Patent Publication Number: US-2011067360-A1

Title: Method for manufacturing high porosity graphite capillary structure

Description:
(a) TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to manufacturing of a heat dissipation device, such as a heat spreader, through electroplating and graphite physical vapor deposition in order to realize a novel method for manufacturing high porosity graphite capillary structure having a desired thinned configuration at a low temperature. 
     (b) DESCRIPTION OF THE PRIOR ART 
     The existing manufacturing techniques for heat plates and heat spreaders are subjected to certain limitations: 
     (1) Grooves: A plurality of grooves in the same direction is formed on an inside surface. Capillary structure of this type shows consistent pore size but the porosity cannot be improved. Although a thinned configuration is available, yet the heat dissipation performance is poor. 
     (2) Sintering: Bonding of copper powders or power meshes to a surface is performed through high temperature sintering to form a capillary structure. Although heat dissipation is excellent for capillary structure of this type, yet the high temperature treatment makes the strength poor, preventing thinning of the product and increasing the material cost. Further, it is difficult to obtain consistent capillary structures and quality Thus, the size of pore that determines the thermal conductivity cannot be effectively controlled, leading to inconsistent quality. 
     (3) Diffusion jointing: Copper powders and copper fiber nets are jointed through diffusion jointing. This type of structure requires high temperature treatment, which makes the strength poor of the base material, making it hard for thinning processing and increasing the costs of materials. 
     (4) Foamed metal: Foamed metal is used to form capillary structure, wherein the void size of the foamed metal is hard to control, leading the instability of the manufacturing process. 
     (5) Copper spring bonded to pre-laid capillary structure: The process is complicated and bonding capability is poor, leading to poor performance of heat dissipation. 
     (6) Carbon nanotube: An array of carbon nanotubes is formed on a base material with the array of carbon nanotubes serving as a capillary structure. The performance of heat dissipation is good, but the manufacturing process is complicated, requires expensive equipments, and must be heated to a high temperature to soften the base material. 
     (7) Application of photolithography or precision electroforming to form a micro metal structure: This process can form uniform and tiny capillary structure, but the manufacturing cost is high. 
     (8) Application of reactive ion etching (RIE) of semiconductor manufacturing process to form capillary structure on a silicon substrate: This process forms a capillary structure showing excellent capillarity, but the materials usable are limited by the semiconductor manufacturing process and the manufacturing cost is high. 
     Thus, it is desired to provide a novel manufacturing method that overcomes the drawbacks and limitations of the above discussed known processes in order to meet the needs for efficient heat dissipation and thinned configuration. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a method for manufacturing high porosity graphite capillary structure, which directly forms high porosity capillary structure on a surface of base material to realize the advantages of thinned configuration, low thermal resistivity, high heat dissipation performance, simplified process, consistent quality, and low costs of installation and manufacturing so as to reduce the rate of flaw products. 
     To achieve the above objective, the present invention first provides an electrically conductive receptacle portion and lid portion that are mateable to form an enclosed hollow container with areas where no micro-structure is to be formed covered with insulation material and connection being made to a negative terminal of a power source; an electroplating (or precision electrochemical machining) process is carried out in an electroplating reaction chamber that is filled with electrolyte solution with a positive terminal of the power source connected to a target material, which is placed, together with the electrically conductive portion connected to the negative terminal, into the electrolyte solution, the power source being then activated to fast form a layer of basic micro-structure on a surface of the receptacle portion or the lid portion through electroplating, or alternatively, the precision electrochemical machining is applied to the lid portion for removal shaping; a PVD sputtering process is applied to perform physical vapor deposition inside a PVD sputtering reaction chamber in order to deposit graphite, through sputtering, on the basic micro-structure of the lid portion to form a capillary structure that is primarily formed of graphite; and finally, the receptacle portion and the lid portion on which the high porosity graphite capillary structures are formed are combined together to form an enclosed container, of which an interior space is subjected to air evacuation for forming vacuum and is then filled with a working fluid. The electrically conductive portions may first be coupled to heat dissipation fins and then the high porosity graphite capillary structure is formed, in order to protect the high porosity graphite capillary structure from losing capillarity due to the high temperature applied in mounting the heat dissipation fins, whereby flaw product rate can be effectively reduced. For applications where support pillars are needed, an insulation mold that shows a complementary configuration to the support pillars can be first coated on the basic micro-structure of the electrically conductive portion and then electroplating is applied to form the support pillars on and of the basic micro-structure. The arrangement of the basic micro-structure is modifiable through adjustment of electrical current and period of time applied to form the arrangement. 
     The foregoing objectives and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. 
     Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a receptacle portion and a lid portion that are mateable to form an enclosed container according to the present invention. 
         FIG. 2  is a schematic view showing the receptacle portion and the lid portion are covered with insulation material according to the present invention. 
         FIG. 3  is a schematic view showing an electroplating reaction chamber according to the present invention. 
         FIG. 4  is a schematic view showing basic micro-structures formed on the receptacle portion and the lid portion according to the present invention. 
         FIG. 5  is a schematic view showing a reaction chamber for physical vapor deposition of a sputtering step according to the present invention. 
         FIG. 6  is a schematic view showing formation of high porosity graphite capillary structure on the previously formed basic micro-structure of the lid portion according to the present invention. 
         FIG. 7  is a schematic view showing formation of high porosity capillary structure support pillar according to the present invention. 
         FIG. 8  is a schematic view showing formation of high porosity graphite capillary structure according to the present invention. 
         FIG. 9  is a schematic view showing combination of the receptacle portion and the lid portion according to the present invention. 
         FIG. 10  is a block diagram showing a flow chart of a method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
       FIG. 10  shows a flow chart of a method according to the present invention, which comprises a step of preparation, a step of electroplating (or precision electrochemical machining) reaction, a step of PVD (physical vapor deposition) sputtering, and a step of final production. These steps will be explained in details: 
     In the step of preparation, as shown in  FIG. 1 , a receptacle portion  11  and a lid portion  12  that collectively form an enclosed hollow container  10  are first prepared by being made of conductive (copper-contained) materials, wherein the lid portion  12  is provided with heat dissipation fins  12 A mounted thereto. 
     In the step of electroplating (or precision electrochemical machining) reaction, as shown in  FIG. 2 , the receptacle portion  11  and the lid portion  12  of the enclosed container  10  are first applied with an insulation material  20  covering areas of the two portions where no micro-structure is to be formed. As shown in  FIG. 3 , a power source  30  and an electroplating reaction chamber  40  that receives therein an electrolyte solution (such as aqueous solution of copper sulfate) are provided. The lid portion  12  (or the receptacle portion  11 ) is connected to a negative terminal  32  of the power source  30 , while a positive terminal  31  of the power source  30  is connected to a target material (graphite)  50 , both being placed in the electrolyte solution inside the electroplating reaction chamber  40 . The power source is activated to form a basic micro-structure  111 ,  121  of a predetermined thickness deposited (electroplated) on a surface of the receptacle portion  11  and the lid portion  12 , as shown in  FIG. 4 . Opposite to the deposition shaping process, precision electrochemical processes (PEM, PECM, and ECM) can be adopted for removal shaping applied to the lid portion  12 . 
     In the step of PVD sputtering, the PVD sputtering is a physical vapor deposition process, which as shown in HG  5 , is a phenomenon that occurs when application of high energy particles inside a PVD sputtering reaction chamber  40 ′ impact a target material (graphite)  50  in order to separate molecules or atoms from the target material (graphite)  50 . The principle is that with the target material (graphite)  50  as a cathode (negative terminal  32 ) and the lid portion  12  as an anode (the positive terminal  31 ) in an Ar (argon) atmosphere of 10 to the power of minus 2 (10 −2 ) Torr (vacuum), a high voltage is applied to ionize argon gas adjacent the cathode into Ar+, which then collides the cathode. The graphite molecules or atoms that are impacted by Ar+ ions moves toward and hits the lid portion  12  to be deposited thereon to form a this film. As shown in  FIG. 6 , graphite is sputtered and deposited on the previously formed basic micro-structure  111 ,  121  of the lid portion  12  to form a high porosity graphite capillary structure  112 ,  122 . As shown in  FIG. 7 , an insulation mold  21 , which shows a complementary configuration to support pillars, is alternatively first coated on the basic micro-structure  121  that is formed on the lid portion  12 , and then support pillars  123  of a desired height is formed through electroplating on the basic micro-structure, as indicated by the arrow of  FIG. 7 . Afterwards, a layer of high porosity graphite capillary structure  122  is formed through sputtering to form the arrangement shown in  FIG. 8 . 
     In the final production step, as shown in  FIG. 8 , the receptacle portion  11  and the lid portion  12  on which the high porosity graphite capillary structures  112 ,  122  are formed are combined together to form an enclosed container  10 , as shown in  FIG. 9 . The high porosity graphite capillary structures  111 ,  121  of the enclosed container  10  collectively form an internal space  60  that is then subjected to air evacuation for forming vacuum and subsequent filling therein with a working fluid. 
     The graphite capillary structures so formed can be of a micro structure arrangement of spots, fibers, tree branches, or a combination thereof. 
     According to embodiments of the present invention, the conductive materials usable in the present invention include metals or alloys of copper, aluminum, nickel, and iron, or materials that are surface treated for electrical conductivity. They can be of shapes other that those shown and described herein. 
     According the embodiments of the present invention, the target material usable in the present invention includes metals or alloys of copper, nickel, and aluminum. 
     According the embodiments of the present invention, the heat dissipation fins can be materials of high thermal conductivity, including metals or alloys of copper, aluminum, nickel, and iron. 
     According the embodiments of the present invention, the electrolyte solution usable in the present invention includes aqueous solution of copper sulfate or the electrolyte solutions that are commonly used with the target materials. 
     According the embodiments of the present invention, the sputtering material usable in the present invention includes graphite, silicon, or silicon oxide. Graphite is of better hydrophility and shows better thermal conductivity than silver, copper, aluminum, and iron, and even higher than pure copper. 
     According to embodiments of the present invention, the high porosity graphite capillary structure is of an arrangement that is modifiable through adjustment of electrical current and time period applied to form the arrangement. 
     According to embodiments of the present invention, the method for manufacturing high porosity graphite capillary structure is applicable directly to a base material, a chip, or an electronic device to form thereon a high porosity capillary structure for realization of multiple advantages of low temperature manufacturing, simple steps, easy processing, and efficiency and low costs. 
     It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. 
     While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.