Abstract:
A method and apparatus provide a leadless imager packaging structure having an integrated leadframe and a first encapsulant with an opening, which is covered by a transparent plate to form a cavity. The cavity contains an integrated circuit having a light sensitive area facing the transparent plate and which is electrically connected to the leadframe. The integrated circuit is encapsulated within the cavity by a second encapsulant.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments herein relate to the field of integrated circuit packaging, and more specifically to integrated circuit imager packaging. 
       BACKGROUND OF THE INVENTION 
       [0002]    As the final step in the fabrication of a semiconductor integrated circuit, an integrated circuit is placed in packaging. The packaging serves to protect the integrated circuit from the environment and to provide a means for electrically connecting the integrated circuit to external components. As portable electronic devices have become smaller and more sophisticated, the challenge of minimizing the space used by integrated circuits and their respective packaging has continued to increase. 
         [0003]    In conventional integrated circuit packaging techniques, the integrated circuits are packaged in a fully encapsulated manner, in which molding is used to fully enclose the integrated circuit for protection. However, if the integrated circuit is to be used as an imager device, light must be able to pass to the imager&#39;s photodetection area. Therefore, fully encapsulated packaging is not suitable for use with imager integrated circuits. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a cut-away side view of a leadless imager device packaging structure in accordance with an embodiment described herein. 
           [0005]      FIG. 2   a  is a cut-away side view of a leadless imager device packaging structure at a stage of manufacture in accordance with an embodiment described herein. 
           [0006]      FIG. 2   b  is a top-down view of the leadless imager device packaging structure at the stage of manufacture shown in  FIG. 2   a.    
           [0007]      FIG. 3  is a cut-away side view of a leadless imager device packaging structure at a stage of manufacture in accordance with an embodiment described herein. 
           [0008]      FIG. 4  is a cut-away side view of a leadless imager device packaging structure at a stage of manufacture in accordance with an embodiment described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments described herein. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made. 
         [0010]    One embodiment described herein provides a method of fabricating an imager device packaging structure using half encapsulation technology by which an integrated circuit is partially encapsulated by encapsulation material and further encapsulated by a transparent plate. 
         [0011]      FIG. 1  shows a partial side view of a leadless imager device packaging structure  100  in accordance with an embodiment. The leadless imager device packaging structure  100  includes an integrated circuit  110  formed on a semiconductor substrate  112 . The integrated circuit  110  includes a pixel array (not shown) arranged adjacent a surface  114  of the integrated circuit  110  for detecting light and may also include peripheral circuitry (not shown) for capturing, digitizing, and processing image signals produced by the pixel array. 
         [0012]    The integrated circuit  110  is mounted inside a cavity  130  of the package formed by a first encapsulant  116   a , a second encapsulant  116   b , and a transparent plate  118 . The transparent plate  118  is formed of a transparent material, for example, glass, such as borosilicate glass, or transparent polymer, such as polycarbonate. The transparent plate  118  is arranged such that light may enter the leadless imager device packaging structure  100  through an opening  126  in the first encapsulant  116   a  and impinge upon the pixel array. The transparent plate  118  is coupled to the first encapsulant  116   a  by a sealant  120 . A leadframe  122  is arranged in first encapsulant  116   a . The leadframe  122  includes first conductor traces  122   a  to be electrically coupled to the integrated circuit  110  and second conductor traces  122   b  to be electrically coupled to an external device. The second conductor traces  122   b  have a flat portion  134  over a flat portion  136  of the first encapsulant  116   a.    
         [0013]    The first conductor traces  122   a  of the leadframe  122  may be coupled to the integrated circuit  110  by interconnect materials such as bumps  124 , which may be formed of an electrically conductive material such as solder, and pads  132 , which are part of the integrated circuit  110  and which may be formed of electrically conducting materials such as gold, copper, or aluminum. The integrated circuit  110  is bonded to the first conductive traces  122   a  by the solder bumps  124 . The first conductor traces  122   a  of the leadframe  122 , the integrated circuit  110 , pads  132 , and bumps  124  may also be further held together using one or more adhesives  128 , such as Anisotropic Conductive Film (ACF), Anisotropic Conductive Paste (ACP), Non-conductive Film (NCF), and Non-conductive Paste (NCP). 
         [0014]    An example method of making a leadless imager device packaging structure  100  in accordance with an embodiment is now described.  FIG. 2   a  shows a step in which the leadframe  122  is attached to the first encapsulant  116   a  to form an integrated structure which has an opening  126  therein. The first encapsulant  116   a  and the leadframe  122  surround the opening  126 . The integrated structure of the first encapsulant  116   a  and the leadframe  122  may be accomplished through injection molding or transfer molding. The first encapsulant  116   a  may be formed of ceramic, plastic, epoxy, or other molding compounds known in the art. In one embodiment, the first encapsulant may be a liquid crystalline polymer or other material having a high modulus and high temperature resistance. The encapsulant may be particle-free to prevent contamination on the pixel array ( FIG. 1 ).  FIG. 2   b  shows a top-down view of the first encapsulant  116   a , leadframe  122 , and opening  126  of  FIG. 2   a . The embodiment shown in  FIG. 2   b  shows three first conductor traces  122   a  and second conductor traces  122   b  on each side of the packaging structure  100 , but other embodiments may have more or fewer conductor traces depending on the number of connections needed to the integrated circuit  110 . 
         [0015]    After the leadframe  122  is attached to the first encapsulant  116   a , a transparent plate  118  is attached to a lower flat surface of the first encapsulant  116   a  as shown in  FIG. 3 , forming the cavity  130 . The transparent plate  118  may be attached to encapsulant  116   a  using a sealant  120 . The sealant may be, for example, an epoxy or acrylic resin, and may be cured by heat or ultraviolet light. The cavity  130  may be filled with a transparent material such as air or an inert gas, or may be a vacuum. 
         [0016]    Next, as shown in  FIG. 4 , the integrated circuit  110  is mounted on the leadframe  122 . The integrated circuit  110  is flipped upside-down in a configuration known as “flip-chip” packaging. In one embodiment, the integrated circuit  110  may be a type of integrated circuit known as a “Quad Flat package No leads” (QFN). A QFN has no leads extending out from the integrated circuit  110 . Interconnect material, such as pads  132  and solder bumps  124  are used to electrically couple the integrated circuit  110  to the first conductor traces  122   a  using heat compression bonding, such as ultrasonic bonding, or flip-chip bonding. 
         [0017]    One or more adhesives  128 , such as Anisotropic Conductive Film (ACF), Anisotropic Conductive Paste (ACP), Non-conductive Film (NCF), and Non-conductive Paste (NCP), may be used to couple the integrated circuit  110  to the leadframe  122  and first encapsulant  116   a . If ACF or NCF is used, the ACF and NCF may be pre-cut and attached to the first conductor traces  122   a . If ACP, NCP, or a type of underfill is used, the ACP or NCP or underfill may be dispensed onto the first conductor traces  122   a.    
         [0018]    After mounting the integrated circuit  110 , the integrated circuit may be encapsulated, for example by dispensing or by a Boschman processes, with a second encapsulant  116   b , which may be the same or different material than the first encapsulant  116   a  used to form the cavity  130 . 
         [0019]    The integrated circuit  110  is thus partially encapsulated by the first encapsulant  116   a  and the second encapsulant  116   b  and is further encapsulated by the transparent plate  118 . The integrated circuit  110  will therefore be protected within the package while still allowing light to reach the pixel array  114 . Furthermore, the half-encapsulated packaging structure allows the transparent plate  118  to be located close to the pixel array, which may provide better optical performance in an imager device. In one embodiment, the leadless imager device packaging structure  100  may be fabricated using existing leadframe molding equipment and known cost effective molding materials. 
         [0020]    The above description and drawings illustrate embodiments, which achieve the objects, features, and advantages described herein. However, it is not intended that the invention be strictly limited to the described and illustrated embodiments. For example, although embodiments have been described as being useful for producing an imager device, it should be appreciated that embodiments could be used to mount other types of integrated circuits as well, including, but not limited to, integrated circuits requiring an input light transmission. Furthermore, although the method embodiments have been described with regard to one package, it should be appreciated that multiple packages may be formed by this process at one time.