Abstract:
An apparatus for supporting at least one electrical connector body, the apparatus includes a connector housing mountable to a printed circuit board (PCB). The connector housing includes at least one base member for attachment to the PCB; and at least one support post each spaced apart from one another and extending from the at least one base member. The support posts inserted into one or more clearance holes in the PCB are configured to receive the one or more support posts. When a lateral force is applied to the connector body, the support posts acts as a support and transfers the lateral force to the PCB, thereby reducing a rotational moment at a base of each connector body connected to the PCB.

Description:
TRADEMARKS 
     IBM® is a registered trademark of International Business Machines Corporation, Armonk, N.Y., U.S.A. Other names used herein may be registered trademarks, trademarks or product names of International Business Machines Corporation or other companies. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a method and apparatus for restricting a rotational moment about a longitudinal axis of surface-mount (SMT) connectors, and particularly to a method and apparatus for restricting the rotational moment about the longitudinal axis of SMT DIMM Sockets and other SMT connectors. 
     DESCRIPTION OF BACKGROUND 
     In computer systems such as personal computers, a socket is referred to as an electrical connector generally mounted on a motherboard (main board) in order to connect extension boards such as extended interface boards for peripheral devices or extended memory boards to the motherboard. The motherboard and extension boards can be electrically connected by plugging the extension boards into the electrical connector. 
     The structure of a common electrical connector will be described here with the example of an electrical connector used to connect an extension memory module (hereinafter, “module”) referred to as a DIMM (dual in-line memory module) as illustrated in  FIGS. 1 and 2 . This module corresponds to the extension board described above. 
     A dual in-line memory module (DIMM) is more and more popular for use in the present PC industry, and thus uses a DIMM socket connector mounted on the motherboard for mechanical and electrical interconnect of the corresponding DIMM therein for signal transmission between the motherboard and the DIMM. A main feature of the typical DIMM connector as illustrated in  FIGS. 1 and 2  is that the DIMM connector  10  includes generally a pair of latch/eject members  12  at its two opposite ends so that such DIMM may not only be properly retained in the DIMM connector  10  without possibility of inadvertent withdrawal by vibration or external impact, but also easily ejected from the DIMM connector  10  by rotational movement of the latch/eject member  12 . 
     With more of the industry moving to SMT (Surface Mount Technology) connectors due to PCB wiring density, path length, and electrical signal integrity concerns, new mechanical requirements emerge due to the delicate SMT interface, compared to the more mechanically robust compliant pin and pin-through-hole interfaces in previous applications. This disclosure addresses the forces and strains incurred at the SMT solder joint and pad interface due to rotation about the long axis of an SMT DIMM socket or housing  14 , for example, as well as the possibility of pad delamination at the card surface, by minimizing the overall rotation about the longitudinal axis of the SMT DIMM socket, as illustrated in  FIG. 2 . 
     Rotation about the longitudinal axis of the SMT DIMM socket  14  is caused by a number of factors. One factor is the amount and location of the center of mass of the DIMM module (not shown). The module acts as a cantilevered beam when assembled into the socket  10 , where shock, vibration, and dead load effects can all contribute to moments being applied to the DIMM connector  10 , particularly when the DIMM module is plugged parallel to the ground and perpendicular to a motherboard  16  on which the DIMM connector  10  is surface mounted thereto. Another factor is due to the design of the connector  10  itself, allowing rotation of the DIMM module upon insertion. The traditional DIMM socket allows approximately 10 degrees of rotation centered about a perpendicular plane to a printed circuit board (PCB) surface defined by the motherboard  16 . This allowable rotation, coupled with the high insertion forces required to mate the interface between the DIMM module and the socket, results in a high lateral load forming a torsional moment  17  (e.g., “rotational moment” in  FIG. 2 ) about the longitudinal axis of the connector inducing an undesirable shear stress to the SMT joint and PCB pad, regardless of orientation of the module and connector with respect to gravity. The rotational moment results in a lifting stress at the connector PCB interface indicated with arrow  18  in  FIG. 2 . This stress to the SMT joints, as well as the SMT pad, creates a reliability concern, and the possibility of pad delamination. 
     Previous designs were mechanically anchored to the PCB via the pin-through-hole or compliant pin nature of the PCB leads, as discussed above which provided a larger reaction force to the lateral shear and torsional moments than the present SMT joints provide. With the present surface-mount design, the reaction forces are carried through the SMT joints and PWB solder pads, which are not as robust as pin-in-hole connections to withstand such forces, and pose a reliability concern. 
     SUMMARY OF THE INVENTION 
     The shortcomings of the prior art are overcome and additional advantages are provided through the provision of an apparatus for supporting at least one electrical connector body. The apparatus includes at least one surface mount connector body having at least one support post, and the PCB. The support post is molded or integrated into the connector body. The PCB utilizes clearance holes to accept the one or more Support posts. The support posts may be soldered to the PCB, press fit into the PCB clearance hole, or a back side retainer may be attached to the support post on the back side of the PCB. When a lateral force is applied to the connector body, the support post(s) acts as a support and transfers the lateral force to the PCB, thereby reducing a rotational moment at a base of each connector body connected to the PCB. 
     In another exemplary embodiment, a system includes: a motherboard; a plurality of electrical connectors surface mounted to the motherboard, each electrical connector including a connector body configured to receive and electrically connect an electrical module. The connector body includes at least one base member for attachment to the motherboard; and at least one support post each spaced apart from one another and extending from the at least one base member. The support posts inserted into one or more clearance holes in the motherboard are configured to receive the one or more support posts. When a lateral force is applied to the rigid connector body, the frame assembly acts as a support and transfers the lateral force to the motherboard, thereby reducing a rotational moment at a base of each connector body connected to the motherboard 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  illustrates a perspective view of a conventional DIMM connector; 
         FIG. 2  illustrates an elevation end view of the DIMM connector of  FIG. 1  surface mounted to a PCB surface of a motherboard (show module  14 ); 
         FIG. 3  illustrates an elevation end view of a DIMM connector having a support post mounted to a PCB surface of a motherboard according to a first exemplary embodiment. 
         FIG. 4  illustrates an elevation end view of a DIMM connector having a support post mounted to a PCB surface of a motherboard according to a second exemplary embodiment. 
         FIG. 5  illustrates an elevation end view of a DIMM connector mounted to a PCB surface of a motherboard, the connector having a support post utilizing a retaining member that retains the DIMM connector by attaching to the support post on the opposite surface of the PCB motherboard according to a third exemplary embodiment. 
         FIG. 6  illustrates an exploded isometric view of the DIMM connector of  FIG. 5 . 
         FIG. 7  illustrates an exploded isometric view of a DIMM connector to be mounted to a PCB surface of a motherboard, the connector having a support post utilizing a retaining member that retains the DIMM connector by attaching to the support post on the opposite surface of the PCB motherboard according to a fourth exemplary embodiment. 
     
    
    
     The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings in greater detail, the structure of a common electrical connector will be described here with the example of an electrical connector used to connect an extension memory module (hereinafter, “module”) referred to as a DIEM (dual in-line memory module). This module corresponds to the extension board described above. 
       FIG. 3  is schematic elevation end view illustrating the structure of an electrical connector assembly  100  for a DIMM (not shown) according to the present invention. The electrical connector assembly  100  is an electrical connector which is used in desktop personal computers, for example. In  FIG. 3 , the connector assembly  100  is defined by a housing  140  for housing a respective module (not shown). The modules are arranged in several rows, for example, on a PCB or motherboard  160 . The user inserts a module (not shown) in the housing  140 , allowing memory to be added on. When the housing  140  is arranged standing up on the motherboard  160 , as illustrated in  FIG. 3 , the module is held perpendicular to the motherboard  160 . In order to counteract a lateral force indicated with arrow  162  when inserting a module (not shown) for electrical connection with the connector assembly  100 , a reaction force indicated with arrow  164  may be applied to preserve the integrity of the SMT joint interface between the connector assembly  100  and the motherboard  160 . The reaction force  164  is applied by exemplary Support pins or rigid support posts  103  extending from a bottom of the housing  140  and extending through a corresponding aperture  170  of the motherboard  160 . The reaction force  164  reduces a rotational moment  166  about a longitudinal axis defined by the connector  100  assembly at the SMT joint interface between the connector assembly  100  and the motherboard  160  when the lateral force  162  is applied.  FIG. 3  also indicates that the provision of the support pins or rigid support posts  103  extending from a bottom of the housing  140  and extending thorough a corresponding aperture  170  of the motherboard  160  reduce a rotational moment  166  and results in a reduced lifting stress at the connector/PCB interface as indicated by arrow  180 . 
     In the exemplary embodiment illustrated in  FIG. 3 , the support post  103  includes soldered leads or anchors placed interstitially to the SMT contacts, providing mechanical anchoring through the board  160 , and thus strain relief of the SMT joints. In this embodiment, a pin or support post  103  extends from a base of the housing  140  and is inserted into aperture  170  and then an annulus defined by a space between a wall of the board  160  defining the aperture  170  and a periphery of the support post  103  is filled with solder  182 . The support post  103  surrounded with soldered within the aperture  170  provides an interference fit to the board  160 , and thus anchorage of the connector is achieved after reflow of the solder  182 . 
     In exemplary embodiments, the solderable support post  103  is a metal piece which can be inserted into the base of the connector assembly housing  140 , similar to a board lock used in the industry. However, conventional board locks are for registration, and have no appreciable structural benefit. 
     Still referring to  FIG. 3 , it will be recognized by those skilled in the art that in the force diagram thereof, the opposite (reverse) would be true as well, as the support post  103  counteracts forces applied to both sides of the DIMM connector assembly  100 . The force depicted in  FIG. 3  would be induced by either a non-perpendicular plugging (which is allowed in the connector design), or by gravitational force if the overall assembly was rotated 90 degrees, as is typical in system applications. 
     The support posts  103  acting as interstitial braces can be applied to the connector assembly  100  in various ways, as described hereinbelow. In an exemplary embodiment as illustrated in  FIG. 3 , the support posts  103  are rigid body members extending from a base of the connector assembly  100  and fixed to the motherboard  160  via a fixing member, such as solder  182  as in  FIG. 3 , or other retaining means as discussed in further detail herein below. The fixing member may be a pin, screw, rivet, or any mechanical fastener that is known or will later become known. 
     The geometry of the support post  103  is not specific, as it can be designed for ease of disassembly/rework of the individual connector assemblies  100  in a ganged assembly, or other factors specific to the given application. One advantage to having the support posts  103  configured to allow removal from the motherboard  160  is that it allows for vertical removal of the DIMM connector assemblies  100  in rework. In other words, it is preferable that the support posts are not permanently mounted to the motherboard  160  so as to prevent removal in order to allow for potential removal of the connector assembly  100  from the motherboard  160 . The reworkability of this design is an advantage over one large connector assembly with multiple slots of a ganged assembly. Instead of pulling off an entire large connector assembly with multiple slots in rework, an individual isolated connector assembly  100  can be removed without disturbing the adjacent connector assemblies  100  of a ganged assembly. 
     Referring now to  FIGS. 4-7  illustrating a connector assembly  100  having one or more support posts in accordance with alternative exemplary embodiments to allow for rework.  FIG. 4  is schematic elevation end view illustrating the structure of an electrical connector assembly  100  for a DIMM according to the present invention. In the present embodiment, connector assembly  100  utilizes one or more support posts  105 . Support posts  105  are integrated to connector housing  140  by designing connector housing  140  having support posts  105  or alternatively attaching support posts  105  to connector housing  140  in a secondary process. Support posts  105  are located on the side of connector housing  140  abutting PCB  160  and are located at various distances along connector assembly  100 . It is preferable that connector  100  utilize at least two support posts  105  located at either end of connector assembly  100  (e.g., on the underside of collector assembly  100  near each a corresponding latch mechanism  12 ). When connector assembly  100  is installed to PCB  160 , support posts  105  are accepted into one or more clearance holes (not shown) in PCB  160 . Support posts  105  can be press fit into the clearance holes or later soldered to the PCB, or retained by one or more retaining members  106  as shown in  FIGS. 5 and 6 . Retaining member  106  attaches to support post  105  on the opposite side of PCB  160  as the connector housing  140  (i.e. the back side of PCB  160 ). 
     In this embodiment of  FIGS. 5 and 6 , the retaining member  106  is configured as an expansion pin and is inserted into the support post  105  configured as an expansion sleeve, after reflow. The retaining member  106  and support post  105  provide an interference fit to the PCB  160  to replace the board lock used on many connectors. Then after the retaining member  106 , configured as an expansion pin, is installed into the expandable sleeve, the combination provides an larger interference fit with the PCB hole, and thus anchorage of the connector assembly  100  is achieved after reflow. 
     This is beneficial for rework, and requires no actions that would result in a negative impact to the card/connector assembly prior to SMT attach (i.e. mis-registration of neighboring components). The risk of solder smear and similar defects is greatly reduced. 
     An alternative retaining member  108  is shown in  FIG. 7 . When a lateral force is applied to the connector body  140  in the direction of arrow  162 , one or more support posts  105  act as supports transferring the lateral force to PCB  160 , thereby reducing a rotational moment at a base of each connector assembly  100  connected to the PCB  160 . 
     In this embodiment of  FIG. 7 , the support posts  105  extends through both sides of the PCB  160  and the retaining member  108  is configured as a compliant spring member which is inserted and locked onto the end of the support post  105 , providing compression of the connector assembly housing  140  down onto the PCB  160 , as well as locking the support post  105  into place. This embodiment has similar benefits provided by the embodiments of  FIGS. 5 and 6 , in that it is assembled post-reflow, thus having little impact on the manufacturability of the component/card assembly during reflow and can provide similar board lock functions via a raised rib on a shaft defining the support post which interferes with the PCB hole. 
     In exemplary embodiments, the support posts  105  of  FIGS. 4-7  may simply be mold modifications to the SMT connector housing. Material selections different from that of the connector housing are not required. Thus, standard liquid crystal polymers (LCP&#39;s), high-temperature nylons, etc., are suitable for these features. 
     From the above described exemplary embodiments, the following attributes of the present invention are disclosed. A connector assembly includes a body having a support post extending therefrom, wherein the support post extends into a corresponding aperture of a PCB to which the connector assembly is mounted. In this manner a lateral force applied thereto is distributed across the support post which is either press-fit or soldered to the PCB thereby reducing the rotational moment at the base of each connector assembly, thus reducing a lifting stress of the connector assembly as a result of the reduced rotational moment. The support post may be placed in multiple locations for each connector assembly. More and more support posts can be used depending on the expected amount of lateral force (the more force expected, the more support posts, thereby distributing the rotational moment across all support posts. 
     While the preferred embodiments to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.