Abstract:
A fastener ( 20 ) comprises a fixing post ( 21 ) and a washer ( 25 ). The fixing post has a locking tongue ( 213 ) and a slot ( 2110 ) just above the locking tongue. The washer defines a hole ( 253 ) and has at least one tab ( 255 ) near the hole. The fixing post extends through a heat sink ( 100 ) and engages with the washer by fitting the washer into the slot, whereby the washer is sandwiched between the locking tongue and a base ( 12 ) of the heat sink and the fixing post is securely attached to the heat sink. The tab engages with a straight side of the locking tongue. The fixing post is used for threadedly engaging with a screw thereby attaching the heat sink to an electronic device mounted on a printed circuit board.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a fastener for a heat dissipation device, and particularly to a fastener that can be fixed to the heat dissipation device to attach the heat dissipation device to another assembly. 
         [0003]    2. Description of Related Art 
         [0004]    Electronic devices such as central processing units (CPUs) generate a lot of heat during normal operation. If the heat generated by the electronic devices is not timely and properly dissipated it can affect their operational stability and damage associated electronic devices. A heat dissipation device is often attached to a top surface of the CPU secured on a printed circuit board to remove the heat from the CPU to ensure the normal operation of the CPU. 
         [0005]    Generally, a fastener is used to secure the heat dissipation device on the printed circuit board. However, most of the related fasteners cannot be securely fixed on the heat dissipation device. Thus the related fastener mounted on the heat dissipation device may easily become detached from the heat dissipation device during transportation. Furthermore, assembling the heat dissipation device with the related fastener is a troublesome and laborious process. 
       SUMMARY OF THE INVENTION 
       [0006]    A fastener comprises a fixing post and a washer. The fixing post has a locking tongue formed thereon, with a slot defined in the fixing post adjacent to the locking tongue. A washer defines a hole therein and has at least one tab formed extending toward the hole. The fixing post is attached to a heat sink by having the washer fitted into the slot and the tab engaging with a straight side of the tongue. A screw is used to extend upwardly through a printed circuit board and thereadedly engage with the fixing post, whereby the heat sink is securely mounted on a heat-generating electronic component on the printed circuit board. 
         [0007]    Other advantages and novel features of the present heat dissipation device will become more apparent from the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the present device can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is an assembled, isometric view of a heat dissipation device in accordance with a preferred embodiment of the present invention; 
           [0010]      FIG. 2  is similar to  FIG. 1 , but shown from an opposite bottom aspect; 
           [0011]      FIG. 3  is an exploded, isometric view of  FIG. 2 ; 
           [0012]      FIG. 4  is a cross-sectional view of a fixing post of a fastener of the heat dissipation device of  FIG. 3 , taken along line IV-IV thereof; 
           [0013]      FIG. 5  is a cross-sectional, isometric view of the fastener in an unlocked position; and 
           [0014]      FIG. 6  is a cross-sectional, isometric view of the fastener in a locked position, taken along line VI-VI of  FIG. 2 ; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    As shown in  FIG. 1  and  FIG. 2 , a heat dissipation device  100  in accordance with a preferred embodiment of the present invention is configured (i.e., structured and arranged) for dissipating heat generated by a heat generating device (not shown), such as a CPU on a printed circuit board (not shown). The heat dissipation device  100  comprises a heat sink  10  and two fasteners  20 . The fasteners  20  can be fixed to the heat sink  10  and used to secure the heat sink  10  on the heat-generating device on the printed circuit board. 
         [0016]    The heat sink  10  comprises a square base  12  and a plurality of parallel fins  15  extending vertically and upwardly from a top surface of the base  12 . All of the fins  15  are rod-like and spaced from each other. Each fin  15  has a square cross-section in a horizontal direction. Four ears  120  adjacent to four corners of the base  12  extend out from two opposite sides (not labeled) of the base  12  in the horizontal direction. The four ears  120  each have a cylindrical configuration and define a stepped hole  121  therein. The stepped hole  121  comprises an upper hole (not labeled) adjacent to the fins  12  and a lower hole (not labeled) having a smaller diameter than the upper hole. Thus a step  123  is formed between the upper hole and the lower hole. 
         [0017]    As shown in  FIG. 3  and  FIG. 4 , each fastener  20  comprises a fixing post  21 , a washer  25  engaging with the fixing post  21  and a spring  23  to be received in the upper hole of a corresponding stepped hole  121 . 
         [0018]    The fixing post  21  has a shaft-like configuration. The fixing post  21  has a cylindrical shaft portion  210 . A cap  215  is formed on a top end of the shaft portion  210 . A cross-like slot  216  is defined in the cap  215  for fittingly receiving a screwdriver (not shown), thus the fixing post  21  can be manipulated. From another end opposite to the cap  215  of the shaft portion  210 , an engaging portion  211  vertically and coaxially extends from a bottom end of the shaft portion  210 . The engaging portion  211  has a smaller diameter than that of the shaft portion  210 . A cylindrical extension portion  212  vertically and coaxially extends from a free end of the engaging portion  211 . The extension portion  212  has a smaller diameter than that of the engaging portion  211 . A locking tongue  213  is circumferentially formed at a joint of the engaging portion  211  and the extension portion  212  of the fixing post  21 . The locking tongue  213  has an annular configuration with two vertical sections cut away symmetrically from two opposite sides thereof. Thus a periphery of the locking tongue  213  is enclosed by two opposite arc sides in a longitudinal direction and two opposite straight sides connecting the arc sides in a latitudinal direction. A diameter of the arc sides of the locking tongue  213  is substantially equal to the external diameter of the shaft portion  210 . Thus a slot  2110  is circumferentially defined between the locking tongue  213  and the shaft portion  210  and around the engaging portion  211 . A threaded hole  218  is defined in the extension portion  212  extending into the shaft portion  210  of the fixing post  21 . The threaded hole  218  of the fixing post  21  is adapted to receive a screw (not shown) engaged with the printed circuit board, thereby connecting the fixing post  21  and accordingly the heat dissipation device  100  to the printed circuit board. 
         [0019]    The spring  23  is substantially spiral. An internal diameter of the spring  23  is larger than the external diameter of the shaft portion  210  and smaller than an external diameter of the cap  215 ; thus, the spring  23  can be disposed around the shaft portion  210  and abuts against the cap  215  of the fixing post  21 . An external diameter of the spring  23  is smaller than an internal diameter of the upper hole and larger than the lower hole of the stepped hole  121  of the base  12 . Accordingly, when the spring  23  is accommodated in the stepped hole  121 , a bottom end of the spring  23  sits on the step  123 . 
         [0020]    The washer  25  may be made of metal or plastic. The washer  25  is a substantially circular piece and comprises a circular base  251 . A central hole  253  is defined in the base  251 . An outline of the hole  253  is enclosed by two opposite arc sides and two opposite straight sides which are similar to that of the locking tongue  213  and slightly larger than the locking tongue  213  of the fixing post  21 . Two triangular tabs  255  extend outwardly from the two arc sides of the hole  253  and can be turned upward or turned downwards relative to the base  251 . The base  251  has two square cutouts  256  defined in a circumferential periphery therein, corresponding to the two opposite straight sides of the hole  253 . When the washer  25  is assembled to the fixing post  21  by fitting the washer  25  in the slot  2110 , the spring  23  can be elastically compressed between the cap  215  and the step  123 . 
         [0021]    Referring to  FIG. 5  and  FIG. 6 , in assembly, the two springs  23  are firstly each arranged in a stepped hole  121  of the two ears  120 , and the bottom end of the spring  23  is disposed on the step  123  of the base  12 . Secondly, the fixing post  21  are extended through the spring  23  and the stepped hole  121  from the top surface of the base  12 , until the slot  2110  of the fixing post  21  is completely exposed out of a bottom surface (not labeled) of the base  12 , meanwhile the cap  215  of the fixing post  21  compresses the spring  23  abutting against the step  123  with a compression force exerted on the step  123  that gradually strengthens. Thirdly, the washer  25  is placed around the extension portion  212 , the hole  253  corresponding to the locking tongue  213 , and then pushed upwards along an axis of the fixing post  21 , until the circular base  251  reaches a position corresponding to the slot  2110  of the fixing post  21 . The washer  25  is then rotated  900  relative to the fixing post  21  or the fixing post  21  is rotated  900  relative to the washer  25 , causing upper surfaces of the locking tongue  213  corresponding to the arc sides of the locking tongue  213  to be moved to press against a bottom surface of the washer  25  corresponding to the straight sides of the washer  25 . Finally, the tabs  255  of the washer  25  are compressed towards the straight sides of the fixing post  21 . Then the tabs  255  are positioned adjacent to or abutting against the straight sides of the fixing post  21 . Thus the tabs  255  cooperate with the locking tongue  213  to restrict relative movement between the fixing post  21  and the washer  25 . Thus the washer  25  is securely engaged to the fixing post  21 ; furthermore, the fastener  20  is securely fixed to the heat sink  10 . 
         [0022]    Disassembly is carried out by detaching the tabs  255  of the washer  25  from the straight sides of the fixing post  21 . Firstly a screwdriver is used to abut against the fixing post  21  to push the locking tongue  213  of the fixing post  21  apart from the washer. The washer  25  is then rotated  900  relative to the fixing post  21  or the fixing post  21  is rotated 90° relative to the washer  25 , to cause the arc sides of the locking tongue  213  to be positioned in aligned with the arced sides of the central hole  253  of the washer  25 . Finally, the washer  25  is removed from the fixing post  21  along the axis of the fixing post  21 . Thus the fixing post  21  can be detached from the heat sink  10 . 
         [0023]    In assembly of the heat dissipation device  100 , the heat sink  10  combined with the fasteners  20  is disposed on the heat generating device, with the fasteners  20  spatially corresponding to a plurality of holes (not shown) defined in the printed circuit board, a plurality of screws (not shown) are then placed in the holes of the printed circuit board from a bottom side of the printed circuit board and engaged in the threaded holes  218  of the fixing posts  21 . Thus the heat dissipation device  100  can be securely attached to the printed circuit board and have an intimate contact with the heat generating device. 
         [0024]    Alternatively, the fastener  20  can be fixed to a plate or other components, such as a back plate on the bottom side of the printed circuit board by extending a plurality of screws of the back plate through the printed circuit board to engage in the threaded holes  218  of the fixing posts  21 . 
         [0025]    It is to be understood, however, that even though numerous characteristics and advantages of the present heat dissipation device 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.