Patent Publication Number: US-2005135071-A1

Title: Package structure of optical sensitive device and method for packaging optical sensitive device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a package structure of optical sensitive device and a method of packaging optical sensitive device, and in particular to a method used to package optical sensitive device by package process.  
      2. Description of Related Art  
       FIG. 1  illustrates a package structure of an optical sensitive device after wafer package process in prior art is performed. A plurality of optical sensitive devices are fabricated on a silicon wafer (not shown), and the silicon wafer is cut into several separate optical sensitive devices  10   a  (becomes singulated) via wafer dicing process. A supporting pad  30   a  is attached to a printed circuit board (PCB) substrate  20   a  so that a cavity  21   a  is provided. Then, the optical sensitive device  10   a  is positioned on the cavity  21   a  of the PCB substrate  20   a  by adhesive, and the adhesive is heated to solidify. Wire bonding is performed on the optical sensitive device  10   a , and adhesive is applied to the supporting pad  30   a  which is covered with a glass plate  40   a . However, there are some shortcomings in the conventional optical sensitive device as described below: 
          1. The conventional package process is performed after a plurality of optical sensitive devices are fabricated on a silicon wafer. The conventional package process includes wafer dicing, applying adhesive and wire bonding to package the optical sensitive devices. In this regard, it is likely for particles to adhere to the optical sensitive area of the optical sensitive devices during package process. Purification of processing environment (or cleanroom) is strictly required, so cost of packaging is increased significantly.     2. The package structure of conventional optical sensitive device is bulky because the volume of the supporting pad is large, thereby resulting in increasing cost of packaging and limiting the optical sensitive device applications.        
      Thus, there is need to development for a method to package an optical sensitive device without particle contamination.  
     SUMMARY OF THE DISCLOSURE  
      It is an object of the present invention to provide a package structure of an optical sensitive device and a method of packaging optical sensitive device. The method in accordance with the present invention packages an optical sensitive area of the optical sensitive device at an early stage in the package process, thereby resulting in virtually eliminating particle containment and requiring lower purification of processing environment so as to decrease cost of packaging.  
      It is another object of the present invention to provide a package structure of optical sensitive device and a method of packaging optical sensitive device. The method of the present invention has volume of a supporting pad to be decreased, so volume of package structure of the optical sensitive device is decreased.  
      In order to accomplish the object of the present invention, the present invention provides a package structure of optical sensitive device. According to the present invention, the package structure includes a silicon substrate, an optical sensitive device, a supporting pad, a transparent plate and a plurality of conductive wires. The optical sensitive device has an optical sensitive area and a plurality of bonding pads, and the optical sensitive device is positioned on the silicon substrate. The supporting pads are provided around the periphery of the optical sensitive area, and the transparent plate is fixedly positioned on the supporting pad and corresponds to the optical sensitive area of the optical sensitive device. In addition, the conductive wires are respectively electrically connected between the bonding pads of the optical sensitive device and the substrate.  
      In order to accomplish the object of the present invention, the present invention provides a method of packaging optical sensitive device. The method according to the present invention, comprising: 
          fabricating a plurality of optical sensitive devices on a silicon wafer, and each of the optical sensitive devices having an optical sensitive area and a plurality of bonding pads;     positioning a plurality of separate supporting pads on the silicon wafer, and each of the supporting pads positioned around the supporting pad and corresponding to the optical sensitive area;     positioning a plurality of transparent plates on the supporting pads, and the transparent plates corresponding to the optical sensitive areas; and     cutting the silicon wafer and obtaining separate optical sensitive devices.        

      Thus, the present invention virtually eliminates particle containment on the optical sensitive devices and has the volume of the package structure of the optical sensitive devices to be decreased. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The present invention can be fully understood from the following detailed description and preferred embodiment with reference to the accompanying drawings in which:  
       FIG. 1  is a cross-sectional view of a package structure of a conventional optical sensitive device;  
       FIG. 2  is a cross-sectional view of a package structure of an optical sensitive device in accordance with the present invention;  
       FIG. 3  is a top plan view of a silicon wafer including a plurality of the optical sensitive device in accordance with the present invention;  
       FIG. 3A  is an enlarged top plan view of the optical sensitive device indicated by arrow A of  FIG. 2 ;  
       FIG. 4  is a top plan view of the optical sensitive device of  FIG. 3  with a supporting pad mounted;  
       FIG. 5  is a cross-sectional view of the silicon wafer of  FIG. 3 ;  
       FIG. 6  is a cross-sectional view of the silicon wafer of  FIG. 3  with transparent plates mounted;  
       FIG. 7  is a cross-sectional view of a package structure in accordance with the present invention when the optical sensitive device is positioned on the silicon wafer;  
       FIG. 8  is a cross-sectional view of the present invention of  FIG. 7 ; and  
       FIG. 9  is a cross-sectional view of the present invention of  FIG. 8  with electrical wires connected between the optical sensitive device and the silicon wafer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims.  
      Referring to  FIG. 2 , a package structure of the present invention includes a substrate  10 , an optical sensitive device  20 , supporting pads  30 , a transparent plate  40  and electrical wires  50 . The substrate  10  can be a printed circuit board (PCB). The optical sensitive device  20  has an optical sensitive area  21  and bonding pads  22 , and the bonding pads  22  are positioned near the edges of the optical sensitive device  20 . The supporting pads  30  are positioned around the optical sensitive area  21  of the optical sensitive device  20 . The transparent plate  40  is fixedly positioned on the supporting pads  30  and corresponds to the optical sensitive area  21 . The transparent plate  40  can be, but not limited to a glass plate or a transparent resin plate. The transparent plate  40 , the supporting pads  30  and optical sensitive area  21  of the optical sensitive device  20  are used to form a cavity  23 . In addition, the electrical wires  50  are electrically connected between the bonding pads  22  and the substrate  10 . A molding material  60  (i.e. Epoxy) is applied the periphery of the optical sensitive device  20  and the substrate  10  to prevent the electrical wires  50  from exposed and damaged. Thus, the package structure with small footprint is achieved.  
       FIGS. 3-9  illustrate how to fabricate the package structure of the optical sensitive device in accordance with the present invention. Referring to  FIGS. 3 and 3 A, a plurality of optical sensitive devices  20  are fabricated on a silicon wafer  70 . As described above, each of the optical sensitive devices  20  has an optical sensitive area  21  and bonding pads  22 . As shown in  FIGS. 4 and 5 , the supporting pads  30  are separately positioned on the silicon wafer  70  and can be UV curable adhesive or thermosetting resin. The supporting pads  30  are positioned near and correspond to the periphery of the optical sensitive area  21 .  
      Referring to  FIG. 6 , the transparent plates  40  are respectively positioned on the supporting pads  30  and correspond to the optical sensitive area  21 . Then, the supporting pads  30  which are made of UV curable adhesives are subjected to ultra-violet ray so that the supporting pads  30  are fixedly attached to the optical sensitive devices  20  and the transparent plates  40 .  
      Referring to  FIG. 7 , an adhesive layer  80  is attached to the bottom of the silicon wafer  70 , and the silicon wafer  70  is cut into several separate optical sensitive devices  20  via wafer dicing process. Then, the adhesive layer  80  is forcedly separated from the optical sensitive devices  20 , and the optical sensitive devices  20  is attached to the substrate  10  as shown in  FIG. 8 .  
      Referring to  FIG. 9 , the electrical wires  50  are electrically connected between the bonding pads  22  and the substrate  10 . As shown in  FIG. 2 , the molding material  60  is applied the periphery of the optical sensitive device  20  and the substrate  10  so that the optical sensitive area  21  of the optical sensitive devices  20  is encapsulated by the supporting pads  30  and the transparent plates  40 . Thus, it results in virtually eliminating particle containment and requiring lower purification of processing environment so as to decrease cost of packaging.  
      While the invention has been described with reference to the preferred embodiments, the description is not intended to be construed in a limiting sense. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as may fall within the scope of the invention defined by the following claims and their equivalents.