Abstract:
An insulator electrically insulates a bolster plate. The insulator preferably includes a sheet of insulating material sized and shaped to insulate the bolster plate and at least one hole through the sheet of insulating material for accommodating a fastener for securing the sheet of insulating material to the bolster plate.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of using a bolster plate to support a circuit board, e.g., a backplane. More particularly, the present invention relates to the field of insulating the bolster plate from the supported circuit board. 
     BACKGROUND OF THE INVENTION 
     Computers and their peripheral devices are used for a wide variety of purposes including, data storage, communication, and document creation. Peripheral Component Interconnect (PCI) is a local bus that is commonly used to connect a computer with one or more peripheral devices. A PCI bus provides a high-speed connection with peripherals and can connect multiple peripheral devices to the host computer. The PCI bus typically plugs into a PCI slot on the motherboard of the host computer. 
     CompactPCI was introduced in 1995 and has since become one of the fastest-growing industrial bus architectures to date. Initially targeted at the telecommunications and industrial control markets, CompactPCI takes the popular PCI interface and packages it into a smaller, more rugged unit. The most noticeable change made to the architecture was the adoption of a form factor in which all dimensions and mechanical components are standardized by the Institute of Electrical and Electronics Engineers (IEEE). Consequently, numerous vendors can supply mechanically interchangeable components. 
     One particularly interesting use of the CompactPCI is in a blade server, also called an ultradense server. Blade servers are comprehensive computing systems that include processor, memory, network connections, and associated electronics, all mounted on a single motherboard called a blade. There are many types of blades - server blades, storage blades, network blades and more. 
     The server blade, along with storage, networking and other blades, are typically installed in a rack-mountable enclosure that houses multiple blades that share common resources such as cabling, power supplies, and cooling fans. With its modular, hot-pluggable architecture, the easily accessible blade server offers increased computing density while ensuring both maximum scalability and ease of management. 
     Blade servers are smaller than traditional rack-mounted servers and have thinner Printed Circuit Boards (PCBs). These thinner server PCBs require reinforcement for attachment of central processing unit (CPU) and Central Electronic Complex (CEC) chips much like their thicker rack-mounted counterparts. CompactPCI does not allow much physical room for the necessary bolster plates or their attachment hardware. It is very difficult to pre-assemble the necessary attachment hardware to the bolster plate prior to assembling it to the blade. The bolster plates require a high stiffness that often requires that they be constructed from a metallic material. 
     However, because the bolster plate is a metallic and, therefore, conductive component, the bolster plate must be insulated from the server blade or other circuit board that is being supported. Otherwise, the bolster plate may cause shorts in the circuit board being supported. 
     In the past, layers of insulation have been secured to the bolster plate with an adhesive. However, this tends to cause a number of problems. 
     First, this adhesive must be flame retardant so as to prevent the possibility of being ignited by the heat and electricity of the server blade or other adjacent circuit board. Thus, it becomes necessary to identify and use a Network Equipment Building Standards (NEBS) Level 3+ compliant flame-retardant adhesive, which poses some difficulty. 
     Additionally, such adhesives tend to wick out of the bonded joint between the bolster plate and the insulator. The adhesive then wicks up through the vias of the server printed circuit board or other supported circuit board. This causes contamination, and potential malfunction, of the supported circuit board. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention provides an insulator for electrically insulating a bolster plate. The insulator includes a sheet of insulating material sized and shaped to insulate the bolster plate and at least one hole through the sheet of insulating material for accommodating a fastener for securing the sheet of insulating material to the bolster plate. 
     In another embodiment, the present invention provides a sub-assembly that includes a bolster plate for supporting a circuit board and an insulator for insulating the bolster plate from the circuit board. The insulator is secured to the bolster plate with one or more fasteners. Preferably, these fasteners are screws where each screw has a threaded portion, a head and an unthreaded portion between the head and the threaded portion. The insulator and the bolster plate are held on the unthreaded portion of the screw between the threaded portion and the head. 
     In another embodiment, the present invention provides a method of forming a sub-assembly by providing a bolster plate for supporting a circuit board, providing an insulator for insulating the bolster plate from the circuit board and securing the insulator to the bolster plate with one or more fasteners. 
    
    
     Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate preferred embodiments of the present invention and are a part of the specification. Together with the following description, the drawings demonstrate and explain the principles of the present invention. The illustrated embodiments are examples of the present invention and do not limit the scope of the invention. 
     FIG. 1 is an illustration of an insulator for use on a bolster plate according to one embodiment of the present invention. 
     FIG. 2 is a detailed illustration of a hole through the insulator illustrated in FIG.  1 . 
     FIG. 3 is an illustration of the insulator of FIG. 1 along with a bolster plate and fastening screws for securing the insulator to the bolster plate according to one embodiment of the present invention. FIG. 3 also represents an exploded view of a bolster plate sub-assembly according to one embodiment of the present invention. 
     FIG. 4 is an illustration of an assembled bolster plate-insulator sub-assembly according to one embodiment of the present invention. 
     FIG. 5 is an illustration of a screw used in a bolster plate sub-assembly according to one embodiment of the present invention. 
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an insulator or sheet of insulation according to one embodiment of the present invention. The insulator ( 100 ) of FIG. 1 is sized and shaped to insulate a bolster plate from a server blade or other circuit board being supported by the bolster plate. 
     As shown in FIG. 1, the insulator ( 100 ) may have a generally rectangular shape with rounded corners. This shape may correspond to the shape of the bolster plate which the insulator ( 100 ) will be used to insulate. 
     The insulator ( 100 ), according to principles of the present invention, includes one or more holes through the insulator ( 100 ). In the embodiment shown in FIG. 1, there are four such holes ( 101 ) distributed in the four corners of the rectangular insulation sheet ( 100 ). 
     FIG. 2 is a more detailed illustration of one of the holes through the insulator shown in FIG.  1 . As shown in FIG. 2, the hole ( 101 ) through the insulator ( 100 ) preferably includes a generally round central portion ( 102 ). 
     Extending from this generally round central portion ( 102 ) of the hole ( 101 ) are additional slots ( 103 ) of the hole ( 101 ). In the embodiment of FIG. 2, there are four of these slots ( 103 ) evenly spaced around the perimeter of the central portion ( 102 ) of the hole ( 101 ). 
     These slots ( 103 ) of the hole ( 102 ) define tabs ( 104 ) of insulator ( 100 ) that extended into the hole ( 101 ) between the slots ( 103 ). These tabs ( 104 ) are sized to interfere with the threads on a screw that is being driven through the hole ( 102 ). Consequently, as will be discussed below, the insulator ( 100 ) can be secured to a bolster plate using screws. 
     FIG. 3 is an illustration of the insulator of FIG. 1 along with a bolster plate and fastening screws for securing the insulator to the bolster plate according to one embodiment of the present invention. FIG. 3 also represents an exploded view of a bolster plate sub-assembly according to one embodiment of the present invention. 
     As shown in FIG. 3, a bolster plate ( 110 ) is provided. The bolster plate ( 110 ) can be used to structurally support a server blade ( 150 ) or other circuit board. 
     The insulator ( 100 ), as noted above, is sized and shaped to insulate the bolster plate ( 110 ) from the supported circuit board (not shown). In the embodiment illustrated, the insulator ( 100 ) and bolster plate ( 110 ) are of essentially the same size and shape, each is generally rectangular with rounded corners. 
     The bolster plate ( 110 ) includes holes ( 111 ) therethrough that match the position of the hole or holes ( 101 ) in the insulator ( 100 ). A screw or screws ( 112 ) are threaded through the holes ( 111 ) in the bolster plate ( 110 ) and the holes ( 101 ) in the insulator ( 100 ) to secure the insulator ( 100 ) and bolster plate ( 110 ) together into a captive sub-assembly. 
     FIG. 4 illustrates a fully assembled version of the embodiment illustrated in FIG.  3 . As shown in FIG. 4, the insulator ( 100 ) is placed on the bolster plate ( 110 ) so as to insulate the bolster plate ( 110 ) from the supported circuit board. The hole or holes ( 101 ) in the insulator ( 100 ) are aligned with the hole or holes in the bolster plate ( 110 ). A screw ( 112 ) is then completely threaded through each pair of aligned holes. 
     The result is a completed sub-assembly that includes the bolster plate ( 110 ) to which is secured the insulator ( 100 ). The sub-assembly can be secured to the circuit board being supported and/or to other components of the system. The screws ( 112 ) may be used to further secure the sub-assembly in place or secure components to the sub-assembly. 
     FIG. 5 is a more detailed illustration of a screw ( 112 ) according to principles of the present invention. As shown in FIG. 5, the screw ( 112 ) includes a head ( 115 ) from which the screw ( 112 ) is driven, a tip ( 114 ) and a length along which threads ( 113 ) are disposed. As indicated above, the threads ( 113 ) interfere with the tabs ( 104 ) that extend into the hole ( 102 ) in the insulator ( 100 ). Thus, the screw ( 112 ) can be screwed through the insulator ( 100 ). 
     In one embodiment, the screw shaft, between the threads ( 113 ) and the head ( 115 ) has a shaft portion ( 116 ) that does not bear any threads. This shaft portion ( 116 ) is sized to fit through the central portion ( 102 ) of the hole ( 101 ) in the insulator ( 100 ). 
     When the screw ( 112 ) has been screwed completely into the bolster plate ( 110 ) and the insulator ( 100 ), the insulator ( 100 ) and bolster plate ( 110 ) are held between the head ( 115 ) and threads ( 113 ) of the screw ( 112 ) on the shaft portion ( 116 ). Consequently, the screw ( 112 ) can be turned or driven at its head ( 115 ), and the screw ( 112 ) will rotate freely within the holes ( 101 ,  111 ) in the insulator ( 100 ) and the bolster plate ( 110 ). The unthreaded portion ( 116 ) of the screw ( 112 ) will turn freely within the holes ( 101 ,  111 ) in the insulator ( 100 ) and the bolster plate ( 110 ). 
     In this way, the screw ( 112 ) can be driven to secure the sub-assembly to another component, e.g., the circuit board to be supported by the bolster plate ( 110 ). The screw ( 112 ) will not be removed from the sub-assembly and the sub-assembly disassembled unless the direction in which the screw ( 112 ) is driven is reversed and the screw ( 112 ) is unscrewed from the assembly. 
     When unscrewed, the threads ( 113 ) of the screw ( 112 ) will again interfere with the tabs ( 104 ) in the holes ( 101 ) of the insulator ( 100 ). This moves the insulator ( 100 ) toward the tip ( 114 ) of the screw and, eventually, out of engagement with the screw ( 112 ). 
     In another embodiment, the threads on the screw shaft continue to the base of the head. The insulator is typically so thin that even if the threads go all the way to the base of the head the screws can still be driven. 
     In summary, there are many advantages to the present invention. First, as just explained, the screws ( 112 ) are captive in the sub-assembly unless actively unscrewed. Thus, the sub-assembly can be assembled and the screws ( 112 ) used to attach the sub-assembly to other components remain captive in the sub-assembly until needed to secure the sub-assembly in place. 
     Additionally, there is no need to use an adhesive to secure the insulator ( 100 ) to the bolster plate ( 100 ). Thus, there is no need to source a NEBS 3+ compliant flame-retardant adhesive. There is also no concern about adhesive wicking out from the joint between the bolster plate and the insulator and contaminating the supported circuit board. 
     It should also be noted that because of these various advantages, the present invention is particularly well suited for use with CompactPCI form factor. 
     The preceding description has been presented only to illustrate and describe the invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. 
     The preferred embodiment was chosen and described in order to best explain the principles of the invention and its practical application. The preceding description is intended to enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims.