Abstract:
A mold for use in encapsulating an integrated circuit, wherein an encapsulant is injected into the mold during packaging of the integrated circuit. The improvement to the mold is a shaped member having an abutting surface for contacting a surface of the integrated circuit and thereby substantially preventing encapsulant from adhering to the surface of the integrated circuit, whereby the surface of the integrated circuit is left exposed. Because the surface of the integrated circuit is left exposed, the encapsulant used to encapsulate the integrated circuit does not form a thermal barrier between the integrated circuit and the exterior of the package. Thus, the packaged integrated circuit is able to more efficiently conduct heat away from the integrated circuit.

Description:
FIELD 
     This invention relates to the field of integrated circuits. More particularly this invention relates to increasing the thermal dissipation capacity of integrated circuit packages. 
     BACKGROUND 
     Integrated circuits, specifically monolithic integrated circuits, are typically packaged prior to use. The package provides a variety of benefits for the use of the integrated circuit. For example, the package tends to protect the integrated circuit from physical damage, such as chemical damage that may result from contact between the integrated circuit and materials in a corrosive environment, or mechanical damage that may result from the integrated circuit being forcefully contacted during shipping, use, or other handling. 
     The package for an integrated circuit may also provide the additional benefit of making electrical contact to the integrated circuit much easier to accomplish. This is generally done by providing electrical continuity between the very small and closely spaced electrical contacts on the integrated circuit and relatively larger and farther spaced electrical contacts on the outside of the package. 
     As integrated circuits operate, they tend to consume an amount of electricity that is used to operate the various electrical components of the integrated circuit. As the speed of integrated circuits increases, so also does the amount of electricity which they consume increase. The electricity consumed by an integrated circuit tends to be predominantly discarded as heat. Thus, as the speed of integrated circuits has increased, so to has the amount of heat which the integrated circuits produce increased. 
     Some integrated circuit manufacturing methods use molds to form the integrated circuit packages. The protective coatings of the package typically completely encompass the integrated circuit, wire bonds, and electrical contacts of the integrated circuit carrier or substrate. Unfortunately, the protective coatings also tend to function as an insulating layer, and may substantially impede thermal dissipation from the integrated circuit. Thus, the heat dissipation of such integrated circuit packages is degraded due to the configuration of the protective coatings of the package. 
     What is needed therefore, is system for protecting the sensitive components of the integrated circuit package without unduly impeding the heat dissipation capacity of the integrated circuit package. 
     SUMMARY 
     The above and other needs are provided by a mold for use in encapsulating an integrated circuit, wherein an encapsulant is injected into the mold during the manufacture of the integrated circuit. The improvement to the mold is a shaped member having an abutting surface for contacting a surface of the integrated circuit and thereby substantially preventing encapsulant from adhering to the surface of the integrated circuit, whereby the surface of the integrated circuit is left exposed. 
     Because the surface of the integrated circuit is left exposed, the encapsulant used to encapsulate the integrated circuit does not form a thermal barrier between the integrated circuit and the exterior of the package. Thus, the packaged integrated circuit is able to more efficiently conduct heat away from the integrated circuit. 
     In various preferred embodiments, only a portion of the surface of the integrated circuit is left exposed. Most preferably, any electrical connections on the surface of the integrated circuit are sealed within the encapsulant and not left exposed. The shaped member may be either an integral part of the mold, or a mold insert. In a most preferred embodiment the shaped member is formed of silicone. 
     In another aspect, the invention includes an integrated circuit packaged in an encapsulant, where the improvement is a void formed in the encapsulant, whereby at least a portion of a surface of the integrated circuit is exposed through the void in the encapsulant. In various embodiments, the integrated circuit may be either a flip-chip or a wire bonded chip. Further, a thermally conductive material may be disposed within the void formed within the encapsulant. The thermally conductive material preferably forms a heat conduction path to conduct heat away from the integrated circuit. In a most preferred embodiment, a heat sink is disposed adjacent the thermally conductive material. The heat sink absorbs and dissipates the heat conducted through the thermally conductive material. 
     In yet another aspect, the invention includes a method of packaging an integrated circuit in an encapsulant, where the improvement is the step of forming a void in the encapsulant, whereby at least a portion of a surface of the integrated circuit is exposed through the void formed in the encapsulant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
     FIG. 1 is a cross-sectional view of a prior art integrated circuit package including a molded body, 
     FIG. 2 is a cross-sectional view of an open mold and partially completed integrated circuit package in accordance with the invention, 
     FIG. 3 is a cross-sectional view of the closed mold encompassing the partially completed integrated circuit package in preparation for injecting encapsulant therein, in accordance with the invention, 
     FIG. 4 is a cross-sectional view of the completed integrated circuit package including a molded body in accordance with the invention, 
     FIG. 5 is a cross-sectional view of the integrated circuit package, including heat dissipation components, and 
     FIG. 6 is a cross-sectional view of another embodiment of the mold and partially completed integrated circuit package. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1 there is shown a cross-sectional view of a conventional integrated circuit package  13 , including a molded body  14 . The integrated circuit package  13  includes a substrate  26  whereupon one or more electrical interconnection systems  28  are disposed. A integrated circuit  30  is disposed upon a substrate  26 , and a layer of material  32  adheres the integrated circuit  30  to the substrate  26 . A plurality of wires  34  electrically connect contacts located on the top surface  36  of the integrated circuit  30  to the electrical interconnection systems  28 . 
     As depicted, the molded body  14  completely encompasses the integrated circuit  30 . The molded body  14  protects the electrical components of the integrated circuit package  13  from contamination and unwanted interaction with other electrical systems. However, due to the material properties of the molded body  14 , which generally include a relatively low thermal conductivity, the molded body  14  also operates as an insulating layer, limiting the thermal dissipation capacity of the integrated circuit package  13 . Due to the molded body  14 &#39;s low thermal conductivity, heat dissipation from the integrated circuit  30  to any external heat sink, such as the ambient environment or heat sink  8 , is substantially reduced. Since the integrated circuit package  13  tends to be unable to efficiently conduct heat away from the integrated circuit  30 , the life expectancy and operation of the integrated circuit package  13  is typically compromised. 
     With reference now to FIGS. 2 and 3, there is depicted a cross-sectional view of a partially completed integrated circuit package  10  and a mold in accordance with a preferred embodiment of the invention. FIGS. 2 and 3 depict the partially completed integrated circuit package  10  before the mold is used to create a protective molded body  14 . As described in greater detail below, the mold is preferably designed to create a protective molded body  14  that does not tend to degrade the thermal dissipation capacity of the complete integrated circuit package  13 . 
     Once the mold is used to create the protective molded body  14 , preferably during a latter manufacturing step, a complete integrated circuit package  13  is provided according to the manufacturing process. As described in greater detail below, the mold includes the structural features that define the structural topography of the protective molded body  14  when the mold is utilized during the manufacture of the integrated circuit package  13 . 
     With continuing reference to FIGS. 2 and 3, the mold includes a top mold piece  16  and a bottom mold piece  18 . During the manufacturing process, the top and bottom mold pieces  16  and  18  are located adjacent a partially completed integrated circuit package  10 . The top and bottom mold pieces  16  and  18  are constructed so that when the top and bottom mold pieces  16  and  18  are placed around a partially completed integrated circuit package  10 , the partially completed integrated circuit package  10  is fully preferably encompassed by the mold pieces  16  and  18 . However, other configurations of the top mold piece  16  and bottom mold piece  18  which do not completely encompass the partially completed integrated circuit package  10  are also contemplated, such as those in which the bottom mold piece  18  does not completely enclose the bottom of the partially completed integrated circuit package  10 . 
     The bottom mold piece  18  is preferably a substantially flat planar surface, providing a supporting base for the partially completed integrated circuit package  10  and the peripheral surfaces  19  which extend from the top mold piece  16 . Alternately, the inner surface of the bottom mold piece  18  is adapted to fit the configuration of the bottom of the substrate  26 , in those cases where the bottom of the substrate  26  is not flat. 
     The top mold piece  16  preferably includes a means for injecting an encapsulant into the mold, such as one or more through-holes  20  extending through the top mold piece  16 . The encapsulant may be in either a completely liquefied state or in a thixotropic state. The top mold piece  16  preferably also includes a lower formation surface  22 , bounded by the peripheral surfaces  19 . The lower formation surface  22  of the top mold piece  16  includes the structure that defines the topographical features of the protective molded body  14  during the molding process. As described in more detail below, the lower formation surface  22  of the top mold piece  16  preferably includes a shaped member  24  for defining additional features of the protective molded body  14 . Most preferably the shaped member  24  is formed of silicone, but may alternately be composed of other materials that are compatible with the processes and elements as described herein. 
     Alternatively, the shaped member  24  is a separate component distinct from the mold. In this arrangement, the shaped member  24  is strategically located adjacent the partially completed integrated circuit package  10  before disposing the mold to encompass the shaped member  24  and the partially completed integrated circuit package  10 . As described further below, the dimensions of the shaped member  24  correspond to the type of integrated circuit package  13  being manufactured. 
     The top and bottom mold pieces  16  and  18  are located to encompass the partially completed integrated circuit package  10  in preparation for injecting the encapsulant therein, as depicted in FIG.  3 . The partially completed integrated circuit package  10  is located on top of the bottom mold piece  18 . Thereafter, the top mold piece  16  is located over the partially completed integrated circuit package  10  and bottom mold piece  18 . The top mold piece  16  is preferably in place when its peripheral portions  19  are disposed adjacent the bottom mold piece and enclose the partially completed integrated circuit package  10 . 
     Once the top and bottom mold pieces  16  and  18  are in place, a space  38  is created about the partially completed integrated circuit package  10 . However, the shaped member  24  is shaped so that the top surface  36  of the integrated circuit  30  is substantially contacted by the abutting surface  40  of the shaped member  24 . The shaped member  24  preferably does not contact the various electrical components located on the top surface  26  of the integrated circuit  30 . This physical arrangement between the abutting surface  40  of the shaped member  24  and the top surface  36  of the integrated circuit  30  preferably leaves no space therebetween in which encapsulant can flow during a subsequent injection step. It is preferred that the shaped member  24  be shaped according to the top surface dimensions of the integrated circuit  30  so that the wires  34  remain within the space  38  defined by the mold and partially completed integrated circuit package  10 . Thus, when encapsulant is injected into the mold  12  the wires  34  are covered by the encapsulant, and thereby protected by the encapsulant. 
     Once the top and bottom mold pieces  16  and  18  are in place so that the abutting surface  40  of the shaped member  24  is adjacent the top surface  36  of the integrated circuit  30 , an injection mechanism injects the encapsulant into the mold. Preferably, the encapsulant is a thermoplastic resin, but may be some other encapsulant as known in the art. The encapsulant is preferably injected such as through the through-holes  20  of the mold and into the space  38  defined by the mold, the partially completed integrated circuit package  10 , and the shaped member  24 . 
     As the encapsulant is injected into the space  38 , the encapsulant flows around the partially completed integrated circuit package  10 , encompassing a number of electrical components thereon. As described above, however, the abutting surfaces  40  and  36  preferably prevent the encapsulant from flowing over and adhering to a substantial portion of the top surface  36  of the integrated circuit  30 . Once the encapsulant is sufficiently cured the mold is removed from the complete integrated circuit package  13  as depicted in FIG.  4 . 
     As shown in the cross-sectional view of FIG. 4, the complete integrated circuit package  13  includes the protective molded body  14 . According to the invention, the protective molded body  14  is distinguished from the conventional protective coatings by the exposed portion  42  of the top surface  36  of the integrated circuit  30  which remains after removing the mold. The protective molded body  14  covers and protects the wires  34 , electrical interconnection system  28 , at least portions of the substrate  26 , and at least a portion  43  of the integrated circuit  30 . 
     The unique structure of the protective molded body  14  tends to allow the integrated circuit package  13  to dissipate heat in a highly efficient manner. It should be noted that the present invention is useful for a variety of integrated circuits, including flip-chips and wire bonded integrated circuits, and the invention is not intended to be limited to only the specific examples detailed herein. 
     Referring now to FIG. 5, the integrated circuit package  13  may receive a thermally conductive material  44  that at least partially covers the exposed portion  42  of the top surface  36  of the integrated circuit  30 . Preferably, the thermally conductive material  14  is selected so as to not damage the integrated circuit  30  in any manner, or to interfere with the proper operation of the integrated circuit  30 . The thermally conductive material  44  preferably provides a medium for efficient heat conduction from the integrated circuit  30  of the integrated circuit package  13 . Once the thermally conductive material  44  is in place, a heat sink  46  may be placed in contact with the thermally conductive material  44 , for absorbing and dissipating the heat conducted through the thermally conductive material  44 . 
     It is appreciated that it may be desirable in some applications to leave the top surface  42  of the integrated circuit  30  exposed. In this manner, the circulation of air or other fluid of the ambient environment is used to convect the heat produced by the operation of the integrated circuit  30  away from the integrated circuit  30 . 
     An alternate embodiment of the invention is shown in FIG.  6 . According to this alternate embodiment, the shaped member  24  is a separate component from the top mold piece  16 , such as a mold insert, which is disposed between the partially completed integrated circuit package  10  and the top mold piece  16 . 
     In this alternate embodiment, the partially completed integrated circuit package  10  includes a flip-chip integrated circuit  30 . Again, the shaped member  24  is fashioned to abut against the upper surface  36  of the flip-chip integrated circuit  30 . The flip-chip  30  preferably does not have wire bonded connections on the upper surface. Instead, the flip-chip  30  is connected to the substrate  26  and the electrical interconnection system  28  through an arrangement of electrical connections  50 , such as the solder bumps depicted. Accordingly, the shaped member  24  is configured so that the abutting surface  40  preferably contacts substantially all of the upper surface  36  of the flip-chip integrated circuit  30 , since there are no wires to design around in this embodiment. 
     The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as is suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.