Abstract:
An electronic package device is disclosed including a microelectronic package and a heat sink positioned over the microelectronic package. A thermal interface element is positioned between the microelectronic package and the heat sink. The thermal interface element is elongated and has differing thicknesses along its length to enhance the dissipation of heat.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a thermal interface element for an electronic package device, and more particularly, to a thermal interface element for conducting heat between a microelectronic package and a heat sink. 
       BACKGROUND OF THE INVENTION 
       [0002]    Typical microelectronic or microprocessor packages have an undesirable thermal resistance between the package and an adjacent heat sink. A cause of this high thermal resistance is a thermal interface material which forms a layer having a thickness over the lid or cover of a housing containing the microprocessor die. The lid housing the microprocessor is typically flat, and the layer of interface material between the lid and the heat sick conforms to the surface of the lid and is therefore of a substantially uniform thickness. 
         [0003]    It would therefore be desirable to enhance thermal conduction between a heat sink and microprocessor package. It would also be desirable to enhance thermal conduction without unduly structurally burdening the microprocessor package, and in a cost efficient manner. 
       SUMMARY OF THE INVENTION 
       [0004]    In an aspect of the present invention, an electronic package device includes a microelectronic package, a heat sink positioned over the microelectronic package, and a thermal interface element for dissipating heat. The thermal interface element is elongated and has differing thicknesses along a length, and the thermal interface element is positioned between the microelectronic package and the heat sink. 
         [0005]    In a related aspect, the thermal interface element is substantially concave. 
         [0006]    In a related aspect, the thermal interface element is substantially concave and conforming to a convex top surface of the microelectronic package. 
         [0007]    In a related aspect, the thermal interface element includes a middle region having a first thickness along a specified length of the element. 
         [0008]    In a related aspect, the thermal interface element includes a middle region having a first thickness along a first specified length of the element, and two end regions substantially continuous with the middle region each having a second thickness along second specified lengths of the element. 
         [0009]    In a related aspect, the first specified length of the element has a first thickness that is less than a second thickness of the second specified lengths of the element. 
         [0010]    In a related aspect, the microelectronic package includes a lid having a convex top surface and a flat bottom surface and the top surface is adjacent to and mates with the thermal interface element to provide a concavely shaped thermal interface element. 
         [0011]    In a related aspect, the thermal interface element is a liquid, film, paste or a gel which is secured to the microelectronic package and the heat sink by heat or pressure or a combination of both. 
         [0012]    In a related aspect, the microelectronic package includes at least one chip positioned in a cavity defined by the lid and chip carrier, the microelectronic package positioned over solder balls connected to a top surface of a circuit board. 
         [0013]    In a related aspect, the device further includes a thermal interface material (TIM) positioned over the at least one chip and contacting an underside of the lid. 
         [0014]    In a related aspect, the package further may include a plurality of chips. 
         [0015]    In a related aspect, the microelectronic package includes a lid having a convex top surface and a convex bottom surface. The top surface is adjacent to and mates with a first thermal interface element to provide a concavely shaped first thermal interface element. A second thermal interface element is positioned between the convexly shaped bottom surface of the lid and a chip or die within the microelectronic package to provide a concavely shaped second thermal interface element for dissipating heat. 
         [0016]    In another aspect of the invention, an electronic package device includes a microelectronic package including a lid having a convex bottom surface and a chip or die within the package. A heat sink is positioned over the lid of the microelectronic package. A thermal interface element for dissipating heat is elongated and has differing thicknesses along a length. The thermal interface element is positioned between the convexly shaped bottom surface of the lid and the chip or die to provide the thermal interface element with a concave shape for dissipating heat. 
         [0017]    In another aspect, a method for dissipating heat in an electronic package includes providing a microelectronic package; positioning a heat sink over the microelectronic package; positioning a thermal interface element between the microelectronic package and the heat sink for dissipating heat from the microelectronic package; and shaping a mating surface area of the microelectronic package to provide a varying thickness along a length of the thermal interface element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawing, in which: 
           [0019]    The FIGURE is a cross sectional side elevational view of a concavely shaped thermal interface element between a lid of a microelectronic package having a convex top surface and a heat sink according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    According to the present invention, an illustrative embodiment of an electronic package  10  is shown in the FIGURE. The electronic package  10  includes a heat sink  15  positioned over a microelectronic package  25  with a thermal interface element  20  therebetween. The microelectronic package  25  includes a lid  30  having a convex top surface  32  and a flat bottom surface  34 . The top surface  32  is adjacent to and mates with the thermal interface element  20  between the heat sink  15  and the top surface  32  of the lid  30 . The thermal interface element  20  is shaped concavely when conforming to the convex shape of the top surface  32  of the lid  30 . The microelectronic package  25  further includes the lid  30  attaching to a chip carrier  35  using feet  33 . The chip carrier  35  is electrically connected to solder balls  40  beneath the chip carrier  35 . The lid  30  and chip carrier  35  combination define a cavity  37  therebetween. 
         [0021]    Typically the lid  30  of the semiconductor package  25  is of metal or of another rigid material. The thermal interface structure  20  may be, for example, any substance which is flexible, compressible and provides for thermal heat transfer. The thermal interface structure  20  can be, for example, a liquid, film, paste or a gel which is secured to the microelectronic package and the heat sink by heat or pressure or a combination of both. The thermal interface element  20  may also be, for example, an adhesive which may be in liquid form, and which may also cure at room temperature or require heat, and singularly or in combination compression. 
         [0022]    The microelectronic package  25  further includes at least one chip  45  positioned in the cavity  37  on top of solder balls  50  which are connected to a top surface of the chip carrier  35 . A thermal interface material (TIM)  60  is positioned over the chip  45  and in adjacent contact with the lid  30 . In another embodiment, the chip  45  may be replaced with multiple chips. 
         [0023]    Further, the thermal interface element  20  has a thickness which varies in relation to the convex shape of the top surface  32  of the lid  30 . A middle region  70  of the element  20  has a first thickness  85  which is thinner than end regions  75   a,    75   b  which have a thickness  80 . The end regions  75   a,    75   b  thus have a second thickness  80  which is greater than the thickness  85  in the middle region  70 . Other geometric shapes of the element  20  would result in variable thicknesses at different regions along the length of the element and may also be used to enhance thermal conductivity. 
         [0024]    Referring to the FIGURE, the thickness  85  of the thermal interface structure  20  is minimalized by using the convex shaped top surface  32  of the lid  30 . The thermal interface structure  20  is thermally conductive and conforms to the convex top surface  32  of the lid  30  to form the thin region  70  of the thermal interface structure  20 . Thus, the thin region  70  provides an enhanced heat transfer region. Thereby, the present invention reduces thermal resistance between the package  25  and the heat sink  15 . The enhanced heat transfer allows the microprocessor  45 , and thereby the microelectronic package  25 , to operate at a cooler temperature. 
         [0025]    In alternative embodiment, the bottom surface  34  of the lid  30  may be shaped convexly in relation to the thermal interface material (TIM)  60  above the chip  45 . Thermally conductive material between the heat sink  60  and a convexly shaped inner side of the cover is thinner than a flat layer of conductive material similar to the conductive layer between the convex lid  30  cover and the heat sink  15  shown in the FIGURE. Thus, the thinner thermally conductive material enhanced thermal conductivity between the cover  30  and the thermal interface material (TIM)  60  above the chip  45 . 
         [0026]    While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in forms and details may be made without departing from the spirit and scope of the present application. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated herein, but falls within the scope of the appended claims.