Abstract:
Provided are a heat sink and a memory module using the heat sink. In one embodiment, the heat sink includes a first and second guide pin respectively disposed in first and second heat spreaders placed around an object to be cooled. The first and second guide pins help prevent misalignment problems from occurring between the first and second heat spreaders, as well, as helping prevent the first and second heat spreaders from contacting each other when the first and second heat spreaders are pressed by pressure applied from the outside.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the benefit of Korean Patent Application No. 10-2006-0092453, filed on Sep. 22, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND 
   1. Field of the Invention 
   The present invention relates to a heat sink and a memory module using the heat sink, and more particularly, to a heat sink that can be applied to a semiconductor package, and a memory module using the heat sink. 
   2. Description of the Related Art 
   In general, the driving speed of a semiconductor package, for example, a ball array semiconductor package, is high resulting in a substantial amount of heat radiation. To maintain performance this heat generated in the semiconductor package must be dissipated. Also in general, a memory module in which a plurality of semiconductor packages (semiconductor chips) are mounted on a printed circuit board (PCB) is used to increase memory capacity. Thus, since the packages of the memory module generate a lot of heat, a heat sink is generally used to dissipate heat to the outside. 
   The heat sink includes a first heat spreader formed as a thin layer on an upper surface of the PCB on which the plurality of semiconductor packages are mounted, and a second heat spreader formed on a rear surface of the PCB on which the plurality of semiconductor packages are mounted. The first and second heat spreaders face and contact the plurality of semiconductor packages mounted on the PCB to transfer the generated heat to the outside. 
   However, in a conventional heat sink, when the first heat spreader formed on the surface of the PCB and the second heat spreader formed on the rear surface of the PCB are coupled, a misalignment is commonly generated between the first heat spreader and the second heat spreader making automation very difficult. 
   In addition, the first and second heat spreaders are pressed against each other in the conventional heat sink when pressure is applied from the outside. Thus the first or second heat spreader contacts a circuit element formed on the PCB, for example, a capacitor, thereby generating a short circuit. 
   SUMMARY 
   Embodiments of the present invention provide a heat sink that enables an automation process for coupling heat spreaders by preventing misalignment between heat spreaders. In addition, these embodiments prevent contact between the heat spreaders and a circuit element formed on a printed circuit board (PCB) can be prevented when pressure is applied from the outside. 
   Additional embodiments of the present invention provide a memory module using the heat sink described above. 
   According to an embodiment of the present invention, a heat sink includes a first heat spreader, a second heat spreader, a first guide pin, a second guide pin, and a coupling unit. The first heat spreader faces and contacts a first component disposed on a first surface of an object to be cooled and directs heat away from the first component. The second heat spreader is disposed on a second surface of the object to be cooled. The second heat spreader faces and contacts a second component to direct heat away from the second component. 
   The first guide pin is disposed in a first extension portion near both edges of the first heat spreader, inserted and fixed in an insertion hole corresponding to the first extension portion, and installed in the object to be cooled. The second guide pin faces the first guide pin and is disposed in a second extension portion near both edges of the second heat spreader. The second guide pin is inserted and fixed in the insertion hole corresponding to the second extension portion and is installed in the object to be cooled. The coupling unit closely adheres and couples the first and second heat spreaders to the object to be cooled. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which. 
       FIG. 1  is a dissected perspective view illustrating a heat sink according to an embodiment of the present invention; 
       FIG. 2  is a cross-sectional view illustrating the heat sink illustrated in  FIG. 1 , according to an embodiment of the present invention; 
       FIG. 3  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention; 
       FIG. 4  is a cross-sectional view of the heat sink illustrated in  FIG. 3 , according to an embodiment of the present invention; 
       FIG. 5  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention; 
       FIG. 6  is a cross-sectional view of the heat sink illustrated in  FIG. 5 , according to an embodiment of the present invention; 
       FIG. 7  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention; 
       FIG. 8  is a cross-sectional view of the heat sink illustrated in  FIG. 7 , according to an embodiment of the present invention; 
       FIG. 9  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention; 
       FIG. 10  is a cross-sectional view of the heat sink illustrated in  FIG. 9 , according to an embodiment of the present invention; 
       FIG. 11  is a plan view of a memory module employing a heat sink, according to an embodiment in the present invention; 
       FIGS. 12 and 13  are respectively a cross-sectional view and a perspective view of a memory module employing a heat sink, according to another embodiment of the present invention; and 
       FIGS. 14 and 15  are schematic views illustrating a method of combining guide pins to a heat spreader, according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention will now be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. 
   Heat Sink 
   Embodiment 1 
     FIG. 1  is a dissected perspective view illustrating a heat sink according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view of the heat sink illustrated in  FIG. 1 , according to an embodiment of the present invention. 
   Referring to  FIGS. 1 and 2 , the heat sink includes a first heat spreader  100 , a second heat spreader  300 , a third heat spreader  500  disposed on the first heat spreader  100 , a first guide pin  106  and a second guide pin  306  respectively installed on the first and second heat spreaders  100  and  300  and inserted into an object  200  to be cooled, and a coupling unit  502  closely adhering and coupling the first and second heat spreaders  100  and  300  to the object  200  to be cooled. 
   The first heat spreader  100  is a thin layer facing and contacting a first component  202  disposed on an upper surface of the object  200  to be cooled and directs away heat generated in the first component  202 . The second heat spreader  300  is a thin layer facing and contacting a second component  204  disposed on a rear surface of the object  200  to be cooled and directs away heat generated in the second component  204 . The third heat spreader  500  is a thin layer disposed above-centered to the object  200  to be cooled, facing and contacting a third component  206  and directs away heat generated in the third component  206 . 
   The first and second components  202  and  204  generate heat at a lower temperature than the third component  206 . Since the first and second heat spreaders  100  and  300  may have a lower heat generation efficiency than the third heat spreader  500 , the first and second heat spreaders  100  and  300  are formed of a material having a first heat transfer coefficient of about 238 W/mK, for example, aluminum. The third heat spreader  500  is formed of a material having a second heat transfer coefficient of about 397 W/mK, for example, copper. 
   In other words, the second heat transfer coefficient of the third heat spreader  500  is greater than the first heat transfer coefficient of the first and second heat spreaders  100  and  300 . In order to increase the surface area of heat dissipation, a plurality of grooves  508  are formed on the upper surface of the third heat spreader  500 . 
   The first and third heat spreaders  100  and  500  are coupled by a coupling unit  502  through a compression process or a welding method. In addition, in order for the intense heat in the first through third components  202 ,  204 , and  206  to be rapidly transferred to the first through third heat spreaders  100 ,  300 , and  500  respectively, thermal interface layers  108 ,  308 , and  504  may be respectively interposed between the first component  202  and the first heat spreader  100 , the second component  204  and the second heat spreader  300 , and the first heat spreader  100  and the third heat spreader  500 . For example, the first through third thermal interface layers  108 ,  308 , and  504  may be formed of a thermally conductive material such as copper. 
   The first guide pin  106  that is inserted and fixed in an insertion hole  208  of the object  200  to be cooled is installed in the first heat spreader  100 . The first guide pin  106  is installed in a first extension portion  104  extending from an inner portion  102  of the first heat spreader  100  near edges of both ends of the first heat spreader  100 . The second guide pin  306  is installed in the second heat spreader  300  and inserted and fixed in the insertion hole  208  of the object  200  to be cooled. The insertion hole  208  of the object  200  to be cooled may pass through the object  200  to be cooled or not. The second guide pin  306  is installed in a second extension portion  304  extending from an inner portion  302  near edges of both ends of the second heat spreader  300 . The cross-section of the first and second guide pins  106  and  306  may be as a cylinder, a V-shape, or a hexahedron depending on the manufacturing method of the first and second guide pins  106  and  306 . 
   The first and second extension portions  104  and  304  do not face and contact the first and second components  202  and  204  of the object  200  to be cooled, and are disposed in a corresponding position with the insertion hole  208  of the object  200  to be cooled. The first and second guide pins  106  and  306  may be pen pins that are respectively formed for the first heat spreader  100  and the second heat spreader  300  through a compression process. The compression process for manufacturing the first and second guide pins  106  and  306  will be described later in more detail. 
   The first guide pin  106  and the second guide pin  306  are inserted and fixed in the insertion hole  208  of the object  200  to be cooled. When the first and second guide pins  106  and  306  are inserted and fixed in the insertion hole  208  of the object  200  to be cooled, the first and second heat spreaders  100  and  300  are effectively prevented from contacting the object  200  to be cooled when the first and second heat spreaders  100  and  300  are pressed by pressure applied from the outside. 
   In particular, the first guide pin  106  and the second guide pin  306  may be separated a predetermined distance apart from each other in the insertion hole  208  of the object  200  to be cooled and be forcibly inserted. In other words, the first and second guide pins  106  and  306  may both be partially inserted into the insertion hole  208  of the object  200  to be cooled and be forcibly inserted. Thus, when the first and second heat spreaders  100  and  300  are pressed by external pressure, the first and second heat spreaders  100  and  300  can be prevented from contacting the object  200  to be cooled more efficiently. 
   The first and second guide pins  106  and  306  guide the first and second heat spreaders  100  and  300  when the first and second heat spreaders  100  and  300  are fixed and coupled to the object  200  to be cooled. Thus, the second heat spreader  300  having the second guide pin  306  corresponding to the insertion hole  208  is formed. Then, the object  200  to be cooled is mounted on the second heat spreader  300  such that the insertion hole  208  of the object  200  to be cooled is inserted and fixed to the second guide pin  306  of the second heat spreader  300 . Next, the first spreader  100  having the first guide pin  106  corresponding to the second guide pin  306  is safely mounted. The first heat spreader  100  is then fixed and coupled to the insertion hole  208  of the object  200  to be cooled. 
   Thus, by using the first guide pin  106  and the second guide pin  306  respectively of the first and second heat spreaders  100  and  300 , all the processes of fixing and coupling the first heat spreader  100  and the second heat spreader  300  to the object  200  to be cooled can be carried out by an automation process. 
   A coupling unit  600  that closely adheres and couples the first and second heat spreaders  100  and  300  to the object  200  to be cooled is installed on the heat sink according to the current embodiment of the present invention. The coupling unit  600  may be an elastic clip and is installed on a rear surface of the first and second heat spreaders  100  and  300 . The coupling unit  600  may also be securely coupled to a fixing portion  107  disposed on the first heat spreader  100 . Due to the coupling unit  600 , the formation of a space between the first through third components  202 ,  204 , and  206  and the object  200  to be cooled is prevented. 
   Embodiment 2 
     FIG. 3  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention.  FIG. 4  is a cross-sectional view of the heat sink illustrated in  FIG. 3 , according to an embodiment of the present invention. 
   In detail, the heat sink according to the current embodiment of the present invention is substantially the same as the heat sink of  FIG. 1  except that the third heat spreader  500  (shown in  FIG. 2 ) is not installed on the surface of the first heat spreader  100 . In  FIGS. 3 and 4 , the reference numerals identical to those of  FIGS. 1 and 2  refer to identical components, and descriptions of the identical components, for example, the connection relationship and the effects, will be omitted. 
   Referring to  FIGS. 3 and 4 , even though the third heat spreader  500  is not installed in a center portion  506  on the surface of the first heat spreader  100 , the heat sink of the current embodiment of the present invention can easily emit heat generated in first through third components  202 ,  204 ,  206  to the outside even with the absence of the third heat spreader  500 . In  FIGS. 3 and 4 , a plurality of grooves  508  are formed on the upper surfaces of the first heat spreader  100 . 
   As such, the manufacturing process for the third heat spreader  500  can be omitted in the current embodiment of the present invention. A coupling unit  600 , e.g., an elastic clip, may again be used to closely adhere and couple the first and second heat spreaders  100  and  300  to the first through third components  202 ,  204 , and  206 . 
   Embodiment 3 
     FIG. 5  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention.  FIG. 6  is a cross-sectional view of the heat sink illustrated in  FIG. 5 , according to an embodiment of the present invention. 
   In detail, the heat sink according to the current embodiment of the present invention is substantially identical to the heat sink of  FIG. 1  except that first and second guide pins  106   a  and  306   a  of the current embodiment have a different shape than the first and second guide pins  106  and  306  of the heat sink of  FIG. 1 . In  FIGS. 5 and 6 , the reference numerals identical to those of  FIGS. 1 and 2  refer to identical components, and descriptions of the identical components, for example, the connection relationship and the effects, will be omitted. In addition, a third heat spreader  500  is included in  FIGS. 5 and 6  but may not be included according to necessity. 
   Referring to  FIGS. 5 and 6 , first and second guide pins  106   a  and  306   a  according to the current embodiment of the present invention are respectively formed integrally with the first and second heat spreaders  100  and  300  of the heat sink of  FIG. 1  and are bent shaped pins. 
   The first and second guide pins  106   a  and  306   a  according to the current embodiment of the present invention do not require a special manufacturing process and can be manufactured using a mold or a metal processing during the manufacture of the first and second heat spreaders  100  and  300  of the heat sink of  FIG. 1 . Accordingly, the heat sink according to the current embodiment of the present invention can be manufactured in a simple process. 
   Embodiment 4 
     FIG. 7  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention.  FIG. 8  is a cross-sectional view of the heat sink illustrated in  FIG. 7 , according to an embodiment of the present invention. 
   In detail, the heat sink according to the current embodiment of the present invention is substantially identical to the heat sink of  FIG. 1  except that first and second guide pins  106   b  and  306   b  of the current embodiment have a different shape than the first and second guide pins  106  and  306  of the heat sink of  FIG. 1 . In  FIGS. 7 and 8 , the reference numerals identical to those of  FIGS. 1 and 2  refer to identical components, and descriptions of the identical components, for example, the connection relationship and the effects, will be omitted. In addition, a third heat spreader  500  is included in  FIGS. 7 and 8  but may not be included according to necessity. 
   Referring to  FIGS. 7 and 8 , the first and second guide pins  106   b  and  306   b  according to the current embodiment of the present invention are respectively formed integrally with the first and second heat spreaders  100  and  300  and are bent shaped pins. In addition, first and second guide pin supporting portions  110  and  310  that respectively support first and second guide pins  106   b  and  306   b  are included in the current embodiment of the present invention. When the first and second guide pin supporting portions  110  and  310  are included, the first and second guide pins  106   b  and  306   b  can be stably formed. Thus, even when first and second heat spreaders  100  and  300  are compressed by large external pressures, the first and second guide pins  106   b  and  306   b  may provide more support than the guide pins of the above described embodiments. 
   The first and second guide pins  106   b  and  306   b  and the first and second guide pin supporting portions  110  and  310  according to the current embodiment of the present invention do not require a special manufacturing process and can be manufactured using a mold or a metal processing during the manufacture of the first and second heat spreaders  100  and  300  of the heat sink of  FIG. 1 . Accordingly, the heat sink according to the current embodiment of the present invention can be manufactured in a simple process. 
   Embodiment 5 
     FIG. 9  is a dissected perspective view illustrating a heat sink according to another embodiment of the present invention.  FIG. 10  is a cross-sectional view of the heat sink illustrated in  FIG. 9 , according to an embodiment of the present invention. 
   In detail, the heat sink according to the current embodiment of the present invention is substantially identical to the heat sink of  FIG. 1  except that first and second supporting bars  114  and  314  supporting first and second heat spreaders  100  and  300  are installed. In  FIGS. 9 and 10 , the reference numerals identical to those of  FIGS. 1 and 2  refer to identical components, and descriptions of the identical components, for example, the connection relationship and the effects, will be omitted. In addition, a third heat spreader  500  is included in  FIGS. 9 and 10  but may not be included according to necessity. 
   Referring to  FIGS. 9 and 10 , the first and second supporting bars  114  and  314  supporting the first and second heat spreaders  100  and  300  may face and contact each other. The first and second supporting bars  114  and  314  may be installed on a rear surface or at a side surface of the first and second heat spreaders  100  and  300 . The first and second supporting bars  114  and  314  may be formed to contact the surface of the object  200  to be cooled, or may be separated from the object  200  to be cooled by a predetermined distance of about 0.1 to about 0.3 mm. The first and second supporting bars  114  and  314  and the first and second heat spreaders  100  and  300  may be installed to have a diverse size and shape according to the design of the first and second heat spreaders  100  and  300 . Thus, when the first and second supporting bars  114  and  314  supporting the first and second heat spreaders  100  and  300  are installed, the first and second heat spreaders  100  and  300  can be prevented from contacting the object  200  to be cooled even when the first and second heat spreaders  100  and  300  are pressed by external pressure. 
   The first and second supporting bars  114  and  314  do not require a special manufacturing process and can be manufactured using a mold or a metal processing as the manufacturing of the first and second heat spreaders  100  and  300  of the heat sink of  FIG. 1 . Accordingly, the heat sink according to the current embodiment of the present invention can be manufactured in a simple process. 
   As described above, the heat sink may have various configurations according to various embodiments of the present invention. In addition, the components of the heat sink according to the various embodiments of the present invention can also be combined. 
   Hereinafter, a memory module using the heat sink according to embodiments of the present invention will be described. The printed circuit board (PCB) forming the memory module may correspond to the object to be cooled of the heat sink. Semiconductor packages forming the memory module may correspond to the first through third components disposed on the upper surface or the rear surface of the object that is to be cooled. Hereinafter, a memory module in which the heat sink of  FIG. 1  is described. However, the heat sink according to the other embodiments or a combination thereof may also be used by the memory module. 
   Memory Module 
   Embodiment 6 
     FIG. 11  is a plan view of a memory module  400  employing a heat sink, according to an embodiment of the present invention, and  FIGS. 12 and 13  are a cross-sectional view and a perspective view of a memory module employing a heat sink according to another embodiment of the present invention. 
   A heat sink is formed on an upper surface and a rear surface of the bare memory module  400 . The bare memory module  400  includes a plurality of first and second semiconductor packages  404  and  406  (not shown in  FIGS. 11 and 13 ) attached to a PCB  402 , an advanced memory buffer (AMB)  408 , a circuit element  410 , for example, a capacitor, and a contact pad  412  contacting a mother board (not shown). 
   The bare memory module  400  can be classified as a single in-lined memory module (SIMM) in which semiconductor packages  404  are attached on only one surface of the PCB  402 , a dual in-lined memory module (DIMM) in which semiconductor packages  404  and  406  are attached on both sides of the PCB  402 , and a fully buffered dual in-lined memory module (FBDIMM) in which AMB  408  is further attached in the center portion of the surface of the PCB  402 . 
     FIGS. 11 through 13  illustrate the FBFIMM as the bare memory module  400 . In  FIGS. 11 through 13 , the number of semiconductor packages attached on the PCB  402  can vary according to the design or the capacity of the memory. In the bare memory module  400 , signals from the outside pass through the AMB  408  and are transmitted to the first and second semiconductor packages  404  and  406  in order to increase the transmission efficiency of the bare memory module  400 . Thus, a large load is concentrated on the AMB  408 , and more intense heat is generated in the AMB  408  than in other first and second semiconductor packages  404  or  406 . 
   In particular, a lot more semiconductor packages can be mounted in the FBDIMM bare memory module  400  to increase the memory capacity and to increase the transmission efficiency of the FBDIMM bare memory module  400 . Thus, a non-circuit region is present only near both edges of the PCB  402  where an insertion hole  208  can be formed. The insertion hole  208  may have a diameter of about 1.5 mm. The insertion hole  208  may or may not pass through the object  200  to be cooled. As described with reference to the heat sink of  FIG. 1 , the first and second guide pins  106  and  306  may be formed in the extension portions  104  and  304  (as shown in  FIGS. 1 and 2 ) near both edges of the first and second heat spreaders  100  and  300 . Also, since intense heat may be generated in the AMB  408 , a third heat spreader  500  may be needed to emit heat more easily. 
   Referring to  FIGS. 11 and 12 , the first semiconductor packages  404  are mounted on the upper surface of the PCB  402 . The first semiconductor packages  404  correspond to the first components  202  of the heat sink of  FIG. 1 . The second semiconductor packages  406  are mounted on a rear surface of the PCB  402 . The second semiconductor packages  406  correspond to the second components  204  of the heat sink of  FIG. 1 . The AMB  408  is mounted in the center portion of the surface of the PCB  402 . The AMB  408  corresponds to the third component  206  of the heat sink of  FIG. 1 . 
   The first and second semiconductor packages  404  and  406  may include a semiconductor chip, a mold surrounding the semiconductor chip, and solder balls arranged on a rear surface of the mold that are electrically connected to the semiconductor chip. The mold passes the thermal interface layers  108  and  308  to face and contact the first and second heat spreaders  100  and  300 . The first and second semiconductor packages  404  and  406  may be a ball grid array (BGA) package, a chip scale package (CSP), a wafer level package (WLP), etc. 
   The first heat spreader  100  faces and contacts the first semiconductor packages  404  and emits heat from the first semiconductor packages  404 . The second heat spreader  300  faces and contacts the second semiconductor packages  406  and emits heat from the second semiconductor packages  406 . The first guide pin  106  that is inserted in the insertion hole  208  formed on the PCB  402  is fixed in the first extension portion  104  near both edges of the first heat spreader  100 . 
   Facing the first guide pin  106 , the second guide pin  306  that is inserted in the insertion hole  208  is fixed in a second extension portion  304  near both edges of the second heat spreader  300 . The first and second extension portions  104  and  304  may not respectively face and contact the first and second semiconductor packages  404  and  406 , but may still correspond to the insertion hole  208  of the PCB  402 . 
   The first and second guide pins  106  and  306  may be separated by a predetermined distance from each other in the insertion hole  208  of the PCB  402 . The first and second guide pins  106  and  306  may be forcibly inserted and fixed in the insertion hole  208  of the PCB  402 . Heat in the AMB  408  is dissipated through the third heat spreader  500  attached to the first heat spreader  100  on the AMB  408 . The first heat spreader  100  and the second heat spreader  300  are closely adhered and coupled to the PCB  402  by a coupling unit  600 , which may be an elastic clip. 
   Method of Manufacturing Guide Pins 
     FIGS. 14 and 15  are schematic views illustrating a method of combining guide pins to a heat spreader, according to an embodiment of the present invention. 
   Referring to  FIG. 14 , the guide pins  106  or  306 , such as pen pins having a diameter of about 1.2 mm, are provided. Then holes  116  or  316  are formed in the heat spreader  100  or  300 . The guide pins  106  or  306  are inserted into the holes  116  or  316  of the first or second heat spreaders  100  or  300 . The guide pins  106  or  306  that are inserted in the holes  116  or  316  of the first and second heat spreaders  100  and  300  are loaded in a compression processing apparatus having a punch  602  and a die  604 . 
   Referring to  FIG. 15 , an upper portion of the guide pins  106  or  306  that is inserted in the holes  116  or  316  of the heat spreaders  100  or  300  is processed using the compression processing apparatus. Thus the guide pins  106  or  306  are inserted and fixed in the holes  116  or  316  of the heat spreaders  100  or  300 . 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 
   As described above, a heat sink according to the present invention includes guide pins inserted and fixed in insertion holes which are formed in extension portions near both edges of first and second heat spreaders and installed in an object to be cooled. Thus when the first heat spreader and the second heat spreader are coupled, a misalignment between the first heat spreader and the second heat spreader does not occur, and an automation process is possible. 
   The heat sink according to the present invention is inserted and fixed in the insertion hole of the object to be cooled, and thus the first and second heat spreaders can be prevented from contacting each other when the first and second heat spreaders are pressed by pressure applied from the outside. 
   The heat sink according to the present invention may also include a third heat spreader that is attached on the first heat spreader and has an excellent heat transfer coefficient to efficiently emit heat regardless of the amount of heat generated in the object to be cooled. 
   When the heat sink according to the present invention is employed in a memory module, a misalignment between the first and second heat spreaders is prevented when the first and second heat spreaders that are disposed on an upper surface and a rear surface of a PCB are coupled, and as such, an automation process is possible. 
   When the heat sink according to the present invention is employed, the first heat spreader or the second heat spreader can be prevented from contacting a circuit element formed on the PCB, for example, a capacitor, when the first and second heat spreaders are pressed by pressure applied from the outside.