Patent Publication Number: US-2015077937-A1

Title: Apparatus for cooling board mounted optical modules

Description:
TECHNICAL FIELD 
     The present invention is directed, in general, to a board mounted cooling apparatus and methods for manufacturing the same. 
     BACKGROUND 
     This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. 
     Optical networking devices often implement an input/output board having multiple independently hot-swappable optical transceivers modules compactly mounted thereon. The transceivers generate substantially amounts of heat which must be removed to ensure the proper operation of the transceivers. Heat generated by increasingly densely packed board mounted optical transceivers (e.g., form-factor transceivers) with ever-increasing power requirements presents a challenge for present thermal management strategies. 
     SUMMARY 
     One embodiment includes an apparatus, comprising a fluid-circulator loop configured to be located on a circuit board, wherein a heat-removal portion of the fluid-circulator loop is configured to be located adjacent to an optical transceiver module on the circuit board. 
     Any embodiments of the apparatus can further include the circuit board and/or a plurality of the optical transceiver modules arranged to situate at least one set of in-line optical transceivers on the circuit board. 
     In any embodiments of the apparatus, optical transceivers can be located inside of one or more transceiver cages of one of more of the optical transceiver modules and the heat-removal portion of the fluid-circulator loop can contact at least one of the transceiver cages or the optical transceivers. 
     In any embodiments of the apparatus, one or more optical transceivers can be located inside of one or more transceiver cages of a plurality of the optical transceiver modules, and the optical transceivers can be small form factor hot-swappable pluggable transceivers. 
     In any embodiments of the apparatus, an optical transceiver can be located inside of a transceiver cage of the optical transceiver module, and the transceiver cage can further include a spring-loaded structure configured to push the optical transceiver towards an interior surface of the transceiver cage, the interior surface being proximate to the heat-removal portion of the fluid-circulator loop that contacts the transceiver cage or the optical transceiver. 
     In any embodiments of the apparatus, the heat-removal portion of the fluid-circulator loop can contact a surface of transceiver cage or the optical transceiver of the optical transceiver modules, and, the transceiver cage and the heat-removal portion can be held together and to the board by a tensioning device. 
     In any embodiments of the apparatus, the heat-removal portion of the fluid-circulator loop can be sandwiched in-between a first set of the transceiver modules having a first set optical transceivers and a second set of the transceiver modules having a second set optical transceivers. 
     In any embodiments of the apparatus, the fluid-circulator loop can form a closed loop locatable entirely within a perimeter of the circuit board. 
     In any embodiments of the apparatus, the heat-removal portion of the fluid-circulator loop can be located adjacent to only a sub-set of the optical transceiver modules, the sub-set can be part of an in-line set of the optical transceiver modules and the sub-set can be the most distally located ones of the plurality of the optical transceiver modules relative to incoming direction of air flow delivered to the circuit board. 
     In any embodiments of the apparatus, the circulating loop can be configured as a heat pipe and the fluid inside of the fluid-circulator loop can be configured to change phase during each circuit around to fluid-circulator loop. 
     In any embodiments of the apparatus, the fluid-circulator loop can be configured as pipe and the fluid inside of the fluid-circulator loop can be configured to remain in a liquid phase throughout each circuit around the fluid-circulator loop. 
     Any embodiments of the apparatus can further include a heat exchanger coupled to a heat-transfer portion of the fluid-circulator loop. In some such embodiments the heat exchanger can be located on the circuit board in a position that allows unobscured access to incoming forced air flow. 
     Any embodiments of the apparatus can further include a fluid pump connected to the fluid-circulator loop and configured to pump fluid through the fluid-circulator loop. 
     In any embodiments of the apparatus, the heat-removal portion of the fluid-circulator loop can contact a cold plate which in turn contacts the transceiver module or the optical transceiver. 
     Any embodiments of the apparatus can further include a liquid coolant manifold, wherein the heat-removal portion is located in between, and fluidly connected to, supply and return line portions of the fluid-circulator loop and the supply and return line portions fluidly connect the heat-removal portion to the liquid coolant manifold. In some such embodiments, the supply and return line portions connected to the liquid coolant manifold can be compliant connections. 
     Another embodiment is a method. The method comprises providing a fluid-circulator loop configured to be located on a circuit board, wherein a heat-removal portion of the fluid-circulator loop is configured to be located adjacent to at least one of a plurality of optical transceiver modules on the circuit board. 
     Any embodiments of the method can further include providing the circuit board and/or positioning the fluid-circulator loop on the circuit board, including locating the heat-removal portion of the fluid-circulator loop adjacent to a transceiver cage of the optical transceiver modules located on the circuit board configured to hold the at least one optical transceiver. 
     In any embodiments of the method, positioning the heat-removal portion of the fluid-circulator loop can include displacing the heat-removal portion connected to compliant supply and return line portions emanating from a single liquid coolant manifold, the displacing being in a direction normal to a mounting surface of the circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are best understood from the following detailed description, when read with the accompanying FIGUREs. Some features in the figures may be described as, for example, “top,” “bottom,” “vertical” or “lateral” for convenience in referring to those features. Such descriptions do not limit the orientation of such features with respect to the natural horizon or gravity. Various features may not be drawn to scale and may be arbitrarily increased or reduced in size for clarity of discussion. Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  presents a isometric view of an apparatus embodiment of the disclosure; 
         FIG. 2  presents a detailed exploded isometric view of another apparatus embodiment of the disclosure; 
         FIG. 3  presents a detailed plan view of an embodiment of the apparatus with cold plates and compliant fluid circulating loops; 
         FIG. 4A  presents a detailed isometric view of another embodiment of the apparatus with cold plates and compliant fluid circulating loops; 
         FIG. 4B  presents a detailed isometric view of another embodiment of the apparatus with cold plates and compliant fluid circulating loops; and 
         FIG. 5  presents a flow diagram illustrating an method embodiments of the disclosure such a method of manufacturing any of the embodiments of the apparatuses discussed in the context of  FIGS. 1-4B . 
     
    
    
     DETAILED DESCRIPTION 
     The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof. Additionally, the term, “or,” as used herein, refers to a non-exclusive or, unless otherwise indicated. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. 
     Thermal management strategies may use a heat sink coupled to a cage that houses one or more optical transceivers mounted to a circuit board. Air is blown over the outer surface of the heat sink and cage to help dissipate the heat generated from the transceivers. This strategy, however, may not provide sufficient heat removal as larger numbers of transceivers are place on a single board. For instance, for some of the optical transceiver modules arranged side-by-side in-line on a board, e.g., those transceivers most distal to the incoming air flow, may not have adequate heat removal due to preheating of the air passing over the transceivers that are more proximate to incoming air flow. 
     The inventors have recognized that heat removal from the transceivers can be enhanced by placing a fluid-circulator loop adjacent to least some of the transceivers. The high latent heat capacity of the fluid in the loop can facilitate large amounts of heat to be absorbed and transferred to another part of the board where heat can be removed from the board. The fluid-circulator loop facilitates the transfer of the heat generated by the transceivers to another location on the circuit board where the heat can be more efficiently removed as compared to blowing air directly over heat sinks coupled to the transceivers. As further illustrated below the fluid-circulator loop can be readily adapted for use with hot-swappable optical transceiver modules and/or form-fit transceiver modules with varying geometric tolerances. 
     One embodiment of the disclosure is an apparatus.  FIG. 1  presents an isometric view of an apparatus  100  of the disclosure. The apparatus  100  comprises a fluid-circulator loop  105  configured to be located on a circuit board  110  (e.g., on a surface  112  of the board  110 ). A heat-removal portion  115  of the circulating loop  105  is configured to be located adjacent to an optical transceiver module  120  on the circuit board  110 . 
     As further illustrated in  FIG. 1 , in some embodiments, the apparatus  100  includes the circuit board  110  and a plurality of the optical transceiver modules  120 . The modules  120  can situate at least one set  122  of optical transceivers  125  on the circuit board  110 . For clarity, some optical transceiver  125  are shown unplugged from the module  120 . For instance, the in-line set  122  of transceivers  125  can be situated along an edge  127  of the board  110  to facilitate plugging and unplugging the transceivers  125  into and out of the modules. 
     In some embodiments of the apparatus  100 , the circuit board  110  can be one of many input/output boards for a communication apparatus  100 . As also illustrated, the circuit board  110  can include various electronic components  130 ,  132 , in addition to the optical transceiver modules  120 . One skilled in the pertinent art would understand how the electronic components  130 ,  132 , can be configured to process digital data encoded in optical signals transmitted through the transceivers  125  on the circuit board  110 . 
     In some embodiments of the apparatus  100 , the optical transceivers  125  are located inside of one or more transceiver cages  135  of one or more of the optical transceiver modules  120  and the heat-removal portion  115  of the circulating loop  105  contacts at least one of the transceiver cages  135  or the optical transceiver  125 . e.g., via an opening  137  in the cage  135 . 
     In some embodiments, the transceivers  125  in the set  122  can be a set of in-line, side-by-side transceivers  120 . For instance, transceivers  125  can be separately housed inside of multiple transceiver cages  135  of multiple modules  120 , or, the transceivers  125  can be housed inside of a single multi-opening cage of a single module  120 . In other embodiments a single module  120  can include a plurality of transceiver cages  135  equal in number to the number of optical transceivers  125 , and each transceiver cage  135  can accommodate individual optical transceivers  125 . One skilled in the pertinent art appreciate other variants of optical transceiver  120  and transceiver cage  135  of the optical module  120 . 
     In some embodiments of the apparatus  100 , one or more optical transceivers  125  are located inside of one or more transceiver cages  135  of a plurality of the optical transceiver modules  120 , and the optical transceivers  125  are small form factor hot-swappable pluggable transceivers. The term, hot-swappable pluggable transceivers, as used herein refers to a transceiver module  120  and transceiver  125  that allows the transceivers  125  to be insertable into or removable from the cage  135  without cessation of power to the circuit board  110  power and/or without a loss in the board&#39;s functionality. Non-limiting industry standard examples of the hot-swappable pluggable transceivers  125  include 10 gigabit small form factor pluggable transceivers (XFP) or, more generally, small form factor pluggable transceivers (SFP). 
       FIG. 2  presents a detailed exploded isometric view of another apparatus  100  embodiment of the disclosure. As illustrated in  FIG. 2  an optical transceiver  125  is located inside of a transceiver cage  135  of the optical transceiver module  120  and the transceiver cage  135  further include a spring-loaded structure  210  configured to push the optical transceiver towards an interior surface  215  (e.g., an upper interior surface) of the transceiver cage  135 . The interior surface  215  is proximate to the heat-removal portion  115  of the fluid circulating loop  105  that contacts the transceiver cage  135  or the optical transceiver  125 . The spring-loaded structure  210  can facilitate direct physical contact between each of the optical transceivers  125  and their respective transceiver cages  135  and thereby reduce the thermal resistance between these components and enhance heat-removal from the transceiver modules  120  to the heat-removal portion  115  of the loop  105 . 
     As further illustrated in  FIG. 2 , the heat-removal portion  115  of the circulating loop  115  contacts a surface  220  of the transceiver cage  135  or the optical transceiver  125  of one the modules  120 . The contact surface  220  can correspond to all or a portion of the side of the cage  135  adjacent to the heat-removal portion  115 . To facilitate heat transfer, the transceiver cage  135  and the heat-removal portion  115  can be held together and to the board  110  by a tensioning device  230 . 
     Some embodiments of the tensioning device  230  can include a spring  232  and screw  234 , but other coupling arrangement would be familiar to those skilled in the pertinent art. The screw  234  can attach to the board  110  and the spring  232  can regulate the amount of pressure applied to the heat-removal portion  115  and the transceiver cage  135 . For instance, the spring  232  can control the pressure applied between the optical transceiver  125 , cage  135  and heat-removal portion  115  of the loop  105  without compromising the plugability optical transceiver  125 . The screw  234  can pass through openings  236  in one or more optical transceiver modules  120 ,  240  and openings  238  in the board  110  to facilitate coupling. 
       FIG. 2  further illustrates that some embodiments of the apparatus  100  can include a first set  122  of the transceiver modules  120  having a first set optical transceivers  125  (e.g., held in cages  135 ) and a second set  240  of the transceiver modules  120  having a second set optical transceivers  120 . In some embodiments there can be multiple transceivers  125  e.g., from 1 to 50 transceivers  125  in the first or second sets  122 ,  240  all located on the board  110 . 
     In some embodiments, to accommodate a large number of transceivers  125 , different in-line sets  122 ,  240  of transceivers  125  can be stacked on top of each other. And, to facilitate heat removal from each of the transceivers  125  from both of the different sets  122 ,  240 , the heat-removal portion  115  of the circulating loop  105  can be sandwiched in-between the first set  122  and second set  240  of the stacked transceiver modules  120 . 
     In some embodiments, the heat-removal portion  115  of the loop  105  includes vapor chambers  245  (e.g., evaporator chambers) embedded within an interposer board  250 . In some embodiments, the vapor chambers  245  and interposer board  250  are configured to locate each vapor chamber  245  located directly over a surface  220  of one of the optical transceiver cages  135  of the modules  120 . As also illustrated in  FIG. 2  the sets  122 ,  240  of transceiver modules  120 , and the interposer board  250 , holding the heat-removal portion  115 , can all be held together and held to the board  110  by the tensioning device  230 . 
     Returning to  FIG. 1 , as illustrated, in some embodiments of the apparatus  100 , the fluid circulating loop  105  forms a closed loop locatable entirely within a perimeter  140  of the circuit board  110 . Having the loop  105  entirely within the board&#39;s  110  perimeter  140  facilitates the board being hot swappable. That is, the board  110  can be replaced with another board without cessation of power to other boards  110  of the apparatus  100  and/or without affecting the functionality of other boards  110  of the apparatus  100 . 
     As also illustrated in  FIG. 1 , in some embodiments of the apparatus  100 , the heat removal portion  115  of the fluid circulating loop  105  can be located adjacent to each one of the plurality of optical modules  120  on the circuit board  110 . The use of fluid with high specific heats, such as water, can accept heat input from the transceivers  125  held in the modules  120  to facilitate high rates of cooling uniformly across the entire set of optical transceiver modules  120 . For instance, in some embodiments, the last module  120 , and transceiver  125 , in the fluid flow direction  145  through the loop  105  can be maintained at substantially within the same temperature (e.g., within ±10 percent in some embodiments) as the first module  120  and transceivers  125  in the fluid flow direction  145 . For instance, in some embodiments, all of the optical transceivers  125  in a set  122  of modules  120  are maintained under an upper acceptable operating temperature of the optical transceivers  125  (e.g., less than about 70° C. for some embodiments). 
     In other embodiments of the apparatus  100 , it can be advantageous for the heat-transfer portion of the circulating loop to be located only adjacent to those transceiver modules  120  found to be overheating, e.g., due to the inadequate cooling being provided from air flow over the board  110 . Locating the heat-transfer portion  115  adjacent to only the over-heating transceiver modules  120  may also increase the ability of the loop  105  to dissipate heat, e.g., by avoiding any heat transfer from non-over-heating module  120  to the fluid circulating in the loop  105  and thereby avoiding preheating the fluid before reaching the over-heating transceiver modules  120 . 
     In some embodiments, for instance, the heat-transfer portion  115  of the circulating loop  105  can be only located adjacent to a sub-set  150  of the optical transceiver modules  120  of transceivers  125 . For instance, in some embodiments, the sub-set  150  can be the most distally located ones of the plurality of the optical transceiver modules  120  in the set relative to an incoming direction  155  of air flow to the circuit board  110 . 
     In some embodiments, the circulating loop  105  is configured as a heat pipe and the fluid inside of the loop  105  changes phase during each circuit around to loop  105 . One skilled in the pertinent art would understand how a small amount of fluid can sealed in a pipe, how the pipe can be evacuated to remove other gases and to reduce the pressure, and, how wicking structures can be introduced into the pipe to aid liquid movement due to capillary action. In such embodiments, the fluid in the loop  105  can be a dual-phase coolant. In such embodiments, the heat-removal portion  115  of the loop  105  can an evaporator portion and different portions of the loop  105  can be condenser portions. 
     In other embodiments, the fluid circulating loop  105  can configured as a pipe and the fluid inside of the loop  105  can remains in a liquid phase throughout each circuit around the loop  105 . 
     As illustrated in  FIG. 1 , in some embodiments to enhance heat removal, the apparatus  100  further includes a heat exchanger  160  coupled to a heat-transfer portion  162  of the loop  105 . For instance, the heat-transfer portion  162  of the loop  105  can be embedded within cooling fins  164  of the heat exchanger  160 . In some embodiments, in facilitate heat removal, the fins  164  can be a row of metallic rectangular-shaped structures whose major surfaces are oriented perpendicular to the forced air flow direction  155  and to the board  110  major surface  112 . In some embodiments, the heat-transfer portion  164  can be a condenser portion of the loop  105 . As illustrated in  FIG. 1 , the flow of fluid exiting the heat-removal portion  115  can be fluidly connected to the heat-transfer portion  162  via a return line portion  166  of the loop  105  and the flow of fluid exiting the heat-transfer portion  162  can be fluidly connected to the heat-removal portion  115  via a supply line portion  168  of the loop  105 , e.g., to form a closed loop. 
     As illustrated in  FIG. 1 , in some embodiments, the heat exchanger  160  is located on the circuit board  100  in a position that allows unobscured access to an incoming forced air flow  155 , e.g., from a fan of the apparatus. That is, at least a portion of the incoming air flow to the board  110  can reach the heat exchanger  160  without being obstructed by any other components  130 ,  132  on the circuit board including transceiver modules  120 . 
     As illustrated in  FIG. 1 , in some embodiments, to facilitate heat removal, the apparatus  100  further includes a fluid pump  170  connected to the loop  105  and configured to pump fluid through the loop  105 . For instance, in some embodiments fluid pump  170  can be a piezoelectric micro-pump and configured to circulate a liquid phase of the fluid through the loop  105 , however, other pumping mechanisms could be employed. In some embodiment, the pump  170  can be located between the heat-transfer portion  162  and heat-removal portion  115 , and in some embodiments, the pump  170  can be fluidly coupled to the supply line portion  168  of the loop  105 . 
     In some embodiments, both the heat exchanger  160  and the fluid pump  170  can be located on the circuit board  110 , e.g., entirely within a perimeter  140  of the circuit board  110 , to facilitate the board  110  having hot-swappable capabilities. 
       FIG. 3  presents a detailed plan view of another embodiment of the apparatus and  FIG. 4  presents a detailed isometric view of another embodiment of the apparatus. 
     As illustrated in  FIG. 3 , in some embodiments of the apparatus  100 , the heat-removal portion  115  of the circulating loop contacts a cold plate  310 , which in turn, contacts a transceiver module  120 . For instance, the cold plate can be made of aluminum, copper or other highly thermally conductive material to facilitate heat-transfer. For instance, the cold plate  310  can contact a transceiver cage  135  or the optical transceiver  125  of a module  120  housing at least one optical transceiver  125  ( FIG. 1 ). For instance, heat-removal portion  115  of the loop  105  can be on or embedded in the cold plate  310 . In some embodiments such as when using high powered (e.g., greater than about 1 W) transceiver modules  120 , it is advantageous for the cold plate  310  to directly contact the optical transceiver  125  through an opening  137  in the cage  135 . In some embodiments such as when using lower powered (e.g., less than or equal to about 1 W) transceiver modules  120 , the cold plate  310  can to directly contact the cage  135 . In either such embodiments a spring-loaded structure  210  mounted in the cage  135  can facilitate contacting the inner surface  215  of the top side of the cage  135 . 
     As illustrated in  FIG. 4 , in some embodiments the cold plate  310  and heat-removal portion  115  can be coupled together via a spring-clip mechanism  410 . The spring-clip mechanism  410  can help to orient the cold plate  310  or heat-removal portions  115  at a desired location on the cage and provide a compressive force to facilitate direct contact and hence effective heat transfer. 
     As further illustrated, some embodiments of the apparatus  100 , further includes a liquid coolant manifold  320 , wherein the heat-removal portion  115  is located in-between, and fluidly connected to, supply and return line portions  322 ,  324  of the loop  105 . The supply and return line portions  322 ,  324  fluidly connect the heat-removal portion  115  to the liquid coolant manifold  320 . In some embodiments, the liquid coolant manifold  310  can be part of the fluid circulating loop  105 , and the liquid coolant manifold  310  can be entirely located on the circuit board  110  and be part of a closed fluid circulating loop. However, in some embodiments the liquid coolant manifold  310  can be connected to a heat exchanger that is extraneous to the board  110 . 
     As illustrated there can be a plurality of separate heat-removal portions  115  and supply and return line portions that  322 ,  324  are each separately connected in parallel to single central liquid coolant manifold  310 . However in series connection with one or more the liquid coolant manifolds  310  are contemplated as are combinations of in series and in parallel connections between heat-removal portions  115  and the manifold  310  or manifolds  310 . 
     In some embodiments, the supply and return line portions  322 ,  324  of the loop  105  are compliant connections. The term compliant connection as used herein refers to the line portions  322 ,  324  having the ability to flex or reversibly displace in a direction  415  ( FIG. 4A ) to accommodate size variations in the optical transceiver module  120  and/or cold plate  310 . The compliant connection is elastically deformable in that the displacement is reversible with substantially no permanent set or deformation. For instance, as illustrated in  FIG. 4A , in some embodiments the compliant supply and return line portions  322 ,  324  are cantilevered connections that protrude or emanate from the liquid coolant manifold  320  portion of the loop  105 . In some embodiments, the cantilevered supply and return line portions  322 ,  324  allow the heat-removal portion  115  or cold plate  310  (e.g., a distal tip  417  of the heat-removal portion  115  or plate  310 ) to be displaceable in a direction  415  ( FIG. 4 ) that is perpendicular a mounting surface  112  of the circuit board  110 . As non-limiting examples, in some cases, the displacement can be a maximum distance of least about 0.1 mm, and in some embodiments, a maximum distance in a range of about 0.1 mm to about 0.2 mm. 
     Having compliant (e.g., cantilevered) supply and return line portions facilitates accommodation of manufacturing variations in geometric tolerances of the optical transceiver module  120 , e.g., the transceiver cage  135 . Manufacturing variations optical transceiver module  120  can cause gaps to exist between a rigid cold plate  310 , or a rigid heat-removal portion  115 , thereby greatly reduce the ability of heat to be removed from the module  120  by the loop  105 . For instance, there can be substantial variations in the efficiency of heat removal from the individual transceiver modules for a set  122  of in-line modules  120  when the adjacent heat removal portion  115  or cold plate  310  has a rigid structure. Having cantilevered supply and return line portions  322 ,  324  can provide individual, independent, mechanically “floating” or compliant heat-removal portions  115  or cold plates  310  to facilitate direct contact with the transceiver cages  135  or the optical transceiver  125 . 
     In some embodiments, compliant connections between the supply and return line portions  322 ,  324  of the loop  105  can be achieved without the use of cantilevered connections. For example, if two or more sets of separate supply (e.g., lines  324  and  430 ) and return coolant lines (e.g., lines  324  and  432 ) are used, the cold plate  310  can be compliantly supported like a trampoline (or hammock) between the first set of lines  322 ,  430  and the second set of lines  324 ,  432  such as illustrated in  FIG. 4B . 
     Another embodiment is a method, e.g., a method of assembling an apparatus.  FIG. 5  presents a flow diagram illustrating a method  500  for assembling an apparatus of the disclosure such as the any of the embodiments of the apparatuses  100  discussed in the context of  FIGS. 1-4B . 
     With continuing references to  FIGS. 1-4B  throughout, as illustrated in  FIG. 5 , the method  500  comprises a step  510  of providing a fluid-circulator loop  105  configured to be located on a circuit board  110 . A heat-removal portion  115  of the circulating loop  105  is configured to be located adjacent to at least one of a plurality of optical transceiver modules  120  on the circuit board  105 . 
     One skilled in the pertinent art would understand how to provide the fluid-circulator loop  105  in accordance with step  510 , so as to have sufficient heat removal capacity and in some embodiments, have to have the optional cantilevered connection portions  322 ,  324 . 
     For instance, one skilled in the pertinent art would understand how solid mechanics and elastic bending theory could be applied to design of the mechanical compliance or flexibility for cantilevered support of the cold plate  310  and/or heat removal portion  115 . For instance, the geometery of supply and return line portions  322 ,  324  can be designed to accommodate the desired vertical deflection  415  needed to assure sufficient cold plate  310  contact to the transceiver module  120 , under the action of the compressive force induced by the spring-clip mechanism  415  during module insertion. For instance, for a given target fluid flow rate through the loop  105  and material composition (e.g., aluminum, copper or other highly thermally conductive material), parameters such as the distance  420  out from the manifold  330 , the diameter  425  and thickness supply and return line portions  322 ,  324  can be calculated based on these theories to provided the desired flexible displacement. 
     Some embodiments of the method  500  further include a step  520  of providing the circuit board  110  and a step  530  of positioning the fluid-circulator loop  105  on the circuit board  110 . Positioning the loop  105 , in step  530  includes locating the heat-removal portion  115  of the loop  105  adjacent to transceiver cages  135  of the optical transceiver modules  120  located on the circuit board  110 . In some embodiments, as part of step  530 , the modules  120 , heat-removal portion  115 , and in some cases, optional cold plate  310  can be held together and to the board  110  using a tensioning device  230  ( FIG. 2 ) or spring-clip mechanism  410  ( FIGS. 3 and 4 ) or combinations thereof. 
     In some embodiments of the method  500 , positioning the fluid-circulator loop  105  (step  530 ) include a step  535  of displacing the heat-removal portion  115 , which is connected to compliant supply and return line portions  322 ,  324  emanating from a single liquid coolant manifold  320 . The displacing in step  535  is in a direction  415  perpendicular to a mounting surface  112  of the circuit board  110 , e.g., so as to accommodate the transceiver cage  135  between the heat-removal portion  115  and the mounting surface  112 . 
     Embodiments of the method  500  can include a step  540  of coupling the heat exchanger  160  to the circuit board  110  or a step  550  of coupling the fluid pump  170  to the circuit board  110 , such as described in the context of  FIG. 1 . Embodiments of the method  500  can include a step  560  of swapping an optical transceiver  125  with a different optical transceiver already plugged into a transceiver cage  135  of one of the transceiver modules  120 . In some embodiments, for instance, swapping in step  560  can be hot-swapping and accomplished without cessation of electrical power to the circuit board  110 . 
     Additional steps to complete assembly, or alter the assembled apparatus  100 , in accordance with the method  500  would be apparent to one skilled in the pertinent arts based on the embodiments discussed above. 
     Although various embodiments of the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the scope of the claimed inventions.