Patent Publication Number: US-6906921-B2

Title: Channeled heat dissipation device and a method of fabrication

Description:
This application is a continuation application of application Ser. No. 10/387,654, entitled “A Channeled Heat Dissipation Device and a Method of Fabrication”, filed Mar. 12, 2003 now U.S. Pat. No. 6,747,873. 

   BACKGROUND 
   Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. As these goals are achieved, microelectronic dice become smaller. Accordingly, the density of power consumption of the integrated circuit components in the microelectronic die has increased, which, in turn, increases the power requirements of other board level components that may be associated with the microelectronic die, such as voltage regulators, which may perform power delivery, for example. If the temperature of these associated components becomes too high, the components may be damaged or destroyed. 
   Various apparatus and techniques have been used and are presently being used for removing heat from microelectronic dice. One such heat dissipation technique involves the attachment of a high surface area heat sink to a microelectronic die.  FIG. 6  illustrates an assembly  200  comprising a microelectronic die  202  (illustrated as a flip chip) physically and electrically attached to a substrate carrier  204  by a plurality of solder balls  206 . A heat sink  208  is attached to a back surface  212  of the microelectronic die  202  by a thermally conductive adhesive  214 . The heat sink  208  is usually constructed from a thermally conductive material, such as copper, copper alloys, aluminum, aluminum alloys, or any suitable combination thereof. The heat generated by the microelectronic die  202  is drawn into the heat sink  208  (following the path of least thermal resistance) by conductive heat transfer. 
   High surface area heat sinks  208  are generally used because the rate at which heat is dissipated from a heat sink is substantially proportional to the surface area of the heat sink. The high surface area heat sink  208  usually includes a plurality of projections  216  extending substantially perpendicularly from the microelectronic die  202 . It is, of course, understood that the projections  216  may include, but are not limited to, elongate planar fin-like structures and columnar/pillar structures. The high surface area of the projections  216  allows heat to be convectively dissipated from the projections  216  into the air surrounding the high surface area heat sink  208 . A fan  218  may be incorporated into the assembly  200  to enhance the convective heat dissipation. However, although high surface area heat sinks are utilized in a variety of microelectronic applications, they may not provide heat dissipation for associated components that may be attached to the substrate carrier  204  (not shown). Additionally, heat sinks such as this may reduce or block airflow to components on a substrate, thereby causing areas of air stagnation, which may result in inadequate heat dissipation for one or more of these components. 
   Therefore, it would be advantageous to develop apparatus and techniques to effectively remove heat from a microelectronic die while providing some capability for heat dissipation for other components associated with the die. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter regarded as embodiments of the claimed subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. Embodiments of the claimed subject matter, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
       FIG. 1  is a side cross-sectional view of a first embodiment of a heat dissipation device attached to a microelectronic die, according to the present invention; 
       FIG. 2  is an oblique view of the cross-sectional view of the heat dissipation device, according to the present invention; 
       FIG. 3  is an alternate side cross-sectional view of a second embodiment of a heat dissipation device attached to a microelectronic die, according to the present invention; 
       FIG. 4  is a side cross-sectional view of a third embodiment of a heat dissipation device attached to a microelectronic die, according to the present invention; 
       FIG. 5  is a bottom plan view of various components of a substrate that may be incorporated as part of the present invention; and 
       FIG. 6  is a side cross-sectional view of a heat dissipation device attached to a microelectronic die, as known in the art. 
   

   DETAILED DESCRIPTION 
   Embodiments of the claimed subject matter may comprise a channeled heat dissipation device and a method of fabrication. One particular embodiment of the claimed subject matter may comprise a heat dissipation device having a base portion, wherein the base portion has a dissipation surface and a substantially opposed mounting surface, and at least one channel formed in the base portion thereof. In this embodiment, the at least one channel may allow air from a fan to flow through the base portion to the substrate carrier, providing airflow to one or more components formed thereon. 
   It is worthy to note that any reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the claimed subject matter. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
   Numerous specific details may be set forth herein to provide a thorough understanding of the embodiments of the claimed subject matter. It will be understood by those skilled in the art, however, that the embodiments of the claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments of the claimed subject matter. It can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the claimed subject matter. 
   Referring now in detail to the drawings wherein like parts are designated by like reference numerals throughout, there is illustrated in  FIG. 1  a microelectronic assembly  100  of the claimed subject matter comprising a heat dissipation device  102  attached to a microelectronic die  104  (illustrated as a flip chip). The microelectronic die has an active surface physically and electrically attached to the primary side  109  of a substrate carrier  108  by a plurality of solder balls  106 , although, in alternative embodiments, the microelectronic die may be electrically attached by use of a socket (not shown). The base portion  118  of the heat dissipation device has a mounting surface  114 , and a heat dissipation surface  116 . The mounting surface  114  of the base portion  118  of the heat dissipation device  102  is attached to the back surface of the microelectronic die  104 , preferably by a thermally conductive adhesive (not shown), as known in the art. Although the heat dissipation device is illustrated as being attached to a microelectronic die  104 , the claimed subject matter is not so limited. The heat dissipation device  102  may be attached to any surface from which removal of heat is desired. Furthermore, the heat dissipation device  102  may be constructed from a thermally conductive material such as copper, aluminum, alloys thereof, and the like. Numerous methods for formation may be incorporated to fabricate a device such as heat dissipation device  102 , including die casting, machining, or molding, but the claimed subject matter is not limited to any particular method of formation. 
     FIG. 2  shows an oblique view of a heat dissipation device  102 , shown in a non-mounted configuration. As shown in  FIGS. 1 and 2 , the heat dissipation device comprises a base portion  118  with a mounting surface  114  and an opposing dissipation surface  116 . A plurality of projections  112  may be formed on the heat dissipation device  102 , and may extend substantially perpendicular from the base portion dissipation surface  116 . The projections may include elongate planar fin-like structures or columnar/pillar structures, and may be formed during the formation of the heat dissipation device, for example. Heat dissipation device  102  may preferably be formed in a molding process, but numerous other methods or combinations of methods of formation may be used in accordance with at least one embodiment. 
   As shown in  FIGS. 1 and 2 , a plurality of channels  110  may extend from the dissipation surface  116  to an opposing mounting surface  114  of the base portion  118  of the device  102 . At least one channel  110  may be substantially perpendicular to the base portion dissipation surface  116 , although numerous configurations may be used in alternative embodiments. In this particular embodiment, a plurality of channels  110  are formed around the periphery of the base portion  118  of the device  102 . The method of formation of these channels may vary, and any method or combination of methods of formation that results in at least one channel being formed in the base portion of a heat dissipation device is in accordance with the claimed subject matter. One method of formation may comprise a series of saw processes, where a sawing tool is applied to selected areas of the base portion  118  of the device  102 , resulting in the formation of a plurality of channels  110 . Additionally, one or more drill processes may be used to form one or more channels  110 , or the channels may be formed in the initial molding process of the device  102 , for example. It may be desirable, in the formation of one or more channels  110 , to provide a portion of the mounting surface  114  free of one or more channels at least as large as the top surface of a microelectronic device  104 , in order to ensure proper mounting to device  104 , as shown in FIG.  1 . 
   Referring now to  FIG. 1 , airflow from a fan  128  may travel parallel to the projections  112 , into the one or more channels  110 . At least a portion of the air may travel through and exit the one or more channels  110 , and may travel across the top surface  109  of the substrate carrier  108 . This may result in heat dissipation in one or more secondary components  130 , which may include, for example, one or more voltage regulators, but the claimed subject matter is not so limited. Heat dissipation of these one or more secondary components may be by convective cooling, which may result from the airflow passing through the one or more channels  110 . 
   It is important to note that the air channel configuration may vary in differing embodiments of the claimed subject matter. For example, the one or more air channels  110  are illustrated in  FIGS. 1 and 2  as having a rectangular cross sectional shape. However, the air channels may have any appropriate shape, including but not limited to elliptical, triangular, or the like. Additionally, the air channels may take on any direction or configuration. The air channels in  FIGS. 1 and 2  are shown as being perpendicular to surfaces  114  and  116  of device  102 , but in alternative configurations, one or more air channels  110  may be formed to run diagonally from the surfaces  114  and  116 , and may have multiple outlets, for example. 
   In an alternative embodiment of the claimed subject matter, there is illustrated in  FIG. 3  an alternate view of a microelectronic assembly  101  comprising a heat dissipation device  102  attached to a microelectronic die  104 . The microelectronic die is physically and electrically attached to a substrate carrier  108  by a plurality of solder balls  106 . A plurality of channels  110  may be formed on the device  102 . One or more secondary components  130 , which may include, for example, one or more voltage regulators, may be formed on substrate carrier  108 . A shroud  126  may be formed proximate to the heat dissipation device  102 , and may be attached to the top surface  109  of substrate carrier  108 . Shroud  126  may be formed out of plastic by use of one or more injection molding processes, but the claimed subject matter is not limited to any particular material or formation process. Shroud  126  may enhance or alter airflow across the top surface  109  of the substrate carrier  108 , by directing the airflow in a particular direction, for example. In operation, shroud  126  may direct air passing through channels  110 , and cause air to flow over one or more secondary components  130  rather than dissipate, for example. It is important to note, however, that the claimed subject matter is not limited to use of a shroud, or is a shroud limited to a configuration illustrated in  FIG. 2 , but any configuration that results in enhanced airflow across a substrate may be in accordance with the claimed subject matter. The embodiment illustrated in  FIG. 3  may be advantageous for use in a microelectronic assembly that incorporates one or more secondary components mounted on the secondary side of a substrate, where heat dissipation of these components may be desirable, for example. 
   In another alternative embodiment of the claimed subject matter, there is illustrated in  FIG. 4  a microelectronic assembly  103  comprising a heat dissipation device  102  attached to a microelectronic die  104 . The microelectronic die is physically and electrically attached to a substrate carrier  108  by a plurality of solder balls  106 . A mounting surface  114  of a base portion  118  of the heat dissipation device  102  is attached to one surface of the microelectronic die  104 , preferably by a thermally conductive adhesive (not shown). A plurality of channels  110  may extend from the dissipation surface  116  to an opposing mounting surface  114  of the base portion  118  of the device  102 . The plurality of channels  110  may be substantially perpendicular to the base portion dissipation surface  116  in one embodiment. In this particular embodiment, a fan  122  may be mounted to a plurality of support members  120 . The support members  120  are shown as being mounted to device  102  by passing through substrate carrier  108 , but alternative embodiments exist. For example, fan  122  may be mounted by use of one or more support members  120  to the secondary side  107  of the substrate carrier  108 . In operation, tan  122  may provide airflow to the secondary surface  107  of the substrate carrier  108 . A substantial portion of the air may be caused to flow parallel to the secondary surface  107 , which may result in airflow being provided to one or more secondary components  124 . This airflow may result in some amount of heat dissipation for the secondary components  124 . The embodiment illustrated in  FIG. 4  may be advantageous for use in a microelectronic assembly that incorporates one or more secondary components mounted on the secondary side of a substrate, where heat dissipation of these components may be desirable, for example. 
     FIG. 5  illustrates a substrate secondary side modification that may be incorporated for use in one or more of the illustrated embodiments, such as the secondary side fan configuration of FIG.  4 . Shown in  FIG. 5  is a secondary side view of a substrate carrier  108 . The substrate carrier secondary side  107  may have formed thereon a plurality of solder balls  136 . The plurality of solder balls  136  may be formed on opposing sides of a microelectronic device footprint  138 , for example. In operation, the secondary side solder balls may be utilized in the microelectronic assembly of  FIG. 4 , and may provide enhanced heat dissipation for one or more secondary side components  124 . Enhanced heat dissipation may be provided in the following manner: airflow may be provided from a fan such as fan  122  of FIG.  4 . At least a portion of the airflow may flow parallel to secondary surface  107 , and may, when encountering the plurality of solder balls  136 , undergo an increase in turbulence. This increase in turbulence may result in enhanced heat dissipation of one or more secondary side components  124  as compared to the heat dissipation provided by laminar airflow. Formation of the solder balls  136  may be performed in a variety of ways, including one or more wave solder processes. It is important to note, however, that the claimed subject matter is not limited to use of any particular formation method, but any method of fabrication that results in the formation of a plurality of solder balls on the secondary side of a substrate carrier is in accordance with the claimed subject matter. 
   It can be appreciated that the embodiments may be applied to the formation of any semiconductor device wherein heat dissipation may be desirable. Certain features of the embodiments of the claimed subject matter have been illustrated as described herein, however, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. Additionally, while several functional blocks and relations between them have been described in detail, it is contemplated by those of skill in the art that several of the operations may be performed without the use of the others, or additional functions or relationships between functions may be established and still be in accordance with the claimed subject matter. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments of the claimed subject matter.