Patent Publication Number: US-2007114646-A1

Title: Die package having an adhesive flow restriction area

Description:
FIELD OF THE INVENTION  
      The present invention relates to a die package; specifically, a die package having an adhesive flow restriction area.  
     BACKGROUND OF THE INVENTION  
      Integrated circuits, including dies, for example, imager dies such as charge-coupled-devices (CCD) and complementary metal oxide semiconductor (CMOS) dies, have commonly been used in photo-imaging applications. Such dies 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.  
      Dies are typically packaged and inserted into imaging devices such as, for example, a digital camera.  FIG. 1  illustrates a cross-sectional view of one conventional die package  100 . The die package  100  includes a die  14  positioned on a substrate  10 . The die  14  includes an array of pixels  16 . The die  14  typically has a transparent element  18  attached to a surface containing the array of pixels  16  by an adhesive material  24 .  
      In operation, light radiation enters the transparent element  18  of the die package  100 . The transparent element  18  filters out IR radiation that can cause color shifts due to cross talk between pixels in the array of pixels  16 . Light radiation is then adsorbed, and image signals are created by the array of pixels  16 , which converts the photons from light radiation to electrical signals. Wire bonds  13  conduct electrical output signals from the die  14  to wiring on the substrate  10 , which, in turn, connects to external circuitry (not shown). The external circuitry may include processing circuits for storing, compressing, manipulating, or displaying an acquired image.  
      The  FIG. 1  die package  100  is formed by placing the die  14  on the substrate  10 , applying adhesive material  24  on the periphery of the die  14 , and finally placing the transparent element  18  over the die  14 . The adhesive material  24  ensures that the transparent element  18  remains attached to the die  14 .  
      While the package illustrated in  FIG. 1  works well, the adhesive material  24  often interferes with the array of pixels  16 . During the process of attaching the transparent element  18  to the die  14 , adhesive material  24  often covers the edge pixels of the array of pixels  16 , as illustrated in  FIG. 1 . As the transparent element  18  is placed over the die  14 , capillary action, as well as the force pushing down on the adhesive material  24 , may force the adhesive material  24  onto the array of pixels  16 , thus interfering with the operation of the die  14 . This can lower the yield of packaged products and may affect the performance of packaged products which pass yield tests.  
      The problem may also be present in packaged dies fabricated to have display pixels, rather than pixels used to receive an image and convert it to electrical signals, resulting in poor visual quality.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention, in its various exemplary embodiments, provides a die package having an adhesive flow restriction area. In a first embodiment, the adhesive flow restriction area is formed as a trench in a transparent element. In a second embodiment the adhesive flow restriction area is comprised of a plurality of concentric trenches. In a third embodiment the adhesive flow restriction area is comprised of a plurality of trenches that extend from edge to edge of the transparent element. A fourth embodiment illustrates the adhesive flow restriction area comprised of a protuberance on a surface of the transparent element. In a fifth embodiment, the adhesive flow restriction area is comprised of a trench in a die. A sixth embodiment has a die with a plurality of concentric trenches comprising an adhesive flow restriction area. In a seventh embodiment, the adhesive flow restriction area is comprised of a protuberance on a die. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      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:  
       FIG. 1  illustrates a cross-sectional view of a conventional die package;  
       FIG. 2  illustrates a cross-sectional view of a die package constructed in accordance with a first exemplary embodiment of the invention;  
       FIG. 3  illustrates a top-down view of a surface of the  FIG. 2  transparent element constructed in accordance with the first exemplary embodiment of the invention;  
       FIGS. 4-9  illustrate cross-sectional views of stages in fabrication of the  FIG. 2  die package in accordance with the first exemplary embodiment of the invention;  
       FIG. 10  illustrates a top-down view of a surface of a transparent element constructed in accordance with a second exemplary embodiment of the invention;  
       FIG. 11  illustrates a cross-sectional view of a die package constructed in accordance with a third exemplary embodiment of the invention;  
       FIG. 12  illustrates a top-down view of a surface of the  FIG. 11  transparent element constructed in accordance with a third exemplary embodiment of the invention;  
       FIG. 13  illustrates a cross-sectional view of a die package constructed in accordance with a fourth exemplary embodiment of the invention;  
       FIG. 14 a  cross-sectional view of a die package constructed in accordance with a fifth exemplary embodiment of the invention;  
       FIG. 15  illustrates a cross-sectional view of a die package constructed in accordance with a sixth exemplary embodiment of the invention; and  
       FIG. 16  illustrates a cross-sectional view of a die package constructed in accordance with a seventh exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      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.  
      The terms “transparent element” or “transparent plate” refer to any material through which light radiation can pass, reflect, or refract. Materials that could form a transparent element include, but are not limited to, glass, for example, zinc selenide (ZnSe), boro-phospho-silicate glass (BPSG), phosphosilicate glass (PSG), borosilicate glass (BSG), silicon oxide, silicon nitride, or silicon oxynitride; an optical thermoplastic material such as tantalum pentoxide (Ta 2 O 5 ), titanium oxide (TiO 2 ), polymethylmethacrylate, polycarbonate, polyolefin, cellulose acetate butyrate, or polystyrene; a polyimide; a thermoset resin such as an epoxy resin; a photosensitive gelatin; or a radiation curable resin such as acrylate, methacrylate, urethane acrylate, epoxy acrylate, or polyester acrylate. The preceding materials are only illustrative examples.  
      The term “adhesive flow restriction area” refers to any structural feature, provided on one or both of a transparent element and a die, which impedes the flow of an adhesive. Exemplary embodiments of the invention illustrate the adhesive flow restriction area as one or more trenches or protuberances provided on at least one of the transparent element and die. The adhesive flow restriction area may be capable of breaking the wicking action of an aqueous solution into a small tube-like structure, or channel. The adhesive flow restriction area may be a separate channel which uses capillary action itself, and diverts aqueous solutions from one area to another. The adhesive flow restriction area may also include a raised structure, or protuberance, that prevents the aqueous solution from entering a channel that the solution may otherwise enter.  
      Referring now to the figures, where like reference numbers designate like elements,  FIG. 2  illustrates an exemplary die package  200  constructed in accordance with a first embodiment of the invention. Specifically, the  FIG. 2  die package  200  includes a die  14  containing an array of pixels  16  electrically connected to a substrate  10  by wire bonds  13 . The die package  200  includes an adhesive flow restriction area  30   a  formed in a lower surface  30   d  of a transparent element  30 , which faces the die  14 . The transparent element  30  is attached to the die  14  by an adhesive material  24 .  
      As illustrated, the adhesive flow restriction area  30   a  in the transparent element  30  is a trench, or channel, designed to fill with any excess adhesive material  24  that has been placed on a periphery  14   b  of the die  14  that might otherwise move onto and interfere with the array of pixels  16  on the die  14  or the wire bonding  13 . The adhesive flow restriction area  30   a  also interferes with any capillary action which might otherwise occur between the lower surface  30   d  of the transparent element  30  and an upper surface  14   a  of the die  14 . Because the adhesive flow restriction area  30   a  hinders the adhesive material  24  from wicking onto and covering pixels of the array of pixels  16  on the die  14 , by capillary action, the packaged structure may have improved image quality and a higher yield.  
      The illustrated configuration may also provide more stability to the overall die package  200 . In this regard, the adhesive material  24  located within the adhesive flow restriction area  30   a  trench acts as posts to stabilize the transparent lens  30  in the die package  200 . Because the surface of the adhesive material  24  is not flat, the transparent lens  30  is less prone to sliding off the adhesive material  24  during processing.  
       FIG. 3  illustrates a top-down view of a side of the  FIG. 2  transparent element  30  having the adhesive flow restriction area  30   a.  The illustrated adhesive flow restriction area  30   a  at least partially defines a predefined area  30   b  of the transparent element  30 . The predefined area  30   b  corresponds to the array of pixels  16  ( FIG. 2 ) on the die  14  ( FIG. 2 ), or an array area  17  (illustrated as dotted lines). Typically, the predefined area  30   b  is larger than the array area  17 . As described above with respect to  FIG. 2 , the adhesive flow restriction area  30   b  hinders the movement of the adhesive material  24  ( FIG. 2 ) onto pixels in the array of pixels  16  ( FIG. 2 ).  
      Although  FIG. 3  illustrates an adhesive flow restriction area  30   a  as a trench around an entire periphery of an array of pixels  16 , it should be noted that the adhesive flow restriction area  30   a  only needs to be provided where an adhesive material  24  ( FIG. 2 ) is used to connect the transparent element  30  to the die  14  ( FIG. 2 ). Accordingly, a continuous peripheral trench  30   a  may not always be needed.  
       FIGS. 4-9  illustrate stages of an exemplary embodiment of a method of forming the  FIG. 2  die package  200 . As illustrated in  FIG. 4 , a die  14  having an array of pixels  16  is positioned over a substrate  10 . The die  14  is electrically connected to conductive lines  7  on the substrate  10  by wire bonds  13 . The conductive lines  7  conduct electrical signals from the die  14  to external circuitry (not shown). For clarity&#39;s sake, the conductive lines  7  will be omitted from subsequent figures.  
       FIG. 5  illustrates adhesive material  24  deposited on the periphery  14   b  of the die  14 , outside of the periphery of the array of pixels  16 .  FIG. 6  illustrates the transparent element  30  over the die. The transparent element  30  is placed over the die such that a surface  30   d  having an adhesive flow restriction area  30   a  is facing the die  14 , as depicted by the patterned arrows. The trench forming the adhesive flow restriction area  30   a  could be formed by any method known in the art. For example, the adhesive flow restriction area  30   a  could be formed by chemical etching, reactive ion etching (RIE), sawing, or other means of creating an adhesive flow restriction area in the transparent element  30 .  
       FIG. 7  illustrates the movement of the adhesive material  24 . As the transparent element  30  is positioned over and attached to the die  14 , downward pressure, and capillary action, causes the adhesive material  24  to move towards the array of pixels  16 , as illustrated by the patterned arrows. As the transparent element  30  is further pressed onto the die  14 , as illustrated in  FIG. 8 , the adhesive material  24  moves further towards the array of pixels  16 , and the adhesive material  24  now moves into the trench of the adhesive flow restriction area  30   a  rather than over the array of pixels  16 , due in part to capillary action. The movement is further illustrated by the patterned arrows.  
       FIG. 9  illustrates the completed die package  200  including a transparent lens  30  attached to a die  14  by an adhesive material  24 . The adhesive material  24 , however, does not occlude an optical light path  11  (illustrated as dotted lines) to the array of pixels  16  due to the adhesive flow restriction area  30   a  preventing the movement of the adhesive material  24  onto the array of pixels  16 .  
      Although the process has been described with reference to first placing the adhesive material  24  (e.g.,  FIG. 4 ) onto the die  14  (e.g.,  FIG. 4 ), the adhesive material  24  could also first be placed on the transparent element  30  (e.g.,  FIG. 5 ) before it is attached to the die  14  (e.g.,  FIG. 5 ). The adhesive flow restriction area  30   a  (e.g.,  FIG. 8 ) may prevent the adhesive material  24  (e.g.,  FIG. 8 ) from moving onto the array of pixels  16  (e.g.,  FIG. 9 ). Additionally, the adhesive material  24  could hermetically seal a vacant space between the array of pixels  16  (e.g.,  FIG. 9 ) and the transparent element (e.g.,  FIG. 9 ); or the adhesive material  24  can be applied over only a portion of the periphery  14   b  of the die  14  (e.g.,  FIG. 9 ) rather than to completely surround the array of pixels  16 .  
       FIG. 10  illustrates a transparent element  50  in accordance with a second embodiment of the invention. The adhesive flow restriction area is comprised of a plurality of trenches  50   a ,  50   a ′,  50   a ″,  50   a ′″ to at least partially define a predefined area  50   b  corresponding to an array area  17 . The plurality of trenches  50   a ,  50   a ′,  50   a ″,  50   a ′″ extend from edge to edge of the transparent element  50 . As described above with respect to  FIGS. 7 and 8 , adhesive material  24  may enter the trenches  50   a ,  50   a ′,  50   a ″,  50   a ′″ rather than entering the array area  17  and occluding the light path to at least some of the pixels of the array of pixels  16 . Additionally, because the trenches  50   a ,  50   a ′,  50   a ″,  50   a ′″ extend to an edge of the transparent element  50 , the adhesive material  24  ( FIG. 7 ) could exit the trenches from the edge of the transparent element in the case that the trenches  50   a ,  50   a ′,  50   a ″,  50   a ′″ are full, thereby preventing any adhesive material  24  ( FIG. 8 ) from moving onto the array of pixels  16  ( FIG. 8 ). The illustrated transparent element  50  could be included in the  FIG. 2  die package  200 .  
       FIG. 11  illustrates a die package  300  constructed in accordance with a third embodiment of the invention. The illustrated die package  300  has a transparent element  40  having an adhesive flow restriction area comprising two trenches  40   a ,  40   a ′ which prevent the adhesive material  24  from occluding the optical light path  11  to the array of pixels  16 . Additionally, the illustrated die package  300  has a flip-chip design, in which conductive pads  38  electrically connect the die  14  to external circuitry (not shown) by conductive tape  36 . Although the trenches  40 ,  40 ′ are illustrated with a curved shape, this is not intended to be limiting, as any profile providing a space which can be filled with adhesive material  24  will work.  
       FIG. 12  illustrates a top-down view of the  FIG. 11  transparent element  40  constructed in accordance with the third embodiment of the invention. The illustrated transparent element  40  has an adhesive flow restriction area comprising two trenches  40   a ,  40   a ′ that define a predefined area  40   b . The predefined area  40   b  corresponds to the array area  17  (illustrated as dotted lines) on the die  14  ( FIG. 11 ). The trenches  40   a ,  40   a ′ fill with adhesive material  24  (e.g.,  FIGS. 7 and 8 ) during processing, as discussed above with respect to  FIGS. 4-9 . Thus, any adhesive material  24  which makes it past the outer peripheral trench  40   a  will be prevented from moving onto the array of pixels  16  by the inner trench  40   a′.    
       FIG. 13  illustrates a die package  400  constructed in accordance with a fourth embodiment of the invention. The illustrated die package  400  has an adhesive flow restriction area  60   a  formed on a transparent element  60 . The transparent element  60 , in turn, is placed over and attached to the die  14 . The illustrated adhesive flow restriction area comprises a protuberance in the form of a mesa  60   a  formed on a lower surface  60   b  of the transmitting element  60 , which prevents adhesive material  24  from moving onto the pixels of the array of pixels  16 . The protuberance  60   a  could have a flat surface, such as a mesa, a pointed surface, or a rounded surface. Additionally, the  FIG. 13  die package  400  has an adhesive material  24  that completely encapsulates the wire bonds  13 , for applications in which the complete protection of the wire bonds  13  is desired. The illustrated adhesive flow restriction area protuberance  60   a  could create a periphery around the periphery of the die  14 , or the protuberance  60   a  could be formed only on locations on the transparent element  60  where the adhesive material  24  is used to attach the transparent element  60  to the die  14 .  
       FIG. 14  illustrates a die package  500  constructed in accordance with a fifth embodiment of the invention. The illustrated die package  500  has an adhesive flow restriction area  70   a  formed within a modified die  70 . The adhesive flow restriction area comprises a trench on a surface of the modified die  70  having the array of pixels  16 . The adhesive flow restriction area  70   a  breaks any wicking force, thereby preventing any adhesive material  24  from moving onto the pixels of the array of pixels  16 . The adhesive flow restriction area trench  70   a  could completely surround a periphery of the array of pixels  16 , or could simply be provided only where the adhesive material  24  is used to attach the transparent element  18  to the die  70 .  
       FIG. 15  illustrates a die package  600  constructed in accordance with a sixth embodiment of the invention. The illustrated die package  600  has an adhesive flow restriction area comprising a plurality of trenches  80   a ,  80   a ′ formed on a surface of a modified die  80  having an array of pixels  16 . The plurality of trenches  80   a ,  80   a ′ that break the capillary action that might otherwise result in the adhesive material  24  moving onto the pixels of the array of pixels  16 . Thus, any adhesive material  24  which makes it past an outer peripheral trench  80   a  will be prevented from moving onto the array of pixels  16  by an inner peripheral trench  80   a ′. The trenches  80   a ,  80   a ′ could be formed to extend to an edge of the die  80 , so that if the trenches  80   a ,  80   a ′ fill with adhesive material  24 , any excess adhesive material  24  could exit from an edge of the die  80 .  
       FIG. 16  illustrates a die package  700  constructed in accordance with a seventh embodiment of the invention. The illustrated die package  700  has an adhesive flow restriction area comprising a protuberance in the form of a mesa  90   a  formed on a surface of a modified die  90  having an array of pixels  16 . As the transparent element  18  is positioned over and attached to the modified die  90 , the adhesive material  24  is prevented from moving onto the pixels of the array of pixels  16 , due, in part, to the adhesive flow restriction area  90   a . The illustrated adhesive flow restriction area protuberance  90   a  could create a periphery around the periphery of the array of pixels  16  on the die  90 , or the protuberance  90   a  could be formed only on locations on the die  90  where the adhesive material  24  is used to attach the transparent element  18  to the die  90 .  
      It should be noted that although the shapes of the trenches and protuberances comprising the adhesive flow restriction areas, e.g.,  30   a ,  40   a ,  50   a ,  50   a ′,  50   a ″,  50   a ′″,  60   a ,  70   a ,  80   a ,  80   a ′,  90   a , have been illustrated as rectangular or curved, the shapes of the adhesive flow restriction areas are inconsequential to the operation of the invention, and may constitute any shape such that adhesive material  24  (e.g.,  FIG. 16 ) is prevented from moving onto the array of pixels  16  (e.g.,  FIG. 16 ).  
      It should also be noted that the various embodiments of the invention may be used with dies (e.g.,  14 ,  70 ,  80 ,  90 ) which have an array of pixels  16  which converts an applied image to electrical signals, or to dies (e.g.,  14 .  70 ,  80 ,  90 ) for image display, which have an array of pixels  16  for generating an image in response to applied signals.  
      In addition, although each of the embodiments has been illustrated and described as having one trench or protuberance or two trenches or protuberances, this is not intended to be limiting. For example, a die package could be formed having a transparent element having an adhesive flow restriction area comprising two or more trenches. Similarly, a modified die could be formed having an adhesive flow restriction area comprising two or more concentric protuberances. Additionally, each trench or protuberance could be formed to extend from an edge to an edge of either a transparent element or die.  
      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.