Patent Application
20070289313
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a cooling assembly 20 is generally shown for cooling an electronic device 22 in
In a first embodiment of the subject invention, as shown in
A rectangular heat sink 34 generally indicated overlies the plate 24 for receiving heat from the plate 24. The heat sink 34 includes a base 36 and a second grease layer 38 disposed over the base 36 of the heat sink 34. The second grease layer 38 establishes a predetermined thermal interface between the base 36 of the heat sink 34 and all the components that come into contact with the base 36 of the heat sink 34. A plurality of heat transfer fins 40 extend upwardly from the base 36 and absorb heat from the plate 24. The heat transfer fins 40 are generally triangular in cross-section but may be any cross-sectional shape known in the art, such as, rectangular, conical or cylindrical. The assembly 20 may include an air moving device 42, such as a fan, disposed adjacent to the heat sink 34 for moving air over the heat sink 34.
The assembly 20 is distinguished by having a generally rectangular thermoelectric module 44 generally indicated disposed between the peripheral portion 26 of the plate 24 and the heat sink 34 for transferring, conveying or pumping heat laterally from the center portion 28 of the plate 24 to the peripheral portion 26 of the plate 24 and then through the thermoelectric module 44 to the heat sink 34.
In
One of the plate 24 and the heat sink 34 includes an extension 54 that extends into the through hole 48 and into engagement with the other of the plate 24 and the heat sink 34. In
In a second embodiment of the subject invention, as shown in
The upper portion 60 includes a plurality of spaced cooling chambers 64 that extend through the housing 56 and a plurality of cooling fins 66 disposed within cooling chambers 64. The cooling chambers 64 are separated in the upper portion 60 of the housing 56 by generally rectangular condenser fingers 68 that extend upwardly in the upper portion 60 from an open space above the refrigerant 62 for receiving the vapor from the refrigerant 62.
The heat in the assembly 20 is rejected into a stream of air flowing through the cooling chambers 64 and over the cooling fins 66. The assembly 20 may include a fan that is disposed adjacent to the housing 56 for moving air through the cooling chambers 64 and over the cooling fins 66. Alternatively, the assembly 20 may include a second refrigerant 62 that flows through the cooling chambers 64 to dissipate heat from the assembly 20. The assembly 20 may also be liquid cooled.
The electronic device 22 may be a computer chip 22. The plate 24 is called a lid or integrated heat sink (IHS) in the chip 22 industry. The plate 24 is typically 1.5-2 mm thick and made out of a copper based alloy. The plate 24 is permanently bonded to the silicon substrate of the electronic device 22 by means of an epoxy layer 70 of low thermal conductivity. In a typical symmetrically designed computer chip 22 most of the heat is dissipated in the central core of the computer chip 22. This leads to heat transfer at a high heat flux (watts/cm2) through the central core of the electronic device 22. Heat transfer at a high heat flux through the central core of the electronic device 22 results in a large temperature drop across the epoxy layer 70.
The second grease layer 38 is used to flexibly attach the external heat sink 34, such as, an air-cooled heat sink, LCU, or thermosiphon, to the plate 24. In the stack up of thermal resistances originating from the silicon substrate of the electronic device 22, the resistance of the second grease layer 38 is the highest. This is primarily due to the low thermal conductivity of the second grease layer 38. Typically, the thermal conductivity of the second grease layer 38 is of the order of 3-6 W/m° C. In comparison the thermal conductivity of pure copper is 380 W/m° C. The transfer of heat at high heat flux through the second grease layer 38 due to minimal lateral heat spreading results in a large temperature drop at the center and a lower temperature drop in the periphery. The ultimate consequence of concentrated heat transfer though the core of the electronic device 22 is the electronic device 22 having a higher surface temperature at the center. The higher the maximum surface temperature of the electronic device 22 the lower the computing speed and reliability of the electronic device 22.
The above fact is shown in
Typically, for a square electronic device 22 of size 35 mm×35 mm, 80% of the total heat is dissipated through the central core having a size of 10 mm×10 mm. Of the total 125 Watts dissipated by the electronic device 22, 100 Watts is dissipated in the central 1 cm2 area leading to a heat flux of 100 W/cm2. The remaining 25 Watts is dissipated in the peripheral region of area 11.25 cm2, resulting in a heat flux of 2.22 W/cm2. Thus the heat flux is non uniformly distributed over the silicon substrate of the electronic device 22. Heat flowing at 100 W/cm2 through the second grease layer 38 of thickness 0.08 mm and conductivity 4 W/m° C., results in a temperature drop of 20° C. just across the second grease layer 38, while heat flowing at the peripheral regions at a heat flux of 2.22 W/cm2 results in a temperature drop of less than 0.5° C. A temperature drop of 20° C. at the central region of the electronic device 22 results in an undesirable significant increase in the maximum temperature of the electronic device 22 at the core.
The thermoelectrically enhanced spreader plate 24, addresses the primary problem of insufficient lateral heat spreading by pumping heat through the peripheral regions. By forcing heat to flow to the peripheral regions through the thermoelectric module 44, the heat flux through the central region is significantly reduced, even though the heat flux distribution at the origin of the electronic device 22 is concentrated at the center. The lateral heat spreading forced by the thermoelectric module 44 thus results in a lower temperature drop across the epoxy layer 70, and much lower temperature drop across the second grease layer 38, leading to a lower maximum surface temperature at the center of the electronic device 22.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
