Abstract:
An image sensor camera module includes a dielectric flex tape and a semiconductor die including an imager array. Die attach pads are formed along one edge of the die. The dielectric flex tape overlaps either the top or the bottom of the die, and connections between the die and the tape are made using solder bumps or wire bonds, for example. No supporting substrate other than the tape is required. A lensing structure can be attached directly to the die.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a compact semiconductor module, and, more specifically, to a chip size image sensor camera module.  
       BACKGROUND OF THE INVENTION  
       [0002]     Integrated circuits, including a semiconductor die such as charge-coupled-devices (CCD) and complementary metal oxide semiconductor (CMOS) sensors have commonly been used in photo-imaging applications. Such sensors typically contain thousands of pixel cells in a pixel array on a single chip. Pixel cells convert light into an electrical signal that can then be stored and recalled by an electrical device such as, for example, a processor.  
         [0003]     Semiconductor dies typically are packaged and inserted into imaging devices such as, for example, digital cameras.  FIG. 1  illustrates a conventional image sensor module  2 , shown in an exploded perspective view. Module  2  includes a semiconductor die  4  disposed on a cushion  6  and having series of bump pad connectors  8  located adjacent the four edges of the top surface of the semiconductor die  4 . Semiconductor die  4  includes a pixel array (not shown). Anisotropic conductive film (ACF)  10  connects flex tape  12  to die  4  and connectors  8 . Flex tape  12  contains electrical traces that link to a connector  14 , and has an opening  16  through which light travels to the pixel array. A stiffener  18  provides additional support to the module  2 . An infrared (IR) filter  20 , aligned in the optical path between the pixel array and a lens assembly  22 , is adhered onto the flex tape  12 . The lens assembly  22  includes a housing  24  supporting a lens barrel  26  containing a lens system for focusing light onto the pixel array.  
         [0004]     In operation, light radiation enters the lens barrel  26  of the module  2 . Harmful IR radiation is filtered out by the IR filter  20 . Light radiation incident on the pixel array of semiconductor die  4  is converted to electrical output signals by the circuitry on semiconductor die  4 . The electrical traces in flex tape  12  conduct the electrical output signals from the semiconductor die  4  to external circuitry (not shown) connected to connector  14 . The external circuitry may include processing circuits for storing, compressing, manipulating, or displaying an acquired image.  
         [0005]     While the package illustrated in  FIG. 1  works well, the assembly process includes several steps, and requires forming flex tape  12  with opening  16 . Also, the form factor of module  2  is increased in width and length by the placement of bond pads  8 . Thus, a semiconductor die package that has a smaller form factor, and which requires fewer assembly steps, is desired.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention, in its various exemplary embodiments, provides a chip size image sensor camera module in which a flex tape substrate having tape terminal pads on one end is connected to die attach pads located on one edge of an image sensor die. An IR filter can be adhered directly to the die. A camera lens structure completes the module. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The above-described features of the invention will be more clearly understood from the following detailed description, which is provided with reference to the accompanying drawings in which:  
         [0008]      FIG. 1  illustrates an exploded perspective view of a conventional semiconductor imager module;  
         [0009]      FIG. 2  illustrates a semiconductor die module, shown in side elevation, constructed in accordance with a first exemplary embodiment of the invention;  
         [0010]      FIG. 3  illustrates the semiconductor die module of  FIG. 2 , shown in top plan view;  
         [0011]      FIG. 4  illustrates a semiconductor die module, shown in side elevation, constructed in accordance with a second exemplary embodiment of the invention;  
         [0012]      FIG. 5  illustrates the semiconductor die module of  FIG. 4 , shown in top plan view;  
         [0013]      FIG. 6  illustrates a step of providing a semiconductor die for assembling an imaging device according to an exemplary embodiment of the present invention;  
         [0014]      FIG. 7  illustrates installing an infrared filter in a further step of assembling an imaging device according to an exemplary embodiment of the present invention;  
         [0015]      FIG. 8  illustrates attaching a flex tape substrate to a bottom surface of the semiconductor die in an alternative step of assembling an imaging device according to an exemplary embodiment of the present invention;  
         [0016]      FIG. 9  illustrates attaching a flex tape substrate to a top surface of the semiconductor die in an alternative step of assembling an imaging device according to an exemplary embodiment of the present invention; and  
         [0017]      FIG. 10  schematically represents a processor system including a semiconductor imaging device according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and show by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that structural, logical, and electrical changes may be made without departing from the spirit and scope of the present invention. The progression of processing steps described is exemplary of embodiments of the invention; however, the sequence of steps is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps necessarily occurring in a certain order.  
         [0019]     As used herein, the term “flexible substrate” is to be understood to include any material, including, but not limited to, epoxy, polyimide, polyester, or any other material capable of withstanding a 180° angle bend at a radius of at least ⅛″ or less. Similarly, a “flexible substrate” may be any material having substantially the same or equivalent properties as DuPont Kapton® or Oasis®. Specifically, the material may have a tensile strength of about 10 kpsi or greater, a tensile modulus of about 200 kpsi or greater, and/or an elongation property of about 25% or more (values based on ASTM D-882-83 Method A).  
         [0020]     Referring now to the drawings, where like reference numbers designate like elements,  FIGS. 2 and 3  illustrate an exemplary semiconductor die module  30  constructed in accordance with a first embodiment of the invention. Specifically,  FIG. 2  illustrates a side elevation view of the semiconductor die module  30 .  FIG. 3  illustrates a plan view of the semiconductor die module  30 . The semiconductor die module  30  has a flex tape substrate  32  supporting a semiconductor die  34 . Semiconductor die  34  contains a pixel array  35  ( FIGS. 6 and 7 ) made up of CMOS pixels, for example. Die attach pads  36  are formed on an upper surface along one edge of the semiconductor die  34 . The semiconductor die module  30  includes a lens barrel  37  containing a lens system for focusing light onto the pixel array  35 . Lens barrel  37  can be held in place by a lens holder  71  ( FIG. 8 ) attached directly to semiconductor die  34 , or to an infrared filter, as described further below. A polyimide stiffener  38  is provided at an end of the tape substrate  32  opposite to the end on which the semiconductor die  34  is attached. Traces  40  formed in or on the tape substrate  32  connect tape terminal pads  42  to connector pads  44 . Wire bonds  46  are attached between die attach pads  36  and tape terminal pads  42 . Module  30  can include a lead shield  48  surrounding lens barrel  37 . Storage capacitors  50  and  52  can be included in semiconductor die  34  on one side of the die under the area occupied by the die attach pads  36 . The benefits of module  30  are discussed below with respect to  FIGS. 6-9 .  
         [0021]     Referring next to  FIGS. 4 and 5 , an exemplary semiconductor die module  60  constructed in accordance with a second embodiment of the invention is shown. Specifically,  FIG. 4  illustrates a side elevation view of the semiconductor die module  60 .  FIG. 5  illustrates a plan view of the semiconductor die module  60 . The semiconductor die module  60  has a flex tape substrate  62  attached to semiconductor die  34 . Semiconductor die  34  contains a pixel array  35  ( FIGS. 6 and 7 ). Die attach pads  36 , formed on the upper surface along one edge of the semiconductor die  34 , preferably are bumped for connection to the tape substrate  62 , as described further below. The semiconductor die module  60  includes a lens barrel  37  containing a lens system for focusing light onto the pixel array  35 . Lens barrel  37  can be held in place by a lens holder (not shown) attached directly to semiconductor die  34  or to an infrared filter, as described further below. A polyimide stiffener  38  is provided at an end of the tape substrate  62  opposite to the end on which the semiconductor die  34  is attached. Traces  66  formed in the tape substrate  62  connect tape terminal pads  64  to connector pads  44 . Die attach pads  36  are connected directly, by reflow, tape automated bonding (TAB), or anisotropic conductive film (ACF), for example, to tape terminal pads  64 . Module  60  can include a lead shield  48  surrounding lens barrel  37 . Storage capacitors  50  and  52  can be included in semiconductor die  34  on one side of the die under the area occupied by the die attach pads  36 . The benefits of module  60  are discussed below with respect to  FIGS. 6-9 .  
         [0022]     Referring to  FIGS. 6-9 , a process of forming modules  30  and  60  begins by providing the semiconductor die  34 , illustrated in  FIG. 6 .  FIGS. 6 and 7  depict steps common to forming modules  30  and  60 , while  FIG. 8  shows additional assembly steps for module  30 , and  FIG. 9  shows additional assembly steps for module  60 . Semiconductor die  34  includes a pixel array  35  and die attach pads  36 . Referring to  FIG. 7 , an infrared (IR) filter in the form of IR cover glass  70  optionally is adhered directly to semiconductor die  34  over pixel array  35 , preferably using an epoxy adhesive  72  applied to adhere around the perimeter of the cover glass  70 , as shown in  FIGS. 8 and 9 . As noted, the steps described in connection with  FIGS. 6 and 7  are common to the assembly of both exemplary modules  30  and  60 . As a further option, a lens holder  71 , shown in  FIG. 8 , can be applied directly to the cover glass  70 . Alternatively, the cover glass  70  need not be installed, and the lens holder can be applied directly to semiconductor die  34 .  
         [0023]     Referring to  FIG. 8 , additional steps proceeding from those shown in  FIGS. 6 and 7  are shown for forming the module  30  according to an exemplary embodiment of the present invention. Module  30  is discussed above in connection with  FIGS. 2 and 3 .  FIG. 8  shows module  30  in a detailed side elevation view after flex tape substrate  32  is attached to semiconductor die  34 , and wire bonds  46  are installed to connect die attach pads  36  to tape terminal pads  42 . An encapsulant  74  can be applied, by a transfer mold process, for example, to further protect the module and lock the flex tape substrate  32  onto the semiconductor die  34 . Although flex tape substrate  32  is illustrated as completely overlapping the bottom surface of semiconductor die  34 , partial overlap of substrate  32  and die  34  also is contemplated by the present invention.  
         [0024]     Referring to  FIG. 9 , additional steps proceeding from those related to  FIGS. 6 and 7  are shown for forming the module  60  according to an exemplary embodiment of the present invention. Module  60  is discussed above in connection with  FIGS. 4 and 5 .  FIG. 9  shows module  60  in a detailed side elevation view after flex tape substrate  32  is attached to the top surface of semiconductor die  34 , and bump pads  36  are connected directly to tape terminal pads  42 . An underfill encapsulant  76  can be applied, by a transfer mold process, for example, to further protect the module  60  and lock the flex tape substrate  62  onto the semiconductor die  34 .  
         [0025]     The flex tape substrates  32  and  62  provide greater resistance to breakage during processing, while preserving the overall rigidity necessary for the placement of the semiconductor die  34 . While any flexible tape substrate  32 ,  62  can be used, exemplary preferred materials for the flex tape substrate  32 ,  62  include epoxy, polyimide, polyester, any other material capable of withstanding a 180° angle bend, preferably at a radius of at least ⅛″ or less, or any material having substantially the same or equivalent properties as DuPont Kapton® or Oasis®, for example, having a tensile strength of about 10 kpsi or greater, a tensile modulus of about 200 kpsi or greater, and/or an elongation property of about 25% or more (values based on ASTM D-882-83 Method A). Additionally, the flex tape substrate  32 ,  62  allows for a more compact design. Because the preferred flex tape substrate material is capable of withstanding a bend of 180° angle at a radius of at least ⅛″, the flex tape substrate  32 ,  62  can fold on top of itself to help space constraints in certain designs. A more compact design is achieved by the placement of die attach pads  36  along one edge of the semiconductor die  34 , thus eliminating extra width required in the conventional module to place connection pads around the entire periphery of the die. Assembly process steps also are eliminated by the design because it is not necessary to provide an opening through the flex tape substrate, and a substrate layer is eliminated. In addition, assembly is simplified, particular in the areas of making electrical connections, because electrical connections are formed only along one edge of the semiconductor die  34 , instead of around the entire periphery of the semiconductor die.  
         [0026]     The semiconductor die  34  is connected to the flex tape substrate  32 ,  62  in order to provide electrical communication between the semiconductor die  34  and an external device (not shown).  
         [0027]     The above-described semiconductor die modules  30 ,  60  are only a few exemplary embodiments of the present invention. For example, although the semiconductor die  34  is illustrated in module  60  as being on an end of the flex substrate  62 , the semiconductor die  34  could be placed anywhere along the length of the substrate  62 , and, therefore, the invention is not limited to the illustrated embodiments.  
         [0028]     Further, semiconductor die modules  30 ,  60  are illustrated with an optional IR cover glass  70  adhered directly to semiconductor die  34 ; however, the IR cover glass  70  could be supported by a frame, or replaced with an IR lens, eliminating the need for the IR cover glass  70  altogether. In certain applications, an IR filter  70  or lens are not needed at all.  
         [0029]     Similarly, the illustrated semiconductor die packages  30 ,  60  have conductive lines  40 ,  66  that are formed within the elastomeric substrate  32 ,  62 ; however, conductive lines  40 ,  66  may be formed on the surface of either the top or bottom side of the flex tape substrate  32 ,  62 .  
         [0030]     Each semiconductor die module  30 ,  60  could further include an optional conventional cushion  6  ( FIG. 1 ) formed underneath the semiconductor die module  30 ,  60 . The semiconductor die module  30 ,  60  can be coupled to peripheral circuitry (not shown), which includes a processor, for example, or inserted into a camera housing, thereby forming an imaging apparatus, e.g., a digital camera.  
         [0031]      FIG. 10  illustrates a diagram of a typical processor system  100  which includes a semiconductor assembly  30 ,  60 , described above. System  100  includes a processor  102  having a central processing unit (CPU) that communicates with various devices over a bus  104 . Some of the devices connected to the bus  104  provide communication into and out of the processor based system  100 ; an input/output (I/O) device  106  and the semiconductor assembly  30 ,  60  are examples of such communication devices. Other devices connected to the bus  104  provide memory, illustratively including a random access memory (RAM)  110  and a non-volatile memory  112 , e.g., a flash memory. The semiconductor assembly  30 ,  60  may receive control or other data from CPU  102  or other components of system  100 . The semiconductor assembly  30 ,  60  may, in turn, provide signals defining images to processor  102  for image processing, or other image handling operations.  
         [0032]     It should be noted that although the invention has been described with specific references to a semiconductor die package containing a semiconductor die with a pixel array, such as a CCD or CMOS sensor, the invention has broader applicability and may be used with any imaging or displaying semiconductor die. In the latter case, an image is displayed on the semiconductor die, and viewed through the lens system.  
         [0033]     The above description and drawings illustrate preferred embodiments which achieve the objects, features, and advantages of the present invention. Although certain advantages and preferred embodiments have been described above, those skilled in the art will recognize that substitutions, additions, deletions, modifications and/or other changes may be made without departing from the spirit or scope of the invention. Accordingly, the invention is not limited by the foregoing description but is only limited by the scope of the appended claims.