US20050039884A1

US20050039884A1 - Conformal heat sink

Info

Publication number: US20050039884A1
Application number: US10/644,375
Authority: US
Inventors: Ivan Pawlenko; Larry Samson
Original assignee: Lucent Technologies Inc
Current assignee: Nokia of America Corp
Priority date: 2003-08-20
Filing date: 2003-08-20
Publication date: 2005-02-24

Abstract

In one embodiment, a heat sink of the invention includes a corrugated plate and a deformable membrane, attached to each other at the periphery to define an enclosed volume. The membrane has a metal foil layer, due to which it can be deformed to conform to a complicated surface geometry of the electronic module to be cooled. To mate the heat sink with the module, air pressure is applied to the enclosed volume through a fitting to force the membrane into close contact with heat generating components of the module. When the air supply is disconnected, the membrane retains its shape due to the malleability of the foil layer. The enclosed volume is then filled with an appropriate heat-conducting fluid, which may optionally be circulated to facilitate heat removal from the module.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to cooling heat-generating electronic devices.
2. Description of the Related Art
Many electronic devices and/or components generate heat during operation. Unless heat is removed to maintain a device within the appropriate operating temperature range, the speed, power, and useful lifespan of the device may be adversely affected. The problem of heat removal is often exacerbated when the device is mounted on a thermally non-conductive substrate, such as an epoxy-composite printed circuit board (PCB). In a typical electronic module, electronic devices are densely packed on a PCB resulting in a complicated surface topology of varying heights, shapes, and profiles.
FIG. 1 shows a three-dimensional perspective view of an electronic module 100 having attached three prior-art heat sinks 110 a-c. More specifically, module 100 includes a plurality of electronic devices, e.g., integrated circuits, mounted on a PCB 102. Each heat sink 110 is attached to a corresponding group of devices, with all devices within the group preferably having similar shapes and dimensions. For example, heat sink 110 a is attached to a group having nine devices 104, heat sink 110 b is attached to a group having nine devices 106, and heat sink 110 c is attached to a group having six devices 108. In addition, a heat sink similar to heat sink 110 may be attached to each individual heat-generating device, e.g., circuit 112. Each heat sink 110 is fabricated of a material having good thermal conductivity, e.g., aluminum or copper, and has the shape of a plate with fins extending from one side of the plate to increase the effective surface area for heat dissipation. The opposite side of the plate is appropriately profiled to match the geometric shape of the group being cooled.
One problem with heat sinks similar to heat sink 110 is that it is tedious and expensive to design, fabricate, and install individual heat sinks for different individual heat-generating devices or groups of such devices, which are typically diverse in placement and shape.

SUMMARY OF THE INVENTION

Problems in the prior art are addressed, in accordance with the principles of the present invention, by a conformal heat sink. In one embodiment, a heat sink of the invention includes a corrugated plate and a deformable membrane, attached to each other at the periphery to define an enclosed volume. The membrane has a metal foil layer, due to which it can be deformed to conform to a complicated surface geometry of the electronic module to be cooled. To mate the heat sink with the module, air pressure is applied to the enclosed volume through a fitting to force the membrane into close contact with heat generating components of the module. When the air supply is disconnected, the membrane retains its shape due to the malleability of the foil layer. The enclosed volume is then filled with an appropriate heat-conducting fluid, which may optionally be circulated to facilitate heat removal from the module.
According to one embodiment, the present invention is a heat sink for cooling heat-generating electrical equipment having a surface profile, the heat sink comprising a plate and a deformable membrane attached to the plate to define an enclosed volume, wherein, when the heat sink is positioned in proximity to the equipment and a deformation force is applied to the membrane, the membrane conforms to the surface profile.
According to another embodiment, the present invention is a method of cooling heat-generating electrical equipment having a surface profile, the method comprising: (A) positioning a heat sink in proximity to the equipment, wherein the heat sink comprises a plate and a deformable membrane attached to the plate to define an enclosed volume; and (B) applying a deformation force to conform the membrane to the surface profile.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and benefits of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which:
FIG. 1 shows a three-dimensional perspective view of an electronic module having attached three prior-art heat sinks;
FIGS. 2A-B show three-dimensional perspective and cross-sectional views, respectively, of a heat sink according to one embodiment of the present invention; and
FIG. 3 shows a cross-sectional view of an electronic module having attached the heat sink shown in FIG. 2 according to one embodiment of the present invention.

DETAILED DESCRIPTION

Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
FIGS. 2A-B show three-dimensional perspective and cross-sectional views, respectively, of a heat sink 210 according to one embodiment of the present invention. Heat sink 210 includes a top panel 212 and a deformable membrane 214, both mounted on a support frame 216. Panel 212 and membrane 214 are attached to each other at the periphery to define an enclosed volume 220. In a preferred implementation, volume 220 is an airtight volume accessible through a pair of fittings 222 a-b. Each fitting 222 is adapted to be connected to an external supply line, e.g., a compressed air line. When necessary, each fitting 222 may be plugged using an appropriate fitting cap.
Panel 212 has the shape of a corrugated plate to increase both the surface area of volume 220 and the effective external area of heat sink 210 for heat dissipation. In one implementation, membrane 214 has at least two layers, a metal foil layer and a thin dielectric layer (not shown). The foil layer provides malleability to membrane 214, due to which it can be deformed into a desired shape and then retain that shape after the deformation force is removed. The dielectric layer is deposited onto the outer (i.e., corresponding to the exterior of heat sink 210) surface of membrane 214 to provide electrical insulation, e.g., between the heat sink and any electronic devices it is in contact with. Conformational freedom of membrane 214 is enabled by the appropriate selection of membrane's size. More specifically, in a fully extended (unfolded) state, the area covered by membrane 214 exceeds by a selected amount (e.g., 30%) that of the planar cross-section of frame 216. As will be further explained below, membrane material in excess of the planar cross-section area is used to conform the shape of heat sink 210 to a complicated surface geometry of the electronic module to be cooled.
FIG. 3 shows a cross-sectional view of an electronic module 300 having attached heat sink 210 (FIG. 2) according to one embodiment of the present invention. Module 300 is similar to module 100 (FIG. 1) and includes a plurality of irregularly shaped electronic devices 304-314 mounted on a PCB 302. Heat sink 210 is mounted on PCB 302 using screws 316, each attached between support frame 216 and the PCB. Using the pliability of membrane 214, the membrane is molded to adapt to the shape of devices 304-314 and to provide good thermal contact between those devices and the membrane.
In one embodiment, the shape of heat sink 210 is conformed to that of module 300 as follows. First, empty heat sink 210 is mounted over the corresponding area of module 300 using screws 316. Then, one of fittings 222 a-b is plugged and the other one is connected to a compressed air source. Air pressure is applied to volume 220 to push membrane 214 toward devices 304-314 and PCB 302. The pressure value is selected such that membrane wraps over each device and is forced into the spaces between different devices thereby adapting to the shape of module 300. When the air pressure is removed, membrane 214 retains its shape due to the malleability of its foil layer. A layer of thermally conducting grease may be placed between membrane 214 and devices 304-314 to further improve the thermal contact. Then, volume 220 is filled with an appropriate heat-conducting fluid, which facilitates heat flow from membrane 214 to panel 212. In one embodiment, the grease and/or fluid are selected from an assortment of thermally conductive gels commercially available from Gel Sciences, Inc., of Bedford, Mass.
Optionally, the heat-conducting fluid may be circulated through heat sink 210 using an external circulation device (e.g., a pump) connected to fittings 222 a-b (FIG. 2). The circulation may be either continuous or intermittent. For example, intermittent circulation may be implemented as follows. Volume 220 is filled with a first portion of relatively cool fluid from an external reservoir. This portion is allowed to remain in heat sink 210, e.g., until the fluid temperature rises, due to the heat generated in module 300, to a certain selected value. Then, the first portion is pumped out of heat sink 210 and a next portion of relatively cool fluid is transferred into volume 220.
In another embodiment, to conform the shape of heat sink 210 to that of module 300, the heat sink is assembled in situ over the module, e.g., as follows. A sheet of membrane material is applied to module 300 to cover the selected area to be cooled. The sheet is then (i) creased to adapt to the shape of devices 304-314 and PCB 302 and (ii) cut around the periphery of the area to be cooled. Support frame 216 is then mounted on PCB 302 and the edge of the membrane is attached to the frame without disturbing the creased portion of the membrane covering devices 304-314. Panel 212 is mounted onto frame 216 and the assembly is sealed around the periphery to form volume 220. To obtain an airtight seal, frame 216 may incorporate suitable gaskets for the attachment of membrane 214 and panel 212. Optionally, a glue or heat treatment may also be used to seal volume 220. Since the shape of so assembled heat sink 210 is already adapted to the shape of module 300, the step of applying air pressure, as described above, is no longer required.
In yet another embodiment, volume 220 of heat sink 210 is filled with a heat-conducting fluid prior to the heat sink attachment to module 300. Preferably, the amount of fluid transferred into volume 220 is chosen such that the volume is in a floppy state, e.g., similar to that of a partially filled sandbag. Heat sink 210, so filled, is then pressed against the surface of module 300 and secured thereon to produce the assembly shown in FIG. 3.
In various embodiments, heat sink 210 may be appropriately designed, for example, to have (i) relatively high turbulence of air and fluid flow around panel 212 for improved heat circulation and exchange, (ii) clips, springs, clamps, or other fasteners for ease of attachment to module 300 and/or (iii) a relatively large size to cover the entire PCB or circuit card. Due to the small thickness of membrane 214, relatively expensive materials, e.g., gold, may be utilized in the membrane without prohibitively increasing the cost of the heat sink. Gases, liquids, gels, fine powders, or various mixtures thereof can be used to fill volume 220. An active or passive heat-exchange device may be used, as known in the art, to cool the fluid circulated through volume 220. More specifically, in an active heat-exchange device, a refrigerant or a thermo-electric cooler is brought into thermal contact with the circulating fluid. In a passive heat-exchange device, the fluid is cooled down via passive dissipation of heat into the (cooler) environment. Advantageously, heat sinks of the invention are relatively easy to mate to different irregularly shaped heat-generating devices and/or modules.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the described embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the principle and scope of the invention as expressed in the following claims.
Although the steps in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular sequence.

Claims

1. A heat sink for cooling heat-generating electrical equipment having a surface profile, the heat sink comprising a plate and a deformable membrane attached to the plate to define an enclosed volume, wherein, when the heat sink is positioned in proximity to the equipment and a deformation force is applied to the membrane, the membrane conforms to the surface profile.

2. The invention of claim 1, wherein, when the deformation force is removed, the membrane retains a conformed shape.

3. The invention of claim 1, further comprising a support frame, wherein:

the plate and the deformable membrane are mounted on the frame; and

the frame is adapted to be mounted on the equipment.

4. The invention of claim 3, wherein:

the support frame has a planar cross-section area; and

the deformable membrane has a surface area greater than the planar cross-section area.

5. The invention of claim 1, wherein the membrane comprises a metal foil layer.

6. The invention of claim 5, wherein the membrane conforms to the surface profile by forming a pattern of creases.

7. The invention of claim 5, wherein the membrane further comprises a dielectric layer located at an outer surface of the membrane with respect to the enclosed volume.

8. The invention of claim 1, wherein the plate has a corrugated shape.

9. The invention of claim 1, wherein the enclosed volume is a sealed volume provided with one or more fittings, which allow the enclosed volume to be filled with an externally supplied substance.

10. The invention of claim 9, wherein the heat sink is configured for fluid circulation through the enclosed volume.

11. The invention of claim 1, wherein the enclosed volume contains a heat conducting fluid having thermal conductivity greater than air.

12. A method of cooling heat-generating electrical equipment having a surface profile, the method comprising:

(A) positioning a heat sink in proximity to the equipment, wherein the heat sink comprises a plate and a deformable membrane attached to the plate to define an enclosed volume; and

(B) applying a deformation force to conform the membrane to the surface profile.

13. The invention of claim 12, wherein, when the deformation force is removed, the membrane retains a conformed shape.

14. The invention of claim 12, wherein:

the heat sink further comprises a support frame;

the plate and the deformable membrane are mounted on the frame; and

the frame is mounted on the equipment.

15. The invention of claim 14, wherein:

the support frame has a planar cross-section area; and

16. The invention of claim 12, wherein the membrane comprises a metal foil layer and a dielectric layer adapted to provide electrical insulation between the heat sink and the equipment.

17. The invention of claim 12, wherein the enclosed volume is a sealed volume provided with one or more fittings, which allow the enclosed volume to be filled with an externally supplied substance.

18. The invention of claim 17, wherein step (B) comprises applying air pressure to the enclosed volume.

19. The invention of claim 12, further comprising transferring a heat-conducting fluid into the enclosed volume, wherein the fluid has thermal conductivity greater than air.

20. The invention of claim 19, further comprising circulating the fluid through the enclosed volume.