Abstract:
An electronic circuit unit for use in an electronic equipment cabinet. The electronic circuit unit has first and second opposite main walls including EMI absorbing material and a motherboard frame between the main walls, the motherboard frame including a plurality of wall segments also including EMI absorbing material. A motherboard is mounted in the motherboard frame by a first locating retainer. The first locating retainer positions the motherboard such that it resides between the main walls of the electronic circuit unit. A signal-processing module forming at least a portion of the first main wall is removably mounted to the motherboard frame by a second locating retainer. The signal-processing module connects with the motherboard through an electrical connector having mating parts. The first and the second locating retainers are positioned relative to one another to allow the mating parts to align and mate when the signal processing module is fastened to said motherboard frame.

Description:
This application is a Division of Ser. No. 09/987,041 filed Nov. 13, 2001, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to assembly and packaging of signal processing devices, in particular to an electronic circuit unit that provides EMI shielding, is simple to assemble and provides good structural integrity. 
     BACKGROUND OF THE INVENTION 
     Devices used in communication networks, such as routers or switches to name a few, are constructed as cabinets with a bay where a plurality of standard size electronic circuit units are inserted. The electronic circuit units all connect to a main circuit board, such as a backplane or a midplane, through which data is transferred from each electronic circuit unit to other components. 
     Electronic circuit units that are currently available suffer from a number of drawbacks. The most significant ones are complexity of assembly and poor structural integrity, which translates into poor connector alignment tolerances for components within the unit or between the unit and the main circuit board of the cabinet. 
     Against this background there exists in the industry a need to provide an electronic circuit unit that is relatively simple to assemble and at the same time provides good structural integrity. 
     SUMMARY OF THE INVENTION 
     In one broad aspect, the invention provides an electronic circuit unit for use in an electronic equipment cabinet. The electronic circuit unit has first and second opposite main walls including EMI absorbing material and a motherboard frame between the main walls, the motherboard frame including a plurality of wall segments also including EMI absorbing material. 
     A motherboard is mounted in the motherboard frame by a first locating retainer. The first locating retainer positions the motherboard such that it resides between the main walls of the electronic circuit unit. A signal-processing module forming at least a portion of the first main wall is removably mounted to the motherboard frame by a second locating retainer. The signal-processing module connects with the motherboard through an electrical connector having mating parts. The first and the second locating retainers are positioned relative to one another to allow the mating parts to align and mate when the signal processing module is fastened to said motherboard frame. 
     This electronic circuit unit is advantageous for a number of reasons. First, the electronic circuit unit is easier to assemble by virtue of the motherboard frame to which the motherboard is directly mounted. Secondly, the structural integrity of the electronic circuit unit is enhanced. 
     In one specific and non-limiting example of implementation, the motherboard frame is generally rectangular and made of metallic material. Both main walls are removably fastened to the motherboard frame by respective locating retainers. An optional feature that enhances the cooling capacity of the electronic circuit unit is to provide each main wall with a heat sink and to thermally couple the two main walls through the motherboard such that heat generated by a component associated to one of the main walls can be transferred to the other main wall. 
     In a second broad aspect, the invention provides a motherboard frame for an electronic circuit unit. The motherboard frame has a plurality of wall segments including EMI absorbing material and arranged in a plane of reference, the wall segments circumscribing a void area having first and second opposite open sides. The wall segments have first, second and third locating devices spaced from one another in a direction that is transverse to the plane of reference. The first locating device is capable of receiving a planar motherboard and placing the motherboard in the motherboard plane, parallel to the plane of reference and in a predetermined position between the second and third locating devices. 
     In a third broad aspect, the invention provides a combination including a motherboard frame and a motherboard. The motherboard frame has a plurality of wall segments including EMI absorbing material and arranged in a plane of reference, the wall segments circumscribing a void area having first and second opposite open sides. At least some of the wall segments carry first, second and third locating devices that are spaced from one another in a direction that is transverse to the plane of reference. The motherboard is generally planar and it has an outline generally corresponding to the outline of the void area such as to allow the motherboard to be mounted in the motherboard frame. The first locating device is capable of receiving the planar motherboard and locating the motherboard parallel to the plane of reference and in a predetermined position between the second and third locating devices. The second locating device and the outline of the motherboard have respective geometrical configurations such that the motherboard can be inserted in the motherboard frame from one of the open sides without interference from the second locating device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of examples of implementation of the present invention is provided hereinbelow with reference to the following drawings, in which: 
     FIG. 1 is a perspective view of an electronic equipment cabinet; 
     FIG. 2 is a front perspective view of an electronic circuit unit for installation in the electronic equipment cabinet shown in FIG. 1; 
     FIG. 3 is a rear perspective view of the electronic circuit unit shown in FIG. 2; 
     FIG. 4 is an exploded perspective view of a motherboard frame of the electronic circuit unit and of a motherboard for insertion in the motherboard frame; 
     FIG. 5 is an exploded view of the electronic circuit unit showing the mounting of electronic processing modules that form one of the main walls of the electronic circuit unit; and 
     FIG. 6 is an exploded view of the electronic circuit unit showing the mounting of a heat sink panel forming the other main wall of the electronic circuit unit. 
    
    
     In the drawings, embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for purposes of illustration and as an aid to understanding, and are not intended to be a definition of the limits of the invention. 
     DETAILED DESCRIPTION 
     FIG. 1 illustrates an electronic equipment cabinet  10 . The cabinet  10  has a frame that defines a bay  11  receiving standardized electronic circuit units  12 . The electronic circuit units  12  are shaped as rectangular boxes that slide in the bay  11  and electrically connect with a main circuit board  14 . The main circuit board  14  may be in the form of a back plane, in the form of a mid plane or under any other suitable configuration without departing from the invention. 
     The function performed by the electronic equipment cabinet  10  is in itself of little importance to the present inventive concept. Accordingly, this function can widely vary without departing from the invention. In one example of implementation, the electronic equipment cabinet  10  is a router. Data transport media (not shown), such as optical fibers connect to couplers  16  on the individual electronic circuit units  12 . The individual electronic circuit units  12  perform the necessary data processing on data received from the data transport media or sent on the data transport media. Data can be exchanged internally from any one of the electronic circuit units  12  to another electronic circuit unit  12  or a different device through the main circuit board  14 . 
     With reference to FIGS. 2 and 3, the electronic circuit unit  12  includes a rectangular motherboard frame  18 . The motherboard frame  18  has a plurality of wall segments all situated in an imaginary plane of reference. The wall segments include a front wall  20 , a rear wall  22 , a top wall  24  and a bottom wall  26 . Two main walls  28  and  30  are attached to the motherboard frame  18  to complete the unit  12 . The main walls  28  and  30  are parallel to the plane of reference of the motherboard frame  18 . 
     The motherboard frame  18  includes a guide for locating the electronic circuit unit  12  in the cabinet  10 . In one form of implementation, the guide includes a pair of grooves  32  formed on the top wall  24  and on the bottom wall  26  (the grooves on the bottom wall are not shown in the drawings). As it can be seen in FIG. 1, the grooves  32  mate with corresponding projections  34  when the electronic circuit unit  12  is inserted in the bay  11 . The grooves  32  and the projections  34  form a registration device allowing to precisely position the electronic circuit unit  12  in the bay  11 . The reader will appreciate that a wide variety of mechanical structures can be used to provide a suitable registration device for use with this invention. 
     The rear wall  22  includes a passage  36  for receiving an electrical connector allowing establishing an electrical connection between the electronic circuit unit  12  and the main circuit board  14 . In a specific and non-limiting example of implementation, such electrical connector includes two mating parts: one formed on the electronic circuit unit  12  and the other on the main circuit board  14 . When the electronic circuit unit  12  is inserted in the bay  11 , the registration device keeps the mating parts in alignment such that when the electronic circuit unit  12  reaches the main circuit board  14 , the mating parts will engage one another and complete the electrical connection. For reference, FIG. 1 shows at  38  the location of the connector parts on the circuit board  14  that mate with connector parts on respective electronic circuit units  12 . 
     With reference to FIG. 4, the motherboard frame  18  is integrally formed from metallic material that provides electromagnetic interference (EMI) shielding. The motherboard frame  18  receives a motherboard  40  therein. More specifically, the motherboard frame  18  defines a void area dimensioned to accurately match the outline of the motherboard  40 . The motherboard  40  is inserted in this void area through one of the open sides of the motherboard frame  18  and retained to the motherboard frame  18  by a locating retainer. In particular, the electronic circuit unit  12  has three such locating retainers. There is one locating retainer for the motherboard  40 , one for the main wall  28  and one for the main wall  30 . Each locating retainer is comprised of a locating device and of a fastening device. The locating device positions the component (motherboard  40 , main wall  28  or  30 ) in a predetermined position with respect to the motherboard frame  18 , while the fastening device locks the component in place. 
     The inner sides of the walls  20 ,  22 ,  24  and  26  (the sides facing the void area) include a projection  42  that is continuous along the periphery of the motherboard frame. The projection  42  integrates the locating devices used to position the motherboard  40  and the main walls  28  and  30 . Specifically, the projection  42  defines a locating device  44  in the form of a rib located intermediate the lateral edges of the projection  42 . The projection  42  also defines two other locating devices  46  and  48  formed by the lateral edges of the projection  42 , respectively. Thus, the locating devices  44 ,  46  and  48  are spaced from one another along a direction that is transverse the plane of reference of the motherboard frame  18 . 
     The motherboard  40  is installed in the motherboard frame  18  by inserting it through the open side of the motherboard frame marked A in FIG.  4 . The outline of the motherboard  40  and the locating device  48  are such that the motherboard  40  will clear the locating device  48  and then abut against the locating device  44 . Screws (not shown) are inserted through apertures  52  in the motherboard  40  and threadedly engaged into tapped bores  54  on the projection  42 . The screws form the fastening device of the locating retainer for the motherboard  40 . It will be plain to a person skilled in the art that fastening devices other than screws can be used without departing from the spirit of the invention. 
     FIG. 5 illustrates the installation of the main wall  28 . That main wall  28  is comprised of a plurality of signal processing modules  56  placed side-by-side that form the main wall  28 . Alternatively, the main wall  28  can be formed by a single signal-processing module, by two signal-processing modules or by more than three signal-processing modules. Each signal-processing module  56  includes opto-electronic signal-processing circuitry  57  mounted to a heat sink  58  in the form of parallel fins. The heat sink  58  is made of metallic material and provides EMI shielding. The signal processing circuitry  57  is housed in a casing dimensioned to clear the locating device  46  when the signal-processing module  56  is mounted to the motherboard frame  18 . The heat sink  58  has a laterally projecting flange  60  that abuts against the locating device  46 . Screws (not shown) secure the signal-processing module  56  to the motherboard frame  18 . The screws are received in tapped bores  62  on the motherboard frame and corresponding slots  64  on the flange  60 . 
     For added support, transverse bars (not shown in the drawings) can be placed across the motherboard frame  18 , extending from the front wall  20  to the rear wall  22 . The bars are located at a juncture between two signal-processing modules  56  such as to provide the motherboard frame  18  with additional load bearing capability in the area where two adjacent signal-processing modules  56  meet. The transverse bars also provide a surface on which an EMI gasket (of a type known in the art) can be applied allowing closing gaps between adjacent signal-processing modules  56 . 
     At least one of the signal processing modules  56  electrically connects with the motherboard  40 . This is effected via an electrical connector (not shown) having two mating parts, one part being formed on the motherboard  40  and one part on the signal-processing module  56 . The locating device  46  serves to position the signal-processing module  56  such that both mating parts of the connector are aligned and will mate when the signal-processing module  56  is fully inserted in the motherboard frame  18 . 
     The installation of the main wall  30  is shown in FIG.  6 . The main wall  30  is a unitary component, however it can be formed as an assembly of smaller components without departing from the spirit of the invention. The main wall  30  includes a heat sink  58  in the form of parallel fins made of metallic material to provide EMI shielding. Optionally, electronic or optical components can be secured to the heat sink  58 . If desired, those components can connect with the motherboard  40  or with other elements of the electronic circuit unit  12 . 
     When the main wall  30  is closed, the electronic circuit unit  12  forms a structure that is completely enclosed by panels including EMI absorbing material to provide effective EMI shielding for internal components. 
     Optionally, the electronic circuit unit  12  has a thermal coupling between the main walls  28  and  30  to allow heat produced by a component mounted to one of the main walls to transfer at least some part of the heat to the other main wall. This feature enhances the cooling capacity of the electronic circuit unit  12 . In a specific example of implementation, two such thermal couplings are provided, one for each of the two lower signal-processing modules  56  (there is no such thermal coupling for the upper signal-processing module  56 ). 
     As shown in FIG. 6, the motherboard  40  is provided with passages  69  to accommodate the thermal couplings. The thermal couplings include material extending transversally from one main wall to the other main wall to provide a pathway over which thermal energy can travel efficiently. In the example shown in FIG. 6, the casing  57  of the two lower signal-processing modules  56  has a projection  70  that is received in the respective passage  69 . The projection  70  holds one or more heat-generating components from the signal-processing module  56 . In one form of implementation, the projection  70  is long enough such as to make physical contact with the main wall  30  when the main wall  30  is mounted to the motherboard frame  18 . Alternatively the main wall  30  includes a projection (not shown) that is aligned and engages the projection  70  when the main wall  30  is mounted to the motherboard frame  18 . Yet another possibility is to provide on the main wall  30  apertures through which fluid heat conductive material is injected to complete the thermal pathway from the projection  70  to the main wall  30 . This fluid heat conductive material is known to those skilled in the art. The material is in the form of a paste that can be injected in the motherboard frame and when it sets it provides an efficient thermal transfer. 
     Although various embodiments have been illustrated, this was for the purpose of describing, but not limiting, the invention. Various modifications will become apparent to those skilled in the art and are within the scope of this invention, which is defined more particularly by the attached claims.