Abstract:
Method and systems for clamping at least one circuit card within a case are provided. The method includes compressing axially at least one resilient element between a head of a shaft and a nut disposed on the shaft so that the at least one resilient element bulges generally perpendicularly to the axial direction and into engagement with the at least one circuit card, exerting a force on the at least one circuit card using the at least one resilient element and maintaining the force on the at least one circuit card using the at least one resilient element.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional application of U.S. patent application Ser. No. 09/918,989 filed Jul. 31, 2001 now U.S. Pat. No. 6,894,907, titled “CLAMPING CASE” and commonly assigned, the entire contents of which is incorporated herein by reference. 
   CROSS RELATED APPLICATION 
   This application is related to co-pending application Ser. No. 11/099,344 entitled CLAMPING RECEPTACLE and filed on even date herewith, which is related to U.S. application Ser. No. 09/919,006, filed Jul. 31, 2001, all of which are hereby incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention relates generally to the field of cases that contain circuit cards and, in particular, to cases that clamp circuit cards within them. 
   BACKGROUND 
   Environmentally protected housings are used in a wide variety of applications, including containing and protecting electronic components of the type used for transferring signals over long distances. For example, the telecommunications industry transfers signals over transmission lines. If the signal is transferred over a long distance, the signal may be too weak by the time it reaches its destination to be useful. Consequently, electronic circuits are used to detect, clean up, and amplify a weak signal for retransmission through another length of transmission line. These electronic circuits are often deployed in environmentally protected housings located above and below ground. 
   Increased demands on the telecommunications industry, such as the advent of HDSL, HDSL2, SHDSL, etc., to meet the increasing needs of internet subscribers has resulted in the need to transfer more and stronger electrical signals over greater distances. One way of accomplishing this is to amplify the signals using electronic circuit cards deployed in environmentally protected housings. To meet the need for transferring stronger electrical signals over greater distances, electronic circuit cards having higher amplification capabilities, and thus greater heat dissipation rates, than the past generations of circuit cards are frequently used. 
   Many of the environmentally protected housings use cases, or receptacles, to confine circuit cards to different locations within the housings. Typically, these cases are thermally conducting and are thermally coupled to the housing to increase the heat transfer from the circuit cards. However, in many instances, gaps exist between the cases and the circuit cards. These gaps produce relatively large thermal resistances and severely limit heat transfer from the circuit cards. In many instances, this results in thermal failure of the circuit cards. 
   For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for eliminating gaps that exist between circuit cards and the cases that confine these circuit cards to different locations within a housing. 
   SUMMARY 
   The above-mentioned problems with gaps that exist between circuit cards and the cases that confine these circuit cards to different locations within a housing and other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention provide cases that clamp circuit cards within them to improve the thermal contact between the circuit cards and the cases. 
   More particularly, in one embodiment, a case for confining at least one circuit card to a location within a housing is provided. The case has at least one slot that contains the circuit card. The case also has at least one actuator adapted to clamp the circuit card within the slot. 
   In another embodiment, a case for confining a pair of circuit cards to different locations within a housing is provided. The case has a pair of opposing sidewalls and first and second end walls. A partition is disposed between the first and second end walls. The partition divides the case into a first slot bounded by a portion of each of the sidewalls, the partition, and the first end wall and a second slot bounded by another portion of each of the sidewalls, the partition, and the second end wall. The first and second slots each contain one of the circuit cards. An actuator is disposed in the first slot between the circuit card in the first slot and the first end wall. The actuator is adapted to bear against the circuit card in the first slot to clamp the circuit card in the first slot, the partition, and the circuit card in the second slot between the actuator and the second end wall. 
   Other embodiments are described and claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an environmentally protected housing according to the teachings of the present invention. 
       FIG. 2  is an enlarged illustration of a circuit card of the type typically housed in environmentally protected housings. 
       FIG. 3  is a top view of an embodiment of a case of the present invention for confining circuit cards to different locations within an environmentally protected housing. 
       FIG. 4  is a top view of an embodiment of a case of the present invention that uses a wedge to clamp circuit cards within the case. 
       FIG. 5  is a side view of an embodiment of the wedge of  FIG. 4  taken along the line  5 - 5  of  FIG. 4 . 
       FIG. 6  is a side view of an embodiment of the wedge in  FIGS. 4 and 5  taken line  6 - 6  of  FIG. 5 . 
       FIG. 7  is a top view of another embodiment of a case of the present invention that uses a wedge for clamping a circuit card within the case. 
       FIG. 8  is a top view of an embodiment of a case of the present invention that uses a cam to clamp circuit cards within the case. 
       FIG. 9  is a side view illustrating an embodiment of a cam used for clamping circuit cards within a case. 
       FIG. 10  is an enlarged view of a cam. 
       FIG. 11  is a side view illustrating another embodiment of a cam used for clamping circuit cards within a case. 
       FIG. 12  is an isometric view of an embodiment of a device that uses resilient elements for clamping circuit cards within a case. 
       FIG. 13  is a front view of  FIG. 12 . 
       FIG. 14  is a side view of resilient elements engaging a circuit card. 
       FIG. 15  is a top view of another embodiment of a case of the present invention that uses a cam for clamping a circuit card within the case. 
       FIG. 16  is a top view of an embodiment of a case of the present invention that has a frame and that uses cams for clamping several circuit cards within the frame. 
       FIG. 17  is an enlarged view of region  1675  of  FIG. 16 . 
       FIG. 18  is a top view of an embodiment of a case of the present invention that has a pair of frames and that uses cams for clamping several circuit cards within the frames. 
       FIG. 19  is an exploded isometric view of an embodiment of a case of the present invention that has a pair of frames and that uses resilient elements for clamping several circuit cards within the frames. 
       FIG. 20  is an isometric view illustrating an embodiment of a case positioned within a housing. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
     FIG. 1  shows an environmentally protected housing  100  according to the teachings of the present invention. Housing  100  has several cases  102   1  to  102   N  that are thermally coupled to the interior surface of wall  104  of housing  100 . Each case  102   1  to  102   N  is adapted to receive either a single circuit card, such as circuit card  106 , or a pair of circuit cards, such as circuit cards  108   a  and  108   b.    
     FIG. 2  is an enlarged view of a circuit card, such as circuit card  106 ,  108   a , or  108   b . In some instances, circuit card  106 ,  108   a , or  108   b  includes a thermally conducting case  110  that encloses circuit board  112 . Circuit board  112  includes components  114  that are frequently thermally coupled to thermally conducting case  110  by a thermal interface material  116 . 
     FIG. 3  is an enlarged top view of a case  102  containing a pair of circuit cards  108   a  and  108   b . Case  102  has end walls  118  and  120 , sidewalls  122  and  124 , and partition  126  that are typically fabricated from a thermally conducting material such as aluminum, copper, brass, bronze, or the like. Case  102  is thermally coupled at end wall  118  to the interior surface of wall  104  of housing  100  by a heat-sink device  128  that conforms to the contour of the interior surface of wall  104 . In one embodiment heat-sink device  128  is a solid block of material having thermal properties suitable for heat sinks, e.g., copper, aluminum, brass, bronze, or the like. 
   Normally, relatively intimate thermal contact exists between circuit cards  108   a  and  108   b  and sidewalls  122  and  124 , enabling a portion of the heat dissipated by circuit cards  108   a  and  108   b  to be transferred to sidewalls  122  and  124 . This portion of the heat is then conducted through sidewalls  122  and  124  into heat-sink device  128 . 
   On the other hand, gaps  130  and  132  respectively exist between circuit cards  108   a  and  108   b  and partition  126 , and gaps  134  and  136  respectively exist between circuit cards  108   a  and  108   b  and end walls  118  and  120 , as shown in  FIG. 3 . Another portion of the heat dissipated by circuit card  108   a  is conducted and radiated to partition  126  and end wall  118  across the gaps  130  and  134 , respectively. Another portion of the heat dissipated by circuit card  108   b  is conducted and radiated to partition  126  and end wall  120  across the gaps  132  and  136 , respectively. Heat conducted and radiated to end wall  118  is conducted through end wall  118  into heat-sink device  128 . Heat conducted and radiated to partition  126  and end wall  120  is respectively conducted through partition  126  and end wall  120  into sidewalls  122  and  124 , which conduct the heat to heat-sink device  128 . 
   Unfortunately, the respective gaps produce relatively large thermal resistances and severely limit the total heat transfer from circuit cards  108   a  and  108   b  to case  102 . In many instances, this results in thermal failure of circuit cards  108   a  and  108   b.    
   Embodiments of the present invention provide cases that clamp circuit cards within them to improve the thermal contact between the circuit cards and the cases. This substantially increases the heat transfer from circuit cards relative to the heat transfer from circuit cards that occurs when the circuit cards are not clamped within the cases, thus reducing the risk of thermal failure. In various embodiments, an actuator, such as a wedge, cam, resilient elements, or the like clamps the circuit cards within the cases. 
   Case  400 , illustrated in  FIGS. 4-6 , is one embodiment of the present invention.  FIG. 4  is a top view of case  400 ,  FIG. 5  a side view taken along the line  5 - 5  in  FIG. 4 , and  FIG. 6  a view taken along the line  6 - 6  of  FIG. 4 . Embodiments of the present invention provide cases that clamp circuit cards within them to improve the thermal contact between the circuit cards and the cases. Case  400  is used to confine circuit cards, e.g., circuit cards  408   a  and  408   b  to particular locations within an environmentally protected housing, e.g., environmentally protected housing  401 . In one embodiment, circuit cards  408   a  and  408   b  are similar to circuit cards  108   a  and  108   b  and environmentally protected housing  401  is similar to housing  100 . In one embodiment, case  400  confines circuit cards  408   a  and  408   b  to a location adjacent a wall  402  of environmentally protected housing  401 . In another embodiment, a heat-sink device, such as heat-sink device  403 , thermally couples case  400  to an interior surface of wall  402 . In one embodiment, heat-sink device  403  is a solid block of material having thermal properties suitable for heat sinks, e.g., copper, aluminum, brass, bronze, or the like. 
   Case  400  has end walls  404  and  406 , sidewalls  409  and  410 , and partition  412 . End walls  404  and  406 , sidewalls  409  and  410 , and partition  412 , in one embodiment, are fabricated from any thermally conducting material, such as aluminum, copper, brass, bronze, or the like. Partition  412  divides case  400  into slots  414  and  416  that respectively contain circuit cards  408   a  and  408   b.    
   Partition  412 , in one embodiment, is in slidable contact with sidewalls  409  and  410  and can slide toward end walls  404  and  406 , respectively. Circuit cards  408   a  and  408   b , in another embodiment, are in slidable contact with sidewalls  409  and  410  and can slide toward end walls  404  and  406 , respectively. In other embodiments, thermally conducting grease is disposed between partition  412  and sidewalls  409  and  410  and/or between circuit cards  408   a  and  408   b  and sidewalls  409  and  410 . The thermally conducting grease increases the thermal contact, and thus the heat transfer, between the partition  412  and sidewalls  409  and  410  and/or between circuit cards  408   a  and  408   b  and sidewalls  409  and  410 . When circuit cards  408   a  and  408   b  are respectively inserted into slots  414  and  416 , gaps  418  and  420  respectively exist between circuit cards  408   a  and  408   b  and partition  412  and gaps  422  and  424  respectively exist between circuit cards  408   a  and  408   b  and end walls  404  and  406 , as shown in  FIG. 4 . 
   Case  400  includes wedge  428  insertable into gap  424 . Wedge  428 , in one embodiment, is fabricated from nylon, plastic, metal, or the like. In another embodiment, wedge  428  has a tab  430 , and in other embodiments, an aperture  432  passes through tab  430 , as shown in  FIGS. 4-6 . Tab  430  and aperture  432  facilitate insertion and removal of wedge  428  respectively into and from gap  424 . 
   Wedge  428  is pressed into gap  424 , causing wedge  428  to engage and to exert a force on circuit card  408   b . The force slides circuit card  408   b  into contact with partition  412 . Circuit card  408   b  exerts a force on partition  412  that slides partition  412  into contact with circuit card  408   a . Partition  412  exerts a force on circuit card  408   a  that slides circuit card  408   a , in one embodiment, into contact with end wall  404 . This respectively closes gaps  420 ,  418 , and  422  and clamps circuit card  408   a , partition  412 , circuit card  408   b , and end wall  404  in direct thermal contact. 
   Direct thermal contact between partition  412  and circuit cards  408   a  and  408   b  substantially increases the heat transfer from circuit cards  408   a  and  408   b  to partition  412  relative to the heat transfer that occurs if gaps  418  and  420  are present. Similarly, direct thermal contact between end wall  404  and circuit card  408   a  substantially increases the heat transfer from circuit card  408   a  to end wall  404  relative to the heat transfer that occurs if gap  422  is present. Consequently, this increases the total heat transfer from circuit cards  408   a  and  408   b  to case  400 , reducing the risk of thermal failure. 
     FIG. 7  shows case  700 , another embodiment of the present invention. Case  700  is used to a confine circuit card, e.g., circuit card  706 , to a particular location with in an environmentally protected housing, e.g., environmentally protected housing  701 . In one embodiment, circuit card  706  is similar to circuit card  106  and environmentally protected housing  701  is similar to housing  100 . In another embodiment, case  700  confines circuit card  706  to a location adjacent a wall  702  of environmentally protected housing  701 . In other embodiments, a heat-sink device, such as heat-sink device  703 , thermally couples case  700  to an interior surface of wall  702 . Heat-sink device  703 , in one embodiment, is a solid block of material having thermal properties suitable for heat sinks, e.g., copper, aluminum, brass, bronze, or the like. 
   Case  700  has end walls  704  and  705  and sidewalls  708  and  710 . In one embodiment, end walls  704  and  705  and sidewalls  708  and  710  are fabricated from any thermally conducting material, such as aluminum, copper, brass, bronze, or the like. Case  700  defines a slot  712  that receives a circuit card  706 . Circuit card  706 , in one embodiment, is in slidable contact with sidewalls  708  and  710  and can slide toward end walls  704  and  705 , respectively. In one embodiment, thermally conducting grease is disposed between circuit card  706  and sidewalls  708  and  710 . When circuit card  706  is inserted into slot  712 , gaps  714  and  716  respectively exist between circuit card  706  and end walls  704  and  705 . 
   Case  700  includes wedge  728 . Wedge  728  is pressed into gap  716 , causing wedge  728  to engage and to exert a force on circuit card  706 . The force, in one embodiment, slides circuit card  706  into direct contact with end wall  704 , thereby closing gap  714  to clamp circuit card  706  and end wall  704  in direct thermal contact. In one embodiment, wedge  728  is as described for wedge  428  above. 
     FIG. 8  illustrates case  800 , another embodiment of the present invention. Elements that are common to  FIGS. 4 and 8  are numbered as in  FIG. 4  and are as described above. Case  800  includes a cam  810  that is disposed within gap  424  between end wall  406  and circuit card  408   b.    
   Cam  810 , in one embodiment, is rotated from position  802  to position  804  so that a portion of cam  810  engages and exerts a force on circuit card  408   b . The force slides circuit card  408   b  into contact with partition  412 . Circuit card  408   b  exerts a force on partition  412  that slides partition  412  into contact with circuit card  408   a . In one embodiment, partition  412  exerts a force on circuit card  408   a  that slides circuit card  408   a  into contact with end wall  404 . This respectively closes gaps  420 ,  418 , and  422  and clamps circuit card  408   a , partition  412 , circuit card  408   b , and end wall  404  in direct thermal contact. 
   Cam  810 , in one embodiment, is fabricated from metal, e.g., steel or aluminum, plastic, or the like. In another embodiment, serrations  812  are distributed over the curved surface of cam  810 , as shown in  FIG. 10 , which is the surface that bears against circuit card  108   b . In another embodiment, serrations  812  are rubber and are molded onto cam  410 . Serrations  812  improve the contact resistance between cam  810  and circuit card  408   b  and facilitate the clamping of circuit card  408   a , partition  412 , circuit card  408   b  between cam  810  and end wall  404 . In one embodiment, cam  810  has aperture  814  passing through it for receiving a shaft, such as shaft  817  shown in  FIG. 9 . 
     FIG. 9  is a side view of region  850  in  FIG. 8  corresponding to one embodiment of case  800 . As seen in  FIG. 9 , cam  810  is rotatably attached to end wall  406  using a bracket  816  and a shaft  817 . Bracket  816  includes protrusions  818  and  820 , respectively having apertures  824  and  826  passing therethrough. Cam  810  is rotatably attached to end wall  406  by positioning cam  810  between protrusions  818  and  820  to align aperture  814  of cam  810  with apertures  824  and  826  and passing shaft  817  through apertures  824 ,  814 , and  826 . Cam  810  rotates about the longitudinal axis of shaft  817  and moves relative to protrusions  818  and  820  of bracket  816 . 
   Bracket  816 , in one embodiment, is fabricated from metal, e.g., steel or aluminum, plastic, or the like and is fixed to end wall  406  by welding, gluing, bolting, or the like. In one embodiment, cam  810  is secured to shaft  817  using cap screws, set screws, an interference fit, or the like. Shaft  817 , in one embodiment, is fabricated from metal, e.g., steel, aluminum, or the like, plastic, or the like. Shaft  817 , in one embodiment, has a head  828  at one of its ends that is hexagonal, as shown in  FIG. 8 , square, slotted, Phillips, Allen, or the like. In one embodiment, a nut  830  that is hexagonal or square is threaded onto shaft  817  at end  832  of shaft  817 . To rotate cam  810 , a torque is applied to head  828  using an appropriate wrench, screwdriver, or the like. 
     FIG. 11  is a side view of region  850  in  FIG. 8  corresponding to another embodiment of case  800 . The embodiment of  FIG. 11  includes two cams  1010  that are rotatably attached to end wall  406  in tandem using a bracket  1016  for each cam  1010  and shaft  1017  that passes through the respective brackets  1016  and cams  1010 . In other embodiments, bracket  1016  and cams  1010  are as described above for bracket  816  and cam  810 . Shaft  1017 , in one embodiment, has a head  1028  at one of its ends that is hexagonal, as shown in  FIG. 11 , square, slotted, Phillips, Allen, or the like. In one embodiment, a nut  1030  that is hexagonal or square is threaded onto shaft  1017  at end  1032 . Cams  1010  are rotated into engagement with circuit card  408   b  by applying a torque to head  1028  using an appropriate wrench, screwdriver, or the like. 
     FIG. 12  is an isometric view of region  850  in  FIG. 8  corresponding to yet another embodiment of case  800 .  FIG. 13  is a side view of  FIG. 12 , and  FIG. 14  illustrates the embodiment of  FIG. 12  in operation. In the embodiment of  FIG. 12 , end wall  1206  replaces end wall  406  and resilient elements  1202  and  1204  replace cam  810 . 
   End wall  1206  includes recess  1208 . In one embodiment, a bracket  1210  and a nut  1212  are disposed within recess  1208  and are respectively fastened to wall  1206  using fasteners  1214  and  1216 , as shown in  FIGS. 12 and 13 . Bracket  1210  and nut  1212 , in one embodiment, are fabricated from metal, such as steel or aluminum, plastic, or the like. Fasteners  1214  and  1216 , in one embodiment, are screws or bolts. Alternatively, bracket  1210  and nut  1212 , in other embodiments, are fastened to end wall  1206  by welding, gluing, or the like. In another embodiment, bracket  1210  and nut  1212  are fastened to a wall with no recess, such as end wall  406 . 
   Bracket  1210  has an aperture  1218  passing through it, as shown in  FIGS. 12 and 13 . A sleeve  1220  passes through aperture  1218  and is slidable within aperture  1218 . A shaft  1222  passes through sleeve  1220  and is movable therein. An end  1224  of shaft  1222  is threaded into nut  1212 . Shaft  1222 , in one embodiment, is fabricated from metal, e.g., steel, aluminum, or the like, plastic, or the like. Shaft  1222 , in one embodiment, has a head  1226  at an end opposite end  1224  that is hexagonal, as shown in  FIGS. 12 and 13 , square, slotted, Phillips, Allen, or the like. 
   In one embodiment, shaft  1222  sequentially passes through a washer  1228 , an aperture  1230  in resilient element  1202 , a washer  1234 , sleeve  1220 , a washer  1236 , an aperture  1238  in resilient element  1204 , and a washer  1242  and threads into nut  1212 , as shown in  FIG. 13 . Resilient element  1202  is sandwiched between washers  1228  and  1234 , and resilient element  1204  is sandwiched between washers  1236  and  1242 . Washers  1234  and  1236  respectively abut sleeve  1220  at ends  1244  and  1246  of sleeve  1220 , while washers  1228  and  1242  respectively abut head  1226  of shaft  1222  and nut  1212 . Shaft  1222  is movable within washer  1228 , aperture  1230  of resilient element  1202 , washer  1234 , washer  1236 , aperture  1238  of resilient element  1204 , and washer  1242 . 
   Resilient elements  1202  and  1204 , in one embodiment, are elastomers, e.g., polyvinyl, rubber, or the like. Washers  1228 ,  1234 ,  1236 , and  1242 , in one embodiment, are metal, e.g., aluminum or steel, plastic, or the like and are circular, as shown in  FIG. 12 , square, etc. 
   In operation, a torque is applied to head  1226  of shaft  1222  using an appropriate wrench, screwdriver, or the like to thread shaft  1222  into nut  1212 , causing shaft  1222  to move axially into nut  1212 . This compresses resilient elements  1202  and  1204  axially between head  1226  and nut  1212 , causing resilient elements  1202  and  1204  to bulge in generally the radial direction, as shown in  FIG. 14 . As resilient elements  1202  and  1204  bulge radially, resilient elements  1202  and  1204  engage circuit card  408   b  to exert a force on circuit card  408   b , as shown in  FIG. 14 . This force closes gaps  420 ,  418 , and  422  and clamps circuit card  408   a , partition  412 , circuit card  408   b , and end wall  404  in direct thermal contact, as described above. 
   More specifically, when a torque is applied to head  1226  of shaft  1222 , head  1226  exerts an axial force on washer  1228 , which in turn exerts an axial force on resilient element  1202 . A portion of the axial force exerted on resilient element  1202  compresses resilient element  1202  axially, causing resilient element  1202  to bulge in generally the radial direction, as shown in  FIG. 14 . Another portion of the axial force exerted on resilient element  1202  is transmitted to washer  1234 , which in turn exerts an axial force on end  1244  of sleeve  1220 . The axial force exerted on sleeve  1220  slides sleeve  1220  relative to bracket  1210  within aperture  1218  of bracket  1210 . This causes end  1246  to exert an axial force on washer  1236 , which in turn exerts an axial force on resilient element  1204 . The axial force exerted on resilient element  1204  compresses resilient element  1204  axially between washer  1236  and washer  1242 , causing resilient element  1204  to bulge in generally the radial direction, as shown in  FIG. 14 . 
     FIG. 15  illustrates case  1500 , another embodiment of the present invention. Elements that are common to  FIGS. 15 and 7  are numbered as in  FIG. 7  and are as described above. Cam  1510  is rotated from a position  1520  to a position  1530 , as shown in  FIG. 15 , so that a portion of cam  1510  engages circuit card  706  to exert a force on circuit card  706 . The force, in one embodiment, slides circuit card  706  into direct contact with end wall  704 , thereby closing gap  714  to clamp circuit card  706  and end wall  704  in direct thermal contact. 
   In one embodiment, region  1550  of  FIG. 15  is as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 9 and 10 , and cam  1510  is as described for cam  810 . In another embodiment, region  1550  of  FIG. 15  is as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIG. 11 , and a pair of cams in tandem engages circuit card  706  to exert a force on circuit card  706 . In yet another embodiment, region  1550  of  FIG. 15  is as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 12-14 , and a pair of resilient elements engages circuit card  706  to exert a force on circuit card  706 . 
     FIG. 16  illustrates receptacle  1600 , another embodiment of the present invention. Receptacle  1600  includes sidewalls  1602  and  1604  and end walls  1606  and  1607  that are fabricated from materials having suitable thermal and structural properties, such as aluminum, copper, brass, bronze, or the like. 
   Receptacle  1600  includes a frame  1608  divided into sub-frames  1608 , and  1608   2  by partition  1610 . Sub-frame  1608   2  and partition  1610 , in one embodiment, are in slidable contact with sidewalls  1602  and  1604 . Sub-frames  1608   1  and  1608   2  are respectively partitioned into an array of slots having slots  1620   1  to  1620   N  by partitions  1612   1  to  1612   N  that are perpendicular to partition  1610 , as shown in  FIG. 16 . Each slot of slots  1620   1  to  1620   N  respectively confines one of circuit cards  1622   1  to  1622   N  to a particular location within case  1600 . Frame  1608  is fabricated from materials having suitable thermal and structural properties, such as aluminum, copper, brass, bronze, or the like. Circuit cards  1622   1  to  1622   N , in one embodiment, are as described above for circuit card  106   108   a , or  108   b.    
   A gap  1624  separates frame  1608  from end wall  1606 . Cams  1611  are disposed within gap  1624 . Cams  1611  are rotated into and out of engagement with frame  1608 . When cams  1611  engage frame  1608 , cams  1611  respectively exert a force on frame  1608 , and, in particular, sub-frame  1608   2 . 
   In one embodiment, regions  1650  of  FIG. 16  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 9 and 10 , and cams  1611  are as described for cam  810 . In another embodiment, regions  1650  of  FIG. 16  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIG. 11 , and two tandem pairs of cams engage frame  1608  to exert a force on frame  1608 . In yet another embodiment, regions  1650  of  FIG. 16  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 12-14 , and two pairs of resilient elements engage frame  1608  to exert a force on frame  1608 . In other embodiments, a single region  1650  midway between sidewalls  1602  and  1604  replaces regions  1650 , and a single cam, a tandem pair of cams, or a pair of resilient elements are located midway between sidewalls  1602  and  1604 . 
     FIG. 17  is an enlarged view of region  1675  of  FIG. 16  and corresponds to when a force, as represented by arrow  1750 , is initially exerted on sub-frame  1608   2 , for example, by cam  1611 .  FIG. 17  shows, in one embodiment, that the circuit cards  1622   1  to  1622   N , e.g., circuit cards  1622   1  and  1622   N , extend beyond sub-frames  1608   1  and  1608   2  and partitions  1612   1  to  1612   N , e.g.,  1612   1  and  1612   N , by a distance  1702 . In other embodiments, the distance  1702  is substantially zero, and circuit cards  1622   1  to  1622   N  are substantially flush with sub-frames  1608   1  and  1608   2  and partitions  1612   1  to  1612   N . Moreover, circuit cards  1622   1  to  1622   N , e.g., circuit cards  1622   1  and  1622   N , are each separated from partition  1610  by a gap  1704 . 
   When a force, as indicted by arrow  1750 , is exerted on frame  1608  at sub-frame  1608   2 , the force slides sub-frame  1608   2  so that the circuit cards of circuit cards  1622   1  to  1622   N  that are in sub-frame  1608   2  contact partition  1610  and exert a force on partition  1610 . The force exerted on partition  1610  slides partition  1610  into contact with the circuit cards of circuit cards  1622   1  to  1622   N  that are in sub-frame  1608   1 . In this way, the circuit cards of circuit cards  1622   1  to  1622   N  contained in the slots of sub-frame  1608   2  are clamped between sub-frame  1608   2  and partition  1610 , and the circuit cards of circuit cards  1622   1  to  1622   N  contained in the slots of sub-frame  1608   1  are clamped between and partition  1610  and sub-frame  1608   1 . Therefore, circuit cards  1622   1  to  1622   N  are clamped in direct contact with frame  1608 , which is in contact with end walls  1606  and  1607  and sidewalls  1602  and  1604  of case  1600 . This substantially increases the heat transfer from circuit cards  1622   1  to  1622   N  to case  1600  relative to situations where circuit cards  1622   1  to  1622   N  are not clamped in direct contact with frame  1608 . 
     FIG. 18  illustrates receptacle  1800 , another embodiment of the present invention. Receptacle  1800  includes sidewalls  1802  and  1804  and end walls  1806  and  1807  that are fabricated from materials having suitable thermal and structural properties, such as aluminum, copper, brass, bronze, or the like. 
   Receptacle  1800  includes frames  1808  and  1809 , respectively divided into sub-frames  1808   1  and  1808   2  by partition  1810  and sub-frames  1809   1  and  1809   2  by partition  1811 . Sub-frames  1808   2  and  1809   2  and partitions  1810  and  1811 , in one embodiment, are in slidable contact with sidewalls  1802  and  1804 . Sub-frames  1808   1  and  1808   2  are partitioned into an array of slots having slots  1820   1  to  1820   N  by partitions  1812   1  to  1812   N  that are perpendicular to partition  1810 , as shown in  FIG. 18 . Sub-frames  1809   1  and  1809   2  are partitioned into an array of slots having slots  1821   1  to  1821   N  by partitions  1813   1  to  1813   N  that are perpendicular to partition  1811 , as shown in  FIG. 18 . Each slot of slots  1820   1  to  1820   N  respectively confines one of circuit cards  1822   1  to  1822   N  to a particular location within frame  1808 . Each slot of slots  1821   1  to  1821   N  respectively confines one of circuit cards  1823   1  to  1823   N  to a particular location within frame  1809 . 
   Frames  1808  and  1809  are fabricated from materials having suitable thermal and structural properties, such as aluminum, copper, brass, bronze, or the like. Circuit cards  1822   1  to  1822   N  and circuit cards  1823   1  to  1823   N , in one embodiment, are as described above for circuit card  106 ,  108   a , or  108   b.    
   Frames  1808  and  1809  are separated by a gap  1824  that contains cams  1825 . Each cam  1825  is rotatably attached to frame  1808 , and, in particular, to sub-frame  1808   2  of frame  1808 . Cams  1825  are rotated into and out of engagement with frame  1809 , and, in particular, into and out of engagement with sub-frame  1809   2  of frame  1809 . When cams  1825  engage sub-frame  1809   2 , cams  1825  respectively exert a force on sub-frame  1809   2  producing a reaction force that is exerted on sub-frame  1808   2 . In this way, when each cam  1825  is rotated into engagement with frame  1809 , a force is exerted on both frames  1809  and  1808 , and, in particular, on both sub-frames  1809   2  and  1808   2 . 
   In one embodiment, the regions  1830  and  1840  are as described for region  1675  in  FIG. 16 . When a force is exerted on both sub-frames  1809   2  and  1808   2 , e.g., by each of cams  1825 , the force slides sub-frame  1808   2  so that the circuit cards of circuit cards  1822   1  to  1822   N  that are in sub-frame  1808   2  contact partition  1810  and exert a force on partition  1810 . The force exerted on partition  1810  slides partition  1810  into contact with the circuit cards of circuit cards  1822   1  to  1822   N  that are in sub-frame  1808   1 . In this way, the circuit cards of circuit cards  1822   1  to  1822   N  contained in the slots of sub-frame  1808   2  are clamped between sub-frame  1808   2  and partition  1810 , and the circuit cards of circuit cards  1822   1  to  1822   N  contained in the slots of sub-frame  1808   1  are clamped between and partition  1810  and sub-frame  1808   1 . 
   The force also slides sub-frame  1809   2  so that the circuit cards of circuit cards  1823   1  to  1823   N  that are in sub-frame  1809   2  contact partition  1811  and exert a force on partition  1811 . The force exerted on partition  1811  slides partition  1811  into contact with the circuit cards of circuit cards  1823   1  to  1823   N  that are in sub-frame  1809   1 . In this way, the circuit cards of circuit cards  1823   1  to  1823   N  contained in the slots of sub-frame  1809   2  are clamped between sub-frame  1809   2  and partition  1811 , and the circuit cards of circuit cards  1823   1  to  1823   N  contained in the slots of sub-frame  1809   1  are clamped between and partition  1811  and sub-frame  1809   1 . 
   In one embodiment, regions  1850  of  FIG. 18  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 9 and 10 , and cams  1825  are as described for cam  810 . In another embodiment, regions  1850  of  FIG. 18  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIG. 11 , and two tandem pairs of cams are attached to frame  1808  and are rotated to engage frame  1809  to exert a force on both frames  1808  and  1809 . In yet another embodiment, regions  1850  of  FIG. 18  are as described for region  850  of  FIG. 8  above for the embodiment of case  800  shown in  FIGS. 12-14 , and two pairs of resilient elements are attached to frame  1808  and engage frame  1809  to exert a force on both frames  1808  and  1809 . In other embodiments, a single region  1850  midway between sidewalls  1802  and  1804  replaces regions  1850 , and a single cam, a tandem pair of cams, or a pair of resilient elements are located midway between sidewalls  1802  and  1804 . 
   In one embodiment, region  1875  of  FIG. 18  is as shown in the exploded view of  FIG. 19 . In this embodiment, sub-frame portions  1908   2  and  1909   2  respectively replace the portions of sub-frames  1808   2  and  1809   2  contained within region  1875 , and gap  1924  replaces gap  1824 . Sub-frame portions  1908   2  and  1909   2  respectively have recesses  1910  and  1911 , with the recess  1910  having resilient elements  1902  and  1904  disposed therein. In one embodiment, resilient elements  1902  and  1904  are as described above in conjunction with  FIGS. 12-14 . 
   Resilient elements  1902  and  1904  are compressed axially between head  1918  of shaft  1920  and nut  1922  when a torque is applied to head  1918  to thread shaft  1920  axially into nut  1922 . This causes resilient elements  1902  and  1904  to bulge in generally the radial direction. As resilient elements  1902  and  1904  bulge generally radially, resilient elements  1902  and  1904  engage sub-frame portion  1909   2  within recess  1911 . When resilient elements  1902  and  1904  engage sub-frame portion  1909   2 , resilient elements  1902  and  1904  respectively exert a force on sub-frame portion  1909   2  producing a reaction force that is exerted on sub-frame portion  1908   2 . In this way, a force is exerted on both sub-frame portions  1908   2  and  1909   2 . 
   In one embodiment, a pair of cases  1800  is located within a housing, such as housing  2000  shown in  FIG. 20 . Housing  2000  has two compartments  2002  that are closed by covers  2004 . Each of compartments  2002  receives a case  1800 , as shown in  FIG. 20 , which, in one embodiment, is thermally coupled to housing  2000 , as described in U.S. patent application Ser. No. 09/804,129, entitled MECHANICAL HOUSING, which application is incorporated herein by reference. 
   CONCLUSION  
   Embodiments of the present invention have been described. The embodiments provide cases that clamp circuit cards within them to improve the thermal contact between the circuit cards and the cases, thereby reducing the risk of thermal failure. 
   Although specific embodiments have been illustrated and described in this specification, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. For example, although cam  810  is portrayed in the accompanying figures as being oval, cam  810  can also be circular, elliptical, or any suitable shape. Moreover, serrations  412 , as shown in  FIG. 10 , can be eliminated from the curved surface of cam  810 , or serrations  412  can be of a material other than rubber, such as plastic, metal, or the like. Although resilient elements  1202  and  1204  are shown to be hollow cylinders in  FIG. 13 , resilient elements  1202  and  1204  can have other geometries, such as cubes having apertures passing through them. Further, although cams  1611  are rotatably attached to end wall  1606 , as shown in  FIG. 16 , and are rotatable into engagement with frame  1608 , cams  1611  can be rotatably attached to frame  1608  and can be rotated into engagement with end wall  1606 . Although cams  1825  are rotatably attached to frame  1808 , as shown in  FIG. 18 , and are rotatable into engagement with frame  1809 , cams  1825  can be rotatably attached to frame  1809  and can be rotatable into engagement with frame  1808 .