Abstract:
A fastener comprises a fastener post, a clasping element and an elastic element. The fastener post comprises a head, a post body and a threaded portion. The post body has a first extension section connecting with the head, a second extension section connecting with the threaded portion and a recess section connected between the first and second extension sections. The clasping element comprises an annular clasping body, a first clasping portion axially extending from the clasping body and a second clasping portion extending outwardly and then downwardly from the clasping body. The clasping body encloses the post body, the first clasping portion engages with the recess section of the post body, and the second clasping portion engages with the heat sink. The elastic element is set around the post body and located between the head and the clasping body.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to heat dissipation devices and, particularly, to a fastener attached to a heat sink, and an electronic device including such a heat sink and a fastener. 
     2. Description of Related Art 
     With the miniaturization development of the computers, electronic elements mounted on the motherboards of the computers are ever more dense; and spaces to mount heat sinks become ever smaller. 
     Conventionally, a number of bolts are used to secure a heat sink to a printed circuit board. First of all, the bolts each are secured to the heat sink by an O-shaped ring. The heat sink has a bottom plate defining a number of through holes therein. The O-shaped ring has an inner edge and an outer edge, and the inner edge of the O-shaped ring defines a number of slits to render the O-shaped ring some elasticity. Each bolt extends through the through hole of the bottom plate of the heat sink from top to bottom; the O-shaped ring sets around the bolt from bottom to top and clips on the bolt to thereby secure the bolt to the bottom plate of the heat sink. Then each bolt extends through the printed circuit board to secure the heat sink to the printed circuit board. 
     However, spaces between the bolt and the adjacent electronic elements are relatively small, therefore, the outer edge of the O-shaped ring may contact and interfere the adjacent electronic elements. During the securing process, the O-shaped ring may rotate together with the bolt; thus, the O-shaped ring may collide and damage the adjacent electronic elements. 
     What is needed, therefore, is a fastener and an electronic device including such a fastener which can overcome the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present apparatus 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 apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an assembled, isometric view of an electronic device in accordance with an embodiment of the disclosure. 
         FIG. 2  is an exploded, isometric view of the electronic device of  FIG. 1 . 
         FIG. 3  is an enlarged view of a fastener of the electronic device of  FIG. 1 . 
         FIG. 4  is a partially sectional view of the electronic device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  and  FIG. 2 , an embodiment of an electronic device including a printed circuit board  10 , a backboard  20 , a heat sink  30  and four fasteners  40 . 
     The printed circuit board  10  in accordance with the preferred embodiment is a motherboard, which supports a number of electronic elements thereon. For example, a number of first electronic elements  11  are mounted on a main area of the printed circuit board  10 , and a number of second electronic elements  12  are mounted on an edge area of the printed circuit board  10 . The first electronic elements  11  are main heat generating elements, and the heat sink  30  are configured to contact with the first electronic elements  11  to dissipate heat thereof. The printed circuit board  10  defines four first through holes  101  therein. The first through holes  101  generally surround the first electronic components  11 . 
     Four nuts  21  are mounted to four corners of the backboard  20 , respectively. The four nuts  21  each include a riveting portion  211  engaged with the backboard  20  and a screw portion  212  extending upwardly from the riveting portion  211 . The screw portion  212  of each one of the four nuts  21  defines a screw hole  2120  along an axial direction thereof. The screw holes  2120  of the four nuts  21  of the backboard  20  align with the four first through holes  101  of the printed circuit board  10 , respectively. 
     The heat sink  30  is integrally made of copper, aluminum or other materials with high heat dissipation capability. The heat sink  30  includes a rectangular bottom plate  31 , a first fin set  310  and a second fin set  320 . The bottom plate  31  includes a middle portion  31   a  and two lateral portions  31   b  connected with two sides of the middle portion  31   a  of the bottom plate  31 . A thickness of the middle portion  31   a  is larger than that of each of the two lateral portions  31   b . That is, top surfaces of the middle portion  31   a  and two lateral portions  31   b  are coplanar; a bottom surface of the middle portion  31   a  is below bottom surfaces of the two lateral portions  31   b . Thus, spaces are formed between each of the bottom surfaces of the two lateral portions  31   b  and the printed circuit board  10 , thereby facilitating setting fasteners  40  and mounting some periphery electronic elements therein. 
     The first fin set  310  is disposed on a top surface of the middle portion  31   a  of the bottom plate  31 ; the two second fin set  320  are disposed on top surfaces of the two lateral portions  31   b  of the bottom plate  31 , respectively. The first fin set  310  includes a number of first fins protruding from the top surface of the middle portion  31   a  of the bottom plate  31  and extending along a lengthwise direction of the middle portion  31   a  of the bottom plate  31 . The first fin set  310  communicates with two ends of the middle portion  31   a  of the bottom plate  31 . A length of the first fin set  310  is equal to that of the middle portion  31   a  of the bottom plate  31 . The first fins are parallel with each other and define a number of airflow passages therein. Each of the two second fin sets  320  includes a number of second fins protruding from the top surface of each of the two lateral portions  31   b  of the bottom plate  31  and extending along a lengthwise direction of the corresponding lateral portion  31   b  of the bottom plate  31 . The second fins are parallel with each other and define a number of airflow passages therein. A length of the second fin set  320  is less than that of each of the two lateral portions  31   b  of the bottom plate  31 . Each lateral portion  31   b  defines two engaging portions  330  each of which is located between one of two ends of each lateral portion  31   b  and one of two ends of a corresponding second fin set  320 . Each engaging portion  330  defines a second through hole  331  corresponding to the first through hole  101  of the printed circuit board  10  and two clasping holes  332  located at two sides of the second through hole  331 . In the present embodiment, a center of the second through hole  331  is equidistantly spaced from the two clasping holes  332 . 
     Referring to  FIGS. 2 and 3 , each of the fasteners  40  includes a fastener post  410 , an elastic element  420  and a clasping element  430 . The fastener post  410  is an integral structure and includes a head  411 , a post body  412  and a threaded portion  413 . The head  411  and the threaded portion  413  are connected to two opposite ends of the post body  412 . The head  411 , the post body  412  and the threaded portion  413  are coaxial. The post body  412  includes a first extension section  4121  connected with the head  411 , a second extension section  4122  connected with the threaded portion  413  and a recess section  4123  connected between the first and second extension sections  4121 ,  4122 . A diameter of the recess section  4123  is less than a diameter of each of the first and second extension sections  4121 ,  4122 . A diameter of the threaded portion  413  is less than that of the second extension section  4122  of the post body  412 . The elastic element  420  is a helical spring, and an inner diameter of the elastic element  420  is larger than the diameter of the post body  412  at the first and second extension sections  4121 ,  4122  and less than the diameter of the head  411 . 
     The clasping element  430  is integrally made of plastic material. The clasping element  430  includes a first clasping portion to engage with the recess section  4123  of the post body  412  of the fastener post  410  and a second clasping portion to engage in the clasping holes  332  of the engaging portion  330  of the bottom plate  31  of the heat sink  30 . In the present embodiment, the clasping element  430  includes an annular body  431 , two clasps  432  and a number of resilient claws  433 . The two clasps  432  function as the second clasping portion of the clasping element  430 , the resilient claws  433  function as the first clasping portion of the clasping element  430 . An inner diameter of the elastic element  420  is larger than an inner diameter of the body  431 , and an outer diameter of the elastic element  420  is less than an outer diameter of the body  431 ; thus, the elastic element  420  abuts a top of the body  431  at a portion between inner and outer edges thereof, when the elastic element  420  and the clasping element  430  are assembled together. As a result, the body  431  of the clasping element  430  functions as a washer positioned between the elastic element  420  and the bottom plate  31  of the heat sink  30 , thereby preventing the elastic element  420  from scraping the top surface of the bottom plate  31  of the heat sink  30  to produce a number of metallic scraps which may fall to the printed circuit board  10  to affect a normal work of the electronic elements mounted on the printed circuit board  10 . 
     The body  431  of the clasping element  430  has an aperture  4310 , an inner wall  4311  and an outer wall  4312 . The resilient claws  433  extend downwardly from a bottom edge of the inner wall  4311  of the body  431  along an axis of the body  431 . The resilient claws  433  are equidistantly arranged on a circumference of the bottom edge of the inner wall  4311  of the body  431  to enclose a cylinder  434  having an inverted cone-shaped hole. A diameter of a top end of the cylinder  434  where the resilient claws  433  connect with the body  431  is equal to that of the aperture  4310  of the body  431 ; a diameter of the bottom end of the cylinder  434  is less than that of the aperture  4310  of the body  431 . The diameter of the bottom end of the cylinder  434  is less than that of the second extension section  4122  of the post body  412  and equal to or slightly larger than that of the recess section  4123  of the post body  412 . The diameter of the cylinder  434  decreases gradually from the top end to the bottom end thereof. 
     The diameter of the aperture  4310  of the body  431  of the clasping element  430  is slightly larger than that of the second extension section  4122  of the post body  412  of the fastener post  410  to enable the second extension section  4122  of the post body  412  extending therethrough to enter the cylinder  434 . The diameter of the bottom end of the cylinder  434  is less than that of the aperture  4310  of the body  431  of the clasping element  430 . When the second extension section  4122  of the post body  412  of the fastener post  410  moves to the bottom end of the cylinder  434 , the resilient claws  433  expand outwardly to enable the second extension section  4122  of the post body  412  to pass through the cylinder  434 . The resilient claws  433  fitly clasp the recess section  4123  of the post body  412  of the fastener post  410  and abut a top of the second extension section  4122  of the post body  412  of the fastener post  410 . In addition, the clasping element  430  can slide on the recess section  4123  of the post body  412  along a lengthwise direction of the post body  412 . An outer diameter of a circle cooperatively defined by outer peripheries of the claws  433  is equal to or slightly less than a diameter of the second through hole  331  of the bottom plate  31  of the heat sink  30  to enable the claws  433  to fitly/interferentially engage in the second through hole  331  of the bottom plate  31  of the heat sink  30 , whereby the resilient claws  433  are restrained by the bottom plate  31  to firmly engage with the fastener post  410 . 
     The two clasps  432  are symmetrically disposed on two sides of the center of the body  431 . In detail, each clasp  432  includes a horizontal portion  4321  extending outwardly from the outer wall  4312  of the body  431 , a vertical portion  4322  extending downwardly from a free end of the horizontal portion  4321 , and a hook  4323  extending outwardly from a free end of the vertical portion  4322 . The vertical portion  4322  of each clasp  432  is resilient to enable the hook  4323  thereof to engage the bottom of the engaging portion  330  of the bottom plate  31  of the heat sink  30  after the vertical portion  4322  has been inserted through the clasping hole  332 . It is understood that the number of the clasps  432  of the clasping element  430  and the clasping holes  332  of the engaging portion  330  of the heat sink  30  is not limited, so long as the clasping element  430  can be secured to the heat sink  30 . 
     For assembling the fastener  40 , the elastic element  420  and the clasping element  430  are mounted onto the fastener post  410  in sequence; the elastic element  420  is located between the head  411  of the fastener post  410  and the body  431  of the clasping element  430 . The threaded portion  413  and the second extension section  4122  of the post body  412  are brought to extend through the body  431  of the clasping element  430  and the cylinder  434  enclosed by the resilient claws  433 ; the resilient claws  433  fitly clasp the recess section  4123  of the post body  412  of the fastener post  410 , whereby the elastic element  420 , the clasping element  430  and the fastener post  410  are assembled together. 
     For fixing each of the fasteners  40  to the heat sink  30 , the second extension section  4122  of the post body  412  of the fastener post  410  and the resilient claws  433  attached on the recess section  4123  of the post body  412  are inserted in the second through hole  331  of the engaging portions  330  of the bottom plate  31  of the heat sink  30 ; the threaded portion  413  of the post body  412  of the fastener post  410  extends through the second through hole  331  and locates below a bottom surface of the lateral portion  31   b  of the bottom plate  31  of the heat sink  30 . The two clasps  432  of the clasping element  430  clasp in the two clasping holes  332  of the engaging portion  330  of the bottom plate  31  of the heat sink  30 , respectively, whereby the two hooks  4323  of the two clasps  432  abut against the bottom surface of the lateral portion  31   b  of the bottom plate  31  of the heat sink  30 . By this manner, the four fasteners  40  can be assembled to the heat sink  30 . In assembling the fastener  40  to the heat sink  30 , the wall defining the second through hole  331  of the engaging portion  330  of the bottom plate  31  of the heat sink  30  can prevent the fastener post  410  from disengaging from the clasping element  430 , thereby facilitating installing the fastener post  410  to the engaging portion  330  of the bottom plate  31  of the heat sink  30 . 
     For securing the heat sink  30  to the printed circuit board  10  and the backboard  20 , the threaded portions  413  of the four fasteners  40  sequentially extend through four first through holes  101  of the printed circuit board  10  and screw in the four screw portions  212  of the four nuts  21  mounted on the backboard  20 , whereby four corners of the bottom plate  31  of the heat sink  30  are secured to the printed circuit board  10  and the backboard  20 . Simultaneously, the middle portion  31   a  of the bottom plate  31  of the heat sink  30  thermally contacts with the first electronic elements  11 . It is understood that the threaded portion  413  of each of the fasteners  40  and the nut  21  of the backboard  20  can be other engagement relations, so long as the heat sink  30  can be secured to the printed circuit board  10  and the backboard  20 . 
     Regarding an assembly of the heat sink  30 , the printed circuit board  10  and the backboard  20 , the spaces defined between the two lateral portions  31   b  of the heat sink  30  and the printed circuit board  10  is used to install the fasteners  40 . In the assembly of the heat sink  30 , the printed circuit board  10  and the backboard  20 , only the hooks  4323  of the clasps  432  of the clasping element  430  locate in the spaces between the lateral portions  31   b  of the bottom plate  31  of the heat sink  30  and the printed circuit board  10 . The hooks  4323  of the clasps  432  of the clasping element  430  have a relatively small size, whereby the spaces for installing the fasteners  40  can be effectively reduced. In the present embodiment, a height of each of the hooks  4323  is about 2 millimeters. In addition, after the two clasps  432  of the clasping element  430  clasp in the two clasping holes  332  of the engaging portion  330  of the bottom plate  31  of the heat sink  30 , when the fastener post  410  is rotated to screw the threaded portion  413  thereof into the screw portion  212  of a corresponding nut  21  mounted on the backboard  20 , the two clasps  432  do not rotate together with the fastener post  410 , thereby avoiding an interference between the clasps  432  and neighboring electronic elements thereof. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the apparatus and function of the embodiments, 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 embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.