Patent Publication Number: US-2004052611-A1

Title: Heat sink fastener

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to heat sinks for dissipating heat from a semiconductor device, for example, a computer processor chip, and more particularly, to a fastener for fastening a heat sink.  
       [0003] 2. Description of the Related Art  
       [0004]FIG. 1 shows a heat sink fastener according to the prior art. This structure of heat sink fastener  90  comprises a bolt  91 , a coiled spring member  92 , and a C-shaped retainer  95 . The bolt  91  has an annular groove  93  around the periphery near the end for receiving the C-shaped retainer  95 . As shown in FIG. 2, when in use, the bolt  91  is inserted through the spring member  92  and then the corresponding holes  99  of the heat sink  97  and the circuit board  98 , and then the C-shaped retainer  95  is fastened to the annular groove  93  of the bolt  91  to secure the bolt  91  to the heat sink  97  and the circuit board  98 , keeping the spring  92  supported between the head of the bolt  91  and the top side of heat sink  97 .  
       [0005] This structure of heat sink fastener  90  has drawbacks as follows:  
       [0006] 1. Unstable pressure: Because the coiled spring member must have a certain number of turns so as to provide a linear spring power, the fastener requires much vertical installation space. When designed for use in a limited space, for example, inside a notebook computer, the number of turns of the coiled spring member is limited, resulting in insufficient linear spring power and unstable pressure to the heat sink.  
       [0007] 2. Applicable to chips having the heat emitting point at the center: As shown in FIG. 3, when used to hold down the heat sink  97  on a processor chip  89  having a protruded heat emitting side, the aforesaid prior art fastener cannot keep the heat sink  97  in horizontal, resulting in poor heat dissipation effect. Therefore, the aforesaid prior art fastener can only be used to hold down a heat sink on a processor chip having its heat emitting point at the center area.  
       SUMMARY OF THE INVENTION  
       [0008] The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a heat sink fastener, which provides a stable holding down pressure to the heat sink.  
       [0009] It is another object of the present invention to provide a heat sink fastener, which is practical for use to hold down a heat sink on any of a variety of computer chips.  
       [0010] To achieve these objects of the present invention, the heat sink fastener comprises a bolt for insertion into a mounting hole of a heat sink and a corresponding mounting hole of a circuit board to hold down a heat sink on a processor chip at the circuit board, and a springy cushion having a center through hole for receiving said bolt and a top surface contacted to a bottom surface of a head of the bolt. Wherein the top surface of the springy and the bottom surface of the head of the bolt are flat. The bolt has a positioning structure, which enables the bolt to be inserted into the mounting hole of the heat sink and the mounting hole of the circuit board and, prohibits the bolt from backward movement after insertion into the mounting hole of the heat sink and the mounting hole of the circuit board. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is an exploded view of a heat sink fastener according to the prior art.  
     [0012]FIG. 2 illustrates an application example of the prior art heat sink fastener.  
     [0013]FIG. 3 illustrates the heat sink tilted on the protruded top heat emitting side of a processor chip according to the prior art.  
     [0014]FIG. 4 is an exploded view of a heat sink fastener according to the present invention.  
     [0015]FIG. 5 is an assembly view of the heat sink fastener according to the present invention.  
     [0016]FIG. 6 is a schematic drawing showing an application example of the present invention.  
     [0017]FIG. 7 is a sectional view showing the heat sink fastener fastened to a heat sink and a circuit board according to the present invention.  
     [0018]FIG. 8 shows two alternate forms of the bolt for the heat sink fastener according to the present invention wherein one bolt has a polygonal head, and the other bolt has a round head.  
     [0019]FIG. 9 shows still another alternate form of the bolt for the heat sink fastener according to the present invention.  
     [0020]FIG. 10 shows still another alternate form of the bolt for the heat sink fastener according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0021] Referring to FIGS. 4 and 5, a heat sink fastener  10  is shown comprised of a bolt  11  and a springy cushion  21 .  
     [0022] The bolt  11  has an expanded head  12  at one end (of the shank thereof) and a positioning structure  16  at the other end (of the shank) remote from the head  12 . According to this embodiment, the head  12  has a flat, circular shape. The positioning structure  16  is formed of two barbs symmetrically disposed at two sides (of the shank).  
     [0023] The springy cushion  21  is a short cylindrical springy block made of silicon rubber, having a center through hole  22 . By means of the center through hole  22 , the springy cushion  21  is sleeved onto the (shank of the) bolt  12 , keeping the flat top surface of the springy cushion  21  attached to the flat bottom surface of the expanded head  12  of the bolt  11 .  
     [0024] Referring to FIGS. 6 and 7, four heat sink fasteners  10  are respectively installed in the four mounting holes  32  of the heat sink  31  and the corresponding mounting holes  52  of the circuit board  51  to hold down the head sink  31  on the processor chip  41  at the circuit board  51  in balance. When inserting the bolt  11  of one heat sink fastener  10  through one mounting hole  32  of the heat sink  31  and the corresponding mounting hole  52  of the circuit board  51 , the positioning structure (the barbs)  16  is compressed inwards, for enabling the bolt  11  to pass. When passed, the positioning structure (the barbs)  16  immediately returns to its former shape and stopped at the bottom sidewall of the circuit board  41 , and at the same time the expanded head  12  is pressed on the springy cushion  21  against the top sidewall of the heat sink  31 , and therefore the heat sink  31  is positively held down in balance on the processor chip  41 .  
     [0025] The expanded head  12  of the bolt  11  may be variously shaped. FIG. 8 shows two alternate forms of the bolt. The bolt  11 ′ at the right side in FIG. 8 has a polygonal head  12 ′. The bolt  11 ″ at the left side in FIG. 8 has a round head  12 ″ of semispherical shape.  
     [0026]FIG. 9 shows still another alternate form of the bolt. According to this embodiment, the positioning structure  16 ′ is formed of an outer thread extended around the shank of the bolt onto which a lock nut  54 ′ is threaded and stopped at the bottom side of the circuit board  51 ′.  
     [0027]FIG. 10 shows still another alternate form of the bolt. According to this alternate form, the positioning structure  16 ″ is an annular groove extended around the periphery of the shank to which a C-shaped retainer  54 ″ is fastened and stopped at the bottom side of the circuit board  51 ″.  
     [0028] As indicated above, the heat sink fastener of the present invention has the following advantages:  
     [0029] 1. Ensured pressure: Because the cushion  21  is made of silicon rubber, it provides a springy holding-down effect. Further, because the cushion  21  is a flat member, it provides effective linear spring power within a short stroke. Because the pressure produced by the cushion  21  can be well controlled, the cushion  21  is superior to a coiled spring member.  
     [0030] 2. Applicable to processor chips that emit heat eccentrically: When the heat sink fastener used to fix a heat sink to a circuit board and to hold down the heat sink on a processor chip at the circuit board that has a protruded top heat emitting side, the cushion offsets biasing force from the heat sink, keeping the heat sink in balance and in close contact with the protruded top heat emitting side of the processor chip for quick dissipation of heat from the processor chip.