Abstract:
A flatwire assembly includes a pair of elongate flatwire segments that are interconnected with a thin, flexible patch that overlies the opposed longitudinal ends of the segments. Conductive traces on the bottom face of the patch are electrically connected to the respective conductive traces of the segments by solder layers that, upon reflow under heat and pressure, respectively extend past an edge of the patch, whereupon visual confirmation of the solder joints between the traces of the patch and the segment is readily obtained. A layer of a thermally-activated or pressure-sensitive adhesive is disposed between the patch and each segment to further mechanically couple the patch to each segment during solder reflow. Longitudinal extensions of the patch substrate are bonded by the adhesive layer to respective portions of the segments farther removed from the segment ends than the solder layer extensions provide enhanced strain relief.

Description:
FIELD OF INVENTION 
     The invention relates generally to electrically- and mechanically-interconnected flatwire segments. 
     BACKGROUND OF THE INVENTION 
     In order to reduce vehicle weight while increasing the reliability of a vehicle&#39;s electrical systems, the automotive industry is increasingly utilizing flexible flatwire busses extending between various electronic sites and/or systems in a vehicle. Each flatwire bus is preferably formed of a plurality of interconnected flatwire segments in order to afford greater flexibility in the assembly and customization of the vehicle&#39;s electrical system while further capitalizing on an increased integration of such bus segments into other vehicle components, such as HVAC ducts, instrument panel structures, and the like. 
     In accordance with a known approach for interconnecting such flatwire segments, the segments are respectively outfitted with male and female connectors, whereupon the connectors are joined and locked together to complete the interconnection. Much attention has been focused on achieving a satisfactory electrical connection between the conductive traces of each flatwire segment and the corresponding connector tips. However, such use of electrical connectors along the length of the resulting flatwire bus may nonetheless degrade bus performance, while the weight and bulk of such electrical connectors continue to limit design flexibility and attendant gains in system integration. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a flatwire assembly featuring a mechanical and electrical interconnection between a pair of flatwire segments, and an associated method for interconnecting the pair of flatwire segments, that overcomes the deficiencies of the prior art. 
     Under the invention, two flatwire segments are mechanically joined, and the respective conductive traces of the flatwire segments are electrically interconnected, by a flatwire jumper patch that is secured to the top face of the segments&#39; opposed longitudinal ends by a layer of a suitable adhesive. Conductive traces exposed on the top face of each flatwire segment are respectively electrically interconnected with corresponding conductive traces exposed on the bottom face of the patch by a solder layer. 
     At least one and, preferably, each solder layer extends generally longitudinally of the segment traces, out slightly beyond an edge of the patch overlying the respective flatwire segment. The edge of the patch overlying the respective flatwire segment is either a longitudinal end of the patch or, preferably, is an edge defined by a peripheral portion of an aperture or “window” defined in the patch. The solder layer extensions atop the segment traces permit a visual inspection of the resulting flatwire assembly, by which to confirm the successfully electrical interconnection between the respective traces of the patch and each flatwire segment. 
     In accordance with another aspect of the invention, the patch preferably includes a flexible substrate defining longitudinal extensions that overlie respective portions of each flatwire segment that are farther removed from the segment&#39;s end than the visible solder layer extensions. Further, the flatwire assembly&#39;s adhesive layer preferably extends between the patch substrate extensions and the corresponding portions of the flatwire segments such that, once the patch is bonded to the flatwire segments, the patch substrate extensions advantageously provide improved mechanical strain relief to the resulting flatwire assembly. 
     Also under the invention, a method is provided for interconnecting a pair of flatwire segments, each flatwire segment including a top face, a longitudinal end, and a plurality of conductive traces exposed on the top face proximate to the longitudinal end. The method includes positioning a patch directly atop the opposed ends of the flatwire segments, with the patch including a generally-flat, flexible substrate, a bottom face, a top face, a plurality of edges, a plurality of conductive traces exposed on the bottom face of the patch, and a solder layer formed on the traces of the patch. 
     The method also includes applying heat and pressure to a portion of the top face of the patch overlying the solder layer to thereby reflow the solder layer generally along the traces of the flatwire segments to a point slightly beyond a respective one of the edges of the patch, whereby at least one solder layer extension is formed on a given trace of each segment. The method further includes inspecting the solder layer extensions to confirm an electrical interconnection by the solder layer of the respective traces of the patch and the segments. The method preferably also includes covering the solder layer extensions with a protective layer after inspecting, as with a self-adhesive tape cover. 
     In accordance with another aspect of the invention, the method preferably includes preparing the patch by applying the solder layer to the traces of the patch, prior to position the patch atop the segment ends, either as a solder paste by stenciling or as solder plating. The ends of the segments are preferably prepared by applying a flux to the traces of the segments prior to positioning the patch. 
     In accordance with yet another aspect of the invention, the method preferably includes applying a layer of either a thermally-cured adhesive or a pressure-sensitive adhesive to a portion of the bottom face of the patch prior to positioning the patch atop the segment ends. By way of example only, in a preferred method, the adhesive is a thermoplastic adhesive having a curing temperature lower than the reflow temperature of the solder. The adhesive is thereby advantageously formed into a suitable adhesive layer and activated/cured during the step of applying heat and pressure to reflow the solder layer. 
     Additional features, benefits, and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the subsequent description of several exemplary embodiments and the appended claims, taken in conjunction with the accompanying Drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings, wherein like reference numerals are used to designate like components in each of the several views, and wherein the relative thickness of certain components has been increased for clarity of illustration: 
     FIG. 1 is a view in perspective of a first exemplary flatwire assembly that includes a pair of flatwire segments whose ends have been interconnected in accordance with the invention, with the top cover partially broken away for clarity; 
     FIG. 2 is a top view of the first flatwire assembly, with the top cover removed; 
     FIG. 3 is a sectional view of the first flatwire assembly, taken along line  3 — 3  of FIG. 2, but further showing the assembly&#39;s top cover; 
     FIG. 4 is a bottom view of the jumper patch of the first flatwire assembly, immediately before being placed atop the juxtaposed longitudinal ends of the two flatwire segments; 
     FIG. 5 is a perspective view of a jumper patch being placed atop of the juxtaposed ends of the two flatwire segments, further showing the prepared segment ends; 
     FIG. 6 is a top view of the first flatwire assembly during manufacture, with the jumper patch positioned directly atop the ends of the flatwire segments, and further illustrating, in broken lines, a first heating zone upon which heat is applied under pressure to cause reflow of the pre-applied solder layer during assembly manufacture, and a second heating zone upon which heat is applied under pressure to cause both reflow of the pre-applied solder layer and cure of the adhesive layer during assembly manufacture; and 
     FIG. 7 is a top view a second exemplary flatwire assembly, in accordance with another aspect of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first exemplary flatwire assembly  10  in accordance with the invention, featuring a pair of flatwire segments  12  that are electrically- and mechanically-interconnected by a flatwire “jumper” patch  14 , is illustrated in FIGS. 1-4. Each flatwire segment includes a generally flat, flexible substrate  16  generally defining a top face  18  and a longitudinal end  20  of the flatwire segment  12 . A plurality of longitudinally-extending electrically-conductive traces  22  are secured, as by an adhesive layer (not shown), to the top face  18  of the flatwire substrate  12 . As best seen in the cross-sectional view of FIG. 3, while the traces  22  along the length of each flatwire segment  12  are generally covered with an electrically-insulative polymeric masking layer  24 , in order to expose the traces  22  on the respective longitudinal end  20  of each flatwire segment  12 , the masking layer  24  proximate to each segment&#39;s longitudinal end  20  is either omitted during fabrication or removed in a preliminary step, as illustrated in FIG.  5 . 
     Returning to FIGS. 2 and 3, the flatwire jumper patch  14  of the first flatware assembly  10  similarly includes a generally-flat, flexible substrate  26  defining a bottom face  28  of the patch  14 . A pair of generally rectangular apertures  30  are formed in the patch substrate  26 , each aperture  30  exposing a portion  32  of the top face  18  of a respective flatware segment  12 . A peripheral portion of each aperture  30  defines a respective edge  34  on the pa patch  14  that overlies the traces  22  exposed on the top face  18  of the flatwire segment  12 . As best seen in the bottom view of the patch illustrated in FIG. 4, a plurality of electrically-conductive traces  36 , formed of a suitable material such as copper, are exposed on the bottom face  28  of the patch  14 . 
     Returning to FIG. 3, a solder layer  38  is disposed between respective pairs of the exposed traces  36 , 22  of the patch  14  and the segments  12  to thereby electrically interconnect the traces  22  of the flatwire segments  12  via the traces  36  of the patch  14 . The invention contemplates use of any suitable type of solder  38 , including, for example, a pre-plated solder, a solder paste dispensed onto the traces of the patch as with a stenciling process, or a solder pre-form. 
     As best seen in FIGS. 3 and 4, an adhesive layer  40  is also disposed between the respective top faces  18  of the flatwire segments  12  and the bottom face  28  of the patch  14 , generally on portions of the bottom face  28  of the patch  14  adjacent to the traces  36  and about the periphery of the patch&#39;s bottom face  28 . The adhesive layer  40  serves to further mechanically couple the patch  14  to each flatwire segment  12 . While the invention contemplates use of any suitable adhesive, in the exemplary flatwire assembly  10 , the adhesive layer is a thermally-cured adhesive, such as an epoxy or urethane having a curing temperature lower than the reflow temperature of the solder layer  38 , or a pressure-sensitive adhesive, such as an acrylic- or silicone-based adhesive. By way of example only, where the adhesive is a thermally-cured thermoplastic, the adhesive is conveniently applied to the bottom face  28  of the patch  14  as an adhesive film. 
     As best seen in FIGS. 2 and 3, the solder layers  38  bridging the traces  36 ,  22  of the patch  14  and the segments  12  each include longitudinal extensions  42  that extend out beyond the adjacent edge  34  of the patch substrate  26 , into the “window” or “inspection area” defined by the aperture  30 . As described further below, the solder layer extensions  42  are formed by applied heat and pressure during solder reflow. The solder layer extensions  42  permit an inspection of the resulting electrical interconnect achieved between the respective traces  36 ,  22  of the patch  14  and flatwire segments  12 , prior to encapsulation of the interconnected segments  12  and patch  14  between two sheets of self-adhesive covers  44 . 
     It is noted that the patch&#39;s flexible substrate  26  is formed of a suitable material, preferably selected to minimize the effect on the patch substrate of a subsequent application of heat and pressure that is required to reflow the solder layers  38 , and to form and activate/cure the adhesive layer  40  bonding the patch  14  to the ends  20  of the flatwire segments  12 . By way of further example, when the substrate  16 ,  26  of any of the flatwire segments  12  or the patch  14  is formed of a relatively-low-temperature thermoplastic material such as polyethylene terephthalate (PET), the pressure applied during solder reflow is preferably tailored to control and/or limit the flow of the substrate  16 ,  26 . 
     Referring again to FIG. 3, in accordance with another aspect of the invention, the patch substrate  26  includes longitudinal extensions  46  that overlie respective portions  48  on the top face  18  of each flatwire segment  12  that are farther removed from the segment&#39;s end  20  than the visible solder layer extensions  42 . And, as best seen in FIG. 3, the flatwire assembly&#39;s adhesive layer  40  extends between the patch substrate extensions  46  and the corresponding portions  48  of the flatwire segments  12  such that, once the patch  14  is bonded to the segments  12 , the patch substrate extensions  46  advantageously provide improved mechanical strain relief to the resulting flatwire assembly  10 . 
     Referring to FIGS. 5 and 6, under an exemplary method for practicing the invention, two flatwire segments  12 , preferably of similar construction with a plurality of “mirror-image” conductive traces  22  extending longitudinally on the respective top face  18  of each segment&#39;s flexible substrate  16 , are positioned relative to one another such that the segment ends  20  are placed in opposition, with the respective traces  22  of each segment  12  in substantial alignment. A suitable liquid flux  50  is preferably applied to each exposed trace  22  of the segments  12  before overlaying the patch  14  directly atop the opposed segment ends  20 , to lower surface tension and to otherwise encourage generally longitudinal reflow of the solder layer relative to the segment&#39;s traces  22 . The patch  14  is then positioned atop the opposed segment ends  20  such that the traces  36  of the patch  14  overlie the respective traces  22  of the segments  12 . The alignment of the segments  12  and the patch  14  is facilitated, for example, through use of alignment holes  52 , in conjunction with a fixture having complementary alignment pins (not shown). 
     Referring to FIG. 6, heat and pressure is then applied to the top face  54  of the patch in the vicinity of the solder layer  38 , designated as the two first heating zones  56  in FIG. 6, to reflow the solder longitudinally relative to the flatwire segments  12  and thereby electrically interconnect the respective traces  36 ,  22  of the patch  14  and the segments  12 . Additional heat and/or pressure is preferably also applied over nearly the entirety of the patch&#39;s top face  54 , designated as the second heating zone  58  in FIG. 6, to form or otherwise activate/cure the adhesive layer  40  that bonds the patch  14  to each flatwire segment  12  (as shown in FIG.  4 ). 
     The solder layer extensions  42 , which then appear as illustrated in FIG. 2, are inspected to confirm that the respective traces  36 , 22  of the patch  14  and the flatwire segments  12  have been electrically interconnected by the assembly&#39;s solder layers  38 , as illustrated in FIG. 3. A protective layer, such as a self-adhesive cover sheet  44 , also as illustrated in FIG. 3, is applied over the bottom face  60  of each flatwire segment  12 , and the respective top faces  18 ,  54  of the segments  12  and the patch  14 , to thereby provide environmental protection for the resulting flatwire assembly  10 . 
     A second exemplary flatwire assembly  62  in accordance with the invention is illustrated in FIG. 7 as including a pair of flatwire segments  12  whose longitudinal ends  20  are joined by a jumper patch  14 . In the second flatwire assembly  62 , the patch includes a polygonal peripheral edge  64  that serves to define both the edges  66  overlying the respective segment traces  22 , out from which the solder layer  38  will longitudinally flow to form the desired solder layer extensions  42  for inspection, and a plurality of patch substrate extensions  68 . The patch substrate extensions  68 , each of which overlies a respective portion  70  of the upper face  18  of each segment  12  that is farther removed from the segment end  20  than the solder layer extensions  42 , provides the second flatwire assembly  62  with enhanced strain relief. 
     While the above description constitutes the preferred embodiment, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims. For example, while the flatwire segments of the exemplary flatwire assembly feature identical patterns of conductive traces, the invention is suitable for interconnecting flatwire segments whose traces are of different sizes. It will also be appreciated that the invention contemplates a wide variety of configurations of fixturing apertures and fiduciary marks to assure proper placement and maintenance of the patch and flatwire segments when interconnecting the flatwire segments under the invention.