PATENT DOCUMENT

Publication Number: US-7861768-B1
Application Number: US-19134305-A
Country: US
Kind Code: B1

Title: Heat sink

Abstract:
A heat sink having an embedded heat pipe and fins attached to opposite sides of a base plate having a heat spreader component made of a diamond copper composite is disclosed. In various embodiments, the diamond copper composite heat spreader contains channels for receiving a main heat pipe as well as auxiliary heat pipes.

Claims:
What is claimed is: 
     
       1. A heat sink, comprising:
 a main heat pipe; 
 at least one pair of auxiliary heat pipes coupled to said main heat pipe, said auxiliary pipes extending substantially perpendicular to said main heat pipe, and the combined diameter of each said at least one pair of auxiliary pipes is substantially similar to the diameter of said main heat pipe; 
 a base plate, said base plate having channels to receive said main heat pipe and said auxiliary heat pipes, said base plate extending substantially perpendicular to a plane of a heat source with which said heat sink is used; 
 a diamond copper composite heat spreader disposed between the base plate and the heat source; and 
 a plurality of fins coupled to opposite sides of said base plate, said fins extending substantially parallel to the plane of said heat source; 
 wherein heat from the heat source is conducted through the heat spreader to the base plate and dissipated through the at least one heat pipe and the plurality of fins. 
 
     
     
       2. The heat sink of  claim 1 , wherein the diamond copper composite heat spreader comprises a first copper layer and a second copper layer, the first and second copper layers disposed on opposite sides of and in contact with a diamond copper layer. 
     
     
       3. The heat sink of  claim 2 , wherein the first copper layer comprises at least one channel to receive at least one heat pipe. 
     
     
       4. The heat sink of  claim 2 , wherein the diamond copper layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       5. The heat sink of  claim 1 , wherein each fin in the plurality of fins is aligned with each pipe in the plurality of auxiliary pipes along a flow length. 
     
     
       6. The heat sink of  claim 1 , wherein each pipe in the plurality of auxiliary heat pipes has an end portion that wraps partially around the main heat pipe. 
     
     
       7. The heat sink of  claim 1 , wherein the main heat pipe comprises an inner, diamond copper composite layer and an outer copper layer that is wrapped around the inner layer. 
     
     
       8. The heat sink of  claim 7 , wherein the inner diamond copper composite layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       9. The heat sink of  claim 1 , wherein at least one of the auxiliary heat pipes comprises an inner diamond copper composite layer and an outer copper layer that is wrapped around the inner layer. 
     
     
       10. The heat sink of  claim 9 , wherein the inner diamond copper composite layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       11. The heat sink of  claim 7 , wherein the inner diamond copper composite layer comprises DiaCu material. 
     
     
       12. The heat sink of  claim 9 , wherein the inner diamond copper composite layer comprises DiaCu material. 
     
     
       13. A heat sink, comprising:
 a main heat pipe; 
 at least one pair of auxiliary heat pipes coupled to the main heat pipe, each pipe in the at least one pair of auxiliary pipes having a diameter that is less than a diameter of the main heat pipe; 
 wherein said auxiliary pipes extend substantially perpendicular to said main heat pipe; and 
 a diamond copper composite heat spreader is disposed between and in contact with the auxiliary heat pipes; 
 a wrap around plate that covers the main heat pipe and auxiliary heat pipes; and 
 a plurality of fins coupled to opposite sides of the wrap-around plate; 
 wherein pairs of auxiliary heat pipes are disposed proximate to opposite sides of the wrap around plate and are aligned along a length of the main heat pipe. 
 
     
     
       14. The heat sink of  claim 13 , wherein the diamond copper composite heat spreader comprises a first copper layer and a second copper layer, the first and second copper layers disposed on opposite sides of and in contact with a diamond copper layer. 
     
     
       15. The heat sink of  claim 14 , wherein the first copper layer comprises at least one channel to receive at least one heat pipe. 
     
     
       16. The heat sink of  claim 14 , wherein the diamond copper layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       17. The heat sink of  claim 13 , wherein each fin in the plurality of fins is aligned with each pipe in the plurality of auxiliary pipes along a flow length. 
     
     
       18. The heat sink of  claim 13 , wherein each pipe in the plurality of auxiliary heat pipes has an end portion that wraps partially around the main heat pipe. 
     
     
       19. The heat sink of  claim 13 , wherein channels are formed on an outer surface of the wrap around plate to receive the plurality of fins. 
     
     
       20. The heat sink of  claim 13 , wherein the main heat pipe comprises an inner, diamond copper composite layer and an outer copper layer that is wrapped around the inner layer. 
     
     
       21. The heat sink of  claim 20 , wherein the inner diamond copper composite layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       22. The heat sink of  claim 13 , wherein at least one of the auxiliary heat pipes comprises an inner diamond copper composite layer and an outer copper layer that is wrapped around the inner layer. 
     
     
       23. The heat sink of  claim 22 , wherein the inner diamond copper composite layer comprises 93% compressed diamond dust and 7% compressed copper. 
     
     
       24. The heat sink of  claim 20 , wherein the inner diamond copper composite layer comprises DiaCu material. 
     
     
       25. The heat sink of  claim 22 , wherein the inner diamond copper composite layer comprises DiaCu material.

Description:
RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 10/460,629, filed Jun. 11, 2003, which is co-pending and incorporated by reference herein in its entirety, and also is a continuation in part of U.S. patent application Ser. No. 10/934,958, filed Sep. 2, 2004, which is co-pending and incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to heat removal devices, and more particularly to a heat sink for electronic components. 
     BACKGROUND 
     Electronic components are capable of generating undesirable levels of heat during operation. For example, microprocessors in computer systems can generate enough heat that they can either slow down or cease to function if heat is not removed. Moreover, higher transistor counts on smaller die areas and increasing frequencies of operation clocks have further increased the heat produced by microprocessors. Maintaining actual junction temperatures within a reliable junction value is critical to support higher frequencies and to secure the normal functioning of the electronic components. Thus, dissipation of the heat produced by such electronic components is important to stabilize their operation and extend their operational life. 
     Existing heat removal devices, such as a fan, employ forced convention. Some electronic systems use one large fan to cool all of the heat-producing components within a system. Other electronic systems have individual fans for each heat-producing element. However, fans often generate unacceptable levels of noise and require separate power sources. Moreover, because fans utilize moving parts, they are susceptible to mechanical failure. 
     Other heat removing devices employ natural convention in which heat produced by electronic components is dissipated by a heat sink. Prior art heat sinks include heat dissipation fins attached to a base plate. The base plate is meant to spread out the heat produced by the heat-producing element to all the fins.  FIG. 1A  illustrates a prior art heat sink that includes many thin plates and pins disposed on a base plate. These heat sinks are constructed of materials having high thermal conductivity such as aluminum and copper. Heat produced by the heat-producing element is conducted to the heat dissipation fins via the thermally conductive base section or base plate. The heat is then transferred over the surface of the heat dissipation fins and dissipated into the air blown by a cooling fan. 
     In order to improve the performance of the cooling device, heat is most desirably distributed evenly throughout the base plate, and dissipated through all of the heat dissipation fins. However, as illustrated in  FIG. 1B , heat emitted from the heat-producing element tends to be conducted predominantly to the heat dissipation fins disposed right above the heat-producing element, and the amount of heat conducted to the peripheral heat dissipation fins is relatively small. Because the heat-producing element is much smaller than the base plate, the contact area between them is also very limited. Consequently, the fins as a whole dissipate heat very inefficiently. Moreover, the heat sink is very large relative to the heat source, placing undesirable constraints on the design of a product with high heat generation density. 
     Thus, to help ensure the continuing safe performance of heat generating electronic components, it is desirable to remove heat from such components in a quiet, efficient and reliable manner. Particularly, what is needed is a heat sink having a highly conductive base plate that maximizes heat dissipation along the entire length and width of the base plate and fins. The thermal properties of such a base plate would enable cooling of components with extremely high heat flux. 
     SUMMARY 
     Embodiments of a heat sink having at least one embedded heat pipe and fins attached to opposite sides of a base plate having a diamond copper heat spreader are described. In an embodiment, the base plate includes a main heat pipe and auxiliary heat pipes coupled to the main heat pipe. The fins are aligned with the auxiliary heat pipes. 
     There are numerous other embodiments that are described herein, and these embodiments generally relate to heat sinks that provide efficient heat dissipation for use in computer systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG. 1A  illustrates a prior art heat sink. 
         FIG. 1B  illustrates another prior art heat sink. 
         FIG. 2  illustrates an embodiment of a heat sink. 
         FIG. 3A  illustrates a perspective view of an embodiment of a heat sink. 
         FIG. 3B  illustrates a front view of an embodiment of a heat sink. 
         FIG. 3C  illustrates a top view of an embodiment of a heat sink. 
         FIG. 3D  illustrates a side view of an embodiment of a heat sink. 
         FIG. 4  illustrates an embodiment of base plate for a heat sink. 
         FIG. 5A  illustrates a top view of a base plate with fins attached on either side. 
         FIG. 5B  illustrates an enlarged side-view of fins coupled to one side of a base plate. 
         FIG. 6  illustrates a partial see-through view of an embodiment of a heat sink having a base plate with fins coupled to both sides. 
         FIG. 7A  illustrates a side view of the heat pipe shown in  FIG. 6 . 
         FIG. 7B  illustrates a cross-sectional view of the heat pipe shown in  FIG. 6 . 
         FIG. 8  illustrates a cross-sectional view of the heat sink shown in  FIG. 6 . 
         FIG. 9A  illustrates an enlarged cross-sectional view of a main heat pipe and auxiliary heat pipes. 
         FIG. 9B  illustrates another enlarged cross-sectional view of a main heat pipe and auxiliary heat pipes. 
         FIG. 10  illustrates an alternative embodiment of a heat sink. 
         FIG. 11  illustrates an embodiment of a computer assembly having a cooling system. 
         FIG. 11A  illustrates an alternative embodiment of a computer assembly having a heat sink comprising a diamond-copper composite heat spreader. 
         FIG. 12  illustrates a diamond-copper composite slug heat sink baseplate. 
         FIG. 13  illustrates a diamond slug heat sink baseplate used in a tower chassis application. 
         FIG. 14  illustrates a heat pipe utilizing a diamond-copper structure. 
         FIG. 15  illustrates an alternative embodiment of a heat pipe utilizing a diamond-copper structure. 
         FIG. 16  illustrates a heat spreader slug disposed to receive a heat pipe according to the present invention. 
         FIG. 17  illustrates an alternative embodiment of a heat spreader slug in which multiple channels can be formed in a copper layer to accommodate more than one heat pipe. 
         FIG. 18  illustrates a rectangular heat pipe. 
         FIG. 19  illustrates a round heat pipe. 
         FIG. 20  illustrates a heat slug having channels configured to accommodate round heat pipes as well as rectangular heat pipes. 
         FIG. 21  illustrates a section view of a copper layer that is incorporated into a heat slug and faces the die. 
         FIG. 22  illustrates a block diagram of a computer that may be used with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth such as examples of specific components, circuits, processes, etc., in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice the present invention. In other instances, well known components or methods have not been described in detail in order to avoid unnecessarily obscuring the present invention. 
     The term “coupled” as used herein means connected directly to or indirectly connected through one or more intervening components, structures or elements. The terms “above,” “below,” and “between” as used herein refer to a relative position of one component or element with respect to other components or elements. As such, one component disposed above or below another component may be directly in contact with the other component or may have one or more intervening component. Moreover, one component disposed between other components may be directly in contact with the other components or may have one or more intervening components. 
     Embodiments of a heat sink are described. In an embodiment of the present invention, the heat sink is adapted for use in computer assemblies, such as desktop or personal computer systems. In alternative embodiments, the heat sink may be adapted for use with laptops, cell phones, and handheld computers. The heat sink includes a base plate and multiple fins coupled to opposite sides of the base plate. The double-sided fin configuration maximizes the heat dissipated through the base plate by allowing simultaneous axial and lateral heat transmission to all the attached fins. The base plate and fins are made of high heat conducting materials. The base plate also includes one or more embedded heat pipes to form a network that provides greater heat conductivity. Thus the combination of materials, fin orientation, and heat pipes results in a heat sink that can handle the high heat flux challenges in contrast to the prior art. 
       FIG. 2  illustrates an embodiment of a heat sink that may be used to dissipate heat from electronic components, for example, a microprocessor on a printed circuit board (“PCB”) in a computer system (e.g., a motherboard). Typically, PCBs have heat-producing elements such as microprocessors or power supplies mounted on one or more surfaces.  FIG. 2  illustrates two heat-generating sources in the form of central processing units (“CPUs”)  206  and  208  disposed on a motherboard  201 . Motherboard  201  is oriented vertically as would be mounted, for example, in a tower case or chassis of a computer system. Heat sink  202  is disposed over heat source  206  and heat sink  204  is disposed over heat source  208 . Each heat sink has a centralized base plate ( 210 ,  212 ) with fins extending from opposite sides of the centralized base plate. The double-sided array of fins for heat sink  202  is represented by fins  221  through  224 , and the double-sided array of fins for heat sink  204  is represented by fins  225  through  228 . In an embodiment of the present invention, the double-sided fins disposed on a centralized base plate (e.g.,  210 ) provide efficient heat transport through the base plate, and through fins that extend along a flow length of the base plate for maximum heat transfer. As indicated by the arrows for heat sinks  202  and  204 , the heat path starts from the heat source and extends to all the fins. As described in greater detail below, alternative embodiments for heat sinks  202  and  204  may have a network of heat pipes embedded within the base plate to further increase the dissipation of heat through the heat sink.  FIG. 2  illustrates the use of two heat sinks for a dual-processor system, although embodiments of a heat sink described herein may be utilized with any number of CPUs that are part of a computer system. 
       FIGS. 3A-3D  illustrate various views of an embodiment of the present invention.  FIG. 3A  illustrates a perspective view of heat sink  300  having base plate portion  304  with fin arrays  310  and  312  disposed on opposite sides of base plate  304 . Spreader plate  302  may be disposed near one end of base plate  304 . Spreader plate  302  may also be referred to herein as a “slug” or “heat spreader.” Spreader plate  302  is designed to conduct the heat produced by a heat-producing element to heat sink  300 . In an embodiment of the present invention, spreader plate  302  may be made of copper. In another embodiment, spreader plate  302  is constructed from a diamond copper composite described below. Spreader plates are known in the art; accordingly, a detailed description is not provided herein. 
     In an embodiment of the present invention, base plate  304  may be substantially rectangular in shape, with base plate  304  having a width  305 , a heat flow length  306 , and a thickness  307 . The perspective view of  FIG. 3A  and the front view of  FIG. 3B  illustrate heat sink  300  with an array of fins (e.g.,  310 ,  312 ) disposed on opposite sides of base plate  304 . The group of fins  310  represented by fins  321 ,  322 , and  323  are coupled to base plate  304  in an orientation that is substantially perpendicular to base plate  304 . In an embodiment of the present invention, the fins may be disposed perpendicularly in a series along an entire width  305  of the base plate  304 . As illustrated by  FIG. 3C , which shows a top view of heat sink  300 , each fin ( 321 - 325 ) may have a heat flow length substantially similar to the flow length  306  of base plate  304 .  FIG. 3D  illustrates a side view of heat sink  300  with fins  321 ,  331  disposed on opposite sides of base plate  304 . In an embodiment of the present invention, fins  321 ,  331  may be substantially the same size and shape. With respect to  FIGS. 3A-3D , heat sink  300  may be oriented such that spreader plate  302  is coupled to a heat source such as CPU. In this orientation, heat sink  300  extends perpendicularly from the CPU disposed on a motherboard, with the fins oriented parallel to the motherboard and the CPU (similar to heat sinks  202 ,  204  of  FIG. 2 ). 
     In an embodiment of the present invention, base plate  304  and fins  310 ,  312  may be made of a high-heat conducting material such as aluminum or copper. In an alternative embodiment, base plate  304  may be made of pyrolytic graphite alone or in combination with aluminum and/or copper. Pyrolytic graphite is a form of graphite manufactured by decomposition of a hydrocarbon gas at very high temperature resulting in an extremely anisotropic material. Pyrolytic graphite has a high conductivity in the axial direction (i.e., perpendicular to the heat generating source as illustrated in  FIG. 2 ) making it a suitable material for base plate  304 . 
       FIG. 4  illustrates an enlarged view of an embodiment of base plate  304  described above with respect to  FIGS. 3A-3D . Base plate  304  has one or more channels formed on top side  315  and bottom side  316 . For example, top side  315  may have channels  350 ,  351 , and  352 . Bottom side  316  may have channels  360 ,  361 ,  362 , and  363 . The channels may extend along an entire length  306  of base plate  304 . Although base plate  304  may be any size suitable to be part of a heat sink, base plate  304  may, in an embodiment, have a width  305  of 200 mm, a flow length  306  of 150 mm, and a thickness  307  of 25 mm. Each channel (e.g.,  350 ,  360 ) may have a diameter of 6-8 mm. As described in greater detail below, each channel may be compatible for housing or coupling to a heat pipe, a fin, or other heat pipe element. 
       FIGS. 5A-5B  illustrate an embodiment of an array of fins coupled to base plate  304  described above with respect to  FIG. 4 .  FIG. 5A  shows a top view of base plate  304  with fins attached on both sides. In the embodiment shown, the fins are staggered such that a pair of fins (e.g.,  321 ,  331 ) coupled to base plate  304  are not directly opposite of each other. For example, one side of base plate  304  has fins  321 ,  322 ,  323 , and  324 . The opposite side of base plate  304  has fins  331 ,  332 , and  333 . In an alternative embodiment, two fins on opposite sides of each other may be directly aligned with each other (as shown in  FIG. 3B ). Each fin is coupled to base plate  304  near the channels described above with respect to  FIG. 4 . For example, fin  321  is coupled to base plate  304  near channel  360 , and fin  331  is coupled to base plate  304  near channel  350 . 
       FIG. 5B  shows an enlarged side-view of fins coupled to one side of base plate  304 . As discussed above, each channel formed within base plate  304  is configured to be compatible with one end of a fin. For example, fin  321  has an end that fits into channel  360 . In an embodiment of the present invention, each fin may have thickness  308  of up to 1 mm and gap  309  between each fin of up to 2 mm. Up to 70 fins may be disposed on each side of base plate  304  for a total of up to 140 fins. In an embodiment of the present invention, fin  321  may be coupled to base plate  304  by crimping one end of fin  321  into channel  360 . In an alternative embodiment, one end of fin  321  may be soldered into channel  360 . Methods to couple fins to a base plate are known in the art; accordingly, a detailed description is not provided herein. 
       FIG. 6  illustrates a partial see-through view of an embodiment of a heat sink  400  having fins (e.g., fins  421 - 424  and  431 - 434 ) coupled to opposite sides of base plate  404 . One or more heat pipes may be embedded within base plate  404 . For example, main heat pipe  440  may be disposed within base plate  404  along width  405 . Additional heat pipes (e.g., pipes  450 ,  452 ) may be disposed within base plate  404  along flow length  406  with respect to opposing pairs of fins (e.g., fins  421  and  431 ). Main heat pipe  440  is disposed near one side of base plate  404 , and auxiliary heat pipes  450 ,  452  are oriented perpendicular to main heat pipe  440  and aligned with opposing fins  421 ,  431 . In an embodiment of the present invention, heat sink  400  is attached to a heat source (e.g., a CPU) such that one end of main heat pipe  440  is oriented directly above the heat source. The heat dissipates through width  405  of main pipe  440  and along flow length  406  of each auxiliary heat pipe and out the fins. As discussed in greater detail below, auxiliary heat pipes  450 ,  452  have combined diameters that are similar to the diameter of main heat pipe  440 . 
     For clarity of description, this particular view of heat sink  400  shows two auxiliary heat pipes  450 , 452  in addition to main heat pipe  440 . However, an auxiliary heat pipe exists for every fin attached to base plate  404 . In alternative embodiments of the present invention, any number of auxiliary heat pipes may be disposed within base plate  404 . The combination of heat pipes embedded within base plate  404  and fins coupled to both sides of base plate  404  increases the efficiency of heat dissipation throughout entire width  405  and flow length  406  of base plate  404  and the fins. 
       FIGS. 7A and 7B  illustrate isolated views of heat pipe  440  described above with respect to  FIG. 6 . In an embodiment of the present invention, the following description of heat pipe  440  may be analogous or applicable to auxiliary heat pipes  450 , 452 . Heat pipes are typically cylindrical structures containing water. As heat is absorbed within the cylinder, the water boils to a vapor phase and passes through a wick structure lining an inner surface of the pipe. The heat is then released into an outer portion of the cylinder wall and the vapor condenses back into liquid form. Gravity and the condensation of liquid along the wick return the liquid to a lower portion of the cylinder. Heat pipes are well-known in the art; accordingly, a detailed description is not provided herein. 
       FIG. 7A  shows a side view of heat pipe  440  having outer wall  442 , wick  444  disposed along an inside of wall  442  and cooling material  446  (e.g., 
     H2O) disposed within an inner lumen of heat pipe  440 .  FIG. 7B  shows a cross-sectional view of heat pipe  440  showing the relationship of wall  442 , wick  444 , and cooling material  446 . H2O and low melt-alloys are just a few examples of a cooling material  446  that may be used with heat pipe  440 . Other materials or liquids for cooling material  446  are known in the art; accordingly, a detailed description is not provided herein. As heat passes through heat pipe  440 , liquid  446  vaporizes into wick  444  and through wall  442 , subsequently spreading out through the fins. 
       FIG. 8  illustrates a cross-sectional view of heat sink  400  shown in  FIG. 6  through a flow length (e.g.,  406 ) of fin  421 , auxiliary heat pipes  450 ,  452 , and fin  431 . This cross-section of base plate  404  shows, in an embodiment, the orientation of main heat pipe  440  and auxiliary heat pipes  450 ,  452 , with main heat pipe  440  disposed near one side of the base plate (not shown). The cylindrical structures of main heat pipe  440  and auxiliary heat pipes  450 , 452  have closed ends. Auxiliary heat pipes are separated by a fixed distance from each other throughout a flow length with ends that partially wrap around main heat pipe  440 . This structural configuration of auxiliary heat pipes with respect to main heat pipe  440  allows heat to be transferred efficiently from main heat pipe to an entire flow length of each auxiliary heat pipe. As discussed above, fins  421 ,  431  have flow length  411  and flow height  412  corresponding to the dimensional length and width of each fin. Main heat pipe has diameter  413  that may be substantially similar to the combined diameters of auxiliary heat pipes  450 , 452 . 
     In an embodiment of the present invention, heat fins  421  and  431  are substantially similar in size and shape having flow length  411  of up to 300 mm, and flow height  412  of up to 75 mm. Main heat pipe  440  may have diameter  413  of up to 30 mm. In an alternative embodiment, heat fins  421 ,  431  and main heat pipe  440  may have other dimensions. 
       FIG. 9A  illustrates an enlarged cross-sectional view of heat sink  400  through main heat pipe  440  and auxiliary heat pipes  450 , 452 , but without fins  421 ,  431 . One end portion of each auxiliary heat pipe  450 ,  452  wraps partially around main heat pipe  440 . Each auxiliary heat pipe has a diameter that is less than the diameter of main heat pipe  440  and includes wick structures  451 ,  453  that form channels  454 ,  455 . The heat pipes are held together by wrap-around plate  465  that covers the outer dimensions of auxiliary heat pipes  450 ,  452 . In an embodiment of the present invention, wrap-around plate  465  may be the base plate discussed herein (e.g., base plates  304 ,  404 ). Wrap-around plate  465  is made of a heat conducting material such as aluminum or copper. 
     In an embodiment of the present invention, main heat pipe  440  may have diameter  414  of 25 mm and auxiliary heat pipe  450  may have diameters  470 ,  471  of up to 10 mm. Combined length  411  (i.e., heat flow length) of main heat pipe  440  and auxiliary heat pipes  450 ,  452  as shown in this cross-section may be approximately 200 mm. Auxiliary heat pipes  450 ,  452  are separated by a distance  472 , and in an embodiment, may be separated by heat-conducting spacer  460  having a thickness of up to 6 mm. In an alternative embodiment of the present invention, heat-conducting spacer  460  may be an aluminum heat spreader. 
       FIG. 9B  illustrates a cross-sectional view of heat sink  400  that is perpendicular to the flow length cross-sectional view shown with respect to  FIG. 9A . Four pairs of auxiliary heat pipes are covered by wrap-around plate  465 . Auxiliary heat pipes are represented by reference numerals  450 ,  452 ,  456 , and  458 . Each pair of auxiliary heat pipes are separated by a heat spreader (e.g.,  459 ,  460 ). Fins  421 - 424  are attached to one side of wrap-around plate  465  and fins  431 - 434  are attached to the opposite side of wrap-around plate  465 . Grooves or channels  480 - 483  are formed on an outer surface of wrap-around plate  465  for fins  421 - 424  and channels  484 - 487  are formed for fins  431 - 434 . In an alternative embodiment, channels  480 - 483  and  484 - 487  may be similar to channels  350 - 352  and  360 - 363  described above with respect to  FIG. 4 . 
     As discussed above, the base plate or the wrap-around plate is made of a high heat-conducting material such as aluminum or copper. In an alternative embodiment of the present invention, the base plate may be made of multiple materials that provide an advantage over a single, uniform material.  FIG. 10  illustrates an alternative embodiment of heat sink  500  having fins  521 - 524  and  531 - 534  disposed on opposite sides of base plate  540 . Portion  542  of base plate  540  is made of pyrolytic graphite while the remainder of base plate  540  is made of a different heat conducting material such as aluminum or copper. Portion  542  of base plate  540  may be extruded during the base plate manufacturing process to produce this combination. Base plate  540  may also include multiple auxiliary heat pipes  550 ,  552  to help dissipate the heat along the flow length of base plate  540  and to the double-sided fins. Auxiliary heat pipes may be embedded within base plate  540  for every fin coupled to base plate  540 . In an alternative embodiment of heat sink  500 , auxiliary heat pipes may not be necessary. Because pyrolytic graphite has a high conductivity in the axial direction, portion  542  may be disposed directly over a heat source (e.g., a CPU), thereby allowing the heat to dissipate to all the fins along the heat flow length that is perpendicular to portion  542 . Heat sink  500  may have a network of heat pipes (e.g., a main heat pipe and auxiliary heat pipes discussed above with respect to  FIGS. 6-9B ). 
       FIG. 11  illustrates an embodiment of computer assembly  600  having a cooling system. In particular, cooling system  610  dissipates heat generated by a CPU disposed on a motherboard.  FIG. 11  illustrates an internal view of the computer chassis with motherboard  602  in a vertical position. A substrate  604  (e.g., a silicon substrate) is disposed on motherboard  602 . Heat-generating CPU  606  is disposed above substrate  604 . Heat-spreading element or slug  608  is disposed above CPU  606 . As discussed above, heat spreader  608 , in an embodiment, may be made of a heat-conducting material such as copper that spreads heat from CPU  606  to heat sink  610 . In an embodiment, heat spreader slug  608  is constructed from a diamond copper composite described below. Heat sink  610  is disposed above slug  608  with base plate portion  612  extending perpendicularly from motherboard  602 . It should be noted that the computer assembly illustrated in  FIG. 11  is not necessarily drawn to scale. In particular, heat sink  610  has been enlarged to provide a better understanding of its structure and orientation. 
     Multiple fins  614  and  616  are disposed on both sides of base plate  612 . Fins  621 ,  622 , and  623  are representative of fins disposed on one side of base plate  610 , and fins  631 ,  632 , and  633  are representative of fins disposed on the opposite side of base plate  612 . Any number of fins may be disposed on both sides of base plate  612  and is not limited to the number a fins illustrated with respect to  FIG. 11 . One or more heat pipes (not shown) may be embedded within base plate  612 , as discussed above with respect to  FIGS. 6 ,  7 A, and  7 B. For example, a main heat pipe (not shown) may be disposed along a width of base plate in addition to one or more auxiliary heat pipes (not shown) extending along a flow length of base plate  612  between opposing fins (e.g., fins  621  and  631 ). Base plate  612  is coupled to heat spreader  608  near a corner portion of base plate  612 . This relative position of base plate  612  to heat spreader  608  allows the heat generated by CPU to spread efficiently throughout heat sink  610 . In an embodiment of the present invention, the main heat pipe may be embedded within base plate  612  such that it aligns over heat spreader  608  and CPU  606 . A cooling fan (also not shown) may be disposed near heat sink  610  to force air through the fins of heat sink  610  in the direction indicated by arrows  640 . As such, in an embodiment, heat dissipates from CPU  606  efficiently towards the outer dimensions of all the fins disposed on both sides of base plate  612 . 
       FIG. 11A  illustrates an alternate embodiment of computer assembly  650  having a cooling system  651 . In particular, cooling system  651  comprises a diamond-copper composite heat spreader  660 .  FIG. 11A  illustrates an internal view of the computer chassis similar to one described in  FIG. 11  above. A substrate  604  (e.g., a silicon substrate) is disposed on motherboard  602 . Heat-generating CPU  606  is disposed above substrate  604 . Heat-spreading element or slug  608  is disposed above CPU  606 . Heat spreader  608 , in an embodiment, may be made of a heat-conducting material such as copper that spreads heat from CPU  606  to heat sink  610 . In an embodiment, heat spreader slug  608  is constructed from a diamond copper composite described below. The core layer  658  of the heat spreader  608  comprises a diamond copper composite material that is composed of 93% compressed diamond dust, and 7% compressed copper, while the two outer facing surfaces of the composite layer  658  are fused between pure copper skins,  657  and  659  creating a solid composite sandwich heat spreader  608 . Outer skins  657  and  659  can be designed to a wide variety of thicknesses and shapes to allow machined grooves for round or flattened heat pipes. Also, in an embodiment, heat spreader slug  608  may contain channels such as channel  660  in the surface layer  659  of heat spreader slug, which can be dimensioned to receive heat pipe  662 . In an embodiment, the depth of channel  660  is approximately the radius of the heat pipe it receives. The thermal interface may be a grease or gel, and may contain a boron nitride material having particle sizes of less than one micron. 
     Heat sink  651  is disposed above slug  608  with base plate portion  612  extending perpendicularly from motherboard  602 . It should be noted that the computer assembly illustrated in  FIG. 11A  is not necessarily drawn to scale. In particular, heat sink  610  has been enlarged to provide a better understanding of its structure and orientation. 
       FIG. 11A  shows multiple fins  614  and  616  that are disposed on both sides of base plate  612 . Fins  621 ,  622 , and  623  are representative of fins disposed on one side of base plate  610 , and fins  631 ,  632 , and  633  are representative of fins disposed on the opposite side of base plate  612 . Any number of fins may be disposed on both sides of base plate  612  and is not limited to the number a fins illustrated with respect to  FIG. 11A . 
     One or more heat pipes may be embedded within base plate  612 . For example, main heat pipe  662  may be disposed within base plate  612  along width  663 . Additional heat pipes (e.g., pipes  682 ,  683 ) may be disposed within base plate  612  along flow length  664  with respect to opposing pairs of fins (e.g., fins  623  and  633 ). Main heat pipe  662  is disposed near one side of base plate  612 , and auxiliary heat pipes  682 ,  683  are oriented perpendicular to main heat pipe  664  and aligned with opposing fins  623 ,  633 . Base plate  612  is coupled to heat spreader  608  near a corner portion of base plate  612 . In an embodiment of the present invention, heat sink  651  is attached to a heat source (e.g., a CPU) such that one end of main heat pipe  662  is oriented directly above the heat source. The heat dissipates through width  663  of main pipe  662  and along flow length  664  of each auxiliary heat pipe and out the fins. As discussed in greater detail below, auxiliary heat pipes  682 - 683  have combined diameters that are similar to the diameter of main heat pipe  662 . 
     Directing attention to  FIG. 12 , in an alternative embodiment, the axial channel described can be improved by alleviating heat flux bottlenecks at the heat sink slug, heat pipe wall, and heat pipe wick. In this embodiment, DiaCu is utilized as composite heat spreader slug  700  at the base of the heat sink to spread heat from the die into a bigger sink region, thus quickly decreasing the overall flux into standard heat pipes or cooling channels. The following description of heat spreader slug  700  can also be implemented in an alternative embodiment of heat spreader  608  described above. The diamond copper composite is composed of 93% compressed diamond dust, and 7% compressed copper, while the two outer facing surfaces of the composite are fused between pure copper skins, creating a solid composite sandwich. Pure diamond has a thermal conductivity around 1500 W/mK, but the middle of the sandwich is about 1000 W/mK. Outer copper skins have the thermal conductivity of standard copper at 390 W/mK. Outer skins can be designed to a wide variety of thicknesses and shapes to allow machined grooves for round or flattened heat pipes. As illustrated, heat spreader slug  700  is separated by thermal interface layer  702  from silicon layer  704  and ceramic layer  706 . Also, in an embodiment, heat spreader slug  700  may contain channels such as channel  708  in the surface of heat spreader slug, which can be dimensioned to receive heat pipe  710 . In an embodiment, the depth of channel  708  is approximately the radius of the heat pipe it receives. The thermal interface may be a grease or gel, and may contain a boron nitride material having particle sizes of less than one micron. 
     An embodiment of the present invention incorporates a cavity above the die&#39;s hot spot for pure diamond film. Preferably, the targeted area is approximately 3 mm by 3 mm, but other configurations can be used. In an embodiment, about 40 mm of heat pipe length is embedded in the slug for ideal heat transfer. Several 6 mm or 8 mm diameter heat pipes can be used, but the number of heat pipes for any given design is determined by power, operating temperature, available area, pipe diameter, pipe shape, pipe radius, and pipe length. It is also possible to solder a 1″ pipe to the slug in applications utilizing the larger pipe described above. 
     Heat spreader slug  700  may also be used in tower chassis applications. As shown in  FIG. 13 , heat spreader slug  700  is disposed in a vertical configuration, separated again by thermal interface layer  702  from chip  712  and stacked boards  714 ,  716 . 
     On the outer skin facing the heat sink (not die side), about 4.25 mm of copper can be added which enables two to four axial grooves for 4.0 mm deep channels that can accept 8 mm diameter heat pipes. Likewise, for a 6 mm pipe implementation, the dimensions of the copper skin can be reduced to 3.25 mm thickness with 3.0 mm axial groove channels. If circular grooves cannot be included for pipe attachment due to mechanical constraints, then flattened pipes can be directly soldered, but this defeats the purpose of an idealized round heat pipe in an integrated slug, as round pipes perform better than flattened pipes. Either a disc or rectangle can be implemented without adverse effects as long as the slug-to-die-area ratio is increased by a factor of 5× to 20× above the die. 
     Heat pipe length is limited by current manufacturing processes for DiaCu and the physical vapor properties associated with industry standard heatpipes for any given pipe diameter. For standard heat pipe walls that are 0.3 mm thick copper, this composite structure provides an improved heat pipe. Preferred implementations of the present invention include low-profile heat pipes where bending is not required over a large length. Good dimensions are 0.25 mm (outer copper skin with DiaCu process)+&lt;1.0 mm (composite DiaCu)+0.25 mm (inner copper skin of DiaCu for axial wick grooves or porous sintered copper). 
     A wide variety of thermal interface materials can be used between the die and the disc. Copper-to-copper attach can be achieved through silver brazing, silver solder, and gold-tin solder. Standard solder can also be used. 
     Various profile configurations are considered for the heat pipe of the present invention. Directing attention to  FIG. 14 , heat pipe  720  includes outer copper skin  722  that wraps around diamond-copper layer  724 . In an embodiment, diamond-copper layer  724  has similar concentrations of compressed diamond and copper dust as described above for heat spreader slug  700 . Wick layer  726  includes a plurality of axial grooves that run the length of heat pipe  720 . In an embodiment, wick layer  726  is made from copper. Either or both of wick  728  or channel  730  can be constructed from the diamond-copper mixture described above for heat spreader slug  700 . 
       FIG. 15  illustrates another embodiment of a heat pipe of the present invention. Heat pipe  740  can include diamond-copper tube  742 , having attached to its interior face sintered diamond copper disposed between carbon fibers. 
       FIG. 16  illustrates a heat spreader slug disposed to receive a heat pipe according to the present invention. Heat spreader slug  750  includes copper layer  752  having a channel that receives heat pipe  754 . Copper layer  752  is disposed adjacent diamond-copper layer  756 , which is sandwiched between copper layer  752  and copper layer  758 .  FIG. 17  illustrates an alternative embodiment of heat spreader slug  750 , in which multiple channels can be formed in copper layer  752  to accommodate more than one heat pipe  754 . In an alternative embodiment of heat spreader slug  750 , copper layer  752  can have channels to receive round heat pipes ( FIG. 19 ) and/or rectangular heat pipes ( FIG. 18 ). Various configurations of copper layer  752  are shown in  FIGS. 20 and 21 .  FIG. 20  illustrates copper layer  752  machined to have channels for rounded heat pipes as well as rectangular heat pipes.  FIG. 21  illustrates the side of copper layer  752  that faces the die. As illustrated, an aperture extends through the core of copper layer  752  to receive pure diamond vapor. Pure diamond is expensive and so its size is limited to the hot spot area on the silicon. Pure diamond has higher thermal conductivity than sintered diamond copper. 
       FIG. 22  is a block diagram of a computer that may be used with an embodiment of the present invention. In an embodiment, exemplary system  1200  includes a processor having one or more arithmetic logical units (“ALUs”), a process executed by the processor from a memory. Note that while  FIG. 22  illustrates various components of a computer system, it is not intended to represent any particular architecture or manner of interconnecting components, as such details are not germane to the present invention. It will also be appreciated that networked computers, handheld computers, cell phones, and other data processing systems which have fewer components or perhaps more components may also be used with the present invention. 
     As shown in  FIG. 22 , computer system  1200 , which is a form of a data processing system, includes bus  1202  coupled to microprocessor  1203  and ROM  1207 , volatile RAM  1205 , and non-volatile memory  1206 . Microprocessor  1203 , is coupled to cache memory  1204  as shown in the example of  FIG. 22 . Bus  1202  interconnects these various components together and also interconnects components  1203 , 1207 , 1205 , and  1206  to a display controller and display device  1208 , as well as to input/output (I/O) devices  1210 , which may be pointing devices, keyboards, modems, network interfaces, printers, and other devices that are well known in the art. Typically, input/output devices  1210  are coupled to the system through input/output controllers  1209 . Volatile RAM  1205  is typically implemented as dynamic RAM (DRAM) that requires power continuously in order to refresh or maintain the data in the memory. Non-volatile memory  1206  is typically a magnetic hard drive, magnetic optical drive, optical drive, or a DVD RAM or other type of memory system that maintains data even after power is removed from the system. Typically, non-volatile memory  1206  can be implemented as a random access memory, although this is not required. While  FIG. 22  shows that non-volatile memory  1206  is a local device coupled directly to the rest of the components in the data processing system, it will be appreciated that the present invention may utilize a non-volatile memory which is remote from the system, such as a network storage device that is coupled to the data processing system through a network interface such as a modem or Ethernet interface. Bus  1202  may include one or more buses connected to each other through various bridges, controllers, and/or adapters, as is well-known in the art. In an embodiment, I/O controller  1209  includes a Universal Serial Bus (“USB”) adapter for controlling USB peripherals. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.

Metadata:
Filing Date: 20050727
Publication Date: 20110104
Grant Date: 20110104
Priority Date: 20030611
Inventors: GHANTIWALA NAYANA V.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28D15/0275", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L23/367", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/427", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28D15/0275", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L23/427", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/367", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/0002", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 43384861