Abstract:
An interposer for connecting a semiconductor and a circuit board includes an insulating material sheet, a through hole which is formed in the insulating material sheet and an elastic conductive contact which is formed from an elastic conductive sheet and provided in the through hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-223178 filed on Sep. 28, 2009, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiment discussed herein is related to an interposer and an electronic device. 
       BACKGROUND 
       [0003]    An interposer is used to connect terminal electrodes formed on a bottom surface of an integrated circuit to electrode patterns formed on a substrate in a process of mounting the integrated circuit on the circuit board. 
         [0004]    In a related art process of mounting a semiconductor Integrated Circuit (IC) on a circuit board, leads extending from side surfaces of an IC package are inserted in through holes of lands of a circuit pattern formed on the circuit board, and are electrically connected to the lands by soldering. Recently, the number of input/output terminals of the IC is increasing as IC integration density increases. In addition, higher frequency performance is in demand as operating frequency of the IC becomes high. In view of these recent trends, mounting an IC on a circuit board with higher density, with shorter connection distances and with narrower pitches is now increasingly demanded. 
         [0005]    In order to meet these demands, a technique has been proposed to mount input/output terminals on a circuit board using an interposer. The input/output terminals are arranged on a bottom surface of an IC package in a grid array pattern, which helps efficiently arrange the input/output terminals. An interposer is a high terminal density thin connector formed of an insulating material sheet having through holes formed at positions corresponding to the input/output terminals of the IC package arranged in a grid array pattern and having electric conductors (i.e., connectors) placed in the through holes for the conduction of the front and back surfaces of the insulation material. Terminal patterns are formed in a similar grid array pattern on the circuit board. Here, mounting of an IC package on a circuit board using an interposer will be described with reference to  FIGS. 1A to 1C . 
         [0006]      FIG. 1A  illustrates an interposer  2  to which the present application is applied being disposed between a circuit board  3  and an IC package  1 .  FIG. 1B  is a side view of  FIG. 1A . In  FIG. 1B , the interposer  2  is illustrated in cross section. Input/output terminals (i.e., electrodes)  4  are arranged in a grid array pattern on a back surface of the IC package  1 . Terminal patterns (i.e., electrodes)  6  are formed at positions opposite to the input/output terminals  4  on the circuit board  3  on which the IC package  1  is to be mounted. Although not illustrated, other circuit patterns and electronic parts are provided on the circuit board  3  for the connection with the terminal patterns  6 . 
         [0007]    The interposer  2  is disposed between the IC package  1  and the circuit board  3  to connect the input/output terminals  4  formed on the back surface of the IC package  1  to the terminal patterns  6  formed on the circuit board  3 . The interposer  2  is a high terminal density thin connector formed of an insulation material sheet (hereinafter, referred to as an interposer substrate) having through holes  9  formed at positions corresponding to the input/output terminals  4  of the IC package  1  arranged in a grid array pattern and having connectors  5  placed in the through holes  9 . The connectors  5 , which are of the same length, are electric conductors for the conduction of the front and back surfaces of the interposer substrate  8 . 
         [0008]    Usually, as illustrated in  FIG. 1C , the interposer  2  is attached to an inner side of a socket  7 , which in turn is mounted on the circuit board  3  by soldering or other means. The socket  7  facilitates mounting and dismounting of the IC package  1  on and from the circuit board  3 . 
         [0009]    In the thus-configured interposer  2 , the structure of the connectors  5  as conductors for the conduction of the front and back surfaces of the interposer substrate  8  is important. The connectors  5 , which will be pressed between the input/output terminals  4  formed on the back surface of the IC package  1  and the terminal patterns  6  formed on the circuit board  3 , elastically compressed by the pressure from the upper and lower sides for the conduction between the input/output terminals  4  and the terminal patterns  6 . 
         [0010]    Japanese Laid-open Patent Publication No. 2004-47986 discloses elastic connectors (“electrically conductive contacts” in the Document) that are made of foam metal or a combination of foam metal and an elastomer. Foamed metal is produced by various processes from electrically conductive metals, such as copper, copper alloy, silver, silver alloy, gold, nickel and molybdenum. The foaming process includes: bubbling gas through molten metal, stirring a foaming agent through the molten metal, consolidating metal powder with a particulate foaming agent, pressure infiltrating the molten metal into wax or a foam polymer precursor, and performing a vapor deposition process for the deposition of metal onto the foam polymer precursor. 
       SUMMARY 
       [0011]    According to an aspect of the embodiment, an interposer for connecting a semiconductor and a circuit board includes an insulating material sheet, a through hole formed in the insulating material sheet and an elastic conductive contact formed from an elastic conductive sheet and provided in the through hole. 
         [0012]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1A  illustrates an interposer to which the present application is applied being disposed between a circuit board and an IC package; 
           [0015]      FIG. 1B  is a side view, partially cross-sectioned, of  FIG. 1A ; 
           [0016]      FIG. 1C  is a side view in which the interposer illustrated in  FIG. 1B  is attached to a socket; 
           [0017]      FIG. 2A  is a perspective view illustrating an original shape of a mesh elastic conductive sheet used as an elastic contact according to the present application; 
           [0018]      FIG. 2B  is a perspective view of the mesh elastic conductive sheet of  FIG. 2A  which is being rolled up; 
           [0019]      FIG. 2C  is a perspective view of the assembly of the interposer of the present application illustrating a rolled mesh elastic conductive sheet being placed in one of through holes formed in an interposer substrate; 
           [0020]      FIG. 2D  is a partially enlarged sectional view of the mesh elastic conductive sheet illustrated in  FIG. 2C  assembled in the interposer; 
           [0021]      FIG. 2E  is a partially enlarged sectional view of the interposer illustrated in  FIG. 2D  connecting a pair of counter electrodes in a compressed state; 
           [0022]      FIG. 3A  is a partially enlarged plan view of an example of the interposer placed in one of the through holes in a case in which a longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  is shorter than an inner circumference of the through hole formed in the interposer substrate; 
           [0023]      FIG. 3B  is a partially enlarged plan view of an example of the interposer placed in one of the through holes in a case in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  equals to the inner circumference of the through hole formed in the interposer substrate; 
           [0024]      FIG. 3C  is a partially enlarged plan view of an example of the interposer placed in one of the through holes in a case in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  is slightly longer than the inner circumference of the through hole formed in the interposer substrate; 
           [0025]      FIG. 3D  is a partially enlarged plan view of an example of the interposer placed in one of the through holes in a case in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  is more than twice as long as the inner circumference of the through hole; 
           [0026]      FIG. 3E  is a partially enlarged plan view of an example of the interposer formed in a spiral shape and placed in one of the through holes in a case in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  is more than twice as long as the inner circumference of the through hole formed in the interposer substrate. 
           [0027]      FIG. 3F  is a partially enlarged plan view of an example of the interposer placed in a sectionally square-shaped through hole formed in the interposer substrate, in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  equals to a circumference of an inscribed circle of the square; 
           [0028]      FIG. 3G  is a partially enlarged plan view of an example of the interposer placed in a sectionally triangular-shaped through hole formed in the interposer substrate, in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  equals to a circumference of an inscribed circle of the triangle; 
           [0029]      FIG. 3H  is a partially enlarged plan view of an example of the interposer placed in a sectionally oval-shaped through hole formed in the interposer substrate, in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A  equals to a circumference of the oval; 
           [0030]      FIG. 4  is a perspective view of the assembly of an example of the interposer to be placed in a sectionally hexagonal-shaped through hole formed in the interposer substrate, in which the longitudinal dimension of the mesh elastic conductive sheet illustrated in  FIG. 2A , formed as a hollow hexagonal cylinder, equals to a circumference of the hexagon; 
           [0031]      FIG. 5A  is a plan view of a mesh structure of the mesh elastic conductive sheet according to a first embodiment; 
           [0032]      FIG. 5B  is a plan view of the mesh elastic conductive sheet illustrated in  FIG. 5A  which is rolled up and joined at edges to form a cylinder; 
           [0033]      FIG. 5C  is a side view of the cylindrical mesh elastic conductive sheet according to the first embodiment illustrated in  FIG. 5B ; 
           [0034]      FIG. 5D  is a partially enlarged sectional view of the interposer in which the mesh elastic conductive sheet according to the first embodiment illustrated in  FIG. 5C  is placed in one of the through holes; 
           [0035]      FIG. 6A  is a plan view of a mesh structure of the mesh elastic conductive sheet according to a second embodiment; 
           [0036]      FIG. 6B  is a plan view of a mesh structure of the mesh elastic conductive sheet according to a third embodiment; 
           [0037]      FIG. 6C  is a plan view of a mesh structure of the mesh elastic conductive sheet according to a fourth embodiment; 
           [0038]      FIG. 7A  is a partially enlarged plan view of the mesh elastic conductive sheet according to the first embodiment; 
           [0039]      FIG. 7B  illustrates the mesh elastic conductive sheet according to the first embodiment illustrated in  FIG. 7A  deformed under pressure; 
           [0040]      FIG. 7C  is a partially enlarged plan view of the mesh elastic conductive sheet according to the second embodiment; 
           [0041]      FIG. 7D  illustrates the mesh elastic conductive sheet according to the second embodiment illustrated in  FIG. 7C  deformed under pressure; 
           [0042]      FIG. 7E  is a partially enlarged plan view of the mesh elastic conductive sheet according to the third embodiment; 
           [0043]      FIG. 7F  illustrates the mesh elastic conductive sheet according to the third embodiment illustrated in  FIG. 7E  deformed under pressure; 
           [0044]      FIG. 7G  is a partially enlarged plan view of the mesh elastic conductive sheet according to the fourth embodiment; and 
           [0045]      FIG. 7H  illustrates the mesh elastic conductive sheet according to the fourth embodiment illustrated in  FIG. 7G  deformed under pressure. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0046]    Hereinafter, embodiments of an interposer according to the present application will be described in detail along with various examples with reference to the accompanying drawings. The interposer according to the present application has a function similar to that of the interposer  2  disposed between the IC package  1  and the circuit board  3  illustrated with reference to  FIGS. 1A to 1C . In the following description, components similar to those illustrated in  FIGS. 1A to 1C  will be denoted by the same reference numerals. 
         [0047]    First, a basic form of the interposer according to the present application will be described with reference to  FIGS. 2A to 2E .  FIG. 2A  illustrates an original shape of a mesh elastic conductive sheet  10  used as an elastic contact in the present application. The rectangular-shaped mesh elastic conductive sheet  10  may be made by etching elastic sheet metal, such as stainless steel. In this example, a width dimension H of the mesh elastic conductive sheet  10  is larger than the thickness of an interposer substrate  8  illustrated in  FIGS. 1A to 1C . In this example, a longitudinal length W of the mesh elastic conductive sheet  10  is slightly longer than an inner circumferential length of a through hole  9  formed in the interposer substrate  8  illustrated in  FIGS. 1A to 1C . 
         [0048]    Longitudinal edges of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  are rolled up in one direction as illustrated in  FIG. 2B  and joined to form a cylinder illustrated in  FIG. 2C . The cylindrical mesh elastic conductive sheet  10  is placed in one of the through holes  9  formed in the interposer substrate  8 . As described above, since the longitudinal length W of the mesh elastic conductive sheet  10  is slightly longer than the inner circumferential length of the through hole  9 , longitudinal edges of the cylindrical mesh elastic conductive sheet  10  slightly overlap each other. 
         [0049]      FIG. 2D  illustrates an interposer  20  in which the rolled mesh elastic conductive sheet  10  is placed in one of the through holes  9  formed in the interposer substrate  8 . Because of its elasticity, the mesh elastic conductive sheet  10  tries to unroll toward an inner circumferential surface of the through hole  9  when placed in the through hole  9 . Thus the mesh elastic conductive sheet  10  would not remove from the through hole  9  without any fixing measures. The mesh elastic conductive sheet  10  is placed in the through hole  9  in a manner such that projection height H 1  from an upper surface of the interposer substrate  8  and projection height H 2  from a lower surface are the same. However, the sameness in the projection heights H 1  and H 2  are not important because the projection height H 1  or H 2 , whichever is larger, will be pressed first when the interposer  20  is used so that the projection heights H 1  and H 2  will be the same eventually. 
         [0050]      FIG. 2E  illustrates the interposer  20  of  FIG. 2D  with an upper end attached to the IC package  1  and a lower end placed on the circuit board  3 . The upper end of the mesh elastic conductive sheet  10  of the interposer  20  is pressed against one of input/output terminals  4  of the IC package  1  and the lower end is pressed against one of terminal patterns  6  on the circuit board  3 . The mesh elastic conductive sheet  10  is compressed by the pressure force. Thus the input/output terminal  4  and the terminal pattern  6  are connected to each other via the mesh elastic conductive sheet  10 . A current path for the conduction is formed by multiple beams which constitute the mesh elastic conductive sheet  10 . 
         [0051]    Here, various forms (i.e., examples) of the mesh elastic conductive sheet  10  and the through hole  9  will be described with reference to  FIGS. 3A to 3H  and  4 . In  FIGS. 3A to 3H , dashed lines represent the mesh elastic conductive sheet  10 , of which edges marked with black circles. 
         [0052]      FIG. 3A  illustrates an example in which the longitudinal length W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  is shorter than the inner circumference of the through hole  9 . In this case, longitudinal edges of the mesh elastic conductive sheet  10  are disposed with a small gap therebetween. Although such a small gap is acceptable, a too large gap may help collapse the cylindrical mesh elastic conductive sheet  10  when pressed from upper and lower directions. 
         [0053]      FIG. 3B  illustrates an example in which the longitudinal length W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  equals to the inner circumference of the through hole  9 . In this example, longitudinal edges of the mesh elastic conductive sheet  10  are joined together. In this case, dimensional control is important because the mesh elastic conductive sheet  10  would not try to unroll after being placed in the through hole  9 . With the dimensional control, it is not necessary to join the longitudinal edges of the mesh elastic conductive sheet  10  even if the longitudinal length W of the mesh elastic conductive sheet  10  equals to the inner circumference of the through hole  9 . 
         [0054]      FIG. 3C  illustrates an example in which the longitudinal length W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  is slightly longer than the inner circumference of the through hole  9 . The example illustrated in  FIG. 3C  is similar to that illustrated in  FIGS. 2A to 2E  and description thereof will be omitted. 
         [0055]      FIG. 3D  illustrates an example in which the longitudinal dimension of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  is more than twice as long as the inner circumference of the through hole  9 . In this case, a double-wide current path is provided between the upper and lower ends of the cylindrical mesh elastic conductive sheet  10 , as compared with the examples illustrated in  FIGS. 3A to 3C . Such a wider current path has lower resistance values between the upper and lower ends of the cylindrical mesh elastic conductive sheet  10 . The double-rolled cylindrical elastic conductive sheet  10  may be obtained by rolling up a single mesh elastic conductive sheet  10  twice as described above or, alternatively, by rolling up two mesh elastic conductive sheets  10  in an overlapped manner. 
         [0056]      FIG. 3E  illustrates an example similar to that illustrated in  FIG. 3D , in which the longitudinal dimension of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  is more than twice as long as the inner circumference of the through hole  9 . In the example illustrated in  FIG. 3D , the mesh elastic conductive sheet  10  is placed in the through hole  9  in a simply rolled-up manner. In the example illustrated in  FIG. 3E , the mesh elastic conductive sheet  10  is formed to have a spiral shape during the rolling up process. Thus the mesh elastic conductive sheet  10  keeps a spiral shape when seen in a plan view. 
         [0057]      FIG. 3F  illustrates an example in which the through hole  9  formed in the interposer substrate  8  is square-shaped in cross section. In this case, the longitudinal dimension W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  may equal to the circumference of an inscribed circle of the square. The longitudinal edges of the mesh elastic conductive sheet  10  may or may not be joined together before the mesh elastic conductive sheet  10  is placed in the through hole  9 . 
         [0058]      FIG. 3G  illustrates an example in which the through hole  9  formed in the interposer substrate  8  is triangular-shaped in cross section. In this case, the longitudinal dimension W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  may equal to the circumference of an inscribed circle of the triangle. The longitudinal edges of the mesh elastic conductive sheet  10  may or may not be joined together before the mesh elastic conductive sheet  10  is placed in the through hole  9 . 
         [0059]      FIG. 3H  illustrates an example in which the through hole  9  formed in the interposer substrate  8  is oval-shaped in cross section. In this case, the longitudinal dimension W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A  may equal to a circumference of the oval. The longitudinal edges of the mesh elastic conductive sheet  10  may or may not be joined together before the mesh elastic conductive sheet  10  is placed in the through hole  9 . 
         [0060]      FIG. 4  illustrates an example in which the through hole  9  formed in the interposer substrate  8  is hexagonal-shaped in cross section. In this example, the longitudinal dimension W of the mesh elastic conductive sheet  10  illustrated in  FIG. 2A , formed as a hollow hexagonal cylinder and placed in the through hole  9 , equals to a circumference of the hexagon. The longitudinal edges of the mesh elastic conductive sheet  10  may or may not be joined together before the mesh elastic conductive sheet  10  is placed in the through hole  9 . 
         [0061]      FIG. 5A  illustrates a mesh elastic conductive sheet  11  according to a first embodiment. In the first embodiment, a mesh structure is constituted by rectangular holes arranged in a row in the longitudinal direction and in an array in the width direction. In the array, the rectangular holes in the odd number lines are displaced from those in the even number lines by the half length of each the rectangular holes.  FIG. 5B  illustrates a cylindrical mesh elastic conductive sheet  11  of  FIG. 5A  rolled up and joined at longitudinal edges thereof.  FIG. 5C  is a side view of the cylindrical mesh elastic conductive sheet  11  according to the first embodiment illustrated in  FIG. 5B .  FIG. 5D  illustrates the interposer  20  in which the mesh elastic conductive sheet  11  according to the first embodiment illustrated in  FIG. 5C  is placed in one of the through holes  9 . 
         [0062]      FIG. 6A  illustrates a mesh elastic conductive sheet  12  according to a second embodiment of the present application. In the second embodiment, a mesh structure is constituted by V-shaped holes  12 A arranged in a row in the longitudinal direction and in an array in the width direction.  FIG. 6B  illustrates a mesh elastic conductive sheet  13  according to a third embodiment of the present application. In the third embodiment, a mesh structure is constituted by zigzag slits  13 A arranged in a row in the longitudinal direction.  FIG. 6C  illustrates a mesh elastic conductive sheet  14  according to a fourth embodiment of the present application. In the fourth embodiment, a mesh structure is constituted by rhombus holes  14 A arranged with their oblique sides adjoining one another. 
         [0063]    As described above, the mesh elastic conductive sheet  10  used in the present application may include various mesh structures as illustrated in the first to fourth embodiments. With each of the structures, the mesh elastic conductive sheet  10  rolled up and placed in the through hole  9  may be compressed in the vertical direction when pressed in the vertical direction. 
         [0064]    This requirement is satisfied by any of the mesh elastic conductive sheets  11  to  14  according to the first to fourth embodiments illustrated in  FIGS. 5A to 5D  and  6 A to  6 C. In the mesh elastic conductive sheet  11  according to the first embodiment illustrated in  FIG. 7A , beams constituting the mesh structure bend in the vertical direction to absorb pressure force as illustrated in  FIG. 7B  when the mesh elastic conductive sheet  11  is pressed in the vertical direction. In the mesh elastic conductive sheet  12  according to the second embodiment illustrated in  FIG. 7C , beams constituting the mesh structure moves in the lateral direction as illustrated in  FIG. 7D  to absorb pressure force when the mesh elastic conductive sheet  12  is pressed in the vertical direction. 
         [0065]    In the mesh elastic conductive sheet  13  according to the third embodiment illustrated in  FIG. 7E , the slits  13 A are compressed along their lengths as illustrated in  FIG. 7F  to absorb pressure force when the mesh elastic conductive sheet  13  is pressed in the vertical direction. In the mesh elastic conductive sheet  14  according to the fourth embodiment illustrated in  FIG. 7G , beams constituting the mesh structure bend in the vertical direction to absorb pressure force as illustrated in  FIG. 7H  when the mesh elastic conductive sheet  14  is pressed in the vertical direction. 
         [0066]    As described above, the interposer related to the present application provides stability in multi-pin connection and high reliability with a simple structure. Thus the interposer according to the present application improves signal quality and reliability in mounted stacks of high speed and large sized packages, which may help develop devices of higher speed and higher density. 
         [0067]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.