Abstract:
A heat spreader ( 100 ) includes a metal casing ( 60 ) formed by electrodeposition and defining a vapor chamber ( 40 ) therein, and a mesh ( 12   b ) lining an inner surface of the metal casing. A method for manufacturing the heat spreader includes: providing a core ( 60   a ) having a mesh layer ( 12   a ) including a plurality of pores and a filling material ( 14 ) filled in the pores of the mesh layer and a major space enclosed by the mesh layer; electrodepositing a layer of metal coating ( 60   b ) on an outer surface of the core; removing the filling material from the coating layer and the pores of the mesh layer; and filling a working fluid into the coating layer and hermetically sealing the coating layer to thereby obtain the heat spreader with therein a wick structure ( 12 ) formed by the mesh layer and the vapor chamber formed by said major space.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for transfer or dissipation of heat from heat-generating components, and more particularly to a heat spreader having a vapor chamber of a complicated configuration and a method of manufacturing the heat spreader. 
   2. Description of Related Art 
   It is well known that heat is generated during operations of a variety of electronic components, such as integrated circuit chips. To ensure normal and safe operations, cooling devices such as heat sinks and/or electric fans are often employed to dissipate the generated 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 flow of heat to the other portions of the heat sink base which are not in direct contact with 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. Typically, the heat spreader includes a vacuum vessel defining therein a vapor chamber, a wick structure provided in the chamber and lining an inside wall of the vessel, and a working fluid contained in the wick structure. As an 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 comes into contact with a cooler surface of the vessel, it releases its latent heat of vaporization and condenses. The condensate returns 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. In the chamber of the heat spreader, the thermal resistance associated with the vapor spreading is negligible, thus providing an effective means of spreading the heat from a concentrated source to a large heat transfer surface. 
   Conventionally, the wick structure of the heat spreader is a grooved or sintered type. However, in view of traditional manufacturing processes, it is difficult to manufacture a heat spreader having a complicated configuration since it is difficult to carve tiny grooves or sinter complicated porous structures in an inner surface of a complicated configuration. Thus, the heat spreader can not be used in a complicated system, which causes the heat generated by the chips of the complicated system can not be timely removed. Therefore, it is desirable to provide a method of manufacturing a heat spreader which may have a complicated configuration. 
   SUMMARY OF THE INVENTION 
   The present invention relates, in one aspect, to a method for manufacturing a heat spreader. The method for manufacturing a heat spreader includes: providing a core, the core having a mesh including a plurality of pores and a filling material filled in the pores of the mesh and a major space enclosed by the mesh; electrodepositing a layer of metal coating on an outer surface of the core; removing the filling material from the coating layer and the pores of the mesh; and filling a working fluid into the coating layer and hermetically sealing the coating layer to thereby obtain the heat spreader with therein a wick structure formed by the mesh and a vapor chamber formed by said major space. By this method, the heat spreader is easily made to have a complicated configuration. Also, the mesh is integrally formed with the metal casing of the heat spreader as a single piece, which decreases the heat resistance therebetween and thereby increasing heat removal capacity of the heat spreader. 
   The present invention relates, in another aspect, to a heat spreader applicable for removing heat from a heat-generating component. The heat spreader includes a metal casing formed by electrodeposition and defining a chamber therein, and a mesh lining an inner surface of the metal casing. The mesh is integrally formed with the metal casing of the heat spreader as a single piece, which decreases the heat resistance therebetween and thereby increasing heat removal capacity of the heat spreader. 
   Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 

   
     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  60   a  is provided with a round hole  11   a  defined in a middle portion and four columns  16   a  extending from two opposite ends thereof, as shown in  FIG. 4 . The core  60   a  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  60   a  has a mesh layer  12   a  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  12   a . The filling material  14  binds with the mesh layer  12   a.    
   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  60   a . 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  60   a  to be formed and includes four columned tubes (not shown) for formation of the columns  16   a  of the core  60   a . A layer of woven mesh  12   b  is arranged in the cavity  26 , lining an inner surface of the cavity  26  of the mold  20  for formation of the mesh layer  12   a  of the core  60   a . The mesh  12   b  is woven by a plurality of flexible metal wires, such as copper wires or stainless steel wires so that the mesh  12   b  has an intimate contact with the inner surface of the cavity  26  of the mold  20 . Alternatively, the mesh  12   b  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  12   b  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  12   b  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  12   b  and the cavity  26  of the mold  20  are filled with the filling material  14  and the core  60   a  is obtained. The columns  16   a  of the core  60   a  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  60   a  filled with the filling material  14 , whereby the outer surface of the core  60   a  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  16   a  of the core  60   a . Then, the core  60   a  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  60   a . After electrodepositing for a specific period of time, the core  60   a  is taken out of the electrodeposition bath  50  and a layer of metal coating (coating layer  60   b ) is accordingly formed on the outer surface of the core  60   a , as shown in  FIG. 6 . 
   Then, the liquefiable filling material  14  in the core  60   a  is removed away from the mesh layer  12   a  of the core  60   a  and the coating layer  60   b  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  60   a  and the coating layer  60   b  by vibrating the filling material  14 . The filling material  14  is removed from the mesh layer  12   a  of the core  60   a  and the coating layer  60   b  via the ends  16  formed by the coating layer  60   b  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.