Abstract:
Disclosed herein is a system for mounting circuit boards in a computer bay, comprising: a plurality of distinct rails fastenable within a common base board to enable receipt of differently sized circuit boards. Further disclosed herein is a method of mounting circuit boards to a base board, comprising: identifying a particular rail from a plurality of rails that are compatible with a common base board, said identified rail being receptive to a target circuit board; engaging the target circuit board with the rail and causing electrical connection of the circuit board with the base board.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The disclosed invention relates to a method and apparatus for modular electronic equipment. More particularly, it relates to methods and apparatus for selectively mounting and securing circuit cards and guide rails within electronic equipment.  
         [0002]     Modular construction techniques are widely used to manufacture a variety of electronic equipment. For example, manufacturers of computer equipment use modular construction techniques extensively. With modular techniques, a manufacturer can economically and expeditiously assemble several variations of an electronic device using different combinations of preassembled modular circuits. Additionally, vendors may routinely assemble electronic systems from basic units at a point of sale. Further, end users are usually capable of reconfiguring and/or upgrading modular electronic systems with little effort. In most instances, replacing and/or adding modular electronic circuits in a system requires no more than a simple screwdriver and minimal mechanical skill.  
         [0003]     For instance, a conventional personal computer (PC) system generally comprises arrays of prefabricated electronic components mounted on printed circuit boards (PCBs), to form combinations of PCB assemblies. PC manufacturers typically mount a variety of PCB assemblies on a common chassis, along with other components, to form a basic but often incomplete version of a final PC system. Then, in response to a customer request for a particular model having specific capabilities, a manufacturer or vendor adds one or more PCB assemblies and other components to the basic version to produce the appropriate configuration for the model requested. Later, the customer may wish to personally augment the capabilities of or upgrade the PC system. In that case, the manufacturer could provide the customer with the appropriate option cards, which the customer would self-install.  
         [0004]     More specifically, a PC, an embedded computer or other modular system usually contains a main circuit board assembly, called a motherboard, or base board, which typically comprises a relatively large PCB on which many of the device&#39;s main components mount. The base board normally mounts on a chassis, which often forms a part of an outer casing or a computer bay that encloses the system components. Finally, unused card connectors and supports, which are equipped to accept certain option cards to be installed at some future time, are also located in a basic system. These unused connectors and supports are ordinarily associated with circuit card guide rails that help installers insert option cards quickly and accurately in their proper locations within the system.  
         [0005]     Card guide rails that are attached to the base board are made to accept a card of a particular width. Alternate cards may be manufactured that have different widths and are therefore not dimensionally compatible with the card guide rails.  
         [0006]     Accordingly there is a need in the art to improve the interchangeability of different card sizes within a specific base board.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     Disclosed herein is a system for mounting circuit boards in a computer bay, comprising: a plurality of distinct rails fastenable within a common base board to enable receipt of differently sized circuit boards.  
         [0008]     Further disclosed herein is a method of mounting circuit boards to a base board, comprising: identifying a particular rail from a plurality of rails that are compatible with a common base board, said identified rail being receptive to a target circuit board; engaging the target circuit board with the rail and causing electrical connection of the circuit board with the base board. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:  
         [0010]      FIG. 1  depicts a perspective view of a base board assembly in accordance with an embodiment of the invention;  
         [0011]      FIG. 2  depicts a top view of a carrier board of an embodiment of the invention;  
         [0012]      FIG. 3  depicts a partial side view of a peripheral component interface mezzanine card (PMC) assembled to a carrier board and positioned relative to a base board in accordance with an embodiment of the invention;  
         [0013]      FIG. 4  depicts a partial side view of a guide rail supporting the carrier board of  FIG. 3  relative to a base board;  
         [0014]      FIG. 5  depicts a partial front view of the guide rail, carrier board and base board of  FIG. 4 ; and  
         [0015]      FIG. 6  depicts a partial front view of a second carrier board and base board in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring to  FIG. 1 , a base board assembly  10  may be used in a personal computer (PC), embedded computer or any other computer platform and is mounted within a computer bay (not shown). A base board  18  forms the main circuit board of the base board assembly  10  and supports a plurality of electrical components such as integrated circuit  14  for example as well as cable connectors, switches, display lights, etc. (not shown). An electrical connector  22  supplied on the base board  18  allows for electrically connecting optional carrier circuit boards  26 , for example, to expand the capabilities of a basic computer system. Several standards exist for these connectors  22 , often referred to as bus connectors, such as: Advanced Mezzanine Card Base Specification (PICMG AMC.0) and Peripheral Component Industry Standard Architecture (PCI-ISA) Passive Backplane Standard (PICMG 1.0), for example. The standards for these bus connectors define the dimensional requirements as well as the electrical requirements for the mating connectors that plug into them, such as connector  34  shown on the carrier board  26 .  
         [0017]     The carrier boards  26  serve as adaptors for adapting the input and output of the standardized connectors  22  with standard circuit boards known as mezzanine cards  42 . Several mezzanine card standards exist that define the dimensional requirements for the mezzanine card  42  and the carrier boards  26  as well as for the electrical requirements for them. The following mezzanine card standards will be used as examples in more detail below: Peripheral Component Interface Mezzanine Card (PMC) and Advanced Mezzanine Card (AMC). Mezzanine card standards allow manufacturers to produce, and for customers to purchase generic mezzanine cards  42  with confidence that the mezzanine cards  42  will be compatible as long as the standards are followed. The use of generic mezzanine cards  42  allows computer manufacturers to keep costs lower than if they had to custom design and manufacture such cards.  
         [0018]     Since carrier boards  26  are frequently assembled to the base boards  18  by relatively unskilled people, it is important that the assembly process be as mistake-proof as possible, and that the resulting assembly be robust. Therefore, guide rails  30  are used to align the carrier boards  26  such that the electrical connector  34  of the carrier board  26  is properly aligned with the electrical connectors  22  on the base board  18  prior to and after their mating. The guide rails  30  also support and retain the carrier boards  26  relative to the base board  18  to assure that the connectors  22  and  34  do not move relative to each other, since such movement could result in momentary open circuits which may cause malfunction of the computer system including crashing the system and the potential loss of unsaved data.  
         [0019]     The dimensions of mezzanine cards  42  and the associated carrier boards  26 , as specified by the standards associated with each mezzanine card  42 , create problems of proper fit of the carrier boards  26  with the guide rails  30 . For example, if a carrier board is wider than the width provided by the guide rails  30 , the carrier board  26  will not assemble to the base board  18 . Embodiments of the invention to overcome such conditions will be described below.  
         [0020]     Referring to  FIGS. 2 and 3 , a first carrier board  78  (top) assembled to a PMC  50  (bottom) is shown. The PMC  50  has stand-offs  54  that hold the first carrier board  78  a specified distance apart from the PMC  50 . Screws  58  thread into holes in the stand-offs  54  through holes in the first carrier board  78 . Circuit components can be mounted to both sides of both boards  78  and  50  as long as they stay within predefined volumes specified by the published PMC and AMC standards. The AMC standards call for a component free zone  62  along the length of each side of the card to be at least 2.0 mm. This component free zone  62  provides a margin for safety from handling damage for the components, as well as, assuring available space for the guide rails  30  to interface with the edges of the boards  78 .  
         [0021]     A bridge circuit  66  is used to adapt a peripheral component interface bus  70  of the PMC  50  to a male peripheral component interface bus  74  located on the end of the first carrier board  78 , so that it is compatible with a female peripheral component interface bus  86  of the connector  22 .  
         [0022]     Referring now to  FIG. 4 , a right side view of the assembly of  FIGS. 2 and 3  are shown with the addition of a first right guide rail  106  that is holding the first carrier board  78  relative to the base board  18 . The first right guide rail  106  is fastened to the base board  18  by fasteners which are illustrated in this embodiment as screws  90 . The screws  90  are threadably engaged in fastener receptacles illustrated here as holes  94  in the guide rail  106  through holes  98  in the base board  18 . A center distance  102  between the base board fastener receiving features illustrated here as holes  98 , may be standardized to facilitate ease of design and manufacture of various guide rails  30  and various base boards  18 .  
         [0023]     Referring to  FIG. 5 , a front view of the assembly of  FIG. 4  is shown with the first right guide rail  106  and a first left guide rail  110  holding the first carrier board  78  to the base board  18  with screws  90 . The guide rails  106 ,  110  are designed and made to form a rail gap width  118 , thereby serving as a circuit board engaging feature to frictionally engage the outer lateral edges  122 , which form the width of the first carrier board  126 . The width of the first carrier board  126  is 77.0 mm in accordance with the PMC  50  width as specified in the PMC standards. If the center-to-center distance  130  of the holes  98  in the base board  18  is 94.0 mm, (an arbitrary dimension chosen by the computer manufacturer) then the guide rails  106 ,  110  each need an offset dimension  134  of 10.0 mm. That is, the distance from the center of the hole  94  to a first contact surface  138  of the guide rails  106 ,  110 , needs to be 10.0 mm. Thus, when guide rails  106  and  110  are screwed to the base board  18 , through holes  98 , preformed in the base board  18 , the guide rails  106 ,  110  will be in the proper location to frictionally engage the carrier board  78  during and after installation to the base board  18  and connector  22 .  
         [0024]     There are a variety of other dimensions associated with the alignment and support of the first carrier board  78  with the base board  18 , however, they may remain constant when changing between different mezzanine cards  42  and are therefore not pertinent to embodiments of the invention and are not described here in more detail.  
         [0025]     Referring now to  FIG. 6 , a front view, similar to that of  FIG. 5 , for an AMC is depicted. The AMC standards specify a card width of 72.9 mm, as opposed to the PMC width of 77.0 mm. Thus, a second carrier board  150  with a width of 72.9 mm between second lateral edges  154  is utilized with AMC  158 . Since the same base board  18  is utilized, the center-to-center distance  130  of the holes  98  in the base board  18  remain 94.0 mm apart. Therefore, guide rails  106  and  110  with rail gap width  118  of 77.0 mm will not frictionally engage the second lateral edges  154  of the second carrier board  150  due to the 1.1 mm narrower width of the second carrier board  150 , and are therefore not adequate to be utilized with the second carrier board  150 . In accordance with an embodiment of the invention a second right guide rail  162 , and a second left guide rail  166 , are used to accommodate the second carrier board  150 . A second guide rail offset dimension  170 , of 10.55 mm, between the center of hole  94  and second contact surface  172 , is used on guide rails  162  and  166  in order to create a necessary rail gap width  174  of 72.9 mm, thereby serving as a circuit board engaging feature, which matches the width of the second carrier board  178  in accordance with the AMC standards.  
         [0026]     It should be appreciated by one skilled in the art that other guide rails in accordance with embodiments of the invention may permit an infinite number of unique carrier board widths to be utilized with a single base board.  
         [0027]     Additionally, embodiments of the invention permit the identification of guide rails from a variety of guide rails. To properly engage a specific circuit board with a common base board. Such identification involving finding guide rails that have a specific offset dimension that results in a frictional engagement between the lateral edges of a carrier board with contact surfaces of the guide rails.  
         [0028]     Advantages of embodiments of the invention may include: proper fit of guide rails with any carrier board, ease of assembly of guide rails to base boards and flexibility to use an infinite variety of circuit board widths with a common base board.  
         [0029]     While the embodiments of the disclosed method and system have been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the embodiments of the disclosed method and system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiments of the disclosed method and system without departing from the essential scope thereof. Therefore, it is intended that the embodiments of the disclosed method and system not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the embodiments of the disclosed method and system, but that the embodiments of the disclosed method and system will include all embodiments falling within the scope of the appended claims.