first lead frame  210  of the initial lead frame plate material is reserved  290  for the reflective wall  214 . Afterwards, the plate material in the reserved region is bended according to the bending line in the drawing to form a reflective surface. The two lead frames  210  and  212  in this embodiment are made using the same plate material  290 . Two opposite reflective walls  214  are reserved. The lead frame is usually made of a metal material, such as Au, Ag, Cu, Fe, Al, or their alloy.  
         [0033]     Although the above-mentioned reflective walls are made of the same material as the lead frames, the region of the reflective walls is preferably coated with a material with a high reflectivity. For example, silver can be coated on the lead frame made of an iron or copper alloy to achieve a higher reflectivity. This can reduce a lot of energy loss.  
         [0034]     As shown in  FIG. 4 , the lead frame material is bended to form the reflective walls by stamping in another embodiment of the invention, stamping a cup-shaped recession in the lead frame plate material  490 . The first lead frame  410  is disposed with an LED chip  430  and connected to the reflective wall  414 . The interface is indicated by a bending line. The interface between the reflective wall  414  and the first lead frame  410  is also a bending structure. A tail portion  416  is connected to the reflective wall  414 . The tail portion  416  is formed by injection molding, with one portion embedded inside the packaging body and one portion exposed as the external lead pin, as the exposed portion  210   b  in  FIG. 2A . Likewise, the second lead frame  412  in this embodiment is concurrently made using the same plate material too.  
         [0035]     There is one advantage for the lead frame structure obtained using the stamping method. The reflective walls formed by stamping almost surround the chip. Therefore, the reflective region provided by the inside of the packaging body is wider. The effects must be greatly enhanced. In the above two embodiments, the connection portion of the two lead frames in the plate material can be cut off after the packaging body is formed by injection molding and the two lead frames are covered, thereby forming independent electrode lead pins.  
         [0036]     With reference to  FIG. 3 , the disclosed manufacturing method of the LED packaging structure according to a preferred embodiment of the invention includes the following steps. A lead frame and a reflective wall connected to the lead frame are formed using the same plate material (step  302 ). A portion of a packaging body covers a portion of the lead frame and the reflective wall by injection molding (step  304 ). A chip fixing step is employed to fix the chip on the lead frame (step  306 ). A bonding step is employed to connect the chip with another lead frame (step  308 ). A gluing step is employed to fill the chip accommodating space (step  310 ). Before the injection molding, the reflective wall can be coated with a highly reflective material such as silver.  
         [0037]     The step of forming the lead frame and the reflective wall is detailed as follows. The plate material is reserved with a reflective wall connected to any of the lead frames. The interface between the reflective wall and the lead frame is bended to form the reflective wall, as illustrated in  FIG. 2B .  
         [0038]     One may first form a cup-shaped recession in a portion of the plate material by stamping. Two adjacent surfaces of the cup-shaped recession are the first lead frame and the reflective wall, as shown in  FIG. 4 . It should be noted that the recession structure thus formed does not limit the correspondence relation between any surface and any device. For example, the top-view and side-view devices can have different definitions.  
         [0039]     In accord with the preferred embodiments, the invention has at least the following advantages. The reflective wall is defined in the same step as the lead frame, so that the final packaging structure reduces its energy loss and increases the light output efficiency with the help of the reflective wall. The reflective wall also helps dissipating heat from the device. Besides, the high reflectivity of the reflective wall renders the light output control of the LED device easier, unlike the conventional packaging body that has uncertainty in light output angle.  
         [0040]     The method of concurrently forming the reflective wall and the lead frame does not require additional special equipment. Therefore, its production is simple, and the material cost is low.  
         [0041]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.