Abstract:
A fastener for a heat sink of the present invention includes a length-variable operating member ( 10 ), a piston member ( 20 ), an embracing member ( 30 ), a resilient member ( 40 ) and a post ( 58 ) extending from a printed circuit board ( 50 ). The piston member is movable in the operating member when the operating member varies between a shortest length and a longest length. The resilient member covers around the piston member. The embracing member is controllable cooperatively by the piston member and the resilient member to grasp the post or release the post.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to fasteners, and more particularly to a fastener for securing a heat sink to an electronic component.  
         [0003]     2. Description of Prior Art  
         [0004]     Numerous modern electronic components such as central processing units (CPUs) of computers generate large amounts of heat during operation. The heat must be efficiently removed from the CPU; otherwise, abnormal operation or damage may result. Typically, a heat dissipation device such as a heat sink is mounted on the CPU to remove heat therefrom.  
         [0005]     Mostly, holes are defined in printed circuit boards (PCBs). Screws are inserted through the heat sink and engaged within the holes of the PCB to mount the heat sink on the CPU. However, attachment and detachment of the screws are unduly laborious. Furthermore, the PCB is prone to be deformed due to overloaded force on partial portions thereof.  
         [0006]     For overcoming the above-mentioned problems, metal piece clips are developed. This kind of clip commonly has a M-shaped profile. The clip comprises a central pressing portion and a pair of engaging portions extending perpendicularly from the pressing portion. The pressing portion is for pressing the heat sink toward the CPU. The engaging portions are for engaging with a socket or a retention module in order to secure the heat sink and to render the heat sink in contact with the CPU. Unfortunately, tools are required to have the engaging portions engaged with the socket or the retention module. Engagement and disengagement of the clip with and from the socket or the retention module are still unduly laborious.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, an object of the present invention is to provide a fastener for a heat sink which is convenient to attach the heat sink to an electronic component.  
         [0008]     In order to achieve the object set out above, a fastener for a heat sink in accordance with a preferred embodiment of the present invention comprises a length-variable operating member, a piston member, an embracing member, a resilient member and a post extending from a printed circuit board. The piston member is movable in the operating member when the operating member varies between a shortest length and a longest length. The resilient member covers around the piston member. The embracing member is controllable, cooperatively by the piston member and the resilient member, to grasp the post or release the post.  
         [0009]     Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an exploded, isometric view of fasteners in accordance with a preferred embodiment of the present invention, a heat sink, and an electronic component mounted on a PCB; and  
         [0011]      FIG. 2  is a pre-assembled view of  FIG. 1 ;  
         [0012]      FIG. 3  is a cross-sectional view of  FIG. 2 , taken along line III-III;  
         [0013]      FIG. 4  is an assembled view of  FIG. 1 ; and  
         [0014]      FIG. 5  is a cross-sectional view of  FIG. 4 , taken along line V-V. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Referring to  FIGS. 1-5 , four fasteners in accordance with the preferred embodiment of the present invention are for attaching a heat sink  70  to an electronic component  60  mounted on a PCB  50 .  
         [0016]     The PCB  50  defines four through holes (not labeled) therein spaced from and symmetrically around the electronic component  60 . The posts  58  are formed from an enhancing plate (not labeled) underlying the PCB  50 , and pass through the PCB  50  via the through holes (not labeled). Certainly, it is viable that the posts  58  are directly formed from the PCB  50 . Each of the posts  58  defines an annular groove  582 . The heat sink  70  has a flat base  72  defining four openings  74  therein, and a plurality of fins  73  for dissipating heat. The openings  74  are aligned with the posts  58  protruding from the PCB  50 .  
         [0017]     Each fastener comprises an operating member  10 , a piston member  20 , an embracing member  30  capable of clasping posts  58  protruding from the PCB  50 , and a resilient member  40 .  
         [0018]     The operating member  10  of the fastener has a cylindraceous shape, and comprises a static part  12  resting on the base  72  of the heat sink and an active part  14  above the static part  12 . The static part  12  has a curved joint surface  124 . The active part  14  has a curved joint surface  144 . The joint surfaces  124 ,  144  respectively have a lowest diameter line (not labeled) and a topmost diameter line (not labeled). The curved joint surfaces  124 ,  144  are inosculated (see  FIG. 2 ), that is to say, the lowest diameter line of the active part  14  overlays the lowest diameter line of the static part  12 . The topmost diameter line of the active part  14  overlays the topmost diameter line of the static part  12 . At this stage, the operating member  10  has a shortest length. The operating member  10  defines a piston hole  16  and a room  18  coaxial with the piston hole  16 . The room  18  is completely arranged in the static part  12 . A handle  142  integrally extends from the active part  14 . Via operation on the handle  142 , the active part  14  is rotatable to slide on the joint surface  124  so that the lowest diameter line of the active part  14  rests on the topmost diameter line of the static part  12  (see  FIG. 4 ). On the point, the operating member  10  has a longest length.  
         [0019]     The piston member  20  is extendable through the piston hole  16  of the operating member  10  and is further extendable through the room  18  of the operating member  10  (see  FIG. 3 ). The piston member  20  comprises a head  22  integrally formed at an end of the piston member  20 , and defines an annular notch  24  adjacent an opposite end of the piston member  20 . The head  22  rests on the active part  14 . The resilient member  40 , such as a spring, covers around the piston member  20  in the annular notch  24 .  
         [0020]     The embracing member  30  is secured to an end of the piston member  20  opposing the head  22 . The resilient member  40  is disposed in room  18  and between the static part  12  and the embracing member  30  (see  FIG. 3 ). The embracing member  30  is movable up and down in a corresponding opening  74  of the heat sink  70 . The embracing member  30  comprises three spaced embracing arms  32  for embracing a corresponding post protruded from the PCB  50 . Each embracing arm  32  forms an inward hook  322  at a distal free end which is distant from the piston member  20 . An outer protrusion  324  is formed at a middle of each embracing arm  32 .  
         [0021]     In use of the fastener as above-described, the static part  12  of the operating member  10  rests on the base  72  of the heat sink  70 . The embracing member  30  is positioned into a corresponding opening  74  of the heat sink  70  from bottom of the heat sink  70 . Referring to  FIG. 3 , the operating member  10  is in a state that the curved joint surfaces  124 ,  144  are inosculated, so that the operating member  10  has the shortest length. The resilient member  40  is in a natural state or in a slight compressed state. The protrusions  324  on the embracing member  30  are disposed between the heat sink  70  and the PCB  50 . The embracing arms  32  are relaxed, and loosely surround a corresponding post  58  protruded from the PCB  50 .  
         [0022]     Rotating the handle  142 , the active part  14  slides on the joint surface  124  of the static part  12 , until the lowest diameter line of the active part  14  rests on the topmost diameter line of the static part  12 . The operating member  10  has the longest length as shown in  FIGS. 4-5 . The movement of the active part  14  causes the piston member  20  to be lift. The piston member  20  drags the embracing member  30  upwardly. The embracing member  30  thus moves away from the PCB  50 , enters deep into the room  18  and compresses the resilient member  40  toward the static part  12 . Simultaneously, the outer protrusions  324  enter the corresponding opening  74  of the heat sink  70 . The embracing arms  32  are inwardly forced at the protrusions  324  by the base  72  of the heat sink  70 , and are deformed to employ the hooks  322  to grasp the corresponding post  58  at the annular groove  582 .  
         [0023]     In the present invention, the operating member  10  and the embracing member  30  are positioned between opposite ends of the piston member  20 . The resilient member  40  is disposed between the operating member  10  and the embracing member  30 . Furthermore, the static part  12  of the operating member  10  rests on the base  72  of the heat sink  70 , and cannot move in a direction toward the heat sink  70 . Accordingly, once the active part  14  of the operating member  10  is moved to lengthen the operating member  10 , the active part  14  of the operating member  10  can do nothing but move to be further away from the heat sink  70  than it is in original location. The piston member  20  moves along with the movement of the active part  14  of the operating member  10 . Therefore, the embracing member  30  goes deep into the room  18  of the static part  12  and compresses the resilient member  40  toward the static part  12 . The hooks  322  of the embracing member  30  grasp the corresponding post  58  at the annular groove  582 . The compressed resilient member  40  exerts resilient force on the operating member  10  and the embracing member  30  toward opposite ends of the piston member  20 . Simultaneously, the piston member  20  exerts contrarious forces on the operating member  10  and the embracing member  30 .  
         [0024]     To remove the heat sink  70  from the PCB  50 , the handle  142  is rotated. The operating member  10  goes back to its original state to have the shortest length as shown in  FIGS. 2-3 . The resilient member  40  is thus released to push the piston member  20  and the embracing member  30  toward the PCB  50 . The protrusions  324  slide out of the opening  74  of the heat sink  70  and are disposed between the heat sink  70  and the PCB  50 . The embracing arms  32  stretch outwardly to their original state and release the post  58  from the hooks  322 .  
         [0025]     It is feasible in the present invention that the piston member  20  is integrally formed from the active part  14  of the operating member  10 , so far as the piston member  20  can move with the movement of the active part  14 . It is also feasible in the present invention that the static part  12  and the active part  14  of the operating member  10  are interacted by means of whorl without curved joint surfaces  124 ,  144 , so far as the active part  14  can move upward and downward relative to the static part  12 .  
         [0026]     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.