RELATED APPLICATIONS 
     This application claims priority from Taiwanese Application No. 04214788 filed Aug. 26, 2005, Taiwanese Application No. 95211043 filed Jun. 28, 2006, and Chinese Application No. 200520105229.8 filed Aug. 26, 2005, all of which are incorporated by reference herein in their entirety. 
     Technical Field 
     The present invention relates to a base for a heat radiator, a heat dissipation assembly for a central processing unit, and a method of using the same. 
     Background 
     A conventional heat dissipation module  2  for a central processing unit  1 , as shown in  FIG. 1 , usually comprises a heat radiator  21  mounted on the central processing unit  1  and a heat dissipation fan  22  arranged above the heat radiator  21 . The heat generated by the central processing unit  1  is transferred to the heat radiator  21  and then removed with the heat dissipation fan  22 . Thus, the operational temperature of the central processing unit  1  can be maintained at a desired level to ensure normal operation of the central processing unit. 
     The installation of the heat dissipation module  2 , as shown in  FIGS. 1 and 2 , comprises mounting a base  23  to an underside of a circuit board  3  supporting the central processing unit  1 . Arms  231  extend from four corners of the base  23 . The arms  231  define through holes  2311  through which posts  25  extend. Further, four corners of the heat dissipation module  2 , e.g., the heat dissipation fan  22 , are provided with locking tubes  221 , which correspond to the through holes  2311  of the arms  231 . The locking tubes  221  receive threaded fasteners  27  extending therethrough. A resilient element  28  is fit over an outer circumference of each threaded fastener  27 . Thus, the heat dissipation module  2  can be securely fixed to the central processing unit  1  by extending the threaded fasteners  27  through the locking tubes  221  and through holes  31  defined in the circuit board  3  to threadedly engage the upper, hollow and threaded heads of posts  25  provided on the arms  231  of the base  23 . 
     The mounting base  23  is often used because the heat dissipation module  2  cannot be directly screwed to the circuit board  3 , which generally has a weak mechanical strength, to avoid undesired deformation of the circuit board  3  which may be caused by the installation of the heat dissipation module  2  and may affect the operation of the central processing unit  1 , Thus, mounting base  23  is added to the underside of the circuit board  3  in most, but not all, cases. The base  23  must have a sufficient strength in order to stably position the heat dissipation module  2 . Thus, currently all manufacturers make the base  23  with metal in order to obtain better strength. When the base  23  is made of metal, in order to avoid short circuits of or undesired interference with the electrical paths of the circuit board  3 , an insulation piece  24  must be arranged between the base  23  and the circuit board  3 . The insulation piece  24  has a shape exactly corresponding to the base  23  and is also provided with arms  241  extending from four corners thereof, the arms  241  defining through holes  2411 . With the provision of the insulation piece  24 , interference with the electrical paths of the circuit board  3  can be avoided. 
     In addition, in the mounting of the heat dissipation module  2 , the base  23  and the insulation piece  24  are put together first and then the posts  25  are inserted through the holes  31  of the circuit board  3 . The upper ends of posts  25  are sized and/or shaped to be insertable through holes  31  of PCB  3  and holes  2411  of insulator  42 . To temporarily and stably retain the base  23  and the insulation piece  24  on the circuit board  3 , a C-clip  26  is required to fit over each post  25 . The base  23  and the insulation piece  24  are thus prevented from separating from the circuit board  3  during the assembly process by forming a stop with the C-clips  26 . Additionally or alternatively, glue can be used to temporarily and stably retain the base  23  and the insulation piece  24  on the circuit board  3 . 
     The conventional heat dissipation module  2 , although effective in effecting heat dissipation from the central processing unit  1 , has the following disadvantages:
         (1) Since the base  23  is made of metal, certain interference, such as electrical field interference, with the electrical paths of the circuit board  3  exists despite the presence of insulation piece  24 .   (2) The conventional heat dissipation module  2  requires the arrangement of an additional insulation piece  24  and the application of glue between the base  23  and the circuit board  3 , which increase costs.   (3) A C-clip  26  must be used to temporarily retain the base  23  of the conventional heat dissipation module  2  on the circuit board  3 , which increases the number of manufacturing/mounting steps.       

     Thus, there is a need for a base for a heat radiator, a heat dissipation assembly for a central processing unit, and a method of using the same to overcome the drawbacks of the conventional heat dissipation module. 
     SUMMARY 
     In an aspect, a heat dissipation assembly for a central processing unit comprises a heat radiator adapted to contact the central processing unit from above, and a base adapted to support the central processing unit from below. The base comprises at least a snap-on fastening mechanism adapted to snap into a through hole formed in a supporting substrate of the central processing unit. The heat radiator comprises at least a fastener receiving portion for receiving an elongated fastener and aligning the elongated fastener with a matching engaging element of the snap-on fastening mechanism. 
     In a further aspect, a base for use with a heat radiator on top of a central processing unit is adapted to support the central processing unit from below. The base comprises at least a snap-on fastening mechanism adapted to snap into a through hole formed in a supporting substrate of the central processing unit; and an engaging element within said snap-on fastening mechanism and adapted to engage with an elongated fastener used for fastening, in use, the heat radiator to said base with the central processing unit positioned therebetween. 
     In a further aspect, a method of mounting a heat radiator on top of a central processing unit using a base is provided. The base comprises at least a snap-on fastening mechanism and an engaging element within said snap-on fastening mechanism. The method comprises snapping a through hole formed in a supporting substrate of the central processing unit over the snap-on fastening mechanism of said base to temporarily fixing said central processing unit on said base; and fastening the heat radiator placed on top of the central processing unit to said base using an elongated fastener that engages with the engaging element of said base. 
     Additional aspects and advantages of the disclosed embodiments are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the disclosed embodiments. The aspects and advantages of the disclosed embodiments may also be realized and attained by the means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed embodiments are illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout. 
         FIG. 1  is an exploded view of a conventional heat dissipation module. 
         FIG. 2  is a cross sectional view illustrating the conventional heat dissipation module in use. 
         FIG. 3  is an exploded view of a heat dissipation module in accordance with an embodiment of the present invention. 
         FIG. 3A  is an exploded view of a heat dissipation module in accordance with a further embodiment of the present invention. 
         FIG. 4  is a cross sectional view showing the heat dissipation module of  FIG. 3  in use. 
         FIG. 4A  is a cross sectional view showing the heat dissipation module of  FIG. 3A  in use. 
         FIG. 5  is an exploded view of a heat dissipation module in accordance with a further embodiment of the present invention. 
         FIG. 6  is a sectional view showing the heat dissipation module of  FIG. 5  in use. 
         FIG. 7  is an exploded view of a heat dissipation module in accordance with a further embodiment of the present invention; 
         FIG. 8  is a sectional view showing the heat dissipation module of  FIG. 7  in use. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, that the embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
       FIG. 3  shows a heat dissipation module  4  for a central processing unit in accordance with an embodiment of the present invention. The heat dissipation module  4  comprises a heat radiator  5 , a heat dissipation fan  6 , and a seat or base  7 . 
     The heat dissipation fan  6  is arranged above the heat radiator  5 . Locking tubes  61  are arranged at four corners of the heat dissipation fan  6 . Each locking tube  61  receives a threaded fastener  62 . A resilient element  63 , e.g., a coil spring, is fit over the threaded fastener  62 . The threaded fastener  62  has a lower end forming a threaded section  621 . A circumferential slot  622  is formed at a location above the threaded section  621 . The circumferential slot  622  is to receive an annular, e.g., O-ring, clip  64 . The O-ring clip  64  is fit into the circumferential slot  622  to effect blocking after the threaded fastener  62  is inserted into the locking tube  61  to thereby allow the threaded fastener  62  to freely move up and down in the locking tube  61  without separating from the locking tube  61 . Other shapes and/or configurations of clip  64  are within the scope of the present invention. 
     O-ring clip  64  can be omitted if the threaded fastener  62  is of a type disclosed in the copending application entitled “FASTENER WITH SNAP-ON FEATURE, HEAT DISSIPATION ASSEMBLY FOR CENTRAL PROCESSING UNIT AND METHOD OF USING THE SAME,” Ser. No. 11/467,443, which is incorporated by reference herein in its entirety. 
     The base  7  is preferably made of high strength plastic, including but not limited to polybutelyne with glass filled nylon and other nylon materials. However, other suitable materials are not excluded. An arm  71  extends from each of four corners of the base  7 . Each arm  71  has a snap-on fastening mechanism  72 , preferably integrally formed therewith. The snap-on fastening mechanism  72  comprises two semi-tubular projections  721  (see the magnified view in  FIG. 3 ) extending upwardly from the arm  71 . The upper ends of the projections  721  together define a truncated cone shape  7211  and the lower ends of the projections  721  together form a cylinder shape  7212 . The truncated cone shape  7211  has a bottom that has an outside diameter greater than the cylinder shape  7212 , thereby providing the snap-on fastening mechanism  72 . The snap-on fastening mechanism  72  is formed, e.g., by molding, to surround a post  73  which has a hollow head  731 . Other methods of forming the snap-on fastening mechanism  72 , such as gluing, are not excluded. 
     The post  73  is preferably made of metal and formed with threads in an interior of the hollow head  731  to threadedly engage the threaded fastener  62 . The head  731  extends upwardly beyond the snap-on fastening mechanism  72 . The head  731  has an outside diameter greater than an inside diameter of the snap-on fastening mechanism  72 . The post  73  has a neck  732  at a location below the head  731 . The snap-on fastening mechanism  72  abuts against the neck  732  and the post  73  is fit and retained in the snap-on fastening mechanism  72  without separation from the base  7 . Post  73  can also be made from plastic or other suitable material. Post  73  and the respective snap-on fastening mechanism  72  can be integrally formed as a single item which is attached to base  7  by any suitable methods, such as gluing, pressing, etc. or which is formed directly off of base  7  so as to be integral with base  7 . 
     As shown in  FIG. 4 , to mount the heat dissipation module  4  to a circuit board  8 , the base  7  is mounted to the circuit board  8  from an underside of the circuit board  8 , and the snap-on fastening mechanisms  72  of the base  7  extend into through holes  81  defined in the circuit board  8 , respectively. At this time, the snap-on fastening mechanisms  72  and the posts  73  are simultaneously fit into and through the through holes  81  of the circuit board  8 , with the circuit board  8  secured by the snap-on fastening mechanisms  72 , whereby the base  7  is temporarily secured on the circuit board  8 . 
     In an embodiment, the lip defined by truncated cone shape  7211  is radially flexible so as to allow the snap-on fastening mechanisms  72  with the posts  73  received therein to be passable, with snap action, through the through holes  81 . 
     In a further embodiment, the space  7299  between two halves  721  allows halves  721  to flex inwardly. The size and/or shape of neck  732  of post  73  is/are configured such that there is a clearance between neck  732  and inner walls of projections  721  when post  73  is received in the respective snap-on fastening mechanism  72 . As a result, the presence of post  73  between halves  721  will not completely destroy flexibility of halves  721 , which are allowed to flex sufficiently inwardly to, in turn, allow the snap-on fastening mechanism  72  with the post  73  received therein to be passable, with snap action, through the respective through hole  81 . 
     After the base  7  has been temporarily secured on the circuit board  8 , the threaded fasteners  62  are tightened to engage with the matching threads within the hollow heads  731  of the posts  73 , and thus the heat radiator  5  abuts against the central processing unit  9 . The heat from the central processing unit  9  can be transferred to the heat radiator  5  and then dissipated by the heat dissipation fan  6 . 
       FIG. 3A  shows a heat dissipation module  4  for a central processing unit in accordance with a further embodiment of the present invention. The embodiment of  FIG. 3A  is different from the embodiment of  FIG. 3  in that the snap-on fastening mechanism  72  is a tubular member which is formed to surround each post  73 . The snap-on fastening mechanism  72  has a circular groove  721 A in which is fitted a resilient O-ring  722 . The O-ring  722  has an outer diameter greater than that of the tubular member. 
     As shown in  FIG. 4A , to mount the heat dissipation module  4  to a circuit board  8 , the seat  7  is mounted to the circuit board  8  from an underside of the circuit board  8 , the snap-on fastening mechanisms  72  of the seat  7  extend into through holes  81  defined in the circuit board  8 , respectively, and the O-rings  722  are radially inwardly deformed (or moved if they are spring loaded) to allow the snap-on fastening mechanisms  72  to pass through the holes  81 . The snap-on fastening mechanisms  72  and the posts  73  are simultaneously fit into the through holes  81  of the circuit board  8 . After the O-rings  722  have cleared the holes  81 , the O-rings  722  return to their initial state or position and securing the seat  7  temporarily on the circuit board  8 . Further, the threaded fasteners  62  are tightened, and thus the heat radiator  5  abuts against the central processing unit  9 . The heat from the central processing unit  9  can be transferred to the heat radiator  5  and then dissipated by the heat dissipation fan  6 . 
       FIGS. 5 and 6  illustrate a further preferred embodiment of the present invention, in which the upper end of a tubular member of the snap-on fastening mechanism  72  is provided with an elastically deformable lug  723  which is shaped as a portion of a truncated cone member. When the seat  7  is mounted to the circuit board  8  from an underside of the circuit board  8 , the snap-on fastening mechanisms  72  of the seat  7  extend into through holes  81  defined in the circuit board  8 , respectively, and the lugs  723  are radially inwardly deformed to allow the snap-on fastening mechanisms  72  to pass through the holes  81 . The snap-on fastening mechanisms  72  and the posts  73  are simultaneously fit into the through holes  81  of the circuit board  8 . After the lugs  723  have cleared the holes  81 , the lugs  723  spring back radially outwardly and securing temporarily seat  7  on the circuit board  8 . Further, the threaded fasteners  62  are tightened, and thus the heat radiator  5  abuts against the central processing unit  9 . 
       FIGS. 7 and 8  illustrate a further embodiment of the present invention, in which the circumferential surface of the snap-on fastening mechanism  72  has a plurality of spaced-apart recesses in each of which is fitted a resilient ball  74 . When the seat  7  is mounted to the circuit board  8  from an underside of the circuit board  8 , the snap-on fastening mechanisms  72  of the seat  7  extend into through holes  81  defined in the circuit board  8 , respectively, and the balls  74  are radially inwardly deformed (or moved if the balls are spring loaded) to allow the snap-on fastening mechanisms  72  to pass through the holes  81 . The snap-on fastening mechanisms  72  and the posts  73  are simultaneously fit into the through holes  81  of the circuit board  8 . After the balls  74  have cleared the holes  81 , the balls  74  return to their initial state or position and securing the seat  7  temporarily on the circuit board  8 . Further, the threaded fasteners  62  are tightened, and thus the heat radiator  5  abuts against the central processing unit  9 . 
     The effect of the embodiment is that the base  7  can be temporarily retained on the circuit board  8  by providing the snap-on fastening mechanisms  72 , which encompass the posts  73 , on the arms  71  of the base  7 . Thus, C-clips serving as retainers or application of back glue will no longer be needed. The mounting the base  7  can thus be simplified. Further, in embodiments where the base  7  is made of high strength plastic, the conventional arrangement of additional insulation parts can be omitted, which in turn effectively reduces the costs of heat dissipation module  4  and also reduces interference with the electrical paths of the circuit board  8  caused by the base  7 . 
     In each of the disclosed embodiments, each post  73  can be made integrally with, i.e., from the same high strength plastic material as, the respective snap-on fastening mechanism  72 . Each post  73  and the respective snap-on fastening mechanism  72  can be also made of metal or other suitable material. 
     In further embodiments, posts  73  can be independently fit through the holes  81  without the respective snap-on fastening mechanism  72 . 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications could be made herein without departing from the scope of the described embodiments as defined by the appended claims. Furthermore, although elements of the described embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.
A heat dissipation assembly for a central processing unit includes a heat radiator adapted to contact the central processing unit from above and a base adapted to support the central processing unit from below. The base includes at least a snap-on fastening mechanism adapted to snap into a through hole formed in a supporting substrate of the central processing unit. The heat radiator includes at least a fastener receiving portion for receiving an elongated fastener and aligning the elongated fastener with a matching engaging element of the snap-on fastening mechanism.