Abstract:
A load cell is provided for interconnecting first to second structures with a desired amount of force. The load cell includes a screw that has a body. The body includes a threaded portion along a first end and a head at a second end opposite the first end. The load cell includes a spring received over the body. The spring has first and second ends opposite one another and is configured to exert a desired amount of force when compressed. The load cell includes a spring retention member that has an opening therethrough receiving the body of the screw. The spring retention member includes a bushing secured to at least one of the spring and the body and a washer that extends outward from the bushing. The first and second ends of the spring press against the washer and the head respectively.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Certain embodiments of the present invention generally relate to a screw for securing surfaces together. More particularly, certain embodiments of the present invention relate to a load cell that secures a heat sink to electronic components.  
           [0002]    Many electronic components with electrical contacts mating with each other are used in applications in which controlled load forces press against the electronic components. Typically the electronic components are secured to other components, such as a heat sink, by a fastening device that delivers a load force against the electronic component and the heat sink that facilitates mating between contacts. If too much load force is applied to the electronic components, the components may fracture. However, if too little load force is applied to the electronic components, the electrical contacts may form a weak electrical connection. In order to deliver an appropriate load force, a load cell is used to secure an electronic component to a heat sink.  
           [0003]    A typical load cell for use with electronic components is described in U.S. Pat. No. 6,196,849 and No. 6,164,980 issued to Goodwin. The load cells of the &#39;849 and &#39;980 patents include a shoulder screw, a compression spring, and a washer. The screw includes a screw head, a shaft, a threaded body, and a barb. The barb extends circumferentially around the shaft under the head of the screw. At least one turn of the spring is positioned between the screw head and the barb with the spring suspended along the shaft and the threaded body of the screw. Connectable electronic components such as a bolster plate, electronic socket, and a heat sink all have threaded apertures that are aligned with each other, so the threaded body of the screw may be inserted into the aligned threaded apertures and secure the electronic components to each other. The washer is unattached to the load cell and may be positioned on the shaft below the spring when the threaded body of the screw is rotatably inserted into the threaded apertures. The spring is compressed as the threaded body is rotatably inserted, and the washer prevents the compressed spring from damaging component surfaces. The spring size and screw length correspond to each other in such a way that, when the spring is fully compressed, a fixed length of the threaded body is inside, and secures, the electronic components as the spring applies a controlled load along the load cell to the electronic components.  
           [0004]    The typical load cell suffers from a number of drawbacks. First, the load cell utilizes a standard washer that has a large tolerance. The larger the tolerance for a washer, the greater the compression of the spring relative to the length of the screw. Hence, large washer tolerances cause a range of large loads to be applied to electronic components that may damage such components.  
           [0005]    Secondly, securing electronic components to each other with the load cell is time consuming and difficult. The washer is first placed around the threaded aperture on the heat sink surface, and then the screw is rotatably inserted into the threaded aperture until the spring is compressed between the screw head and the washer. This two-step process is further complicated when the heat sink includes a standoff and/or fins situated around the threaded aperture.  
           [0006]    Thus a need exists for a load cell that is easy to install and that provides better loading control.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    Certain embodiments provide a load cell for securing a first structure to a second structure with a desired amount of force. The load cell includes a screw that has a body with a threaded portion along a first end and a head along a second end opposed to the first end. The load cell also includes a spring that is received over the body, having a first end and a second end opposite one another configured to exert a desired amount of force when the spring is compressed. The load cell further includes a spring retention member. The spring retention member includes an opening therethrough that receives the body of the screw. The spring retention member has a bushing secured to at least one of the spring and the body and a washer extending outward from the bushing. The first end and the second end of the spring press against the washer and the head, respectively.  
           [0008]    Certain embodiments provide a load cell for threadably joining a heat sink to a second structure with a desired amount of force. The load cell includes a screw that has a body with a threaded portion along a first end and a head along a second end opposed to the first end. The load cell also includes a spring that is received over the body, having a first end and a second end opposite one another configured to exert a desired amount of force when the spring is compressed. The load cell further includes a spring retention member. The spring retention member includes an opening therethrough that receives the body of the screw. The spring retention member has a bushing secured to at least one of the spring and the body and a washer extending outward from the bushing. The first end and the second end of the spring press against the washer and the head, respectively. The load cell also includes a heat sink that has a base and heat dissipating fins. The base includes threaded openings therethrough that are configured to secure the heat sink to an electronic component. 
       
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 illustrates a side sectional view of a load cell formed in accordance with an embodiment of the present invention.  
         [0010]    [0010]FIG. 2 illustrates an isometric view of a heat sink formed in accordance with an embodiment of the present invention.  
         [0011]    [0011]FIG. 3 illustrates a side sectional view of the load cell of FIG. 1 fully inserted into the top surface of the heat sink of FIG. 2.  
         [0012]    [0012]FIG. 4 illustrates a side sectional view of a load cell formed in accordance with an alternative embodiment of the present invention.  
         [0013]    [0013]FIG. 5 illustrates a side sectional view of a load cell formed in accordance with an alternative embodiment of the present invention. 
     
    
       [0014]    The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    [0015]FIG. 1 illustrates a side sectional view of a load cell  10  formed in accordance with an embodiment of the present invention. FIG. 2 illustrates an isometric view of a heat sink  11  formed in accordance with an embodiment of the present invention. The load cell  10  is positioned for insertion into the heat sink  11  to secure the heat sink  11  to an electronic component  9 . The load cell  10  includes a screw  15 , a spring  20 , and a spring retention member  25 . The heat sink  11  includes a top surface  12 , heat release fins  13 , standoffs  14 , and threaded apertures  16 . Some of the standoffs  14  and threaded apertures  16  are completely surrounded by the heat release fins  13 . The rectangular heat release fins  13  are formed integrally with, and extend perpendicularly upward from, the top surface  12  of the heat sink  11 .  
         [0016]    The heat release fins  13  are parallel to each other and direct heat that escapes from the electronic component  9  outward and away from the heat sink  11 . The cylindrical standoffs  14  are formed integrally with, and extend upward from, the top surface  12  and encircle the threaded apertures  16 . The standoffs  14  receive and are encircled by the spring retention members  25  to secure the spring retention members  25  around the threaded apertures  16 . The threaded apertures  16  threadably receive and retain the screw  15  of the load cell  10 . The threaded apertures  16  are situated above similar threaded apertures (not shown) of the electronic component  9 , so the heat sink  11  may be secured to the electronic component  9  by the load cell  10 .  
         [0017]    The screw  15  is aligned along a longitudinal axis  17  and includes a disk-shaped head  30 , mounted to a generally cylindrical shoulder  40  which is mounted to a threaded portion  35 . The head  30  and the threaded portion  35  are formed integrally with the shoulder  40 . The shoulder  40  includes a spring capture section  45  that joins a body section  50  that joins a recessed lower rim  55 . The spring capture section  45  extends above the body section  50 , and the recessed lower rim  55  extends below the body section  50 . The spring capture section  45 , the body section  50 , and the recessed lower rim section  55  include first, second, and third walls  65 ,  70 , and  75 , respectively. The first wall  65  has a diameter that is greater than a diameter of the second wall  70 , and the diameter of the second wall  70  is greater than a diameter of the third wall  75 . The spring  20  encircles the spring capture section  45 , the body section  50 , and the recessed lower rim section  55 . The body section  50  includes a flat, ring shaped bottom surface  80  that perpendicularly intersects the third wall  75 . The bottom surface  80  resists any further rotational progress of the screw  15  into the threaded aperture  16  upon contact of the bottom surface  80  with the standoffs  14 .  
         [0018]    The body section  50  includes a triangular retention barb  85  that is formed integrally with, and extends out circumferentially from, the second wall  70  and that has an outer diameter greater than the diameter of the first wall  65 . The retention barb  85  includes a flat ring-shaped top surface  90  that extends perpendicularly from the first wall  65 . The top surface  90  retains a portion of the spring  20 , and thus holds the spring  20  along the shoulder  40 . The retention barb  85  also includes a sloped bottom surface  95  that extends at an acute upward angle from the second wall  70  and intersects the top surface  90 . The sloped bottom surface  95  pushes the spring  20  outward and away from the shoulder  40  so the spring  20  assumes a barrel shape and therefore may be more easily compressed.  
         [0019]    The head  30  extends above the spring capture section  45  of the shoulder  40 . The head  30  includes a ring shaped bottom surface  100 , a circular top surface  105 , and a cylindrical side wall  110 . The bottom surface  100  is perpendicular to the first wall  65  and parallel to the top surface  105 . The side wall  110  extends circumferentially outward beyond the first wall  65 . The bottom surface  100  forms a first retention gap  120  with the first wall  65  and the top surface  90  of the retention barb  85 . A portion of the spring  20  is retained in the first retention gap  120 , suspending the spring  20  along the shoulder  40 . As the screw  15  is tightened into the standoff  14 , the bottom surface  100  engages and resists the portion of the spring  20  retained in the first retention gap  120 , compressing the spring  20  in the direction of arrow A against the heat sink surface  12 . The top surface  105  includes a tool cavity  125  that is aligned along the longitudinal axis  17  and that extends downward from the top surface  105  toward the spring capture section  45 . The tool cavity  125  is shaped to correspond to, and receive, a head of a rotational insertion tool such as a screwdriver (not shown). The sidewall  110  includes vertical rectangular grip ridges  130  that are formed with, and extend out from, the side wall  110  and that are aligned concentrically along the side wall  110 . The grip ridges  130  frictionally engage the fingers or gripping tools of an operator touching the head  30 , so the operator may better retain and position the screw  15 .  
         [0020]    The threaded portion  35  extends below the recessed lower rim section  55  of the shoulder  40 . The spring retention member  25  and a portion of the spring  20  encircle the threaded portion  35 . The threaded portion  35  includes a cylindrical wall  135 , a flat, ring-shaped top surface  140 , and a chamfered circular bottom portion  145 . The wall  135  includes threads  142  that encircle the wall  135  and correspond to the threaded apertures  16  in the heat sink  11 . When the bottom portion  145  is positioned into one of the threaded apertures  16  and the load cell  10  is rotated downward onto the heat sink  11 , the wall  135  threadably engages the threaded aperture  16  retaining the threaded portion  35  in the threaded aperture  16 . Thus, the threaded portion  35  secures the heat sink  11  to the electronic component  9 . The load cell  10  is prevented from being positioned too deeply into the heat sink  11  and electronic component  9  when the bottom surface  80  contacts a resisting surface on the threaded aperture  16 . The top surface  140  perpendicularly extends from the third wall  75  of the shoulder  40 . When the load cell  10  is fully screwed into the threaded aperture  16 , the top surface  140  is positioned proximate the top surface  12  of the heat sink  11 .  
         [0021]    The spring  20  is cylindrical and aligned along the longitudinal axis  17 . The spring  20  encircles the shoulder  40  and threaded portion  35  of the screw  15  and a bushing  180  of the spring retention member  25 . The spring  20  includes flexible, cylindrically shaped turns  150  that are parallel to each other. The turns  150  wrap circularly upward along the shoulder  40  in a clockwise direction at an angle B to a horizontal plane  155 . The turns  150  include a top turn  160  and bottom turn  165 . The top turn  160  includes a flat top side  167  and the bottom turn  165  includes a flat bottom side  169 . As the screw  15  is rotatably inserted into the threaded aperture  16 , the top side  167  engages the bottom surface  100  of the head  30  and the bottom side  169  engages the spring retention member  25 , compressing the spring  20 . The top and bottom sides  167  and  169  are horizontally flat, therefore, the top and bottom sides  167  and  169  directly engage the head  30  and the spring retention member  25 , respectively, and the load exerted by the compressed spring  20  is delivered in a generally vertical, and thus more controlled, vector along the load cell  10 . The spring  20  is fully compressed when the bottom surface  80  is pressed against the standoff  14 . The compressed spring  20  resists further insertion by the threaded portion  35  and applies a controlled load along the load cell  10  to the heat sink  11  and the electronic component  9 . The controlled load presses electrical contacts (not shown) located in the electronic component  9  into mating contact with each other.  
         [0022]    The top and bottom turns  160  and  165  both have a spring end diameter. The spring  20  has a middle diameter located equidistant between the top turn  160  and the bottom turn  165 . The middle diameter is larger than the spring end diameter so the spring  20  has a barrel shape. The smaller spring end diameter prevents the top turn  160  and bottom turn  165  from sliding off of the shoulder  40  and the spring retention member  25 , respectively. The barrel shape allows for the other turns  150  to freely travel vertically along the shoulder  40  as the spring  20  is compressed. With the turns  150  freely travel, the spring  20  may be further compressed so the screw  15  may be rotatably inserted further into the heat sink  11  for a more controlled load.  
         [0023]    The spring retention member  25  is aligned along the longitudinal axis  17  and encircles the threaded portion  35 . The spring retention member  25  includes the tube shaped bushing  180  and a thin ring-shaped washer  185 . The bushing  180  has a first end and an opposite second end and is positioned between the threaded portion  35  and the spring  20 . The washer  185  is formed integrally with, and extends circumferentially outward from, the first end of the bushing  180 . The washer  185  includes a ring-shaped top surface  190  and bottom surface  195 . When the screw  15  is rotatably inserted into the standoff  14 , the washer  185  encircles the washer standoff  14 , the top surface  190  engages and resists the bottom turn  165 , and the bottom surface  195  engages and presses against the top surface  12  of the heat sink  11 . The washer  185  has a small tolerance, so the washer  185  has limited interference with the load produced by the spring  20 , allowing the load cell  10  to deliver a more controlled load to the heat sink  11  and electronic component  9 .  
         [0024]    The bushing  180  includes a cylindrical interior wall  200  and a cylindrical exterior wall  202 . The interior wall  200  has a diameter that is slightly larger than the diameter of the second wall  70  of the shoulder  40 , so the bushing  180  may receive and encircle the body section  50  as the screw  15  is rotatably inserted into the standoff  14 . The exterior wall  202  includes a triangular retention barb  205  that is formed integrally with, and extends circumferentially outward from, the second end of the bushing  180 . The triangular retention barb  205  includes a flat, ring shaped bottom surface  210  that extends perpendicularly from the exterior wall  202 . The bottom surface  210  forms a second retention gap  220  with the exterior wall  202  and the top surface  190  of the washer  185 . The triangular retention barb  205  retains the bottom turn  165  of the spring  20  in the second retention gap  220 , and thus holds the spring retention member  25  upon the screw  15 . The triangular retention barb  205  also includes a sloped top surface  215  that extends at an acute angle from the exterior wall  202  and intersects the bottom surface  210 . The sloped top surface  215  pushes the spring  20  outward and away from the spring retention member  25  so the spring  20  assumes a barrel shape.  
         [0025]    [0025]FIG. 3 illustrates a side sectional view of the load cell  10  of FIG. 1 fully inserted onto the top surface  12  of the heat sink  11  (FIG. 2). The spring  20  is compressed. The bushing  180  encircles the body section  50  and recessed lower rim section  55  of the screw  15  and the top surface  140  of the threaded portion  35  is positioned proximate the top surface  12  of the heat sink  11 . The height of the shoulder  40 , the size of the spring  20 , and the small tolerance of the washer  185  all correspond to each other in such a way that, when the spring  20  is compressed, the threaded portion  35  may not be rotatably inserted any further into the standoff  14 , and the load cell  10  exerts a controlled load on the heat sink  11  (FIG. 2) and the electronic component  9  (FIG. 2).  
         [0026]    In an alternative embodiment, the interior wall  200  of the bushing  180  includes threads that correspond to threads on the second wall  70  of the shoulder  40 . As the threaded portion  35  is threadably rotated into the standoff  14 , the bushing  180  engages, the top surface  12  of the heat sink  11 . The bushing  180  is thus threadably retained along the shoulder  40 .  
         [0027]    [0027]FIG. 4 illustrates a side sectional view of a load cell  51  formed in accordance with an alternative embodiment of the present invention. The bushing  180  includes a securing rib  330  that is formed integrally with, and extends radially inward from, the interior wall  200 . The screw  15  includes a support collar  335  that is integrally formed with, and extends circumferentially outward from, the shoulder  40 . The support collar  335  includes a ring-shaped top surface  340 . Prior to rotatably inserting the screw  15  into the heat sink  11  (FIG. 2), the bushing  180  is retained along the shoulder  40  by the securing rib  330  engaging the top surface  340  of the support collar  335 . Therefore, retention barbs are not required, and the spring  20  is partially compressed and retained between the head  30  and the washer  185 . As the threaded portion  35  is rotatably inserted into the threaded aperture  16  (FIG. 2), the spring  20  pushes the spring retention member  25  downward so the securing rib  330  presses against the support collar  335  until the washer  185  engages, and is resisted by, the top surface  12  of the heat sink  11 . As the top surface  12  resists the downward progress of the spring retention member  25 , the spring  20  is further compressed, the threaded portion  35  rotatably proceeds further into the threaded aperture  16  (FIG. 2), and the support collar  335  proceeds downward away from the securing rib  330  while the spring  20  applies a controlled load along the load cell  10  to the heat sink  11  and the electronic component  9  (FIG. 2).  
         [0028]    [0028]FIG. 5 illustrates a side sectional view of the load cell  61  formed in accordance with an alternative embodiment of the present invention. The washer  185  includes a circular inner wall  350  and a circular outer wall  355 . The inner wall  350  receives and encircles the threaded portion  35 . The bushing  180  is integrally formed with, and extends upward from, the outer wall  355  of the washer  185 . The bushing  180  includes an interior wall  360  and a top end  370 . The interior wall  360  includes a second triangular retention barb  375  that is formed integrally with, and extends radially inward from, the top end  370  of the bushing  180  toward the threaded portion  35 . The second retention barb  375 , the interior wall  360  of the bushing  180 , and the top surface  190  of the washer  185  form a second retention gap  380 . The spring  20  is suspended along the screw  15  with the top turn  160  of the spring  20  positioned within the first retention gap  120 . The spring retention member  25  is suspended along the screw  15  by the spring  20  with the bottom turn  165  positioned in the second retention gap  380 . In operation, the load cell  61  performs similarly to the load cell  10  described in FIGS. 1 and 3.  
         [0029]    The load cell  10  of the various embodiments confers several benefits. First, the load cell  10  applies a more controlled load to the heat sink  11  and the electronic component  9  because the washer  185  has a small tolerance. A controlled tension load is necessary when attaching a heat sink  11  to an electronic component  9  because too little tension will result in a weak electrical connection between electric contacts situated within the electronic component  9 , and too much tension will result in a ruptured electronic component  9 . Secondly, because the washer  185  is already attached to the load cell  10 , the washer  185  does not have to be separately aligned with the washer standoff  14  before inserting the screw  15  into the heat sink  11 . Therefore, assembly time is reduced, and an operator may more easily insert the load cell  10  into threaded apertures  16  in the heat sink  11  that are surrounded by heat release fins  13  or other obstructions.  
         [0030]    While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.