Abstract:
In a package including an image sensor die with an interconnect extending therethrough, a cover allowing light to pass is coupled to the die using at least one solder ball and a corresponding number of pads on each of the cover and die. Such pads are added to the cover despite the die&#39;s interconnect allowing contact with external devices at a location distal from the cover. The solder balls help govern the parallel orientation (or an alternate orientation) between the die and the cover. In addition, connectors other than solder balls may be used; multi-layered covers with connectors between the layers may be used; and packages other than imagers may be assembled.

Description:
TECHNICAL FIELD  
       [0001]    Embodiments of the invention relate generally to semiconductor device packaging. More specifically, embodiments of the invention relate to imager device packaging. 
       BACKGROUND  
       [0002]    Imagers are devices configured to sense radiation and generate signals corresponding to an image based on that radiation. Imagers include complimentary metal oxide semiconductor (CMOS) imagers as well as charge coupled devices (CCDs). Such imagers may be constructed on and within a semiconductor substrate. These imagers may also be packaged in order to protect them from damage and contamination. Packaging may also redistribute an imager die&#39;s signal access points for easier communication with other devices. At least one portion of the package may be transparent to the radiation wavelengths the imager is configured to detect. For example, a glass lens or flat glass panel may be placed over a CMOS imager configured to detect visible light. 
         [0003]    In terms of attaching the glass to the die or to other parts of the package, background art includes U.S. Pat. No. 7,141,869, which suggests using a ring of solder bonded to a ring-shaped contact on the imager die as well as to a similarly-shaped contact, on the glass. Patent &#39;869 describes previous glass attachment attempts using a solid ring of solder and warns that air trapped between the ring, glass, and die may increase solder joint failure. Patent &#39;869 proposes using an initial open ring configuration that is eventually closed with polymer Patent &#39;869 also generally warns about how dispensing techniques and materials may contaminate the image sensing area. (&#39;869 at col. 10-11.) 
         [0004]    This current application further notes that techniques involving dispensing material from a needle or similar device may cause “spattering.” This may, in turn, result in contaminating the light sensitive portions of the imager. In addition, a sealant, around the Sight sensitive portions of the imager may subsequently introduce contaminants into the sealed area by way of outgassing. 
         [0005]    Returning to &#39;869, its glass has conductive traces and contacts thereon. As for &#39;869&#39;s imager die, illustrations depict conductive contacts only on the side of the die facing the glass. &#39;869 refers to prior art wherein contacts are on the opposite side of the die, but &#39;869 teaches that providing such involves critical drawbacks including the complexity of the structure and process, high manufacturing costs, and low yield. (&#39;869 at col 2-3;  FIG. 3 .) As a result, signals from a contact on &#39;869&#39;s imager die face travel through a solder ball to a contact on the glass; a conductive trace extends from the glass contact, along the surface of the glass, to a bigger contact on the glass; that bigger contact is in turn coupled to a bigger solder ball configured to communicate with external devices. 
         [0006]    U.S. Pat. No. 6,943,423 also discloses an imager die connected to glass by way of solder joints between contacts on the glass and contacts on the side of the imager die facing the glass. As in &#39;869, &#39;423&#39;s illustrations depict conductive contacts only on the side of its die facing the glass, &#39;423 refers to the same prior art discussed &#39;869, wherein contacts on the opposite side of the die involve many more process steps. (Compare &#39;869 at col. 2-3,  FIG. 3  with &#39;423 at col. 2,  FIG. 4 . It should also be noted &#39;869 and &#39;423 share the same inventor and assignee.) Concerning the contacts on &#39;423&#39;s glass, three sets of contacts are described: a first set for electrical interconnection with the die; a second set for electrical interconnection with external circuitry; and a third set for electrical interconnection with passive components such as decoupling capacitors. Patent &#39;423 also teaches isolating the light sensitive portions of the imager with flux around the solder joints. 
         [0007]    U.S. Pat. No. 6,864,116 ultimately seals the light sensitive portions of its imager using a polymer dust seal. Patent &#39;116 also discloses conductive paths extending from contacts on the die side facing the glass, through solder bumps, to contacts on the glass, along conductive traces on the surface of the glass, to bigger contacts on the glass and bigger solder bumps configured to communicate with external devices. As in the patents discussed above &#39;116&#39;s illustrations depict conductive contacts only on the side of its die facing the glass. &#39;116 refers to the same prior art discussed &#39;869 and &#39;423 concerning contacts on the opposite side of the die; and &#39;116 raises similar criticisms of such a configuration. (See &#39;116 at col. 1-2;  FIG. 2 .) 
         [0008]    Still other imager die include a contact in addition or alternative to a contact facing the transparent component. Such imager die include those having a conductor extending through the die in a direction generally perpendicular to the plane defined by the contact. U.S. Pat. No. 7,199,439 discloses such an imager die. Such a conductor may be referred to in the art as a “through silicon via,” a “through silicon interconnect,” or a “through wafer interconnect” (assuming the interconnect was formed on a wafer-scale workpiece). That conductor may be coupled to a conductive contact on the die side facing away from the glass. That contact may, in turn, be directly connected to a solder ball. As an addition or alternative, that contact may be coupled to a conductive trace leading to another contact with a solder ball thereon. 
         [0009]    Accordingly, there is a need in the art for improved alternatives for packaging those types of imager die as well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1A  is a cross-sectional view of an embodiment of the invention. 
           [0011]      FIG. 1B  is a perspective view of that embodiment. 
           [0012]      FIGS. 2-5  depict embodiments directed to forming a device. 
           [0013]      FIGS. 6-8  picture device embodiments of the invention. 
           [0014]      FIG. 9  is a top-down view of a wafer used in an embodiment of the invention. 
           [0015]      FIGS. 10-18  picture device embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]      FIG. 1A  illustrates an embodiment of the invention, wherein the embodiment includes a die  2 . For purposes of explanation and not limitation, the die  2  is assumed to be a CMOS imager formed in and on a workpiece made of a semiconductor such as silicon. The die  2  may support a layer of patterned resist which forms a color filter array  4 . The color filter array  4  may be divided into segments  5 , wherein each segment  5  may be colored to detect a certain wavelength of visible light. A microlens  6  may be located over one or more segments  5  of the color filter array  4 . Other components may be fabricated within the die  2 , such as at least one photodiode (not shown) in the form of a doped silicon region. That region may coincide with a depth corresponding to where a photon having a certain wavelength may be absorbed by the silicon, thereby generating an electron-hole pair. Also formed on and within the die  2  include transistors and capacitors (not shown) respectively configured to move and store the generated electron. Still other transistors may be included as part of peripheral circuitry (not shown). Eventually, an electric signal resulting from the absorption of a photon may end up at an electrically conductive contact  8  on the surface  10  of the die  2 . This contact  8  is coupled to an interconnect  12  extending through the die  2  in a direction generally perpendicular to the plane defined by the surface  10  of the die  2 . 
         [0017]    The interconnect  12  may be formed using techniques known in the art. One such technique involves removing material, including silicon, under the contact  8  (and perhaps removing a portion of the material forming contact  8  itself). Removal may be accomplished using a dry etch, wet etch, laser, or combinations thereof. Further, the removal process may be begin at the surface  10  or the opposing surface  1 . 4  of the die  2 . If the removal process begins at the surface  10 , the removal process may not extend ail the way through the die; and the surface  14  of the die  2  may be ground away until the opening is exposed. 
         [0018]    An electrical insulator (not shown) may be used to line the opening defined by the removal process. An electrical conductor may then extend through the opening. The conductor may fill the opening. Alternatively, the conductor may only line the opening. In such an alternative, a non-conductor may be added to fill the remainder of the opening for support. As still another alternative, a wire may extent through the opening using techniques such as those taught in U.S. Published Application 2006/0228825. Formation of interconnect  12  may occur before, during, or after fabricating the imager components discussed above. 
         [0019]    The interconnect  12  extends to the surface  14  of the die  2 . Electrical connection with external devices may be established at that point, but often the connection point, is relocated in order to accommodate the conductive terminals of the external devices. As a result, a conductive redistribution trace  16  may be added. Again, techniques are known in the art for adding such. For example, a continuous electrical conductor may be added to the surface  14  of the die  2  and then etched according to a patterned resist. Alternatively, a damascene process may be employed, wherein a continuous electrical insulator may be added to the surface  14  of the die  2 , with trenches etched from the insulator according to a patterned resist. An electrical conductor may then be added in the trenches. 
         [0020]    Regardless of how the trace  16  is formed, it may be covered for the most part by a passivation layer  18 , which exposes the trace  16  in at least one region where contact with an external device may be desired. In that region, a solder ball  20  may be added. 
         [0021]    Despite the connection provided by solder ball  20  on the side  14  of the die  2  facing away from the glass  26 , this embodiment adds a solder ball  22  to the contact  8  on the surface  10  of the die  2  facing the glass  26 . Further in spite of the connection provided by solder ball  20 , a conductive contact  24  is added to the glass  26 . 
         [0022]    Adding the conductive contact  24  to the glass  26  may be accomplished using techniques known in the art. One such technique involves sputtering aluminum or copper onto the glass  26 . Photoresist may be added and patterned to cover the contact sites, and the uncovered metal may be etched. If aluminum is sputtered, a nickel-palladium or nickel-palladium-gold alloy may be electrolessly plated so that the contact  24  may be sufficiently wettable with respect to the solder bail  22 . If copper is sputtered, it alone may exhibit sufficient wettability, and plating may not be performed. Given the connection provided by solder ball  20  on the side  14  of the die  2  facing away from the glass  26 , a conductor extending from the conductive contact  24  and along glass  26  for connection with external devices may not be needed; and the time, money, and effort of adding such a conductive extension may be saved or applied elsewhere in this embodiment. As a result, the contact  24  of this embodiment may be considered to be in “pad” form—defining no predominant axis of extension, in contrast to a trace or a trace/pad combination. In this embodiment, the pad is generally square-shaped from a top-down point of view. 
         [0023]    The conductive contact  24  is located on glass  26  such that, when the glass  26  and die  2  are combined, the contact  24  is aligned with the solder ball  22 . Adhesion between the glass  26  and the die  2  may be assisted by the cohesion of solder ball  22  as well as the wettability of solder ball  22  with respect to the conductive contact  24  and the contact  8 /interconnect  12 . 
         [0024]    Moreover, it is noted that commercially available solder balls tend to be sufficiently consistent in size. For example, solder balls touted as having a certain size may vary by only five microns in diameter. As a result, the solder ball  22  may assist in keeping the glass  26  generally parallel to the die  2 . Given the length and width of the glass  26  and die  2 , as well as the size of the solder ball  22 , some embodiments use more than one solder ball  22  to assist in keeping the glass  26  generally parallel to the die  2 . In addition, some embodiments locate the solder balls  22  toward the periphery of the glass  26  and die  2 . In such embodiments, the parallel nature of the glass  26  and die  2  may be established to the point where the glass  26  height from the die  2  may differ by at most 5 microns from one end of the glass  26  to the other. 
         [0025]    Still further, known techniques for placing solder bails tend to be a relatively clean process—without the spattering that may be associated with techniques using needles or other dispensers. 
         [0026]    Moreover given the size and location of the of the solder balls  22 , adjacent solder balls  22  define an opening  27  therebetween, as seen in  FIG. 1B . In at least one embodiment, that opening is maintained at least to the point where the die  2 /glass  26  combination is attached to another substrate, such as a printed circuit board (PCB) (not shown) configured to fit inside a camera or other product. Once the solder balls  22  have been placed between the die  2  and glass  26  and experienced a reflow temperature, they may experience such temperatures again briefly (10-20 seconds, for example) during reliability testing or while the die  2 /glass  26  combination is attached to a PCB. If flux was used in the soldering process, some outgassing may occur, but the opening  27  defined by the solder balls  22  may prevent the gas from being trapped near the light-sensitive portions of the die  2 . If gold is used as a pad material, there may be no flux and therefore no outgassing. In addition, the opening  27  defined by the solder balls  22  may assist in some embodiments with undesirable cracking or flexing if the die  2 /glass  26  combination, either alone or as part of larger product, is subjected to a pressure change. 
         [0027]    Once the die  2 /glass  26  combination is attached to a PCB, underfill may or may not be added between the die  2  and the PCB. Additional covering (not shown) may be placed around the die  2 /glass  26 /PCB in preparation for (or as part of) incorporating that combination into a larger product. Such covering may help prevent contamination from passing through the opening  27  defined by adjacent solder balls  22  to the light-sensitive portions of the imager. 
         [0028]    Furthermore, even though the contacts  24  on the glass  26  and the solder balls  22  do not carry signals to external devices, such components in at least some embodiments may address coefficient of thermal expansion (CTE) mismatch. Once the die  2 /glass  26  combination is attached to a PCB and heated, there may be a tendency for the die  2  to expand more or faster than the PCB. The result may be a tearing of the solder ball  20 . However, the contacts  24  on the glass  26  and the solder balls  22  in some embodiments may help the glass  26  to restrain the thermal expansion of die  2 , thereby helping to maintain the integrity of solder ball  20  and the reliability of the product. 
         [0029]    To further detail an embodiment of the invention concerning a method of forming the devices addressed above, a plurality of imagers may be formed on and in a silicon substrate in the form of a wafer, which may be generally circular in shape from a top-down view. Wafers that are commercially available as of the time of writing this application include those having a diameter of 200 mm or 300 mm.  FIG. 2  illustrates a wafer  28  comprising at least one die site  2 ′.  FIG. 3  illustrates the wafer  28  after a certain amount of processing, where color filter array  4 ; microlenses  6 ; doped regions, circuitry including transistors and capacitors (not shown); contacts  8 ; and interconnects  12  have been added at or within a plurality of die sites  2 ′. Solder balls  22  may be added to the contacts  8 /interconnects  12 . The wafer  28  may then be diced into separate die  2 . Testing of the imagers may be performed before and after dicing, and the die  2  that pass testing may be placed on FIG.  4 &#39;s second wafer  30  comprising at least one glass site  26 ′ having a scale similar to that of die  2 . It is noted that second wafer  30  has undergone a process, such as a molding or patterned etching, to define at least one lens shape. Redistribution traces  16 , a passivation layer  18 , and solder balls  20  may then be added on the surface  14  of the die  2  using the procedures mentioned above. Alternatively, the redistribution traces  16 , passivation layer  18 , and solder bails  20  may be added to the die  2  before attaching to the glass and, indeed, before singulating the die  2 . Dicing the second wafer  30  may then result in the device illustrated in  FIG. 1 . 
         [0030]    One of ordinary skill in the art can appreciate that additional embodiments of the invention address modifications from the embodiments addressed above. For example, embodiments include those wherein joining the glass  26  and die  2  occur while one or both are in singulated form, partial wafer form, or wafer form. Moreover, “wafer form” may include a workpiece such as that illustrated in  FIG. 5 , wherein singulated elements (glass  26  or die  2 ) populate an adhesive (and possibly flexible) material  32  surrounded by a generally rigid frame  34  having a perimeter comparable to that of wafer  28  or  30 . 
         [0031]    Further, concerning the method of combining the die  2 , solder ball  22 , and glass  26 ; the solder ball  22  may be initially added to the contact  24  of glass  26 , and the glass  26 /solder hall  22  combination may then be connected to the die  2 . 
         [0032]    As for the glass  26 , embodiments include those pictured in  FIG. 6 , where the portion of glass  26  over the color filter array  4  is flat rather than defining a curved lens. Moreover, as illustrated in  FIG. 7 , there may actually be a plurality of glass components  26 ,  26 ′,  26 ″ over the die  2 ; the glass components may have contacts  24  on the glass top and bottom; and solder balls  22  may be used to help provide parallelism between the neighboring elements. 
         [0033]    Adding contacts on the top and bottom may be achieved by processing one side of the glass  26  as described above while it is part of wafer  30 , then placing the processed side of wafer  30  on an adhesive carrier, and subsequently processing the now-exposed second side of wafer  30 . Glass  26  may then be singulated from the rest of wafer  30  using a dicing technique such as those involving a saw, a laser, or a combination thereof. Regardless of whether the adhesive carrier remains intact or is diced is well, the carrier material may ultimately be delaminated from glass  26 , leaving a glass  26  having contacts  24  on both of the major sides. Alternatively, wafer  30  may be singulated after processing one side but before processing the other, and singulated glass  26  components may be placed on a carrier such as that illustrated in  FIG. 5  for further processing. 
         [0034]    Still further, the glass  26  may not include integral supports  36  spacing the glass  26  from the die  2  or another glass component  26 ′. Rather, as shown in  FIG. 8 , the glass  26  may be adhered to a discrete spacer  38  which, in turn, includes an electrically conductive contact  40  such that, when the spacer  38  and die  2  are combined, the contact  40  is aligned with the solder ball  22 . 
         [0035]    As for fabricating the spacer  38 , that may begin with FIG.  9 &#39;s workpiece  42  having a perimeter comparable to that of wafer  28  or  30 . Although not required, the workpiece  42  may be made of silicon, glass, or of some other material that generally matches the CTE of glass  26 . A contact  40  may be added at the periphery of a spacer site  38 ′ of the workpiece  42  in much the same manner contact  24  is added to glass  26 . A window  44  may be etched through the workpiece  42  in a location central to the spacer site  38 ′. Eventually the spacer site  38 ′ may be singulated from the rest of the workpiece  42 , resulting in spacer  38  as illustrated in  FIG. 10 . However, assembly of the spacer  38  with die  2  and glass  26  may take place while any of those elements are in wafer form, partial wafer form, or die form. Additionally, in joining spacer  38  with die  2 , the solder balls  22  may initially be added to either spacer  38  or die  2 . 
         [0036]    Furthermore, spacer  38  may have contacts  40  on opposite sides, as illustrated in  FIG. 11 . Adding contacts on the opposite sides may be achieved in a manner similar to that which may be performed in order to process both sides of glass  26 , as described above. 
         [0037]    In another embodiment, illustrated in  FIG. 12 , the solder ball  22  acts as a spacer in place of the fabricated structure  38  illustrated in  FIGS. 8 ,  10 , and  11  or FIG.  7 &#39;s integral supports  36  spacing the glass  26 . 
         [0038]    In still another embodiment, a conductive contact  8  may not be needed in a particular region of the die  2  as a terminal for an electric signal. Nevertheless a conductive contact  8  may be added to couple to a solder ball  22 . In such an embodiment the contact  8  and interconnect  12  need not be coupled to circuitry on or within the die  2 . In yet another embodiment illustrated in  FIG. 13 , a contact  8 ′ is added without forming an accompanying interconnect, and the contact  8 ′ is not coupled to any other portion of the circuitry of the die  2 . 
         [0039]    As indicated above, embodiments of the invention include connectors that are generally spherical before placing them on the contact of the die  2 , glass  26 , or spacer  38  and may wet to the contacts thereon. Such connectors include gold/tin-based solder balls, indium-based solder balls, and generally lead free solder balls. In such embodiments, the contacts of the die  2 , glass  26 , or spacer  38  may be nickel, nickel-palladium, nickel-palladium-gold, or at least include an outer layer of such materials. Still other connectors that may be used in embodiments of the invention include a polymer bead from Sekisui Chemical Company; for example, that polymer bead may be located within a solder ball, in addition, embodiments include those where the connector may be in stud form at least before connection. For instance, in one embodiment a solder stud may be placed on the die  2  or glass  26  (or spacer  38 ) through electroplating before connection, but that stud may melt into a sphere as part, of the connection process. Another example involves a copper stud, which may stay in pillar form throughout the processes. In such an embodiment, tin may be plated onto the copper stud to wet to the contacts. 
         [0040]    As noted above, commercially available solder balls are generally consistent in size in that balls touted has having a certain diameter may vary within tolerances acceptable to embodiments of the current invention. In general, minor variations in solder ball height may be addressed by the force applied by other solder balls. As a result, if one solder ball is slightly larger than others connecting the glass  26  and the die  2 , the other balls may cause the larger solder ball to compress to a greater degree, and sufficient parallelism may be maintained in embodiments where such is desired. However, in some embodiments, non-parallelism may be desired. In which case, solder bail size and location may be arranged so that neighboring glass  26 , die  2  and spacer  38  elements define an angle. In  FIG. 14 , glass components  1426 ,  1426 ′, and  1426 ″ are respectively attached to die  1402 ,  1402 ′, and  1402 ″, which are in turn attached to PCB  1400 ; and die/glass combinations located closer to the perimeter of the PCB  1400  define more of an angle. This is achieved by using different sized solder balls  1422  to attach the glass to its respective die. 
         [0041]    Other embodiments address non-CMOS imager devices, wherein the die  2  may be a CCD or some other radiation-sensing component. Still other embodiments address non-imager devices such as memory.  FIG. 15  illustrates a die  1502  that may include predominantly memory, such as DRAM, SRAM, or Flash memory. As an addition or alternative, die  1502  may include microprocessing circuitry. Die  1502  includes conductive contacts (not shown) that may allow electrical communication with other devices. The surface  1510  of die  1502  also includes at least one electrically conductive contact  1508  that may not be coupled to other conductors on or within the die  1502 . In the embodiment depicted in  FIG. 15 , there are a plurality of contacts  1508  on one side of the die  1502 . Die  1502 ′ may be a non-imager device of the same type as that of die  1502 , although embodiments include those wherein die  1502  and  1502 ′ are of different types. Die  1502 ′ includes a plurality of conductive contacts (not shown in  FIG. 15 ) on its surface  1514  and also on one side of the die  1502 ′. The conductive contacts on die  1502 ′ are located thereon such that, when the die  1502  and  1502 ′ are stacked in a shingle configuration (wherein a die overhangs or at most partially overlaps an underlying die), each die&#39;s contacts are aligned with the other die&#39;s contacts.  FIG. 16  illustrates the contacts  1508 ′ of die  1502 ′ connected to the contacts  1508  of die  1502  by way of solder balls  1522 . External devices may electrically communicate with the dies  1502  and  1502 ′ at regions exposed as a result, of the shingle configuration of the stack  FIG. 16  may be understood to depict a face-to-face die connection (wherein the circuitry of each die is formed on or near the same surface of the contacts) as well as a face-to-back die connection (wherein the circuitry of one of the die  1502 ,  1502 ′ is formed on or near the surface opposite that of the contacts). 
         [0042]    There are also embodiments of the shingle-stack type wherein the components of the stack are non-planar.  FIG. 17  illustrates a shingle stack wherein the solder ball  1708  size and location may be arranged so that the die  1702 ,  1702 ′,  1702 ″ are non-parallel, thereby defining a “tan” configuration.  FIG. 18  illustrates die  1802 ,  1802 ′, and  1802 ″ stacked along a common central axis in a non-shingle configuration., but the neighboring components of the stack are still non-planar due to the size and location of solder balls  1808 . Such embodiments may help in cooling the stack. 
         [0043]    The embodiments addressed above demonstrate to one of ordinary skill in the art that still other embodiments of the invention exist. Accordingly, embodiments of the invention are not limited except as stated in the claims.