Abstract:
A double ended guide pin assembly includes a first guide pin body having a first rotation axis and a first keying surface. A second guide pin body has a second rotation axis and a second keying surface. A fastener element connects the first guide pin body to the second guide pin body such that the first and second guide pin bodies are independently rotatable on the first and second rotation axes, respectively. The first and second keying surfaces are selectively positionable at different orientations with respect to each other.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates generally to circuit board connectors and, more particularly, to a double ended guide pin assembly for mechanically interconnecting circuit boards.  
         [0002]     At least some electronic systems, such as some computer systems, and in particular, rack and panel computer systems, include a primary circuit board, such as a backplane board or card, connected to one or more peripheral circuit boards, called daughter cards. In order to save space on the circuit boards, it is common to mount the backplane boards and daughter cards at a right angle to each other. Electrical connectors establish electrical communication between various daughter cards via a backplane card. Typically, one or more guide pins are used to mechanically link the circuit boards together. The guide pins provide preliminary alignment or preliminary guidance between the circuit boards so the circuit boards are positioned to facilitate proper mating of the electrical connectors. The guide pins may also provide load carrying capability between the circuit boards as well as keying and electrostatic discharge (ESD) protection.  
         [0003]     In another technique for saving board space, a feed-through type connector is used to mount components to both sides of the circuit board. In a feed-through connection, alignment of the components must be addressed on both sides of the circuit board. In at least some double ended guide pin designs, the guide pin includes multiple components and are prone to misalignment between the ends of the guide pins on opposite sides of the circuit board. Additionally, such guide pins typically do not provide keying capabilities on both sides of the circuit board.  
         [0004]     A need remains for a double ended guide pin that addresses the above mentioned shortcomings as well as other concerns in the prior art.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one aspect of the invention, a double ended guide pin assembly is provided. The guide pin assembly includes a first guide pin body having a first rotation axis and a first keying surface. A second guide pin body has a second rotation axis and a second keying surface. A fastener element connects the first guide pin body to the second guide pin body such that the first and second guide pin bodies are independently rotatable on the first and second rotation axes, respectively. The first and second keying surfaces are selectively positionable at different orientations with respect to each other.  
         [0006]     Optionally, the first guide pin body includes an elongated shaft extending along a longitudinal axis between a tapered end and a base. The first guide pin body also includes a threaded channel sized to receive an end of the fastener, and the shaft includes the first keying surface. The second guide pin body includes an elongated shaft extending along a longitudinal axis between a first end and a base. The second guide pin body further includes a through hole extending along the longitudinal axis, and the shaft includes the second keying surface. The first guide pin body and the second guide pin body each includes a base having a base ring and a keying boss. Each keying boss includes a keying protrusion and at least one centering rib.  
         [0007]     In another aspect, a double ended guide pin assembly is provided that includes a first guide pin body having a first rotation axis and a first keying surface and a second guide pin body having a second rotation axis and a second keying surface. A fastener element connects the first guide pin body to the second guide pin body such that the first and second guide pin bodies are independently rotatable on the first and second rotation axes, respectively. The first and second keying surfaces are selectively positionable at different orientations with respect to each other. The first guide pin body and the second guide pin body include a space therebetween when joined. The space is variable within a range between a predetermined minimum space and a predetermined maximum space.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a circuit board assembly in accordance with an embodiment of the present invention.  
         [0009]      FIG. 2  is a side view of a guide pin assembly formed in accordance with an exemplary embodiment of the present invention.  
         [0010]      FIG. 3  is an exploded view of the guide pin assembly shown in  FIG. 2 .  
         [0011]      FIG. 4  is a partial view of a circuit board with a guide pin mounting hole.  
         [0012]      FIG. 5  is a side view of an exemplary guide pin assembly installed in a circuit board having a maximum thickness.  
         [0013]      FIG. 6  is a side view of an exemplary guide pin assembly installed in a circuit board having a minimum thickness.  
         [0014]      FIG. 7  is an exploded view of a guide pin assembly formed in accordance with a alternative embodiment of the present invention.  
         [0015]      FIG. 8  is a side view of the assembled guide pin assembly shown in  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  illustrates a circuit board assembly  100  formed in accordance with an exemplary embodiment of the present invention. The assembly  100  includes a backplane board  102 , a first daughter card, or daughter board  104 , connected to a first side  106  of the backplane board  102  and a second daughter card  108  connected to a second side  110  of the backplane board  102 .  
         [0017]     The backplane board  102  includes a number of the electrical connectors  114  that may be feed-through connectors that electrically connect circuits on the first daughter card  104  to circuits on the second daughter card  108 . The backplane board  102  may also include electrical modules  118  that may be connected to one or both of the daughter cards  104  and  108 . The backplane board  102  also includes a number of double ended guide pins  120  that are used in mechanically connecting the daughter cards  104  and  108  to the backplane board  102  as will be described.  
         [0018]     The daughter card  104  includes connectors  126  that are configured to mate with the connectors  114  on the backplane board  102 . An electronic component  128  is configured to mate with the module  118 . A number of keying guide modules  132  are provided on the daughter card  104  that are configured to receive the guide pins  120  on the backplane board  102 . The guide pins  120  and the guide modules  132  cooperate to provide preliminary positioning and guidance to position the connectors  114  and  126  and the modules  118  and  128  for mating. In addition, the guide pin  120  and guide modules  132  cooperate to provide keying features and may provide protection from electrostatic discharge (ESD) when an ESD spring or other ESD shielding is provided.  
         [0019]     The second daughter card  108  is configured similarly to the first daughter card  104  including connectors (not shown) that electrically mate with connectors (not shown) on the second side  110  of the backplane board  102 . The daughter card  108  also includes guide modules (not shown) that receive a second end (not shown) of the guide pins  120 .  
         [0020]     While the invention is herein described in the context two daughter cards connected to a backplane board to form a circuit board assembly, it is to be understood that other assemblies are contemplated between circuit boards or other components wherein the benefits of the invention may be appreciated. In particular, no limitation is intended in the particular arrangement or number of the guide pins used in the assembly or in the number, type, or arrangement of the electrical connectors or modules described herein.  
         [0021]      FIG. 2  illustrates the guide pin assembly  120 . The guide pin assembly  120  includes a first guide pin body  140 , a second guide pin body  144 , and a fastener  146 . The fastener  146  joins the first guide pin body  140  and the second guide pin body  144  along a common longitudinal axis A. The second guide pin body  144  includes a through hole  148  shown in phantom outline. The through hole  148  extends along the longitudinal axis A. The first guide pin body  140  includes an elongated shaft  150  and a base  152 . The base  152  includes a threaded channel  154  sized to receive a threaded end of the fastener  146 . The second guide pin body  144  also includes a base  156 . A space  158  between the base  152  and the base  156  is variable within a range to accommodate a thickness of a circuit board as will be described.  
         [0022]      FIG. 3  illustrates an exploded view of the guide pin assembly  120 .  FIG. 4  illustrates a portion of a circuit board  160  with which the guide pin assembly  120  may be used. The circuit board  160  includes a guide pin mounting hole  162  and keying apertures  164  and  166 . The keying apertures  164 ,  166  may be positioned at any point on the perimeter of the mounting hole  162 . In some embodiments, there may be only one keying aperture  164 ,  166 . The first guide pin body  140  ( FIG. 3 ) includes an elongated shaft  150  that extends along the longitudinal axis A between a tapered end  170  and the base  152 . The shaft  150  includes a first keying surface  172 . In an exemplary embodiment, the keying surface  172  is substantially flat. However, the keying surface  172  may be formed with other contours in other embodiments. The base  152  includes a transition region  176  that joins the shaft  150  to a base ring  180 . A keying boss  182  extends from the base ring  180  opposite the transition region  176 . The keying boss  182  includes a keying protrusion  184  and at least one centering rib  188  both of which are formed on a perimeter of the keying boss  182 . The keying protrusion  184  is aligned with the first keying surface  172 . The keying boss  182  is received in the guide pin mounting hole  162 . The keying protrusion  184  is received in one of the keying apertures  164 ,  166 . The keying protrusion  184  is complementary in shape to one of the keying apertures  164 ,  166  in the circuit board  160  in which the guide pin assembly  120  is mounted thereby orienting the first guide pin body  140  with respect to the circuit board  160 . The keying protrusion  184  may have any geometry. The centering rib  188  is provided to center the first guide pin body  140  in the mounting hole  162  in the circuit board  160 . The centering rib  188  also engages the circuit board material to assist in retaining the first guide pin body  140  in position in the circuit board  160 .  
         [0023]     The second guide pin body  144  includes an elongated shaft  192  that also extends along the longitudinal axis A. The elongated shaft  192  extends between a fastener receiving end  194  and the base  156  and includes the through hole  148 . The shaft  192  includes a second keying surface  198 . In an exemplary embodiment, the second keying surface  198  is substantially flat. However, the second keying surface  198  may be formed with other contours in other embodiments. The first and second guide pin bodies  140  and  144  are formed separate and distinct from one another, thereby enabling the first and second keying surfaces  172  and  198  to be rotated or adjusted with respect to one another and to be oriented independent from one another. That is, when installed in a circuit board, the first and second guide pin bodies  140  and  144  may be oriented at different predetermined positions about the axis A with respect to one another.  
         [0024]     The base  156  includes a transition region  202  that joins the shaft  192  to a base ring  206 . A keying boss  208  extends from the base ring  206  opposite the transition region  202 . The keying boss  208  includes a keying protrusion  210  and at least one centering rib  214  both of which are formed on a perimeter of the keying boss  208 . The keying protrusion  210  is aligned with the second keying surface  198 . The keying boss  208  is received in the guide pin mounting hole  162  ( FIG. 4 ). The keying protrusion  210  is received in one of the keying apertures  164 ,  166 . The keying protrusion  210  is complementary in shape to the keying apertures  164 ,  166  in the circuit board  160 , in which the guide pin assembly  120  is mounted, thereby orienting the second guide pin body  144  with respect to the circuit board  160 . The keying protrusion  210  may have any geometry. The centering rib  214  is provided to center the second guide pin body  144  in the mounting hole  162  in the circuit board  160 . The centering rib  214  also securely engages the circuit board material to assist in retaining the second guide pin body  144  in position in the circuit board  160 . The first and second guide pin bodies  140  and  144  are joined to one another and oriented to extend along a common axis, namely longitudinal axis A. Before being secured in position, the first and second guide pin bodies  140  and  144  may be rotated with respect to one another about the longitudinal axis A.  
         [0025]     The base  156  on the second guide pin body  144  includes undercut areas  220  which form standoffs  222  that rest on the circuit board  160  ( FIG. 4 ) when the guide pin assembly  120  is installed in the circuit board  160 . Similar undercut and standoff features are also formed on the base  152  of the first guide pin body  140 .  
         [0026]     The fastener  146  includes a tapered head  230  and a shaft portion  232  that includes a threaded end  234 . The shaft portion  232  is received in the through hole  148  in the second guide pin body  144 . The threaded end  234  engages threads in the threaded channel  154  of the first guide pin body  140  to join the first and second guide pin bodies  140  and  144  along the longitudinal axis A. The tapered head on the fastener  146  provides pickup capability, or initial guidance for the second guide pin body  144  when a daughter card is attached to the circuit board  160 . Because the first and second guide pin bodies  140  and  144  are separable, independent keying of the first and second guide pin bodies  140  and  144  with respect to one another is achieved.  
         [0027]      FIG. 5  illustrates a side view of the guide pin assembly  120  installed in a circuit board having a maximum allowable thickness T 1 .  FIG. 6  illustrates a side view of the guide pin assembly  120  installed in a circuit board having a minimum allowable thickness T 2 . When installed in a circuit board, the guide pin assembly  120  includes a space  158  between the bases  152  and  156  of the first guide pin body  140  and the second guide pin body  144 , respectively. The space  158  represents a distance between the standoffs  222  on the base rings  180  and  206  and is variable dependent upon the thickness of the circuit board. The space  158  corresponds to a circuit board thickness and is variable within a range from a predetermined maximum space, corresponding to a maximum circuit board thickness T 2 , to a predetermined minimum space corresponding to a minimum circuit board thickness T 2 . The first and second guide pin bodies  140  and  144  may therefore be separated from one another by different spacings between T 1 , and T 2  along the axis A.  
         [0028]     The space  158  is depicted in  FIG. 5 . Although the threaded end  234  of the fastener  146  extends only to a depth D 1  at the maximum circuit board thickness T 1 , the depth D of the threaded channel  154  is established to receive the threaded end  234  of the fastener  146  at the minimum circuit board thickness T 2 . The depth D of the threaded channel  154  is limited so that the first guide pin body  140  is not substantially weakened by the presence of the channel  154 . The material from which the guide pin bodies  140  and  144  are fabricated can be selected to provide the needed strength or load carrying capacity. In one embodiment, the guide pin bodies  140  and  144  are fabricated from die cast zinc while the fastener  146  is fabricated from stainless steel. For added strength, one or both of the guide pin bodies  140 ,  144  may be fabricated from a material such as stainless steel. In an exemplary embodiment, the maximum space  158 , or maximum circuit board thickness T 1  is about 7.5 millimeters.  
         [0029]     The minimum space  158  is depicted in  FIG. 6 . The minimum allowable circuit board thickness T 2  is selected such that the keying boss  182  on the first guide pin body  140  and the keying boss  208  on the second guide pin body  144  do not interfere or abut one another. When the space  158  is at the minimum, or the circuit board has a minimum thickness T 2 , the threaded end  234  of the fastener  146  is received a distance D 2  in the threaded channel  154 . In an exemplary embodiment, the minimum space  158 , or minimum circuit board thickness T 2  is about 3.6 millimeters.  
         [0030]      FIG. 7  is an exploded view of a guide pin assembly  300  formed in accordance with a alternative embodiment of the present invention.  FIG. 8  is a side view of the assembled guide pin assembly  300 . The assembly  300  includes a first guide pin body  302  and a second guide pin body  304 . The first guide pin body  302  includes a threaded extension  310  that joins the first guide pin body  302  and the second guide pin body  304  along a longitudinal axis B. The first guide pin body  302  includes an elongated shaft  312  that extends along the longitudinal axis B between a tapered end  314  and a base  320 . The shaft  312  includes a keying surface  322 . In an exemplary embodiment, the keying surface  322  is substantially flat. However, the keying surface  322  may be formed with other contours in other embodiments. The base  320  includes a transition region  326  that joins the shaft  312  to a base ring  328  on the base  320 . A keying boss  330  extends from the base ring  328  opposite the transition region  326 . The keying boss  330  includes a keying protrusion  334  and at least one centering rib  336  both of which are formed on a perimeter of the keying boss  330 . The keying protrusion  334  is aligned with the keying surface  322 . The keying boss  330  is received in a guide pin mounting hole, such as the mounting hole  162  ( FIG. 4 ) as previously described. The keying protrusion  334  may have any geometry. The centering rib  336  is provided to center the first guide pin body  302  in the mounting hole  162  in a circuit board  160  ( FIG. 4 ). The centering rib  336  also engages the circuit board material to assist in retaining the first guide pin body  302  in position in the circuit board. The base  320  includes undercut areas  340  which form standoffs  342  that rest on the circuit board  160  ( FIG. 4 ) when the guide pin assembly  300  is installed in the circuit board  160 .  
         [0031]     The second guide pin body  304  includes an elongated shaft  350  that also extends along the longitudinal axis B. The elongated shaft  350  extends between a tapered end  354  and a base  356  and includes a threaded channel  358  sized to receive the threaded extension  310  on the first guide pin body  302 . The base  356  includes a boss  360  that is not keyed. Thus in this embodiment, only the first guide pin body  302  is keyed.  
         [0032]     In an alternative embodiment, the second guide pin body  304  can be replaced with an appropriately sized nut to provide a single ended guide pin. In any of the above described embodiments, a thread locking material may be applied to the threads on the fasteners or threaded extensions to inhibit separation of the guide pin bodies or the nut from the guide pin body in applications wherein the circuit boards are subjected to shock or vibration or both.  
         [0033]     The embodiments thus described provide a double ended guide pin assembly  120  that is suitable for connecting components, such as daughter cards, to both sides of a circuit board  160 . Each guide pin body  140 ,  144  has a keying surface  172 ,  198  that is independent of the keying surface on the other guide pin body. The guide pin assembly  120  can be adjusted to accommodate a range of circuit board thicknesses. The guide pin bodies  140 ,  144  are received in similarly keyed guide modules attached to the daughter cards. The double ended guide pin assembly  120  provides preliminary guidance for the electrical connectors between the circuit boards. The keying features reduce the possibility of damage to the connectors or circuits on the circuit boards being interconnected.  
         [0034]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.