Abstract:
A method and apparatus for holding a screw captive to a printed circuit board (PCB), with a channel formed through the apparatus and a mounting hole formed through the PCB being in alignment to allow a screw to pass therethrough.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related to hardware used to mount other hardware in fixed relation to a printed circuit board (PCB).  
         ART BACKGROUND  
         [0002]    The vast majority of current day computer systems make use of one or more printed circuit boards (PCBs) mounted within a computer system&#39;s chassis by way of screws protruding through holes formed in those PCBs. However, with such use of screws comes the attendant disadvantage and inconvenience of the screws being loose components.  
           [0003]    An increasingly commonplace solution is captive screws, i.e., screws that are held captive to the PCB with which they are associated by way of a captivating component often referred to as a ferrule, or in some cases, referred to as a retainer. A ferrule, or retainer, retains itself to the PCB, and in turn, retains a screw to the PCB by retaining the screw to itself. Various forms of ferrules exist, but with various drawbacks including risk of damage to the PCB and/or requirements for a hole that is much larger than would actually be required for the screw to be used, alone. A further drawback is that many of the current types of ferrule protrude through the PCB, and this protrusion can be difficult to accommodate in various chassis designs. Yet another disadvantage is that at the time the PCB is assembled, the ferrule typically requires a separate step to be installed, thereby adding to the time and/or cost required when installing components on a PCB (also commonly referred to as ‘populating’ a PCB).  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    The objects, features, and advantages of the present invention will be apparent to one skilled in the art in view of the following detailed description in which:  
         [0005]    [0005]FIG. 1 is a perspective view of one embodiment of the present invention.  
         [0006]    [0006]FIG. 2 is a perspective view of another embodiment of the present invention.  
         [0007]    [0007]FIGS. 3 a  and  3   b  are both combined side and sectional views of still another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0008]    In the following description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention.  
         [0009]    The present invention concerns mounting hardware to mount other hardware into a fixed relationship with a PCB. Specifically, the present invention concerns using a ferrule (or retainer) mounted to the surface of a PCB by way of commonly used surface mount soldering techniques for PCBs. This ferrule is used to hold a screw captive to the PCB for use in mounting the PCB.  
         [0010]    [0010]FIG. 1 is a perspective view of one embodiment of the present invention. The body of ferrule  110  is comprised of solder flange  112 , tube  114  and capture flange  116 . Formed through all three of solder flange  112 , tube  114  and capture flange  116  is screw channel  118  through which a screw to be held captive would protrude. On the depicted surface of PCB  150  is solder ring  152  centered about the periphery of mounting hole  158 .  
         [0011]    Ferrule  110  is shown positioned over PCB  150  such that screw channel  118  formed through the body of ferrule  110  is aligned with mounting hole  158  of PCB  150 . Solder flange  112  provides a soldering extension that comes into contact with solder ring  152  to fixedly attach ferrule  110  to PCB  150  through any of a number of widely known surface mount circuit board assembly or populating techniques. When ferrule  110  is fixedly attached to PCB  150 , capture flange  116  provides a capture extension that may be used to hold a screw captive to PCB  150  such that the captive screw (not shown) protrudes at least through screw channel  118  when PCB  150  is not mounted, and such that the captive screw protrudes through both screw channel  118  and mounting hole  158  when PCB  150  is mounted.  
         [0012]    [0012]FIG. 2 is a perspective view of another embodiment of the present invention. In a manner generally corresponding to ferrule  110  of FIG. 1, the body of ferrule  210  is comprised of solder flange  212 , tube  214  and capture flange  216 , with screw channel  218  formed through all three of solder flange  212 , tube  214  and capture flange  216 .  
         [0013]    Ferrule  210  is shown installed on the surface of PCB  250 , ferrule  210  having been attached to PCB  250  through any of a number of widely known surface mount circuit board assembly or populating techniques. Though not visible in FIG. 2, this use of a widely known surface mount circuit board assembly or populating technique has resulted in solder flange  212  being soldered to a solder ring on the surface of PCB  250 , underneath ferrule  210 . Also not visible in FIG. 2 is that ferrule  210  has been installed at a location on PCB  250  such that screw channel  218  is aligned with a mounting hole formed through PCB  250  (and underneath ferrule  210 ) to form an continuous opening through both ferrule  210  and PCB  250 .  
         [0014]    Captive screw  230 , installed within overmold  220 , is shown positioned over ferrule  210  such that captive screw  230  is aligned with screw channel  218  of ferrule  210  installed on PCB  250 . Overmold  220  is comprised of head  222  and extensions  224 . When captive screw  230  is installed at least through screw channel  218 , extensions  224  of overmold  220  engage capture flange  216  of ferrule  210  to hold captive screw  230  captive to PCB  250 .  
         [0015]    Although overmold  220  is depicted as having a distinct head  222  and extensions  224  that engage capture flange  216  of ferrule  210 , the exact shape or configuration of overmold  220  can be changed without departing from the spirit and scope of the invention as hereinafter claimed.  
         [0016]    [0016]FIGS. 3 a  and  3   b  are both combined side and sectional views of still another embodiment of the present invention. In a manner generally corresponding to ferrule  210  of FIG. 2, the body of ferrule  310  of FIGS. 3 a  and  3   b  is comprised of solder flange  312 , tube  314  and capture flange  316 , with screw channel  318  formed through all three of solder flange  312 , tube  314  and capture flange  316 .  
         [0017]    In both FIGS. 3 a  and  3   b , Ferrule  310  is shown installed on the surface of PCB  350 , ferrule  310  having been attached to PCB  350  through any of a number of widely known surface mount circuit board assembly or populating techniques, resulting in solder flange  312  being soldered to solder ring  352  on the surface of PCB  350 , underneath ferrule  310 . As shown, ferrule  310  has been installed at a location on PCB  350  such that screw channel  318  is aligned with mounting hole  358  formed through PCB  350  to form a continuous opening through both ferrule  310  and PCB  350 .  
         [0018]    In both FIGS. 3 a  and  3   b , captive screw  330 , installed within overmold  320 , is shown positioned so as to extend through screw channel  318  of ferrule  310 . Overmold  320  is comprised of head  322  and extensions  324 . With captive screw  330  installed, as shown, so as to protrude through at least screw channel  318 , extensions  324  of overmold  320  engage capture flange  316  of ferrule  310  to hold captive screw  330  captive to PCB  350 . In FIG. 3 a , captive screw  330  is positioned such that it does not protrude beyond the side of PCB  350  opposite ferrule  310 , which is a position that captive screw  330  might have prior to PCB  350  being mounted using captive screw  330 . In this position, extensions  324  of overmold  320  limit the extent to which captive screw  330  may be pulled away from PCB  350  by engaging capture flange  316  of ferrule  310 .  
         [0019]    However, in FIG. 3 b , captive screw  330  is positioned such that it does protrude beyond the side of PCB  350  opposite ferrule  310 , which is the position that captive screw  330  would have when PCB  350  is mounted using captive screw  330 . In this position, the threads of captive screw  330  engage whatever hardware is on the side of PCB  350  opposite ferrule  310 , and in so doing, the head of captive screw  330  presses ferrule  310  against PCB  350 , thereby pressing PCB  350  against whatever hardware is on the side of PCB opposite ferrule  310 , and PCB  350  is thereby mounted.  
         [0020]    As depicted in FIGS. 3 a  and  3   b , screw channel  318  formed through ferrule  310  changes diameter part of the way through ferrule  310 . This change in diameter is made so as to create a ledge about the periphery of where the diameter is reduced, providing a surface against which a spring (not shown) could be installed at least partly within ferrule  310 , surrounding the portion of captive screw  330  that protrudes through screw channel  318 , and pressing either against the underside of the portion of captive screw  330  installed within head  322  of overmold  320  or against head  322  of overmold  320 , itself. Alternatively, screw channel  318  could be formed through ferrule  310  with a single and unchanging diameter, and such a spring could be installed against the surface of PCB  350  that faces ferrule  310 . Either way, the installation of such spring could be used to bias captive screw  330  into the position depicted in FIG. 3 a  when captive screw  330 , making this position into a predetermined position for captive screw  330  when captive screw  330  is not otherwise being used to mount PCB  350 . As an alternative to or in addition to the use of a spring, extensions  324  of overmold  320  could be configured to press against the outer surface of tube  314  of ferrule  310 , thereby causing friction between extension  324  and ferrule  310  that could be used to selectively hold captive screw  330  in either of the positions depicted in FIGS. 3 a  and  3   b , or any of a number of positions in between.  
         [0021]    Although solder ring  352  is depicted as being only a ring of solder on the surface of PCB  350  facing ferrule  310 , those skilled in the art will recognize that mounting hole  358  formed through PCB  350  could be plated through with solder with a second solder ring (not shown) on the opposite surface of PCB  350  (i.e., the surface of PCB  350  facing away from ferrule  310 ). Plating through mounting hole  358  and having such a second solder ring on the opposite surface of PCB  350  may be done to assist in ensuring a desired electrical connection between a conductor of PCB  350  and the surface to which PCB  350  is mounted using captive screw  330 .  
         [0022]    Although captive screw  330  is depicted as having a substantially flat head, those skilled in the art will recognize that the exact shape or configuration of captive screw  330  can be changed without departing from the spirit and scope of the invention as hereinafter claimed. Also, although overmold  320  is depicted as having a distinct head  322  and extensions  324  that engage capture flange  316  of ferrule  310 , the exact shape or configuration of overmold  320  can be changed without departing from the spirit and scope of the invention as hereinafter claimed. Furthermore, although captive screw  330  and overmold  320  are depicted a separate pieces with captive screw  330  installed within overmold  320 , those skilled in the art will appreciate that other combinations of parts could be used to create the equivalent of the combination of captive screw  330  and overmold  320  without departing from the spirit and scope of the invention as hereinafter claimed. Indeed, captive screw  330  and overmold  320  may also be fabricated as a single piece.  
         [0023]    Although ferrules  110 ,  210  and  310  have all been depicted as having a capture flange  116 ,  216  and  316 , respectively, that is meant to be engaged as part of holding a screw captive, those skilled in the art will recognize that one or more of ferrules  110 ,  210  or  310  may hold a screw captive using a different shape or configuration that would have a different form of capture extension other than capture flange  116 ,  216  or  316 . Also, although ferrules  110 ,  210  and  310  have all been depicted as having a solder flange  112 ,  212  and  312 , respectively, that is meant to provide the surface to be used in surface mounting ferrules  110 ,  210  and  310  to a PCB, those skilled in the art will recognize that one or more of ferrules  110 ,  210  or  310  may have a different form of soldering extension using a different shape or configuration that would provide sufficient soldering surface area to enable surface mounting to a PCB.  
         [0024]    The invention has been described in conjunction with the preferred embodiment. It is evident that numerous alternatives, modifications, variations and uses will be apparent to those skilled in the art in light of the foregoing description. Although the invention has been discussed repeatedly as being used in conjunction with a substantially cylindrical and tubular ferrule (or retainer), it will be understood by those skilled in the art that the present invention may be practiced in conjunction with ferrules of other shapes and configurations. Furthermore, although the example embodiments of the present invention are described in the context of holding a screw captive to a PCB, the present invention may be practice in conjunction with holding other types of fasteners or other hardware captive to a PCB.