Patent Publication Number: US-2007120213-A1

Title: Wire under dam package and method for packaging image-sensor

Description:
BACKGROUND OF THE INVENTION  
      The present invention is related to an image-sensor package and a method for packaging image-sensor. The frame bank is attached to the substrate with the rear ends of the soldering wires sandwiched between the frame bank and the substrate. Accordingly, the width and size of the package are minified.  
      A conventional image-sensor includes an image-sensing chip and a base seat in which the image-sensing chip is installed. The base seat is molded with a lead frame or formed of a printed circuit board, ceramic/porcelain substrate and frame bank sealed and covered by a transparent glass board.  
      Currently, the image-sensors are widely applied to various electronic products such as digital cameras, cellular phones and PDA. These electronic products require cheap and small-size image-sensors. By means of the new generation of flip chip package, CSP image-sensors are producible. However, such CSP image-sensors are relatively expensive.  FIG. 6  shows one of the popular packages of the image-sensors. The package includes a substrate  60 , a frame bank  61 , a chip  62  and a transparent glass board  63 . Multiple circuits  601  are laid on the surface of the substrate. The circuits extend to outer side of the chip to electrically connect with the soldering wires  621  and soldering pads of the chip. The transparent glass board  63  is adhered to the frame bank for sealing the chip. In such package, a sufficient gap must be reserved between the chip  62  and the frame bank  61  for the circuits  601  on the surface of the substrate. Therefore, such package has a considerable width.  
       FIG. 7  shows an improved image-sensor package including a substrate  70 , a frame bank  71 , a chip  72  and a transparent glass board  73 . The main difference between the two packages is that one end of the soldering wire  721  is soldered on upper side of the frame bank  71 . Therefore, the size of the frame bank is only slightly larger than that of the chip and thus the volume of the package is greatly reduced. However, such design is still not optimal. For example, the soldering pad  701  is laid on the upper side of the frame bank  71 . A lead  702  extends from the soldering pad  701  along outer side of the frame bank to the bottom face of the substrate. It is hard to manufacture the lead  702 .  
     SUMMARY OF THE INVENTION  
      It is therefore a primary object of the present invention to provide wire under dam package and method for packaging image-sensor. Multiple inner electric contacts are arranged on a first surface of the substrate. The soldering pads of the sensing chip and the inner electric contacts are electrically connected via soldering wires. A frame bank is attached to the first surface. Rear ends of the soldering wires soldered with the inner electric contacts are sandwiched between the frame bank and the first surface. Accordingly, the area of the substrate is reduced to minify the size of the package.  
      According to the above object, the method for packaging image-sensor of the present invention includes steps of:  
      preparing a substrate having a first surface and a second surface;  
      arranging multiple inner electric contacts on the first surface;  
      laying a sensing chip on the first surface of the substrate, the sensing chip having multiple soldering pads;  
      electrically connecting the soldering pads with the inner electric contacts with soldering wires;  
      adhering a frame bank to the periphery of the first surface, whereby rear ends of the soldering wires soldered with the inner electric contacts are sandwiched between the frame bank and the first surface; and  
      laying a transparent board on the frame bank.  
      The present invention can be best understood through the following description and accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a first embodiment of the image sensor package of the present invention;  
       FIG. 2  is a sectional view of a second embodiment of the image sensor package of the present invention;  
       FIG. 3  is a sectional view showing that the soldering wire is pressed down by the frame bank of the present invention;  
       FIG. 4  is a perspective exploded view of the image sensor package of the present invention, showing that the bottom face of the frame bank is formed with multiple recesses in which the rear ends of the soldering wires are accommodated;  
       FIG. 5  is a flow chart of the packaging method of the present invention;  
       FIG. 6  is a sectional view of a conventional image sensor package; and  
       FIG. 7  is a sectional view of another conventional image sensor package. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Please refer to  FIG. 1  which shows the image-sensor package of a first embodiment of the present invention. The package includes a substrate  10  having a first surface  11  and a second surface  12 . A sensing chip  2  is laid on the first surface. The sensing chip has multiple soldering pads  21 .  
      Multiple inner electric contacts  13  are arranged on the first surface  11 . The soldering pads  21  and the inner electric contacts  13  are electrically connected via soldering wires  22 .  
      Multiple outer electric contacts  14  are arranged on the second surface  12  of the substrate for connecting with an external circuit of another circuit board. As shown in  FIG. 1 , multiple guide holes  15  are formed through the substrate between the inner electric contacts  13  and the outer electric contacts  14 . Conductive material is filled in the guide holes  15  to electrically connect the inner electric contacts  13  with the outer electric contacts  14 . Alternatively, as shown in  FIG. 2 , the inner electric contacts  13  extend along the lateral side of the substrate to electrically connect with the outer electric contacts  14 .  
      A frame bank  3  is adhered to the first surface with adhesive glue. A transparent board  4  is adhered to upper side of the frame bank  3 . The frame bank  3  has a bottom face  31  facing the first surface. A rear end of the soldering wire soldered with the inner electric contact is sandwiched between the bottom face  31  of the frame bank and the first surface  11 . In order to avoid thickening of the package, as shown in  FIG. 4 , the bottom face  31  of the frame bank is formed with multiple recesses  32  in each of which the rear end of a corresponding soldering wire is accommodated.  
      In addition, several bosses  33  are disposed under the bottom face of the frame bank and the substrate is formed with several sockets  16  corresponding to the bosses  33 . Accordingly, the bosses  33  can be inserted in the sockets  16  to more accurately associate the frame bank with the substrate.  
      The soldering wires have good extensibility and flexibility. Therefore, when the frame bank is attached to the substrate, the rear ends of the soldering wires near the inner electric contacts can be pressed down as shown in  FIG. 3 . Therefore, the frame bank can surround the chip in a position closer to the periphery of the chip. Accordingly, the package can have a size nearly equal to the size of the chip.  
       FIG. 5  shows the packaging method of the present invention, including steps of: 
          a) preparing a substrate  10  having a first surface  11  and a second surface  12 , multiple inner electric contacts  13  being arranged on the first surface  11 ;     b) laying a sensing chip  2  on the first surface of the substrate, the sensing chip having multiple soldering pads;     (c) electrically connecting the soldering pads with the inner electric contacts with soldering wires  22 ;     (d) painting adhesive glue on a periphery of the first surface  11  of the substrate and adhering a frame bank  3  to the first surface, whereby rear ends of the soldering wires soldered with the inner electric contacts are sandwiched between the frame bank and the first surface; and     (e) laying a transparent board  4  on the frame bank.        
      The image sensor achieved by the above packaging method has a reduced volume. In addition, the image sensors can be mass-produced in such a manner that a substrate connecting board having multiple substrates is provided. The substrates are interconnected with each other. After all the chips are laid on the substrate connecting board and lined, a frame bank connecting board having multiple frame banks is attached to the substrate connecting board. A transparent board with an area equal to that of the frame bank connecting board is attached to the frame bank connecting board. Finally, the substrate connecting board is cut along the sides of the substrates into independent image sensor packages.  
      The above embodiments are only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the above embodiments can be made without departing from the spirit of the present invention.