A DRUM-BASED VAPOR CHAMBER WITH AN INSERTABLE WICK SYSTEM

CROSS REFERENCE TO RELATED APPLICATION This application claims priority to and incorporates by reference U.S. Patent

Application No. 60/978,763 filed October 10, 2007.

TECHNICAL FIELD

This application relates to cooling devices, and more particularly, to vapor chambers. BACKGROUND

As the performance of electronic components continues to increase, the electronics industries have greater demands for higher capability coolers. Vapor chambers, which utilize the heat-pipe principle, have increasingly been considered as promising substitutes for traditional heatsinks. Still, several problems prevent vapor chambers from wide-spread usage. Among these is the amount of time and effort to custom develop a solutions for potential customers.

Generally, vapor-chamber providers use a design-in process to customize products for a potential end-user. Besides being a very time-consuming and expensive process, the main problem with this design-in process lies in the time lag between the design cycle of electronic components/systems and the time to develop a sample of the relevant vapor chamber. The minimization of this time-lag is critical to the successful design of an electronic system/component, but current vapor chambers typically utilize wicking structures that require extensive and time-consuming retooling for each design. Consequently, the cost structure cannot scale effectively, while on the user side, it has become typical for electronic components/systems to be designed without an identified cooling solution.

In general, the disadvantages of current vapor chambers can be summarized as follows:

1. Bridging wick formation processes: The wick at the evaporation and condensation region must necessarily be an integral part of the chamber surface (i.e., by directly etching the wick onto the surface or by using a metallurgical bonding process to attach the wick onto the surface) in order to minimize any contact resistances and to ensure operational consistency/reliability. A "bridging" wick is generally employed to bring the condensate from the condensation region to the evaporation region. In heatpipes, this "bridging" path generally flows along the axial direction of the cylinder surface (i.e., the adiabatic region), but in vapor chamber configurations, this bridging path is a more complex three-dimensional path and is thus generally formed along with the wicks at the evaporation/condensation regions. Since these bridging wicks are generally formed along the side -wall through customized processes such as diffusion bonding or sintering, this results in the need for chamber specific tooling for individual sizes and shapes.

2. Material selection: The wick formation processes typically require sintering and diffusion bonding which are difficult to implement with aluminum. Groove wicks which can be used for aluminum typically cannot generate the capillary pressure for the proper functioning in a vapor chamber. Consequently, the vast majority of vapor chambers utilize copper, whose price has increased by many folds in the last 5 years.

3. Chamber format: To maximize material utilization, current chambers are typically formed by placing one panel on top of another panel that has been

stamped to create a cavity. However, the consequence is that each chamber size or thickness would require re -tooling, which means that the chamber needs to be made "to order". That is, the production of chamber becomes a customization process, and consequently, it has run into severe difficulty to achieve the necessary cost reduction and break into the mass market. Also, the turning corners of a stamped chamber is mechanically weak against bending moments, and thus in order to prevent the chamber from collapsing under vacuum, thicker working material is needed along with a significant number of internal support columns. As a result, what seemed like an efficient format (in terms of materials utilization) may actually turn out to be inefficient.

Embodiments of the invention overcome these and/or other limitations of vapor chambers.

SUMMARY

Embodiments of the present invention overcome the limitations of existing vapor chambers by:

1. Providing a drum format to enable a higher efficiency in material usage and to alleviate the need for format-specific toolings.

2. Providing an insertable "bridging" wick system to enable the return of condensate along the side-walls without needing format-specific toolings.

3. Applying one of the two above techniques to enable the utilization of alternative materials in the construction of vapor chambers. Specifically, this enables the utilization of aluminum and/or polymers to achieve a significant material-cost reduction relative to the utilization of copper.

In the present invention, the Vapordrum comprises two Coverskins and a Frame, which may be made of metals (including aluminum that may be untreated, anodized, plated and/or laminated), elastomers, polymers, composites, ceramics and/or some combination thereof, and which can be assembled to give rise to chambers of different dimensions. The Coverskins are functionally joined (through soldering, brazing, welding, diffusion bonding or any other similar methods known in the arts) to the frame to give rise to a "drum" enclosure whereby similar to membranes on a drum, the two Coverskins resist deformation mainly through tensile forces along the plane of the skins, and thus much thinner materials, such as a copper foil, could be used. To enable this condition, the frame would operate similar to the cylindrical body of a drum in providing the necessary bending resistance so as to keep the Coverskins in a state of relative tension when it is subject to external loading. The net result of this arrangement is that each

component would largely be responsible for only one type of force (i.e., tension or bending), and thus a state of maximum efficiency could be achieved. Consequently, the strength of the Coverskins (to resist collapse) is less dependent on its thickness, and a state of minimum thickness can thus be achieved. The Frame itself may comprise one or more brackets that are formed by mass production processes such as rolling, drawing, forging, molding, extrusions or any similar methods known in the arts, and which may themselves be functionally joined together through diffusion bonding, soldering, brazing, welding, or any other methods known in the arts. The top Coverskin (condensing side) may have integrated fin structures (formed through molding, extrusion, cutting, skiving, swaging or any other processes known in the arts) or have fins functionally disposed thereon. As the Coverskins and brackets could be cut from larger stocks, this enables the production of a large family of chambers (with different dimensions and aspect ratios) without retooling delays.

To further increase the Vapordrum's ability to withstand the large forces generated by the vacuum or internal vapor pressure, the contact interface between the Coverskins and the Frame may partially extend into the internal chamber (via support bars) to increase the amount of contact surface and decrease the separation distances between the supporting structures of the Coverskins. Also, as the support bars may be an integral part of the frame, it can be planarized through grinding, polishing, cutting or any other methods known in the arts, to ensure the appropriate co-planarity.

For the Vapordrum to function as a vapor chamber, at least one evacuation/charging tube needs to be functionally connected to the Coverskins and/or the Frame. A vacuum is applied and the appropriate working fluid (such as water, acetone,

ammonia or any other known in the arts) is charged within. Wicking structures are functionally disposed onto the internal surfaces of the chamber to enable the appropriate flow of condensate from the condensation region toward the evaporation region.

On the top Coverskin (condensing side), the wicks may comprise sintered powder, grooves (formed through sawing, machining, chemical etching or any other methods known in the arts) and/or wire mesh that has been bonded through welding, soldering, sintering, diffusion bonding or any other methods known in the arts. To enable rapid turnaround, these wicks may be formed during assembly (i.e., through sawing or machining) or may be preformed onto a large stock (i.e., through chemical etching or sintering) from which the top Coverskin is cut. Similarly, at least a portion of the bottom Coverskin (i.e., at the evaporation region) may have wicks (sintered powder, grooves and/or mesh) functionally disposed thereon either during assembly or during the formation of the larger stock.

For the sidewalls, an insertable wick system is disposed comprising optional "fill- in" wicks and a "retainer" which is essentially a mechanical spring-like structure such as a clip, a coarse wire-mesh, a folded plate with grooves formed thereon, or any other similar mechanism known in the arts. Besides providing wicking purpose this "retainer" may also serve to keep in-place the optional "fill-in" wicks which may comprise wire mesh, foams, un-sintered powder or any other similar wick structures known in the arts. As the "retainer" is in functional contact with the top and bottom Coverskin (the optional "fill-in" wick in functional contact with the side-walls), the resulting insertable wick system fulfills the critical function of providing the condensate flow path from the top Coverskin, through the side and ultimately toward the evaporation region of the bottom

Coverskin. The critical point here is that the "bridging" function can now be fulfilled by an insertable wick system which is adaptable to virtually any chamber thickness and sizes without incurring retooling delays. For the purpose of the present invention, an insertable wick is a component capable of drawing condensate toward the outer edge of the vapor chamber and at least one of the components should be in operational contact with at least a portion of the chamber surface without forming a metallurgical bond to the said chamber surface.

To further improve the functioning of the Vapordrum, the above-mentioned wick structures may further be implemented as part of a Multi-Wick structure with or without Boiling Enhancement as disclosed in our earlier U.S. patent application numbers 11/272,145 and 11/164,429, which are incorporated herein by reference. The details of one or more implementations of the present invention are set forth in the accompany drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawing and from the claims.

DESCRIPTION OF DRAWINGS

Fig. Ia - Cross-sectional isometric view of a Vapordrum showing the major components

Fig. Ib - Schematic showing the Frame to comprise only one bracket Fig. Ic - Schematic showing the Frame integrated with the bottom Coverskin

Fig. 2 - Planar view of the top Coverskin showing the wick structures

Fig. 3a - Isometric view of the retainer

Fig. 3b - Cross sectional view of the retainer

Fig. 3c - Schematic showing the retainer comprising a wire-frame Fig. 4a - Cross sectional isometric view of a composite Vapordrum

Fig. 4b - Side view of a composite Vapordrum with functional interface with a heatsource and fins

DETAILED DESCRIPTION

Figure Ia shows a cross-sectional view of the an embodiment of the Vapordrum

100 comprising a top Coverskin 110, a Frame 120, a charging tube 130, a bottom Coverskin 140, an insertable wick system 150, and a Boiling-enhancement structure 160. The boiling-enhancement structure 160 is in thermal contact with a heat-producing device, 170. The Frame 120 may comprise one or more brackets 121 which may be functionally joined together 122 and where each bracket 121 may contain an additional support bar 123, which could be functionally joined to the Coverskins for additional strengthening purposes. Figure Ib shows the Frame 120 to comprise only one bracket while Figure Ic shows the Frame 120 integrated with the bottom Coverskin 140. The charging tube 130 is used for connection to a vacuum pump and liquid supply, and is sealed through crimping, soldering, welding or any other methods known in the arts, after completion of evacuation and working-fluid charging processes.

Fins 111 can be integrated onto the top (condensing side) Coverskin 110, and Figure 2 shows the wick structure 150 comprises grooves 212 and/or mesh 213 that has been functionally disposed on the surface. In turn, these wicks (212 and 213) shall be in functional contact (as shown in Figure Ia) with the retainer component 151 of the insertable wick system 150. As shown in Figures 3a and 3b, this retainer 350 may be made out of metal and may be a folded sheet containing groove structures 351 (formed by cutting, etching or any methods known in the arts) that serve, as shown in Figure Ia, to channel the condensate away from the condensing surface 110 toward the mesh- wick component 152 or unsintered powder component 153 of the insertable wick system 150, and ultimately brings the condensate back to the boiling enhancement structure 160 at the

evaporation region. Alternatively, as shown in Figure 3c, this retainer 350 may also comprise a folded wire frame .

The wick structure as disclosed above can also be a type of Multi-wick structure as disclosed in U.S. patent application #11/272,145, wherein the wicking power of the wick on the condensing surface (213 and 212) is less than that at the side-wall (i.e. the insertable wick system 150) and/or that at the evaporation region 160. Furthermore, a Boiling-Enhancement structure may optionally be utilized at the evaporation region 160, so as to give rise to a Boiling-Enhanced Multi-wick structure, which as disclosed in U.S. patent application #11/164,429, may take the form of fins, pins, grooves, foam, porous structures ( inclusive of mesh), or any combination thereof. Figure 1 shows the Boiling- enhancement structure 160 to be fin structures that can be obtained by selective machining (or any other processes known in the arts) of the bottom Coverskin, 140.

For weight reduction purposes, the Vapordrum may be made out of composite materials. Figure 4a shows a cut-away and a cross-sectional view of a composite Vapordrum 400 comprising a composite Coverskin 410, a composite Frame 420 with a charging tube 430. The Frame 420 has an inner core 421 made of either polymer or metal (such as aluminum) which is functionally joined with a non-polymer 422, which may be a ceramic or a metal (plated, laminated or deposited on). This Frame 420 is functionally joined to composite Coverskin 410 that comprises an outer layer (made of metals such as aluminum or polymer) 411 and a non-polymer inner layer 412. Figure 4b shows selected locations on the Coverskins to be uncovered for interfacing with heating surfaces 436 and/or metallic fins 437.