Patent Publication Number: US-2009224344-A1

Title: Packaging method of image sensing device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor packaging method, and more particularly, to a packaging method of an image sensing device. 
     BACKGROUND OF THE INVENTION 
     In recent years, solid-state image sensors such as charge coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) image sensors have been widely applied to electronic products for converting light into electrical signals. The applications of image sensor components include monitors, cell phones, transcription machines, scanners, digital cameras, and so on. 
     Integrated circuits (ICs) are manufactured as wafers, each wafer containing many individual circuits (die). After fabrication, a wafer is cut (“singulated”) into individual die. Each die is then encapsulated in a plastic or ceramic package or is attached to a ceramic cap. 
     Each die includes several electrical contact pads. During packaging, each of these contact pads is connected to a respective lead or another external structure. In one common practice, a bonding wire is welded between each contact pad and a respective lead. The leads or other structures are used to electrically connect a completed IC to a circuit board or the like, such as by soldering. These solder connections often also provide the sole mechanical connection between the IC and the circuit board. 
     For example, U.S. Pat. No. 6,268,231 discloses a CCD package  10  as shown in  FIG. 1 . The CCD package  10  includes a plastic base structure  12  for support beneath a flexible circuit board  18 . Electrical conductors are formed upon flexible circuit board  18 . Plastic ring frame  14  is placed on top of the flexible circuit board  18  creating a sandwich area defined by the base structure  12  and plastic ring frame  14  with flexible circuit  18  in between. The plastic ring frame  14  provides depth for an image sensor to be contained therein. The image sensor electrical connectors that make electrical contact with conductor pattern on the flexible circuit  18 . The ring frame  14  provides support for a cover glass  16  that provides isolation from ambient conditions for the enclosed CCD while allowing light to pass and become incident upon the CCD. 
     However, packaging an individual die can be time consuming and expensive, because each die must be packaged individually. Given the reliance of the electronics industry on ICs, reducing the cost of each IC can lead to a substantial overall cost saving. Therefore, a packaging method that can reduce the production time and cost is desired. 
     SUMMARY OF THE INVENTION 
     Accordingly, the prior arts are limited by the above problems. It is an object of the present invention to provide a packaging method that can reduce the production time and cost of an image sensing device. 
     In accordance with an aspect of the present invention, a packaging method for an image sensing device, includes the steps of a) providing a wafer having at least an image sensing module with a light-receiving region exposed; b) forming a barrier around the light-receiving region on the image sensing module; c) dicing the wafer for forming an individual device with the image sensing module; and d) forming a transparent lid supported by the barrier above the light-receiving region of the image sensing module. 
     Preferably, the packaging method further includes the steps of e) providing an annular dam on a substrate; f) mounting the image sensing module inside the annular dam on the substrate; g) connecting the image sensing module and the substrate via a plurality of bonding wires; h) filling an adhesive between the barrier and the annular dam with the plurality of bonding wires being encapsulated. 
     Preferably, the packaging method further includes a step of cutting off the annular dam. 
     Preferably, the image sensing module includes complementary metal oxide semiconductor (CMOS) image sensor or charge coupled device (CCD) image sensor. 
     Preferably, the substrate includes aluminum nitride ceramic, fiberglass-reinforced epoxy resin, or bismaleimide-triazine resin. 
     Preferably, the barrier is formed by transfer molding, pot molding, injection molding, photolithographic process, exposure development process, laser cutting process, or stereolithographic process. 
     Preferably, the barrier is defined using a photoresist mask. 
     Preferably, the barrier is made of epoxy, solder mask, or photoresist. 
     In accordance with another aspect of the present invention, an image sensing device includes a substrate; an image sensing module mounted on the substrate, having a light-receiving region exposed; a plurality of bonding wires for connecting the image sensing module and the substrate; a barrier formed around the light-receiving region on the image sensing module; an adhesive filled around the barrier with the plurality of bonding wires being encapsulated; and a transparent lid formed above the light-receiving region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  illustrates an image sensing device according to the prior art. 
         FIGS. 2A-2I  illustrate an embodiment of a packaging method for an image sensing device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiment. It is to be noted that the following descriptions of the preferred embodiment of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Please refer to  FIGS. 2A-2I . They illustrate an embodiment of a packaging method for an image sensing device according to the present invention.  FIG. 2A  is a top view diagram of an integrated circuit (IC) wafer  20 . The wafer  20  contains at least one image sensing module  21  which is also known as “die”. Usually, a wafer has hundreds or thousands of image sensing modules depending on the size of each image sensing module. The smaller size of each image sensing module is, the more modules the wafer can accommodate.  FIG. 2B  is a cross-sectional diagram cut along line A-A in  FIG. 2A  showing five image sensing modules  21 . 
     The image sensing modules  21  each has a light-receiving region  22  exposed and a barrier  23  formed around the light-receiving region  22 , as shown in  FIG. 2B . The barrier  23  can be made of epoxy, solder mask, or photoresist, and can be formed by transfer molding, pot molding, injection molding, photolithographic process, exposure development process, laser cutting process, or stereolithographic process. 
     Traditionally, a barrier is formed on an image sensing module after the image sensing module is singulated from the wafer. However, since the barrier  23  has a certain volume and height, the barrier  23  of each image sensing modules  21  can be formed concurrently, for example, by applying a photoresist mask on the wafer  20  before the wafer is diced. By this way, the production time and cost may be reduced. 
     After the barrier  23  is formed on each of the image sensing modules  21 , the wafer  20  is diced to form an individual device with the image sensing module  21 , as shown in  FIG. 2C . Later, a transparent lid  24  is disposed on the barrier  23  above the light-receiving region  22  of the image sensing module  21 , as shown in  FIG. 2D . Conventionally, a transparent lid is not added until the packaging process is to be finalized and a protection layer is introduced to protect a light-receiving region from being damaged or polluted during packaging process. In contrast, the transparent lid  24  of the present invention acts as a protection layer to protect the light-receiving region  22 , and therefore, the cost and time are saved for producing and removing such protection layer. 
     Once the transparent lid  24  is added, the packaged image sensing module  21  is mounted on a substrate  25  inside an annular dam  26  provided on the substrate  25 , as shown in  FIGS. 2E and 2F . Then, the image sensing module  21  is connected to the substrate  25  via bonding wires  27 , as shown in  FIG. 2G . The annular dam  26  can be made of plastic, fiberglass-reinforced epoxy resin, or bismaleimide-triazine resin. Meanwhile, the substrate  25  can be made of aluminum nitride ceramic, fiberglass-reinforced epoxy resin, or bismaleimide-triazine resin for improving the thermal conductivity. 
     Furthermore, the image sensing module  21  is mounted on the substrate  25  in a conventional manner such as tape lamination process. Usually, there are a lot of connecting pads (not shown) disposed on the image sensing module  21  and the substrate  25 . Accordingly, those connecting pads of the image sensing module  21  and the substrate  25  are conducted via the bonding wires  27 . 
     Next, an adhesive  28  is filled between the barrier  23  and the annular dam  26  with the bonding wires  27  being encapsulated, as shown in  FIG. 2H . The adhesive  28  is used to prevent the bonding wires  27  from being damaged. 
     Finally, the annular dam  26  and a part of the substrate  25  are cut off to reduce the size of the image sensing device, as shown in  FIG. 2I . 
     In practice, the image sensing module  21  of the present invention could be complementary metal oxide semiconductor (CMOS) image sensor or charge coupled device (CCD) image sensor. 
     In conclusion, the present invention discloses a packaging method that forms a barrier on an image sensing module concurrently on wafer-level and uses a transparent lid as a protection layer which in turn reduces the overall production time and cost. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.