Patent Application
20120168123
This application is directed, in general, to a heatsink.
Some modern electronic devices are capable of dissipating a large amount of power during operation. For example, some integrated devices, such as microprocessors, may generate as much as 50-150 watts. In general this heat must be conducted from the device to prevent an excessive temperature rise that may hinder proper operation or reduce the lifetime of the device.
One aspect provides an apparatus. The apparatus includes a supporting member, a cooling stage and a translating member. The cooling stage has a surface for contacting an electronic device. The cooling stage is translatably coupled to the supporting member. The translating member is coupled to the supporting member and attached to the cooling stage. The translating member is operable to translate the cooling stage relative to the supporting member to urge the cooling stage surface against the electronic device.
Another aspect provides a method. In a first step of the method a supporting member is provided. A translatable member is coupled to the supporting member. A cooling stage is attached to the translatable member. The cooling stage has a surface for contacting an electronic device. The cooling stage is operable via the translatable member to translate the cooling stage relative to the supporting member to urge the cooling stage surface against the electronic device
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Some prior art heatsink assemblies include a cooling stage thermally and mechanically coupled to heat-radiating fins. The cooling stage may be placed in contact with an electronic device to be cooled. Heat from the device is conducted by the cooling stage to the heat-radiating fins and dissipated to the surrounding air. Such prior art heatsink assemblies typically include mounting hardware such as threaded inserts to join the assembly to a circuit board that includes the electronic device to be cooled.
The prior art heatsink is typically mounted to the circuit board using fasteners such as screws that pass through holes in the circuit board. Signal and power traces on the circuit board must be routed around these holes. As electronic systems become more complex it is sometimes desirable or necessary to route a large number of circuit traces near the electronic device. Thus the prior art heat sink is not well suited to such high-density circuit board layouts due to the space requirements of mounting the heatsink to the circuit board.
Another inadequacy of prior art heatsinks concerns damage to the electronic device being cooled. In some cases the electronic device is a semiconductor device in a lidless package. Typically such a device is packaged in a flip-chip configuration so that the underside of the semiconductor substrate upon which the device is formed is accessible. The cooling stage is placed in contact with the substrate to provide the desired cooling of the device.
The substrate is typically thinned in the manufacturing process to a final thickness of about 250 μm, and is thus fragile. If the cooling stage contacts the substrate with excessive force, the substrate may fracture. Such may occur, e.g., if the surface of the cooling stage is not substantially coplanar with the surface of the substrate when the cooling stage contacts the substrate.
The prior art heatsink assemblies must therefore be installed with a high degree of precision to limit the risk of substrate damage. Such precision may increase the installation time, and may not reduce the risk of damage below a desired limit.
The inventors have recognized that the aforementioned limitations of the prior art may be eliminated or substantially ameliorated by attaching the heatsink assembly, or a cooling stage thereof, to a supporting member such as an enclosure panel that is located over the electronic device. The enclosure panel may be, e.g. a cover that is attached to a circuit board that includes the electronic device, or attached to a support to which the circuit board and the cover are both attached. The heatsink assembly includes a translating member located between the cooling stage and the supporting member. The supporting member may include a compression assembly that may hold the cooling stage at a distance from the electronic device to prevent contact between the electronic device and the cooling stage while the enclosure panel and attached heatsink assembly are fastened over the electronic device. After the enclosure panel is installed, and its position relative to the electronic device is fixed, the compression assembly may be adjusted to urge the cooling stage against the electronic device, thus thermally coupling the electronic device to the cooling stage. Heat from the electronic device may then be transferred to the ambient with the aid of cooling fins, heat pipes, vapor chambers, etc.
Turning first to
The cooling stage 110 is attached to a translating member 120, e.g. a screw shaft. In some embodiments the cooling stage 110 and the translating member 120 are rotatably attached, such as by employing a ball joint. In such embodiments the translating member 120 may turn about an axis 121 while the cooling stage 110 remains stationary with respect to the axis 121. The translating member 120 is translatably coupled to a supporting member 130 via the translating member 120. By translatably coupled, it is meant that the translating member 120 may move vertically with respect to the supporting member 130 as
The translating member 120 may be configured to maintain a non-zero distance 170 between the cooling stage 110 and the electronic device 160. In this way, sufficient clearance may be maintained between the cooling stage 110 and the electronic device 160 when the supporting member 130 is joined to the substrate 140 to ensure that cooling stage 110 does not contact the electronic device 160.
The supporting member 130 may in some embodiments be attached directly to the substrate 140 via standoffs 150 as illustrated in
Referring to
Referring the
The housing 230 includes an opening through which an annular portion 240 of the cooling stage 205 passes. The annular portion 240 supports the spring 220 via a ridge 245 such as a washer. The clearance between the housing 230 and the annular portion 240 may be, e.g. about 750 μm (˜30 mil) to allow the cooling stage 205 to rotate relative to the supporting member 210, such as to accommodate non-coplanarity of the supporting member 210 and the electronic device to be cooled.
The spring 220 is compressed between a washer 250 attached to the screw 225 and the ridge 245. The ridge 245 and the washer 250 may be attached to the spring 220, e.g. by a tack weld or adhesive. Vertical movement of the washer 250 is constrained by the screw 225. Motion of the ridge 245 is limited by the housing 230, but may move in the direction of the supporting member 210 as the spring 220 is further compressed or when the screw 225 is withdrawn from the threaded hole 235. The annular portion 240 is formed such that a gap 255 remains between the housing 230 and the cooling stage 205 when the ridge 245 rests against the annular portion 240. The gap 255 is not limited to any particular value, but in an illustrative embodiment is about 1 mm.
In some embodiments the washer 250 is captured by the screw 225 such that the washer may rotate relative to the screw 225. In such embodiments the washer 250, spring 220, ridge 245, translating member 215 and cooling stage 205 may rotate as a unit relative to the screw 225. Thus the cooling stage 205 is rotatably attached to the screw 225 in such embodiments.
When the screw 225 is withdrawn sufficiently from the threaded hole 235 the spring 220 may be placed in tension, and the cooling stage 205 may be pulled up until it rests against the housing 230. The apparatus 200, and more specifically the contact surface 260, may then be placed proximate, but not touching, an electronic device to be cooled. Any desired mechanical adjustments that affect the relative position of the contact surface 260 and the electronic device may be made without contact therebetween. When the position of the contact surface 260 is rigidly fixed relative to the electronic device, then the screw 225 may be inserted further into the threaded hole 235, causing the cooling stage 205 to translate away from the supporting member 210 until the contact surface 260 contacts the electronic device. Further insertion of the screw 225 may compress the spring 220, thereby urging the contact surface 260 against the electronic device.
In the illustrated embodiment the enclosure 410 at least partly encloses a space that includes the electronic device 450, the apparatus 200 and the radiating fins 460. A fan (not shown) may cause air to flow within the enclosed space, thereby transferring heat from the radiating fins 460 to the air.
The apparatus 400 may be initially configured such that the cooling stage 205 is translated toward the enclosure 410 to the maximum extent possible. The enclosure 410 may then be attached to the circuit board 420 without the cooling stage 205 contacting the electronic device 450, thereby reducing the chance of damage to the electronic device 450 during assembly. After assembly, the screw 225 may be partially or fully inserted to cause the cooling stage 205 to translate away from the enclosure 410 and toward the electronic device 450. The contact surface 260 is expected to be substantially coplanar with the surface of the electronic device 450, so pressure therebetween is expected to be about evenly distributed over the electronic device 450. The spring constant of the spring 220 may be selected to result in a compressive force between the cooling stage 205 and the electronic device 450 that results in low thermal resistance therebetween without placing excessive force on the electronic device 450.
Those skilled in the pertinent art will appreciate that a heat pipe is a closed volume that includes a working fluid that that may transport heat from one location within the heat pipe to another location within the heat pipe via a vaporization-condensation cycle. Heat pipes are often cylindrical but need not be. Movement of the condensed phase of the working fluid may include transport within a wick placed along the inner surface of the heat pipe. Those skilled in the pertinent art will also appreciate that a vapor chamber is an analog of the heat pipe that uses first and second surfaces that may be opposing. A heat source may be placed in thermal contact with the first surface, and an internal vaporization-condensation cycle may transport heat from that location to another location on the first surface, or to the second surface.
The supporting member 510 and a substrate 560 such as a circuit board are rigidly attached either directly, such as by standoffs, or indirectly by way of an external mechanical assembly as previously described. The cooling stage 530 is urged against an electronic device 570, also as previously described.
In the illustrated embodiment a captive quarter-turn fastener 580 is used to compress the spring 220 after the cooling stage 530 is located over the electronic device 570. The fastener 580 and the spring 220 are configured such that when the fastener 580 is in an initial position the cooling stage 530 is retracted, e.g. translated toward the supporting member 510. A non-zero distance may thereby be maintained between the cooling stage 530 and the electronic device 570 during assembly of the apparatus 500. After rigidly attaching the supporting member 510 to the substrate 560 the fastener 580 may be rotated about 90°. The fastener 580 includes a pin 581 that engages a cam (not shown) to compress the spring 220 and thereby translate the cooling stage 530 toward the electronic device 570. The cooling stage 530 may thereby be urged against the electronic device 570 as previously described. The cam may include a recess into which the pin 581 may be retained in the compressed or uncompressed positions to ensure stability of the position of the cooling stage 530.
Turning now to
The method begins with a step 610, in which a supporting member is provided, such as one of the supporting members 130, 210, 510 or the enclosure 410. Herein and in the claims, “provided” means that the supporting member may be manufactured by the individual or business entity performing the disclosed methods, or obtained thereby from a source other than the individual or entity, including another individual or business entity.
In a step 620 a translatable member is attached to the supporting member. The translatable member is exemplified by the translating members 120, 215, 520.
In a step 630 a cooling stage is coupled to the translatable member. The cooling stage is exemplified by the cooling stages 110, 205, 530. The cooling stage has a surface such as the contact surface 260 for contacting an electronic device. The translatable member is thereby operable to translate the cooling stage relative to the supporting member to urge the cooling stage against the electronic device.
In an optional step 640 heat-radiating fins such as the radiating fins 460 are thermally coupled to the cooling stage. In an optional step 650 a heat pipe such as the heat pipe 540 is attached to the cooling stage.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
