Patent Publication Number: US-2010120266-A1

Title: Backplane To Mate Boards With Different Widths

Description:
TECHNICAL FIELD 
     The invention relates to the technical field of backplanes for electronic assembly magazines. 
     BACKGROUND 
     The hardware of electronic systems such as e.g. telecommunications systems comprises a number of circuit board assemblies. Based on the technology of today these boards are typically mounted in magazines having horizontal shelves.  FIG. 1  shows a magazine  101  with a top shelf  102 , a bottom shelf  103 , top rails  104  and bottom rails  105  and a backplane  106  with sockets  107 . When the circuit board assembly  108  is inserted in the magazine it is guided through the top and bottom rails towards a socket  107  mounted to the backplane. The circuit board assembly has a plug  109  at an edge portion of the circuit board assembly. The plug and socket are shown more in detail in the enlarged section C in  FIG. 1 . The rails are located in relation to the socket or sockets at the back plane such that the plug is guided to mate with the socket or sockets and thus establishing an electrical contact between the circuit board assembly and the backplane. The backplane includes electrical connections to allow for communications between the circuit board assemblies in the magazine and communications with other parts of the telecommunications system. 
       FIG. 2  shows how to arrange for further guidance of the circuit board assembly  108  towards the socket. The plug  201  is supplied with ribs  202  at each side which are adapted to mate with corresponding slots  203  at the inner side walls of the socket  204 . 
       FIG. 3  shows the backplane  301  with vertical stripes of sockets  302 . The enlarged section A shows the sockets  303  and connector pins  304 . 
     Backplane designs following different standards such as VME (Versa Module Eurocard), cPCI (Compact Peripheral Component Interconnect) and ATCA (Advanced Telecom Computing Architecture) have traditionally been designed with a fixed distance between the boards, e.g. 0.8 inch for VME and cPCI and 1.2 inch for ATCA. 
     The optimal board width varies depending on what&#39;s mounted on the board and the amount of power and cooling required. A simple interface board may only need a 10 mm slot, a CPU (Central Processing Unit) board can be fitted in a 15 mm slot, if PMC (Peripheral component interconnect Mezzanine Card) adapters are used 20 mm is more suitable, and for boards with AMC (Advanced Mezzanine Card) adapters 25 mm is needed. A slot is defined as the width required for a certain circuit board assembly. 
     When the backplane basic board width has been decided all board widths must be adapted to a multiple of this value, and regardless of what is chosen it will never be optimal for all designs. Different boards will not be able to coexist in the same magazine unless they are designed for the same basic board width. This basic board width is henceforth called the pitch for the backplane. If a pitch of 15 mm is chosen for a backplane this means that all boards belonging to the magazine with this backplane have to have a width being a multiple of 15 i.e. 15, 30, 45 . . . millimetres. 
     A sufficiently small pitch, such as 5 mm, may in theory be used to overcome this problem, but in practice the sockets needed to implement this design will be very narrow, and the number of connections to each possible board position, whether they are used or not, will be unnecessarily large. For practical reasons this solution is not useful. 
     Hence there is a need to accommodate circuit board assemblies with a greater flexibility in using different widths within the same magazine in order to accomplish efficient use of the magazine space available. 
     SUMMARY 
     It is therefore the objective of the invention to provide a backplane for a magazine, as well as a magazine and a method for arranging sockets, the backplane comprising a first backplane surface and an opposite second backplane surface, the backplane being equipped with sockets on the first backplane surface, the sockets having a number of contact points and are arranged to receive a mating plug, mounted at a rear edge of a circuit board assembly for establishing an electrical contact between the circuit board assembly and the backplane, the circuit board assembly having a certain width and having a first circuit board surface and an opposite second circuit board surface, both circuit board surfaces being perpendicular to the backplane, which can solve the problem to conveniently accommodate circuit board assemblies with different widths within the same magazine. 
     This object is achieved by a backplane where the sockets are arranged such as to accomplish rows of the contact points being perpendicular to the first circuit board surface and the second circuit board surface. 
     Instead of placing the backplane sockets in stripes parallel to the circuit board surfaces, mating one board per stripe, the idea is to position the stripes of sockets perpendicular to the circuit board surfaces and be able to mate boards with different widths to a wider or narrower part of one or several stripes in a flexible manner. Each circuit board assembly can have several plugs along a rear edge of the board, each plug mating with a stripe of sockets being perpendicular to the circuit board surfaces. 
     For telecommunications equipment the backplane may provide connections to for example:
         Redundant 48 V power supply   Redundant 10/100/1000 Mbps Ethernet for control and/or payload   One ore several redundant 10 Gbps Ethernet for payload   IPMI (Intelligent Platform Management Interface)       

     The list is not exhaustive. 
     Connections to different resources may be repeated with different intervals. Power needs to be available within every basic circuit board assembly width i.e. within the selected pitch, but  10  Gbps Ethernet can for most cases be limited to every second or every third pitch. This is an implementation decision within the scope of the invention. 
     A certain pitch has to be decided for each backplane and is fixed for each backplane. However the pitch defines the basic circuit board assembly width and hence the smallest width possible for the circuit board assembly. If a pitch of 5 mm is selected then the circuit board assemblies can have widths or slot sizes which are multiples of 5 mm, i.e. 5, 10, 15, 20 . . . and they can be mixed arbitrarily within the same magazine. 
     All available space within a magazine with a backplane with flexible slot size may be used efficiently regardless of how different board types are combined. This makes it possible to create compact solutions with a minimal infrastructure overhead such as power supplies, chassis and interconnections. 
     Further advantages are achieved if the invention also is given one or several of the characteristics of the dependent claims such as e.g.
         equal distance between contact points in a direction perpendicular to the circuit board surfaces   the contact points in the sockets are realized as male or female contacts   creating one or several stripes of sockets in a direction perpendicular to the circuit board surfaces and extending over part of the width of the backplane or along the full width of the backplane.   board positions for communication switch boards are allocated in the middle of the magazine   communication boards are according to Ethernet standard   the plugs have ribs, on each side perpendicular to the circuit board surfaces, which are adapted to mate with corresponding slots at inner sides of side walls of the sockets   power supply to the circuit board assembly is arranged by connecting two rows of connector pins with strips of a conductive material such as copper   IPMI (Intelligent Platform Management Interface) connection is arranged in a similar way as the power supply.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a perspective view of a prior art magazine 
         FIG. 2  schematically shows a plug and socket with guiding means according to prior art. 
         FIG. 3  schematically shows a perspective view of a backplane according to prior art. 
         FIG. 4  schematically shows a magazine with a backplane according to the invention. 
         FIG. 5  schematically shows a plug and socket with guiding means according to the invention. 
         FIG. 6  schematically shows a perspective view of a backplane according to the invention. 
         FIG. 7  schematically shows an arrangement for power supply distribution to the circuit board assemblies. 
         FIG. 8  schematically shows an example of how to allocate 10/100/1000 Mbps Ethernet connections. 
         FIG. 9  schematically shows an example of how to implement 10 Gbps Ethernet connections. 
         FIG. 10  schematically shows a method how to arrange sockets on a backplane. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will in the following be described in detail with reference to the drawings. 
     A backplane according to the invention is described in  FIG. 4  which shows a magazine  401  with a top shelf  402 , a bottom shelf  403 , top rails  404  and bottom rails  405  and a backplane  406  with sockets  407 . When a circuit board assembly  408  is inserted in the magazine it is guided through the top and bottom rails towards the socket  407  mounted to the backplane. The circuit board assembly has a plug  409  at an edge portion of the circuit board assembly. The plug and the socket are shown more in detail in enlarged section D in  FIG. 4 . The rails are located in relation to the socket or sockets at the back plane such that the plug is guided to mate with the socket or sockets and thus establishing an electrical contact between the circuit board assembly and the backplane. The circuit board assembly has a first circuit board surface  411  and an opposite second circuit board surface  412 . The backplane, which e.g. can be manufactured as a conventional Printed Circuit Board (PCB), includes electrical connections, in one or several layers, to allow for communications between the circuit board assemblies in the magazine and communications with other parts of the telecommunications system. The backplane can e.g. be manufactured by glass fibre reinforced epoxy, such as FR-4. 
       FIG. 5  shows how to arrange for further guidance of the circuit board assembly  408  towards the socket  504 . The plug  501  is supplied with ribs  502  at each side which are adapted to mate with corresponding slots  503  at inner side walls of the socket  504 . 
     The backplane  406  can have one or several stripes  410  of sockets  407  in a direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412 . The distance between the stripes is adapted to the needs for the intended application. The stripes can be located as close to each other as allowed by the physical design of the sockets. The distance between the plugs on the rear edge of the circuit board assembly has to be designed so as to fit into the socket locations on the backplane. 
       FIG. 6  shows the backplane  601  with stripes  602  of sockets  603  in a direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412 . The enlarged section B shows rows  605  of contact points  604 , in the direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412 . In this example the contact points are realized as connector pins. The enlarged section B also shows the sockets  603 , short ends  606  and side walls  607  and  608  of the socket  603 . The backplane has a width  611 , a first backplane surface  609  and an opposite second backplane surface  610 . 
     A practical basic circuit board assembly width or pitch, can be 5 mm. In the description connector points in the socket are henceforth exemplified with connector pins even if also female contact points may be used. The spacing between the connector pins, in a direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412 , must be adapted to the pitch. If the pitch is 5 mm the connector pin spacing can be 5/1=5.0 mm, 5/2=2.5 mm, 5/3=1.67 mm, 5/4=1.25 mm or 5/5=1.0 mm. Wider spacing may be desirable for power supply pins and closer spacing for data signals. The spacing between the connector pins, in the direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412 , within a socket/s or a stripe/s on the backplane is normally the same, i.e. the backplane has normally a fixed spacing between connector pins in this direction. The spacing between connector pins, in a direction parallel to the first circuit board surface  411  and the second circuit board surface  412 , within a socket is normally the same as the spacing in the direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412  but may also be different. Within a stripe of sockets the distance between connector pins, in the direction parallel to the first circuit board surface  411  and the second circuit board surface  412 , is usually constant but may also differ from socket to socket depending on how the magazine is equipped with different types of circuit board assemblies having different types of plugs. The thickness of the connector pins are typically the same within a stripe of sockets but may vary from row to row and socket to socket. 
     The magazine has a number of possible board positions depending on the selected pitch. If a magazine has an effective width of 300 mm and a pitch of 5 mm, the magazine has 60 possible board positions. If the magazine is equipped only with circuit board assemblies with a width of 10 mm, the magazine can hold 30 boards, each board taking up two positions. 
     The backplane normally has two redundant predefined locations reserved for communication switch boards, henceforth exemplified with Ethernet, to provide connectivity within the magazine, just like any other modern fixed slot size backplane. Ethernet is a common communication protocol used in the ATCA standard (Advanced Telecom Computing Architecture). However other communication protocols as e.g. PCI Express (Peripheral Component Interconnect) or RapidIO may be used. The predefined locations for the Ethernet switch boards are in the middle of the magazine according to the ATCA standard. Other standards can have other predefined Ethernet switch board positions. If an Ethernet board with a width of 15 mm is used and the backplane has a pitch of 5 mm, each Ethernet board will take up three board positions of the magazine. 
     Each position is identifiable by means of a unique bit pattern. This could be achieved by coding a binary, parity checked, data word at each possible board position of the backplane by using a combination of a number of grounded and ungrounded connector pins, unique for each board position. 
     Each board within a magazine should receive an input with information about the number of board positions, counted from one side of the magazine, which have been used. Each board should also forward information to the next one about which board positions it has used itself, i.e. increment the received number by one, or possibly more in case of a complex board which utilizes more than one board position. If the backplane contains a control bus, such as IPMI (Intelligent Platform Management Interface), it could be used to transfer this information. 
     Unused board positions should need no external electrical terminations, and the connection information should be passed through such slots passively. 
     The mechanical guide rails for the circuit boards assemblies must have the same spacing as the backplane pitch. Special consideration should be taken when designing this to allow adequate air flow for cooling to pass through them. The rails and the top and bottom shelves can e.g. be perforated. 
       FIG. 7  shows how the power supply to the circuit board assemblies in the magazine can conveniently be arranged by connecting two rows  701  and  702  of connector pins  703  with broad strips  704  and  705  of a conductive material as e.g. copper, each strip connecting one row of connector pins. 
     The communication internally within the magazine and externally can be arranged through e.g Ethernet, PCI Express (Peripheral Component Interconnect) or RapidIO. Each circuit board assembly  408  normally has a connection to a communication means here exemplified by Ethernet. Some circuit boards might only pick up power supply from the backplane and external communication is arranged by means of connectors at the front panel of the circuit board assembly. In order to save connector pins, various solutions are possible. The solutions are based on that not all possible board positions have available Ethernet connections. A standard Ethernet connection for 10/100/1000 Mbps (Megabits per second) requires 8 contact pins on the socket. A 300 mm magazine with 5 mm pitch has 60 board positions. If an Ethernet connection should be available at each position it would require 60×8=480 connector pins only for Ethernet connections. 
     Another way is to use the information about the number of boards and the average widths of the boards together with the physical position and use this to select one connection out of several available at each position. In this case a selected number of connections are available for the whole magazine, and as long as not all narrow boards are placed to one side and all wide boards to the other side it will be possible to select a separate connection for each used board position.  FIG. 8 , which can be imagined to extend further to the right, shows 13 board positions  801 - 813 , each board position has a width of 5 mm, i.e. the pitch is 5 mm. Each square  814  at a board position has 8 connections. With a connector pin distance of 5/4=1.25 mm, the pins can be arranged in two rows with 4 pins/row. The squares are arranged in a matrix in an x/y plane defined by coordinate symbol  815 . Squares ⅓-4/3 has access to an Ethernet  1  connection, ½-4/2 Ethernet  2 , 1/1-4/1 to Ethernet  3  and so on. If 10 mm boards are used they will require two board positions each. Board nr  1  will require board position  1  and  2  and can use Ethernet  1 , board nr  2  requires positions  3  and  4  and can use Ethernet connection nr  2  and so on. Board nr  5  will use positions  9  and  10  and Ethernet 5. When it comes to board nr  6  it will not find a free Ethernet connection as can be seen in  FIG. 8 . Board nr  6  has to have a width of 15 mm to be able to pick up Ethernet connection nr  6 . This solution will limit the flexibility for Ethernet connections but it will save connector pins needed and it will have sufficient flexibility for most practical applications when boards of different widths are mixed. This is just an illustration of one possible solution. Many other solutions are of course possible within the scope of the invention. 
     10 Gbps (Gigabits per second) Ethernet could be implemented similarly to 10/100/1000 Mbps Ethernet.  FIG. 9  shows the same 10 Gbps Ethernet port connected to two adjacent positions, and three boards of different widths use one Ethernet port each.  FIG. 9  also shows  7  board positions  901 - 907 , each position of 5 mm width. Each square  908  has 16 connector pins which is required for 10 Gbps when 10 Gbase CX-4 standard is used. Board no  1  has a width of 10 mm, distance  909 , and can use 10G no  1 , board  2  has a width of 15 mm, distance  910 , and can use 10G no  2 , board  3  has a width of 10 mm, distance  911 , and can use 10G no  3 , and so on. (10 Gbase-T standard only requires  8  connector pins but has other limitations) 
     The IPMI (Intelligent Platform Management Interface) standard defines a set of common interfaces used to monitor system status and to manage the system. IPMI is a multidrop I 2  C (Inter-integrated circuit) based architecture and could easily be implemented in the same way as the power supply as described in association with  FIG. 7  above. In this case the conductive strips can be made narrower as very low power is needed. 
     If circuit board assemblies, designed for use with a backplane with stripes of sockets in the direction parallel to the first circuit board surface  411  and the second circuit board surface  412 , is desired to be used together with the backplane according to the invention this can be solved by increasing the depth of the magazine and insert an adapter between the circuit board assembly and the backplane. The adapter contains logics and mechanical adjustments needed for the conversion. 
       FIG. 10  schematically illustrates a method of arranging  1001  sockets on a backplane. The sockets are mounted  1002  short end to short end with side walls aligned  1003  in the direction perpendicular to the first circuit board surface  411  and the second circuit board surface  412  thus creating at least one stripe of sockets in the direction perpendicular to the first circuit board surface  411  and the second surface board surface  412 . The stripe can extend along the full width  611  of the backplane or part of the width  611  of the backplane. 
     The invention has been described for applications within the telecommunications field but can e.g. also be used within the field of computers and any other field within electronics where there is a need for a backplane to connect a number of circuit board assemblies. 
     The invention is not limited to the embodiments above, but may vary freely within the scope of the appended claims.