Abstract:
A system, method, and device for electrical connection is disclosed. The system comprises a leaf-spring connector member having a leaf-spring connector housing and a plurality of leaf-spring elements for carrying electrical signals, and a pad connector member having a base and a plurality of electrically conductive pad elements aligned to be pressed against the plurality of leaf-spring elements. The leaf-spring elements are pre-loaded to exert increased spring forces when compressed by the electrically conductive pad elements, resulting in decreased ohmic resistance between the leaf-spring elements and the electrically conductive pad elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Embodiments of this invention relate to Provisional Application Ser. No. 60/044,806 filed on Apr. 24, 1997. The contents of that application are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of this invention relate generally to printed-circuit board (PCB) connectors, and in particular embodiments, to methods and devices for coupling electrical conductors of physically separate electrical circuits by utilizing pre-loaded leaf-spring elements that exert increased spring forces when compressed by mating conductors, resulting in decreased ohmic resistance between the leaf-spring elements and the mating conductors, and systems incorporating the same. 
     2. Description of Related Art 
     In many electronic devices and systems, electrical circuitry is not confined to a single physical structure such as a PCB, but extends over multiple PCBs or other components. While hard-wiring physically dispersed electrical circuitry together with permanent connections such as soldered wires will suffice electrically, such methods of assembly are often impractical from a production or maintenance standpoint. Assembly or disassembly can often be more efficiently achieved by providing connectors on each physically distinct structure which are capable of being mated together or with other components to make the necessary electrical connections, or conversely, de-mated for repairs, maintenance, or upgrades. 
     Conventional PCB connectors often take the form of pin-and-socket arrangements, where multiple pins in one connector are physically inserted into multiple sockets in another connector. The compressive forces of the socket against the pin makes the physical and electrical connection. Pin-and-socket connectors also generally provide good protection for the pins and sockets, which are often recessed within their separate connector housings to provide protection in both the uncoupled and coupled configurations. However, the friction of the sockets against the pins necessitates high insertion and removal forces, making automated assembly difficult. 
     Pin-and-socket connectors are often a poor choice when centrally located on PCBs, or in any instance where surface mounting of components is desired to eliminate the need for through-mounting holes or vias which interfere with the routing of circuit traces within the PCB. While certain pin-and-socket connectors can be surface-mounted to eliminate through-mounting vias, their high insertion forces cause other problems. When connectors are surface mounted to the PCB, their solder connections may be an integral part of their securement to the PCB, and mating or de-mating of high insertion force surface mounted pin-and-socket connectors may result in mechanical stress and damage to the solder connections. In extreme cases;, these forces may cause the entire surface mounted connector to be pulled off the PCB. In addition, pin-and-socket connectors require precise alignment, and when several such connectors are located on a PCB, manufacturing and assembly tolerances may prevent the proper mating of all connectors. 
     Conventional leaf spring connectors solve some of the problems of pin-and-socket connectors. Leaf-spring connectors typically have flat rectangular blades or contacts which protrude above the surface of the connector when unloaded. A spring force is encountered by the blades of a mating connector when compressing the leaf-spring elements. The spring force of the leaf-spring element against the mating connector blades makes the physical and electrical connection. Minimal force is needed to deflect the leaf-spring element from its unloaded position, and thus assembly is simplified. Depending on how the leaf-spring element is formed, these low connection forces may place less mechanical stress on the solder joints of the connector. Additionally, leaf-spring elements are necessarily wide and flat to create the desired spring action, and such contacts are more tolerant of positional errors during assembly. 
     However, leaf-spring connectors are not without problems. The protrusion of the leaf-spring elements above the connector housing increases the vulnerability of the leaf-spring element to damage caused by snagging other structures during, for example, manufacture, transportation, and installation. In addition, the small forces typically needed to deflect the leaf-spring element from its unloaded position, while desirable from an assembly standpoint, may also lead to increased corrosion of the contacts, high ohmic resistance, and a poor electrical connection, especially in high current applications. 
     SUMMARY OF THE DISCLOSURE 
     Therefore, it is an object of embodiments of the invention to provide a system, method, or device for coupling electrical conductors of physic ally separate electrical circuits or components by utilizing pre-loaded leaf-spring elements that exert increased spring forces when compressed by mating conductors, resulting in decreased ohmic resistance between the leaf-spring elements and the mating conductors and improved electrical connections. The improved electrical connectivity also decreases resistive heating and corrosion of the contacts, especially in high current applications. 
     It is a further object of preferred embodiments of the invention to provide a system, method, or device for coupling electrical conductors of physically separate electrical circuits or components by compressively retaining and pre-loading leaf-spring elements within a leaf-spring connector housing, wherein the retained ends of the leaf-spring elements are hidden within a recess of the connector housing to preclude snagging and damage to the leaf-spring elements by foreign objects. 
     It is a further object of preferred embodiments of the invention to provide a system, method, or device for coupling electrical conductors of physically separate electrical circuits or components by compressively retaining and pre-loading leaf-spring elements within a leaf-spring connector, wherein the leaf-spring elements are formed and located within the connector such that compression of the contacts results in load forces upon the connector housing instead of solder connections. 
     These and other objects are accomplished according to a preferred embodiment of the present invention wherein an electrical connector system comprises a leaf-spring connector member having a housing and a plurality of pre-loaded leaf-spring elements for carrying electrical signals, and a pad connector member having a base and a plurality of electrically conductive pad elements. The pre-loaded leaf-spring elements exert increased spring forces when pressed against the electrically conductive pad elements, resulting in decreased ohmic resistance between the leaf-spring elements and the electrically conductive pad elements and improved electrical conduction. 
     These and other objects, features, and advantages of embodiments of the invention will be apparent to those skilled in the art from the following detailed description of embodiments of the invention, when read with the drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an electrical connector system of electrical circuits according to an embodiment of the invention. 
     FIG. 2 is a perspective view of a leaf-spring connector member aligned near a notch on a PCB according to an embodiment of the invention. 
     FIG. 3 is a perspective view of a leaf-spring connector member aligned near a notch on a PCB, illustrating the ends of the leaf-spring elements and PCB pads (shown in phantom) according to an embodiment of the invention. 
     FIG. 4 is a perspective views of a leaf-spring connector member according to an embodiments of the invention. 
     FIG. 5 is a cross-sectional view of a leaf-spring connector member positioned near a PCB according to an embodiment of the invention. 
     FIGS. 6 a ,  6   b ,  6   c , and  6   d  are rear, side, top, and front views, respectively, of a leaf-spring connector member according to an embodiment of the invention. 
     FIG. 7 is a perspective view of a pad connector member according to an embodiment of the invention. 
     FIG. 8 is a perspective view of a cap positioned to receive a leaf-spring connector member according to embodiments of the invention. 
     FIGS. 9 a ,  9   b ,  9   c , and  9   d  are rear, side, top, and front views, respectively, of a cap according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention. For example, while embodiments of the invention can be used with structures other than PCBs (e.g. printed wiring boards, housings, and chassis&#39;), preferred embodiments are described herein primarily with respect to PCB embodiments for purposes of simplifying the disclosure. 
     In many electronic devices and systems, electrical circuitry is not confined to a single physical structure such as a PCB, but extends over multiple PCBs and other components. While hard-wiring physically dispersed electrical circuitry together with permanent connections will suffice electrically, such methods of assembly are often impractical from a production or maintenance standpoint. Assembly or disassembly can often be more efficiently achieved by providing connectors on each physically distinct structure which are capable of being mated together or with other components to make the necessary electrical connections, or conversely, de-mated for repairs, maintenance, or upgrades. 
     Leaf spring connectors are sometimes used on PCBs to facilitate this removable interconnection. Leaf-spring connectors typically have flat rectangular blades or contacts protruding from the surface of the connector when unloaded, such that a spring force is encountered by the blades of a mating connector when compressing these leafspring elements. 
     An electrical connector system  2  composed of multiple separately manufacturable structures is shown in FIG.  1 . The electrical connector system  2  comprises at least two structures (a PCB  6  and a system housing  10  in the illustrated embodiment) which carry electrical components and which area electrically connectable to each other. A leaf-spring connector member  4  is coupled to one structure (the PCB  6 ) and a pad connector member  8  is coupled to the other structure (the system housing  10 ). The pad connector member  8  comprises a pad connector base  50  and electrically conductive pad elements  14 . An embodiment of the pad connector member  8  is illustrated in FIG.  7  and is described in more detail below. Referring again to FIG. 1, the leaf-spring connector member  4  comprises a plurality of leaf-spring elements  12  (four in FIG. 1) which are coupled to a first electrical circuit  52  (depicted symbolically in FIG. 1) such that circuit nodes within the first electrical circuit  52  are in electrical communication with the leaf-spring elements  12 . A second electrical circuit  54  is coupled to the pad connector member  8  such that circuit nodes within the second electrical circuit  54  are in electrical communication with the electrically conductive pad elements  14 . 
     According to preferred embodiments of the invention, the first electrical circuit  52  is a spindle motor stator commutation driver circuit on the PCB  6 , and the second electrical circuit  54  is a spindle motor stator mounted on the system housing  10 . During assembly of the electrical connector system  2 , the leaf-spring connector member  4  is secured to the PCB  6  and electrically connected to the first electrical circuit  52 . The pad connector member  8  is secured to the system housing  10  and electrically connected to the second electrical circuit  54 . Then, the PCB  6  is inserted and secured within the system housing  10  such that the leaf-spring elements  12  are contacted and compressed by the electrically conductive pad elements  14  of the pad connector member  8 , making the necessary electrical connections between the nodes of the first and second electrical circuits. 
     FIG. 2 is an enlarged view of the leaf-spring connector member  4  positioned to be secured to the PCB  6 . As shown in FIG. 2, the leaf-spring connector member  4  comprises a leaf-spring connector housing  24  and a plurality of electrically conductive leaf-spring elements  12 . The leaf-spring connector housing  24  comprises a base member  70 , a retaining member  72 , side members  22 , and substantially parallel grooves  20  formed in the side members  22 . At least one first opening  74  in the leaf-spring connector housing  24  exposes a portion of each of the electrically conductive leaf-spring elements  12 . In preferred embodiments of the invention, the leaf-spring connector housing  24  is formed as a single, unitary structure, and is made of electrically insulating materials such as plastics or ceramics. 
     The PCB  6  comprises a planar sheet of material whose thickness is approximately the height of the grooves  20  in the side members  22  of the leaf-spring connector housing  24 . A substantially rectangular notch  16  is formed on one side of the PCB  6 , creating substantially parallel inward-facing tongues  18  which are received in grooves  20 . The grooves  20  are slidable over the tongues  18  to produce a tongue-in-groove straddle mount of the leaf-spring connector member  4  to the PCB  6 , as illustrated in FIG.  1 . 
     Referring to FIG. 3, the leaf-spring connector member . 4  includes a plurality of securable contact ends  26  which are arranged to electrically connect with a corresponding plurality of electrically conductive PCB pads  28  (shown in phantom in FIG. 3) on the underside of PCB  6 , upon the leaf-spring connector member  4  being received within the notch  16 . Once the leaf-spring connector member  4  is fully inserted into the notch  16 , the securable contact ends  26  of the leaf-spring elements  12  place a compressive force on, and make frictional contact with, the electrically conductive PCB pads  28 . In preferred embodiments of the invention, the securable contact ends  26  are soldered to the electrically conductive PCB pads  28  for electrical connectivity, while structural connectivity is provided (primarily, or more preferably, entirely) by the tongue-in-groove straddle mounting of the leaf-spring connector member  4  to the PCB  6 . 
     FIG. 4 illustrates an embodiment of the leaf-spring connector member  4 . The electrically conductive leaf-spring elements  12  are exposed within the first opening  74 , and are protected on five sides by the base member  70 , side members  22 , rear wall  76 , and front wall  78 . The leaf-spring elements  12  only protrude beyond the surfaces of the leaf-spring connector housing  24  at the retaining member  72 . 
     FIG. 5 is a cross-sectional view of an embodiment of a leaf-spring connector member  4 . Referring to FIG. 5, the retaining member  72  includes a lip  82  for retaining leaf-spring elements  12 . Each leaf-spring element  12  in the leaf-spring connector member  4  comprises a retained end  30 , an exposed length portion  80 , a first bend which forms an apex  38  between the exposed length portion  80  and the retained end  30 , a securable contact end  26 , and a footing portion  34  between the exposed length portion  80  and the securable contact end  26 . Each leaf-spring element  12  is bent against its natural state to defined a second bend  84  between the exposed length portion  80  and the footing portion  34  such that the retained end  30 , apex  38 , and exposed length portion  80  are positioned over the footing portion  34 . The natural spring force created by the second bend  84  urges the retained end  30  against the lip  82  and urges the footing portion  34  against the base member  70 . By retaining the retained ends  30  of the leaf-spring elements  12  within the leaf-spring connector housing  24 , the retained ends  30  are protected from being snagged by foreign objects (not shown). 
     When the apexes  38  are contacted by the electrically conductive pad elements  14  (not shown in FIG. 5) of the pad connector member  8  (not shown in FIG.  5 ), a retained end compression force  40  is required to compress the retained ends  30  toward the footing portions  34  and increase the second bends  84 . The retained end compression forces  40  needed to compress the retained ends  30 , when the leaf-spring elements  12  are pre-loaded, are greater than the forces needed if the retained ends  30  were unloaded, due to the presence of the retained end pre-load spring forces  36 . The increased retained end compression forces  40  required to compress the leaf-spring elements  12  when the electrically conductive pad elements  14  (not shown in FIG. 5) press against the apexes  38  decreases the ohmic resistance between the two and improves electrical connectivity between the leaf-spring elements  12  and the electrically conductive pad elements  14 . 
     Referring to FIG. 1, the pad connector member  8  may be coupled to a system housing  10  or another PCB (not shown in FIG.  1 ). By aligning the electrically conductive pad elements  14  on the pad connector member  8  with the exposed length portions  80  and apexes  38  of the leaf-spring elements  12 , and pressing the PCB  6  together with the system housing  10  or other PCB (not shown in FIG.  1 ), electrical connectivity between the first electrical circuit  52  and the second electrical circuit  54  can be achieved. 
     Referring again to FIG. 5, the securable contact end  26  of each leaf-spring element  12  is in an unloaded position prior to insertion of the leaf-spring connector member  4  into the notch  16  (not shown in FIG. 5) of the PCB  6 . However, when the leaf-spring connector member  4  is inserted into the notch of the PCB  6 , the securable contact ends  26  contact the electrically conductive PCB pads  28  and are slightly deflected so as to apply a securable contact end spring force  42  to the electrically conductive PCB pads  28 . The application of the securable contact end spring force  42  upon the electrically conductive PCB pads  28  decreases the ohmic resistance and improves electrical connectivity between the securable contact ends  26  and the electrically conductive PCB pads  28 . In preferred embodiments of the invention, solder may be applied to the securable contact ends  26  and electrically conductive PCB pads  28 . 
     When retained end compression force  40  is applied to the apex  38 , the retained end  30  compresses, the second bend  84  increases, and a connector load force  32  is applied by the footing portion  34  to the base member  70  of the leaf-spring connector housing  24  in a direction substantially perpendicular to the direction of insertion  86  of the leaf-spring connector member  4 . Because the leaf-spring connector housing  24  is securably straddle-mounted to the PCB  6 , the connector load force  32  is transmitted directly to the PCB  6  and no mechanical stress is applied to the securable contact end  26 , preventing damage to any solder connection made between the securable contact end  26  and the electrically conductive PCB pads  28 . 
     In embodiments of the present invention, automated machinery may be utilized to slidably insert the leaf-spring connector member  4  onto the PCB  6 . In such automated assembly processes it is preferred that components to be assembled have minimum positional error and/or the ability for some self-alignment. FIGS. 6 a  through  6   d  illustrate an embodiment of the present invention which has self-alignment capability. Referring to FIGS. 6 a  through  6   d , the leading edges  44  of the grooves  20  in the side members  22  of the leaf-spring connector housing  24  are chamfered so that the tongues  18  (not shown in FIG. 6) of the PCB  6  (not shown in FIG. 6) will deflect off the chamfered edges if misaligned and properly enter the grooves. The tips  56  of the securable contact ends  26  are also bent to more easily receive the PCB  6 . 
     The walls of the grooves  20  have at least one malleable chamfered vertical rib  46  projecting vertically within the grooves  20 . The vertical rib  46  contacts the tongues  18  as they are inserted further into the grooves  20 , raising up the tongues  18  to provide additional correction of vertical misalignment. The walls of the grooves  20  also have at least one malleable chamfered horizontal rib  48  projecting horizontally within the grooves  20  to correct for horizontal misalignment. Although one vertical rib  46  and one horizontal rib  48  are shown in the drawings, embodiments of the invention may employ more than one vertical and horizontal rib  46  and  48  within each groove  20 . The malleable chamfered vertical and horizontal ribs  46  and  48  narrow the grooves  20  to such an extent that as the tongues  18  are slidably guided into the grooves  20 , the ribs abut the tongues  18  and are necessarily compressed and deformed to accommodate the tongues  18 , increasing the frictional self-retention of the tongues  18  within the grooves  20 . 
     In automated assembly systems utilizing embodiments of the invention, leaf-spring connector members  4  may be delivered to the notch  16  on the PCB  6  by feeder tubes (not shown). Proper stacking and protection of leaf-spring connector members  4  within these tubes is essential for smooth automated operation. In an embodiment of the invention shown in FIG. 8, caps  58  are installed over the leaf-spring connector members  4  for proper stacking in the feeder tubes and for protecting the exposed apexes  38  of the leaf-spring elements  12  during, for example, shipping, storing, installation on a PCB, and following such installation. The cap  58  is dimensioned to fit the feeder tubes, and may have indentations and surface formations  68  for alignment in the feeder tubes or use with other automated machinery. 
     In an embodiment of the invention, the cap  58  has a bottom wall  88 , a top wall  90  with partial side walls  92 , and a back wall  94  connecting top and bottom walls  90  and  88 . The space between the top and bottom walls  90  and  88 , at the cap front, defines a mouth  60  for receiving a leaf-spring connector member  4 . The mouth  60  has chamfered edges  62  to slidably receive the leaf-spring connector member  4  and provide a measure of self-alignment of the leaf-spring connector member  4  to the cap  58 . The cap  58  is made of a plastic or other suitable material and formed such that the mouth height  64 , shown in FIG. 9, is slightly less than the leaf-spring connector housing height  66 . As the leaf-spring connector member  4  is slidably inserted into the cap  58 , the back wall  94  of the cap  58  flexes, widening the mouth height  64  to accommodate the leaf-spring connector member  4 . The flexing of the back wall  94  causes the cap  58  to apply compressive force against the leaf-spring connector member  4  and securably retain the leaf-spring connector member  4  within the cap  58  between the top and bottom walls  90  and  88 . 
     In embodiments of the invention, additional automated assembly steps may include the insertion of the PCB  6  into the system housing  10 , as depicted in FIG.  1 . In such an automated step, alignment of the leaf-spring elements  12  with the electrically conductive pad elements  14  is necessary. Wide, flat leaf-spring elements  12 , liberally spaced, allow for proper coupling of the leaf-spring elements  12  to the electrically conductive pad elements  14  even with a certain amount of misalignment. 
     The above embodiments of the invention therefore provide advantages in the broad categories of electrical connectivity and manufacturability. The use of pre-loaded leaf-spring elements allows the coupling of electrical conductors of physically separate electrical circuits or components with increased spring forces, decreased ohmic resistance between the leaf-spring elements and the mating conductors and improved electrical connections. The improved electrical connectivity also decreases resistive heating and corrosion of the contacts, especially in high current applications. 
     In addition, embodiments of the invention increase the reliability of assembly processes. Leaf-spring elements are retained within a recess of the connector housing to preclude snagging and damage to the leaf-spring elements by foreign objects, and are formed and located within the connector such that compression of the leaf-spring elements results in load forces upon the connector housing instead of solder connections. Chamfered leading edges of grooves in the connector, and chamfered ribs within the grooves, aid in self-alignment of the connector and increase tolerance to positional errors during insertion of the connector onto structures like PCBs. Wide, flat leaf-spring elements also are more tolerant of positional errors when the leaf-spring connector and pad connector are pressed together. Finally, use of caps over the connector housing protect the connectors and allow the connectors to be used in the feeder tubes of automated assembly systems. 
     The foregoing description of preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.