Patent Publication Number: US-2009230421-A1

Title: Semiconductor package structure, lead frame and conductive assembly for the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 200810085425.1 filed in China, P.R.C. on Mar. 14, 2008 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a light emitting diode package structure, in particular, to a light emitting diode package structure, and a lead frame and a conductive assembly for the same. 
     2. Related Art 
     With the continuous progress in photoelectric technology, the light-emitting diode (LED) technique is becoming mature. Due to the advantages of long service life, power-saving, and small size, LEDs has gradually replaced the conventional incandescent lamp for illumination or warning purpose. 
     In recent years, high-performance LEDs have been developed to satisfy the users&#39; demands for higher efficiency, and Piranha type LED is the most outstanding one. Compared with the conventional LED, the Piranha type LED provides higher luminance and wider illumination angles. Further, the Piranha type LED has four electrical pins, which are contributive to thermal dissipation and steadily supporting the LED. 
       FIGS. 1A and 1B  are schematic views of a conductive assembly and a lead frame for a conventional Piranha type LED. 
     Referring to  FIG. 1A , the conductive assembly  10  of a conventional Piranha type LED includes a chip support  11  and a bonding support  12 . The chip support  11  has a carrier surface  13  for carrying a light-emitting chip  14  thereon. The light-emitting chip  14  is electrically connected to the bonding support  12  through a wire  15 , so as to form a chip bonding area with the carrier surface  13  as its center. Afterwards, a package body  16  made of epoxy resin, silica gel, and phosphor powder is used to encapsulate the chip bonding area to form a complete Piranha type LED. 
     Referring to  FIG. 1B , a common lead frame  20  with a pin spacing of 12.7 mm is taken as an example. Electrical pins  17  extending from two sides of each half-finished conductive assembly are respectively connected by two operating bars  21 , and thus the half-finished conductive assemblies are serially-connected. During the manufacturing of the conductive assemblies, the operating bars are clamped by conveyor machines to go through the stamping and electroplating processes, so as to achieve the purpose of automatic production. Finally, after the packaging of the conductive assembly, the operating bars are removed to form a single finished product of the Piranha type LED. 
     In the package structure of the conventional Piranha type LED, the chip bonding area is limited to the periphery of the carrier surface of the chip support, and the light-emitting chip relies only on a single bonding area formed by electrically connecting the wire and the bonding support. Thus, during the packaging process, the stress variation and thermal expansion and cold shrinkage of the package body focus on the juncture of the package body and the conductive assembly. Moreover, the package body made of a resin material has a thermal expansion coefficient different from that of the conductive assembly made of a metal material, so the wire may be easily broken under the effect of the stress (dragging force) inside the package structure, resulting in that the Piranha type LED cannot emit lights. 
     The price of metal materials is continuously rising currently, for example, the price of copper and iron used in the Piranha type LED is increased by about 110%-200%. The operation bars which are eventually discarded as waste materials and increased amount of electroplating silver used in the electroplating process of an over-sized lead frame will greatly increase the material cost of the Piranha type LED. Thus, the manufacturers have to raise the product price to balance the cost. Otherwise, the manufacturers have to lower the profit to stimulate the sales. 
     Therefore, it is a problem in urgent need of solutions to prevent the breaking of the wire under different stresses caused in the packaging process and effectively utilize the space of the lead frame, so as to further reduce the volume of the operating bars to be removed. Thus, the manufacturer may improve the quality of the Piranha type LED, and also reduce the manufacturing cost. 
     SUMMARY OF THE INVENTION 
     In view of the above problem, the present invention provides a light emitting diode package structure, and a lead frame and a conductive assembly for the same, so as to solve the problem that the product reliability is impaired due to the breaking of the wire under different stresses in the conventional Piranha type LED. 
     The light emitting diode package structure of the present invention includes a conductive assembly, a semiconductor chip, and a package body. The conductive assembly further includes a chip support and a bonding support. The chip support has a carrier surface and at least one first electrical pad extending from the carrier surface. The bonding support has at least one wiring portion surrounding the carrier surface and interdigitated with the carrier surface, and at least one second electrical pad extending from the wiring portion. The semiconductor chip is disposed on the carrier surface and electrically connected to the wiring portion through at least one wire. The package body encapsulates the semiconductor chip, the wire, the carrier surface, and the wiring portion to form the light emitting diode package structure. 
     In addition, the bonding support of the present invention also has an extending portion surrounding the carrier surface and interdigitated with the carrier surface, and is encapsulated by the package body, so as to provide the lead frame with several bonding areas to choose therefrom. 
     The advantage of the present invention lies in that, at least one wiring portion extends from the bonding support, so as to solve the problem that the wire may be easily broken due to the inner stress (dragging force) caused by different thermal expansion coefficients of the package body and the conductive assembly in the course of the packaging of the semiconductor, and thus the reliability of the light emitting diode package structure is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1A  is a perspective view of a conventional conductive assembly; 
         FIG. 1B  is a schematic plan view of a conventional lead frame; 
         FIG. 2  is a schematic plan view of a lead frame of the present invention; 
         FIG. 3A  is a perspective view of a conductive assembly of the present invention; 
         FIG. 3B  is a perspective view of a conductive assembly of the present invention; and 
         FIG. 4  is a perspective view of a light emitting diode package structure of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  is a schematic view of a lead frame for a light emitting diode package structure of the present invention. The lead frame  120  of the present invention includes a chip support  111 , a bonding support  112 , and two operating bars  121 . The chip support  111  has a carrier surface  113 , and two first electrical pads  117  respectively extending from the carrier surface  113  in Y and −Y directions. The bonding support  112  includes a central wiring portion  1123 , and two second electrical pads  118  respectively extending from the central wiring portion  1123  in Y and −Y directions. 
     The lead frame  120  is designed to have two operating bars  121 . The two operating bars  121  are respectively disposed on the upper and lower sides of the lead frame  120 , and further connected to the two first electrical pads  117  and the two second electrical pads  118  respectively. Further, the two operating bars  121  function as a position control unit (medium) for conveying, i.e., operate like a chain conveyor, thus achieving the purpose of automatic production. As far as one side (in the Y direction) of the lead frame  120  is concerned, the first electrical pad  117  and the second electrical pad  118  respectively have a first end  1171  and a second end  1181 , and the two ends  1171 ,  1181  are located within the operating bar  121 . Further, the two ends  1171 ,  1181  are located between a first outer border B  1  and a first inner border B 1 ′ of the operating bar  121 . 
     Accordingly, the positions of the ends of the electrical pads  117 ,  118  may determine the positions of the inner/outer borders of the operating bar  121 . Similarly, the first electrical pad  117  and the second electrical pad  118  on the other side (in the −Y direction) of the lead frame  120  may also have a first end  1172  and a second end  1182  respectively, and the two ends are located between a second outer border B 2  and a second inner border B 2 ′ of the operating bar  121  on this side. 
     As described above, without influencing the conveying and positioning function and automatic stamping and electroplating processes of the operating bars, the lead frame  120  architecture of the present invention not only enhances the structural strength of the lead frame  120 , but also reduces the width of the conventional lead frame  120  from 25.4 mm to 20.4 mm. Thus, the total volume of the lead frame  120  is greatly reduced, thereby further reducing the amount of material used by the lead frame  120  and the material and manufacturing costs of the electroplating process. 
     In addition, the bonding support  112  further includes wiring portions  1121 ,  1122  surrounding the periphery of the carrier surface  113 , so as to provide the lead frame  120  with several bonding areas to choose therefrom. 
       FIGS. 3A and 4  are perspective views of a light emitting diode package structure and a conductive assembly for the same according to the present invention. The light emitting diode package structure  100  of the present invention includes a conductive assembly  110 , a semiconductor chip  140 , and a package body  160 . The light emitting diode package structure  100  of the present invention is an LED package structure. 
     The conductive assembly  110  of the present invention includes a chip support  111  and a bonding support  112 . The chip support  111  has a carrier surface  113  and two first electrical pads  117  extending from the carrier surface  113 . The bonding support  112  includes two wiring portions  1121 ,  1122  surrounding the periphery of the carrier surface  113 , and a second electrical pad  118  extending from the two wiring portions  1121 ,  1122  respectively. A first wire  150  and a second wire  151  are respectively electrically connected to the semiconductor chip  140  and the wiring portions  1121 ,  1122 . In the present invention, the chip support  111  and the bonding support  112  respectively has two electrical pads  117 ,  118 . One of the electrical pads  117 ,  118  of the chip support  111  and the bonding support  112  respectively have a first end  1172  and a second end  1182 , for electrically connecting an electrode (not shown) to provide an electric power to the conductive assembly  110 . The other electrical pads  117 ,  118  of the chip support  111  and the bonding support  112  also respectively have a first end  1171  and a second end  1181 , which are contributive to the thermal dissipation of the light emitting diode package structure  100 , thus increasing the thermal dissipation area of the light emitting diode package structure  100 . 
     Moreover, the two wiring portions  1121 ,  1122  and the carrier surface  113  form an interdigitated structure. In addition to providing multiple choices of bonding areas, a safe area free from the impact of the inner stress of the frame bending angle is also provided. Therefore, the problems of wire breaking or frame deformation caused by the inner stress in the subsequent process are avoided. 
     Further, besides the design of two wiring portions  1121 ,  1122  surrounding the carrier surface  113  in  FIG. 3A , as shown in  FIG. 3B , a single wiring portion  1122  surrounding the carrier surface  113  may also be adopted. A second electrical pad  118  electrically connected to the electrode extends from the wiring portion  1122 . In addition, the first wire  150  is electrically connected to the semiconductor chip  140  and the wiring portion  1122 . 
     The semiconductor chip  140  of the present invention is a light-emitting chip disposed on the carrier surface  113  of the chip support  111 . Through the first wire  150  or the second wire  151  that electrically connects the semiconductor chip  140  to one second electrical pad  118  of the bonding support  112 , in which the second electrical pad  118  is electrically connected to the electrode, the semiconductor chip  140  is electrically conducted to emit lights. It should be noted that according to the design of the semiconductor chip  140 , the bonding support  112  of the present invention may further selectively electrically connect the two second electrical pads  118  to the electrode, such that the semiconductor chip  140  can be respectively connected to the two wiring portions  1121 ,  1122  of the bonding support  112  through the two wires  150 ,  151 , thereby avoiding the breaking of a single wire and enhancing the reliability of the product. 
     However, the chip support  111  and the bonding support  112  of the conductive assembly  110  of the present invention may also be designed to respectively have a single electrical pad  117 ,  118 . Further, a first end  1172  and a second end  1182  respectively extend from the electrical pads  117 ,  118  for electrically connecting an electrode, which is not limited to the embodiment of the present invention. 
     Further, referring to  FIG. 4 , the package body  160  is mainly made of epoxy resin or silicone coated with or mixed with phosphor powder, for encapsulating the carrier surface  113 , at least one wiring portions  1121 ,  1122 , the semiconductor chip  140 , and the first wire  150  to form the light emitting diode package structure  100 . The wiring portions  1121 ,  1122  of the bonding support  112  are disposed on the periphery of the carrier surface  113 , so as to form a safe bonding area that endures least impacts of stress and deformation for the package body  160 . Therefore, the stress impact caused by different thermal expansion coefficients of resin and metal materials between the bonding support  112  and the package body  160  can be effectively reduced, so as to avoid the breaking of the first wire  150  under the inner stress generated in the hardening of the package body  160 . 
     In other words, the bonding support  112  and the chip support  111  of the light emitting diode package structure  100  are partially interdigitated. The interdigitated area is formed by any lateral extending portion of the bonding support  112  (for example, the wiring portions  1121 ,  1122  in the X direction) and the carrier surface  113 . Therefore, the inner stress is not concentrated on semicircular notches at two ends of the package body  160  but on the interlaced area (the central area). As a result, the inner stress dragging outwardly generated during the hardening process of the package body  160  at the juncture between the package body  160  and the conductive assembly  110  is reduced accordingly. 
     Further, the first wire  150  is not located in a direction where the inner stress dragging outwardly is greater, but at a position perpendicular to the direction of the greatest stress. 
     In addition, the wiring portions  1121 ,  1122  of the present invention are designed to surround the carrier surface  113  of the chip support Ill according to the analysis result of Finite Element Analysis (FEA). The analysis simulation data is described as follows. The amount of deformation in the chip bonding area of the conventional Piranha type LED is between 0.0172 to 0.0315 mm, and the amount of deformation in the chip bonding area of the conductive assembly  110  of the present invention is between 0.0161 to 0.0295 mm which is apparently smaller than the conventional Piranha type LED. Therefore, the design of the wiring portion  1121  in the present invention can effectively solve the problem that the first wire  150  may be easily broken under the stress (dragging force) inside the light emitting diode package structure  100  caused by difference thermal expansion coefficients of the materials adopted by the package body  160  and the conductive assembly  110 . 
     According to the light emitting diode package structure, and the lead frame and the conductive assembly for the same provided by the present invention, at least one wiring portion surrounding the carrier surface extends from the bonding support, so as to reduce the probability of breaking of the wire under the stress (dragging force) during the packaging, thereby enhancing the reliability of the light emitting diode package structure.