Abstract:
A lead frame structure of a light emitting diode includes a ceramic bed, a metal layer and a plastic seat. The metal layer has a first metal circuit area, a second metal circuit area, a gap dividing the first metal circuit area and the second metal circuit area, and a metal ring surrounding the first metal circuit area, the second metal circuit area and the gap. The plastic seat has a hollow function area. The first metal circuit area, the second metal circuit area and a part of the metal ring expose the function area to make the metal (circuit) layer of the function area has no gap to avoid excess glue. This can efficiently accomplish to increase intensity, quality and reliability of the packaged products.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to a lead frame structure, particularly to a lead frame for a light emitting diode using an annular gapless metal ring to avoid excess glue. 
     2. Related Art 
     Light emitting diodes (LEDs) possess advantages of long life, low power consumption, no warm-up time and quick response time. Thus applications of LEDs become more and more prevalent. In a manufacturing process of LEDs, a packaging process must be implemented after a die bonding process to protect an LED chip. 
     A conventional packaging process, as shown in  FIG. 1 , forms a metal circuit layer  20  on a ceramic bed  10 , in which the metal circuit layer  20  uses at least one gap  30  to divide two electrodes  22 ,  24 . A resin  50  is applied at openings of gaps  30  between electrodes  22 ,  24  to prevent excess glue. However, after sequent processes and resin has formed, excess glue still may occur in a function area of an LED. Because of the processing property of the resin  50 , there may still be tiny slits in the resin  50  at the gap  30 . Thus it cannot solve the problem of excess glue. As a result, the light emitted from an LED cannot be concentrated, the intensity is reduced and the process reliability is not good enough. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a lead frame structure for a light emitting diode, whose metal (circuit) layer of the function area does not contain any slit to prevent excess glue. This can efficiently increase intensity, quality and reliability of the packaged products. 
     To accomplish the above object, the lead frame structure of the invention includes a ceramic bed, a metal layer and a plastic seat. The ceramic bed has a first surface and a second surface corresponding thereto. The metal layer has a first metal circuit area, a second metal circuit area, a gap dividing the first metal circuit area and the second metal circuit area, and a metal ring surrounding the first metal circuit area, the second metal circuit area and the gap. The first metal circuit area, the second metal circuit area and the metal ring are formed on the first surface of the ceramic bed. The plastic seat is formed on the first surface and partially covers the metal ring. The plastic seat has a hollow function area. The first metal circuit area, the second metal circuit area and a part of the metal ring are exposed in the function area. 
     The invention also has other advantages. The metal layer of the invention is directly electroplated to form the first metal circuit area, the second metal circuit area and slitless or indentless metal ring. The metal layer of the invention uses a single process of electroplating, sputtering, vapor deposition or electroless plating to accomplish an effect of distinguishing positive and negative electrodes. This can efficiently simplify the manufacturing process and reduce the manufacturing cost. The metal ring can further prevent the gap of the function area from generating excess glue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing excess glue formed between electrodes in a conventional LED lead frame; 
         FIG. 2  is a plan view of the metal layer of the first embodiment of the invention; 
         FIG. 3  is a schematic view of the first embodiment of the invention; 
         FIG. 4  is a cross-sectional view of the metal layer of the first embodiment of the invention; 
         FIG. 5  is a plan view of the metal layer of the second embodiment of the invention; 
         FIG. 6  is a schematic view of the metal layer of the second embodiment of the invention; and 
         FIG. 7  is a cross-sectional view of the metal layer of the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIGS. 2-4 , which show the first embodiment of the invention. As shown, the lead frame structure for an LED of the invention includes a ceramic bed  100 , a metal layer  110  and a plastic seat  170 . The ceramic bed  100  has a first surface  102  and a second surface  104  corresponding to the first surface  102 . The metal layer  110  includes a first metal circuit area  120 , a second metal circuit area  130 , a gap  140  which divides the first metal circuit area  120  and the second metal circuit area  130 , and a metal ring  150  which gaplessly surrounds the first metal circuit area  120 , the second metal circuit area  130  and the gap  140 . The first metal circuit area  120 , the second metal circuit area  130  and the metal ring  150  are separately formed on the first surface  102  of the ceramic bed  100 . 
     The metal layer  110  is directly formed on the first surface  102  of the ceramic bed  100  by an electroplating, sputtering, vapor deposition or electroless plating process. The preferable material for the metal layer  10  is gold, copper, silver, aluminum or their alloy with great conductivity. As shown in  FIG. 4 , the ceramic bed  100  is further provided with two through holes  106  which penetrate through the first and second surfaces  102 ,  104  and are located apart. When the metal layer  110  is formed on the ceramic bed  100 , the first and second metal circuit areas  120 ,  130  will separately fill corresponding through holes  106  and form on the second surface  104  to provide the first and second surfaces  102 ,  104  of the ceramic bed  100  electric conduction. 
     When the first and second metal circuit areas  120 ,  130  are formed on the first and second surfaces  102 ,  104  of the ceramic bed  100 , the gap  140  will divide the first and second metal circuit areas  120 ,  130  to distinguish positive and negative electrodes. When the first and second metal circuit areas  120 ,  130  separately penetrate corresponding through holes  106  to form on the second surface  104 , the first and second metal circuit areas  120 ,  130  still stay separate without connection. 
     In this embodiment, because the metal layer  110  is formed by an electroplating, sputtering, vapor deposition or electroless plating process, the first and second metal circuit areas  120 ,  130  and the metal ring  150  separately protrude from the first surface  102 . The first and second metal circuit areas  120 ,  130  and the metal ring  150  are the same in height. Their heights are flush with each other, so the structure and manufacturing process of the lead frame of the invention can be simplified, and the manufacturing cost can be reduced. 
     In this embodiment, the metal ring  150  further includes an inner metal ring  152  and an annular interval  154  dividing the inner metal ring  152 , the gap  140 , and the first and second metal circuit areas  120 ,  130 . The inner ring  152  can obstruct excess glue during manufacturing the plastic seat  170 , this will be described below. This embodiment further includes an outer metal ring  160  and ribs  156  connecting the outer metal ring  160  and the inner metal ring  152 . The ribs  156  can enhance strength of the outer metal ring  160  and connectivity between the outer metal ring  160  and the plastic seat  170  to prevent the outer metal ring  160  and the inner metal ring  152  from separating during sequent etching process. 
     As shown in  FIGS. 2 and 3 , the outer metal ring  160  is approximately identical to the inner metal ring  152  in width, about 0.5-1.0 mm. The outer and inner metal rings  160 ,  152  are integratedly formed with the first and second metal circuit areas  120 ,  130 . Additionally, a plurality of spaces  158  are formed in the outer and inner metal rings  160 ,  152 , each of the ribs  156  separately passes one of the spaces  158  to connect the outer and inner metal rings  160 ,  152 . 
     After the first and second metal circuit areas  120 ,  130  have been formed on the first and second surfaces  102 ,  104  of the ceramic bed  100  by an electroplating, sputtering, vapor deposition or electroless plating process, a die  180  bonding process and lead  182  bonding process will be performed. After that, a mold (not shown) is completely attached on and corresponds to the inner metal ring  152  in the function area  172  to make the plastic seat  170  by an injection molding process. 
     Because the metal ring  150  is gapless, when the metal ring  150  is being pressed on the function area  172 , the protrudent inner metal ring  152  can prevent the liquid plastic seat  170  from infiltrating the gap  140  of the metal (circuit) layer  110 . This can effectively overcome the problem of excess glue. As a result, excess glue can be avoided in the metal (circuit) layer  110  of the function area  172  to improve intensity (luminous efficiency), quality and reliability of the packaged products. 
     The embodiment shown in  FIGS. 3 and 4  further includes a die  180  disposed in the first metal circuit area  120  and two leads  182  electrically connecting the die  180  and the second metal circuit area  130 . In this embodiment, the first metal circuit  120  occupies a larger area to be mounted by the die  180 , while the second metal circuit area  130  occupies a smaller area. The two leads  182  connect between the die  180 /first metal circuit area  120  and the second metal circuit area  130  for electric conduction. As a result, the die  180  can be lit up by the power from the first and second metal circuit areas  120 ,  130 . However, in other embodiments, the area and quantity of the first and second metal circuit areas  120  can be varied according to demand and design. 
     The plastic seat is formed on the first surface  102  and partially covers the metal ring  150  by an injection molding process. The plastic seat  170  has a hollow function area  172  with silicone or other available plastics to package it. The first metal circuit area  120 , the second metal circuit area  130  and a part of the metal ring  150  are exposed in the function area  172 . 
     Preferably, the plastic seat  170  is made of a polymer material such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), polycarbonate (PC), ortho-phenyl phenol (OPP), oriented polystyrene (OPS), linear low-density polyethy (LLDPE), polyacetal (POM), polymerized siloxanes or polysiloxanes (also known as silicone). Any other available materials are optional. 
     Please refer to  FIGS. 5-7 , which show the second embodiment. As shown, this embodiment differs from the above embodiment in that the metal ring  150  is a periphery of the first metal circuit area  120 . In other words, the metal ring  150  does not have an inner metal ring  152  and annular interval  154 . The gap  140  dividing the first and second metal circuit area  120 ,  130  is preferably formed as a closed annularity. The rest are the same as the above embodiment. 
     The outer metal ring  160  is directly connected to the metal ring  150  by the ribs  156  so as to reinforce structural strength of the outer metal ring  160  and connecting strength between the outer metal ring  160  and the plastic seat  170 . This can prevent the outer metal ring  160  and the metal ring  150  from separating. Additionally, a plurality of spaces  158  are formed in the outer metal ting  160  and the metal ring  150 , and the ribs pass the spaces  158  to connect the outer metal ring  160  and the metal ring  150 . 
     In the second embodiment, when the plastic seat  170  is being injection molded, it will be attached on the periphery (i.e., the metal ring  150 ) of the first metal circuit area  120  in the function area  172  by a mold. The protrudent and gapless metal ring  150  can prevent the liquid plastic seat  170  from infiltrating the gap  140  of the metal (circuit) layer  110 . This can effectively overcome the problem of excess glue. As a result, excess glue can be avoided in the metal (circuit) layer  110  of the function area  172  to improve intensity (luminous efficiency), quality and reliability of the packaged products. 
     It is noted that the metal layer  110  is directly electroplated on the first and second metal circuit areas  120 ,  130  and the metal ring  150 . The metal layer  110  of the invention uses a single process of electroplating, sputtering, vapor deposition or electroless plating to accomplish an effect of distinguishing positive and negative electrodes. This can efficiently simplify the manufacturing process and reduce the manufacturing cost. The metal ring  150  can further prevent the gap  140  of the function area  172  from generating excess glue. 
     It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.