Abstract:
A circuit to printed circuit board stored energy connector. The connector precisely aligns and interconnects conductors of “flexible circuits” (including conductive ink circuits (CIC), flexible printed circuits (FPC), and/or flat flexible cables (FFC)) directly to mating contacts on printed circuit boards. The connector is a zero insertion force (ZIF) type, and is a high density surface mount. The connector comprises mainly an actuator with an activation ridge, a deflectable flat spring contact in a spring support module, and circuit alignment features that use the flexible circuit&#39;s existing features—the outline and conductors—to accurately align the conductors of the flexible circuit to their corresponding mating spring contacts. The connector also includes circuit locators, a circuit compression flap and conductor alignment notches which work cooperatively to align and interconnect a flexible circuit to its spring contact. The connector provides a micro-wiping action that will not damage the flexible circuit, and also provides secure connection with a two point, redundant contact.

Description:
This Application is a Continuation In Part of application Ser. No. 09/206,779, filed Dec. 7, 1998, (now allowed) now U.S. Pat. No. 6,074,220, which is a Divisional of application Ser. No. 08/645,671, filed May 14, 1996, and currently issued as U.S. Pat. No. 5,873,739, and also claims priority to a Provisional Application, filed May 31, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to electrical connectors. More particularly this invention relates to zero insertion force electrical connectors. Most particularly this invention relates to a low cost, high density connector to interconnect primarily conductive ink circuits (CIC), flexible printed circuits (FPC), and/or flat flexible cables (FFC), with out the presence of at least one additional stiffener, as required with conventional zero insertion force connectors. 
     BACKGROUND OF THE INVENTION 
     In today&#39;s electronics market, manufacturers are placing emphasis on increasing their product&#39;s reliability and reducing assembly costs to remain competitive. A primary focus of each manufacturer is to reduce the cost and increase the circuit density associated with interconnecting the sub-assemblies and components found within its products. Another emerging focus in today&#39;s electronics market is to pack more electronic functions into smaller packages. This means higher density (for example 0.0125 inches on center) modules, each requiring multiple high density interconnections to other modules. 
     In electrical systems, flexible printed circuits are employed as electrical jumpers or cables for interconnecting rows of terminal pins or pads of printed circuit boards. Such flexible printed circuits are generally connected to a printed circuit board using a connector. Conventional connector manufacturers compete with each other using the same basic technology, individual stamped contacts molded into a plastic housing. This structure is then soldered to a printed circuit board (PCB) and is then ready to receive a flexible jumper or interconnect circuit. Many of these conventional connectors are of the zero insertion force (ZIF) variety, which require the application of minimal forces during the process of inserting the flexible circuit into the connector. These ZIF connectors thus reduce the likelihood of circuit damage during the connection process. 
     All of today&#39;s ZIF connectors use either the edge of the interconnect circuit or a precisely located hole to accurately align the conductors of the flexible circuit to the connector&#39;s contacts. This requires circuit manufacturers to precisely control both the thickness and width of a flexible circuit&#39;s terminating ends. If a circuit is too thin, the contacts will not attain the required deflection needed to achieve and maintain the desired contact force. Generally, tolerances must be maintained within 0.003 inches. To accurately outline a circuit and control the required tolerances requires an expensive precise outline die. 
     Another obstacle encountered in conventional circuit connector technology centers around a tendency of flexible circuits to shrink somewhat after their manufacture. When working with larger flexible circuits, the shrinkage problem can be significant enough to result in significant alignment problems. As such, outline dies are usually constrained to outline a 6 inch by 6 inch area. This size restriction adds labor costs and reduces yield. 
     In addition to size restrictions, flexible circuits also require the precise attachment of a support stiffener. This stiffener is required to lift the flexible circuits into connection with a conventional connector&#39;s contacts and add the structural support necessary to ensure the thin flexible circuit enters into the connector&#39;s opening. The precise outlining and stiffener attachment process is cumbersome and costly, and frequently the cause of poor yields and system failures. 
     In addition, existing ZIF connectors incorporate a high pressure wiping contact system. This approach, although effective on copper circuits, destroys conductive ink circuits (CIC). 
     Existing ZIF connectors also do not adequately restrain the flexible circuit and are notorious for having circuits pop out during assembly and even during use. The inability of current systems to adequately restrain the circuit leads to the potential of causing a catastrophic system failure. To add to the instability problem, existing connectors offer a one point contact system. Having only one point of contact has been a source of numerous failures attributed to contact falling over plating voids, a spot of adhesive or other foreign material on the conductor of the flexible circuit. 
     Thus, there is a need for a low cost, high density, circuit to printed circuit board stored energy connector that can interconnect the delicate contacts of conductive ink circuits, flexible printed circuits, and/or flat flexible cables to printed circuit boards. 
     SUMMARY OF THE INVENTION 
     A circuit to printed circuit board stored energy connector is disclosed which is intended to be a low cost, high density connector. Also disclosed is a method of interconnection using the connector of the present invention. The connector is designed to precisely align and interconnect conductors of conductive ink circuits (CIC), flexible printed circuits (FPC), round wire interconnects (RWI) and/or flat flexible cables (FFC), (collectively referred to hereinafter as “flexible circuits”) to a conductive spring in the connector. The spring is then connected to mating contacts on printed circuit boards (PCB&#39;s). The disclosed connector relies in part upon the flexible circuit conductors themselves for alignment purposes and thus eliminates the need for precise control of the outside dimensions of a flexible circuit&#39;s dielectric backplane or a precisely located alignment hole in the flexible circuit. The connector is of the zero insertion force (ZIF) variety and is a high density surface mount connector capable of terminating conductors on 0.006 inch pitch centers. 
     The disclosed circuit to printed circuit board stored energy connector comprises the following major components: an actuator that cooperates with a component retaining shell, and at least one spring contact housed in a spring support module. 
     The connector uses the flexible circuit&#39;s existing features (its outline and conductors) to initially accurately align the conductors of the flexible circuit to their mating spring contacts in the connector. Unlike previous systems, the invention uses a “built-in” circuit to contact alignment mechanism. The mechanism includes circuit locating arms, a circuit compression flap, and conductor alignment notches. For initial general alignment, the flexible circuit is slid into a circuit alignment cavity which allows the tapered alignment notches to accurately locate the leading edge of the flexible circuit. The flexible circuit is held in place by a circuit retaining button designed to deflect the flexible circuit into a receptacle found in the component retaining shell. 
     In order to further align the flexible circuit in the connector, circuit locating arms, positioned on each side of the flexible circuit aid in locating the conductors of the flexible circuit over the tapered alignment notches. Finally, as an actuator is closed over the flexible circuit, the compression flap forces the conductors of the flexible circuit into the tapered alignment notches, completing the alignment process. Circuit to circuit (flexible circuit to printed circuit board) interconnection is then achieved as the actuator applies the force necessary to provide the desired contact pressure between the subject circuit and the spring contact. A micro-wiping action occurs as the spring contact slides across the back of the dielectric of the flexible circuit while applying an ever increasing force to each contact of the flexible circuit until the desired interconnection results are achieved. To further insure a stable contact, the invention provides a redundant two point contact. 
     Thus an aspect of the invention is to provide a low cost, high density connector usable with conductive ink circuits, flexible printed circuits, and/or flat flexible cable. 
     Another aspect of the invention is to provide a connector that does not require the attachment of any added stiffeners in order to align a subject circuit to its contacts. 
     A further aspect of the invention is that the invention does not require that the thickness of the subject circuit be tightly controlled. The invention can accommodate varying thicknesses. 
     A still further aspect of the invention is that the invention eliminates the need for strain relief/alignment holes to be installed in the subject circuit by using the subject circuit itself to aid in alignment. 
     Yet another aspect of the invention is that the invention eliminates the conventional high pressure wiping contact of prior connectors, thus allowing the invention to be used with subject circuits that are typically damaged or destroyed by conventional connectors. 
     Another aspect of the invention provides a two point locking system to lock the subject circuit in place in the connector. 
     In addition, another aspect of the invention provides redundant two points of contact between the subject circuit and the printed circuit board which enhances reliability. 
     A further aspect of the invention provides accommodation of varying thickness of the subject circuit, in that the spring contact is self-setting and adjusts to the thickness of the particular circuit inserted into the connector, and provides a less severe wiping contact upon activation of the actuator and spring contact. The spring contact can, however, also be shaped to provide a traditional wiping contact for use with metal based circuits. 
     A further aspect of the invention is that, because the spring contact is flat and self-setting it is much less expensive and complex to manufacture. 
     These and further aspects and embodiments of the invention will become readily apparent from the following exemplary detailed description and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cut-away view of the whole connector, fully closed and activated. 
     FIG. 2 is a side cut-away view of the actuator/activator and spring support module not yet activated. 
     FIG. 3 is a side cut-away view of the actuator/activator and spring support module activated, with redundant contact points. 
     FIG. 4 is a side cut-away view of the connector, activated, showing the actuator/activator and spring support module. 
     FIG. 5 is a perspective view of the actuator/activator and the spring support module, activated. 
     FIG. 6 a  is a simplified side view of the spring contact showing the spring contact with a “free floating” end. 
     FIG. 6 b  is a simplified side view of the spring contact showing the spring contact as a “bridge”. 
     FIG. 6 c  is a top view illustrating the individual contacts of the spring contact. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Figures, in which like reference numerals correspond to like elements throughout, a most basic embodiment of the invention is a circuit to printed circuit board stored energy connector  10  for interconnecting conductive ink circuits (CIC), flexible printed circuits (FPC), and/or flat flexible cables (FFC), hereinafter referred to as at least one “flexible circuit”  12 , to a printed circuit board (PCB). 
     As shown in FIGS. 1-, the connector comprises an actuator or activator  14  that cooperates with a component retaining shell  16 , and at least one flexible spring contact  18  housed in a spring support module  20 . Spring contact  18  has a lead end which exits connector  10  and is soldered, or otherwise electrically attached or connected, to the PCB. The electrical signal is carried through flexible circuit  12  then passed through spring contact  18  into corresponding contacts on the PCB as flexible circuit  12  and spring contact  18  are pressed together in connector  10 . 
     The actuator  14  interconnects the conductors of flexible circuit  12  to their corresponding individual contacts on spring contact  18  by applying the required engagement force through the back of the dielectric of flexible circuit  12 . Actuator  14  slides across the back of the dielectric while applying an ever increasing contact force until it achieves desired, programmed results. The motion of actuator  14  vertically interconnects flexible circuit  12  and spring contact  18  while minimizing contact “wipe” as the connection is made. Minimizing wipe is necessary to prevent fracturing or scraping the fragile conductive ink off of a CIC during the attachment/connection process. 
     To preform its intended function, actuator  14  has formed thereon a contact activation ridge  22  whose primary function is to apply, on demand, the required force necessary to achieve the desired contact pressure and provide a limited “micro-wipe” between a CIC flexible circuit  12  and spring contact  18 . Activation ridge  22  compresses the conductors of flexible circuit  12  against deflectable flat spring contact  18 , which holds and compresses the particles of a conductive ink conductor together, as an ever increasing pressure is applied as actuator  14  is closed. This technique allows the limited micro-wipe of the CIC to enhance the contact surface. The micro-wipe occurs as more of the CIC&#39;s surface is compressed against deflecting spring contact  18  by activation ridge  22 . 
     Two tapered_circuit locating arms  24  built in to actuator  14  align flexible circuit  12  to spring contact  18 . Circuit locating arms  24  eliminate conventional critical circuit outlining and punching operations as well as the need to apply a costly alignment stiffener to the flexible circuit. 
     A circuit retaining button  26  is also centrally formed as part of actuator  14  and serves as part of the alignment process. Retaining button  26  locks flexible circuit  12  in place, offers strain relief and circuit pull-out (for example from pulling on flexible circuit  12  ), and, because of its central location, allows flexible circuit  12  to pivot on an axis about the location where circuit retaining button  26  is pressing on flexible circuit  12 , as circuit locating arms  24  engage and align flexible circuit  12 . Flexible circuit  12  is wedged between the circuit locating arms  24  as actuator  14  is closed. thereby placing flexible circuit  12  into position over the tapered conductor alignment notches  32  of component retaining shell  16 . 
     As a final step as actuator  14  is closed, a compression flap  28  formed on actuator  14  forces the conductors of flexible circuit  12  into tapered conductor alignment notches  32  formed in the back wall of component retaining shell  16 , thereby completing the alignment process. At least one strain relief extension  30  is formed on actuator  14  to lock flexible circuit  12  in place onto component retaining shell  16  and to prevent externally applied force on flexible circuit  12  from disengaging the connection. 
     Component retaining shell  16 , as mentioned above, and as best shown in FIG. 1, has formed therein tapered conductor alignment notches  32  which automatically align each conductor of flexible circuit  12  to its corresponding contact of spring  18  as actuator  14  is closed. Component retaining shell  16  also contains a circuit receiving cavity  34  to initially align flexible circuit  12  as it is first inserted into connector  10 . Circuit receiving cavity  34  has tapered side walls which form tapered alignment wedges  34   a  into which flexible circuit  12  is inserted. Circuit receiving cavity  34  correctly positions the leading edge of flexible circuit  12  as it is initially inserted into connector  10 . 
     There is also a circuit retaining button receptacle  36  formed in component retaining shell  16  to receive circuit retaining button  26  of actuator  14  and the now-depressed flexible circuit  12 , thereby allowing flexible circuit  12  to move as circuit locating arms  24  engage and align flexible circuit  12 . The interlocking of actuator  14  and its circuit retaining button  26  and compression flap  28  with component retaining shell  16  and its tapered conductor alignment notches  32  prevent contact discontinuity under vibration, and provide an accurate means for aligning each individual contact of flexible circuit  12  to its corresponding mating contact on spring  18 . 
     Spring contact  18  is shown in FIGS. 1-3 and FIGS. 6 a-c,  and may be preferably a flat, flexible “free floating” “bridge” spring. By way of further explanation, conventional contact and/or support springs control their engagement angle, applied force, and depth of deflection by first forming a spring into a pre-defined configuration and then relying on a mating contact to accurately deflect the spring into its pre-defined configuration. Unfortunately, every bend formed introduces a new error or tolerance and all tolerances must be summed to determine the spring contact&#39;s required range of motion. A typical contact may require three bends at a +/−0.002 inch tolerance per bend. Three bends would thus require a forgiveness tolerance of 0.006 inches. When backing a flat flexible circuit, a spring must also be capable of accommodating the manufacturing tolerances of the flat flexible circuit, which are typically +/−0.003 inches (in thickness). When the circuit thickness tolerance is added to the spring contact&#39;s required “activation range” of 0.006 inches, this results in needing a spring that has a 0.015 inch “active range”. This is both mechanically and economically impractical in a connector with a thickness of less than 0.100 inches. 
     Spring contact  18  eliminates typical tolerance problems associated with a formed spring, and also provides a non-damaging micro-wipe. Spring contact  18  stores and applies the required energy necessary to achieve the desired contact pressure and to provide a micro-wiping action which breaks through surface oxidation on flexible circuit  12  to make a reliable high pressure electrical connection. The micro-wipe is especially important when connecting CIC&#39;s because a conventional wiping action, under full contact pressure, would significantly damage the circuit&#39;s delicate conductive ink composition. 
     Spring contact  18  may be a “flat”, “bridge” spring, as shown in FIGS. 6 a  and  6   b,  and is free from the typical manufacturing tolerances of formed springs, because it does not require the shaping or bending and heat treatment of a conventional formed spring. In addition, the lack of manufacturing tolerances in spring contact  18  significantly increases its positional accuracy in connector  10 , and insures the correct contact force is applied to flexible circuit  12 . The present spring contact  18  eliminates structural limitations, including factors such as beam length, width, thickness and material, which control all operating parameters. By eliminating spring contact forming, the present spring contact reduces manufacturing and assembly costs. In addition, the “free floating” or “bridge” end of spring contact  18  can be formed and positioned to any desired shape to accommodate and provide a traditional wiping contact if desired for example for metal based circuits. 
     FIG. 6 a  shows spring contact  18  with a “free floating” end. With a spring contact  18  that is designed to be restrained at only one end, the unrestrained “free floating” end is free to move as spring contact  18  is deflected, thus offering or allowing a wider range of deflection. 
     FIG. 6 b  shows spring contact  18  as a complete “bridge”, without a completely “free floating” end, (as also shown in FIGS. 1-5) wherein a second, redundant point of contact with each conductor of flexible circuit  12  is provided. 
     Each spring contact  18  contains individual spring contacts, as shown in FIG. 6 c  to mate with the individual contacts of flexible circuit  12 . Each individual spring contact applies independent contact pressure and in so doing, compensates for the variations/tolerances in thickness of flexible circuit  12 , by compressing into conductor alignment notches  32  as required to compensate for thickness variations in flexible circuit  12 . Because spring contact  18  is activated for the first time upon insertion of flexible circuit  12  into connector  10 , spring contact  18  becomes “self-setting” by adjusting the amount of deflection to the thickness of flexible circuit  12  as actuator  14  is closed. Spring contact  18  may also be tapered to offer significant technical versatility while still maintaining the required contact pressure. 
     As noted briefly above, spring contact  18  may also be formed in connector  10  such that connector  10  provides a redundant, two point contact, as shown in FIGS. 1-3 and  6   b,  to further enhance the security and reliability of the contact formed in connector  10  by tightly securing flexible circuit  12  in connector  10 . Thus even if one point of contact is broken or inadequate, contact is still maintained at the second contact point, thus averting a system failure. The redundant two points of contact are illustrated at letter “a” in FIGS. 1-3. 
     Spring contact  18  is housed in spring support module  20 , as seen in all Figures. Spring support module  20  accurately locates spring contact  18  to the tapered conductor alignment notches/troughs  32  of component retaining shell  16 . Spring support module  20  accomplishes alignment of sprint contact  18  using spring contact alignment troughs  38 , as shown in FIGS. 1-3 and  5 , a contact deflection trough  40  also shown in FIGS. 1-3 and  5 , and at least one circuit locating arm receptacle  42  also shown in FIGS. 1-3 and  5 . 
     The invention also comprises a method of interconnecting at least one flexible circuit  12  to a printed circuit board using a connector  10 , comprising the steps of: inserting flexible circuit  12  into tapered circuit receiving cavity  34  in component retaining shell  16  to initially align flexible circuit  12  in connector  10 ; holding flexible circuit  12  essentially in place (while allowing limited movement) using circuit retaining button  26  of actuator  14  and its corresponding circuit retaining button receptacle  36  in component retaining shell  16 ; using the two circuit locating arms  24  of actuator  14  to align flexible circuit  12  in position over tapered conductor alignment notches  32  (in retaining shell  16 ) and spring contact  18  (in spring support module  20 ) as a second alignment step; providing further alignment and support of the connection using locating arm receptacles  42  in spring support module  20  to receive and interact with locating arms  24  of actuator  14 ; closing actuator  14  onto retaining shell  16  containing flexible circuit  12 , wherein compression flap  28  of actuator  14  forces or guides the individual contacts of flexible circuit  12  into tapered alignment notches  32 ; providing support and additional alignment for spring contact  18  using spring contact alignment troughs  38  to further align the individual contacts of flexible circuit  12  to the individual contacts of spring contact  18  in spring support module  20 ; applying force, and a non-damaging micro-wipe, to flexible circuit  12  by fully closing actuator  14 , using contact activation ridge  22  on actuator  14 ; whereby the individual contacts of flexible circuit  12  are “micro-wiped” as they are pressed into firm connection with the individual contacts of spring contact  18  in contact deflection trough  40  (into which flexible circuit  12  and spring contact  18  are finally pressed by contact activation ridge  22 ); and additionally using strain relief extension  30  on actuator  14  to provide further stabilization to the resulting connection. The interconnection is completed by finally soldering or otherwise electrically attaching or connecting the leading edge of spring contact  18  (which extends out from connector  10 ) to a printed circuit board (not shown). Thus, the method works sequentially to move flexible circuit  12  into alignment with spring contact  18  to connect their respective individual mating contacts. 
     FIGS. 2 and 3 show the connector (without component retaining shell  16  shown) in first an open, unconnected position (FIG. 2) and then in a closed, connected position (FIG. 3) to illustrate the connection process. FIG. 1 shows the complete connector  10 , closed and connected, including component retaining shell  16 . 
     FIG. 4 is a simplified, side view of the connector, minus the component retaining shell  16  for ease of viewing. FIG. 5 is a perspective view of the connector, without component retaining shell  16 . The view in FIG. 5 better illustrates the spring contact alignment troughs  38  of spring support module  20 , and also the compression flap  28  of actuator  14 . FIGS. 6 a-c  are simplified top and side views of spring contact  18  showing a “free floating” end, a complete “bridge”, and the individual contacts. 
     While various other changes coming within the scope of the invention may suggest themselves to those skilled in the art, the invention is not limited to the specific embodiments shown or described above, but rather the same is intended to be merely exemplary. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of the invention.