Abstract:
A system and method for reworking, repairing and upgrading flatwire is disclosed. A repair tool for reworking and/or repairing the flatwire is disclosed for creating subsequent electrical and mechanical joints of equal or greater quality as compared to the original system. The repair tool includes a heating blade, a power controller, a tool assembly, an inerting system, a cooling system, a flatwire cassette, a tool material, a flatwire material, an upgrade/repair procedure and various other aspects for rapidly heating flatwire two join two separate portions of the flatwire. The system and method of the present invention addresses the challenges of working with substrate materials which typically degrade at temperatures commonly used to form solder joints. Further, the soldering tool of the present invention may be a portable, lightweight unit that can be used in the field, for automotive and aerospace applications.

Description:
TECHNICAL FIELD 
     The present invention relates to flatwire conductive systems and method and to methods and devices for repairing and replacing portions of the flatwire conductive systems. 
     BACKGROUND 
     Flatwire conductors are being proposed and developed for automotive applications to increase valuable packaging space. The continuous and totally integrated interconnect network has eliminated conventional interconnect nodes where easy repairs and reworks were performed. 
     The lack of practical repair/rework methods has slowed the application of flatwire technology. Therefore, a strategy for reworking, repairing and upgrading flatwire systems is critical to the implementation of the technology, The necessary equipment and operational procedures for the rework and repair should provide an electrical and mechanical joint of equal or greater quality as compared to the original system. 
     Furthermore, a new and improved system and method for repairing flatwire systems should address the challenges of (a) working with substrate materials which typically degrade at temperatures commonly used to form solder joints, (b) working in the service field, (c) providing an accelerated joining process thereby preventing damage to the plastic substrate, (d) joining various polyesters, polyamides and other polymeric substrate materials having various trace geometries and interconnected materials (i.e. solder), and (e) preventing ignition of flammable vapors during the repair process. 
     SUMMARY 
     In an aspect of the present invention a method for reworking, repairing and upgrading flatwire technology is provided. Furthermore, a repair tool for reworking and/or repairing the flatwire is provided for creating subsequent electrical and mechanical joints of equal or greater quality as compared to the original system. 
     In an embodiment of the present invention, a heater, a heating blade, a power controller, a tool assembly, an inerting system, a cooling system, a flatwire cassette, a tool material, a flatwire material, an upgrade/repair procedure and various other aspects for rapidly heating flatwire two join two separate portions of the flatwire is provided. 
     The present invention addresses the challenges of working with substrate materials which typically degrade at temperatures commonly used to form solder joints. 
     The soldering tool of the present invention is a portable, lightweight unit that can be used in the field, for automotive and aerospace applications. 
     The soldering tool uses a rapid peak temperature rise with feedback control and a controlled contact mechanism for adjoining the flatwire (with or without a patch) for the purpose of establishing a metallurgical interconnection. The joining process is accelerated to occur in a brief time (less than 1 second) in order to not damage the plastic substrate. 
     A heat pulse waveform is provided by the soldering to be used with polyester, polyimide and other polymeric substrate materials, various trace geometries and interconnect materials (i.e. solder). 
     An inerting system is also provided to prevent ignition of flammable vapors around the heater during repair. The system maintains an oxygen level which is below 5 percent. The system also maintains cooler exterior tool surfaces. 
    
    
     These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 a  is a perspective view of a soldering tool, in accordance with the present invention; 
     FIG. 1 b  is an end view of the soldering tool, in accordance with the present invention; 
     FIG. 1 c  is a perspective view of a heater for use in the soldering tool, in accordance with the present invention; 
     FIG. 1 d  is a perspective view of an alternate heater embodiment for use with a soldering tool, in accordance with the present invention; 
     FIG. 1 e  is a perspective view of yet another embodiment of a heater for use with a soldering tool, in accordance with the present invention; 
     FIG. 1 f  is a perspective view of still another heater embodiment for use with a soldering tool, in accordance with the present invention; 
     FIG. 1 g  is a perspective view of still another embodiment of heater assembly for use in the soldering tool, in accordance with the present invention; 
     FIG. 1 h  is an exploded view of the heater illustrated in FIG. 1 g , in accordance with the present invention; 
     FIG. 1 i  is an exploded view of a heater subassembly shown in FIG. 1 h , in accordance with the present invention; 
     FIG. 1 j  is a perspective view of a housing for transmitting electrical energy to the heater element shown in FIG. 1 i , in accordance with the present invention; 
     FIG. 1 k  is a block diagram of a heater control system for controlling heat generated by the heater element in the solder tool, in accordance with the present invention; 
     FIG. 1 l  is a chart illustrating the electrical current input to the heater in the corresponding temperature output at the working surface of the blade, in accordance with the present invention; 
     FIG. 1 m  is a schematic representation of the soldering tool illustrating the flow of inert gas between the upper and lower portions of the soldering tool frame, in accordance with the present invention; 
     FIGS. 2 a - 2   d  are plan views of a flatwire, in accordance with the present invention; 
     FIG. 2 e  is a cross-sectional view through the flatwire at a location indicated in FIG. 2 d , in accordance with the present invention; 
     FIGS. 3 a - 3   b  are plan and cross-sectional views through a flatwire and molded housing, in accordance with the present invention; 
     FIG. 4 a  is a cross-sectional view illustrating a punch method for severing the flatwire, in accordance with the present invention; 
     FIG. 4 b  is a front view of a punch cutting tool for punch cutting the flatwire, in accordance with the present invention; 
     FIG. 4 c  is a front view of a cutting tool for severing the flatwire, in accordance with the present invention; 
     FIGS. 5 a - 5   d  are cross-sectional views through a flatwire and flatwire cutting tool illustrating a rotary method for severing the flatwire, in accordance with the present invention; 
     FIGS. 6 a - 6   c  are plan and cross-sectional views of a mending patch for mending flatwire, in accordance with the present invention; 
     FIGS. 7 a - 7   b  illustrate a flatwire having preformed solder repair portions, in accordance with the present invention; 
     FIGS. 7 c - 7   d  are top and cross-sectional views of a flatwire having soldering of windows disposed opposite the preformed solder repair zones; in accordance with the present invention; 
     FIGS. 8 a - 8   c  are crossectional views through the flatwire and the repair tool (shown schematically) illustrating a method for joining two flatwire portions using a mending patch, in accordance with the present invention; 
     FIGS. 9 a - 9   c  are cross-sectional views through the flatwire and soldering tool (shown schematically) illustrating a method for joining two flatwire portions using an overlap joining process, in accordance with the present invention; and 
     FIGS. 10-10 c  are cross-sectional views through two flatwire portions and a mending patch illustrating a method for joining the mending patch to the flatwire potions by heating solder disposed on the patch through windows in the patch, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides a soldering tool  20  as illustrated in FIG. 1 a  and  1   b  in perspective and end views for upgrading, repairing and/or servicing flatwire  48  (shown in FIG. 2 a ). Tool  20  is compatible with several flatwire materials. For example, the present invention contemplates flatwire materials comprised of PET (polyethylene terephthalate), FR-4 (thin), FR-5 (thin), or polyamide or similar material. Such flat wire material is generally flexible and typically has a thickness of 1-5 mils. Soldering tool  20  is configured to position and align two separate portions or pieces of flat wire  48  and then join the two pieces by reflowing solder disposed on the pieces. 
     Accordingly, soldering tool  20  includes a top inerting manifold  22 , a bottom inerting manifold  24 , a heater  26 , a cassette  28  and clamping arms  30  and  32 . Cassette  28  slidably engages bottom inerting manifold  24 . Heater  26  opposes cassette  28  and is affixed to top inerting manifold  22 . Inerting gas is pumped into top inerting manifold  22  through inerting passages  34  and through bottom inerting manifold  24  through bottom inerting passages  36 . A pair of arms or handles  30  and  32  are affixed to top inerting manifold  22  and to bottom inerting manifold  24  respectively, providing means for a tool operator to grasp tool  20 . 
     The tooling pins  27 ,  29  disposed on cassette  28  assist in easy handling and alignment of the flatwire. A loading feature  35  of cassette  28  ensures that flatwire  48  stays flat against a loading surface  31  of cassette  28  and the cutting location is exposed. Loading feature  35  may be spring-loaded to stretch or tension the features. 
     In order to improve the efficiency of tool  20 , cassette  28  may either be covered with a low thermally conductive material or may be preheated. Examples of low thermal conductive materials include ceramic paper, polyimide or Teflon©. Cassette  28  may be preheated using a flexible flat heater  33  (see FIG. 1 a ) made of silicon-rubber and having heating wire or elements disposed therein on a silicon rubber substrate. 
     Heater  26  is configured to have a high thermal efficiency, quick heating response, uniform temperature over the heating edge, capability to self-adjust the temperature during soldering, materials impervious to solder and flux (non-adherent, as welt), good thermal shock resistance, and good thermal wear resistance. 
     In an embodiment of the present invention, heater  26  includes a heating element  37  that is planar, as shown in FIG. 1 c . Further, heating element  37  has a resistor  41  in the shape of a repeating U-pattern and is bonded to a ceramic substrate  43 . An exposed side of the element or heating side is covered by a dielectric to prevent an electrical short The heating side of the element directly contacts a metal blade  39  so that the heating element heats the blade more efficiently. In order to heat blade  39  more uniformly, an additional heating element  37  may be attached to opposite sides of the blade. If the overall size of the blade and the heating elements is a concern, a single element on one side of the blade is acceptable. A slot  45  is provided on either side of blade  38  to hold the heating elements  37  in position. If space is available, heating element  37  may be placed on a top surface  46  of blade  39 . 
     In an alternate embodiment of heater  26 , as shown in FIG. 1 d , a plurality of short-tube heating elements  50  are provided. Short-tube heating elements  50  are inserted into apertures  52  of blade  39 ′. Generally, the thick resistance film  41  is spirally bonded to either a tube or cylinder type of substrate while the resistor is electrically protected with a dielectric coating. For example, a resistance heating alloy wire, coated with a dielectric, can be spiraled over a ceramic tube to form a similar heating element. The through holes  52  at the lower region  54  of blade  39 ′ hold elements  50  in place. In operation, the heating elements  50  heats up blade  39 ′ from the inside of holes  52 . 
     In yet another embodiment a probe type of heating element  26 ″ is provided to heat a blade  39 ″ illustrated in FIG. 1 e . The probe-heating element  26 ″ can be made of either a thick resistance film or a resistance alloy wire  55 , spirally wound over the surface of a ceramic tube  56 . A plurality of deep holes disposed in blade  39 ′ receive wire  55  bringing the heating tips  57  closer to a heating. edge  59  of blade  39 ″. A dielectric coating is deposited on the heating elements that provide good thermal conduction and electrical isolation as well. The upper part of the heating element provides a mechanical fixture and a ceramic tube for passing electrical connectors. 
     Still alternatively, a longitudinal-tube type heater  26 ′″ is provided, as shown in FIG. 1 f . Heater  26 ′″ is constructed using either a thick resistance film or a resistance alloy wire  63  spiraled over a ceramic tube  65 . The resistor wire  63  is coated with a dielectric forming a plurality of dielectric layers, which provide good thermal conduction and electrical protection. A through-hole  67  is drilled in blade  39 ′″ along the longitudinal direction of the blade so that the wire  63  and ceramic tube  65  assembly may be inserted into through-hole  67  of blade  39 ′″. 
     Longitudinal tube type heater  26 ′″ has a heat spreader  69  disposed over wire  63  and ceramic tube  65 . Heat spreader  69  improves temperature uniformity across blade  39 ′″. The heat spreader  69  is made of a high thermally conductive metal such as copper while the blade is made preferably of titanium. The heat sourced from wire  63  will be redistributed by spreader  69  so that uniform temperature will be provided along a blade surface  59 ′″. Additionally, in order to improve heat transfer through a blade to the flatwire, an air gap can be added between spreader  69  and the heating element, on the three sides not in the critical heat transfer path. 
     In all of the heating element embodiments mentioned above, the resistors are connected to the electrical connectors or lead frames by various conventional methods so that electrical power can be supplied to resistors. Preferably, the mechanical load is only applied to a top surface of the blade. 
     Preferably, for all heater embodiments described above, the heating elements should be physically close to the heating-edge  59 ″,  59 ′″, so that any temperature modification in the heating element are reflected at the edge of the blade closest to the flatwire as quickly as possible. 
     The blade  59  may be constructed of metals, such as brass, molybdenum, and stainless steel. However, to avoid the solder and flux adhering to the heating edge of the blade and reduce heat lose from blade, a titanium blade is preferred. 
     In yet another embodiment, a heater  81  is illustrated in FIG. 1 g  is provided for heating flatwire to reflow solder paste disposed thereon. Heater  81  is fixedly mounted within tool  20  and attached to the upper portion  22  through a plurality of fastener holes  83  disposed in a cover  85 . Further, heater  81  includes a pair of heater subassemblies  87   a  and  87   b . A connector plug  86  is further provided for communicating electrical power to the heater subassemblies  87   a  and  b.    
     Referring now to FIG. 1 h , an exploded perspective view of heater  81  is illustrated. As shown, a housing  89  is sandwiched between heater subassemblies  87   a  and  87   b . Preferably housing  89  is made of a thermally non-conducting material, such as plastic. Further, cover  85  includes two portions  85   a  and  85   b , which meet to form cover  85 . 
     Referring now to FIG. 1 i , an exploded perspective view of the heater subassemblies  87   a  and  87   b  is illustrated. Heater subassemblies  87   a  and  b  include a heating element  95  comprised of a ceramic substrate having a resistive heating wire screen printed thereon. Heating element  95  is positioned against a blade  97  preferably made of brass and configured to transmit heat to a flatwire surface. A metal cover  99  is placed over heating element  95 . In order to concentrate the heat energy emanating from heating element  95 , a plurality of heating blades  101  are disposed on the outer surfaces of the metal cover, heating element, metal bade assembly. 
     Referring now to FIG. 1 j , a detailed illustration of housing  89  is shown. Housing  89  includes a metal lead frame  103  for providing power to heating element  95 . Lead frame  103  include power connection ends  105  and heating element connector ends  107 . Preferably, lead frame  103  is insert molded within, housing  89 . 
     Preferably, temperature sensor  61  (thermocouples) are placed in blade  39 ′″, in order to monitor the temperature level at the heating edge. For example, a thermocouple may be placed at one of comers of the blade  39 ′″ and extend as far as the middle of the blade (see FIG. 1 f ). For example, a thermocouple is placed inside of the blade or attached to the outer surface of the blade, where it can be close to the middle point of the soldering surface. The thermocouple should be as close to the hot surface or working surface  59 ′″ as possible, preferably less than 1 mm. Preferably the thermocouple is sensitive to temperature changes. The maximum delay time should be less than 0.1 seconds. 
     A control circuit for controlling heater  26  is illustrated in FIG. 1 k . A power control unit  71  is provided to supply AC/DC, with either a variable current at a constant voltage or a variable voltage to supply a constant current, to heater  26 . The temperature response of the heater to current input  73  is shown in FIG. 1 l . Power control unit  71  in the control loop monitors the temperature level read by thermal sensors at finite time increments and adjusts the current supply to keep heater temperature  75  within a narrow window. 
     In operation, the power is switched on and an initial high current pulse  77  (under a constant voltage) brings the heater temperature up very quickly as shown in FIG.  11 . Meanwhile, the control unit keeps scanning all data channels from thermal sensors. When the temperature readings exceed the operation temperature at a time t1, the current is reduced to set the temperature back to the expected level. At time t 2 , the heater temperature drops sharply while heater comes into contact with the repair area. When the control unit detects such temperature drop, another high current pulse raises the temperature upwards to an operational level (i.e. reflow the solder). At a time t 3 , the current is reduced again as the temperature readings are satisfied. A time t 4  the cooling process is initiated. At a time t 5 , the power is switched off and the heater cools down gradually. 
     In order to ensure the safety of the operator, when near fuel (aerospace or automotive), soldering tool  20  is blanketed with an inert gas, such as nitrogen. The inert gas will prevent oxygen from getting to the heated areas (i.e. heater  26 ) of the tool. Soldering tool  20  is attached to a nitrogen source (not shown) and has channels surrounding heater  26 . Thus, a blanket of an inert gas around tool  26  is provided. The flow of inert gas (as indicated by arrows q will extend to the flatwire and cassette  28 , enveloping portions of the tool having elevated temperatures, as shown in FIG. 1 m . The inert gas is also fed into cassette  28  to assist in cooling the flatwire, after the soldering process. 
     This inerting system maintains an inert atmosphere (less than 12,000 ppm oxygen) around heater  26  to prevent ignition of fuel vapors while in operation. The blanket of inert gas eliminates the need for an enclosure and provides cool exterior surfaces of tool  20  by shielding the hot regions of the tool (i.e. heater  26 ). Similarly, the inert gas flow keeps adjacent flatwire regions cool during repair and provides rapid cooling of heater  26  after use. 
     With reference now to FIGS. 2 a - 2   e , flatwire  48  typically has a plurality of copper layers  40  and dielectric layers  42 . An adhesive  43  is used between the copper and dielectric layers, or in other embodiments of the present invention, flatwire  48  is adhesive-less. Along any section or portion of flatwire  48 , there may be multiple traces  44  of the same or varying widths and spacings. Any given section or portion of flatwire  48  should be singulated into widths of 10 mm to 100 mm. Furthermore, flatwire  48  may be either single or double sided, having copper traces  44  of 1-4 ounces disposed onto a top surface or bottom surface of dialectric layer  42 . 
     Generally, the section of flatwire  48  to be soldered will have a width less than or equal to 80 mm. A plurality of tooling holes  50  are provided on an outside edge  52  of the flatwire, and are disposed in line with or near a soldering zone  54 . Portions of traces  44  that are in soldering zone  54  are protected with either a SnPb plating (at least 0.5 mil thick), HASL, OSP or immersion silver deposit. A solder mask is deposited on portions of traces  44  that are not in soldering zone  54 , as well as on the dielectric between copper traces  44 . Alternatively, a protection tape may be used over this deposit/preservative. Preferably the tape would be placed over soldering zone  54  during manufacturing, and removed prior to soldering. 
     In another embodiment of the present invention each soldering zone  54  of flatwire  48  (original, upgrade, repair and service pieces), is designated and labeled with a bar code. The bar code will be read prior to any changes, in order to ensure proper materials and processes are used during the upgrade, repair and/or service. 
     The original flatwire piece will have the reliability equal to the reliability of the copper traces under the soldermask (not in the soldering zone). The original flatwire piece is cut prior to assembling the upgrade/repair flatwire and completing the soldering process. 
     In yet another embodiment of the present invention flatwire  48  is fitted with cassette  28 . Cassette  28  acts as a support base or fixture that ensures the integrity of flatwire  18  during repair. Cassette  28  is a low-profile platform that is slidably positioned under an original and a replacement flatwire portions. Cassette  28  supports to the underside of soldering zone  54 , and acts as a thermally insulated handling device for ease of use and safety by a tool operator. Further, cassette  28  assists in nitrogen inerting of the tool and nitrogen cooling of the flatwire, heater(s) and the tool. A pair of alignment pins  27  and  29  ensures alignment of traces  44 . 
     Cassette  28  is keyed to soldering tool  20 , such that there is only one way to insert cassette  28  into the tool, and such that only the designated areas on the flatwire/repair patch are exposed to the heaters or cutting blade. The cassette ensures intimate contact between flatwire portions to be joined/soldered prior to tool operation. 
     A flatwire repair patch may be used, where the patch is placed over the flatwire. Otherwise, the two flatwire portions may be joined by overlapping the flatwire creating a lap joint. 
     If the repair is a double sided repair, a second repair patch may be placed in cassette  28  first, before placing the flatwire portions to be joined on top. Alternatively, a second patch may be added later in the soldering process. 
     As shown in FIGS. 2 b - 2   e , two predefined alignment holes  60  positioned on the same side of a cutting line  62  are used for aligning the cutting line with the cassette or a cutter edge. Another pair of alignment holes  64  are located opposite alignment holes  60  such that cutting line  62  is disposed between alignment holes  60  and  64 . This configuration allows a cutting tool easy access to the cutting line from either side of the cable, at an operator&#39;s convenience. After cutting along line  62 , flatwire portions A and B have a repair zone  63 . So the possibility of miscutting is eliminated no matter which portion A or B needs repairing. For example, if portion A needs repairing (as shown in FIG. 2 d ) the operator would cut along cut line Ca and if portion B needs repairing the operator would cut along cut line Cb. 
     Where flatwire is connected to a molded housing, as shown in FIG. 3, two cutting lines  72  and  74  are required in the soldering zone. After cutting, the cut strip can be peeled off from flatwire to disconnect the original electrical circuit. At least two predefined alignment holes  76  and  78  adjacent each cutting line, are used to align the desired cutting lines with a cutter edge. Thus, the cutting tool can easily access the cutting position from the opposite direction of the flatwire at an operator&#39;s convenience. 
     In an embodiment of the present invention, tools for cutting FFC, FFS or other flatwire at a repair or soldering site so that the damaged or nonfunctional units can be removed is provided. The cutting tools provide a precise, clean and effective way to separate failed nonfunctional flatwire. The cutting tools perform punch cutting, gradual cutting, and rotator cutting. In embodiments of the present invention, the cutting tools are configured to be portable, have a bar code reading and GPS positioning capabilities (with the appropriate software). 
     With reference to FIGS. 4 a - 4   d , flatwire cutting methods are illustrated, in accordance with the present invention. Punch cutting, as illustrated in FIG. 4 a , is primarily used for flatwire that is not supported by a molded housing (as shown in FIG. 3 a ). A punch cutting tool  90  includes a cutter  92 , a support base  94 , alignment pins  96  with an adjuster, and a clamping plate  98 . In operation, the alignment pins  96  are inserted into a pair of alignment holes in the flatwire and are used to align the cutting line on base  94 . Clamping plate  98  contacts the flatwire to stabilize the cutting line. Cutter  92  having a cutting edge  100  is driven towards the flatwire, equally by a force-through mechanism in a direction indicated by arrow f, to separate the flatwire along the cutting line at one time by a shearing action. The punch cutting tool  90  is preferably used to cut flatwire having fine traces. 
     FIG. 4 c  illustrates a method for cutting flatwire referred to herein as gradual cutting. A gradual cutting tool  110  includes a gradual cutter  112 , a base  114 , alignment pins  118  with an adjuster, and a clamping plate  120 . In operation, alignment pins  118  are inserted into a pair of positioning or alignment holes in the flatwire to align the cutting line with respect to base  114 . Clamping plate  120  contacts the flatwire to secure the cutting line and keep the flatwire from moving. When gradual cutter  112  having cutting edge  122  pivots toward base  114 , the flatwire is sheared and separated along the cutting line. Gradual cutting tool  110  is preferably used on flatwire having heavy or wide traces. 
     With reference to FIGS. 5 a - 5   b , a rotary cutting method is illustrated. Rotary cutting is particularly useful for severing flatwire attached to a molded housing (as shown in FIG. 3 a ). A rotary cutting tool  150  includes either a single- or double-cutting-edge. The cutter  152  can be driven by either an electric motor or by a manually applied force in a direction indicated by arrow R. In the manual version, tool  150  includes a rotator cutter(s), cutter holder, cutting depth adjuster, adjustable spring position pins, guiding ruler, and a handle. In the automated version, an electric motor is added. In operation, a movable position pin is adjusted so that the position pins can fit in alignment holes disposed in the flatwire. The cutting depth or cutter  152  may be adjusted to avoid over-cut and further damage of molding substrate  154 . 
     A clamping force is applied to the flatwire using a clamp  156  to hold rotary tool  150  against the flatwire. A push handle  158  is directed toward flatwire to drive the cutter  152  forward while rotating over the cutting lines. After cutting, cutter  152  is lifted from the flatwire and a cut strip  160  containing the flatwire is removed, as shown in FIG. 5 c . However, if a subsystem  162  has failed then the entire subsystem is removed. In either case, a protective tape or film  164  covering the circuit traces is removed exposing same. 
     The cutting tools described above are configured to be used with or without cassette  28 . After a flatwire circuit failure, the flatwire is removed from the system using a cutting device such as previously described, the protective films are peeled off from repair zones on the original portion and on the flatwire replacement portion or patch. 
     A flatwire replacement patch  180  is illustrated in FIGS. 6 a - 6   c  with and without soldering windows  191 . Flatwire replacement patch  180  is constructed of a dielectric layer or substrate  182  supporting and a plurality of copper traces  190 . Generally, the Substrate  182  may be a polyimide or similar material. The weight of the copper traces match the traces on the original flatwire part. Patch  180  may have an adhesive layer or be adhesive-less. The patch as shown is single sided. Since the original flatwire part and the replacement part or patch may be double sided, and may have a complex trace geometry, more than one patch may be used. 
     As shown in FIG. 6 b  patch  180  has windows  191  through the polyimide substrate exposing the copper traces  190 . Windows  191  are temporarily protected with a removable window film. The window films disposed both sides of the patch. After a repair is complete, the protective film  186  is placed over the soldering windows. 
     In operation polyimide is in the path of the heat transfer between the heater  26  and solder  185 . Since polyimide is a low thermal conductive material, it will take longer to reflow the solder if there isn&#39;t a solder window directly to the copper. However, advantageously a polyimide film placed over a low temperature substrate can prevent the substrate from over heating, especially for polyester substrates. The polyimide film also acts to keep surfaces of heater  26  clean. 
     In an embodiment of the present invention, bar code information located near the repair zones will specify the appropriate patch required. If more than one patch  180  is used, the sum of the patches traces will match the original and replacement part requirements. All patches are pre-fluxed during their manufacturing, and will have either a HASL or a SnPb finish. A protection tape  186  over the patch may be used to promote a long shelf-life. Protection tape  186  may have sufficient or extra flux in the adhesive. Each patch has at least four alignment holes for cooperating with to the original and replacement flatwire portions. The patch length (parallel to the copper traces) is approximately 12 mm. Preferably, repair patch  180 , as shown in a cross-sectional view in FIG. 6 c , has copper traces  190  having preformed solder  185  on a bottom-side, which is protected during storage, with a removable film  186 . 
     As shown in FIGS. 7 a  and  7   b , an embodiment of a flatwire  48 ′ having a polyester substrate  192  is provided. For this configuration of flatwire, a mending patch, as illustrated in FIGS. 6 a - 6   c , is required. 
     As described in previously embodiments, flatwire  48 ′ has alignment apertures  170  along either side of substrate  192 . Further, a plurality of copper traces  173  are adhered or similarly mounted to a surface  172  of substrate  192 . As illustrated in a cross-sectional view in FIG. 7 b  preformed solder  174  is disposed at predefined intervals along traces  173 . The preformed solder  174  is spread with a protective film  175  to prevent debris from contaminating the solder. In yet another embodiment, a flatwire  48 ″ has a polyester substrate  176  and an integrated repair patch, as shown in FIGS. 7 c  and  7   d . Thus, no separate repair patch is required. Further, in this embodiment, flatwire  48 ″ has a polyimide material disposed in a soldering window  177  instead of polyester material. However, a polyimide material may be used for both the substrate and the window. As in the previous embodiments, flatwire  48 ″ has a plurality of conductive traces  173 , preferably made of copper, mounted to substrate  176 . Opposite the soldering windows  177  is disposed preformed solder on traces  173 . A removable protective film  178  is placed over the soldering window  177  as well as over the preformed solder  179 . This flatwire configuration is directly solderable to any other flatwire without a mending patch. 
     Direct contact between heater  26  and copper traces  40 , in an open soldering window  190  format provides an improved process, and enables the pulsed heater  26  to repair heavy copper power traces and flatwire that are attached to large heat sinks. Moreover, since the direct contact between the heater and the copper traces helps to heat up the solder quickly, the heat dissipation effect becomes less significant. However, it is possible that melted solder and flux will adhere to the surface of heater. Preferably, the heater is coated with a non-wetting metal, such as titanium, to alleviate the problem. Otherwise, the heater will need to be cleaned frequently. 
     With reference to FIGS. 8 a - 8   c , a method for repairing flatwire will now be described. In one embodiment of the present invention, flatwire  48  is repaired using mending patch  180 , by first feeding flatwire  48  into soldering tool  20  (shown as a partial cut-away). The flatwire  48  is positioned and held in place by alignment pins  27  and  29  (see FIG. 1 a ) disposed on cassette  28  in soldering tool  20 . Next, the mending patch  180 , after removal of protective film  186 , is laid over flatwire  48  such that a pre-soldered side  189  faces and aligns with copper traces  40  on a flatwire  48 . Clamp  35  (in the cassette) is actuated to hold mending patch  180  against flatwire  48  in alignment therewith. In the meantime, heater  26  is turned on and heated-up to an operating temperature (which generally will take a few seconds). Once the temperature of heater  26  (shown schematically) reaches an operating level, the heater is released from a holding position and is pressed against the soldering windows of patch  180 . The heater temperature is held at a reflow temperature level until the solder in the solder window melts. Thereafter, the heater supply power is switched off so that the heater temperature generally cools down to form high quality solder joints. The present invention contemplates using this repair method with all types or variations of polymeric substrates. 
     In an alternative embodiment of the present invention, a method for repairing flatwire  48  without using a separate mending patch  180  is provided. As shown in FIGS. 9 a-c , after removal of the protective films, a first flatwire portion  196  positioned onto cassette  28 ′, aligned and held in place by position pin  27  and  29  (not shown), and then a second flatwire portion  195  is laid over the first flatwire portion forming a lap joint  197 . Further, the pre-soldered side of the copper traces face and align to the copper traces on the first flatwire portion  196 . Clamp  35  is actuated to hold the over laid flatwire portions  195 , 196  in alignment In the meantime, heater  26  is switched on and heated-up to an operating temperature. Once the heater temperature reaches the operating temperature, heater  26  is released from a holding position (shown in FIG. 9 b ) and is pressed against the soldering windows of the flatwire (as shown in FIG. 9 c ). The heater temperature is held at the reflow temperature level until solder in the solder windows melt. Thereafter, the heater supply power is switched off so that the heater temperature cools down gradually to form high quality solder joints. 
     In embodiments where the flatwire  48  is attached to a plastic molded housing  198 , a replacement flatwire  48 ′ is pre-aligned using two temporary alignment pins  200 , as illustrated in FIG. 10 a . A mending patch  202  is loaded onto a clamp plate  35  with the exposed traces facing flatwire  48 , 48 ′. Next, soldering tool  20  is placed at the repair zone by inserting four alignment pins  204  into position holes  206  after the temporary alignment pins  200  are removed. Now that the flatwire  48 , 48 ′ and repair patch  202  are aligned on clamp plate  35  and the tool is held in place, the heater power is switched on to bring the temperature up to an operating level. Once the heaters are at the operating temperature, heaters  26  are moved to contact the soldering window, as illustrated in FIG. 10 c . The heaters  26  maintain a contact pressure and temperature until pre-formed solder  208  reflows. Then the electrical power supply is switched off so that the solder  208  can solidity gradually as the temperature cools down. 
     In still another embodiment of the present invention, the bar code is disposed adjacent each soldering zone. The bar code will designate the type of patch, upgrade/repair piece, process conditions for cutting and the soldering tool, as well as which cassette to use. 
     As any person skilled in the art of flatwire conductive systems will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.