Abstract:
A structure for removing heat from a packaged electronic component. The structure includes three, main elements. First, a heat sink has a pedestal with opposing ends and a plurality of fins separated by spaces and disposed on the pedestal. The heat sink dissipates heat generated by the packaged electronic component. Second, parallel rails are disposed adjacent the opposing ends of the pedestal, each rail having a catch. Third, a spring clip has (a) end hooks which engage the catches to retain the spring clip on the rails, and (b) a strut extending between the hooks, fitting into the space between adjacent fins, and including an apex which contacts substantially centrally the pedestal and applies a force pressing the heat sink toward the packaged electronic component. Thus, the heat sink is removably attached at least indirectly to the packaged electronic component. Also disclosed is a method of using the structure.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to semiconductor device packaging and, in particular, to a structure and method for removably attaching a heat sink to an electronic package which is, even more particularly, a surface mount package. 
     BACKGROUND OF THE INVENTION 
     In order to safely operate modem computers and other electronic devices, thermal energy must be removed from components which generate large amounts of heat and which cannot dissipate the heat fast enough to avoid harmful consequences. As the art moves towards smaller, higher-power integrated circuits such as static random access memory (SRAM) integrated circuits, heat transfer from the integrated circuit package (IC package) becomes increasingly difficult and more important. (The term “IC package” includes the heat-generating integrated circuit as well as the packaging surrounding the integrated circuit.) As chip density and the speed of IC chips increase, chips often require high-performance surface mount packages assembled very close to each other on circuit cards. These packages generate heat and, because they are packed very close to each other, they become hot. 
     One conventional method used to dissipate the accumulating heat of an electronic device such as an IC package is to force air over the device, thereby removing the heat by convection. This method has been substantially improved by attaching a heat dissipating device, also known as a heat sink, to the electronic device. The heat sink is designed to dissipate heat at a significantly greater rate than the electronic device alone. A heat sink typically has projections such as pins or fins, exposing a greater surface area to the flow of air for greater dissipation of heat. 
     When the heat sink is placed in thermal contact with the electronic device, the electronic device transfers heat by conduction to the heat sink. The heat to sink then dissipates accumulating heat by convection to the ambient environment. This method has become standard in the computer industry for dissipating the large amounts of heat generated by the new generation of computer processors. 
     Of importance, the heat sink must be reliably attached to the electronic device. In the case of IC packages, such attachment must not undesirably is stress or damage the IC package or the circuit board to which the IC package is connected. One conventional technique is to employ a thermally conductive adhesive which bonds the heat sink to the IC package. Thermally conductive adhesives do not adhere well to plastic IC packages, however, resulting in an unacceptably high incidence of bond failure between the plastic IC package and the heat sink. Further, once the heat sink is bonded with the thermally conductive adhesive, it is difficult to remove the heat sink from the IC package without causing damage to the IC package, the heat sink, or the circuit board. Still further, it is desirable to have a removable heat sink to readily allow chip repair, rework, or replacement. Accordingly, it is preferable to avoid the use of thermally conductive adhesives altogether. 
     Other methods have been used to secure the heat sink to the electronic device, including the use of clips to fasten the assembly together. It is preferred that any attachment method allow for quick and easy installation and removal of the heat sink while providing a secure attachment during operation and normal handling. Electronic devices must be removed and replaced from time to time; therefore, the heat sink must be easy to remove and install without sacrificing reliability or effectiveness. Clips offer the advantages of being relatively inexpensive, simple, operational over a multiple number of assembles and disassembles, and reasonably secure so that the heat sink does not disconnect or dislodge from the electronic device. 
     A wide variety of different clips are known. Two-piece dips are disclosed by U.S. Pat. No. 5,617,292 issued to Steiner. As Steiner teaches, however, previous two-piece clips used to fasten heat sinks generally lack sufficient rigidity and strength, particularly at the junction between the two parts of the clip, and separation of the assembly is a potential risk. In general, two-piece clips are constructed so that the intersection of the separate leg and the leaf spring member forms a loose hinge about which rotation at least to some degree in several directions is possible. Thus, the force holding the assembly together is exerted substantially entirely in a direction normal to the electronic component. The hinge mechanism is relatively weak and prone to failure, particularly under prolonged use and shock and vibration. Holding the necessary tolerances during manufacturing imposes additional difficulty in producing two-piece clips. 
     One-piece clips avoid some of the drawbacks inherent in two-piece clips. Such clips generally extend over the heat sink and attach at each end to the electronic device or its socket at specially provided ports or bosses. Clips of this design require modification of the electronic device or its socket and may deleteriously affect performance of those components. To avoid these problems, other clips attach removable heat sinks directly to the circuit board to which the IC package is connected. 
     For example, Tseng discloses, in U.S. Pat. No. 6,043,984 assigned to Intel Corporation, a removable heat sink that uses clips or fasteners to attach the heat sink to an IC package. The IC package is mounted to a substrate such as a circuit board. The clip has four L-shaped ears that are inserted through clearance holes in the substrate and corresponding attachment holes in the heat sink. The four L-shaped ears extend from a center plate portion. The L-shaped ears are bent during insertion through the holes. Once beyond the attachment holes of the heat sink, the L-shaped ears snap back so as to permit the clip to exert a spring force that pushes the heat sink into the integrated circuit package. 
     As described in U.S. Pat. No. 6,154,365, also assigned to Intel Corporation, the clip taught by Tseng has several drawbacks. From one electrical assembly to the next, the spring force from the L-shaped ears is not consistent due to the variations within part manufacturing tolerances. Moreover, the L-shaped ear technique does not permit a technician to adjust the spring force from the L-shaped ears so as to evenly distribute this force over the surface of the substrate. Without an even distribution of force, the substrate is more likely to bend which may cause the substrate or the integrated circuit within the integrated circuit package to crack. When attached directly to the IC package in the manner disclosed, the heat sink exerts undue force on the IC package which can damage and ultimately destroy the IC package. 
     Post-type fastening members are also used to secure a heat sink to an electronic device. FIG. 1 is a side view of an electronic device  8  which includes a heat sink  10  directly attached by post-type fastening members  12 A to a circuit board  14 . Located between the heat sink  10  and the circuit board  14  is an IC package  16  which generates heat during use. The IC package  16  is typically electrically connected to the circuit board  14  by one or more circuit interconnections, e.g., solder, which are not illustrated in FIG. 1 for purposes of clarity. The fastening members  12 A urge the heat sink  10  towards the circuit board  14  and down onto the IC package  16  to make the thermal contact between the heat sink  10  and the IC package  16 . 
     Although providing the force necessary to make the thermal contact between the heat sink  10  and the IC package  16 , the fastening members  12 A cause the heat sink  10  to press unevenly on the IC package  16 . In particular, the IC package  16  acts as a pivot between the heat sink  10  and the circuit board  14  so that the end  10 A of the heat sink  10  is urged away from the end  14 A of the circuit board  14  as indicated by the arrows  18 . This causes the force exerted by the heat sink  10  on the IC package  16  to be greater at the side  16 A of the IC package  16  than at the side  16 B. This uneven force distribution can damage and even crack the IC package  16 . Further, this uneven force distribution can create a gap between the side  16 B and the heat sink  10  resulting in poor heat transfer between the IC package  16  and the heat sink  10 . Alternatively, or in addition, this uneven force distribution can cause circuit interconnection failure near the side  16 B of the IC package  16 . As those skilled in the art understand, these conditions can ultimately cause failure of the device  8 . 
     To avoid these drawbacks, it has become known in the art to attach both sides of the heat sink  10  to the circuit board  14 . As an example, second post-type fastening members  12 B illustrated by dashed lines in FIG. 1 can be employed. This tends to equalize the force exerted by the heat sink  10  on both the sides  16 A and  168  of the IC package  16 . This also causes the ends  14 A,  14 B of the circuit board  14  to be pulled up, however, by the fastening members  12 B,  12 A, respectively, relative to the die attach region  14 C of the circuit board  14  to which the IC package  16  is attached. This bending force, indicated by arrows  20 , causes the circuit board  14  to warp such that the circuit board  14  is displaced to a position  22 . Over time, such bending can cause the device  8  to fail, e.g., from failure of circuit interconnections between the IC package  16  and the circuit board  14 . U.S. Pat. No. 6,125,037, issued to Bollesen, discusses the post-type fastening members illustrated in FIG.  1  and described above. 
     FIG. 2 shows a product designed by Intel Corporation illustrating still another mechanism used to secure a heat sink to an electronic device. As with many electronic packages used in the computer industry, the Intel product includes a layered region of five stacked components: (1) a circuit board  14 , (2) a socket  30 , (3) a processor (not shown), (4) a thermal pad (also not shown), and (5) a heat sink  10  designed to dissipate heat generated by the processor. The heat sink  10  is retained in position over the processor, for the illustrated structure available from Intel, by a pair of retention modules  40  placed alongside two opposing sides of the heat sink  10 . Two screws  42  engage mating screw holders  44  in the circuit board  14  to affix each retention module  40  in position. A spring clip  46  fits over each retention module  40  and exerts a downward force on an edge portion of the heat sink  10 , peripheral to the cooling fins of the heat sink  10 , to retain the heat sink  10 . 
     Thus, the conventional Intel structure requires multiple components. The Intel structure specifically requires two retention modules  40 , four screws  42 , four screw holders  44 , and two spring clips  46 . The spring clips  46  require a separate tool for assembly and disassembly. When the first spring clip  46  is assembled, the downward force exerted on an edge of the heat sink  10  pivots upward the unrestrained opposite side of the heat sink  10 . Such pivoting action may damage the interface (typically a thermally conductive pad, grease, or oil) between the heat sink  10  and the processor. 
     To overcome the shortcomings of conventional mechanisms, a new device and method for retaining heat sinks on electronic devices such as IC packages is provided. An overall object of the present invention is to provide an improved heat sink retention structure and method. Another object is to reduce the space occupied by the retention structure on the underlying electronic package. 
     Still another object is to ease the assembly and disassembly of the heat sink. A related object is to eliminate some of the components required by conventional retention structures, including separate tools for assembly and disassembly. Additional objects of the present invention are to locate the retention force substantially centrally on the heat sink or in the region of the fins of the heat sink and to distribute the force evenly. It is still another object to avoid possible damage to the package or thermal interface material during assembly and disassembly of the heat sink. Yet another object of this invention is to provide stiffness to and avoid bending of the circuit board which underlies the heat sink. Also an object is to minimize the disruption of air flow through the heat sink. 
     SUMMARY OF THE INVENTION 
     To achieve these and other objects, and in view of its purposes, the present invention provides a structure for removing heat from a packaged electronic component. The structure includes three, main elements. The first element is a heat sink having a pedestal with opposing ends and a plurality of fins separated by spaces and disposed on the pedestal. The heat sink dissipates heat generated by the packaged electronic component. The second element is a set of parallel rails disposed adjacent the opposing ends of the pedestal of the heat sink, each rail having a catch. The third element is a spring clip having (a) end hooks which engage the catches on the rails to retain the spring dip on the rails, and (b) a strut extending between the hooks, fitting into the space between adjacent fins of the heat sink, and including an apex which contacts substantially centrally the pedestal of the heat sink and applies a force pressing the heat sink toward the packaged electronic component. Thus, the heat sink is removably attached at least indirectly to the packaged electronic component. 
     The present invention further provides an electronic package. The electronic package includes a circuit board; a socket affixed to the circuit board; a processor fitted in the socket and generating heat; a thermal pad engaging the processor and transmitting the heat generated by the processor; a heat sink having a pedestal with opposing ends and a plurality of fins separated by spaces and disposed on the pedestal, the heat sink engaging the thermal pad and dissipating the heat generated by the processor and transmitted by the thermal pad; and an attachment structure removably attaching the heat sink to the thermal pad. The attachment structure includes: (a) parallel rails disposed adjacent the opposing ends of the pedestal of the heat sink, each rail having a catch, and (b) a spring clip having (1) end hooks which engage the catches on the rails to retain the spring clip on the rails and (ii) a strut extending between the hooks, fitting into the space between adjacent fins of the heat sink, and including an apex which contacts substantially centrally the pedestal of the heat sink and applies a force pressing the heat sink toward the thermal pad. 
     The present invention still further provides a method of removably attaching a heat sink to a packaged electronic component whereby the heat sink dissipates heat generated by the packaged electronic component. The heat sink has a pedestal with opposing ends and a plurality of fins separated by spaces and disposed on the pedestal. The method includes arranging parallel rails adjacent the opposing ends of the pedestal of the heat sink, each rail having a catch. A spring clip is installed pursuant to the method. The spring clip has (a) end hooks which engage the catches on the rails to retain the spring clip on the rails, and (b) a strut extending between the hooks, fitting into the space between adjacent fins of the heat sink, and including an apex which contacts substantially centrally the pedestal of the heat sink and applies a force pressing the heat sink toward the packaged electronic component. Thus, the heat sink is removably attached at least indirectly to the packaged electronic component. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
     FIG. 1 is a side view of an electronic device which includes a heat sink directly attached by post-type fastening to a circuit board in accordance with a conventional structure; 
     FIG. 2 shows a product marketed by Intel Corporation illustrating still another conventional mechanism used to secure a heat sink to an electronic device; 
     FIG. 3 is separated view showing several of the components used in an exemplary embodiment of the structure of the present invention; 
     FIG. 4 illustrates a first embodiment of the support structure of the present invention, which is typically used to support a single IC package, having a frame with a pair of parallel rails; 
     FIG. 5 is a perspective view of an exemplary embodiment of the spring clip according to the present invention; 
     FIG. 6 is a perspective view of an exemplary embodiment of the heat sink according to the present invention; 
     FIG. 7 is a side, transparent view showing the spring clip of FIG. 5 as assembled to the heat sink of FIG. 6 according to the present invention; 
     FIG. 8 illustrates an embodiment of the present invention in which one pair of relatively short rails forms a separate support structure for each individual processor; 
     FIG. 9 illustrates another embodiment of the rails of the support structure of the present invention in which the rails are configured to bridge all of the processors in one line on the circuit board; 
     FIG. 10 is a partial perspective view of the rails of the support structure shown in FIG. 9, highlighting use of the rails and the spring clip to retain the heat sink; 
     FIG. 11 is a perspective view of the assembly, with the rails of the support structure bridging all four of the processors in one line on the circuit board, according to the present invention; 
     FIG. 12 illustrates an initial step in the procedure used to assemble embodiments of the socket, processor, thermal pad, heat sink, and spring dip of the present invention on a circuit board, specifically placing the hook of the spring clip in the two alignment slots on the heat sink; 
     FIG. 13 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which the technician rocks the spring clip back into the spaces between the fins of the heat sink and slides the spring clip back and up into the fin spaces until an end of the spring clip slips over the corners of the fins; 
     FIG. 14 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which the technician tips an end of the heat sink down and secures the hook of the spring clip under the catches in the rail of the support structure; 
     FIG. 15 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which the two ends of the heat sink are placed in the pockets of the retention rails and the pedestal of the heat sink rests on the thermal pad atop the processor; 
     FIG. 16 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which a downward pressure is applied to a hook of the spring clip; 
     FIG. 17 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which the hook of the spring clip is pushed down past the corresponding catches in the rail; 
     FIG. 18 illustrates another step of the procedure used to assemble the components shown in FIG. 12 in which the hook of the spring clip is pushed under the catches in the rail to complete installation; and 
     FIG. 19 is a perspective view of an embodiment of a tool used to facilitate installation of the retention structure according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing, in which like reference numbers refer to like elements throughout the various figures that comprise the drawing, FIG. 3 shows a structure as manufactured pursuant to the invention. The structure includes five stacked components: (1) a circuit board  14 , (2) a socket  30 , (3) a processor  50 , (4) a thermal pad  60 , and (5) a heat sink  10  designed to dissipate heat generated by the processor  50 . The heat sink  10  must be retained in position over the processor  50  and on the thermal pad  60 . A spring clip  80  is provided to achieve that function. 
     A. Structure of the Invention 
     The integrated circuits of the processor  50  generate heat which must be removed from the circuits. The thermal pad  60  is thermally coupled to the integrated circuit package to provide a thermal path for the heat generated by the processor  50 . Rather than a thermal pad  60 , any of the known interfaces may be used between the heat sink  10  and the processor  50 . Such interfaces include thermally conductive greases or oils; an exception is any material that also acts as an adhesive. 
     The heat sink  10  is mounted to the thermal pad  60  to further facilitate the removal of heat. The heat sink  10  typically contains a plurality of fins  24  which extend from a pedestal  26 . The pedestal  26  has a mounting surface  28  which mates with a corresponding surface of the thermal pad  60 . The mounting surfaces of the thermal pad  60  and the heat sink  10  must be relatively flat to ensure that there are no air voids when the components are assembled. Air voids will significantly increase the thermal impedance between the thermal pad  60  and the heat sink  10 . 
     Turning to FIGS. 4,  5 , and  6 , three, specific components of the present invention are illustrated. FIG. 4 illustrates a first embodiment of the support structure of the present invention. In this embodiment, the support structure is a frame  70  having a pair of parallel rails  72 . A pair of parallel legs  74  connect the rails  72 , creating a rectangular frame  70 . Each rail  72  has a pair of feet  76 , with holes  78  disposed in the feet  76 . The holes  78  receive fasteners (screws, bolts, or the like) to mechanically affix the frame  70  to the circuit board  14 . In a second embodiment of the support structure, the legs  74  can be omitted. 
     In either of the first two alternative embodiments of the support structure, one pair of short rails  72  is provided for each processor  50 . This configuration is illustrated in FIG.  8 . These embodiments sacrifice the advantage of stiffening (achieved by the third embodiment discussed below) of the circuit board  14  but increase flexibility: the support structure can be used on circuit boards  14  with processors  50  in different orientations and on different sides of the circuit board  14  (as shown in FIG.  8 ). While the circuit board assembly illustrated in FIG. 8 has heat sinks mounted to both sides of the circuit board, the heat sinks can be mounted on one or both sides of the board according to embodiments within the scope of this invention. 
     According to a third, exemplary embodiment of the invention, the support structure includes two opposing rails  72 . These rails  72  are illustrated in FIG.  9 . The rails  72  bridge all of the processors in one line on the circuit board  14  providing stiffness to the circuit board  14  otherwise unavailable when each heat sink  10  is retained individually (as in the first two embodiments of the support structure). This configuration is illustrated in FIGS. 10 and 11. Such stiffness minimizes the risk of bending of the circuit board  14 . In addition, the bridging rails  72  save space on the circuit board  14  as compared to separate rails  72  for each processor  50 . 
     The embodiment of the invention illustrated in FIG. 11 shows a structure for each group of electronic packages which consists of two rails  72 , four heat sinks  10 , four clip springs  80 , four thermal pads  60 , and eight fasteners such as screws  42 . The number of electronic packages served by this structure can vary as needed. Thus, the structure meets the requirement of a single circuit board  14  with eight processors  50  on two buses. Each bus has four processors  50  and one supporting Application-Specific integrated Circuit or ASIC—all on the same side of the circuit board  14  and all in line. The structure also meets the requirement that the processors  50  be more tightly spaced than on conventional systems and also be orientated with the air flow perpendicular (i.e., at ninety degrees) to the bus whereas in conventional systems the air flow was oriented along the length of the bus. These two requirements make the use of previous heat sinks  10  and retention solutions impractical. The solution offered by the present invention, however, meets these requirements. 
     Both rails  72  are identical, fostering economy and minimizing the number of different parts. Each rail  72  has one or more pockets  68  formed in the surface of the rail  72  that faces the heat sink  10 . The pockets  68  are illustrated, for example, in FIG.  9 . Regardless of the embodiment of the support structure, the rails  72  have a plurality of catches  66 . 
     The rails  72  are preferably made of sheet metal. Such material of construction provides several advantages for systems requiring low quantities. Initial tooling costs are low. Manufacturing turn around is fast. Moreover, rails  72  formed of sheet metal have some flexibility, which provides intimate contact between the rails  72  and the corresponding heat sinks  10 . Of course, the rails  72  may be made in other ways or of other materials if production quantities justify the cost of tooling. 
     The spring clip  80  is an integral, monolithic, one-piece construction. As illustrated in FIG. 5, the spring clip  80  has two U-shaped end hooks  82 . The hooks are connected by two V-shaped struts  84 . The central apex of each V-shaped strut  84  forms a contact point  86 . One of the hooks  82  has a centrally located nose  88 . The other hook may have a slit  90 , extant because clip  80  is preferably formed from a single piece of approximately twelve-pound spring wire. 
     The heat sink  10  of the present invention includes a number of conventional features. Specifically, the heat sink has a plurality of fins  24  affixed to a pedestal  26 . The pedestal  26  is substantially rectangular in shape, having opposing ends and sides, a top to which the fins  24  are affixed, and a bottom or mounting surface  28  which contacts the thermal pad  60 . 
     The heat sink  10  of the present invention also includes a number of features that are not conventional. Specifically, the heat sink  10  has one or more alignment protrusions  38 . The heat sink  10  also has vertical alignment slots  36  cut in (or, alternatively, marks on) its ends to align the spring clip  80  relative to the heat sink  10 . 
     The pockets  68  of each rail  72  are designed to mate with the corresponding protrusions  38  provided on each end of the heat sink  10 . The pockets  68  retain the heat sink  10  in the two directions parallel to the surface of the circuit board  14 . The pockets  68  are sufficiently deep that the rails  72  do not restrain the heat sink  10  in the direction perpendicular to the surface of the circuit board  14  when a processor  50  is in position in its socket  30  beneath the heat sink  10 . Absent a processor  50  in position, however, the pockets  68  are not so deep that an installed heat sink  10  would contact the empty socket  30 . Thus, the pockets  68  allow the heat sink  10  to “float” in the vertical direction while restraining the heat sink  10  in is the horizontal directions, reducing the accuracy needed in construction and assembly of individual components. 
     The catches  66  on the rails  72  are designed to engage the hooks  82  of the spring clip  80 . The spring clip  80  is restrained in all directions by the catches  66  of the rails  72 . The nose  88  on one hook  82  helps to align the hook between  20  adjacent catches  66  and to hold hook  82  in position, restricting movement of hook  82  with respect to catches  66 . As illustrated in FIG. 9, the feet  76  of the rails  72  (by which the rails  72  are affixed to the circuit board  14 ) are located proximate the points of contact between the catches  66  and the hooks  82  to minimize bending in the circuit board  14 . The alignment slots  36  of the heat sink  10  align the spring clip  80  relative to the heat sink  10 . 
     The spring clip  80  is shown assembled to the heat sink  10  in FIG.  7 . As assembled, the central contact point  86  in each strut  84  of the spring clip  80  contacts the pedestal  26  of the heat sink  10 , applying a downward spring force to retain the heat sink  10  against the processor  50 . The force is disposed at the center of the package and, therefore, distributed evenly. The spring clip  80  may be designed to provide force on the heat sink  10  by deflection either in bending or in torsion; the preferred version, as illustrated, applies force by bending. Each of the struts  84  of the spring clip  80  fit between adjacent fins  24  of the heat sink  10  without any special modification to the heat sink  10  and the fin-pitch is uninterrupted by the presence of the spring clip  80 , which achieves minimal disruption of the air flow through the heat sink  10 . 
     B. Method of Use 
     Provided below is a step-by-step description of the procedure used to assemble a socket  30 , a processor  50 , a thermal pad  60 , a heat sink  10 , and a spring clip  80  of the present invention on a PC-assembly or circuit board  14 . The procedure applies equally to a number of different processors  50 . Preliminary steps include soldering to the circuit board  14  an appropriate socket  30  for the processor  50  and installing on the circuit board  14  appropriate retention rails  72  for the heat sink  10 . 
     Next, the thermal pad  60  is applied to form the interface between the heat sink  10  and the processor  50 . The thermal pad  60  should be placed on the lid of the processor  50 . The thermal pad  60  is centered on the processor  50  and then pressed down firmly. Care must be taken to ensure that the thermal pad  60  is smooth and free of voids or lumps. A protective sheet may remain or be placed on the top of the thermal pad  60  until the technician  100  is ready to put the heat sink  10  on the processor  50 . This protective sheet will minimize any contamination on the surface of the thermal pad  60 . 
     The technician  100  is now ready to install the spring dip  80  onto the heat sink  10 . The heat sink  10  is the same on both ends (i.e., the heat sink  10  is symmetrical). The two alignment slots  36  near the center of the pedestal  26  of the heat sink  10  on each end identify the correct fin-spaces into which the spring clip  80  is to be placed. The two upright portions of one U-shaped hook  82  of the spring clip  80  are placed in these two alignment slots  36  as shown in FIG.  12 . The technician  100  then rocks the spring clip  80  back into the spaces between the fins  24 ; slides the spring clip  80  back and up into the fin-spaces until the end of the spring dip  80  without the slit  90  slips over the corners of the fins  24 ; and holds the spring clip in the position shown in FIG. 13 in preparation for the next step. 
     The technician  100  next installs the heat sink  10  and one side of the spring clip  80 . Both ends of the pedestal  26  of the heat sink  10  have at least one alignment protrusion  38  that fits into a mating pocket  68  in the retention rail  72 . The two hooks  82  of the spring clip  80  differ in that one hook  82  is solid and the other hook  82  is split by the slit  90 . The split hook  82  should be installed first on its rail  72 , and it should go on the more inaccessible rail  72 . 
     As shown in FIG. 14, the technician  100  tips the end of the heat sink  10  down and secures the split hook  82  of the spring clip  80  under the catches  66  in the rail  72 . Keeping a light tension on the spring clip  80 , the technician  100  rocks the heat sink  10  and spring clip  80  down while rotating upward the lowest end of the heat sink  10 . Rotation continues, as shown in FIG. 15, until the two ends of the heat sink  10  sit in the pockets  68  of the retention rails  72  and the pedestal  26  of the heat sink  10  rests on the thermal pad  60  atop the processor  50 . 
     Installation is now ready to be completed. Successful installation is possible, with care, without using any tools. Alternatively, the technician  100  may use a standard tool such as a screwdriver  4  as shown in FIG.  16 . The technician  100  may find installation much easier and quicker, however, using the tool  92  shown in FIG.  19 . The tool  92  has a body  94 , adapted for easy manipulation by the technician  100 , and an arm  96  ending in a finger  98  sized to engage the spring clip  80 . The tool  92  reduces the likelihood, more prevalent when using either no tools at all or a screwdriver  4 , that the technician  100  will slip and damage a component. The tool  92  is conveniently stored in a position on the cover of the circuit board  14 . 
     Regardless of whether the technician  100  uses no tool, a screwdriver  4 , or the tool  92 , the solid hook  82  of the spring clip  80  is pushed down past the corresponding catches  66  in the rail  72 . Such action is illustrated in FIG.  17 . Then, without relaxing downward pressure, the solid hook  82  of the spring clip  80  is pushed under the catches  66 . Such action is illustrated in FIG.  18 . If a screwdriver  4  or tool  92  is used, this action can be accomplished by rotating the screwdriver  4  or tool  92  away from the heat sink  10 . Clearly, slippage of the screwdriver  4  off (and, therefore, disengagement from) the spring clip  80  is more likely than for the tool  92  as rotation occurs. Finally, the technician  100  relaxes the downward pressure allowing the solid hook  82  of the spring clip  80  to rise until the catches  66  stop the solid hook  82 . 
     Finally, the technician  100  should inspect the assembly for proper installation. The heat sink  10  should press evenly on the thermal pad  60  and, in turn, on the processor  50 . The alignment protrusions  38  on the ends of the heat sink  10  should float in the pockets  68  of the retention rails  72 . Upon confirmation of successful installation, the technician  100  may replace the tool  92  into its position on the cover of the circuit board  14  if the tool  92  was used. 
     The procedure to remove the heat sink  10 , typically to eliminate or service the underlying processor  50 , is simply the reverse of the assembly procedure described above. Once a hook  82  of the spring clip  80  is released from a corresponding catch  66 , the spring clip  80  automatically moves upward and away from the circuit board  14 . The same steps are required whether the technician  100  is removing the processor  50  to depopulate the circuit board  14  or to replace the is processor  50  with another processor  50 . The replacement may be to upgrade to a higher-performance processor  50  or to replace a presumed defective processor  50 . 
     Although illustrated and described above with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. For example, the order of the various steps of the method of using the structure of the present invention may be altered.