Heat sink with integrated fluid circulation pump

A heat dissipation device including a base portion having a plurality of projections extending radially therefrom. A cooling fluid and circulation tubes are used to increase the efficiency of the heat dissipation device by pumping the heat (via the cooling fluid) from the hot base portion to the tips of the projections. The cooling fluid is circulated by a small centrifugal pump, which is driven by a fan attached to the heat dissipation device used for creating forced air-cooling.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to apparatus and methods for removal of heat
 from electronic devices. In particular, the present invention relates to a
 fluid circulation pump in conjunction with a heat sink for the removal of
 heat from a microelectronic die.
 2. State of the Art
 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 average junction
 temperature of the microelectronic die. If the temperature of the
 microelectronic die becomes too high, the integrated circuits of the
 microelectronic die 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. 5 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, and the like. 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.
 Although high surface area heat sinks are utilized in a variety of
 microelectronic applications, they have not been completely successful in
 removing heat from microelectronic dice that generate substantial amounts
 of heat. Therefore, it would be advantageous to develop apparatus and
 techniques to effectively remove heat from microelectronic dice.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
 Although the figures illustrate various views of the present invention,
 these figures are not meant to portray microelectronic assemblies in
 precise detail. Rather, these figures illustrate microelectronic
 assemblies in a manner to more clearly convey the concepts of the present
 invention. Additionally, elements common between the figures retain the
 same numeric designation.
 FIG. 1 illustrates a microelectronic assembly 100 of the present invention
 comprising a heat dissipation device 102 attached to a microelectronic die
 assembly 104. The microelectronic die assembly 104 comprises a
 microelectronic die (illustrated as a flip-chip 106) attached to and in
 electrical contact with an top surface 108 of an interposer substrate 112
 by a plurality of small solder balls 114. Traces (not shown) extend
 through the interposer substrate 112 to connect with external contacts 116
 (shown as solder balls) formed on a bottom surface 118 of the interposer
 substrate 112. The microelectronic die assembly 104 is exemplary of
 organic land grid array (OLGA) assemblies.
 As shown in FIG. 2, the heat dissipation device 102 comprises a base
 portion 122, which is preferably substantially cylindrical, and a
 plurality of projections or fins 124 extending from the base portion 122.
 The heat dissipation device 102 is preferably fabricated from a thermally
 conductive material, such as, but not limited to, copper, copper alloys,
 aluminum, aluminum alloys, and the like. The projections 124 are generally
 molded during the formation (e.g., forging, extrusion, etc.) of the heat
 dissipation device 102 or machined therein after formation (e.g.,
 skiving). It is, of course, understood that although the projections 124
 are shown as fins having a triangular cross-section, the projections may
 include, but are not limited to, elongate planar fin-like structures
 (i.e., rectangular cross-section) and other such configurations.
 Preferably, the projections 124 extend radially in a substantially planar
 orientation with a centerline 126 (see FIG. 3) of the base portion 122. As
 shown in FIG. 1, a lower surface 128 of the heat dissipation device 102 is
 attached to a back surface 132 of the flip-chip 106, preferably by a
 thermally conductive adhesive (not shown). Although the heat dissipation
 device 102 is illustrated as being attached to the flip-chip 106, the
 invention is, of course, not so limited. The heat dissipation device 102
 may be attached to any surface in which heat removal is desired.
 As shown in FIGS. 1 and 3, a fan 134 is positioned adjacent to an upper
 surface 136 of the heat dissipation device 102. Air is blown in direction
 138 into space between the projections 124. The fan 134 is illustrated as
 a fan blade assembly within a housing in FIG. 1 and as a fan blade
 assembly without a housing in FIG. 3.
 As shown in FIGS. 2 and 3, the heat dissipation device 102 includes a
 chamber 142 in the base portion 122 thereof. A pumping apparatus 144 is
 housed within the chamber 142. The pumping apparatus 144 is shown as a
 centrifugal pump having an impeller 146 set within the chamber 142 and
 sealed with a cap 148 (see FIG. 3). An axle 152 attaches to the fan 134
 and extends through the cap 148 to contact the impeller 146. The rotation
 of the fan 134 also drives the impeller 146 of the pumping apparatus 144.
 The pumping apparatus 144 also includes at least one circulation tube 154
 (illustrated embodiment shown with two circulation tubes 154 and 154' in
 FIGS. 1 and 3). The circulation tubes 154 and 154' are preferably
 fabricated from a thermally conductive material, such as, but not limited
 to, copper, copper alloys, aluminum, aluminum alloys, and the like. As
 shown in FIG. 2, the circulation tube 154 extends from an exit port 156 of
 the pumping apparatus 144 to an outer periphery 158 of the projections 124
 (the outer periphery 158 is emphasized with a dashed line in FIG. 2). The
 circulation tube 154 follows the outer periphery 158 around the heat
 dissipation device 102 and returns to an inlet port 162 of the pumping
 apparatus 144. The circulation tube 154 preferably makes contact with each
 of the projections 124.
 A cooling fluid, such as water, fluorocarbon liquid, freon, silicone fluid,
 and the like (not shown), is circulated through the circulation tubes 154,
 154' by the pumping action of impeller 146 when the fan 134 is in
 operation. The hottest portion of the heat dissipation device 102 is the
 base portion 122, because it makes closest contact with the heat source
 (i.e., flip-chip 106). It is well known that the temperature within the
 heat dissipation device 102 decreases as the heat moves further from the
 heat source, i.e., along the projections 124. This is demonstrated in FIG.
 4 is a graph, wherein a length of the projection 124 is the X-axis and
 temperature is the Y-axis. The temperature at the base 164 (see FIG. 2) of
 the projections 124 is on the left-hand side of the X-axis and the
 temperature at the tips 166 (see FIG. 2) of the projections 124 is on the
 right-hand side of the X-axis. Curve 172 is an illustration of the
 temperature gradient of the heat dissipation device 102 without the use of
 the cooling fluid and circulation tubes 154, 154'. It is, of course,
 understood that the graph in FIG. 4 is merely exemplary and is not meant
 to portray a specific temperature range or a specific projection length.
 When the cooling fluid and the circulation tubes 154, 154' of the present
 invention are employed, a cooling fluid is heated as it is pumped through
 the chamber 142 (i.e., the hottest portion of the heat dissipation device
 102). The cooling fluid is then pumped to the heat dissipation device
 outer periphery 158, as previously described. As the cooling fluid travels
 the heat dissipation device outer periphery 158, heat is dissipated from
 the cooling fluid convectively from the circulation tubes 154, 154'. The
 heat is also dissipated conductively into the projections 124 where the
 circulation tubes 154, 154' make contact therewith. This is demonstrated
 in FIG. 4 as curve 174. The temperature at the base 164 (see FIG. 2) of
 the projections 124 (left-hand side of the X-axis in FIG. 4) is lower than
 curve 172 because heat is being extracted from the base portion 122 by the
 cooling fluid. The temperature at the tips 164 (see FIG. 2) of the
 projections 124 (right-hand side of the X-axis in FIG. 4) is higher that
 curve 172 because the projection tips 166 are being heated by the cooling
 fluid, as previously described. Thus, the overall heat dissipated will be
 greater for the embodiment of the heat dissipation device 102 of the
 present invention.
 Having thus described in detail embodiments of the present invention, it is
 understood that the invention defined by the appended claims is not to be
 limited by particular details set forth in the above description, as many
 apparent variations thereof are possible without departing from the spirit
 or scope thereof.