Abstract:
A technique for installing circuit cards on a motherboard in an electronic device. A motherboard, having a plurality of keyhole apertures and locking apertures, mounts in the electronic device. Cardguide pairs mount on the motherboard to form expansion ports for receiving circuit cards. Each cardguide pair has two parallel card guides. Each card guide has an elongated body with a bottom member and a longitudinal groove. Entrance ports and ramps located at either end of the body communicate with the groove. Mushroom mounting lugs and resilient locking hooks mount on the bottom member. A cardguide installer places each card guide on the motherboard while passing each mushroom lug into a wide segment of a keyhole aperture. The installer then slides the card guides parallel to the plane of the motherboard to move the mushroom lugs into a narrow segment of the keyhole apertures, while the hooks couple to the locking apertures.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to techniques of assembling modular electronic equipment. More particularly, it relates to methods and apparatus for selectively mounting and securing card guides within electronic equipment. 
     2. Description of the Prior Art 
     Modular construction techniques are widely used to manufacture a variety of electronic equipment. For example, manufactures 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. 
     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. 
     More specifically, a PC, a peripheral device or other modular system usually contains a main circuit board assembly, called a motherboard, which typically comprises a relatively large PCB on which many of the device&#39;s main components mount. The motherboard normally mounts on a chassis, which often forms a part of an outer casing that encloses the system components. In addition, a basic system usually includes other components that mount on the chassis and connect to the motherboard. 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 special card guides that help installers insert option cards quickly and accurately in their proper locations within the system. 
     Manufacturers normally mount card guides on strong, rigid members, such as the walls of a sheetmetal chassis. One common card guide has a plastic body and resilient mounting lugs with barbs that protrude from the bottom surface of the body. When installing these card guides, an installer begins by drilling appropriate mounting holes at suitable locations on a rigid structure. Next, the installer aligns the card guide so that the mounting lugs mate with the drilled holes. Finally, the installer presses on the card guide or strikes the guide with a hammer or other tool until the lugs snap into the holes. 
     To enhance the physical construction of some modular equipment and further simplify the instillation of option cards, it has been suggested that some option cards be piggybacked on a motherboard. Consequently, efforts are underway to develop techniques for mounting card guides directly on a fully populated motherboard. Although prior art techniques for mounting card guides have served their intended purpose, they have proved to be unreliable when used to install card guides on the relatively thin, flexible and delicate structure of an ordinary motherboard. Thus, manufacturers have rejected proposals to use the conventional card guides and the installation techniques described above. Manufacturers have found that the insertion forces exerted on a motherboard, as a result of snapping the barbed mounting lugs into their mounting holes, frequently flex and damage etched conductors and other components located on an ordinary motherboard. 
     SUMMARY OF THE INVENTION 
     The present invention solves this problem in the art by providing reliable techniques for installing card guides directly on a populated circuit board. One aspect of the present invention includes a card guide having an elongated body with a top member, a bottom member and a longitudinal open groove. An entrance port, located at one end of the body, communicates with the groove. At least one mounting lug is fixed to the bottom member while a guide fastener projects from the body. The mounting lug and the guide fastener enable the card guide to be fixed to a populated circuit board while retaining the structural and functional integrity of the circuit board. 
     Another aspect of the invention involves an apparatus for holding circuit cards in an electronic device. The apparatus includes a circuit board having a plurality of mounting holes. At least one cardguide pair mounts on the circuit board. Each cardguide pair has first and second parallel card guides with each card guide having an elongated body with a top member, a bottom member and a longitudinal open groove. An entrance port, located at one end of the body, communicates with the groove. At least one mounting lug is fixed to the bottom member and mates with a mounting hole. A guide fastener projects from the body and couples to a locking hole in the circuit board. 
     Still, another aspect of the invention includes a method of installing a card guide on a circuit board. The method includes the following steps: forming the card guide with an elongated body having at least one mounting lug projecting from the body and a guide fastener fixed to the body; forming at least one mounting hole in the circuit board with each mounting hole having a first hole segment and a second hole segment, the first hole segment being larger than said second hole segment and the mounting lug; forming at least one locking hole in the circuit board; placing each card guide on the circuit board while passing the mounting lug into the first hole segment; and moving each card guide with respect to the circuit board in a direction parallel to the plane of the circuit board to move the mounting lug from the first hole segment to the second hole segment, and to mate the guide fastener with the locking hole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded pictorial view of a modular electronic device showing an installed option card piggybacked on a motherboard in accordance with the present invention; 
     FIG. 2 is a side elevation of a righthand card guide in accordance with the present invention; 
     FIG. 3 is a top view of the righthand card guide illustrated in FIG. 2; 
     FIG. 4 is a bottom view of the righthand card guide illustrated in FIG. 2; 
     FIG. 5 is an enlarged cross section taken on the line 55 of FIG. 2 and looking in the direction of the arrows; 
     FIG. 6 is an enlarged cross section taken on the line 66 of FIG. 2 and looking in the direction of the arrows; 
     FIG. 7 is a cross section, with parts broken away, taken on the line 77 of FIG. 5 and looking in the direction of the arrows; 
     FIG. 8 is a pictorial view of a PCB in accordance with the present invention; and 
     FIG. 9 is an exploded pictorial view, with parts broken away, illustrating the installation of a card guide pair on a PCB in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, FIG. 1 depicts modular electronic device 10, which may be a PC, a peripheral device (e.g., a modem), or other modular electronic system. Device 10 includes motherboard 11, chassis 12, cover 13 and similarly shaped circuit cards 15A and 15B. Motherboard 11 comprises PCB 18, on which card connectors 14 and other components are mounted. The walls of chassis 12 have several openings for containing a variety of conventional components, such as cable connectors, switches, display lights, option cards, etc. Solid plates (not shown) normally cover any unused openings in chassis 12. For simplicity, FIG. 1 shows only a limited number of components on motherboard 11. However, like most finished PCB assemblies, motherboard 11 would normally contain a plethora of etched conductors and other components. Furthermore, reference characters appear in FIG. 1 for only significant components and structures of electronic device 10, while other structures are simply shown and not described. 
     Electronic device 10 further includes expansion slots 22 and 23, which are accessed through openings in the front wall of chassis 12. Each of the expansion slots 22 and 23 contains a cardguide pair mounted on PCB 18 in alignment with a corresponding connector 14 and an opening in the front wall of chassis 12. Each cardguide pair includes two parallel card guides, namely, lefthand card guide 25 and matching righthand card guide 26. Card guides 25 and 26 are preferably molded from plastic or other electrically nonconductive material. FIGS. 2-7 and 9 and the corresponding description below disclose the structural details of card guides 25 and 26. 
     FIG. 1 further shows circuit cards 15A and 15B each comprising a generally rectangular PCB assembly 21. Card connectors 17 are located on an edge of PCB assemblies 21. An opposite edge of each PCB assembly 21 holds an interface device 20 for communicating with a conventional external device (not shown) in a known manner. Interface device 20 comprises faceplate 31, connector 32 and a pair of panel fasteners 33. In addition, each PCB assembly 21 has parallel mounting edges 29 that are sized to mate with card guides 25 and 26 in a manner to be described below in detail. Circuit cards 15A and 15B represent examples of common option cards found in many conventional electronic systems. Thus, the usual conductors and other components that populate a PCB of a conventional option card have been omitted here for clarity. 
     Two openings in the front wall of chassis 12 (only one opening is visible in FIG. 1) function as access ports for expansion slots 22 and 23. The two openings of expansion slots 22 and 23 enable a user to install circuit cards 15A and 15B without having to remove cover 13 from chassis 12. Illustratively, FIG. 1 shows circuit card 15A fully installed in expansion slot 22, while circuit card 15B is shown spaced from and in alignment with the opening of expansion slot 23. When a user wishes to install a particular option card, say circuit card 15B, in an unused expansion slot, say expansion slot 23, the user first removes any blank plate that may be covering the chassis opening for slot 23. Next, the user inserts card 15B into slot 23 with connector 17 inserted first, as illustrated in FIG. 1. The user gradually slides card 15B into expansion slot 23 until faceplate 31 contacts the front wall of chassis 12. Connector 17 will automatically mate with its corresponding card connector 14 as the user slides card 15B into slot 23. Finally, the user threads panel fasteners 33 into chassis 12 to secure circuit card 15B within expansion slot 23. 
     It is a goal of the present invention to provide suitable mounting techniques for installing card guides 25 and 26 onto a populated PCB assembly, such as motherboard 11, without damaging any circuit components and/or etchings located thereon. Ideally, a card installer should be capable of manually mounting card guides 25 and 26 on a fully populated motherboard 11 with only moderate effort and no special tools. In addition, the installation procedure should be such that the structural and functional integrity of motherboard 11 is not jeopardized. To accomplish this goal, mounting structures are provided that permit guides 25 and 26 to be installed manually, without the use of tools and with no forces being directed transverse to the plane of PCB 18. 
     More specifically, FIGS. 2-7 and 9 depict the structural details of card guides 25 and 26, while FIGS. 8 and 9 show details of PCB 18. As best seen in FIGS. 1, 2 and 9, lefthand card guide 25 and righthand card guide 26 are mirror images of each other. Thus, FIGS. 2-7 illustrate only the details of righthand card guide 26. Similar details with respect to card guide 25 are shown in FIG. 9. 
     As best seen in FIGS. 2-7, card guide 26 comprises top member 43, bottom member 44 and longitudinal groove 45. Groove 45 has a height that is greater than that of edge 29 on PCB 21, as depicted with phantom lines in FIG. 5. A pair of spaced, mushroom lugs 40 extends from bottom member 44. Lugs 40 include a relatively narrow neck 41 on which a larger head 42 mounts. At the front of card guide 26, ramp 48 extends from one end of groove 45 to front entrance port 51. At the rear of card guide 26, ramp 49 extends from a second end of groove 45 to rear entrance port 52. Hook 55 mounts on card guide 26 just below ramp 48. Specifically, hook 55, which has a barb 56, resiliently attaches to the bottom surface of card guide 26. As mentioned above, card guides 25 and 26 are mirror images of each other; the essential difference between guides 25 and 26 is that their grooves 45 open in opposite directions. Specifically, groove 45 in righthand card guide 26 opens to the left while groove 45 in lefthand cardguide 25 opens to the right. 
     With reference to FIGS. 8 and 9, PCB 18 comprises a number of apertures that operate with mushroom lugs 40 and hook 55 to fix card guides 25 and 26 on motherboard 11. Specifically, PCB 18 includes aligned keyhole apertures 58, which receive mushroom lugs 40, as best seen in FIG. 9. Keyhole apertures 58 each include a relatively large section and a narrower section. The diameter of the large section is greater than the diameter of head 42 on lug 40. The width of the narrower section of aperture 58 is less than the diameter of head 42 and greater than the thickness of neck 41. In addition, a front edge of PCB 18 includes a set of locking apertures 59. Each locking aperture 59 is sized to mate with barb 56 on hook 55. 
     Thus, when installing one of the card guides 25 or 26 on PCB 18, the installer simply passes heads 42 on lugs 40 through the large sections of keyhole apertures 58. That action, which FIG. 9 illustrates with dashed lines 61 and 62, positions the card guide being installed with its bottom member 44 resting on PCB 18 and its hook 55 hanging over the front edge of PCB 18. The installer then slides the relevant card guide towards the rear until its hook 55 snaps into locking aperture 59. At this point, necks 41 on mushroom lugs 40 will reside in the narrower sections of keyhole apertures 58, while heads 42 and bottom member 44 sit on opposite sides of PCB 18. In addition, barb 56 will project into locking aperture 59. Thus, mushroom lugs 40, hook 51, and apertures 58 and 59 essentially operate to anchor card guides 25 and 26 on PCB 18. 
     As such, the installation of card guides 25 and 26 may be reliably performed on a fully populated PCB assembly, such as a finished motherboard 11, without damaging delicate conductive etchings or other circuit components. The only significant installation force required, when installing card guides 25 and 26, is the force required to couple hook 55 with locking aperture 59. The magnitude of that force, which is primarily a function of the flexibility of hook 51, would normally be quite small. In addition, the direction of that insertion force would lie substantially in the plane of PCB 18. Since card guides 25 and 26 are installed in a motion that is parallel to the surface of PCB 18, any installation forces transmitted to PCB 18 will be in line with the &#34;strong&#34; direction of PCB 18. This will result in only negligible flexure of PCB 18 during cardguide installation. Consequently, a guide installer may manually affix guides 25 and 26 with only moderate hand pressure, thereby eliminating the need for a hammer or other tool as is normally required when installing conventional card guides. 
     Various modifications of the invention are contemplated. For example, since card guides 25 and 26 contain entrance ports, viz., ports 51 and 52, at either end thereof, circuit cards may be inserted into grooves 45 from either the front or rear ends of guides 25 and 26. It is also contemplated that card guides 25 and 26 may be constructed with two, back-to-back grooves rather than the single groove, i.e., groove 57, as depicted in the drawings. With a two-groove configuration, card guides could be used as righthand or lefthand guides. Additionally, a single card guide with two grooves may be shared by adjacent expansion ports. Of course, various other modifications and variations are contemplated and may obviously be resorted to in light of the present disclosure. It is to be understood, therefore, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.