Abstract:
Apparatus and methods for secure attachment of a heat sink to its respective retention clip as well as attachment to an electronic device are presented. One embodiment of a retention clip retention apparatus consists of a protruding hip depending from a side of a heat sink protrusion adapted to capture the retention clip between the hip and the heat sink body. One embodiment of a method for forming the hip consists of using a tool to deform the heat sink protrusion. One embodiment of heat sink lateral retention apparatus consists of one or more split bobbins adapted to attach to the retention clip to prevent lateral motion of the heat sink with respect to the clip.

Description:
RELATED APPLICATION(S) 
   This application is a Divisional of U.S. application Ser. No. 10/262,599 filed Oct. 1, 2002 now U.S. Pat. No. 5,947,283 which is incorporated herein by reference 

   Electronic devices, such as integrated circuit (IC) chip packages, are well known and commonly used to perform a variety of electronic functions. In use, it has been found that some electronic devices often produce significant levels of heat. As a consequence, various methods have been employed to assist in cooling electronic devices. 
   One well-known method for cooling IC chip packages, for example, involves mounting a device known as a heat sink to a surface of the IC chip package. The heat sink commonly has a flat surface which contacts a surface of the IC chip package. Commonly, a plurality of fins or pins extend substantially perpendicularly from a surface of the heat sink. The protruding pins assist in transporting thermal energy away from the IC chip package by providing a relatively large surface area for convective heat transfer as compared with the surface are of the IC chip package. The heat sink is fabricated from a material having a high thermal conductivity for efficient thermal transfer between the IC chip package and the surrounding environment. 
   Various methods have been used to mount heat sinks to the surface of IC chip packages. The art has recognized certain advantages of avoiding the use of adhesives, screws, bolts and the like, and has often relied on the use of retaining clips. 
     FIG. 1  is a perspective view of a prior art assembly of a heat sink  10  which includes a heat sink plate  11 , an electronic device  20 , a mounting frame or base  30  and a retaining clip  40 . It shows the prior art heat sink  10  in an assembled configuration with electronic device  20  coupled to mounting frame  30  and heat sink  10  placed upon and in contact with electronic device  20 . Heat sink  10  is thermally coupled to the top surface of the electronic device  20  by clip  40 , the distal ends or legs  42  of which are engaged with tabs  12  that project from opposite sides of mounting frame  30 . 
   Once legs  42  of clip  40  are secured under tabs  12 , clip  40  provides a spring bias force to the heat sink  10  relative to base  30 , thereby forcing a surface of heat sink  10  into contact with the surface of the electronic device  20 . In this embodiment of a prior art clip  40 , the clip comprises a bent wire having two distal legs  42  extending from an elongated clip central portion  44  which extends therebetween. As shown in  FIG. 2 , legs  42  are substantially perpendicular to central portion  44 , and extend, in the embodiment shown, from central portion  44  in opposing directions forming clip  40  into what may be described as a generally Z-shaped configuration. Further, mounting frame  30  as shown in  FIG. 2  is coupled to a substrate  50 , such as a printed circuit board. 
   In the prior art arrangement of  FIG. 1 , the clip central portion  44  is received within a longitudinal groove  52  that is defined between adjacent rows of heat sink pins  54 . The clip central portion  44  is oriented substantially parallel to and rests upon heat sink surface  56  of plate  11  from which pins  54  project. 
   In the arrangement shown in  FIG. 1 , heat sink  10  is secured to the electronic device  20  by tucking an leg or attachment portion  42  of clip  40  under the projecting tabs  12  of the base  30  upon which the electronic device  20  is mounted. Tucking the legs  42  under the tabs  12  provides a torsional spring-bias force to clip  40  that forces clip central portion  44  firmly against heat sink top surface  56  in longitudinal groove  52 . This spring-bias secures heat sink  10  against electronic device  20  to enable good thermal contact between the heat sink  10  and the electronic device  20 . It does not, however, restrain the heat sink  10  from longitudinal sliding movement relative clip  40  along groove  52 . Such relative motion between the clip  40  and heat sink  10  along the axis of clip central portion  44  is also referred to herein as lateral movement of the heat sink. This lateral movement is distinguished from vertical movement of the heat sink  10  away from the surface of electronic device  20 . 
   Further, in the prior art embodiment shown, heat sink  10  and clip  40  comprise two separate parts, which are not secured to each other before assembly with the electronic device  20 . Clip  40  is not secured to the heat sink  10 , but only engages the heat sink  10  when it is mounted with an electronic device  20 . Accordingly, when the heat sink  10  is not attached to electronic device by clip  40 , clip  40  is a loose part. As such, clip  40  may damage other components if it is dropped during assembly. In addition, the clip  40 , being a loose part, precludes preassembly of clip  20  to the heat sink  10  prior to assembly of the heat sink assembly with the electronic device. Attachment of clip  40  to the heat sink  10  prior to assembly provides numerous advantages, such as, but not limited to, ease of assembly during the attachment of the heat sink  10  to the electronic device, reduction of the risks posed by a loose clip  40  including possible damage to other components. 
   It is well recognized that accurately positioning heat sink  10  relative to electronic device  20  is crucial for proper thermal management. For optimal thermal efficiency, the electronic device  20  should be centered and its contact surface should be aligned under, and in full contact with heat sink  10  such as shown in the sectional elevation view of  FIG. 2 . After a surface of heat sink  10  is forced into contact with a surface of the electronic device  20  by the clip  40 , there remains a potential for the heat sink  10  to shift or move laterally along clip central portion  44  relative to the electronic device  20 . Mechanical shock or vibration during transportation and handling, for example, among other possible disturbances, can cause such undesired lateral shifting of the heat sink  10 . 
     FIG. 3  is a cross-sectional view of an embodiment of a prior art device which illustrates a problem caused by lateral shifting of the heat sink  10  along the central portion  44  of clip  40  from the centered position illustrated in  FIG. 2  to a laterally displaced position. Once it is so shifted, heat sink  10  has lost contact with a portion of the top surface of the electronic device  20 . Such lateral heat sink movement is undesirable since it fails to maintain efficient thermal contact between the electronic device  20  and the heat sink  10 . 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective, view of a prior art heat sink, electronic device and clip assembly; 
       FIGS. 2 and 3  are cross-sectional views of a prior art heat sink assembly; 
       FIG. 4  is a detail of a top view of an embodiment of clip retention apparatus in accordance with the present invention; 
       FIG. 5  is detail of a top view of another embodiment of a heat sink clip retention apparatus in accordance with the present invention; 
       FIG. 6  is a cross sectional detail elevation view taken along section line  6 – 6 ′ respectively of  FIG. 5 ; 
       FIGS. 7–12  are cross sectional detail elevation views showing further embodiments of a clip and heat sink assembly with the views taken similarly to the view of  FIG. 6 ; 
       FIGS. 13–16  are top views of further embodiments of heat sink clip retention apparatus in accordance with the present invention; and 
       FIGS. 17–20  are cross sectional detail elevation views of further embodiments of heat sink clip retention apparatus. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings, which are not necessarily to scale, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the apparatus and methods can be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that the embodiments can be combined, or that other embodiments can be utilized and that procedural changes can be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined by the appended claims and their equivalents. In the drawings, like numerals describe substantially similar components throughout the several views. 
   The following figures refer to an electronic device, for example an integrated circuit (IC) chip package, to which a heat sink is attached with a retaining clip to form a heat sink assembly. The invention is not limited to heat sinks used with electronic circuits in computer assemblies. It works with any apparatus having a heat emitting device and a heat sink. 
   Heat sink  10  is manufactured from a material having good thermal conductivity, such as, but not limited to, aluminum and copper. This allows for the efficient conduction of heat from the electronic device  20  to the heat sink  10 . Heat is subsequently conducted through the heat sink plate to the pins  54  and transferred to the surrounding environment by convection and radiation. 
   In one embodiment of the invention, mounting frame  30  incorporates a clip attachment structure, such as the tab  12  shown in  FIG. 1 , to cooperate with the leg portions  42  extending from the ends of clip  40 . The clip attachment tab structure tab  12  projects from opposite sides of mounting frame  30 . In other embodiments, clip attachment structure  12  may be a pocket, protrusion, ledge, or an aperture. The choice of the particular configuration for an attachment structure  12  may depend the specific geometry of the chip mounting arrangement used. 
   In many of the embodiments of the present invention which are illustrated, clip  40  is a formed cylindrical metal wire. In other embodiments the clip  40  may take the form of, for example, but not limited to, a strap, a band, or a flat wire. The clip  40  can be formed from any material suitable for the intended use, such as, but not limited to, metal and plastic. 
   In one embodiment, clip  40  is comprised of a resilient material, such that when it is twisted it produces a torsional spring-bias force tending to return to an original shape. In one embodiment, the clip  40  comprises a spring metal. 
   A thermal conduction aid  26  is commonly applied to the top surface of the electronic device  20 . Thermal conduction aid  26  makes a thermally efficient contact between the mating surface  24  of electronic device  20  and heat sink plate  11 . Examples of suitable thermal conduction aids  26  include, but are not limited to, thermal conductive grease, soft metallic foil, and metal-impregnated paste. 
     FIG. 4  is a top plan view of an embodiment of the invention. In the embodiment shown, heat sink  10  has a plurality of pins  54  extending upwardly from a surface  56  of heat sink plate  11 . The pins  54  are arranged in longitudinally and transversely oriented rows defining lateral longitudinal grooves  52  aligned with central portion  44  of clip  40  and lateral transverse grooves  53  which are substantially perpendicular to grooves  52 . Longitudinal grooves  52  and, in some cases transverse grooves  53 , are adapted for receiving clip central portion  44 . 
   One or more of pins  54  has a retaining member  62  projecting from the surface thereof into groove  52  for retaining the clip central portion  44  in groove  52 . Various embodiments characterized by different configurations of retaining member  62  are also illustrated in  FIGS. 5 through 12  below. 
   In some embodiments retaining member  62  is adapted to allow the insertion of clip central portion  44  into groove  52  to retain clip  40  within groove  52 . One skilled in the art can appreciate that the retaining member  62  projecting from pin  54  can, in further embodiments, take other suitable forms and still function to readily allow the attachment of the clip  40  to the heat sink  10  while resisting unintended separation from it. Retaining members  62  can be provided on just a single pin  54  or can be provided on multiple pins  54  along one or both sides of the groove  52 , as will be discussed in connection with the embodiments of the following examples. 
     FIG. 5  is a top plan view of an embodiment of the assembly where pins  54  are longitudinally extended as fins  55  that extend substantially along the entire length of groove  52  cross the entire width of surface  56  of heat sink plate  11 . Retaining member  62  is provided on a fin  55  which defines one wall of a longitudinal groove  52 . Retaining member  62  keeps central clip portion  44  vertically restrained in groove  52 . 
   Retaining member  62  is shown in various embodiments in  FIGS. 5–9 . In one embodiment, the retaining member  62  may extend for only a portion of the length of the fin  55 . In the embodiment shown in  FIG. 5 , the retaining member  62  extends substantially the entire length of the fin  55 . In yet another embodiment, not shown, a plurality of retaining members  62  extend at least a portion of the length of fin  55 , the plurality of retaining members  62  being substantially collinear and substantially parallel with surface  56 . The geometric relationship of the retaining member  62  and the adjacent fin  55 A defines a clip retaining groove  52  which prevents the undesired removal of the clip  40  from groove  52  by moving it upwardly from surface  56 . 
   There are a number of ways in which retaining members  62  may be formed on pins  54 . In one embodiment, shown in  FIG. 5 , heat sink  10 , fins  55  and  55 A and longitudinal groove  52  between adjacent fins  55  and  55 A are extruded from a billet of material by extruding the material along an extrusion axis corresponding to the axis of longitudinal groove  52 . Transverse cuts may be made, by a suitable and known machining or sawing process, in fins  55  and  55 A to provide separate pins  54  and form transverse grooves  53 , oriented substantially perpendicular to grooves  52 . The sawing divides fins  55  and  55 A into a plurality of pins  54 . Since the faces of fins  55  and  55 A on both sides of groove  52  are formed by extrusion rather than cutting, it can be seen that modification of the extrusion dies can readily facilitate the forming of retaining members  62  as part of an extrusion process. 
   In the embodiment of  FIG. 5 , the retaining member  62  extends from a plurality of adjacent fins  55  and  55 A. That embodiment is an example of a heat sink  10  that is adapted to accommodate a clip  40  having a substantially straight central portion  44 . 
   In various other embodiments, the location of the pins  54  that are selected to have retaining members  62  formed thereon depends on the configuration of the central portion  44  of the clip  40 . As shown in  FIGS. 6–11 , any one or more of pins  54  may have retaining members  62  of various shapes for retaining the clip  40 . A plurality of such retaining members  62  need not necessarily be collinearly arranged. Clips  40  having a central portion  44  that may follow an other than straight path across surface  56  of heat sink  10 , can also be accepted in the embodiments discussed below as shown in  FIGS. 13–20 . 
     FIG. 6  is a sectional elevation view taken along section line  6 – 6 ′ of  FIG. 5  which illustrates an embodiment of the present invention. The heat sink  10  comprises a plate or base  11  having a surface  70  for engaging a surface of a device to be cooled. Heat sink plate  11  has a plurality of pins  54  that extend upwardly from another surface  56 . The plurality of adjacent, generally parallel, rows of pins  54  define at least one longitudinal groove  52  therebetween which is adapted to retain clip central portion  44  therein. At least one pin  54  has a retaining member  62  extending from the surface of pin  54  into groove  52 . 
   In the embodiment shown in  FIG. 6 , retaining member  62  has wedge shape which, when viewed in cross section, includes a face  72  that slopes downwardly toward surface  56  as the body of retaining member  62  projects inwardly into groove  52 . In the embodiment shown, the shape of retaining member  62  is adapted to allow clip central portion  44  to be introduced into groove  52  from above the retaining member  62 , pass between the retaining member  62  and the adjacent pin  54 , and to subsequently be retained between the retaining member  62  and the surface  56  of heat sink plate  11 . The spacing between retaining member  62  and pin  54  lying across groove  52  from it is selected such that central portion  44  of clip  40  is restrained from being readily removed from groove  52 . In one embodiment, one or both of pins  54  and/or the retaining member  62  is resilient to facilitate the insertion of clip  40  into groove  52 . The resiliency is sufficient to allow retaining member  62  to substantially return to its original shape after introduction of the clip  40  in order to restrict the removal of the clip  40  from the groove  52 . 
     FIG. 7  is a cross-sectional view of an embodiment showing the use of a rounded retaining member  62  having a rounded surface  74  extending from a side of pin  54  and extending toward an adjacent pin  54  on the other side of groove  52 . 
     FIG. 8  is a cross-sectional view of another embodiment. At least one pin  54  further comprises a retaining member  62 , resembling in cross-section, a flap extending from a side of the pin  54 . In this embodiment retaining member  62  slopes downwardly and is oriented toward surface  56  and also toward an adjacent pin  54  which defines the other side of groove  52 . It has a partially cut-away lower surface  82 . 
     FIG. 9  is a cross-sectional view of a further embodiment. One or more pairs of opposing retaining members  62  project inwardly into groove  52  in an opposing relationship from adjacent pins  54  which define opposite sides of groove  52 . The spacing and dimensions of the pair of opposing retaining members  62  and width of groove  52  are selected so as to trap and retain central portion  44  of the clip  40  within the groove  52 . In one embodiment, the pair of opposing retaining members  62  are resilient to allow the insertion of clip  40 , with the pair of opposing retaining members  62  substantially returning to an original shape after the insertion of the clip  40  to prevent unintended removal of the clip  40  from the groove  52 . 
   In an embodiment of the invention wherein more than one retaining member  62  projects into groove  52 , the retaining members  62  each project from sides of the pins  54  in a co-linear and co-planar relationship, and at a substantially equal height above surface  56 , such as shown with the pair of retaining members  62  shown in  FIG. 9 . In that embodiment, the retaining members  62  are located at substantially the same distance above the surface  56  such that the clip  40  may be restrained between retaining member  62  and the second surface  56 . Clip  40  in these embodiments may be retained by the retaining members  62  at any one or more of a number of places along the central portion  44  of the clip  40 , as shown, for example, in  FIG. 4 . 
   In other embodiments of the invention, where more than one retaining member  62  extends into longitudinal groove  52 , the retaining members  62  may not project from sides of the adjacent pins  54  in a co-linear and co-planar relationship, as will be discussed in connection with further embodiments below. 
   In several of the embodiments discussed above, retaining member  62  projects into the groove  52  a distance sufficient to retain the clip  40  within the groove. This distance is dependent on the width of the groove  52  and the width of the clip  40 . In an embodiment of the invention, the gap between the end of the retaining member  62  and either adjacent retaining member  62  or pin  54  is less than the width of the clip central portion  44 . 
   In one embodiment of the invention, not shown, wherein the material of clip  40  is in the form of a thin band, clip  40  may be rotated 90 degrees prior to insertion into the groove such that the clip passes beyond the retaining member  62  in an edge-on fashion, and is subsequently rotated 90 degrees to allow retaining member  62  to retain the clip within the groove. 
   Also in some embodiments of the invention, the projection  62  extends from a side face of pin  54  to form a retention barrier in groove  52  which is sufficiently above surface  56  to define a space  51 , shown in  FIG. 12 , in which the central portion  44  is retained. The distance above the surface  56  that the retaining member  62  is located depends, in part, on the height, or the cross sectional diameter, of the clip central portion  44 . In one embodiment, for example, the distance above the surface  56  from which the retaining member  62  extends, as well as the width of the groove  52 , are substantially equal to or slightly greater than either the diameter or the height and width of the central portion  44 . In other embodiments of the invention, it may be advantageous to position the retaining member  62  at a somewhat greater height above surface  56 . 
     FIG. 10  is a cross-sectional view of an embodiment of a heat sink  10  in which at least one pin  54  has a staked retaining member  62 . The assembly manufacturing method utilized for that embodiment comprises inserting a clip  40  into a groove  52  defined by adjacent rows of pins  54 . The inserted clip  40  is retained by staked retaining member  62  in close proximity to surface  56  of the heat sink  10 . The cross section of central portion  44  of clip  40  and the width of groove  52  are configured to substantially match. In the embodiment of  FIG. 10 , a metal working tool such as staking tool  76  is used to deform at least a portion of at least one pin  54  located at one side or wall of the groove  52  into which the clip  40  had previously been placed. When a staking force is applied, tool  76  permanently deforms the pin  54  to form retaining member  62 . A clip retaining space is created between retaining member  62  and the surface  56  to accommodate the portion of clip  40  contained within it so as to retain clip  40  within groove  52 . Other examples of a metal working tool  76  which could be employed include, but are not limited to, chisels or crimping tools. 
     FIG. 11  is a cross-sectional view of a heat sink constructed in accordance with another embodiment of the method. The method comprises inserting central portion  44  of a clip  40  into a groove  52  that is defined by adjacent rows of pins  54 . Clip  40  is also positioned in close proximity to the surface  56  of the heat sink  10 . The width of groove  52  and the width and cross sectional configuration of the central portion  44  of clip  40  are chosen so that the clip lies in the groove  52 . A metal working tool is used to deform at least a portion of pins  54  on opposite sides of groove  52  into which the clip  40  is placed. The tool works pins  54  to form two cooperating opposed retaining members  62  that provide an upper restraining boundary for a clip receiving space in groove  52 . Retaining members  62 , in cooperative relationship, protrude sufficiently into the groove  52  to retain the clip  40  within groove  52 . 
     FIG. 12  is a cross-sectional view of a further embodiment. In that embodiment, the method of retaining a clip  40  in a heat sink  10  comprises initially inserting a clip  40  into a groove  52  defined by adjacent rows of pins  54  so that the clip  40  is placed in space  51  in close proximity to the surface  56  of the heat sink  10 . The width of the clip  40  generally matches that of groove  52 . One or more pins  54  adjoining groove  52  are subsequently deformed by bending them together at their end portions which are distal to surface  56  so as to narrow groove  52  above clip  40  to prevent undesired removal of the clip from groove  52 . In one embodiment, the narrowed groove  52  is formed by the squeezing action of a tool, such as a crimping tool, against opposing pins  54 . 
   The maintenance of proper lateral positioning of heat sink  10  relative to a heat emitting surface of electronic device  20  is also important for proper thermal management. For optimal thermal efficiency, electronic device  20  should remain centered under and in full contact with the heat sink  10  in the aligned arrangement shown in  FIG. 2 . Once heat sink  10  is positioned and restrained against electronic device  20  by clip  40 , it retains a potential for shifting or moving laterally by moving longitudinally along the axis central portion  44  of clip  40  in the plane of contact with the electronic device  20 . When heat sink  10  has undergone such lateral movement relative to clip  40  and electronic device  20  it may assume the sort of misalignment shown in  FIG. 3 , for example. Mechanical shock which may often be encountered during transportation and in the course of handling, for example, can cause such shifting of the heat sink  10 . 
   The present invention provides geometric features for restraining the heat sink from moving or shifting laterally in the plane of the device as well as from lifting vertically off of the electronic device upon which it is mounted. For example,  FIG. 13  is a top view of an embodiment in a heat sink clip  40  providing longitudinal and transverse lateral restraining as well as vertical restraining characteristics. Clip  40  includes a central portion  44  comprised of a first portion  44 A, a second portion  44 B adjacent to and substantially perpendicular to the first portion  44 A, and a third portion  44 C which is adjacent to and substantially perpendicular to the second portion  44 B and substantially parallel with the first portion  44 A. In this embodiment, the first, second, and third portions  44 A,  44 B and  44 C are substantially coplanar. 
   In the embodiment of  FIG. 13 , heat sink  10  is restricted from moving laterally in the plane of the electronic device by the geometric features provided by bends in the central portion  44  of clip  40  which allow portions of it to be inserted in both longitudinal grooves  52  and transverse grooves  53  that are oriented substantially perpendicular to each other. In the embodiment shown, segment  44 A of clip  40  lies in a first longitudinal groove  52 , segment  44 B, which is substantially perpendicular to segment  44 A, lies in a transverse groove  53  which is perpendicular to longitudinal groove  52 . Finally, segment  44 C lies in a further longitudinal groove  52  that is displaced from first longitudinal groove  52  and is substantially perpendicular to transverse groove  53 . Because of the placement of portions of clip  40  in the perpendicularly oriented grooves  52  and  53 , heat sink  10  is restricted from moving laterally in the plane of the electronic device and the lateral plane of the view shown in  FIG. 13 . With the heat sink  10  being restricted from both longitudinal and transverse lateral movement while also being secured from vertical movement perpendicular to the plane of the drawing of  FIG. 13 , heat sink  10  will be retained in its desired position relative to the electronic device  20  upon which it is mounted. 
     FIG. 14  is a top view of another embodiment where a central portion  44  including a first portion  44 A, a second portion  44 B adjacent and perpendicular to the first portion  44 A, a third portion  44 C adjacent and perpendicular to the second portion  44 B and parallel with the first portion  44 A, a fourth portion  44 D adjacent and perpendicular to the third portion  44 C and parallel with the second portion  44 B, and a fifth portion  44 E adjacent and perpendicular to the fourth portion  44 D and substantially collinear with the first portion  44 A. The second, third and fourth portions  44 B,  44 C and  44 D are adapted to provide a geometric feature which places portions of the central portion  44  of clip  40  in perpendicularly intersecting grooves  52  and  53  to secure heat sink  10  against movement laterally and transversely in the plane of the drawing of  FIG. 14 . A portion of the central portion of clip  44  can also be said to partially encircle at least one pin  54 , to restrict movement of the heat sink  10  both laterally and transversely in the horizontal plane while also securing it vertically. In the embodiment shown in  FIG. 14 , the first, second, third, fourth, and fifth portions  44 A,  44 B,  44 C,  44 D and  44 E are all substantially coplanar and parallel to surface  56  of heat sink  10 . 
     FIG. 15  relates to another embodiment and shows a lateral restraining of the clip central portion  44  including several bends that combine to comprise a geometric feature or “kink”  92  in the portion oriented to lie in the plane of surface  56  of heat sink  10 . Kink  92  protrudes into perpendicular groove  52  when the distal ends of central portion  44  are inserted into longitudinal groove  53 . Kink  92  is positioned between and restrained by opposing pins  54  with two protrusions  62  flanking geometric feature  92  and thereby substantially preventing lateral movement of the heat sink  10 . 
     FIG. 16  relates to another embodiment showing of a lateral restraint of clip portion  44 . Central portion  44  has a geometric feature which is a deformation or bulge  94  formed in central portion  44  so that a portion of the geometric feature projects into transverse groove  53  to provide a restraint against longitudinal movement along the axis of central portion  44 . The geometric feature portion  94  restricts transverse longitudinal movement of the heat sink  10  in groove  52  while the central portion  44  of the clip  40  restricts transverse lateral movement of the heat sink  10  relative to clip  40 . 
   In one embodiment, the heat sink geometric feature  94  which provides lateral restraint is formed by a squeezing action of a crimping tool. The crimping tool permanently flattens a portion of the central portion  44  of the clip  40  to form the bulge  94  which extends transversely into one of the transverse grooves  53  to inhibit longitudinal lateral movement. In one embodiment, deformed portion  94  is formed prior to the insertion of the clip  40  into the longitudinal groove  52 . 
   In another embodiment, the geometric feature provided by the deformed portion  94  is formed after the insertion of the clip  40  into the groove  52 . In that embodiment, a location on the central portion  44  is chosen where there is an intersection of two perpendicularly intersecting grooves  52  and  53 . In one embodiment, a metal working tool is used to compress the chosen portion of the central portion  44  between a surface of the tool and the heat sink second surface  56  forming the deformed portion  94 . Deformed portion  94  is adapted to extend into the groove  52  and thereby restrain lateral movement of the heat sink  10 . 
     FIG. 17  shows a detail cross section elevation view of another embodiment. The central portion  44  of the clip  40  bends to provide a geometric feature which is a raised portion  44 C which is parallel to and above surface  56  of heat sink  10  between two non-raised clip portions  44 A and  44 E that are routed closely adjacent to surface  56 . The raised portion  44 C is adapted to cooperate with the retaining members  62  from pins  54  to secure clip portions  44 A and  44 E from vertical movement away from surface  56 . Clip portions  44 A and  44 E are captured between adjacent retaining member  62  and surface  56  and prevent the clip from being vertically withdrawn from the groove  52 . The raised portion  44 C extends above the space between retaining members  62  and the surface  56 . The raised portion  44 C is adapted such that transition portions between segments  44 A and  44 E and raised portion  44 C abuts retaining members  62  to allow them to substantially restrict lateral movement of the heat sink  10  relative to clip central portion  44 . 
   It is understood that in various embodiments heat sink geometric features can comprise many forms and still cooperate with pins  54  and restrain lateral motion of the heat sink  10  relative to retaining clip  40 .  FIG. 18  shows a cut-away view of another embodiment constructed in accordance with the present invention. The central portion  44  of clip  40  has a raised portion  101  comprising an inverted V-shaped kink which engages one or more retaining members  62  from pins  54  on the sides of the groove  52  containing the central portion  44  of clip  40  to prevent substantially all movement of the heat sink  10  relative to clip  40 . 
     FIG. 19  provides a cut-away view of another embodiment in accordance with the present invention. The central portion  44  bends to a raised portion  103  comprising an inverted U-shaped kink which provides the necessary interference with one or more retaining members  62  to substantially prevent longitudinal movement of the heat sink  10  along the central portion  44  of the clip. 
     FIG. 20  illustrates, in cross-section, another embodiment in accordance with the present invention. The raised portion  44 C cooperates with two abutting retaining members  62 A and  62 B from a single pin  54  above and below raised portion  44 C so that portion  44 C is captured between the two retaining members  62 A and  62 B. The raised portion  44 C abuts the retaining members  62 A and  62 B to substantially prevent lateral movement of the heat sink  10  relative to along central portion  44  and parallel to surface  56  as well as restraining it vertically. In one embodiment restraining member  62 A is formed after clip  40  is seated in slot  52  and locks it in place. Thus, the geometry features provided by the bends on central portion  44  of the clip  40  restrain it from movement relative to heat sink  10 . Many other interlocking combinations of retaining members  62  and geometrical features of clip  40  will also serve to lock it to heat sink  10  to restrain undesired movement of heat sink  10  relative to the cooled electronic device. 
   It can also be appreciated, and is within the scope of this invention, that various geometric configurations of the central portion  44  of clip  40  will also restrict undesired movement of the clip  40  relative to the heat sink  10 . For example, in yet another embodiment, not shown, at least a portion of central portion  44  is not aligned with either a groove  52  or a groove  53  but may be placed in a diagonally oriented groove running between pins  54  where it will still contribute to securing heat sink  10  from lateral movement in the plane of the electronic device. 
   It is to be understood that the above description is intended to be illustrative and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.