Abstract:
An apparatus and system for a heat sink assembly, and a procedure for forming a heat sink assembly. The heat sink assembly includes a heat sink having a base and fins extending from the base, and a spring clip disposed on the heat sink between the fins. The spring clip includes a first tab that forms a first angle with respect to the base of the heat sink and including a second tab that forms a second angle with respect to the base of the heat sink. The first and second tabs are attached to the circuit board. By virtue thereof, a heat sink attachment to cage is provided that is space-efficient and permits a higher density of cages on a circuit board than do conventional arrangements.

Description:
FIELD OF THE INVENTION 
     Example embodiments described herein relate generally fixation of heat sinks to circuit boards and, more specifically, fixation of a heat sink to a SFP/XFP cage mounted on a circuit board. 
     DESCRIPTION OF RELATED ART 
     The small form-factor pluggable (SFP) is a standard for compact, hot-pluggable transceivers used for both telecommunication and data communications applications. The ten gigabit small form-factor pluggable (XFP) is a standard for transceivers for high-speed computer network and telecommunication links that use optical fiber. SFP and XFP transceivers are typically inserted into circuit board-mounted receptacles, termed “cages” to retain the SFP and XFP transceivers for connection to components on a circuit board. A transceiver typically generates heat when it is powered and retained in a cage. The SFP and XFP cages are typically constructed of metal and are typically designed to be bezel-mounted to a circuit board, (e.g., an I/O panel) with compliant pins for pressing onto the circuit board. 
     Heat sinks are typically used to dissipate heat generated by a transceiver retained in a cage. For each transceiver, the heat generated is transmitted through a corresponding cage and a heat sink in contact with the metal cage. Typically, the heat sink is retained in contact with the cage using a spring clip that presses the heat sink in contact with the cage. 
     An example of a typical arrangement of a heat sink attached to a cage is shown in  FIG. 1 , which is an isometric view showing an upper part and a side of a circuit board  104 . In  FIG. 1 , a plurality of cages  102  are spaced from each other across the front of the circuit board  104 . Gaps  106  between adjacent cages  102  provide space for spring clips  108  to mount to the sides of the cages  102 . Specifically, along the top edges  110  of the cages  102  are a plurality of holes that receive the spring clips  108  that are each bent to apply a compressive force to press a respective heat sink  112  into contact with a corresponding upper surface  114  of one of the cages  102 . 
     The arrangement shown in  FIG. 1  however requires that each spring clip  108  and/or heat sink  112  extend into the gap  106  between adjacent cages  102 . In order to maximize the density of cages  102  on the board  104 , the dimensions of the gap  106  would have to be made smaller. However, if the gap  106  is made too small, there will not be sufficient space available to dispose the spring clips  108  in the gap  106 . 
     SUMMARY 
     The above and other limitations are overcome by an apparatus and a system for a heat sink assembly, and by a procedure for forming a heat sink assembly. 
     In accordance with one example embodiment herein, the heat sink assembly includes a heat sink having a base and fins extending from the base, and a spring clip disposed on the heat sink between the fins. The spring clip includes a first tab that forms a first angle with respect to the base of the heat sink and includes a second tab that forms a second angle with respect to the base of the heat sink. 
     In accordance with another example embodiment herein, the system includes a circuit board having one or more cages mounted thereto, where each cage has an upper surface formed with an opening therethrough, and a heat sink assembly mountable on at least a respective one of the cages. The heat sink assembly includes a heat sink having a base and fins extending from the base, and a spring clip disposed on the heat sink between the fins. The spring clip includes a first tab that forms a first angle with respect to the base of the heat sink and includes a second tab that forms a second angle with respect to the base of the heat sink. 
     In accordance with another example embodiment herein, the procedure includes placing the heat sink assembly on a cage of a circuit board and securing the first and second tabs to the circuit board. 
     The example embodiments described herein provide for a heat sink attachment to cage such as a transceiver cage (e.g., an SFP/XFP cage) that is space-efficient so that extra spaces need not be provided on a circuit board between adjacent cages for attachment of a heat sink to the cages. Accordingly, the example embodiments described herein permit a higher density of cages on a circuit board than do conventional arrangements. 
     Additional features and benefits of the exemplary embodiments will become apparent from the detailed description, figures and claims set forth below. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The teachings claimed and/or described herein are further described in terms of exemplary embodiments. These exemplary embodiments are described in detail with reference to the drawings. These embodiments are non-limiting exemplary embodiments, wherein: 
         FIG. 1  shows an isometric view showing an upper part and a side of a circuit board. 
         FIG. 2  shows an isometric view showing an upper part and side of a circuit board arranged in accordance with an example aspect of the present application. 
         FIG. 3A  shows an isometric view showing an upper part and a side of a heat sink assembly constructed in accordance with an example aspect of the present application. 
         FIG. 3B  shows an exploded view of a portion of the heat sink assembly shown in  FIG. 3A . 
         FIG. 3C  shows an exploded view of another portion of the heat sink assembly shown in  FIG. 3A . 
         FIG. 3D  shows a section view of the heat sink assembly, taken along section  FIG. 3D - FIG. 3D  shown in  FIG. 3A . 
         FIG. 4  is an assembly drawing showing a portion of a circuit board constructed in accordance with an example aspect herein, and the heat sink assembly shown in  FIG. 3A . 
         FIG. 5  shows a section view of the circuit hoard and heat sink assembly, taken along section  FIG. 5 - FIG. 5  shown in  FIG. 4 . 
         FIG. 6  is an assembly drawing of another heat sink arrangement in accordance with an example aspect herein. 
     
    
    
     DETAILED DESCRIPTION 
     Those of ordinary skill in the art will realize in view of this description that the following detailed description of the exemplary embodiments is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the exemplary embodiments as illustrated in the accompanying drawings. The same reference numbers will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
       FIG. 2  shows a circuit board  200  having a plurality of SFP cages  202  and XFP cages  204  arranged along a front edge  206  of the circuit board  200 . In the specific example illustrated, the circuit board  200  has ten SFP cages  202  and two XFP cages  204 . Each of the cages  202 ,  204  is open along the front edge  206  of the circuit board  200  in order to receive a module  500  ( FIG. 5 ). Each of the cages  202 ,  204  extends diagonally with respect to the front edge  206  toward a rear edge  208  of the circuit board  200 . While the cages  202 ,  204  are shown extending diagonally, in other embodiments the cages  202 ,  204  can extend at other angles such as perpendicular with the front edge  206  of the circuit board  200 , or at other orientations. Each of the cages  202 ,  204  has an upper surface  210 , which is constructed to contact a heat sink  300  ( FIG. 3A ), to be discussed below. The upper surface  210  has at least one opening  212 . In the embodiment shown in  FIG. 2 , the cages  202 ,  204  include one rectangular opening  212 , which is constructed to align with and receive a portion of the heat sink  300 . The cages  202 ,  204  shown in  FIG. 2  are arranged so that there is substantially no (or minimal) gap between adjacent cages  202 ,  204 . 
       FIG. 3A  shows a view of an upper side of a heat sink assembly  302  that includes heat sink  300  and a spring clip  304 . The heat sink  300  includes a base  306  and a plurality of fins  308  extending upwardly in  FIG. 3A  from the base  306 . As would be appreciated by those of skill in the art in view hereof, the fins  308  are arranged to conduct heat away from the base  306  and dissipate heat by convection. 
     The spring clip  304  has a central serpentine portion  310 , a first tab  312  extending from the serpentine portion  310 , and a second tab  314  extending from the serpentine portion  310 . The spring clip  304  is fixed to the heat sink  300  between some of the fins  308  by snap fit connection. As shown in  FIGS. 3B and 3C , at two locations on the heat sink  300 , opposite ends of the serpentine portion  310  are respectively snap fit between adjacent fins  308  of the heat sink  300 . 
     As shown in  FIG. 3D , the serpentine portion  310  of the spring clip  304  extends in a plane substantially parallel to the upper surface of the base  306  of the heat sink  300 . In an uncompressed state shown in  FIG. 3D , the first tab  312  extends at a first angle θ 1  with respect to the upper surface of the base  306 . The first tab  312  extends from the serpentine portion  310  to a first free end  316 . Also, in an initial, uncompressed state shown in  FIG. 3D , the second tab  314  extends at a second angle θ 2  with respect to the upper surface of the base  306 . The second tab  314  extends from the serpentine portion  310  to a second free end  318  which is formed as a u-shaped hook ( FIG. 3A ). 
     Also, as shown in  FIG. 3D , a lower side  320  of the base  306  has a raised section  322  surrounded by a rectangular bezel (not shown). A front edge  328  and a rear edge  330  of the raised section  322  are beveled. 
     The heat sink  300  is generally formed from a metal, such as aluminum. The spring clip  304  is generally formed from a metal, such as steel, and is resilient so that the first and second tabs  312  and  314  can be compressed downward toward the base  306  of heat sink  300  without any permanent deformation of the spring clip  304 . The arrangement of the spring clip  304  facilitates uniformly transmitting the spring force to the heat sink  300  so that suitable contact pressure is applied between the heat sink  300  and a respective cage  202 ,  204  when a module  500  ( FIG. 5 ) is not inserted in the cage  202 ,  204  and between the heat sink  300  and the module  500  when the module  500  is inserted in the cage. 
     Circuit board  200  is shown in  FIG. 4  with a front retaining member  402  that extends across the front edge  206  of circuit board  200 . Above (and offset from) each cage  202 ,  204  a corresponding hole  404  is formed in the retaining member  402  of circuit board  200 . Each hole  404  in the retaining member  402  is constructed to receive and retain the first free end  316  of the first tab  312  of the spring clip  304 . Rearward of each cage  202 ,  204  is a corresponding anchor  406  that is soldered on the circuit board  200 . In the example embodiment shown in  FIG. 4 , each anchor  406  extends upwardly from the circuit board  200  and is a u-shaped latch to latch onto the second free end  318  of the second tab  314 . Thus, in the example embodiment shown in  FIG. 4 , for each cage  202 ,  204  there is at least one corresponding hole  404  in the front retaining member  402  and at least one corresponding anchor  406  in the board  200 . 
     The heat sink assembly  302  is assembled onto the board  200  as follows, in one example embodiment. The heat sink assembly  302  is oriented over a corresponding one of the cages  202 ,  204  so that the first tab  316  extends toward the front edge  206  of the board  200  and the second tab  314  extends toward the rear edge  208  of the board  200 . The first end  316  of the first tab  312  is inserted into a hole  404  in the front retaining member  402  and the raised portion  322  of the heat sink  300  is inserted into the rectangular opening  212  in the cage  202 ,  204  corresponding to the hole  404  in which the first end  316  was inserted. The second tab  314  is compressed toward anchor  406  corresponding to the cage  202 / 204  until the second free end  318  latches onto the anchor  406 . 
     As shown in  FIG. 5 , the cages  202 ,  204  are constructed to receive a module  500 , which includes electrical and optical modules. When the heat sink assembly  302  is attached to the circuit board  200  and no module  500  is present in a corresponding one of cages  202 ,  204 , the spring clip  304  of the heat sink assembly  302  is compressed an initial amount so as to force the bezel of heat sink  300  downwardly to contact the surface  210  of cage  202 ,  204  in a seated position. When the heat sink  300  is seated, the raised section  322  of heat sink  300  extends through a respective opening  212  in the corresponding cage  202 ,  204 . Thus, when the module  500  is not present in the cage, the raised section  322  extends slightly into cage  202 ,  204 . 
     When the module  500  is first introduced into a respective cage  202 ,  204  (as shown in  FIG. 5 ), there will be interference between the module  500  and the raised section  322  extending into the respective cage  202 ,  204 . Owing to the beveled front edge  328  of the raised section  322 , which acts as a guide surface, when module  500  is first inserted into the respective cage  202 ,  204  on which heat sink  300  is seated, module  500  contacts the front edge  328  and displaces the raised section  322  upwardly. As raised section  322  is displaced upwardly, the spring clip  304  is further compressed beyond its initial compression before module  500  was inserted in the cage  202 ,  204 . The spring force exerted by the spring clip  304  urges the raised section  322  to contact the module  500  with suitable pressure to promote conductive heat transfer from the module  500  to the heat sink  300 . 
     The dimensions and positions of the first tab  312  and second tab  314  are such that the torque (Mo(Fa)) exerted on the spring clip  304  by the first tab  312  about point “o” is almost equal and opposite to the torque (Mo(Fb)) exerted on the spring clip  304  by the second tab  314  about point “o”, when the first end  316  is in hole  404  and the second end  318  is latched to anchor  406 . The substantially equal and opposite torques Mo(Fa) and Mo(Fb) permit suitable and even pressure to be applied between raised portion  322  of heat sink  300  and module  500  to enable heat transfer from module  500  to heat sink  300 , which is then convected to air through fins  308 . 
     The beveled front edge  328  and rear edge  330  shown in  FIG. 3D  facilitate placement of the heat sink  300  on a respective one of the cages  202 ,  204  and facilitate self-seating of the heat sink  300  should the heat sink assembly  302  be displaced at least partially from opening  212 , such as when module  500  is first inserted into a respective cage  202 ,  204 . 
     Also, the raised section  322  is located closer to a front end  324  of the heat sink  300  than it is to a rear end  326  of the heat sink  300 . The off-center raised section  322  further facilitates positioning and alignment of the heat sink assembly  302  with respect to a respective one of cages  202 ,  204  by providing a visual indication that the heat sink assembly  302  is oriented properly or improperly with the first tab  312  extending toward the front edge  206  of the circuit board  200  and the second tab  314  extending toward the rear edge  208  of the circuit board  200 , as is shown in  FIG. 4 . As but one example of a visual indicator that the heat sink assembly  302  may be improperly oriented, if the raised section  322  is inserted into an opening  212 , and the bezel surrounding the raised section  322  is seated on upper surface  210  of a cage  202 ,  204 , and the heat sink assembly  302  is oriented such that the second tab  314  extends towards front edge  206  of circuit board  200  instead of towards the rear edge  208  of circuit board, then the second end  318  will not be positioned relative to the circuit board  200  in a manner to enable it to be attached to the circuit board  200 , as described in detail above. 
       FIG. 6  shows an alternative example embodiment of a heat sink arrangement of a plurality of heat sink assemblies  602  assembled onto the circuit board  200 . The heat sink assemblies  602  are the same as heat sink assemblies  302 , except that the heat sink  600  included with each heat sink assembly  602  is different than the heat sink  300  included with each heat sink assembly  302 . In particular, in the embodiment shown in  FIG. 6 , a retention slot  604  is formed in each heat sink  600  to receive a wall  608  of a metal cover  606 . At least one ventilation opening  612  is formed in the cover  606 . The heat sink assemblies  602  are fixed to the circuit board  200  in the same way as they are for the heat sink assemblies  302  described above. When the heat sink assemblies  602  are fixed to the circuit board  200 , the retention slots  604  of the heat sinks  600  align in a substantially straight line  614 , which is shown being substantially parallel to the front edge  206  of the circuit board  200 . Once the heat sink assemblies  602  are fixed to the circuit board  200 , the wall  608  of the cover  606  is inserted into the aligned retention slot  604  and the cover  606  is secured to the retaining member  402  with screw fasteners  616 . 
     The metal cover  606  is removably attached to the retaining member  402  with screw fasteners  616 . As shown in  FIG. 6 , the cover  606  is not attached to retaining member  402 , but is disposed slightly above retaining member  402 . The cover  606  can be removed to permit the heat sink assemblies  602  to be installed and removed. When the cover  606  is attached to retaining member  402  with the wall  608  disposed in retention slots  604 , the wall  608  limits movement of each heat sink  600  in a front-to-back, longitudinal direction along the upper surface  210  of its corresponding cage  202 ,  204 , as well as limits movement in an up-and-down direction. Thus, displacement of the heat sink assemblies  602  caused by, for example, inserting and removing a module  500  ( FIG. 5 ) from a respective cage  202 ,  204 , can be limited. 
     The example embodiments described herein provide for a heat sink attachment to cage such as a transceiver cage (e.g., an SFP/XFP cage) that is space-efficient so that extra spaces need not be provided on a circuit board between adjacent cages for attachment of a heat sink to the cages. Accordingly, the example embodiments described herein permit a higher density of cages on a circuit board than do conventional arrangements. 
     While particular example embodiments have been shown and described, it will be obvious to those of skills in the art that based upon the teachings herein, changes and modifications may be made to the example embodiments without departing from these embodiments and their broader aspects. Therefore, the appended claims are intended to encompass within their scope all such changes and modifications as are within the true spirit and scope of the exemplary embodiments.