WO1992020489A1 - Methods and systems of preparing extended length flexible harnesses - Google Patents

Abstract

The invention relates to systems and methods for the manufacture of flexible printed wiring (FPW) harnesses of unlimited length in three dimensions. In preferred embodiments, continuously updated conductor patterns are imaged on an uninterrupted (i.e., seamless) web-fed base material, or substrate (14). With in-line manufacturing, an FPW harness equivalent to a discrete RWH of unlimited dimension can be fabricated. For example, the substrate (14) can be cut to form circuit layout branches (18 and 20) which are subsequently folded to produce three-dimensional shapes of unlimited size.

Description

METHODS AND SYSTEMS OF PREPARING EXTENDED LENGTH FLEXIBLE HARNESSES

BACKGROUND OF THE INVENTION

Cross-Reference to Related Application

The present application is a continuation-in- part of U.S. Patent Application Serial No. 07/703,724, filed May 21, 1991, the disclosure of which is hereby incorporated by reference in its entirety.

Field of the Invention

The present invention relates generally to systems and methods for designing and fabricating conductive wiring harnesses. More particularly, the invention relates to methods for fabricating wiring harnesses as uninterrupted (i.e., seamless) flexible printed circuitry of unlimited dimension on a continuous, web-fed substrate. The invention can also be used to produce conventional flexible printed circuits.

State of the Art

Presently, round wire harnesses (R Hs) are used in large scale systems (e.g., large appliances, automobiles, office wiring, industrial control panels, and commercial and military aircraft) to interconnect circuit components. An RWH typically includes a bundle of individual wire conductors terminated in connectors for attachment to the various circuit components. Markers are often used to identify the wires and tie wraps are used to hold the bundles together.

While an RWH provides large scale interconnection of components, it suffers from significant drawbacks. For example, because RWH is used in large scale systems, the number of conductive paths is relatively large. The complex routing and connection of the various conductive paths therefore make it difficult to handle the RWH and render assembly of a system using RWH labor intensive. Use of an RWH also results in a highly disorganized wiring scheme in which misconnections of conductors frequently occur and in which location of faults (e.g., breaks in conductive paths) cannot be readily identified and corrected.

RWH includes a large number of individual, round conductors which consume a significant volume of space and which add substantial weight to a system. Because individual wires are routed, an RWH is also highly susceptible to cross-talk and to impedance mismatches with system components.

Further, because an RWH is a bundle of individual wire conductors, the strength of the overall system is limited to the strength of each individual conductor. Therefore, if a single wire is structurally stressed (i.e., typically the shortest conductor), that conductor can break. As mentioned previously, subsequent identification and correction of such breaks are difficult due to the routing complexity of an RWH. Further, this structural limitation often leads to a harness configuration being dictated by strength requirements rather than electrical requirements, such that the harness is often heavier than necessary. Another significant drawback of an RWH is its inability to accommodate modifications in the conductive path layout. Rather, circuit component changes and/or routing modifications of the conductive paths are typically achieved by the addition of new conductive wiring paths, adding to the complexity of the overall system or by a complete redesign of the system, increasing the time required to produce a finished harness.

Another limitation is the inability to directly attach components (e.g., microprocessors, resistors, capacitors, inductors and so forth) to the RWH. Rather, component attachment typically requires the termination of the harness to a conventional printed circuit board. This adds interconnections which are often regarded as the least reliable point in an electronic system.

In small scale applications, efforts have been made to address the foregoing drawbacks with the introduction of flexible printed wiring, or FPW. For example, in the book entitled Handbook of Wiring, Cabling and Interconnecting for Electronics , 1972: McGraw-Hill, Chapter 9 relates to "Flexible Printed Wiring and Connector Systems". Flexible printed circuits are described therein which employ thin, flexible insulation to support circuitry which is covered with a thin overlay of insulation.

In a process schematic shown in Chapter 9, Figure 10 of the aforementioned book, an FPW circuit layout is designed by first creating a circuit layout master. Using the circuit layout master, a layout of conductors is imaged on a photographic negative from which a camera positive is produced. A screen is then fabricated from the camera positive for applying resist to the copper surface of a base material (i.e., substrate) .

Afterwards, chemical etching is used to remove copper left unprotected by the resist. The remaining copper constitutes a desired pattern of conductive paths on the substrate. After the remaining resist is chemically removed, an insulating overlay is subsequently laminated or coated onto the surface, the overlay being of the same material as the base.

In an alternate process described in Chapter 9 of the aforementioned book, the camera negative is used to form the layout of conductive paths. In this process, a photoresist is applied to the entire copper surface. Afterwards, ultraviolet light is passed through the camera negative to "fix" the photoresist material to the base in those areas where conductive paths are to be formed. Unfixed resist is chemically stripped. After unprotected areas of the copper layer have been chemically etched, lamination or coating with an insulating overlay is performed, as described above.

Despite the significant advantages FPW circuits have realized in small scale applications (e.g., cameras, telephones, personal computers, disk drives, and automobile dashboards) , present technology does not provide for the creation of large-scale FPW systems which can replace RWH. For example, screen printing and photographic techniques similar to those described above are currently used to produce flexible printed circuits in a batch fashion. Units, or panels, of limited size (e.g., two feet square) are typically processed one at a time because this is roughly the largest size the image-producing step (e.g., screen printing or photography) can handle easily. Further, current image-production is fairly expensive or slow to alter, resulting in high overhead costs and delays for the small number of runs which would be associated with large-scale FPW.

Because the size limitations associated with FPW have been recognized and accepted by industry, technology in this area has focused on maximizing the use of the available space on a size limited substrate. For example, U.S. Patent No. 4,587,719 discloses a method of batch fabricating flexible circuits in an effort to provide area efficient use of a size limited substrate. As disclosed therein, orthogonal lines of conductors are joined and folded about axes parallel to the conductors. Although the disclosed method permits flexible arrays to be fabricated, its use of traditional imaging techniques imposes size constraints on the overall circuit layout design which prohibit its use as an RWH.

Further, U.S. Patent No. 3,819,989 relates to a printed wiring multiple circuit board assembly wherein printed circuit boards are arranged at right angles to a flexible main tape 10. The flexible main tape is formed with a plurality of conductors and tape tabs 12 through 15 using conventional techniques. The tape tabs connect the main tape 10 and a plurality of overlays 16 through 19. The overlays are formed on each side of the main tape and are bonded to conventional rectangular circuit boards situated in mutually parallel planes perpendicular to the main tape. However, like U.S. Patent No. 4,587,719, the system of U.S. Patent No. 3,819,989 fails to disclose fabrication techniques which would permit the manufacture of RWH replacements. Techniques aimed at joining sectors of FPW to produce the equivalent of an RWH (i.e., a "step and repeat" process) have also been attempted. However, these techniques increase manufacturing complexity and cost, and do not provide a cost effective three- dimensional breakout routing (i.e., branching) capability necessary for RWH replacement. Although individual and unique FPW segments could be combined to produce breakouts suitable for three-dimensional routing, such a combination would significantly increase the number of interconnections, further increasing design and manufacturing complexity and decreasing system reliability.

To address some of the drawbacks associated with the aforementioned step and repeat processes, U.S. Patent No. 3,712,735 discloses a photoresist pattern controlled continuous strip etching apparatus. Here, a continuous loop photographic film transparency of a master pattern is used for contact photo printing of the pattern onto a moving resist coated strip. Because this apparatus merely addresses the problems associated with step and repeat processes by increasing the size of the master film transparency, many of the aforementioned drawbacks associated with small scale FPW applications are incurred. For example, circuits produced by the disclosed apparatus are limited to the size of the master film transparency and are not readily adapted to in-line modifications of the conductor patterns once the master film transparency has been produced.

Thus, while FPW has many recognized advantages relative to RWH, the size limits of FPW have rendered its use in replacing RWH impractical. SUMMARY OF THE INVENTION

Accordingly, a purpose of the present invention is to provide systems and methods for fabricating electrical harnesses capable of replacing RWH. To adequately replace RWH, the harness should provide three-dimensional breakout routing capability and be free of size restrictions. Further, a purpose of the invention is to provide systems and methods for fabricating harnesses such that the circuit layout can be readily modified electronically with limited manipulation of the fabrication process. Such design modifications include, for example, adaptation of a given circuit layout to systems of varied shapes and dimensions. In addition, a purpose of the invention is to provide high throughput of a harness from design to manufacture, and to eliminate high cost inventory requirements associated with the manufacture of traditional RWH.

To achieve these purposes, the invention relates to systems and methods for the manufacture of three dimensional FPW harnesses of unlimited size. In preferred embodiments, an in-line system (e.g., xerography or laser printing) is used to image conductor patterns on a continuous, web-fed base material, or substrate. As the substrate is fed, the image is continuously refreshed.

With in-line manufacturing, an uninterrupted (i.e, seamless) FPW harness equivalent to a discrete RWH of unlimited size in three dimensions can be fabricated. For example, the substrate can be cut to form circuit layout branches which are subsequently folded to produce three-dimensional shapes of unlimited size. The present invention thus overcomes the significant drawbacks associated with traditional RWH. For example, a harness fabricated in accordance with the present invention represents an organized layout of conductive paths having relatively small volume and weight requirements and enabling excellent control of cross-talk and impedance mismatches.

Further, the present invention affords significant advantages not previously realized in fabricating harnesses of any size. For example, the in-line creation of a conductor pattern on a continuously fed substrate provides high throughput while affording optimum design flexibility. An original FPW design and/or subsequent design modifications can be remotely communicated via, for example, telephone networks.

Virtual inventory or electronic inventory can also be exploited in preferred embodiments to avoid any need to maintain a supply of round wire conductors having different sizes and color codes. Only generic raw materials need be maintained in inventory. Because various conductive paths of the layout can be labelled during fabrication, any need to label round wires (traditionally done by direct printing on the wire jacket, color coding or the addition of label sleeves) can be eliminated. Further, because all wires are printed on a common substrate, tie wraps typically used to hold round wire bundles together can be eliminated.

Yet another advantage of the present invention is that the fabrication of a harness as a single FPW element relieves the strain placed on the individual conductors of an RWH. Further, the ability to contour FPW to irregularly shaped surfaces in accordance with the present invention permits increased heat sinking.

In accordance with a preferred embodiment, an extended length flexible printed electrical harness is created by continuously feeding a substrate to an imaging means. In the imaging means, an image of a continuously updated conductor pattern is created electronically on a computer or in hard copy such that the image can be transferred to the substrate. The conductor patter is either directly or indirectly imaged on the substrate. Conductive paths are established on the substrate in accordance with the pattern and are covered with a protective insulating film. The flexible substrate is then cut to form circuit layout breakouts, or branches, and the branches are folded to produce three-dimensional shapes of unlimited size.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments when read in conjunction with the accompanying drawings, wherein like elements have been designated with like numerals, and wherein;

Figure 1 shows an exemplary system for fabricating an FPW harness in accordance with a preferred embodiment;

Figure 2 shows an exemplary, uncut FPW harness formed in accordance with a preferred embodiment; Figure 3 shows a more detailed illustration of an exemplary FPW harness formed, cut and folded in accordance with a preferred embodiment;

Figure 4 shows an exemplary FPW harness formed, cut, folded and placed for a given end use;

Figure 5a shows a portion of an FPW harness which has been formed with electrical components;

Figure 5b shows an equivalent circuit diagram for the Figure 5a FPW harness;

Figure 6 shows a portion of an FPW harness which includes a touch switch;

Figure 7a shows a portion of an FPW harness which includes an electrical component receptacle;

Figure 7b shows an area of an FPW harness where an active electronic component is attached to leads of the FPW harness;

Figure 8 shows a portion of an FPW harness molded into a plastic casing; and

Figure 9 shows a portion of an FPW harness laminated with decorative and adhesive layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment, an extended length FPW harness of conductive paths is fabricated by continuously moving, or web-feeding, an uninterrupted (i.e., seamless) flexible substrate through four general fabrication stations. The first of these includes an imaging means wherein an image of a continuously updated conductor pattern is created electronically on a computer or in hard copy such that the image can be transferred to the substrate. The conductor pattern is either directly or indirectly imaged on the substrate as it is fed. In a second general stage of fabrication, conductive paths are established on the substrate in accordance with the pattern. The conductive paths are subsequently covered with a protective insulating film in a third general stage. The flexible substrate passes to a fourth general stage wherein it is cut to form circuit layout breakouts, or branches. The branches can then be folded to produce three-dimensional shapes.

Each of these stages will now be described in greater detail. It will be appreciated by those skilled in the art that while each of these stages is described separately, any or all of these stages can be combined into a single stage wherein each of the foregoing steps can be performed in sequence. Further, it will be appreciated that appropriate buffering between stages is necessary to accommodate different processing speeds within each stage.

1. Image Conductor Pattern on Substrate

In accordance with preferred embodiments, four general techniques can be used for creating conductive paths on the web-fed substrate: an additive process of forming conductive paths; a subtractive process of forming conductive paths; a conductive ink process; and a tack and peel process. The technique selected for creating the conductive paths will dictate the technique or techniques which can be used to image the conductor pattern, either directly or indirectly, on the substrate. Accordingly, a brief discussion of the four general techniques for creating conductive paths will be provided before discussing the various imaging techniques.

With each of the four general techniques, raster scanning can be used to image a conductor pattern corresponding to the paths of an RWH. Further, patterns can be raster scanned on the substrate for in¬ line testing and inspection of circuits. Alternately, the conductor pattern can be imaged either directly or indirectly or the substrate by rastering with a fixed optical array of energy sources (e.g., row of LEDs or lasers) .

Raster scanning can be effected in a manner similar to that described in the book Imaging Processes and Materials, Sturge, J.M. et al., 8th ed., 1989, the disclosure of which is hereby incorporated by reference in its entirety. For example, Chapter 13 of the aforementioned book is entitled "Non-Impact Printing Technologies" by Werner E. Haas and describes raster scanning with a scanning e-beam tool on page 377. Further, Chapter 18 of the aforementioned book is entitled "Imaging For Microfabrication" , by J.M. Shaw and describes the use of deflectors for raster scanning on page 578. As described on page 578 of the Imaging

Processes and Materials book, raster scanning generally refers to mechanical and electrical scanning with, for example, an electron beam. The beam is switched on and off in accordance with pattern data to image the pattern on a desired surface.

Rastering by a fixed optical array refers to use of a row of LEDs or lasers situated over the moving substrate (direct imaging) or situated over a rotating photocopying drum (indirect imaging) . In either case, varied combinations of the energy sources are activated as the substrate or drum moves past the array to image a pattern on the substrate or array.

In the first technique mentioned above (i.e., additive process) , the substrate is selectively imaged, either directly or indirectly, to create a conductor pattern (e.g., transfer plateable toner) on those portions of the substrate where conductive paths are to be formed. The image may be fixed to the substrate by applying an external source of fusing energy. Once imaged, the patterns are built up (e.g., plated) additively with a conductive material to form the conductive paths.

The second general technique mentioned was a subtractive process, wherein the substrate is coated in its entirety with a conductive material. Afterwards, the substrate is either directly or indirectly imaged for identifying those portions of the substrate where the conductive material is to be removed (positive working resist) or, conversely, imaged for retention to identify those portions where the conductive material is to remain (negative working resist) .

With the third general technique (i.e., plateable ink technology) , an ink-jet printer deposits a catalytic ink (e.g., containing a binder and catalyst such as Sn/Pd) onto selected portions of the substrate surface. The ink may be fixed to the surface by applying an external source of energy. As with the additive process described above, conductive paths can subsequently be formed on these portions of the substrate using a plating process. Alternately, the imaging of a conductor pattern and the establishment of conductive paths on the pattern can be combined into a single stage. More particularly, an ink-jet printer can be used to directly deposit ink containing metal spheres or^*conductive polymers, thus establishing conductive paths which correspond to a desired conductor pattern.

In the fourth general technique, a tacky surface pattern corresponding to a predetermined conductive path is created on the substrate by, for example, transferring electrophotographic or magnetographic toner from a drum, or by ink-jet or dot matrix printing of an adhesive onto the substrate. Alternately, a conductor pattern can be imaged onto a surface coating of the substrate, and the substrate rendered tacky in locally softened imaged areas by light exposure or by chemical or thermal means. Regardless of the technique selected for creating a tacky surface, the surface is subsequently laminated with a metal film. The metal film is then removed (e.g., sucked or peeled) where no tack is available.

If the film is very thin, an electrolytic plating step, as will be described below, may be necessary to build up the conductive paths.

As mentioned above, the substrate can be imaged either directly or indirectly. As referenced herein, direct imaging encompasses image creation of a conductor pattern directly on the substrate. On the contrary, indirect imaging encompasses image creation of a conductor pattern on a drum (e.g., photocopier drum) or photosensitive belt. The image is then transferred to the substrate from the drum or belt.

In both direct and indirect imaging, the image of the conductor pattern is continuously refreshed, or updated, as the substrate is fed. For example, while a conductor pattern is being imaged on the moving substrate, a subsequent conductor pattern stored in memory can be prepared for imaging a down line portion of the substrate.

Direct imaging can be effected using impact or non-impact write-heads, such as: a laser in a laser printer, a nozzle in an ink-jet printer, LEDs, electrophotography (i.e., electrophotographic plateable toner technology) , magnetographic plateable toner technology, and ionography (i.e., ionographic plateable toner technology) . Direct scanning of the substrate can be effected by deflecting light (e.g., laser light) off a mirror surface or by directing light, liquid or solid particles toward the surface through a pivoting head and a shutter. An electrically charged scanning stylus can also be used to electrically erode the substrate to implement a subtractive process. Alternately, the stylus can be any known stylus suitable for piercing, drilling, routing or cutting a surface of the substrate. Any of these direct transfer mechanisms can be situated in clusters or arrays to improve printing speed. For example, rather than scanning the substrate, the rastering of the substrate can also be performed using the aforementioned fixed array of LEDs arranged in a row over the moving substrate. As the substrate moves beneath the row of LEDs, each LED is independently controlled on and off to continuously image the substrate.

The aforementioned nozzles can also be known nozzles for transferring a catalytic ink to form a catalytic pattern on the substrate. As will be described, the pattern of catalytic ink is subsequently plated additively to build up conductive paths on the substrate. In a subtractive process of pattern creation, an ink acting as an etch resist can be transferred to the substrate for subsequent etching. In this latter case, resist can be selectively fixed on the substrate over those areas where conductive paths of the circuit layout are to be formed.

Indirect imaging can be effected by transferring a conductor pattern to be formed on the substrate onto a drum as in conventional photocopying (e.g., electrophotography) using liquid toners or dry toners. Subsequently the pattern on the drum is transferred to the substrate. The pattern on the drum is then continuously refreshed, or updated, as the substrate is fed. As was described with respect direct imaging techniques, indirect imaging can be performed by raster scanning the drum or by rastering the drum with a fixed array of light sources (e.g., LEDs) arranged in a row over the rotating drum. As the drum rotates, each of the LEDs can be independently controlled in on/off fashion to continuously image the drum.

Figure 1 shows an exemplary in-line system for fabricating extended length FPW harnesses of unlimited dimension on a continuous, web-fed substrate using an additive process. In Figure 1, a continuous polymer (e.g., polyimide) substrate 2 formed as a flat sheet is web-fed into an imaging means. In a preferred embodiment, the imaging means is a known laser printer 4, such as a Versatec 8836-11 monochrome laser plotter, Xerox Engineering Systems 8840D, Esselte Meto LIS 1120, Esselte Meto LIS 1520A or Canon LBP-DX. As an insulating substrate, thermoset films such as polyimide films coated with acrylic, epoxy or TFE adhesives, thermoplastic films such as polyester coated with polyester or epoxy adhesives, or polyetherimide (Ultem™) films whose surface acts as an adhesive can be used upon which conductive (e.g., metal) paths can be formed.

In the Figure 1 embodiment, a catalytic plateable toner, such as that described in U.S. Patent No. 4,504,529, is transferred and fixed on the substrate for subsequent electroless plating. For example, using indirect scanning as described previously, a conductor pattern can be imaged onto a continuously refreshed, conventional photocopying drum. As the drum rotates, toner is transferred onto the imaged drum. Afterwards, the toner is transferred from the drum to a continuously moving substrate, and fused to the substrate. As will be further described below, the transfer of catalytic toner in accordance with a continuously refreshed conductor pattern onto the moving substrate 2 permits creation of a flexible printed harness having unlimited dimensions.

The laser printer 4 includes a computer work station 22 which provides in-line computer aided design (CAD) of the conductor pattern on the substrate. Using CAD, original circuit pattern designs and/or modifications can also be received on-line from remote sources (e.g., via telephone networks) and used to update the circuit pattern being imaged (e.g., add or delete patterns) .

CAD can be implemented in a manner similar to that described for conventional printed circuit boards (PCBs) in the article "New Technology Allows Through- Hole and SMT Multilayer Quick Turn Prototype PCBs," PCNetwork, by Bill Schillhamer, Dec. 1990, and U.S. Patent No. 4,767,489, the disclosures of which are hereby incorporated by reference in their entirety. CAD systems such as the Mentor Graphics Cable Station™ can be used to design RWH in three dimensions and to print these harnesses by the techniques described herein on the substrate. Thus, circuit design modifications can be readily implemented during fabrication.

Further, irregular images of multiple different circuits can be printed on the same substrate. These irregular images can be nested in a CAD memory before actual printing. By organizing the irregular shapes on the substrate, space usage of the substrate can be optimized and material waste can be minimized upon forming the conductor patterns to a final shape.

Because conductor patterns can be selectively imaged on either or both sides of the substrate, vias through the substrate can be formed to permit interconnection of these patterns. More particularly, prior to imaging a conductor pattern on the substrate, the substrate is perforated to form the vias.

In a preferred embodiment, perforation of the substrate is performed by the imaging means. Hole punching, cutting, drilling or routing can be effected by, for example:

Scanning laser ablation (e.g., C0₂ or Eximer) ;

High speed numerically controlled knives, drills or routers;

Water-jet cutting; or Scanning abrasive-blaster. Further, a modified impact or dot matrix printer can be used to directly punch through the substrate layer, or high temperature rods can be used to melt through the substrate. The nozzles described previously for imaging the substrate can also be used to effect the aforementioned step of perforating the substrate. The nozzles can dispense chemicals for etching the substrate to form the holes (i.e., perforate the substrate) and to carry out routing. Alternately, the nozzles can dispense eroding particles to perform the etching by boring and routing the substrate in a manner akin to sand-blasting. In addition, the nozzles can direct water toward the substrate for water-jet cutting.

While Figure 1 depicts an exemplary preferred embodiment, it will be appreciated that other imaging techniques, some of which have been mentioned above, can be used. For example, a totally catalytic substrate surface can be formed either by coating the surface with the catalyst or by incorporation of the catalyst into the substrate material. Afterward, a plating resist can be selectively scanned onto the surface with an imaging means such as a photocopier, a laser printer, an LED/ionographic device, or an ink-jet printer. The resist coated portions of the substrate are thus prevented from subsequent plating with conductive materials. For example, "ink"-tape on a normal dot matrix printer can be either a catalyst (for electroless plating) or a resist, depending on whether a non-catalytic or a catalytic substrate is used.

In yet another additive process embodiment, the substrate is coated with a thin metal laminate, and a resist is transferred thereto (e.g., impact or non¬ impact printing) during the imaging stage. The resist is then removed from selected portions of the substrate to image a conductor pattern on the substrate which is subsequently plated to form the conductive paths. Afterwards, removal of the resist and chemical removal of the remaining thin areas which were covered by the resist can be effected.

In alternate additive process embodiments, different toners (e.g., electrophotographic and magnetographic toners) or the catalytic ink in an ink- jet printer can be transferred to form a resist pattern on a metal drum. The drum is then additively or electrolytically plated in areas where no resist is present. Afterward, the conductive paths are peeled off the drum by using a substrate which has been coated with a tacky surface.

As mentioned previously, subtractive techniques can also be used. Subtractive techniques start out with a substrate clad produced by lamination of the polymer substrate with metal films. The polymer film may have the metal (e.g., copper) laminated to one or two sides. An exemplary subtractive method selectively deposits etch resist over areas that are to remain as circuitry. These areas correspond to the conductor patterns which become conductive paths by, for example, chemically etching away the metal left unprotected in the image-producing step.

An ink-jet printer or dot matrix printer can also be modified to selectively deposit the etch resist as an ink directly on the substrate. Alternately, toner can be used as a screen on top of a normal etch resist film to effect a subtractive technique for creating an FPW harness. Subsequent development of an image representing a conductor pattern of the FPW harness can then be used to produce an etch pattern made from common resist films.

Where a resist layer has been non-selectively deposited over a conductive layer, a high powered laser can be used to remove the etch resist film down to the conductive layer. This exposes those portions of the conductive layer which are to be removed. Plasma etching techniques can also be used to remove the resist film. Alternately, to selectively identify those areas where the metal is to be removed, a master can be continuously formed on a transparent surface by, for example, laser printing or ink-jet printing. This master is then synchronously fed into an exposure unit to transfer the conductor pattern image from the transparent film to the photographic etch resist on the metal substrate.

To implement subtractive techniques, electrophotographic or magnetographic toner can also be used as an etch resist. Further, solder can be substituted as an etch-resist. For example, using techniques similar to those described above for ink-jet printers, molten solder can be directly raster scanned as solder resist onto the substrate.

In a related embodiment, information such as bar codes legends, datums and fiducials can be created by any ink-jet printer, laser printer or impact/dot matrix printer that will print on a web. This information facilitates implementation of statistical process control. For example, this information can be printed on the substrate by using the imaging means to label various conductive paths. Such labelling greatly simplifies identification of conductive paths so that accurate connection of the Figure 3 FPW harness to an end system (e.g., see Figure 4) can be attained.

2. Form Conductive Paths on Substrate

In the exemplary Figure 1 embodiment, after the conductor pattern has been imaged on the substrate, the pattern is "fixed" thereto (e.g., thermally, chemically, or other known fixing techniques) . The substrate exiting the laser printer 4 is directed to a continuous roll plating stage 6. In the plating stage, the substrate is continuously transported through plating solutions such that conductive material (e.g., copper) plates the catalytic toner formed during the laser printing stage. The plating takes place catalytically only on the surfaces where an initial catalyst was located (e.g., electroless plating). If necessary, the metal traces which form the conductive paths can be thickened by electroplating over the electroless deposit.

As mentioned previously, exemplary embodiments can be implemented using both additive and subtractive formation of conductive circuitry on a substrate. For example, with additive processes, an FPW harness can be formed using a surface that is rendered catalytic for additive plating processes, as discussed above.

For additive processes, conductive paths can be formed on the substrate using the aforementioned known techniques, including ionographic plateable toner technology (PTT) , electrophotographic plateable toner technology and magnetographic plateable toner technology. However, as described previously, it will be appreciated that the invention is not limited to the use of a catalyst which is subsequently plated. For example, if adhesive toners are used to implement the imaging of a conductor pattern either directly or indirectly, subsequent "tacking off" of metal from a sacrificial sheet is used to transfer a metal pattern for forming the conductive paths. Alternately, if the substrate is melted to image the conductor pattern, metal or catalytic particles are "tacked down" to create the conductive path.

As mentioned previously, conductive paths can also be implemented using known conductive inks. These conductive inks can be put down directly from a modified ink-jet printer thus combining the imaging and formation of conductive paths into a single stage.

For subtractive processes, conductive paths can be formed by chemically etching a substrate formed with a conductive layer, as previously discussed. Once portions of the metal substrate have been exposed, an etching step is initiated to etch away the exposed metal film. Thus, only the metal film covered by the resist remains on the substrate to form the conductive paths of the FPW harness. Continuous etching can, for example, be implemented following the transfer of resist to a metal laminate using either impact or non- impact techniques, as described previously.

3. Cover Conductive Paths with Insulating Layer

In the exemplary Figure 1 embodiment, the substrate is fed from the plating bath 6 through a quality control station 8 (e.g., inspection station) to a lamination station 10 which includes, for example, a hot roll laminator available from General Binding Corp. In the lamination station, an insulating protective cover 12 is formed with vias corresponding to contact points of the conductive paths. The laminate is then pressed onto the substrate as both the laminate and the substrate are unrolled.

A preferred embodiment for a single layer circuit is a protective layer on top of the conductive paths, which can be created by laminating a pre-routed insulative layer (i.e., corresponding to the conductor pattern) onto the substrate layer. Prior to the lamination, openings for component contacts or for path interconnections are provided in the insulative layer by routing/drilling processes similar to those described above for perforating the substrate. Holes (windows) for termination can be opened following lamination by using the aforementioned substrate perforation techniques (e.g., use of a raster scanning laser to ablate the unwanted areas) .

In an alternate embodiment, a lamination film is cured in a pattern on the substrate by scanning a UV-laser on an uncured surface coating. The areas which are not cured by the laser light are subsequently developed away using a known, suitable developer solution to form vias in the lamination.

Electrophotographic or magnetophotographic toner can also be used to create the insulating layer. More particularly, the toner is printed in the desired pattern on the finished conductor layer and then brought to coalesce and cross-link on top of the circuit pattern to create a continuous protective surface with the necessary openings.

In another embodiment, several conductive layers can be formed on the substrate. For example, combining plating additive processes with the formation of a protective layer over each layer of conductive paths makes it possible to build up a multi-layer FPW harness in endless lengths. If several layers have to be laminated, a protective coating can be applied by: raster imaging of insulative toners, screen printing, roller coating with an adhesive or use of a conventional insulative layer after deposition of each conductive layer. The relative position of the layers can be maintained by tacking them down using adhesive dispensed in a manner described previously with respect to creating a tacky surface. Interconnection openings, or pads, between the layers can be formed through the multilayer structure using techniques as described above or by covering areas of the screen where interconnects are desired.

Solder can be reflowed on interconnection pads by applying it through a high temperature ink-jet printer. The molten solder flows into the interconnect holes of the multilayer circuit to electrically connect one or more conductive layers.

4. Slit and Fold of FPW Harness

After the FPW harness has been formed with the conductive paths it can be cut, or slit, to permit folding to its final shape using techniques as described previously (e.g., water jet cutting, laser ablation, and so forth) . Figure 2 shows an extended length flexible conductor harness formed in accordance with a preferred embodiment of the present invention. As shown in Figure 2, the harness includes a plurality of conductive paths formed on a common flexible substrate. Folds for final assembly can be put into the FPW harness, as shown in Figures 3 and 4. The FPW harness shown in Figure 2 can be cut or slit and then folded and/or rolled for shipment. Afterwards, the harness can be unrolled and (if not folded during manufacturing) folded in predetermined directions, as shown in Figure 3. Because the harness can be of unlimited dimension in the direction with which it was formed (e.g., from the left to the right of the harness in Figure 2) , subsequent slitting and folding of the harness permits unlimited fabrication of the harness in three dimensions. Figures 3 and 4 show that creating the FPW harness by slitting and folding permits creation of a printed circuit harness having unlimited dimensions.

To effect the slitting operation in the exemplary Figure 1 system, the laminated substrate 14 is transferred to a cutting station 16. Here, cuts are made in the substrate, as described above, to form harness branches. These branches, such as branches 18 and 20 in the Figure 1 harness, can subsequently be folded to form a three-dimensional harness. In an alternate embodiment, the cuts can be made during formation of the conductive paths, in which case the laminate is formed over only those portions of the substrate which constitute the final FPW harness assembly.

5. Exemplary Uses of Extended Length Flexible Printed Circuit Harnesses

The uses of FPW harnesses are limitless. For example, because an FPW harness produced in accordance with the present invention is relatively flat (e.g., profile thickness less than .25 mm, as opposed to typical RWH thickness of over 5 mm) , it can be readily integrated with structural and cosmetic laminations for use in any device or structure which requires conductive interconnects. Such devices include vehicles, machines, and consumer products (e.g., tools, anti-theft devices, appliances, controllers and so forth) . Structures include buildings and so forth.

The aforementioned uses of FPW harnesses typically involve circuitry such as circuit elements, switches, indicators (e.g., lamps) and so forth. Thus, FPW harnesses in accordance with the present invention can be configured to include such features. For example, Figure 5a illustrates a portion 24 of an FPW harness which can be formed and folded to provide the equivalent circuit shown in Figure 5b.

More particularly, the Figure 5a harness 24 includes a capacitor 26 with first and second electrodes 28, 30, respectively, an inductor 32 and a resistor 34. The Figure 5a circuit can be formed as a portion of an FPW harness in a manner as described above. The exemplary configuration as shown in figure 5a is formed with a first flap 36 and a second flap 38.

When the Figure 5a portion of the FPW harness is to be folded for use in a given environment (e.g., vehicle) , the flap 36 can be folded downward, so as to cover the second electrode 30. The flap 36 will thus serve as a dielectric for the capacitor 26. Afterwards, the flap 38 can be folded to the right hand side of Figure 5a, so as to cover the flap 36. By aligning the first electrode 28 over the second electrode 30, the capacitor 26 is formed.

The capacitance of capacitor 26 can, for example, be varied by adjusting the conductivity of the dielectric 36. The inductance of inductor 32 can be varied by altering the number of turns included therein. The resistance of resistor 34 can be varied by altering the length, width and/or thickness of the conductive path used to form the resistor. The circuit can thus be used as a resistance heater element.

It will be appreciated by those skilled in the art that any circuit can be formed using any number of capacitors, resistors, inductors or other circuit components arranged in any desired order. Further, the printed harness can be fabricated to form controlled impedance FPW by forming inductors and capacitors along the length of the conductive paths.

Further, the FPW harness can be fabricated to include additional circuit components. For example, Figure 6 shows a touch (e.g. membrane) switch 40 which can be conveniently located at any desired location within an FPW harness. During the FPW fabrication process, first and second conductive paths 42, 44 are formed. A plastic covering 46 is formed about at least a portion of the harness with a hole 48 in a bendable plastic flap 50. When the FPW with the flexible plastic covering is ready for installation in, for example, a vehicle, the flap 50 can be bent toward the top of Figure 6 such that hole 48 is located over an exposed, conductive termination node 52 of conductor 44. Afterwards, a flap 54 which includes an exposed, conductive termination node 56 of the conductor 42 can be bent downward such that termination node 56 is located over the hole 50 and the termination node 52. The flap 50 serves as a spacer between nodes 52 and 56.

Printed indicia on an exterior of the plastic covered FPW can be used to indicate the presence of an electrical switch above node 56 or below node 52 and. if desired, to indicate the function of the switch (e.g., "LIGHT"). In operation, the application of external pressure to the FPW at the point where node 56 overlaps node 52 will result in contact between these nodes and activate a circuit connected thereto.

Another component which can be readily implemented in an FPW harness fabricated as described above is an electrical component receptacle 58 (e.g., light receptacle) as shown in Figure 7. Such a feature allows interconnection of electrical components without need for additional connectors. As shown in Figure 7a, first and second conductive paths 57, 59, respectively, are formed on a portion of an FPW harness. The receptacle 58 can be formed as a hole wherein at least a portion of the conductive paths 57 and 59 are exposed to contact conductive leads of an electrical component inserted into the receptacle. It will be apparent to those skilled in the art that additional structural support can be provided for the receptacle if necessary (e.g., form additional plastic around the receptacle). Alternately, connection techniques such as riveting, soldering or wire bonding can be used to connect components to the FPW.

Figure 7b illustrates how an active integrated circuit (IC) package 61 can also be connected (e.g., soldered) to a portion of an FPW harness 63 by attaching (e.g., soldering) leads of the IC to conductive paths of the FPW harness.

Another feature of an FPW harness fabricated in accordance with the present invention is that it can be readily molded into plastic for assembly as a structural component of any device or architecture. For example, Figure 8 shows an FPW harness 60 used to connect to and provide control of a driver side door panel 62. The FPW harness can be fabricated to include control circuitry and touch switches associated with all driver side door panel features (e.g., windows, mirrors, door locks, electric seats and so forth) of an automobile. The FPW harness can be molded into a plastic door liner or panel for easy assembly in the automobile door.

For example, Figure 8 shows a portion of an FPW harness molded into a plastic casing of the door panel 62. Molding of the FPW harness into a plastic door panel avoids any need to fasten (e.g., glue, rivet, screw) the FPW to the doors and thus decreases weight of the door. For example, by coating the FPW harness with a polymer (e.g., polyimide, epoxy, silicone or polyurethane) , the harness can better withstand the heat associated with plastic molding. A similar technique can be used to mold FPW into the exterior casing (i.e., "skin") of any tool, machine, appliance, and so forth, or, for example, into such structural materials as automobile sheet metal.

Further, because of the relatively flat characteristics of an FPW fabricated in accordance with the present invention, it can be laminated with additional materials. For example, the FPW can be laminated with a protective layer or layers; an adhesive layer or layers; a decorative layer, or a layer bearing printed indicia (e.g., label, bar code and so forth) . Thus, as illustrated in Figure 9, an FPW 64 can be laminated for use as an automobile headliner, to include an exterior fabric 66 on one side (e.g., velvet for interior ceiling of vehicle passenger compartment) and an adhesive layer 68 on the other side (for attachment to the metal vehicle roof) . Similarly, the FPW can be used as an underfloor, or it can be used under a floor covering (e.g., beneath carpet and so forth) .

Other specific uses of an FPW harness designed in accordance with the present invention will be readily apparent to those skilled in the art. For example, products made by or integrally formed with an FPW harness made by the foregoing technique include, but are not limited to FPH (flat printed harnesses) , conventional flex circuits, shielded cables, controlled impedance cables such as mircrostrip and stripline, twisted pairs, shielded twisted pairs, heaters, structural assemblies such as control consoles (e.g., dash board assemblies) , antennas, transmitter and receivers, data transmission systems such as 'data buses', solar panel bus bars, active harnesses such as harnesses with active and passive electronic devices (e.g., microprocessors, capacitors, resistors and so forth) directly mounted thereon to serve as local control and monitoring circuits.

It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

What Is Claimed Is:

1. A method for fabricating an extended length printed electrical harness on a flexible substrate, comprising the steps of: providing a continuously moving flexible substrate; creating a continuously updated conductor pattern on the substrate; establishing conductive paths on the substrate in accordance with the conductor pattern; covering said conductive paths with a protective insulating film; and cutting the flexible substrate to form harness branches.

2. A method according to claim 1, further comprising a step of perforating the substrate.

3. A method according to claim 1, wherein the substrate is directly scanned to create said conductor pattern.

4. A method according to claim 3, wherein said direct scanning is performed by directing laser light toward the substrate.

5. A method according to claim 1, wherein said substrate is indirectly scanned to create said conductor pattern.

6. A method according to claim 5, wherein said step of indirectly scanning the substrate further includes steps of: scanning a drum or belt to form said conductor pattern thereon; and transferring said conductor pattern from said drum or belt to the substrate.

7. A method according to claim 1, wherein said step of establishing conductive paths is performed additively.

8. A method according to claim 1, wherein said steps of creating and establishing conductor patterns are performed by applying conductive inks directly to said substrate.

9. A method according to claim 1, wherein said step of creating a conductor pattern further includes a step of applying an adhesive toner to a surface of said substrate, and said establishing step further includes a step of transferring a metal pattern from a sacrificial sheet onto said substrate.

10. A method according to claim 1, wherein said step of creating further includes steps of: laminating said substrate with a conductive layer; depositing resist on the substrate to form said conductor pattern; and said step of establishing further including a step of: continuously etching portions of areas not covered by said resist to form said predetermined conductive paths.

11. A method according to claim 1, further comprising the step of: folding at least one of said harness branches such that at least one of said harness branches extends in a direction perpendicular to at least one conductive path.

12. A method according to claim 1, wherein said steps of creating, establishing and covering are repeated to form plural conductive layers, each having predetermined conductive paths.

13. A method according to claim 12, further comprising a step of establishing holes through said plural conductive layers for interconnecting at least some of said conductive layers.

14. A method according to claim 1, wherein said conductor pattern includes at least one electrical component, said at least one electrical component being a resistive component, a capacitive component, an inductive component, an electrical component receptacle and/or an electrical switch.

15. A method according to claim 1, further comprising a step of molding at least a portion of the extended length printed electrical harness in a moldable plastic casing.

16. A method according to claim 1, further comprising a step of laminating additional decorative and/or adhesive layers to the extended length printed electrical harness.

17. A method according to claim l, wherein said step of creating further includes a step of rastering by a fixed array.

18. A system for fabricating an extended length printed harness on a flexible substrate, comprising: means for continuously feeding a flexible substrate; means for imaging the substrate to create a continuously updated conductor pattern thereon; means for establishing conductive paths on the substrate in accordance with the conductor pattern; means for covering said conductive paths with a protective insulating film; and means for cutting the flexible substrate to form harness branches.

19. A system for fabricating a printed harness according to claim 18, wherein said imaging means includes means for directly scanning the substrate to form said conductor pattern.

20. A system for fabricating a printed harness according to claim 18, wherein said imaging means includes a drum upon which said conductor pattern is indirectly imaged, said conductor pattern being transferred from said drum to the substrate.

21. A system for fabricating a printed harness according to claim 18, wherein said harness is formed with plural conductive layers each having predetermined conductive paths, said system further comprising means for establishing holes through said plural layers for interconnecting at least some of said conductive paths.

22. An extended length printed harness formed on a flexible substrate by a process comprising the steps of: continuously feeding the flexible substrate; imaging the substrate to create a continuously updated conductor pattern thereon; establishing conductive paths on the substrate in accordance with the conductor pattern; covering said conductive paths with a protective insulating film; and cutting the flexible substrate to form harness branches.

23. An extended length printed harness according to claim 22, wherein said process further comprises the steps of: perforating the flexible substrate prior to said imaging step; forming a plurality of vias in said substrate and imaging conductor patterns on opposite sides of said substrate during the imaging step, said patterns and vias be rendered conductive by subsequent plating to form conductive paths on opposite sides of the substrate and through the substrate.

24. An extended length printed electrical harness for use in a vehicle having a vehicle frame and comprising: a flexible substrate; conductive paths formed on the substrate as printed circuitry; a protective insulating film covering the conductive paths, the extended length printed electrical harness further including continuous harness branches which can be mounted to and routed throughout the vehicle frame.

25. An extended length printed electrical harness according to claim 24, wherein said conductive paths formed on the substrate further comprise at least one electrical component, said at least one electrical component including a resistive component, a capacitive component, an inductive component, an electrical switch, and/or an electrical component receptacle.

26. An extended length printed electrical harness according to claim 24, further comprising a plastic laminate for encasing at least a portion of the extended length printed electrical harness, said plastic laminate being molded into a predetermined shape.

27. An extended length printed electrical harness according to claim 24, further comprising additional decorative, adhesive and/or printed layers formed on at least one side of at least a portion of the extended length flexible harness.

28. An extended length printed electrical harness according to claim 25, wherein the capacitive and inductive components are used to form at least one of a shielded cable, a data bus or a conductive path having a controlled impedance.

29. An extended length printed electrical harness according to claim 24, wherein an active electrical device is attached to conductive paths of the harness.