Patent Application
20090166008
1. Field of the Invention
The present invention relates to a heat spreader, and more particularly to a heat spreader with an improved vapor chamber for preventing liquid contained therein from drying out.
2. Description of Related Art
It is well known that heat is generated during operations of electronic components, such as integrated circuit chips. To ensure normal and safe operations, cooling devices such as heat sinks are often employed to dissipate the generated the heat away from these electronic components.
As progress continues to be made in the electronics art, more components on the same real estate generate more heat. The heat sinks used to cool these chips are accordingly made larger in order to possess a higher heat removal capacity, which causes the heat sinks to have a much larger footprint than the chips. Generally speaking, a heat sink is more effective when there is a uniform heat flux applied over an entire base of the heat sink. When a heat sink with a large base is attached to an integrated circuit chip with a much smaller contact area, there is significant resistance to the heat flow to the other portions of the heat sink base which are outside reach of the chip.
A mechanism for overcoming the resistance to heat flow in a heat sink base is to attach a heat spreader to the heat sink base or directly make the heat sink base as a heat spreader. Conventionally, the heat spreader includes a vacuum chamber defined therein, a meshed layer or sintered layer acting as a wick structure provided in the chamber and lining an inside wall of the chamber, and a working fluid contained in chamber. As the integrated circuit chip is maintained in thermal contact with the heat spreader, the working fluid contained in the wick structure corresponding to a hot contacting location vaporizes. The vapor then spreads to fill the chamber, and wherever the vapor rushes into contact with a cooler surface of the chamber, it releases its latent heat of vaporization and condenses. The condensate reflows to the hot contacting location via a capillary force generated by the wick structure. Thereafter, the condensate frequently vaporizes and condenses to form a circulation to thereby remove the heat generated by the chip.
However, in the conventional heat spreader, since a reflowing direction of the condensate back toward the hot contacting location is opposite to a spreading direction of the vapor toward the other cooler locations, a shearing force occurs at an interface between the condensate and the vapor, which obstructs the condensate and render it remote from the hot contacting location. When a quantity of the heat generated by the chip reaches a critical number, a spreading speed of the vapor would be so rapid that the shearing force becomes large enough to bring all of the condensate away the hot contacting location. Therefore, no condensate back to the hot contacting location causes the condensate at this location dries out, and the heat spreader fails to work.
What is needed, therefore, is a heat dissipating device which can overcome the above-mentioned disadvantages.
A heat spreader for cooling an electronic component comprises a lower plate, an upper plate fixed on the lower plate to cooperatively define a chamber, working liquid contained in the chamber, and a wick structure formed between the lower plate and the upper plate. Each of the upper plate and the lower plate defines a cavity receiving a portion of the wick structure therein, and a plurality of grooves extending radially from the cavity to a periphery thereof. The liquid can be transferred from cooler portions of the heat spreader to the cavity through the grooves, which provide different pathways from the chamber in which the vapor spreads. Therefore, a distribution of the vapor flux acting to the liquid flow can be reduced, and a dry-out problem of the heat spreader is resolved.
Other advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
Many aspects of the present apparatus can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
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In use, the heat spreader is disposed on the electronic component with the part corresponding to the cavity 120 of the lower plate 12 contacting the electronic component. As the electronic component operates and generates heat, the working liquid is heated and vapored to vapor. The vapor spreads to fill the chamber between the lower plate 10 and the upper plate 20 along a radial outward direction. As the vapor reaches other cooler portions of the heat spreader outside reach of the electronic component, it exchanges heat with the other portions of the heat spreader and is condensed to liquid, whereby the heat is dissipated by the other portions of the heat spreader to an ambient. The liquid on the other portions of the lower plate 10 which are not in direct contact with the electronic component refluences to the cavity 120 through the grooves 122 of the lower plate along a radial inward direction, via capillary force generated by the grooves 122; the liquid on a bottom of the upper plate 20 refluences to the wick structure 30 through the grooves 222 along the radial inward direction, and then reflows to the cavity 120 of the lower plate 10 via the wick structure 30. The liquid is vapored and condensed continuously, thereby circling the heat exchange between the electronic component and the ambient.
Since there are grooves 122, 222 formed in the upper plate 20 and the lower plate 10, the liquid reflowing in the grooves has a large area contacting inner faces of the grooves 122, 222, and only has a small area exposed within the vapor; that is to say, the reflowing liquid only has a small area influenced by the vapor, whereby a shearing force occurring at the interface between the vapor and the liquid can be controlled to be small. Even if a spreading speed of the vapor is high, the small shearing force can not tack all of the liquid away the cavity 120, 220; therefore, the liquid located near the cavity 120, 220 of the heat spreader is prevented from drying out.
It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
