Abstract:
A printed circuit board (PCB) includes a plurality of electronic devices electrically coupled together and disposed on a first side of the PCB. The PCB also includes a rail that is connected to the underside of the PCB. This rail is configured to cooperatively engage a rail guide connected to the chassis of the computer system such that the rail guide holds the rail and the PCB to the chassis, and the PCB and rail can slide with respect to the chassis.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the assembly of a computer system and more particularly to a method and apparatus for attaching a printed circuit board to the chassis of a computer system. 
     BACKGROUND OF THE INVENTION 
     The primary parts of a basic, desktop computer system include a keyboard, a monitor, and a box that contains most of the electronic devices that make the computer system work. The box includes a chassis or frame that houses the electronic devices in a convenient form factor. Included in the chassis are electronic devices externally apparent to the computer system user such as a disk drive, CD-ROM drive, and various switches, knobs, sockets, and light indicators. Removing the cover that protects these electronic devices reveals many more key electronic devices including, for example, processors, memory units, clocking devices, interfaces, and peripheral components, all of which are electrically coupled together on printed circuit boards (PCBs). One of these PCBs, usually the PCB containing the central processing unit and main memory, is referred to as the motherboard. 
     FIG. 1A is a top-down view of motherboard  11  inside chassis  15  in accordance with the prior art. Motherboard  11  is attached to the bottom of chassis  15  by screws  10 , and is coupled to socket  12  of riser  13 . The edge of motherboard  11  is contained within motherboard edge guide  14 . FIG. 1B is a side view of the structure of FIG. 1A along the length of motherboard  11 , showing how motherboard  11  is affixed to chassis  15  by screws  10 , socket  12 , and motherboard edge guide  14 . Motherboard  11  contains electronic devices and interconnect lines (not shown), many of which are disposed on the top side of the motherboard. 
     Motherboard  11  includes electrical contact regions disposed at the edge of the motherboard in the region inserted into socket  12 . Motherboard edge guide  14  serves to support the edge of motherboard  11  and to guide the motherboard into socket  12 , aligning the electrical contact regions on the edge of the motherboard with corresponding electrical contact regions inside the socket. In this manner, the proper electrical couplings between motherboard  11  and socket  12  are made. 
     As consumers demand increased computer system functionality in smaller form factors, more electronic devices need to be squeezed into the limited space of PCBs, including motherboard  11 . One drawback of the prior art system of FIG. 1A is that there is a significant area of “keep-out” regions on the motherboard. A keep-out region is a region on the PCB where electronic devices cannot be placed because of some mechanical obstruction. For example, screws  10  create keep-out regions in the vicinity of the screw heads, and motherboard edge guide  14  creates a keep-out region in the vicinity of the portion of the guide that overlaps motherboard  11 . 
     As consumers demand lower priced computer systems, it becomes desirable to promote computer system chassis designs that can accommodate PCBs, such as motherboards, from any number of different motherboard vendors. Promoting motherboard competition in this manner typically has the effect of lowering motherboard prices. Motherboards from different vendors, however, may be different sizes. Unfortunately, because the chassis design of the prior art structure of FIG. 1A fixes the distance between motherboard edge guide  14  and the back of chassis  15 , this chassis design is unable to accommodate motherboards of varying lengths. 
     As consumers and computer support personnel demand more easily serviceable computer systems, it becomes desirable to implement a computer chassis design that allows for easy access to the motherboard. Allowing for easy access to the motherboard makes it easier to access key electronic devices such as the processor and system memory so that, for example, a computer system user can quickly upgrade either of these components. Unfortunately, because the chassis design of the prior art structure of FIG. 1A affixes motherboard  11  to the bottom of chassis  15  using screws  10 , it is necessary to remove the PCBs and other electronic devices that may be placed above motherboard  11  inside the chassis before removing the screws. This makes it difficult to access and service the electronic components on the motherboard. 
     SUMMARY OF THE INVENTION 
     A method and apparatus is described for attaching a printed circuit board to a chassis in a computer system. The printed circuit board (PCB) comprises electronic devices electrically coupled together and disposed on a first side of the PCB. The PCB also includes a rail that is connected to the underside of the PCB. This rail is configured to cooperatively engage a rail guide connected to the chassis of the computer system such that the rail guide holds the rail and the PCB to the chassis, and the PCB and rail can slide with respect to the chassis. 
     Other features of the present invention will be apparent from the accompanying drawings and the detailed description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements and in which: 
     FIG. 1A is a top view of a motherboard in a chassis formed in accordance with the prior art; 
     FIG. 1B is a side view of the structure of FIG. 1A; 
     FIG. 2A is a top view of a motherboard in a chassis formed in accordance with one embodiment of the present invention; 
     FIG. 2B is a side view of the structure of FIG. 2A; and 
     FIG. 3 is the structure of FIG. 2B after additional components have been added in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A method and apparatus is described for attaching a printed circuit board (PCB), such as, for example, a motherboard, to a chassis in a computer system. Two rails are attached to the bottom of the motherboard, one near the inside edge (opposite the back of the computer system) and the other approximately located at the center of the motherboard. Two corresponding rail guides are attached to the bottom of the computer chassis. The rails on the motherboard cooperatively engage the rail guides attached to the chassis, allowing the motherboard to slide along the rail guides with respect to the chassis. 
     The cooperative engagement between the rails mounted beneath the motherboard and the rail guides mounted to the chassis provide both support for the motherboard and easy attachment and removal of the motherboard from the chassis, without the need to undo extra screws. This allows for easy access to the motherboard to accommodate servicing of the motherboard. In addition, because the rails are mounted underneath the motherboard, there is no top side encroachment of the rail guides over the motherboard, thereby reducing the area of top side keep-out regions. Also, because the edge of the motherboard is not bounded by a motherboard edge guide, motherboards of varying lengths are supported by this design. 
     The motherboard and chassis design are described in more detail below to provide a more thorough description of how to implement an embodiment of the present invention. Various other configurations and implementations in accordance with alternate embodiments of the present invention are also described in more detail below. 
     FIG. 2A is a top-down view of motherboard  20  inside chassis  24  formed in accordance with one embodiment of the present invention. Motherboard  20  is coupled to socket  22  of riser  23 , and screws  21  are used to couple rails  25  to the underside of motherboard  20 . Rails  25  are coupled to rail guides  26 . FIG. 2B is a side view of FIG. 2A along the length of motherboard  20 , showing how rails  25  are attached to motherboard  20  by screws  21 . Rails  25  fit into corresponding openings in rail guides  26 , as shown, to cooperatively engage rail guides  26 , allowing rails  25 , along with motherboard  20 , to slide along rail guides  26 . Motherboard  20  contains electronic devices and interconnect lines (not shown), many of which are disposed on the top side of the motherboard, some of which may be disposed on the bottom side as well. 
     Motherboard  20  includes a electrical contact regions disposed at the edge of the motherboard in the region inserted into socket  22 . Rail guides  26  serve to support motherboard  20  and to guide the motherboard into socket  22 , aligning the electrical contact regions on the edge of motherboard  20  with corresponding electrical contact regions inside socket  22 . In this manner, the proper electrical couplings between motherboard and socket  22  are made. Socket  22  serves to not only support the edge of motherboard  20 , but also to hold motherboard  20  in place, keeping the motherboard from sliding out along rail guides  20 . For one embodiment of the present invention, an additional latching system is used to prevent the motherboard from sliding back out along the rail guides. 
     In accordance with one embodiment of the present invention, the back of the computer chassis is represented by the upper boundary of chassis  24  in FIG.  2 A. This region includes numerous sockets, many of which extend directly from motherboard  20 , out the back of the computer chassis. These sockets may include, for example, a small computer serial interface (SCSI) port, printer port, telephone jack, keyboard/mouse port, monitor port, network port, or a universal serial bus (USB) socket. Because these sockets extend out the back of the computer system, they are typically attached directly to the back of the computer system chassis to provide support for when users attempt to plug corresponding cable lines into these sockets in the back of the system. Support for motherboard  20  at the edge of the motherboard closest to the back of the chassis, the outside edge, is provided by the attaching of these sockets to the back of the chassis. 
     Therefore, in accordance with one embodiment of the present invention, only the inside edge of the motherboard needs to be supported by a rail because the outside edge of the motherboard is sufficiently supported by the motherboard sockets that are attached to the back of the chassis. For this embodiment, a rail is affixed underneath the motherboard in a region near the inside edge of the motherboard within approximately two inches from the edge of the motherboard. For an alternate embodiment of the present invention, a rail is affixed underneath the motherboard in a region near the outside edge of the motherboard as well, within approximately two inches from the edge of the motherboard. 
     In accordance with one embodiment of the present invention, the center of the motherboard is also supported by the rail and rail guide. For this embodiment, a rail is attached in a region underneath the motherboard near the center of the motherboard, within approximately two inches from the center of the motherboard. 
     For one embodiment of the present invention, only a single rail is attached to the motherboard, located in a position underneath the motherboard where sufficient support is provided to the motherboard when the rail cooperatively engages a rail guide affixed to the chassis. For another embodiment of the present invention, two or more rails are used, along with corresponding rail guides, to attach the motherboard to the chassis, allowing the motherboard to slide along the rail guides. 
     The rails that mate with the rail guides are attached underneath the motherboard rather than at the edge of the motherboard, allowing the edge of the motherboard to be unbounded by a guide. As a result, a computer system chassis designed in accordance with the present invention accommodates different motherboards having different lengths. For one embodiment of the present invention, motherboard lengths in the range of approximately 9 to 14 inches are supported. In addition, for one embodiment of the present invention, motherboard widths in the range of approximately 7 to 10 inches are supported. 
     FIG. 3 is the structure of FIG. 2B after some additional components have been added in accordance with an embodiment of the present invention. An additional socket  29  is attached to riser  23 . PCB  31  contains electronic devices and interconnect lines (most of which are not shown). PCB  31 , to which electronic device  30  is coupled, is inserted into socket  29 , suspending PCB  31  over motherboard  20 . Electronic devices, including processor  27  and memory modules  28 , are shown coupled to the top side of motherboard  20 . 
     For one embodiment of the present invention, just as motherboard  20  includes electrical contact regions disposed at the edge of the motherboard in the region inserted into socket  22 , PCB  31  includes electrical contact regions disposed at the edge of the PCB in the region inserted into socket  29 . The electrical contact regions on the edge of the PCB are aligned with corresponding electrical contact regions inside socket  29 . In this manner, the proper electrical couplings between PCB  31  and socket  29  are made. 
     Riser  23  includes interconnect lines (not shown) that electrically couple electrical contact regions of socket  22  to electrical contact regions of socket  29 . In this manner, electronic devices attached to motherboard  20  are electrically coupled to corresponding electronic devices attached to PCB  31 . For example, for one embodiment of the present invention, electronic device  30  is a digital signal processor that receives a video signal and compresses the signal into a digital format. This compressed signal is then sent along interconnect lines of PCB  31 , through socket  29 , along interconnect lines of riser  23 , through socket  22 , and along interconnect lines of motherboard  20  to processor  27 . Processor  27  processes the signal and stores the results in memory modules  28 . 
     To enhance the capability of this computer system, a user upgrades processor  27  by, for example, swapping processor  27  with a processor that operates at a faster speed, and upgrades memory modules  28  by adding additional memory modules or swapping with memory modules having more memory capacity. To implement either or both of these enhancements, the user needs to directly access motherboard  20 . In accordance with one embodiment of the present invention, this is accomplished by sliding motherboard  20  straight out of socket  22 , along rail guides  26 , and out of the chassis. Note that in accordance with this embodiment of the present invention, there is no need to either remove PCB  31  from socket  29 , or remove screws attaching the motherboard to the bottom of the chassis. 
     In this manner, a motherboard and chassis formed in accordance with the present invention provides for easy access to the motherboard for upgrading electronic devices on the motherboard. In addition, the present invention facilitates the swapping of one motherboard for another, even if they are of different lengths. Also, because top-side encroachment over the motherboard is reduced, there are fewer keep-out regions on the motherboard, allowing more electronic devices to be placed on top of the motherboard. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.