BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a heat sink assembly providing highly efficient heat dissipation at low cost, and with good mechanical strength. 
   2. Description of the Related Art 
   Unlike normal dual inline memory modules (DIMMs) which are connected in parallel to a memory controller, fully buffered dual inline memory modules (FBDIMMs) are connected in a point-to-point serial architecture.  FIG. 1A  depicts the front surface of an FBDIMM, and  FIG. 1B  depicts the back surface of the FBDIMM. An FBDIMM  10  is characterized by an advanced memory buffer (AMB) chip  110  on its front surface. The AMB chip  110  collects and distributes the data from or to the memory chips (i.e. dynamic random access memories, DRAMs)  120  on the FBDIMM  10 , buffers and forwards the data to the next FBDIMM or memory controller. 
   During operation, the AMB chip  110  generates a large quantity of heat. To prevent the AMB chip  110  from failing due to high temperature, a heat sink (not shown) is fastened on the AMB chip  110  via a metallic spring (not shown), absorbing heat from the AMB chip  110  by thermal conduction and then dissipating the heat. 
   The conventional heat sink presents the following drawbacks. The heat sink is slightly larger than the AMB chip  110  in area, thus, heat-dissipation efficiency is poor. Moreover, the heat sink is made of copper which is expensive. Furthermore, the heat sink cannot enhance the mechanical strength of the FBDIMM  10  to meet requirement in the three-point-bending test. 
   BRIEF SUMMARY OF THE INVENTION 
   A heat sink assembly for dissipating heat from a fully buffered dual inline memory module (FBDIMM) is provided. The heat sink assembly includes a first heat-dissipating sheet, a second heat-dissipating sheet and at least one clip. The FBDIMM is sandwiched in between the first heat-dissipating sheet and the second heat-dissipating sheet by the clip fix the heat sink assembly. 
   The first and second heat-dissipating sheets cover the FBDIMM. It is therefore understood that the first heat-dissipating sheet and the second heat-dissipating sheet of the invention are much larger than the conventional heat sink. Thus, the first heat-dissipating sheet and the second heat-dissipating sheet provide excellent heat dissipation and can be made of inexpensive metal (e.g. aluminum). 
   Furthermore, a plurality of embossed strips are formed on the first and second heat-dissipating sheets, and extend in different directions. One of the embossed strips longitudinally extends along a lengthwise direction of the second heat-dissipating sheet, providing the heat sink assembly for sufficient mechanical strength to pass the three-point-bending test. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
       FIG. 1A  depicts the front surface of an FBDIMM; 
       FIG. 1B  depicts the back surface of the FBDIMM; 
       FIG. 2  is an exploded diagram of a heat sink assembly in accordance with the invention; 
       FIG. 3  is a schematic diagram of the first heat-dissipating sheet of  FIG. 2 , observed in direction A; 
       FIG. 4  is a schematic diagram of the second heat-dissipating sheet of  FIG. 2 , observed in direction B; 
       FIG. 5A  is a front view of the clip of the heat sink assembly in accordance with the invention; and 
       FIG. 5B  is a side view of the clip of the heat sink assembly in accordance with the invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
   Referring to  FIG. 2 , a heat sink assembly of an embodiment of the invention includes a first heat-dissipating sheet  30 , a second heat-dissipating sheet  20 , and a plurality of clips  40 . The above-mentioned FBDIMM  10  is sandwiched between the first heat-dissipating sheet  30  and the second heat-dissipating sheet  20 , and fixed by the clips  40  (hereafter the entire assembly is referred to “the assembly”). It is noted that the first heat-dissipating sheet  30  and the second heat-dissipating sheet  20  of this embodiment cover the FBDIMM  10 . It is therefore understood that the first heat-dissipating sheet  30  and the second heat-dissipating sheet  20  of the invention are much larger than the conventional heat sink. Thus, the first heat-dissipating sheet  30  and the second heat-dissipating sheet  20  provide excellent heat dissipation and can be made of inexpensive metal (e.g. aluminum). 
   In the assembly, the front surface of the FBDIMM  10  ( FIG. 1A ) faces the first heat-dissipating sheet  30 . The first heat-dissipating sheet  30  attaches to the AMB chip  110 , allowing heat transmitting from the AMB chip  110  to the first heat-dissipating sheet  30 . Furthermore, the first heat-dissipating sheet  30  is spaced apart from all the memory chips  120  on the front surface of the FBDIMM  10 , preventing heat transmission from the AMB chip  110  through the first heat-dissipating sheet  30  to the memory chips  120 . The back surface of the FBDIMM  10  ( FIG. 1B ) faces the second heat-dissipating sheet  20 , and all the memory chips  120 ′ on the back surface of the FBDIMM  10  attaches to the second heat-dissipating sheet  20 . The purpose of attaching is for heat transmission that can be a directly contact or a non-directly contact wherein the difference between the directly contact and the non-directly contact rest with heat transmission medium, such as thermal adhesive, thermal grease or the combination thereof, whether need by or not. 
   Structurally, each of the first and second heat-dissipating sheets  30  and  20  is substantially rectangular and has two long edges (top and bottom edges) and two short edges. Flanges  320  and  220  are formed on the bottom edge of the first and second heat-dissipating sheets  30  and  20 . In the assembly, the flanges  320  and  220  shield passive electrical components  140  and  140 ′ to avoid damage during assembly process, wherein the passive electrical components  140  and  140 ′ include capacitors, inductors, resistors, or combinations thereof (e.g. “0805 capacitors and inductors”). Furthermore, the passive electrical components  140  and  140 ′ are located above the golden fingers  130  and  130 ′ and arranged in lines on the front and back surfaces of the FBDIMM  10 . 
   Bent portions  350  and  230  are formed on the short edges of the first and second heat-dissipating sheets  30  and  20  to hold FBDIMM  10 , and are against the front surface and the back surface near the edges of the FBDIMM  10  respectively. When an external force is exerted on the first and second heat-dissipating sheets  30  and  20 , not only the AMB chip  110  but also the FBDIMM  10  sustain the external force. Thus, the possibility of damage to the AMB chip  110  can be significantly reduced. 
   An opening  360  is provided on the bent portion  350  of the first heat-dissipating sheet  30 , and a protrusion  240  is correspondingly provided on the bent portion  230  of the second heat-dissipating sheet  20 . In the assembly, the protrusion  240  passes through a notch  150  on the side edge of the FBDIMM  10  into the opening  360 . This kind of structure may promote assembly efficiency and accuracy, and prevent relative motion between the first and second heat-dissipating sheets  30  and  20 . 
   It is understood that the locations of the protrusion  240  and the opening  360  can be exchanged. That is, the protrusion is provided on the bent portion  350  of the first heat-dissipating sheet  30 , and the opening is correspondingly provided on the bent portion  230  of the second heat-dissipating sheet  20 . Such an arrangement has the same function. 
   Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram of the first heat-dissipating sheet of  FIG. 2 , observed in direction A, wherein the first heat-dissipating sheet  30  has an embossed portion  330  of a predetermined height. In the assembly, the embossed portion  330  covers the AMB chip  110 , and the back surface  330 ′ of the embossed portion  330  attaches to the AMB chip  110 . A plurality of heat-dissipating holes  340  is provided on the edges of the embossed portion  330  to enhance the heat-dissipating efficiency of the AMB chip  110 . 
   Please refer to  FIGS. 3 and 4 , wherein  FIG. 4  is a schematic diagram of the second heat-dissipating sheet of  FIG. 2 , observed in direction B. A plurality of indentations  310  and  210  are formed on the top edge of the first and second heat-dissipating sheets  30  and  20 . Holes  370  and  270  are provided under the indentations  310  and  210 . Also referring to  FIGS. 5A and 5B , the clip  40  has a first leg  430 , a second leg  430 ′, and a connecting portion  440  connecting the first and second legs  430  and  430 ′. The connecting portion  440  includes a first end  441  and a second end  441 ′, wherein the first leg  430  extends from the first end  441  of the connecting portion  440 , and the second leg  430 ′ extends from the second end  441 ′ of the connecting portion  440 . Salient points  420  and  420 ′ are formed on the inner surfaces of the first and second legs  420  and  420 ′. In the assembly, the connecting portion  440  of the clip  40  is disposed in the indentations  310  and  210  of the first and second heat-dissipating sheets  30  and  20 . The salient points  420  and  420 ′ of the clip  40  are respectively disposed in the holes  370  and  270  of the first and second heat-dissipating sheets  30  and  20 . By such an arrangement, separation of the clips from the assembly is difficult. 
   Furthermore, in the assembly, the first and second legs  430  and  430 ′ of the clip  40  hold against the first and second heat-dissipating sheets  30  and  20 , respectively. The free end  410  of the first leg  430  is bended, facilitating removal of the clip  40  from the first and second heat-dissipating sheets  30  and  20 . It is noted that the free end  410  of the first leg  430  is not higher than the height of embossed portion  330  of the first heat-dissipating sheet  30 , while the clip  40  holds the first and second heat-dissipating sheets  30  and  20 . 
   As shown in  FIGS. 3 and 4 , a plurality of embossed strips  380 ,  250 , and  260  are formed on the first and second heat-dissipating sheets  30  and  20 , and extend in different directions to enhance mechanical strength of the heat sink assembly in different directions. It is noted that the embossed strip  250  longitudinally extends along a lengthwise direction of the second heat-dissipating sheet  20 , providing the heat sink assembly for sufficient mechanical strength to pass the three-point-bending test. 
   While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
A heat sink assembly for dissipating heat from a fully buffered dual inline memory module includes a first heat-dissipating sheet, a second heat-dissipating sheet and at least one clip. The first heat-dissipating sheet covers the fully buffered dual inline memory module. The clip holds the first heat-dissipating sheet and the second heat-dissipating sheet between which the fully buffered dual inline memory module is sandwiched.