Patent Publication Number: US-2007121300-A1

Title: Back plate assembly for mounting a heat sink assembly to a motherboard

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to a back plate assembly, and more particularly to a back plate assembly which is pre-assembled to a motherboard to facilitate mounting of a heat sink assembly to the motherboard.  
     DESCRIPTION OF RELATED ART  
      Computer electronic devices such as central processing units (CPUs) frequently generate large amounts of heat, which can destabilize operation and cause damage to the electronic devices. A heat sink is placed in thermal contact with an electronic device for transferring heat from the electronic device to atmosphere through conduction and convection. Modern heat sinks are being made larger and larger. Therefore, a back plate is often attached on an underside of a motherboard below an electronic device mounted on the motherboard. The back plate reinforces the motherboard and facilitates the mounting of the heat sink to the motherboard so that the heat sink can have an intimate contact with the electronic device.  
       FIGS. 6-7  show a conventional back plate  1  for attachment below a motherboard  14 . The motherboard  14  has a heat sink assembly  10  secured thereon. The back plate  1  comprises a base  2 , and four U-shaped protrusions  3  extending from four corners of the base  2 , respectively. Each protrusion  3  defines a cutout  4  in an outmost extremity thereof. The motherboard  14  defines four through holes (not labeled). The heat sink assembly  10  comprises four hollow poles  12  depending from an underside thereof.  
      In assembly, the heat sink assembly  10  is attached on the motherboard  14  with the poles  12  extending through the through holes of the motherboard  14 . The back plate  1  is then attached to an underside of the motherboard  14 , with the cutouts  4  of the back plate  1  in communication with the corresponding through holes of the motherboard  14 . The poles  12  extend through the corresponding cutouts  4 . Screws  16  are then extended through the corresponding cutouts  4  to engage in the hollow poles  12  thereby screwing the back plate  1  to the poles  12 .  
      The back plate  1 , the screws  16 , the heat sink assembly  10  and the motherboard  14  are separated from each other before they are assembled together. None of them can be preassembled beforehand. This is disadvantageous in view of inventory management and transportation. Furthermore, the process of assembling the back plate  1 , the screws  16 , the heat sink assembly  10  and the motherboard  14  is time-consuming and inconvenient.  
     SUMMARY OF INVENTION  
      A back plate assembly in accordance with a preferred embodiment of the present invention comprises a back plate, four posts and four plastic rings. The back plate abuts against an underside of a motherboard. The posts extend from the back plate and pass through the motherboard. The rings engage with the posts respectively and elastically abut against an upside of the motherboard. The posts form threaded portions at upper ends thereof. A plurality of fixing components are brought to extend through a heat sink assembly to threadedly engage with the threaded portions thereby securing the heat sink assembly to the motherboard so that the heat sink assembly can effectively take heat away from a heat generating electronic component mounted on the mother board.  
      Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an isometric view of a back plate assembly in accordance with a preferred embodiment of the present invention;  
       FIG. 2  is an exploded view of the back plate assembly of  FIG. 1 ;  
       FIG. 3  is an assembled view of the back plate assembly of  FIG. 1  and a motherboard;  
       FIG. 4  is an enlarged cross-sectional view taken along line IV-IV of  FIG. 3 ;  
       FIG. 5  is an assembled view of the back plate assembly of  FIG. 1 , together the motherboard, a heat sink assembly, and fixing components to secure the heat sink assembly to the motherboard;  
       FIG. 6  is an isometric view of a conventional back plate; and  
       FIG. 7  is a schematic cross-sectional view of the back plate of  FIG. 6  securing a heat sink assembly to a motherboard. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1-5 , a back plate assembly  100  in accordance with a preferred embodiment of the invention comprises a back plate  110 , four posts  160  and four elastic rings  180 . The back plate  110  abuts against an underside of a printed circuit board which may be a motherboard  200  as shown in  FIGS. 3-5 . The motherboard  200  defines four apertures (not labeled). The posts  160  secured to the back plate  110  can pass through the apertures of the motherboard  200  and engage with four fixing components  300 , such as screws to secure a heat sink assembly  400  to the motherboard  200 . The elastic rings  180  clasps the posts  160 , respectively, and elastically abut against an upside of the motherboard  200 .  
      Referring to  FIGS. 1-2 , the back plate  110  comprises a cross-shaped rack  120  and a cross-shaped insulated slice  140 . The rack  120  is made of metallic material in the preferred embodiment, and comprises a rectangular base  122  and four arms  124  extending outwardly from four diagonal corners of the base  122 , respectively. Each arm  124  defines a through hole  126  at an extremity thereof. The insulated slice  140  has a configuration similar to the configuration of the rack  120 . The insulated slice  140  is conformably laid on a top surface of the rack  120  and secured thereto by adhesive. The insulated slice  140  has a rectangular base  142  and four arms  144  extending outwardly from four diagonal corners of the base  142 , respectively. Each arm  144  defines a hole  146  at an extremity thereof. The hole  146  is aligned with a corresponding hole  126  in the rack  120 .  
      Each post  160  comprises a head portion  162 , a pole portion  164 , a neck portion  166  and a threaded portion  168  extending from the neck portion  166 . The pole portion  164  extends from the head portion  162  and has a diameter less than a diameter of the head portion  162 . The neck portion  166  extends from the pole portion  164  and has a diameter less than the diameter of the pole portion  164  and a diameter of the threaded portion  168 . For the back plate assembly  10 , a distance between the neck portion  166  and the insulated slice  140  of the back plate  110  is substantially equal to a thickness of the motherboard  200 . The threaded portion  168  is substantially a hollow cylinder and forms a spiral thread on an inner wall thereof. Referring to  FIGS. 2-4 , the head portions  162  of the posts  160  abut against a bottom surface of the rack  120 . The pole portions  164  engage in the through holes  126  of the rack  120  so that the posts  160  are secured to the back plate  110 . The pole portions  164  further extend upwardly above the insulated slice  140  of the back plate  110 .  
      Each elastic ring  180  is an open C-shaped ring. The rings  180  can be elastically expanded in a radial direction when an expanding force in the radial direction is applied to them, so that the elastic rings  180  are capable of engaging with the neck portions  166  of the posts  160 , respectively. The elastic rings  180  have a slight degree of deformability. In the preferred embodiment, the elastic rings  180  are made of plastic material. An inner diameter of each elastic ring  180  is substantially smaller than the diameter of each neck portion  166  and an outer diameter of each elastic ring  180  is substantially larger than a diameter of each aperture of the motherboard  200  before the elastic rings  180  are brought to clasp the neck portions  166 , so that the elastic rings  180  can securely engage with the neck portions  166  to be combined to the posts  160  and elastically abut against the upside of the motherboard  200 .  
      Particularly referring to  FIGS. 3-4 , in installation of the back plate assembly  100  to the motherboard  200 , the neck portions  166  and the threaded portions  168  of the posts  160  are brought to pass through the apertures of the motherboard  200  until the threaded portions  168  and the neck portions  166  are located above the upside of the motherboard  200 . The insulated slice  140  thus abuts against the underside of the motherboard  200 . The elastic rings  180  are then engaged with the neck portions  166  and elastically abut against the upside of the motherboard  200  to thereby securely attach the posts  160  to the motherboard  200 . Accordingly, the back plate assembly  100  is pre-assembled to the motherboard  200 .  
      It is clearly shown that the elastic rings  180  can have the back plate assembly  100  to be pre-assembled to the motherboard  200 . This is advantageous in view of inventory management and transportation of the back plate assembly  100  and the motherboard  200 . Since the back plate assembly  100  can be pre-assembled to the motherboard  200 , the heat sink assembly  400  can be secured to the motherboard  200  so long as the fixing components  300  are brought to extend through ears (not labeled) of a heat sink (not labeled) of the heat sink assembly  400  and threadedly engage in the threaded portions  168  of the posts  160 . The present invention dramatically simplifies the assembly process of fixing the heat sink assembly  400  to the motherboard  200 . Additionally, since the elastic rings  180  are elastic, they can absorb excessive force exerted on the back plate  110  and the motherboard  200  to protect the back plate  110  and the motherboard  200  from being damaged.  
      It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.