Patent Publication Number: US-2009219702-A1

Title: Electronic Circuit Plug-In Module for a Mounting Rack

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention pertains to an electronic plug-in module to be accommodated in a mounting rack with a module rail in the front region, comprising a circuit board, a circuit board holder and an adapter. 
     BACKGROUND OF THE INVENTION 
     Modularly designed electronic devices feature a mounting rack, into which individual modules in the form of plug-in modules can be inserted. On their rear side, the plug-in modules feature a multicontact plug that is inserted into a plug connector (plug receptacle) on the “backplane” of the mounting rack. The plug of the plug-in module may either consist of an integrated plug, e.g., a connector strip, a connector tab or a “card-edge-connector,” or of a separate connector strip that is fixed on the plug-in module. 
     In order to hold the plug-in modules in their positions within the mounting rack, they are fixed by means of suitable locking elements. Conventional locking devices that prevent an unintentional detachment of the modules consist of screws or quick-acting closures. In this case, it is common practice to either use a lever or lever pull handle that is fixed on the circuit board and cooperates with a front module rail of the mounting rack or to screw a front plate of the plug-in module to the module rail by means of a screw. For this purpose, the plug-in module is pushed into the mounting rack until the front plate tightly contacts the module rail of the mounting rack. The module rail of the mounting rack consists of a transversely extending profiled rail, to the lateral surfaces of which the lateral parts of the mounting rack can be fixed. The module rail features a front side with a locating face that is suitable for positioning and fixing a front plate of a plug-in module thereon. The front side of the module rail contains a plurality of bores, into which screws or mounting elements can extend in order to fix the front plates on the mounting rack. Alternatively, the front side of the module rail may also feature a transversely extending groove, into which a perforated rail with (threaded) bores can be inserted. Consequently, a module rail always provides the option of fixing a front plate thereon. 
     In modern telecommunications systems, plug-in modules are developed in accordance with the AMC standard (Advanced Mezzanine Card) that is defined by the PICMG (PCI Industrial Computer Manufacturers Group). Modules according to this specification are relatively small in comparison with known  19 -modules and have a comparatively shorter front plate that does not protrude over the circuit board of the plug-in module with respect to its height. The front plate may be pre-installed on the circuit board of the plug-in module. It usually has a U-shaped cross section. The plug of the AMC plug-in module is integrated into the circuit board on its rear end in the form of a connector tab (card-edge-connector). 
     Due to their standardized dimensions and permissible tolerances, AMC plug-in modules do not feature conventional mounting flanges on the front plate because the plug-in modules should also be inserted into so-called carriers (adapters) that do not feature a corresponding mounting plane or mounting rail (module rail) on the mounting rack. The depth stop of the modules (in the inserting direction) within the carrier is realized with the rearmost edge of the circuit board. The depth stop is required for reliably contacting the individual contact rows of the connector tab to the plug connector (plug receptacle) of the carrier. A specially standardized locking mechanism of these modules (card-edge-systems) secures their end position. Due to the stricter requirements with respect to the shock and vibration resistance of the systems, however, conventional mounting options are reaching their limitations. 
     Due to the standardized and permitted tolerances of the individual components of AMC systems, particularly the plug-in modules and mounting racks, it is not easy to provide mounting flanges on the front plate that contact a mounting rail of the mounting rack and simultaneously ensure the contact of the plug-in module with the mounting rack in this fashion. For example, if the front plate were tightly screwed onto the mounting rack, an excessively high pressure could possibly be exerted upon the integrated plug of the plug-in module or the connector housing of the plug connector such that the circuit board or the connector tab of the plug-in module could be damaged or destroyed. 
     SUMMARY 
     An exemplary embodiment of a plug-in module to be accommodated in a mounting rack with a rail in the front region comprises a circuit board, a circuit board holder and an adapter. The circuit board holder is fixed on the circuit board in the front corner region thereof. It comprises a coupling structure that is coupled to a corresponding coupling element of the adapter in order to produce a coupling between the circuit board holder and the adapter. The adapter, which is preferably angled, also features a receptacle for a mounting element in order to mount the adapter on the module rail of the mounting rack. The plug-in module is fixed to the mounting rack by the connection between the adapter and the mounting rack, as well as the coupling between the adapter and the circuit board holder. Once the plug-in module is completely inserted into the mounting rack and situated in an end position, the adapter and the circuit board holder cooperate in such a way that the plug-in module is held in its position in the mounting rack. 
     The adapter and the circuit board holder can provide the advantage that it is not dependent on a front plate of the plug-in module. It is furthermore possible, in particular, to retrofit plug-in modules with front plates that do not feature mounting flanges to the mounting device in order to install and mount the front plate and therefore the plug-in module with the front plate fixed thereon in the mounting rack. The mounting device can also be used with plug-in modules that do not feature a front plate. 
     In a new standardized development of the PICMG, AMC plug-in modules are specified that are intended for future use in “ruggedized MTCA” mounting racks with a mounting rail in their front region. Such mounting racks and AMC plug-in modules are adapted to the new stricter requirements with respect to shocks and vibrational stresses. AMC modules used so far that feature a shorter front plate without mounting flanges need to be modified for use in the “ruggedized MTCA” mounting rack. This is realized by replacing the front plates of the modules because the front plates used so far do not provide a front mounting. Thusly modified front plates with mounting flanges can then be fixed on the mounting rail as described in commonly owned, co-pending U.S. application Ser. No. 12/350,025, filed Jan. 7, 2009. 
     A mounting device such as described above also can provide the advantage that “normal” AMC modules can also be retrofitted for MicroTCA mounting racks. Plug-in modules according to the currently valid “AMC.0 Standard” that feature the shorter front plate without mounting flanges can also be used. 
     Due to the utilization of the inventive mounting device, it is possible to forgo the (expensive) replacement of the (partially individualized) front plate in order to mount the plug-in module in the mounting rack in a robust, strong and reliable fashion. The auxiliary adapter makes it possible to continue using the existing front plates. Consequently, retrofitting is much more cost-efficient than replacing the existing front plate with a modified (extended) front plate. The same front plates therefore can be used for all AMC modules and inexpensively produced in large quantities. 
     The cooperation between the adapter and the circuit board holder is particularly suitable for plug-in modules, the circuit board of which comprises an integrated connector (card-edge-connector). In circuit boards of this type, it is particularly important that the forces exerted by a mounting device for installing and mounting the plug-in module are not transmitted to the circuit board or the end of the connector tab in an uncontrolled fashion, but rather controlled. Otherwise, the circuit board may be damaged. 
     This aspect is taken into consideration in an exemplary embodiment by means of the mounting device with the coupling between the circuit board holder and the adapter that allows a relative movement between the two elements. This relative movement is also possible when the adapter of the mounting device is mounted or fixed on the module rail of the mounting rack. In one preferred embodiment, a relative movement between the adapter and the circuit board holder can be realized (during the coupling of the two elements) in such a way that the plug-in module can be moved in the mounting rack (preferably only) in the inserting direction as long as it hasn&#39;t reached the end position in the inserted state. The mounting device (consisting of the adaptor and the circuit board holder), particularly the coupling between the circuit board holder and the adapter, allows a relative movement between the two components such that the force transmitted to the circuit board of the plug-in module can be limited. 
     The relative movement provides the option of initially mounting the adapter on the module rail of the mounting rack, e.g., by means of screws, and to subsequently insert the plug-in module into the mounting rack until the circuit board holder engages with the adapter. Due to the special type of coupling, a plug-in module can be additionally displaced in the inserting direction, namely also after the engagement between the adapter and the circuit board holder, such that the plug-in module can be manually pushed into its end position. After the end position is reached, the two components can no longer be moved relative to one another because the circuit board holder cannot be moved opposite to the inserting direction due to the coupling (and a movement in the inserting direction is not possible in the end position). The plug-in module is reliably held in its position in the mounting rack. Stricter requirements with respect to vibration or shock resistance can also be fulfilled with this embodiment. 
     Since the connector tab of the circuit board is manually pressed into the plug receptacle on the backplane of the mounting rack, the force to be exerted can be easily controlled. The circuit board is not subjected to excessive forces generated by screws or levers. 
     Another advantage of such a plug-in module can be seen in that the conductive contact between the plug-in module and the mounting rack is produced by means of the preferably metallic adapter and the circuit board holder that preferably is also conductive. The (electromagnetic) shielding of the mounting rack is simultaneously improved with this measure. 
     In one preferred embodiment of the plug-in module, the mounting device is designed in such a way that the coupling structure of the circuit board holder consists of a retaining structure and the corresponding coupling element of the adapter consists of a catch element. The coupling between the circuit board holder and the adapter is produced by means of a snap-in connection. The coupling structure and the coupling element consist of two corresponding components, e.g., two catches that can engage into one another. The snap-in connection preferably allows several positions between the two catches in this case. This also allows a relative movement between the adapter and the circuit board holder. The coupling elements may consist, for example, of hooks, tabs or springable elements that engage on a rack rail of sorts that serves as the coupling structure. The catch element preferably engages into a front rack rail referred to the inserting direction during the insertion of the plug-in module, i.e., into a rack rail that is situated as far as possible from the front side of the circuit board. The catch element of the adapter is only snapped into a rack rail near the front side shortly before the end position is reached. 
     Alternatively, the coupling element may consist of a receptacle and the coupling structure may consist of a ratcheting catch that engages in the receptacle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One preferred embodiment of a plug-in module is described in greater detail below with reference to the drawings. The characteristics illustrated therein can be used individually or in combination in order to realize preferred embodiments of the invention. They do not restrict the generality of the invention in any way. In these drawings: 
         FIG. 1  shows a mounting rack with two plug-in modules; 
         FIG. 2  shows an inventive plug-in module with adapter and circuit board holder; 
         FIG. 3  shows a schematic section through a mounting rack with the plug-in module according to  FIG. 2 ; 
         FIG. 4  shows a schematic representation of an embodiment of a plug-in module; 
         FIGS. 5   a - c  show another embodiment of a plug-in module, and 
         FIGS. 6   a - c  show a detailed section through the plug-in module according to  FIG. 5  in a mounting rack. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the following description, like numbers refer to like elements. 
       FIG. 1  shows a mounting rack  1  that is realized in the form of a MicroTCA mounting rack (Micro Telecommunications Computing Architecture). Two module rails  2  arranged in the front region of the mounting rack  1  extend between the two sidewalls  3  that each feature a mounting flange  4  in order to mount the mounting rack  1  in a switchgear cabinet. 
     The module rails  2  each feature a perforated rail that is directed toward the front side of the module rack  1  and contains several bores  2   a,  into which mounting screws can be screwed in order to mount the plug-in modules. The perforated rail may also be realized in the form of a groove, into which clamping elements can be screwed with the aid of screws, for example, in clamping nuts arranged in the groove. 
     Several plug-in modules  5  that comprise a circuit board  6  and a front plate  7  can be accommodated in the mounting rack  1 , wherein the front plate  7  is screwed to the circuit board  6  by means of a (not-shown) circuit board holder. In order to mount the plug-in module  5  in the form of an AMC module within the mounting rack  1 , a locking mechanism  8  is provided that is actuated by means of a locking lever  9 . The locking lever  9  also optionally actuates a switch on the circuit board  6 . 
     The plug-in module  5  is held in the mounting rack  1  by the locking mechanism  8  only. The front plate  7  shown does not feature any mounting flanges so it cannot be screwed to the module rail  2 , and stricter requirements with respect to vibrations cannot be fulfilled. 
     In order to improve the mounting of the plug-in module  5  in the mounting rack  1  and to utilize the mounting options provided by the module rail  2 , it is either necessary to exchange the front plate  7  or to retrofit the plug-in module  5  with an adapter  10  as shown in  FIG. 2 . 
     An inventive plug-in module  5  according to  FIG. 2  features a circuit board  6  and a front plate  7 . Angled adapters  10 , each with a receptacle  12  in the form of an opening  11  that serves for receiving a mounting element  13 , are respectively arranged above and below the front plate  7 . The mounting element  13  consists of a screw  14  that can be screwed into one of the bores  2   a  of the module rail  2  in order to reliably mount the plug-in module  5  in the mounting rack  1 . 
     On its rear end  15 , the circuit board  6  features an integrated plug in the form of a connector tab  16  as is typically used, e.g., on AMC modules. 
     The adapter  10  is coupled to a circuit board holder  17  such that the adapter  10  can be moved relative to the circuit board holder  17  in the longitudinal direction of the circuit board  6 . The circuit board holder  17  is screwed on in the front corner region  18  of the circuit board  6  and holds the front plate  7  of U-shaped cross section, the U-limbs of which extend in the inserting direction. 
       FIG. 3  shows a schematic section through a mounting rack  1 , in which a plug-in module  5  is arranged in its functional position. The functional position is the end position of the plug-in module  5  referred to the inserting direction when the plug-in module  5  is inserted into the mounting rack  1  and the connector tab  16  of the circuit board  6  is completely inserted into a plug connector  20  (plug receptacle) on a backplane  21  of the mounting rack  1 . The upper and lower adapters  10  are respectively coupled to the upper and the lower circuit board holder  17  of the plug-in module  5 . The adapter  10  is simultaneously mounted on the module rail  2 . Since the coupling between the adapter  10  and the circuit board holder  17  does not allow a movement of the circuit board holder  17  relative to the adapter  10  opposite to the inserting direction, the plug-in module  5  is fixed in its end position in the mounting rack  1 . 
       FIG. 3  clearly shows that the AMC module  5  still contains the original face plate  7 , the vertical dimension of which preferably corresponds to the height of the circuit board  6 . The circuit board  6  may nominally also be slightly smaller, e.g., 0.3 mm smaller than the front plate  7 . 
     According to  FIGS. 3-6 , the adapter is preferably angled and forms an L in a longitudinal section. The L-limb  22   a  of the L-shaped adapter  10  that extends in the longitudinal direction of the circuit board  6  features a coupling element  23 . 
     In one preferred embodiment, the coupling between the circuit board holder  17  and the adapter  10  is produced by means of a snap-in connection. The coupling element  23  according to  FIG. 4  is formed by two skid-like coupling plates  24  that extend in the inserting direction and preferably feature several hooks  25  that also extend in the longitudinal direction of the circuit board  6 . The coupling plates  24  are arranged on the outside of the L-limb  22   a.    
     The circuit board holder  17  is realized in a metallic fashion and usually consists of solid material, for example, of a die-cast part. In the embodiment according to  FIG. 4 , the circuit board holder  17  is realized in a U-shaped fashion, wherein the U-base features a coupling structure  26 . The coupling structure  26  corresponds to the coupling element  23 . 
       FIGS. 4-6  also show that the coupling structure  26  preferably forms an integral part of the circuit board holder  17 . Analogously, the coupling element  23  preferably is integrally molded onto the adapter  10 . 
     The coupling structure  26  is formed by two recesses  27  that extend in the longitudinal direction and preferably feature (not-shown) hooks that correspond to the hooks  25  of the coupling plates  24 . In this case, the coupling plates  24  are smaller in their longitudinal direction than the recesses  27  so that the coupling plates  24  can be moved in the recesses  27 . This allows a relative movement between the adapter  10  and the circuit board holder  17 , wherein the hooks  25  only allow a movement of the circuit board holder  17  in the inserting direction relative to the adapter  10 . A relative movement opposite to the inserting direction is prevented by the hooks. 
       FIGS. 5   a - c  show detailed representations of the upper corner region of a plug-in module  5  with a mounting device  50  that consists of the adapter  10  and the circuit board holder  17 . 
     The circuit board  6  is screwed to the circuit board holder  17  by means of a holding screw  28 . A front plate  7  of U-shaped cross section is held on the circuit board holder  17  by means of a clamping connection. The width (dimension transverse to the inserting direction) of the circuit board holder  17  corresponds to the clear width between the two U-limbs of the front plate  7 . The clamping connection is reinforced by means of a form-fitting connection of two holding tabs  19  of the circuit board  16  that are clipped into corresponding openings in the U-limbs of the front plate  7 . The circuit board holder  17  and the front plate  7  may also be screwed to one another. However, it would also be conceivable to realize the circuit board holder  17  and the front plate in one piece, e.g., in the form of a die-cast part. 
     On its upper side  29 , the circuit board holder  17  features an (integrated) coupling structure  26  that corresponds to a coupling element  23  of the adapter  10 . The term “upper side” of the circuit board holder  17  refers to the outer side that extends horizontally and faces away from the circuit board  6 . The upper side  29  is preferably aligned with the long narrow edge  38  of the circuit board  6 . 
     The coupling structure  26  of the upper side  29  is formed by a (fine) toothing  30  with a plurality of adjacently arranged teeth  31  that are inclined toward the front plate  7 . The maximum distance between two adjacent teeth  31  preferably is 1 mm, particularly no more than 0.5 mm. It is particularly preferred to use a toothing  30  in which the maximum distance between two adjacent teeth  31  is 0.2 mm, particularly no more than 0.1 mm. Each individual tooth  31  preferably extends over the entire width of the circuit board holder  17  such that it respectively forms a retaining rail. 
     Two guide tabs  32  of L-shaped cross section are also arranged on the upper side  29  of the circuit board holder  17 , wherein the horizontal L-limb (transverse section  32   a ) extends parallel to the upper side  29 . The two guide tabs  32  correspond to a guide receptacle  33  of the adapter  10 , wherein the guide receptacle  33  features a widened first guide section  34  and a narrowed second guide section  35  that is directed toward the L-limb  22   b  of the adapter  10 . The first guide section  34  of the guide receptacle  33  is realized in such a way that the guide tabs  32  of the circuit board holder  17  fit through the section. The second guide section  35  is realized in such a way that the guide tabs  32  can be displaced therein, but lifting off (in the vertical direction) of the adapter is prevented. Due to these measures, the adapter  10  can be movably coupled to the circuit board holder  17  and still displaced within predetermined limits. On the free end of the L-limb  22   a,  the adapter  10  features a coupling element  23  that is realized in the form of a catch element  40 . The edge  37  of catch element  40  engages in the toothing  30  such that an arrangement of engaged teeth is produced. Due to the inclination of the teeth, an incremental movement is only possible in one direction, namely such that the adapter  10  can be moved relative to the circuit board holder in the direction of the front plate  7 . 
     An elastically springable guide tab  36  is arranged between the two second guide sections  35  of the adapter and also separates the two first guide sections  34 . The guide tab  36  exerts a force upon the adapter  10  such that the adapter  10  is tilted toward the front side of the circuit board  6  as shown in  FIG. 5   b.  This allows a non-engaged displacement of the adapter  10  relative to the circuit board holder  17 . The upper transverse sections  32   a  of the guide tabs  32  are inclined accordingly such that the horizontal L-limb  22   a  of the adapter  10  can also be pivoted upward, wherein the pivoting point consists of the (rounded) angle point  39  of the adapter  10 . 
       FIG. 5   c  shows the mounting device  50  consisting of the adapter  10  and the circuit board holder  17  once the spring tab  36  is overcome by a force acting upon the adapter and the L-limb  22   a  is aligned parallel to the upper side  29 . In this engaged position, the toothed edge  37  of the catch element  40  that is arranged on the front end of the adapter  10  and is slightly angled downward cooperates with the toothing  30  such that the adapter  10  and the circuit board holder  17  can only be moved relative to one another in one direction. The inclined teeth  31  limit the relative movement such that the circuit board holder  17  and therefore the plug-in module can be moved relative to the adapter  10  in the inserting direction. A relative movement opposite to the inserting direction is prevented. 
       FIGS. 6   a - c  show the plug-in module  5  according to  FIGS. 5   a - c,  wherein the plug-in module  5  is inserted into a mounting rack  1 , of which only part of the module rail  2  is shown. In  FIG. 6   a,  the adapter  10  is arranged in its starting position. The guide tab  36  pivots the adapter  10  in such a way that the catch element  40  is spaced apart from the toothing  30 . The L-limb  22   b  is inclined relative to the front side of the module rail  2 . The adapter  10  can be displaced relative to the circuit board holder  17  in a non-engaged fashion, wherein the guide tab  32  is guided in the guide receptacle  33 . 
     In  FIG. 6   a,  the plug-in module  5  is inserted into the mounting rack  1  such that its connector tab  16  contacts the plug receptacle  20  of the backplane  21 . 
       FIG. 6   b  shows the position after the spring force of the guide tab  36  is overcome and the adapter  10  is pivoted so far that its L-limb  22   b  is aligned parallel to the front side of the module rail  2 . The catch element  40  engages into the toothing  30  and cooperates with one of the teeth  31 . The adapter  10  is now mounted on the module rail by means of the screw  14  (the front thread of which is not illustrated in order to provide a better overview), wherein the screw  14  is screwed into the bore  2   a.    
       FIG. 6   c  shows the plug-in module  5  that is additionally displaced by two teeth  31  in the inserting direction with reference to the position in  FIG. 6   b.  In this position, the connector tab  16  is completely inserted into the plug receptacle  20  and produces a reliable electric contact. This figure clearly shows that the design of the catch element  40  and the inclined teeth  31  prevent displacement of the plug-in module because the circuit board holder  17  cannot be moved relative to the adapter  10  opposite to the inserting direction. 
     However, a comparison between  FIGS. 6   b  and  6   c  shows that the plug-in modules can also be fixed within the mounting rack in different positions due to the standardized permissible tolerances of the plug-in modules  5 . In  FIG. 6   b,  a longer circuit board  6  would accordingly be used such that a gap results between the front side of the front plate  7  and the front side of the module rail  2 . The inventive mounting device  50  takes into account such a gap in that the toothing  30  of the circuit board holder  17  allows several positions in the longitudinal direction of the plug-in module. 
     Due to these measures, it is possible to take into account a gap that results between the mounting plane defined by the module rail  2  and the front plate  7  of the plug-in module  5  when the plug-in module  5  completely contacts the plug receptacle  20  of the backplane  21  with its connector tab  16 . The plug-in module  5  must be held in this position and, in particular, cannot be moved out of the mounting rack  1 . The gap resulting in this end position of the plug-in module  5  is between 0 and approximately 1.6 mm. 
     The inventive method for mounting a plug-in module  5  in a mounting rack  1  can be elucidated with reference to  FIGS. 6   a - c.  The method comprises the step of inserting the plug-in module  5  into a contact position in the mounting rack  1 , namely until the integrated connector tab  16  contacts the plug receptacle  20  of the backplane  21 . In another step, the adapter  10  is mounted on the module rail  2  of the mounting rack  1  by means of a mounting element  13  in the form of a screw  14 . In another step, the coupling element  23  of the adapter  10  is engaged with the coupling structure  26  of the circuit board holder  17  in such a way that a coupling is produced between the circuit board holder  17  and the adapter  10 . In another step, the plug-in module  5  is moved in the inserting direction until the plug-in module  5  is transferred from the contact position into the end position (in the completely inserted state), in which the coupling element  23  is coupled to the coupling structure  26  in such a way that the plug-in module  5  is prevented from moving opposite to the inserting direction. 
     The sequence of the above-described steps is arbitrary (variable). However, it is possible and preferred that the adapter  10  be connected (fixed on) the module rail  2  of the mounting rack  1  before the plug-in module  5  is inserted into the mounting rack  1 . After the adapter  10  is fixed on the module rail  2 , the plug-in module  5  can be inserted until the toothed edge  37  of the adapter  10  that forms the coupling element  23  comes in contact and cooperates with the coupling structure  26  in the form of the toothing  30 . In this case, the coupling between the adapter  10  and the circuit board holder  17  makes it possible to displace the plug-in module  5  in the inserting direction. However, the plug-in module  5  can only be pulled out of the mounting rack  1  after removing the screw  14  and the adapter  10 . 
     The foregoing description is of an exemplary and preferred embodiments employing at least in part certain teachings of the invention. The invention, as defined by the appended claims, is not limited to the described embodiments. Alterations and modifications to the disclosed embodiments may be made without departing from the invention. The meaning of the terms used in this specification are, unless expressly stated otherwise, intended to have ordinary and customary meaning and are not intended to be limited to the details of the illustrated structures or the disclosed embodiments.