Abstract:
A strain-resistant electrical connection and a method of making the same is provided. A wire or other conductive lead is connected to a circuit in a manner that makes the connection more resistant to mechanical stresses such as movement or rotation of the lead relative to the circuit. A material is configured around the lead and near the point of connection to the circuit so as to create a region of decreasing flexibility or graduated stiffness near the point of connection. In certain embodiments, the lead may also be coiled or otherwise shaped to provide additional ability to withstand mechanical stresses. In other embodiments, additional elements may be provided to assist in controlling the stiffness near the connection point.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/827,593, filed Apr. 19, 2004, entitled STRAIN-RESISTANT ELECTRICAL CONNECTION, to which Applicants claim priority. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to a strain or fatigue-resistant electrical connection and a method of making the same. More specifically, the present invention provides for a connection between a lead and a circuit in a manner that makes the connection more resistant to damage caused by mechanical stresses such as movement or rotation of the lead relative to the circuit. In the present invention, a material is configured around the lead so as to create a region of decreasing flexibility or graduated stiffness near the point of connection. In certain embodiments, the lead may also be coiled or otherwise shaped to provide additional ability to accommodate mechanical strain without failure.  
       BACKGROUND OF THE INVENTION  
       [0003]     Electrical circuits are used in a variety of environments that can present particular physical, chemical, and electrical factors for which the circuit must either be protected or be designed to endure. The present invention primarily concerns physical factors such as mechanical stress leading to fatigue, which in turn can cause a circuit malfunction by physically breaking or weakening a specific part of the circuit. A typical location for such malfunction is at or near the point of connection of a wire, lead, or other conductor to an electrical circuit. In circumstances where the wire and the connected-to circuit may move or rotate relative to one another, the wire may incur a concentration of mechanical stress and/or fatigue at or near the point of connection to the circuit. Mechanical stresses such as repeated bending or twisting, for example, can lead to a weakening of the wire until a break occurs.  
         [0004]      FIGS. 1 and 2  provide examples of the problems addressed. In  FIG. 1 , lead  20  is connected to a printed circuit board  22  by a soldered connection  24 . As lead  20  is twisted (as illustrated by arrow A), repeatedly bent (as illustrated by arrows B and C), or placed into tension or compression (arrow D), a concentration of stress occurs at or near the point of connection  26 . Over time, as lead  20  is exposed to repeated mechanical cycles that provide for this concentration of stress, lead  20  may eventually weaken due to repeated deformation or cyclical movement. As a result, lead  20  will likely suffer a fatigue failure (or break) either at or near point of connection  26 . Similarly, in  FIG. 2 , lead  20  is connected to printed circuit board  22  by a physical connector  28  that secures the connection of lead  20  by physically compressing or pinching lead  20  between crimping surfaces  30  and  32 . Again, as lead  20  is subjected to a variety of forces as illustrated by arrows A, B, C, and D, lead  20  may weaken and eventually break due to repeated deformations at or near point of connection  34 . An electrical connection more resistant to various forces and less likely to undergo fatigue failure is desirable.  
       SUMMARY  
       [0005]     Various features and advantages of the invention will be set forth in part in the following description, or may be apparent from the description.  
         [0006]     The present invention provides an electrical connection, and a method of creating such connection, that is resistant to mechanical stresses that can occur when a wire or lead is twisted or caused to bend repeatedly about its connection to a circuit. Generally speaking, with the present invention a material is provided that surrounds the lead and associated circuit board and in the area near the point of connection to the circuit creates a region of decreasing flexibility or graduated stiffness near the point of connection. The material is selected and configured with the lead so that it will distribute some of the mechanical stress created by movement or twisting of the lead relative to a substrate or other surface carrying the circuit to which the lead is connected. By providing a region of graduated stiffness/decreasing flexibility near the location of the connection to the circuit, the concentration of stress in the lead at the point of connection to the circuit is minimized (or even avoided) through a greater distribution of the stress over the end of the lead and into the surrounding material. As such, a more robust connection to certain mechanical stresses is realized. In certain embodiments, the lead may also be coiled or otherwise shaped to provide an additional ability to absorb and dissipate mechanical forces. A variety of materials may be used to create the region of graduated stiffness about the lead, and some representative examples are provided herein. Selected exemplary embodiments and methods, including preferred, of the present invention are here summarized by way of explanation of the invention and not limitation of the invention.  
         [0007]     In one exemplary method of the present invention, a process for creating a fatigue-resistant electrical connection is provided in which an electrical conductor having at least one end is configured for connecting to an electrical circuit. A predetermined area proximate such end length of the electrical conductor is configured as a stress distribution area. The stress distribution area is created using stress distributing materials over a predetermined length of the electrical conductor, in some cases over the entire length of the electrical conductor. The stress distribution area can be created in a variety of ways and may include various techniques including various forms of adhesion, gluing, and bonding of stress distributing materials and/or specialized mechanical connection methodologies. The end of the electrical conductor is connected to the electrical circuit. Such connection may include soldering or a mechanical connection such as a crimp. Preferably the electrical conductor is bonded to the stress distributing material, preferably a resilient material, along the predetermined length of the conductor. While a variety of resilient materials might be employed, some examples include rubbers or other elastomeric materials. To further enhance the stress-resistance of the circuit, the conductor may be constructed from a wire that is coiled or otherwise shaped in a manner that helps distribute stress.  
         [0008]     In another exemplary method of the present invention, a process for assembling a strain-resistant electrical connection to an electrical circuit is provided. The process includes providing a resilient material capable of distributing mechanical forces completely encasing a printed circuit board and an electrical conductor connected thereto at a first end thereof to a connection point on the printed circuit board. The resilient material is bonded, for example, using suitable glue, to the printed circuit board and the electrical conductor. The first end of the electrical conductor is connected to the electrical circuit in a manner that fixes the position of the first end relative to the printed circuit board. As such, the resilient material provides a transition zone for the electrical conductor in which the mobility of the conductor along the end in a direction moving along the conductor and towards the electrical circuit is gradually reduced.  
         [0009]     The present invention also provides embodiments of a stress-resistant electrical connection. In one exemplary embodiment of the present invention, a durable connection for an electrical circuit is provided that includes a substrate supporting at least a portion of the electrical circuit. A conductor is included that has at least one connecting end attached to the electrical circuit. A resilient material is positioned proximate to the connecting end and surrounds a predetermined portion of the conductor. The resilient material is attached to the substrate and is configured for gradually restricting the mobility of the conductor along the end in a direction moving along the conductor and towards the electrical circuit.  
         [0010]     In another exemplary embodiment, the present invention provides a strain-resistant electrical connection to an electrical circuit mounted on a printed circuit board that includes a transition zone for distributing stress. A wire conductor is provided having a first end; a portion of the conductor near the first end is coiled and embedded within a material for distributing stress. The wire connection point encloses at least a portion of the stress distributing material and physically contacts and restrains the wire at a location proximate to its first end so as to provide an electrical connection. The material for distributing stress is bonded to the printed circuit board such that the electrical conductor is substantially immovable relative to the circuit. The material for distributing stress is configured to provide a zone of graduated stiffness about the wire at a location proximate to the first end.  
         [0011]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     A full and enabling disclosure of the present subject matter, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:  
         [0013]      FIG. 1  illustrates an example of an electrical connection in which a lead is soldered to a printed circuit board.  
         [0014]      FIG. 2  illustrates an example of an electrical connection in which a lead is mechanically connected to a printed circuit board.  
         [0015]      FIG. 3  illustrates a side cross section of an exemplary embodiment of the present invention.  
         [0016]      FIG. 4  illustrates an enlarged plan view of a portion of the exemplary embodiment illustrated in  FIG. 3 .  
         [0017]      FIGS. 5-10  illustrate various exemplary stress relieving methodologies according to the present invention. 
     
    
       [0018]     Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]     Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a third embodiment. It is intended that the present invention include these and other modifications and variations.  
         [0020]      FIGS. 3 and 4  provide side cross-section and partial plan illustrations respectively of an exemplary embodiment of the present invention. The particular illustrations represent a tire patch as might be used to house tire electronics for mounting in association with a tire. As shown, an exemplary tire electronics circuit element  36  is mounted on printed circuit board  48  and the combination is encased in an elastomeric tire patch  40 . In this embodiment, electrical conductors  38  are connected to circuit element  36  via solder connection  50 , solder pad  51  and a plurality of terminals  37 . Electrical conductors  38  may be coiled and may comprise a dipole antenna for the tire electronics that may, as an example only, comprise a radio frequency identification (RFID) device. The electrical conductors  38  are securely connected to the electronic circuit  36  by embedding at least portions  39  of the coils within solder connection  50 . A portion of the electrical conductors  38  remains free from the solder, yet adjacent printed circuit board  48 . This portion of the electrical conductors  38  is illustrated as residing in zone  5 . Specifically, the coil portions not embedded in solder connection  50  but yet adjacent printed circuit board  48  are embedded in the elastomeric material forming patch  40 . These coil portions of electrical conductor  38  within zone  5  can, within the constraints produced by the elastomeric material forming patch  40 , contract, expand, or rotate so as to further reduce the concentration of stress at the point where the electrical conductor  38  enters the solder. By providing the configuration illustrated in zone  5 , electrical conductor  38  remains adjacent a ridged supporting structure to which the elastomeric material forming the patch  40  is adhered. In addition, the patch  40  forming elastomeric material may be adhered to electrical conductor  38  so that the combination produces a zone of graduated stiffness. Although shown as helical, electrical conductors  38  could also be provided with other shapes, such as, although not limited to, a sinusoidal shape, in order to improve resistance to damage caused by stress.  
         [0021]     Certain aspects of the tire patch itself lend important design consideration to the concept of overall stress reduction. For example, in a tire environment where tire electronics devices such as the illustrated RFID device may be installed in mechanically active areas of the tire, designing the tire patch with the smallest possible dimensions in both thickness and surface area make the patch more compliant and reduce stresses imposed not only on the contained electronics device and connections, but also on the adhesives that may be used to secure the tire patch to the tire. One non-limiting example of this concept may be seen from  FIGS. 3 and 4  wherein the electrical conductors  38  may represent an antenna structure that is 1 mm thick. In such an instance, that portion of the elastomeric tire patch  40  holding the antenna may be 2 mm thick or less allowing approximately 0.5 mm of elastomeric material above and below the antenna to provide support for the antenna as well as protection from attack by chemicals and loose objects within the tire. If any component requires more than 2 mm of height, then such components may be supported with a small “mesa”  46  in the elastomeric material with steeply sloping sides as illustrated at  42  in  FIGS. 3 . In constructing a tire patch in accordance with the present invention, it is beneficial to incorporate at least a 2 mm radius of curvature wherever two or more surfaces of rubber meet, as at  42  and  44  of  FIGS. 3 , to prevent a destructive buildup of stress.  
         [0022]      FIGS. 5 through 10  provide illustrations of six exemplary embodiments of stress reductions methodologies for use with an electrical connection according to the present invention. Features common to each of these embodiments include a printed circuit board  48  as might be found in any electronics device, an electrical conductor  38  and an encasing resilient material housing  40 . The resilient material could be a rubber or another elastomeric material having suitable properties. Using the teachings disclosed herein, one of ordinary skill in the art would understand that a variety of materials could be used for the resilient material of the housing  40 . Housing  40  may form part or all of a tire patch or may represent adjacent portions of a tire&#39;s architecture.  
         [0023]     For these particular examples, a wire or other electrical conductor  38  is connected by way of solder connection  50  to a component (not illustrated) on printed circuit board  48 . Although each of the embodiments illustrates the use of a solder connection  50  of the electrical conductor  38  to printed circuit board  48 , it should be appreciated that other connection methodologies might be employed, such as the crimped connection technique illustrated in  FIG. 2 . While a number of connection methodologies may be used with the present invention, a principle concept common to all the illustrated embodiments resides in the provision of a graduated stiffness in the stress distributing material surrounding the electrical connection. Although a printed circuit board  48  is used to illustrate these particular exemplary embodiments, it should be appreciated that the present invention is not limited to use with only a circuit board. The present technology may, for example, be applied to the electrical connection of a single electrical conductor to a single electrical component not necessarily mounted to a printed circuit board. Finally, with respect to each of these embodiments, although elastomeric housing  40  is illustrated as a generally oval area surrounding the exemplary illustrated components, the housing  40 , none-the-less, is designed to conform to the design principles discussed with respect to  FIGS. 3 and 4  hereinabove.  
         [0024]     With reference now to  FIG. 5 , a representatively illustrated elastomeric housing  40  is shown surrounding printed circuit board  48  and electrical conductor  38 . Electrical conductor  38  is connected to printed circuit board  48  by way of solder connection  50  within a recessed area  52  formed by sloped side walls  54 . Elastomeric material contained within the recessed area  52  and forming a portion of the housing  40  cooperates with the walls  54  of the recessed area  52  to provide an area of increased stiffness in the vicinity of the solder connection  50 . In addition, as illustrated in  FIG. 5 , the electrical conductor  38  is coiled to provide, in cooperation with elastomeric material  40  and the proximity of sloped side walls  54 , a graduated stress reduction zone similar to that described with respect to  FIG. 4 .  
         [0025]     With reference now to  FIG. 6 , an alternative embodiment of the present invention is illustrated. In this embodiment, a recess  56  is created in the printed circuit board  48  and additional stiffening wires  58  are provided and soldered into place along with electrical conductor  38 . The additional stiffening wires  38  extend for a distance from the recess  56  into the elastomeric material forming housing  40  and thereby assist in creating a zone of increased stiffness and thereby additional stress reduction within the housing  40  at the point of connection of the electrical wire  38  to the printed circuit board  48 .  
         [0026]     The embodiment of the present invention illustrated in  FIG. 7  provides a variation of the  FIG. 6  embodiment by providing the function of the stiffening wires  58  in the form of a section  38 ′ of coils in the vicinity of the solder connection  50  within the coiled electrical conductor  38  having a higher pitch, i.e. having a greater number of turns per unit length, than the more remote section  38 ″ of the electrical conductor  38 . The higher number of turns per unit length in the area closest to the solder connection point provides a zone of increased stiffness in the area of the solder connection  50  through interaction of the elastomeric housing material by operation of the housing material surrounding a larger number of coil turns in the area of the solder connection  50  versus the number of coil turns encased in the more remote section  38 ″ of the electrical conductor  38 . By gradually decreasing the mobility of electrical conductor  38  along a transition zone, any stress applied to electrical conductor  38  is distributed throughout its length instead of concentrating the stress in a particular location such as point of connection  50 . As a result, the local strain on electrical conductor  38  is reduced or eliminated at or near the point of connection  50 , and the likelihood of a breaking or weakening the connection at point  50  is also decreased or removed. It should be appreciated that, although the illustrated embodiment features two areas  38 ′,  38 ″ of varying pitch, more that two such areas may be provided and, in fact, the pitch could be continuously varied over the length of the electrical conductor  38 .  
         [0027]     With reference now to  FIG. 8 , yet another embodiment of the present invention is illustrated. In the illustrated embodiment, additional stiffening is provided by a protrusion  60  extending from a portion of the printed circuit board  48 . Protrusion  60  is configured such that one or more coil turns associated with the electrical conductor  38  may fit over the protrusion  60  and be connected thereto by solder connection  50 . As with the previously discussed embodiments, the presence of protrusion within a portion of the coil turns of electrical conductor  38  coupled with the surrounding elastomeric material  40  operates to produce a zone of increased stiffness and thereby functions to distribute any strain applied to the electrical conductor  38 , most particularly at the solder connection  50 .  
         [0028]      FIG. 9  is illustrative of yet another embodiment of the present invention that is somewhat reminiscent of the embodiment illustrated in  FIG. 6 . More particularly, the present embodiment makes use of a stiffening wire  62  in a manner somewhat like stiffening wires  58  illustrated in  FIG. 6 . In this embodiment, however, stiffening wire  62  is actually formed by straightening a portion of the electrical conductor  38  and soldering the straightened wire and at least a portion of one of the coils of the electrical conductor  38  to the circuit board  48 . The straightened portion of the electrical conductor  38  then acts in concert with the surrounding elastomeric material to provide a zone of increased stiffness in much the same manner as stiffening wire  58  of the  FIG. 6  embodiment of the invention.  
         [0029]     Turning finally to  FIG. 10 , still yet another embodiment of the invention is illustrated which features elements much like those of several previous embodiments. Like the embodiment illustrated in  FIG. 9 , this embodiment of the invention makes use of a straightened portion  64  of the electrical conductor  38 . Also like the embodiment shown in  FIG. 8 , this embodiment positions that straightened portion  64  of electrical conductor  38  within several coils of the electrical conductor  38  at one end thereof. When soldered in place to printed circuit board  48  as shown, the straightened portion  64  operates in a manner similar to protrusion  60  of the  FIG. 8  embodiment of the invention to provide, in concert with the surrounding elastomeric material, a zone of increased stiffness that provides distribution of any locally applied strain.  
         [0030]     While several embodiments of the present invention have been illustrated with particularity, there are additional concepts that may be applied to each of these embodiments. As an example, stress resistance can be further enhanced through the geometry or shape used for electrical conductor  38  as has been previously discussed. In addition, electrical conductor  38  may be constructed from a material that increases the resiliency of solder connection  50 . By way of example only, conductive polymer compounds, steel, stainless steel, spring steel, and spring steel coated with brass have been found by applicants to provide for a conductive and yet resilient electrical conductor  38 . However, numerous other materials and shapes may be utilized as one of ordinary skill in the art will understand using the teachings disclosed herein. Additionally, in the event the material used for elastomeric housing  40  is conductive or otherwise negatively affects the conduction of electrical conductor  38 , a nonconductive coating can be included around electrical conductor  38 . By way of example only, using a nonconductive rubber with little or no carbon black present could provide such coating.  
         [0031]     Finally, it will be advantageous if the elastomeric material of the housing  40  is actually bonded to the various components. That is, bonding the elastomeric material to the electrical conductor  38 , for example, will increase the distribution of strain along the length of the electrical conductor  38  by insuring that the electrical conductor  38  does not slide within the elastomeric material. In addition, bonding the elastomeric material to the printed circuit board and, most especially, in the area of the solder connection  50  will assist in ensuring more uniform distribution of applied strain and thus significantly reduce the likelihood of strain induced damage to the solder connection  50  and other components within the tire electronics.  
         [0032]     Using the teachings disclosed herein, one of ordinary skill in the art will appreciate that other embodiments of the present invention exist that fall under the scope of the appended claims. In fact, it should be appreciated by those skilled in the art that modifications and variations can be made to the connection and method as described herein, without departing from the scope and spirit of the claims. It is intended that the invention include such modifications and variations as come within the scope of the appended claims and their equivalents.