Patent Publication Number: US-2007108561-A1

Title: Image sensor chip package

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is related to a co-pending U.S. patent applications (Attorney Docket No. US7591), entitled “DIGITAL CAMERA MODULE”, by Steven Webster et al. Such application has the same assignee as the present application and has been concurrently filed herewith. The disclosure of the above identified application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD  
      The present invention generally relates to IC (integrated circuit) chip packages, and more particularly to an image sensor chip package which is reduced in size and cost and still has high reliability.  
     BACKGROUND  
      Image sensors are widely used in digital camera modules in order to convert the optical image data of an object into electrical signals. In order to protect the image sensor from contamination or pollution (i.e. from dust or water vapor), the image sensor is generally sealed in a structural package.  
      A typical image sensor chip package  100  is illustrated in  FIG. 1 . The image sensor chip package  100  is constructed to include a base  10 , a chip  12 , a plurality of wires  13 , an adhesive glue  14  and a cover  15 . The base  10  includes a board portion  101 , a frame portion  102  upwardly extending from a periphery of the board portion  101 , and a cavity  103  cooperatively formed by the board portion  101  and the frame portion  102 . A plurality of top contacts  104  and bottom contacts  105  are respectively mounted on two sides of the board portion  101 , and the top contacts  104  are contained in the cavity  103 . A plurality of conductive interconnecting portions  106  are arranged inside the board portion  101  so as to electrically connect the top and bottom contacts  104 ,  105 . The chip  12  includes an active area  121  and a number of pads  122  formed thereon. The chip  152  is received in the cavity  103  and adhered to the board portion  101  of the base  10 . The wires  13  are provided to electrically connect the pads  122  of the chip  12  and the top contacts  104  of the base  10 . The cover  15  is transparent and secured to the top of the frame portion  102  via the adhesive glue  14 , thereby hermetically sealing the cavity  103  and allowing light beams to pass therethrough.  
      In the foresaid package  100 , the base  10  is essentially made from ceramic, which is expensive. In addition, during the process of forming the contacts  104 ,  105  and the interconnecting portions  106  on the base  10 , a number of interconnection holes are punched in the base  10 , then the base  10  is copper plated, via electroless or electrolytic deposition onto the surface of the base  10  and onto the surfaces created by the interconnecting holes. Finally, the contacts  104 ,  105  are formed by means of etching. Accordingly, the contacts  104 ,  105  and the interconnecting portions  106  are electrically connected with each other. It is obvious that this method of forming the contacts  104 ,  105  and the interconnecting portions  106  is complex and as a result it is expensive. Furthermore, water vapor can enter the cavity  103  via the interconnection portions  106 . Thus, the chip  12  may be polluted, even be damaged.  
      Additionally, the cavity  103  of the base  10  must contain both of the top contacts  104  and the chip  12  therein, and there must define a space between an outer periphery of the chip  12  and an inner periphery of the frame portion  102  of the base  10  for allowing movement of a wire bonding tool, which accordingly results in a relative large volume of the package  100  relative to the volume of the chip  12 .  
      Furthermore, the relative large volume of the package  100  results in more dust-particles adhering to the cover  15 , the board portion  101  and the frame portion  102  of the base  10 . Thus, more dust-particles will drop onto the chip  12 . The dust-particles obscure the optical path and produce errors in the image sensing process. Accordingly, the quality and/or reliability of the package  100  may be affected.  
      Therefore, an improved image sensor chip package is desired in order to overcome the above-described shortcomings.  
     SUMMARY OF THE INVENTION  
      In one aspect, an image sensor chip package includes a carrier, an image sensor chip, a number of wires and a holder. The carrier includes a base and a leadframe embedded in the base. The base has a board, a sidewall extending from a top surface of the board and a cavity cooperatively defined by the board and the sidewall. The leadframe includes a plurality of conductive leads spaced from each other. Each conductive lead has a first terminal portion exposed from a top surface of the sidewall of the base, a second terminal portion exposed through a bottom surface of the board, and an interconnecting portion connecting the first and second terminal portion. The chip is mounted on the base and received in the cavity, and includes an active area and a plurality of contacts. The wires electrically connect the contacts of the chip and the first terminal portions of the leadframe. The holder is mounted on the carrier enclosing the cavity of the carrier, and allows light passing therethrough to reach the active area of the chip.  
      Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the present image sensor chip package can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the image sensor chip package. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a schematic, cross-sectional view of a typical image sensor chip package;  
       FIG. 2  is a schematic, top plan view of an image sensor chip package according to a preferred embodiment, wherein the holder is not shown;  
       FIG. 3  is a cross-sectional view of the package in  FIG. 2  along a line III-III, wherein the holder is show; and  
       FIG. 4  is a cross-sectional view of the package in  FIG. 2  along a line IV-IV, wherein the holder is show. 
    
    
     DETAILED DESCRIPTION OF THE PERFERRED EMBODIMENTS  
      Referring to  FIGS. 2 through 4 , an image sensor chip package  200  in accordance with a preferred embodiment is illustrated. The image sensor chip package  200  includes a carrier  20 , a chip  30 , a number of bonding wires  50  and a holder  60 .  
      The carrier  20  of the package  200  includes a plastic base  21  and a leadframe (not labeled). The leadframe and the plastic base  21  cooperatively form the carrier  20  by injection molding.  
      The base  21  is essentially made from plastic materials such as polyphenylene oxide (PPO), polyphenylene sulfide (PPS) and the like. The base  21  may have various perimeter shapes, such as a square, rectangular, a circular etc. The base  21  includes a base board  211 , a sidewall  213  upwardly extending from a periphery of the base board  211 , and a cavity  24  cooperatively formed by the base board  211  and the sidewall  213  for receiving electronic components. As shown in  FIG. 2 , the sidewall  213  includes a front sidewall portion  2131 , a rear sidewall portion  2133  positioned opposite to the front sidewall portion  2131 , a left sidewall portion  2132 , and a right sidewall portion  2134  positioned opposite to the left sidewall portion  2134 . The top surfaces of two opposite sidewall portions of the sidewall  213 , such as the left and right sidewall portion  2132 ,  2134 , each have a slot  217  longitudinally defined therein. The cavity  24  has a uniform cross section between the base board  211  and the sidewall  213 .  
      Referring to  FIGS. 3 and 4 , the leadframe is made of conductive metal material, which has good electrical conductivity and thermal conductivity, such as copper or iron-nickel alloy, in order to enhance the signal transmission characteristic and thermal transmission characteristic of the package  200 . The leadframe includes a die pad  231  and a number of conductive leads  233 . The conductive leads  233  are formed by either punching or etching on a metal sheet. Each of the conductive leads  233  includes a first terminal portion  235 , a second terminal portion  236  and a connecting portion  237 , and the connecting portion  237  interconnecting the first and second terminal portions  235 ,  236 . The first and second terminal portions  235 ,  236  are spaced apart and aligned in parallel to each other. The interconnecting portions  237  are slanted relative to the first and second terminal portions  235 ,  236 . Correspondingly, the conductive leads  233  are divided into two groups. The two groups are symmetrically arranged and the conductive leads  233  in the same group are parallel to and spaced from each other. The die pad  231  is disposed between the two groups of the conductive leads  233 , and a bottom surface of the die pad  231  is level with the bottom surfaces of the second terminal portions  236  of the conductive leads  233 .  
      During injection molding, the plastic base  21  encapsulates the leadframe, wherein the die pad  231  is disposed in a middle portion of the base board  211 , an upper surface of each first terminal portion  235  is exposed from the top surfaces of the sidewall portions without a slot  217  defined therein, for example, the top surfaces of the front and rear sidewall portions  2131 ,  2133 , and both of a lower surface of the die pad  231  and each second terminal portion  236  are exposed from the bottom surface of the base board  211 . The first and second terminal portions  235 ,  236  both are configured for electrically connecting with other electronic components, for example the first terminal portions  235  can be used to electrically connect to a chip and the second terminal portions  236  can be used to electrically connect with a printed circuit board (PCB), thereby transmitting signals from the chip to the PCB via the leadframe.  
      The image sensor chip  30  is received in the cavity  24 , and is attached to the base board  211 . A top surface of the image sensor chip  30  is arranged with an active area  301  and a number of contacts  302 . The active area  301  is disposed in a middle portion of the top surface of the chip  30 . The contacts  302  are divided into two groups, and the two groups of contacts  302  are symmetrically disposed and formed at regular intervals along a peripheral portion of the top surface of the chip  30 .  
      The wires  50  can be made of a conductive material with good electric conductivity, such as gold or aluminum alloy. One end of each wire  50  is connected/joined with a respective contact  302  of the image sensor chip  30 , and the other end of the wire  50  is connected/joined with a respective top surface of a first terminal portion  235  of the leadframe.  
      The holder  60  is made from opaque material or transparent material with an opaque layer coated thereon. The holder  60  is a hollow case having an opening end and a half-closed end. The half-closed end of the holder  60  has a through hole  601  defined therein. A transparent board  602  can be received in or attached to a perimeter of the through hole  601  to close the half-closed end and allow light to pass therethrough. The opening end of the holder  60  has a first step portion  61  and a second step portion  62 . An inner periphery of the first step portion  61  has a dimension equal to that of an outer periphery of the carrier  20 . An inner periphery of the second step portion  62  has a dimension smaller than that of the outer periphery of the carrier  20 . The second step portion  62  includes a step surface  621  from which the first step portion  61  extends. The step surface  621  has two grooves  623  defined therein for receiving the wires  50  and two ribs  624  projecting therefrom for engaging with the slots  217  of the carrier  20 . The holder  60  receives the carrier  20  mounted with the chip  30  therein, wherein the inner periphery of the first step portion  61  is adhered to the outer periphery of the carrier  20 , the step surface  621  of the holder  60  is adhered to the top surface of the sidewall  213 , each groove  623  receives a group of wires  50 , each rib  624  of the holder  60  is adhered to and engaged with a corresponding slot  217  of the carrier  20 , and the transparent board  602  is positioned above the active area  301  of chip  30 .  
      The base  21  of the carrier  20  is made of plastic material, which is much cheaper than ceramic, and the carrier  20  is formed by injection molding technology, which is a relative simple method for manufacturing the carrier  20 , thus, the cost of the package  200  is accordingly decreased.  
      The leadframe of the barrier  20  is solid and substantially encapsulated by the base  21 , so it is difficult for water vapor to penetrate into the package  200  to pollute the chip  30 , thereby enhancing the reliability of the packaged  200 .  
      The top surfaces of the first terminal portions  235  of the leadframe act as connecting pads, accordingly there is no space restriction on the wire bonding tools&#39; movement. Thus, the size of the carrier  20  can be sufficiently minimized to approach the size of the chip  30 , and the volume of the image sensor chip package  200  can also be minimized.  
      In addition, a relative small volume of the package  200  contains relatively little dust particles therein, the pollution and/or contamination of the active area  301  is reduced and the quality and reliability of the package  200  is much improved.  
      It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.