BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a heat spreader in accordance with a preferred embodiment of the present invention;
FIG. 2 is a cross-sectional view of the heat spreader of FIG. 1, taken along line II-II thereof;
FIG. 3 is a flow chart showing a preferred method of the present invention for manufacturing the heat spreader of FIG. 1;
FIG. 4 is an isometric view of a core for being electrodeposited with a layer of metal coating on an outer surface thereof to manufacture the heat spreader of FIG. 1;
FIG. 5 is a schematic, cross-sectional view of a mold applied for lining a mesh and filling a filling material therein to manufacture the core of FIG. 4; and
FIG. 6 is a schematic, cross-sectional view of an electrodeposition bath for electrodepositing the layer of metal coating on the outer surface of the core of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1 and 2 illustrate a heat spreader 100 formed in accordance with a method of the present invention. The heat spreader 100 is integrally formed and has a flat type configuration. The heat spreader 100 includes a metal casing 60 with a chamber 40 defined therein. A round hole 11 is defined in a middle portion of the metal casing 60 for location of a heat dissipating fan such as a centrifugal blower (not shown). A wick structure 12 is arranged in the chamber 40, lining an inner surface of the metal casing 60 and occupying a portion of the chamber 40. The other portion of the chamber 40, which is not occupied by the wick structure 12 functions as a vapor-gathering region. The metal casing 60 is made of high thermally conductive material such as copper or aluminum. The heat spreader 100 has four open ends 16 extending from two opposite sides thereof, respectively. A working fluid (not shown) is injected into the chamber 40 through the ends 16 and then the heat spreader 100 is evacuated and the ends 16 are hermetically sealed. The working fluid filled into the chamber 40 is saturated in the wick structure 12 and is usually selected from a liquid such as water or alcohol which has a low boiling point and is compatible with the wick structure 12.
In operation, the heat spreader 100 may function as an effective mechanism for evenly spreading heat coming from a concentrated heat source (not shown) to a large heat-dissipating surface. For example, a bottom wall of the heat spreader 100 is maintained in thermal contact with the heat source, and a top wall of the heat spreader 100 may be directly attached to a heat sink base (not shown) having a much larger footprint than the heat source in order to spread the heat of the heat source uniformly to the entire heat sink base. Alternatively, a plurality of metal fins may also be directly attached to the top wall of the heat spreader 100. The working fluid saturated in the wick structure 12 of the heat spreader 100 evaporates upon receiving the heat generated by the heat source. The generated vapor enters into the vapor-gathering region of the chamber 40. Since the thermal resistance associated with the vapor spreading in the chamber 40 is negligible, the vapor then quickly moves towards the cooler top wall of the heat spreader 100 through which the heat carried by the vapor is conducted to the entire heat sink base or the metal fins attached to the heat spreader 100. Thus, the heat coming from the concentrated heat source is transferred to and uniformly distributed over a large heat-dissipating surface (e.g., the heat sink base or the fins). After the vapor releases the heat, it condenses and returns to the bottom wall of the heat spreader 100 via a capillary force generated by the wick structure 12.
As shown in FIG. 3, a method is proposed to manufacture the heat spreader 100. More details about the method can be easily understood with reference to FIGS. 4-6. Firstly, a core 60a is provided with a round hole 11a defined in a middle portion and four columns 16a extending from two opposite ends thereof, as shown in FIG. 4. The core 60a is to form the metal casing 60 of the heat spreader 100 and has a configuration substantially the same as that of the metal casing 60. The core 60a has a mesh layer 12a to form the wick structure 12 of the heat spreader 100, and a filling material 14 filled in a major space and pores of the mesh layer 12a. The filling material 14 binds with the mesh layer 12a.
Referring to FIG. 5, a mold 20 including a first mold 24 and a second mold 22 is provided in order to manufacture the core 60a. The second mold 22 covers and cooperatively forms a cavity 26 with the first mold 24. The cavity 26 of the mold 20 has a configuration substantially the same as that of the core 60a to be formed and includes four columned tubes (not shown) for formation of the columns 16a of the core 60a. A layer of woven mesh 12b is arranged in the cavity 26, lining an inner surface of the cavity 26 of the mold 20 for formation of the mesh layer 12a of the core 60a. The mesh 12b is woven by a plurality of flexible metal wires, such as copper wires or stainless steel wires so that the mesh 12b has an intimate contact with the inner surface of the cavity 26 of the mold 20. Alternatively, the mesh 12b may also be woven by a plurality of flexible fiber wires. A molten or liquid filling material 14 then is filled into the cavity 26 and the pores of the mesh 12b via filling tubes 222 defined at the top of the second mold 22. The filling material 14 is selected from such materials that can be easily removed after the heat spreader 100 is formed. For example, the filling material 14 may be paraffin or some kind of plastic or polymeric material or alloy that is liquefied when heated. Alternatively, the filling material 14 may also be selected from gypsum or ceramic that is frangible after solidified. The filling material 14 solidifies in the cavity 26 and binds with the mesh 12b when it is cooled. After the filling material 14 in the cavity 26 is solidified, the mold 20 is removed. As a result, the pores of the mesh 12b and the cavity 26 of the mold 20 are filled with the filling material 14 and the core 60a is obtained. The columns 16a of the core 60a are simultaneously formed by the filling material 14 filled in the columned tubes of the mold 20.
Thereafter, the method, as shown in FIG. 3, includes an electrodeposition step in order to form the metal casing 60 of the heat spreader 100. In order to proceed with the electrodeposition, an electrically conductive layer (not shown) is coated on an outer surface of the core 60a filled with the filling material 14, whereby the outer surface of the core 60a is conductive. In order to keep the ends 16 of the heat spreader 100 open, there is no electrically conductive layer coated on free ends 160 of the columns 16a of the core 60a. Then, the core 60a with the solidified filling material 14 contained therein is disposed into an electrodeposition bath 50 which contains an electrolyte 51, as shown in FIG. 6. The electrodeposition bath 50 includes an anode 53 and a cathode 52 both of which are immersed in the electrolyte 51 with the cathode 52 connecting with the core 60a. After electrodepositing for a specific period of time, the core 60a is taken out of the electrodeposition bath 50 and a layer of metal coating (coating layer 60b) is accordingly formed on the outer surface of the core 60a, as shown in FIG. 6.
Then, the liquefiable filling material 14 in the core 60a is removed away from the mesh layer 12a of the core 60a and the coating layer 60b by heating the filling material 14 at a temperature above a melting temperature of the filling material 14. The frangible filling material 14 is removed from the core 60a and the coating layer 60b by vibrating the filling material 14. The filling material 14 is removed from the mesh layer 12a of the core 60a and the coating layer 60b via the ends 16 formed by the coating layer 60b after the electrodeposition step. After the filling material 14 is completely removed, a semi-manufactured heat spreader is obtained. Thereafter, an inner space of the semi-manufactured heat spreader is cleaned and the working fluid is injected into the metal casing 60 to be saturated in the wick structure 12. Finally, the metal casing 60 is vacuumed and the ends 16 are sealed and the heat spreader 100 is obtained.
According to the method, the wall thickness of the heat spreader 100 can be easily controlled by regulating the time period and voltage involved in the electrodeposition step. The wick structure 12 is integrally formed with the metal casing 60 of the heat spreader 100 as a single piece by electroforming, which decreases the heat resistance therebetween and thereby increasing heat removal capacity of the heat spreader 100. Since the metal casing 60 of the heat spreader 100 is formed by electroforming, the heat spreader 100 is easily made to have a complicated configuration.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Patent Application
20080087405
