Patent Publication Number: US-2007102797-A1

Title: Electrode package for semiconductor device

Description:
REFERENCE TO RELATED APPLICATION  
      This application is a divisional of U.S. application Ser. No. 10/979,258 filed Nov. 2, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      This invention relates to an electrode package for a semiconductor device and a molded semiconductor device using the electrode package, in particular, the electrode package used for a resin molding of a leadless surface-mounting type package, and the molded semiconductor device.  
      A surface mount technology is a technology for directly soldering electrodes mounted on a surface of a semiconductor device onto a printed circuit board. By using the technology, through-holes for a pin insertion system become unnecessary. Further, miniaturization of electric components, substrates, and increase of packaging density are attained. As an electrode package used for the surface-mounting type semiconductor device, for example, an electrodeposited frame as shown in  FIG. 5  is disclosed in Japanese Patent Application Laid-Open No. 2002-16181. The electrodeposited frame as configured with a plurality of electrodes isolated from each other, as metal lawyers  8   a ,  8   b  in  FIG. 5 , electrodeposited on a flexible flat metal substrate  9 .  
      A semiconductor device molded in a leadless surface-mounting type package is formed with the electrodeposited frame by the steps described below. First, as shown in  FIG. 6A , semiconductor chips  2  are die-bonded on the metal layers  8   b . Then, wires  4  connect bonding pads  12  of the semiconductor chips  2  with the metal layers  8   a  respectively. Each of the metal layers  8   b  is previously deposited larger than a bottom surface of each semiconductor chip  2 . Then, the semiconductor chips  2  wired by the wires  4  are encapsulated by epoxy resin  7 . Then, as shown in  FIG. 6B , the metal substrate  9  is removed from a resin-molded body  11 . Thus, the metal layers  8   a ,  8   b  are exposed from a bottom surface of the resin-molded body  11 . Then, the semiconductor chips  2  are divided into individual semiconductor devices by cutting the resin molded body  11  along a cutting plane line S.  
      Since the isolated metal layers  8   a ,  8   b  are supported by the metal substrate  9 , the electrodeposited frame should be delivered to makers of the semiconductor devices with the metal substrate  9  as shown in  FIG. 5 . Therefore, the heavy electrodeposited frame should be delivered and a delivery cost is high. Further, with each maker, when producing semiconductor devices, the metal substrate  9  should be removed in a production process of the semiconductor devices. However, since the molded electrodeposited frame is so thin (less than 0.7 mm), cracks are often generated in the resin-molded body  11  when the metal substrate  9  is removed. Further, it is difficult to miniaturize the semiconductor devices unless design of the metal layer  8   b  is modified corresponding to each shape of various semiconductor chips  2 . Therefore, since it is necessary to optimize the electrodeposited frame for each shape of the various semiconductor chips  2 , production costs of the semiconductor devices are increased.  
      For resolving the problems described above, an object of this invention is to provide an electrode package for a semiconductor device, which allows the production cost of the surface-mounting type semiconductor device to be lower, and also provide the semiconductor device using the electrode package.  
     SUMMARY OF THE INVENTION  
      In order to attain the object, according to a first aspect of this invention, there is provided an electrode package including a resin plate; and a plurality of isolated electrodes molded in the resin plate, wherein each of the electrodes is exposed from both upper and lower surfaces of the resin plate.  
      According to the above, a surface-mounting type semiconductor device can be produced as follows. Firstly, semiconductor chips are mounted on one of the surfaces of the resin plate. Secondly, conductive wires electrically connect the semiconductor chips with corresponding electrodes molded in the resin plate. Thirdly, the semiconductor chip is encapsulated in a resin package. Therefore, owing to the resin plate supporting a plurality of the isolated electrodes, the electrode package is made without a metal substrate, and be lightweight. Further, when producing the semiconductor device using this electrode package, there is no need to remove the metal substrate.  
      According to this invention, preferably, there is provided the electrode package wherein a cross-sectional area of each of the electrodes is increased with depth from one surface to the other surface of the resin plate.  
      According to the above, setting the one surface downward and the other surface upward makes it difficult for the electrodes to fall out from the resin plate.  
      According to this invention, preferably, there is provided the electrode package wherein the electrodes each having a same shape are arranged in a matrix, and molded in the resin plate.  
      According to the above, the semiconductor chips having various sizes and shapes can be mounted on the resin plate. Therefore, the number of electrode packages applied to the semiconductor chips having various sizes and shapes can be reduced.  
      According to this invention, preferably, there is provided the electrode package wherein a reinforcing frame is provided on a periphery of the resin plate.  
      If rigidity of the thin electrode package is small at each production process, it is difficult for production machines to transfer the package. However, according to this invention described above, by providing the reinforcing frame, the rigidity of the electrode package is increased. Therefore, while the production machines transfer the electrode package, the electrode package can be prevented from being damaged.  
      According to this invention, preferably, there is provided the electrode package wherein the reinforcing frame is formed by a plurality of supports in a longitudinal direction thereof being arranged along the periphery of the resin plate, each end of neighboring supports of the supports being overlapped in a direction perpendicular to the longitudinal direction.  
      According to a structure described above, when a force caused by a difference between coefficients of thermal expansion of the reinforcing frame and the electrode package adjacent to the reinforcing frame is applied to deform the electrode package, the force is cancelled at the overlapped part. Therefore, the deformation of the electrode package can be prevented.  
      According to a second aspect of this invention, there is provided a semiconductor device including the electrode package described above, a semiconductor chip mounted on the electrode package and electrically connected to the corresponding electrodes of the electrode package by conductive wires, and a resin package for encapsulating the wired semiconductor chip.  
      According to the above, owing to the electrode package used for producing the semiconductor device, there is no need to remove the metal substrate during the production. Therefore, a production cost of the semiconductor device can be reduced.  
      According to a third aspect of this invention, there is provided the semiconductor device including the electrode package described above, the semiconductor chip mounted on the other surface of the resin plate of the electrode package and electrically connected to the corresponding electrodes of the electrode package by conductive wires, and a resin package for encapsulating the wired semiconductor chip.  
      According to the above, owing to the electrode package used for producing the semiconductor device, there is no need to remove the metal substrate during the production. Further, mounting the semiconductor chip on the other surface of the resin plate of the electrode package makes it difficult for the electrode, on which the semiconductor chip is mounted, to fall out from the resin plate, even if a bond between the semiconductor chip and the electrode is broken. Therefore, the production cost of the semiconductor device can be further reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a front plan view showing an embodiment of an electrode package according to this invention;  
       FIG. 1B  is a rear plan view showing the electrode package of  FIG. 1A ;  
       FIG. 1C  is a cross-section view taken on line I-I′ in  FIG. 1A ;  
       FIGS. 2A  to  2 F are cross-section views showing an embodiment of a production method of the electrode package of  FIG. 1A ;  
       FIGS. 3A  to  3 C are cross-section views showing an embodiment of a production method of semiconductor devices using the electrode package of  FIG. 1A ;  
       FIG. 4  is an explanatory view for explaining a force F applied to a supports  23   c  and  23   d  of  FIG. 1A ;  
       FIG. 5  is a cross-section view showing an electrodeposited frame as an embodiment of conventional electrode packages; and  
       FIGS. 6A and 6B  are cross-section views showing an embodiment of the conventional production method of semiconductor devices using the electrodeposited frame of  FIG. 5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      An electrode package and a semiconductor device using the electrode package according to this invention will be explained with reference to  FIGS. 1A  to  1 C,  2 A to  2 F,  3 A to  3 C, and  4 . Here, this invention relates to a leadless surface mounting type resin molded semiconductor device, and the electrode package used in production processes of the resin molded semiconductor device will be explained.  
      As shown in  FIG. 1A , an electrode package  20  includes a resin plate  21 . A plurality of isolated metal layers  22  (electrodes) having the same shapes are arranged in a matrix, and molded in the resin plate  21 .  
      Further, the metal layers  22  are exposed from both upper and lower surfaces of the resin plate  21 . Further, a cross-sectional area of each of the metal layers  22  is increased with depth from the upper surface to the lower surface of the resin plate  21 .  
      Each metal layer  22  is configured with a thin Au (gold) or Sn (tin) layer (not shown) having high solderability at the upper surface as shown in  FIG. 1A ; a thin Au or Ag (silver) layer (not shown) being able to be connected to an Au wire at the lower surface as shown in  FIG. 1B ; and a thin Ni (nickel), Ni/Co (cobalt), or Cu (Copper) layer (not shown) formed by electrodepositing, and positioned between said two thin layers. Thicknesses of the Ni, Ni/Co, or Cu layer and the Au, Sn or Ag layer are 20 to 50 μm and 0.05 to 10 μm, respectively.  
      Further, in the electrode package  20 , a reinforcing frame formed by a plurality of supports  23   a ,  23   b ,  23   c ,  23   d  in a longitudinal direction thereof being arranged along the periphery of the resin plate  21  is molded. For example, the supports  23   a ,  23   b ,  23   c ,  23   d  and the metal layers  22  are formed simultaneously by electrodeposition.  
      An embodiment of a production method of the electrode package  20  as shown in  FIG. 1A  will be explained with reference to cross-sections of  FIGS. 2A  to  2 F. First, as shown in  FIG. 2A , a flexible flat metal substrate  30  is prepared for producing the electrode package  20 . The metal substrate  30  is a thin stainless steel plate, having 0.1 mm thickness. Then, a resist film  31  is formed on a surface of the metal substrate  30 , except specific areas where the metal layers  22  or the supports  23   a ,  23   b ,  23   c ,  23   d  are to be formed. In addition, the resist film  31  is formed in a shape that a cross-sectional area is decreased with depth from its surface toward the metal substrate  30 .  
      Then, the metal substrate  30  is dipped in an electrodeposition bath. Then, an electric current is applied between the metal substrate  30  and the electrode in the electrodeposition bath. In this way using an electrocasting process, as shown in  FIG. 2B , by electrodepositing Au or Ag; Ni, Ni/Co or Cu; and Au or Sn sequentially, the metal layers  22  and the supports  23   a ,  23   b ,  23   c ,  23   d  configured with thin Au or Ag; Ni, Ni/Co or Cu; and Au or Sn films (not shown) are formed on areas, on which the resist film  31  is not formed, of the metal substrate  30 . As described above, since the resist film  31  is formed in the shape that the cross-sectional area is decreased with depth from its surface toward the metal substrate  30 , each metal layer  22  is inversely formed in a shape that a cross-sectional area is increased with depth from its surface toward the metal substrate  30 .  
      Next, as shown in  FIG. 2C , the resist film  31  is removed. Then, as shown in  FIG. 2D , resin  21  is coated by, for example, a spin coating. Then, as shown in  FIG. 2E , the whole surface of the resin  21  film is removed to expose the metal layers  22  at the upper surface of the resin  21  film. Then, as shown in  FIG. 2F , the metal substrate  30  is removed to form the electrode package  20 . Since the metal layers  22  and the supports  23   a ,  23   b ,  23   c ,  23   d  are electrodeposited in the metal substrate  30  using the electrocasting process, and the metal substrate  30  is flexible in a plane shape, the metal substrate  30  can be removed from the electrode package  20  easily.  
      In addition, the production process of this invention is not limited to the above-described process. For one example, a process, in which thin layers (not shown) of Au or Ag; Ni, Ni/Co or Cu; and Au or Sn are electrodeposited or vacuum deposited using, for example, a flash evaporation method, and then thin film is removed by etching, except the metal layers  22  and the supports  23   a ,  23   b ,  23   c  or  23   d , can be adapted. For another example, a process, in which firstly only one thin layer of Ni, Ni/Co, or Cu is resin coated, secondly the metal substrate  30  is removed from the resin plate, and thirdly the resin plate is dipped in the electrodeposition bath so that the thin layers are electrodeposited on one layer at both the upper and lower surfaces of the resin plate simultaneously, can also be adopted.  
      The electrode package  20  described above is delivered to a maker of semiconductor devices. At the maker, semiconductor chips are mounted on the electrode package  20  to produce semiconductor devices. In the following, a production method of the semiconductor device using the electrode package  20  will be explained with reference to  FIGS. 3A  to  3 C. At first, as shown in  FIG. 3A , semiconductor chips  32  are mounted and die-bonded on the upward lower surface of the electrode package  20 . Bonding pads  32   a  are formed on a surface of each semiconductor chip  32 .  
      After the semiconductor chips  32  are mounted, as shown in  FIG. 3B , Au wires  33  electrically connect the bonding pads  32   a  of each semiconductor chip  32  with the metal layers  22 . The Au wires  33  are connected by ultrasonic bonding or the like. Then, the electrode package  20 , on which the semiconductor chips  32  are mounted, and wire-bonded, is attached to an upper mold  34 .  
      Epoxy resin is injected into an encapsulated inner space between the upper mold  34  and a lower mold (electrode package  20 ), via a cavity formed on the upper mold  34 . In this mold set, the electrode package  20  works as a lower mold set. In this process, the semiconductor chips  32  connected with the wire  33  are capsulated in the resin, and a resin encapsulated body  35  is formed having the semiconductor chips  32  and the metal layers  22  as shown in  FIG. 3C . Then, semiconductor devices  32  are separated from the resin encapsulated body  35  by cutting it along cutting plane lines S.  
      According to the electrode package  20  of this invention as shown in  FIG. 1A , a plurality of metal layers  22  isolated from each other are supported by the resin plate  21 . Therefore, the electrode package  20  can be made without a conventional metal substrate and can be lighter in weight. Therefore, a delivery cost of the electrode packages  20  to the makers of the semiconductor devices can be reduced. Further, according to this invention, as shown in  FIGS. 3A  to  3 C, there is no need to remove the metal substrate (for example, reference number  9  in  FIG. 5 ) in the production process of the semiconductor devices. Therefore, there is no need for each maker of the semiconductor devices to possess an apparatus for removing the metal substrate. Thus, production costs of the semiconductor devices can be reduced.  
      As shown in  FIG. 1C , the cross-sectional area of each of said metal layers  22  is increased with depth from the upper surface to the lower surface of the resin plate  21 . Therefore, a delivery in a way that the electrode package  20  is faced downward prevents the metal layers  22  from falling out of the resin plate  21 . Therefore, quality of the electrode package  20  is stabilized to reduce the production cost of the semiconductor devices.  
      As shown in  FIGS. 1A and 1B , the metal layers  22  have the same shapes, are arranged in a matrix, and are molded in the resin plate  21  of the electrode package  20 . Therefore, the semiconductor chips  32  having various sizes and shapes can be mounted on the resin plate  21 . Therefore, the number of electrode packages  20  applied to the semiconductor chips  32  having various sizes and shapes can be reduced. This also can reduce the production cost of the semiconductor devices  32 .  
      As shown in  FIG. 1B , a reinforcing frame is formed by a plurality of supports  23   a ,  23   b ,  23   c ,  23   d  along the periphery of the resin plate  21 . The electrode package  20  is thin, about 25 μm thick, and its rigidity is low. Therefore, the reinforcing frame is provided to increase the rigidity of the electrode package  20 . Thus, the number of defective electrode packages caused by deformations of the electrode package  20  decreases to reduce the production cost of the semiconductor devices.  
      In the electrode package  20 , the reinforcing frame is formed by a plurality of supports  23   a ,  23   b ,  23   c ,  23   d  in a longitudinal direction thereof being arranged along the periphery of the resin plate  21 . Further, as shown in  FIG. 4 , each pair of ends of neighboring supports  23   a ,  23   b ,  23   c ,  23   d  are overlapped in a direction Y 1  perpendicular to the longitudinal direction. According to this arrangement, for example, even if the supports  23   a ,  23   b ,  23   c ,  23   d  are made of resin, a difference between coefficients of thermal expansion of the metal layers  22  and the resin plate  21 , both of which are components of the electrode package  20 , causes a difference between coefficients of thermal expansion of the electrode package  20  and the supports  23   a ,  23   b ,  23   c ,  23   d . Thus, if forces F are applied to the electrode package  20  in a direction from each edge to each center of the supports  23   a ,  23   b ,  23   c ,  23   d , the forces F are cancelled at each overlapping part. Therefore, it becomes harder to deform the electrode package  20 .  
      As shown in  FIGS. 3A  to  3 C, the semiconductor chips  32  are mounted on the lower surface of the electrode package  20  on which metal layers  22  have wider cross-section areas. According to this, even if bonds between the semiconductor chips  32  metal layers  22 , on which the semiconductor chips  32  are mounted respectively, are broken, the semiconductor chips  32  are difficult to fall out from the resin plate  22 . Therefore, the number of defective semiconductor devices is reduced and the production cost of the semiconductor devices is also reduced.  
      In the embodiment described above, each metal layer  22  is configured with a thin Au or Sn layer having high solderability; a thin Au or Ag layer being able to be connected to an Au wire; and a thin Ni, Ni/Co, or Cu layer positioned between said two thin layers. However, various configurations can be adopted. For example, in a process of mounting the semiconductor chips  32 , when depositing thin films, the metal layers  22  can be configured with only a thin film of Ni, Ni/Co, or Cu, or with two of the films and any one of an Au or Sn film, or an Au or Ag film. Further, material for the metal layers  22  is not limited to those described above, and various materials, each of which can be an electrode, can be adopted.