Abstract:
An apparatus for providing heat sinks or heat spreaders for stacked semiconductor devices. Alignment apparatus may be included for the alignment of the stacked semiconductor devices. An enclosure may be used as the heat sink or heat spreader.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of application Ser. No. 09/344,284, filed Jun. 30, 1999, pending, which claimed the benefit of U.S. Provisional Application No. 60/091,156 filed Jun. 30, 1998. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an apparatus and method for providing heat sinks or heat spreaders for stacked semiconductor devices.  
           [0004]    2. State of the Art  
           [0005]    Semiconductor device packages or integrated circuit packages typically contain small integrated circuits on a silicon substrate, or the like, typically referred to as IC chips or die or dice. Such IC dice come in an infinite variety of forms, including, for example, Static Random Access Memory (SRAM) dice, Synchronous DRAM (SDRAM) dice, Static Random Access Memory (SRAM) dice, Sequential Graphics Random Access Memory (SGRAM) dice, flash Electrically Erasable Programmable Read-only Memory (EEPROM) dice, and processor dice.  
           [0006]    Packaged IC dice communicate with circuitry external to their packages through lead frames embedded in the packages. These lead frames generally include an assembly of leads that extend into the packages to connect to bond pads on the IC dice through thin wire bonds or other connecting means and extend from the packages to terminate in pins or other terminals that connect to the external circuitry. Exemplary conventional lead frames include paddle-type wore-bond lead frames, which include a central die support and leads which extend to the perimeter of IC dice and connect to the dice through thin wire bonds, Leads-Over-Chip (LOC) lead frames, having leads which extend over an IC die to attach to and support the die while being electrically connected to the die through wire bonds or other connecting means, and Leads-Under-Chip (LUC) lead frames, having leads which extend under an IC die to attach to and support the die from below while being connected to the die typically through wire bonds.  
           [0007]    As with all conductors, the leads in lead frames have an inductance associated with them that increases as the frequency of signals passing through the leads increases. This lead inductance is the result of two interactions: the interaction among magnetic fields created by signal currents flowing to and from an IC die through the leads and magnetic fields created by oppositely directed currents flowing to and from ground (known as “self” inductance).  
           [0008]    While lead inductance in IC packages has not traditionally been troublesome because traditionally slow signal frequencies have made the inductance relatively insignificant, the ever-increasing signal frequencies of state of the art electronic systems have made lead inductance in IC packages significant.  
           [0009]    In an attempt to eliminate such problems, IC die are being mounted on substrates, such as printed circuit boards, using flip-chip type mounting arrangements. This allows for a high density of mounting arrangements for the IC die in a small area and solder balls or conductive epoxy to be used for the connections between the IC die and the substrate. However, the high density of the IC die on the substrate with increased operating speeds for the IC die cause a great amount of heat to be generated in a small confined area which can be detrimental to the operation of the IC die and substrate as well as surrounding components. Such heat must be dissipated as effectively as possible to prevent damage to the IC die.  
           [0010]    Various arrangements have been suggested for use in dissipating heat from IC die on substrates.  
           [0011]    U.S. Pat. No. 5,239,200 illustrates an apparatus for cooling an array of integrated circuit chips mounted on a substrate comprising a thermally conductive cooling plate which has a plurality of integral, substantially parallel, closed-end channels for the circulation of a cooling medium therethrough.  
           [0012]    U.S. Pat. No. 5,379,191 is directed to an adapter for an integrated circuit chip which may be used in a package arrangement for the chip. The package may include a heat sink or heat spreader on the top of the chip.  
           [0013]    U.S. Pat. No. 5,396,403 is directed to a heat sink assembly for a multi-chip module. A thermally conductive plate is bonded to integrated circuit chips on a multi-chip module by indium solder. The plate, in turn, is thermally coupled to a heat sink, such as a finned aluminum member by thermal paste.  
           [0014]    U.S. Pat. No. 5,291,064 is directed to a packaged semiconductor device having a wired substrate. A plurality of semiconductor device chips are connected to the wiring substrate by the use of bumps. A heat sink is bonded through a high heat conductive bonding layer to a surface of each of the semiconductor device chips.  
           [0015]    However, in each instance of the prior art discussed above, the IC die or semiconductor devices are installed on the substrate in a single layer for the cooling thereof.  
           [0016]    A need exists for the cooling of semiconductor devices on a substrate where the substrates and devices are vertically stacked. In such an arrangement the dissipation of the heat from the semiconductor devices is of concern.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention is directed to an apparatus and method for providing heat sinks or heat spreaders for stacked semiconductor devices. Alignment apparatus may be included for the alignment of the stacked semiconductor devices. An enclosure may be used for the heat sink or heat spreader. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a view of a first embodiment of the present invention;  
         [0019]    [0019]FIG. 2 is a view of a second embodiment of the present invention;  
         [0020]    [0020]FIG. 3 is a view of a third embodiment of the present invention;  
         [0021]    [0021]FIG. 4 is a view of fourth embodiment of the present invention;  
         [0022]    [0022]FIG. 5 is a top view of a heat transfer member of the present invention;  
         [0023]    [0023]FIG. 6 is a top view of an alternative heat transfer member of the present invention;  
         [0024]    [0024]FIG. 7 is a top view of an alternative heat transfer member of the present invention;  
         [0025]    [0025]FIG. 8 is a top view of an alternative heat transfer member of the present invention;  
         [0026]    [0026]FIG. 9 is a view of a fifth embodiment of the present invention;  
         [0027]    [0027]FIG. 10 is a top view of the fifth embodiment of the present invention; and  
         [0028]    [0028]FIG. 11 is a view of the sixth embodiment of the present invention.  
     
    
       [0029]    The present invention will be better understood when the drawings are taken in conjunction with the description of the invention hereafter.  
       DESCRIPTION OF THE INVENTION  
       [0030]    Referring to drawing FIG. 1, a first embodiment  10  of the present invention is shown. The stacked assembly  10  having heat transfer members therewith is illustrated on a substrate  12 . The substrate  12  contains a plurality of apertures  14  therein in which the ends of alignment pins  16  are retained, such as using an interference fit, adhesive bonding, threaded connections, etc., the alignment pins  16  may be of any suitable material for use in the aligning of the substrates  12  having sufficient strength and heat conductivity, such as metal, high temperature plastic, etc. The substrate  12  further includes a plurality of circuit traces  18  thereon. Stacked on substrate  12  are a plurality of semiconductor device assemblies  100 , each assembly  100  including a semiconductor device  102  mounted on a substrate  104  having a plurality of circuits thereon connected to bond pads on the semiconductor device  102 . The substrate further includes a plurality of vias or circuits therein for connection to other adjacent substrates by suitable connections therewith. Such suitable connections may be made by the use of reflowed solder balls  106 . As illustrated, located between vertically adjacent assemblies  100  are heat transfer plates  50 . The heat transfer plates  50  are formed having apertures  52  therein through which alignment pins  16  extend and elongated slots  54  through which reflowed solder balls  106  extend to make contact with circuits on adjacent substrates  104 . The heat transfer plates  50  have a portion thereof in contact with the inactive surface of the semiconductor device  102  of the assembly  100  to transfer the heat therefrom during the operation of the semiconductor device  102 . If desired, a thermal grease may be applied to the inactive surface of the semiconductor device  102  and/or the portion of the heat transfer plate  50  which contacts the inactive surface of the semiconductor device  102  to facilitate the transfer of heat from the semiconductor device  102 . The elongated slots  54  have sufficient width to allow no electrical contact from the reflowed solder balls  106  extending therethrough. The reflowed solder balls  106  extending from the bottom surface of the substrate  104  of the lowest assembly  100  in the vertical stack electrically and mechanically contact circuit traces  18  on the upper surface of the substrate  12 . The alignment apertures  52  in the heat transfer plates  50  are typically circular to closely mate with the alignment pins  16  to align the heat transfer plates  50  on the substrate  12  which, in turn, aligns the assemblies  100  located between the heat transfer plates  50  on the substrate  12 .  
         [0031]    To provide additional heat transfer from the upper semiconductor device  102  which has no heat transfer plate  50  associated therewith a finned heat transfer member  60  having a plurality of fins  62  thereon and alignment apertures  64  therein is placed into contact with the inactive surface of the semiconductor device  102 . The fins  62  may be integrally formed on the heat transfer member  60  or may be secured thereto by any suitable means, such as welding, or the like. The fins  62  may extend in any desire direction of the heat transfer member  60  as desired. The alignment apertures  64  are used to locate the heat transfer member  60  using alignment pins  16  secured to the substrate  12 . A thermal grease may be applied to the inactive surface of the semiconductor device  102  and/or a portion of the lower surface of the heat transfer member  60  to aid in heat transfer from the semiconductor device  102 . If desired, a heat transfer plate  50  (shown in dotted lines) such as described herein, may be used between upper semiconductor device  102  and heat transfer member  60  for additional heat transfer from the upper semiconductor device  102 . If desired, a thermal grease may be used between the upper semiconductor device  102  and the heat transfer plate  50  and the heat transfer member  60 .  
         [0032]    Referring to drawing FIG. 2, a second embodiment  20  of the present invention is illustrated. The second embodiment  20  of the present invention being the same as the first embodiment  10  of the invention except as described hereinafter. A plurality of assemblies  100  are vertically stacked on a substrate  12  having a plurality of circuit traces  18  on the upper surface thereof and alignment pins  16  extending therefrom. The heat transfer plates  50  in the second embodiment of the invention illustrated include a plurality of annular heat conductive members  108  therebetween which are retained on the alignment pins  16  between adjacent heat transfer plates  50  in the plurality of vertically stacked assemblies  100 . The annular heat conductive members  108  may be comprised of any suitable material, such as easily deformable metal, a reinforced heat conductive elastomeric material, such as silicon rubber having an annular spirally wound spring  110  therein, etc. The annular heat conductive members  108  helping to transfer heat from one heat transfer plate  50  to an adjacent heat transfer plate  50  and to the heat transfer member  60  to provide an additional heat transfer path for the stacked assemblies  100 .  
         [0033]    Referring to drawing FIG. 3, a third embodiment  30  of the present invention is illustrated. The third embodiment  30  of the present invention is the same as the first embodiment  10  and second embodiment  20  of the present invention except as described hereinafter. The third embodiment  30  of the present invention includes a plurality of vertically stacked assemblies  100  connected to a substrate  12  being aligned thereon by alignment pins  16 . An additional heat transfer path for conducting heat from the individual semiconductor devices  102  connected to substrates  104  is provided by the inclusion of heat transfer spacers  112  located between adjacent heat transfer plates  50  and the bottom of adjacent substrates  104  of assemblies  100 . The heat transfer spacers  112  may be of any suitable material, such as an easily deformable metal, silicon rubber, an annular elastomeric member filled with thermal grease, etc. In this manner, heat transfer from the semiconductor device  102  is provided by heat transfer plate  50 , heat transfer member  60 , annular heat transfer members  108 , and heat transfer spacers  112  to the ambient atmosphere and through heat transfer member  60  to the ambient atmosphere.  
         [0034]    Referring to drawing FIG. 4, a fourth embodiment  40  of the present invention is illustrated. The fourth embodiment  40  of the present invention comprises vertically stacked assemblies  100  as described hereinbefore on substrate  12  using alignment pins  16 . The assemblies  100  are in contact with heat transfer plates  50  and heat transfer members  60 . If desired, annular heat transfer members  108  (show in dotted lines) may be used as well as heat transfer spacers  112  (shown in dotted lines) as described hereinbefore for the transfer of heat from semiconductor devices  102  during operation.  
         [0035]    Referring to drawing FIG. 5, a heat transfer plate  50  is illustrated. The heat transfer plate  50  is generally rectangular in shape having alignment holes  52  therethrough and having elongated slots  54  therein. The heat transfer plate  50  may be of any desired thickness sufficient for the effective heat transfer from semiconductor device  102  (not shown) in contact therewith.  
         [0036]    Referring to drawing FIG. 6, an alternative heat transfer member  50 ′ is illustrated, The alternative heat transfer member  50 ′ is generally shaped having the crossbars of the T&#39;s located at each end and the stems of the T&#39;s joined with alignment apertures  52  formed therein. In this manner, additional clearance for the reflowed solder balls  106  is provided.  
         [0037]    Referring to drawing FIG. 7, another alternative heat transfer member  50 ″ is illustrated. The heat transfer member  50 ″ is generally circular in shape having alignment apertures  52  therein and elongated slots  54  formed therein. The circular shape of the heat transfer member  50 ″ provides additional material for the transfer of heat away from the semiconductor device  102  (not shown) which contacts the member  50 ″.  
         [0038]    Referring to drawing FIG. 8, yet another alternative heat transfer member  50 ′″ is illustrated. The heat transfer member  50 ′″ is generally elipical in shape having alignment apertures  52  therein and elongated slots  54  formed therein. The circular shape of the heat transfer member  50 ′″ provides additional material for the transfer of heat away from the semiconductor device  102  (not shown) which contacts the member  50 ′″.  
         [0039]    Referring to drawing FIG. 9, a fifth embodiment  80  of the present invention is illustrated. The fifth embodiment  80  includes a plurality of vertically stacked assemblies  100 . Each assembly  100  includes a semiconductor device  102  mounted on a substrate  104  as described hereinbefore. Each assembly  100  being electrically and mechanically connected to an adjacent assembly  100  by means of reflowed solder balls  106  extending therebetween. Each substrate  104  of the assembly  100  having circuits thereon, circuits therein, and vias extending therethrough, as required, to make electrical contact as required with the semiconductor device  102 . Surrounding each substrate  104  is a heat transfer member  150 . Each assembly  100  is contained or installed or has extending therearound a heat transfer member  150 . The heat transfer member  150  comprises a member of suitable metal having downwardly extending retention T-shaped flanges  152 , upon a portion of which a substrate  104  sits, and upwardly extending L-shaped members  154 , the upper portion  156  serving as support for the assembly  100  located thereabove having a heat transfer member  150  located therearound. The portion  156  of L-shaped members  154  having an area  158  into which lower portion  160  of retention T-shaped flanges  152  extends to locate, position, and retain the heat transfer member  150  in position with respect to an adjacent heat transfer member  150  as well as locating and positioning the assembly  100  within the heat transfer member  150  with respect to an adjacent assembly  100  in its heat transfer member  150 .  
         [0040]    Referring to drawing FIG. 10, an assembly  100  having heat transfer member  150  located therearound is illustrated. In addition to retention T-shaped flanges  152  and L-shaped members  154  retaining the assembly  100  in the heat transfer member  150 , additional L-shaped members  164  are used on the other sides of the heat transfer member  150 , not illustrated in drawing FIG. 9, to retain the substrate  104  of the assembly  100  in position in the heat transfer member  150 . Some of the additional L-shaped members  164  extend over or above the assembly  100  while other L-shaped members  164  extend therebelow to act as a ledge or support for the substrate  104  of the assembly  100  when it is installed in the heat transfer member  150 . As illustrated, the reflowed solder balls  106  extend in two rows along two portions of the substrate  104 .  
         [0041]    Referring to drawing FIG. 11, a sixth embodiment  180  of the present invention is illustrated. The sixth embodiment  180  includes a plurality of assemblies  100  comprising substrates  104  having semiconductor devices  102  thereon, each substrate  104  being electrically and mechanically connected to an adjacent substrate  104  by reflowed solder balls  106  extending therebetween. The plurality of assemblies  100  are contained within an enclosure  170  having a plurality of vertical heat transfer fins  172  thereon and a plurality of horizontal heat transfer fins  174  extending thereacross. The lowermost assembly  100  is formed having substantially the same shape as opening  178  of the enclosure  170  so that the plurality of assemblies  100  may be retained therein, except for the bottom of the substrate  104  of the lowermost assembly  100  and the reflowed solder balls  106  thereon, and a seal  176  is used to sealingly engage the substrate  104  and enclosure  170  to form an enclosed, lead free member. The enclosure  170  may be made of any suitable material, such as metal, plastic, etc., and may be of any desired suitable geometric shape. Any desired number of heat fins  172  and  174  may be used on the enclosure  170 . The heat transfer fins  172  and  174  may have any desired shape suitable for use on the enclosure  170 . The heat transfer fins  172  and  174  may be integrally formed on the enclosure  170  or attached thereto using any desired suitable attachment devices, such as adhesives, soldering, etc. Any desired number of assemblies  100  may be used in the enclosure  170 , as desired. The enclosure  170  may be filled with a suitable heat transfer fluid, such as thermal grease, oil, etc.  
         [0042]    The present invention may include changes, additions, deletions, modifications which are within the scope of the invention.