Abstract:
In one embodiment the present invention includes a direct-write laser lithography system. The system includes a reel-to-reel feed system that presents the clear film-side of a single-sided metal-clad tape to a laser for direct patterning of the metal. The laser beam is swept laterally across the tape by a moving mirror, and is intense enough to ablate the metal but not so strong as to destroy the tape substrate. In another instance, two specialized lasers are used, one tuned to ablate large field areas, and the other tuned to scribe fine features and lines. The ablated metal blows off in a downward direction and is collected for recycling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part (CIP) application of U.S. patent application Ser. No. 11/544,499, titled “Reverse Side Film Laser Circuit Etching”, filed Oct. 5, 2006. 
     
     BACKGROUND 
       [0002]    The present invention relates to flexible circuits, and in particular to methods, systems, and devices for manufacturing flexible circuits in high volumes and at low costs. 
         [0003]    Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
         [0004]    Radio frequency identification (RFID) device technology is proliferating everywhere and into everything. Right now, a worldwide effort is stepping into high gear to replace the familiar universal product code (UPC) barcodes on products with RFID tags. The ink and labels used to print UPC barcodes is very inexpensive, and the costs of RFID chips and printed circuit antennas are under a lot of pressure to match them. Large, expensive items, of course, are not price sensitive to the cost of a typical RFID tag. But mass produced commodity items need tags that cost only a few cents. 
         [0005]    The majority of printed circuit boards (PCBs) are made by depositing a layer of copper cladding over the entire substrate, then subtracting away the unwanted copper by chemical etching, leaving only the desired copper traces. Some PCBs are made by adding traces to a bare substrate by electroplating. 
         [0006]    Three common subtractive methods are used to make PCBs. Etch-resistant inks can be screened on the cladding to protect the copper foils that are to remain after etching. Photoengraving uses a photomask to protect the copper foils, and chemical etching removes the unwanted copper from the substrate. Laser-printed transparencies are typically employed for phototools, and direct laser imaging techniques are being used to replace phototools for high-resolution requirements. PCB milling uses a 2-3 axis mechanical milling system to mill away copper foil from the substrate. A PCB milling machine operates like a plotter, receiving commands from files generated in PCB design software and stored in HPGE or Gerber file format. 
         [0007]    Additive processes, such as the semi-additive process, starts with an unpatterned board and a thin layer of copper. A reverse mask is then applied. Additional copper is plated onto the board in the unmasked areas. Tin-lead and other surface platings are then applied. The mask is stripped away, and a brief etching step removes the now-exposed thin original copper laminate from the board, isolating the individual traces. 
         [0008]    The additive process is commonly used for multi-layer boards because it favors making plating-through holes (vias) in the circuit board. 
         [0009]    Circuit etching methods that use chemicals, coatings, and acids are slow, expensive, and not environmentally friendly. Mechanical etching has been growing rapidly in recent years. Mechanical milling involves the use of a precise numerically controlled multi-axis machine tool and a special milling cutter to remove a narrow strip of copper from the boundary of each pad and trace. 
         [0010]    Conventional laser etching of circuit traces is from the side with the metal to be etched. The metal, smoke, and debris goes flying directly in the path of the laser beam trying to do its work. The laser and its optics need frequent cleaning in order to maintain etching efficiency. But lasers can be a very fast, environmentally safe way to mass produce printed circuits, e.g., RFIDs on flexible printed circuits (FPC) using DuPont&#39;s KAPTON polyimide film. 
         [0011]    Thus, there is a need for improved systems and methods for electronic circuit formation. The present invention solves these and other problems by providing systems for reverse side film laser circuit etching. 
       SUMMARY 
       [0012]    Embodiments of the present invention improve systems and methods related to the formation of electronic circuits and related electronic components. 
         [0013]    A direct-write laser lithography embodiment of the present invention comprises a reel-to-reel or sheet feed system that presents the reverse side of a single-sided metal-coated media to a laser for direct patterning of the metal. The laser beam is swept laterally across the media by a moving mirror, and is intense enough to ablate the metal but not so strong as to destroy the media substrate. The ablated metal blows off in a downward direction and is collected for recycling. 
         [0014]    According to another embodiment, two or more specialized lasers are used, one tuned to ablate large field areas, and the other tuned to scribe fine features and lines. 
         [0015]    According to another embodiment, a laser movement system moves the laser in relation to the metal-coated media in order to direct the laser beam without mirrors. 
         [0016]    One feature of certain embodiments of the present invention is a system that can produce RFID circuits on flexible printed circuits at a low cost per unit. 
         [0017]    Another feature of certain embodiments of the present invention is a manufacturing method that produces very little waste and that readily recycles the metals ablated from the tapes. 
         [0018]    Another feature of certain embodiments of the present invention is a manufacturing method for flexible printed circuits that allows for continuous production. 
         [0019]    The following detailed description and accompanying drawings provide a better understanding of the nature and advantages of the present invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a block diagram of a direct-write laser lithography system according to an embodiment of the present invention that uses a single laser to ablate metal from film wound reel-to-reel or sheets fed from a sheet feeding system. 
           [0021]      FIG. 2  is a block diagram of a dual direct-write laser lithography system according to an embodiment of the present invention that uses one laser to ablate wide fields of metal, and another laser to ablate narrow fields to form fine lines and features. 
           [0022]      FIG. 3  is a plan view diagram of a RFID device constructed with a flex circuit antenna etched by the system of  FIG. 1 ,  FIG. 2  or  FIG. 4 . 
           [0023]      FIG. 4  is a cross-sectional view diagram of a reverse-side laser ablation system according to an embodiment of the present invention. 
           [0024]      FIGS. 5A-5E  are plan views showing thermal isolation ablation performed on a coated film according to certain embodiments of the present invention. 
           [0025]      FIG. 6  is a flowchart of a method of laser circuit etching according to an embodiment of the present invention. 
           [0026]      FIG. 7  is a block diagram of a control system for controlling laser ablation according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Described herein are techniques for reverse side film laser circuit etching. In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention as defined by the claims may include some or all of the features in these examples alone or in combination with other features described below, and may further include obvious modifications and equivalents of the features and concepts described herein. 
         [0028]      FIG. 1  represents a direct-write laser lithography system embodiment of the present invention, and is referred to herein by the general reference numeral  100 . System  100  is used to manufacture flexible printed circuits (FPC), and comprises a metal-on-film substrate tape  104  wound on a supply reel  106  and a take-up reel  108 . The tape  104  has a transparent film substrate  110  and a thin-film metal cladding  112 . The transparent film substrate  110  may comprise polyimide, PEN, polyester, polycarbonate, etc. The thin-film metal cladding  112  may include copper (Cu), aluminum (Al), platinum (Pt), etc. 
         [0029]    A laser  114  is used to ablate off the metal from the backside of tape  104  as it translates from supply reel  106  to take-up reel  108 . A mirror  116  moves a laser beam  118  to various lateral points across the tape  104 . Once laser beam  118  is positioned properly, a pulse of energy is generated enough to ablate metal  120  away. In such manner, the remaining portions of the metal  112  are patterned to create electrical circuits, e.g., RFID antennas. A metal collection and recycle system  122  captures the ablated metal  120  and recycles it. The metal collection and recycle system  122  may include a vacuum pump. 
         [0030]    Observe in the embodiment shown in  FIG. 1  that the ablated metal  120  does not fly or plume into the path of laser beam  118  because the ablation is on the opposite side to the laser. The result is less laser energy is needed to get the job done. If the laser energy is too high, the ablated material may convert to plasma and the vapors can coat components of the system  100 . One feature of the embodiment shown in  FIG. 1  is to carry away pieces for recycling, so it is often desirable that the ablation dislodges or tears away solid chunks of metal. So breaking the adhesive bond between the metal and the substrate of the tape can be desirable feature of the ablation. 
         [0031]    Gravity and/or vacuum caused airflow is used to assist the falling away and collection of ablated metal  120 . 
         [0032]    The materials used for the transparent film substrate and the wavelength of laser beam  118  are chosen such that the energy absorbed by the substrate will be minimal and be able to pass the laser energy through to concentrate on ablating the metal  120 . This could be assisted by placing an energy absorbing material between the transparent film substrate  110  and a thin-film metal cladding  112 . (Further details regarding the energy absorbing material are provided below with reference to  FIG. 4 .) The choice of type and power level of laser  114  will be empirically derived, but initial indications are that a 15 W diode pumped YAG laser will produce the desired results. 
         [0033]    According to other embodiments, the tape  104  is radiused so the substrate  110  is under compression and the metal cladding  112  is under tension where they encounter the laser beam  118 . Such mechanical stresses and the force of gravity may assist with ablation and not require all the separation energy come from the laser and its heating effects. According to further embodiments, heating, or pre-heating tape  104  may also be used to assist to get the materials up to the points where the metal will ablate more readily and with less violence. According to other embodiments, the tape  104  may be cooled prior to ablation, for example, using liquid nitrogen. Cooling may make a metal such as copper more brittle so that it ablates more easily. The choice of heating, cooling or neither may depend upon the specific material. 
         [0034]    The tape  104  may also be referred to as a coated tape. In general, the term “coated” includes both “laminated”, which refers to an adhesive material between the substrate  110  and the metal cladding  112 , as well as “sputtered”, which refers to a chromium material between the substrate  110  and the metal cladding  112 . These materials help the substrate  110  and the metal cladding  112  to adhere together. 
         [0035]    Although a reel-to-reel tape system is shown in the embodiment of  FIG. 1 , note that other embodiments may instead use a sheet feeder system, or other structure for presenting the tape  104  for ablation. The choice of reel-to-reel tape system, sheet feeder system, or other structure will depend upon various design factors, including the form factor of the coated tape  104 . 
         [0036]    The mirror  116  may be implemented in various ways. According to one embodiment, the mirror  116  is a swinging mirror that may be tilted on one or more axes, for example, the x-axis or the y-axis. The mirror  116  may be part of a galvo head device. According to another embodiment, the mirror  116  may be a rotating mirror, for example, a many-sided prism type structure that is rotated to direct the laser beam. 
         [0037]    For higher throughput, one laser can have two or more galvo heads for ablating simultaneously. 
         [0038]    There is a balance between what kinds of laser beams  118  will be good for wide area ablating of metal, and what kind will provide clean, sharp features. An alternative embodiment of the present invention uses two lasers, one for wide area ablating of metal, and the other set to write clean, sharp features. 
         [0039]      FIG. 2  shows a dual direct-write laser lithography system embodiment of the present invention, and is referred to herein by the general reference numeral  200 . System  200  is used to manufacture flexible printed circuits (FPC), and comprises a metal-on-film substrate tape  204  wound on a supply reel  206  and a take-up reel  208 . The tape  204  has a transparent film substrate  210  and a thin-film metal cladding  212 . The transparent film substrate  210  may comprise polyimide, PEN, polyester, polycarbonate, etc. The thin-film metal cladding  212  may include copper (Cu), aluminum (Al), platinum (Pt), etc. 
         [0040]    A fine laser  244  is used to ablate off fine lines of metal from the backside of tape  204  as it translates from supply reel  206  to take-up reel  208 . A second mirror  226  moves a fine laser beam  228  to various lateral points across the tape  204 . Once fine laser beam  218  is positioned properly, e.g., within 50-micrometers, a pulse of energy is generated to ablate precise lines and spots of metal  230  away. 
         [0041]    A coarse laser  214  is used to ablate off wide fields of metal from the backside of tape  204 , after the fine laser  244 . A first mirror  210  moves a coarse laser beam  218  to various lateral points across the tape  204 . Once coarse laser beam  218  is positioned properly, a pulse of energy is generated to ablate field metal  220  away. Such ablated metal takes heat away and is caught and recycled by metal collection and recycle system  222 . The metal collection and recycle system  222  may include a vacuum pump. 
         [0042]    Gravity and/or vacuum caused airflow is used to assist the falling away and collection of ablated metals  220  and  230 . 
         [0043]    The mirror  210  or the mirror  226  may be swinging mirrors or rotating mirrors as described above regarding  FIG. 1 . 
         [0044]    According to other embodiments, the tape  204  is radiused so the substrate  210  is under compression and the metal cladding  212  is under tension where they encounter laser beams  218  and/or  228 . Such mechanical stresses and the force of gravity can assist with ablation and not require all the separation energy come from the laser and its heating effects. According to further embodiments, heating, or pre-heating tape  204  may also be used to assist to get the materials up to the points where the metal will ablate more readily and with less violence. According to other embodiments, the tape  204  may be cooled prior to ablation, for example, using liquid nitrogen. Cooling may make a metal such as copper more brittle so that it ablates more easily. The choice of heating, cooling or neither may depend upon the specific material. 
         [0045]    Having to balance between what kinds of laser beams would be good for wide area ablating of metal, and what kind would provide clean sharp features is avoided in the system  200  of  FIG. 2  by using the two different specialized lasers  214  and  224 . Otherwise the features and principles of operation are similar between the embodiments of  FIG. 1  and  FIG. 2 . Furthermore, more than two lasers and/or lasers with two or more galvo heads may be used to perform specialized ablations; for example, three lasers may be used to perform course, medium and fine ablations. 
         [0046]    Various materials for substrate  110  and  210  can be used, the best depending on several variables. A typical substrate tape is 460 mm wide. Table I summarizes the properties of several popular materials. (As reported by LPKF Laser &amp; Electronics AG.) 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 KAPTON 
                 APICAL 
                 UPILEX 
                 KALADEX 
                 MYLAR 
                 MAKROFOL 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Tg (° C.) 
                 385 
                 &gt;500 
                 &gt;500 
                 122 
                 80 
                 153 
               
               
                 CTE 
                 15 
                 12 
                 8 
                 20 
                 20 
                 70 
               
               
                 (ppm/° C.) 
               
               
                 tensile 
                 24 
                 15-24 
                 35 
                 32 
                 28-32 
                 20-25 
               
               
                 strength 
               
               
                 Kpsi 
               
               
                 Water 
                 2.9 
                 2.2 
                 1.2 
                 &lt;1 
                 &lt;1 
                 0.35 
               
               
                 absorp. 
               
               
                 (%/wt.) 
               
               
                 dielectric 
                 ? 
                 9.4 
                 6.8 
                 3.4 
                 3.5 
                 2.8 
               
               
                 strength 
               
               
                   
               
             
          
         
       
     
         [0047]    KAPTON, APICAL, and UPILEX are brand names of various forms of polyimide, KALADEX is a polyethylene naphthalate (PEN), MYLAR is a polyester, and MAKROFOL and LEXAN are polycarbonates. 
         [0048]    The choice of metal for cladding  112  and  212  depends on several tradeoffs. In general, the thinner the metal, the easier is the laser ablation. Thinner materials will have higher sheet resistances, as measured in Ohms per square. A balance between these is to be made in each embodiment. Copper is a good choice for circuit wiring, but the copper material absorbs and dissipates heat very efficiently, and that counters the spot heating effects the laser is trying to obtain for ablation. Aluminum is better in this regard, but gold and platinum may have to be used if the application is in a corrosive environment. The metals&#39; reflectivity, absorptivity, and thermal conductivity are key parameters in the choice of metal to use. LPKF Laser &amp; Electronics AG reported on three of these metals, as in Table II. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                   
                 reflectivity 
                 thermal conductivity 
                   
               
               
                 metal 
                 248 nm 
                 (W/(cm 2  ° K) 
                 absorptivity 248 nm 
               
               
                   
               
             
             
               
                 copper 
                 0.366 
                 3.98 
                 0.62 
               
               
                 gold 
                 0.319 
                 3.15 
                 0.66 
               
               
                 aluminum 
                 0.924 
                 2.37 
               
               
                   
               
             
          
         
       
     
         [0049]    Early proof-of-concept tests were made with different thicknesses of metal on a polyethylene terephthalate (PET) substrate, and at different reel-to-reel tape speeds, e.g., 0.2 μm Cu at 2.5 m/s, 0.5 μm Cu at 2.5 m/s, 0.2 μm Al at 3.0 m/s, and 0.5 μm Al at 3.0 m/s. The laser was a 15 W diode pumped YAG laser. 
         [0050]    Many kinds of lasing mediums are used for lasers, and the mediums determine the wavelength of the coherent light produced. The right one to use here depends on the films, metals, and processing speeds decided. Excimer lasers operate in the ultraviolet (UV), below 425 nm. The Argon:Fluorine (Ar:F) laser operates at 193 nm, and Krypton:Fluoride (Kr:F) at 248 nm. The nitrogen UV laser emits light at 337 nm. The Argon laser is a continuous wave (CW) gas laser that emits a blue-green light at 488 and 514 nm. The potassium-titanyl-phosphate (KTP) crystal laser operates in green, around 520 nm. Pulsed dye lasers are yellow and about 577-585 nm. The ruby laser is red and about 694 nm. The synthetic chrysoberyl “alexandrite” laser operates in the deep red at about 755 nm. The diode laser operates in the near infrared at about 800-900 nm. The right laser to use in embodiments of the present invention will probably be the hazardous Class-IV types, e.g., greater than 500 mW continuous, or 10 J/cm 2  pulsed. 
         [0051]    YAG lasers are infrared types that use yttrium-aluniinum-garnet crystal rods as the lasing medium. Rare earth dopings, such as neodymium (Nd), erbium (Er) or holmium (Ho), are responsible for the different properties of each laser. The Nd:YAG laser operates at about 1064 nm, the Ho:YAG laser operates at about 2070 nm, and the “erbium” Er:YAG laser operates at just about 2940 nm. YAG lasers may be operated in continuous, pulsed, or Q-Switched modes. The carbon-dioxide (CO 2 ) laser has the longest wavelength at 10600 mm. 
         [0052]      FIG. 3  represents an RFID device  300  with an antenna on a substrate manufactured with system  100  or system  200  (or system  400  described below with reference to  FIG. 4 ). The RFID device  300  comprises a film substrate  302  on which has been laser-patterned a folded dipole antenna. A RFID chip  304  is attached to a bond area  306 , and these are connected to left and right antenna elements  308  and  310 . The dimensions of the RFID device  300  may vary as desired, for example, between 1 and 4 inches in length. 
         [0053]    The RFID device  300  is one example of an electrical circuit that may be formed according to embodiments of the present invention. Embodiments of the present invention may also be used to form other electrical circuits and electronic devices. As another example, embodiments of the present invention may be used to form thermal circuits such as flexible heaters. 
         [0054]      FIG. 4  represents a reverse-side laser ablatement system embodiment of the present invention, which is referred to herein by the general reference numeral  400 . System  400  comprises a laser  402 , such as a YAG laser that can operate a relatively high power levels, for example, 15 W. It operates in an atmosphere  404  selected with a view toward improving laser operation and reducing the cost of operating the whole of system  404 . For example, some applications will be able to do best with an atmosphere  404  of either normal air, reduced pressure, vacuum, or dry, or inert atmospheres like nitrogen or argon. A beam  406  of laser light travels through atmosphere  404  and enters the “back side” of a coated material  407  comprising a dielectric substrate  408 , an optional intermediate layer  410 , and a metal cladding  412 . If used, the intermediate layer  410  may comprise UV absorption materials, in the case of a UV laser  402 , or other wavelength selective energy absorbing materials coordinated with the selection of laser  402 . A sheet feeder system  430  moves the coated material  407 . 
         [0055]    It is a feature of the embodiment shown in  FIG. 4  that the material that comprises dielectric substrate  408  be substantially transparent to the laser light beam  406  so that a transitioning beam  414  will be able to deposit a maximum of energy in an intermediate heating area  416  (if present) and metal ablatement area  418 . It is desirable that the material of dielectric substrate  408  survive the exposure to laser beam  406  with substantially no damage or heating. It can do that if such material is effective at transmitting the light wavelengths used by laser  402 . So the choice of laser can affect the choice of materials for dielectric substrate  408 , and vice versa. 
         [0056]    Such heating area  416  is used to overpressure ablatement area  418  and stress it to assist in ablating metal  420 . If intermediate layer  410  is not used, then transitioning beam  414  reaches metal ablatement area  418  directly and melts and vaporizes metal to produce ablating metal  420  according to patterns written by a patterning control  422 . The metal cladding  412  may be pre-patterned to reduce the amount of metal that must be ablated on-line in final patterning, e.g., into RFID antenna circuits and other electronics boards. 
         [0057]    In general, metal cladding  412  will comprise material conductive to electricity, and dielectric substrate  408  will comprise electrically insulative materials so that patterning control  422  can produce rigid or flexible printed circuits. Typical metals are copper, aluminum, gold, silver, platinum, etc. Typical insulators are polyimide, polycarbonate, silicon dioxide, alumina, glass, diamond, etc., in tapes, boards, films, and dice. 
         [0058]    Laser  402 , and in particular beam  406 , is positioned in coordination with patterning control  422  by means such as pen-plotter mechanisms, x-y stages, micro-mirrors, a galvo head device, etc. according to design tradeoffs in various embodiments. The patterning control  422  in combination with the sheet feeder system  430  work together so that the laser beam  406  ablates the metal from the coated material  407  at the desired location. Additional lasers can be included to improve job throughput, or they can be specialized to do wide area or fine feature ablations. Such lasers can use different wavelengths and laser types to assist in such specialization and job sharing. According to another embodiment, to improve throughput, a beam splitter may split a beam from a single laser into multiple beams that are directed by multiple galvo head devices. 
         [0059]    The use of a pen-plotter type positioning mechanism for laser  402  permits the propagation distance that beam  406  has to travel through atmosphere  404  to be reduced as compared to certain embodiments that interpose a mirror between the laser and the substrate  408 . Such then would permit atmosphere  404  to be ordinary air, whereas a longer travel distance could necessitate the use of vacuum in certain embodiments. 
         [0060]    The coated material  407  may be implemented in various form factors, and the components of the system  400  may be varied in accordance with the form factor of the coated material  407 . Conversely, the form factor of the coated material  407  may be varied in accordance with the components of the system  400 . For example, a reel-to-reel tape system (similar to that shown in  FIG. 1 ) may be implemented in the system  400 , in which case the coated material  407  may be a coated tape. As another example, the metal layer  412  may have a thickness such that coated material  407  may be in sheet form, in which case a sheet feeder may be implemented in the system  400 . 
         [0061]      FIGS. 5A-5E  are plan views showing thermal isolation ablation performed on a coated film according to certain embodiments of the present invention. In certain embodiments, it is desirable to perform thermal isolation ablation prior to performing structural ablation. The determination of when to perform thermal isolation ablation will depend upon various factors, such as the power of the laser, the type of metal, the thickness of the metal, etc. For example, if the metal being ablated is such that the energy of the laser becomes undesirably dissipated by thermal conduction of the laser energy by other portions of the coated sheet, then thermal isolation ablation may be performed to mitigate this issue. Thermal isolation ablation may be performed by the embodiment shown in  FIG. 1 , the embodiment shown in  FIG. 2 , or the embodiment shown in  FIG. 4 . 
         [0062]      FIG. 5A  shows a portion of a coated sheet  502  prior to laser ablation. The coated sheet may be in the form of a tape or sheet and includes a dielectric layer and a metal layer as described above. 
         [0063]      FIG. 5B  shows the coated sheet  502  after thermal isolation ablation has been performed. The metal has been ablated (for example, by the laser  114 ) from an area  504  in order to thermally isolate a portion  506  from the remaining metal portions of the coated sheet  502 . Note that the metal is ablated and the dielectric substrate remains intact, as discussed above with reference to other embodiments of the present invention. 
         [0064]      FIG. 5C  shows that structural ablation has been performed on the isolated portion  506  (see  FIG. 5B ) to form circuit structures on the coated sheet  502 , such as an RFID antenna  508 . Since the portion  506  has been thermally isolated from the other metal portions of the coated sheet  502  (see  FIG. 5B ), the energy of the laser does not dissipate over the entirety of the coated sheet  502  when structural ablation is being performed. Thus, more of the laser energy remains localized in the ablation area, and can improve the performance and efficiency of the structural ablation as compared to embodiments that do not involve thermal isolation ablation. 
         [0065]      FIG. 5D  shows the coated sheet  502  after a series of thermal isolation ablations have been performed. In certain embodiments, it is desirable to perform a series of thermal isolation ablations prior to performing structural ablation in the thermally isolated portions  506  of the coated sheet  502 . Otherwise the thermal isolation ablation is similar to that discussed above with reference to  FIG. 5B . 
         [0066]      FIG. 5E  shows that structural ablation has been performed on the isolated portions  506  (see  FIG. 5D ) to form circuit structures on the coated sheet  502 , such as the RFID antennas  508 . Otherwise the structural ablation is similar to that discussed above with reference to  FIG. 5C . 
         [0067]      FIG. 6  is a flowchart of a method  600  of laser circuit etching according to an embodiment of the present invention. The method  600  may be implemented by various embodiments of the present invention, such as the embodiment shown in  FIG. 1 , the embodiment shown in  FIG. 2 , the embodiment shown in  FIG. 4 , etc., and variations thereof. 
         [0068]    In step  602 , a coated sheet is provided. As discussed above, the coated sheet comprises a dielectric substrate layer and a metal foil layer. The coated sheet may be in various form factors, such as in tape form or in sheet form. The specific form factor of the coated sheet may depend upon the specific embodiment of the laser etching device. The form factor of the coated sheet may also depend upon the properties of the metal layer. For example, a tape form factor may be suitable for a thinner metal layer, and a sheet form factor may be suitable for a thicker metal layer. 
         [0069]    In step  604 , thermal isolation ablation is performed. Which laser performs the thermal isolation ablation will depend upon the specific embodiment of the invention. For example, for the embodiment shown in  FIG. 1 , the laser  114  may perform the thermal isolation ablation. For the embodiment shown in  FIG. 2 , the course laser  214  may perform the thermal isolation ablation. Alternatively, the fine laser  224  may perform the thermal isolation ablation in other embodiments of the present invention. 
         [0070]    In step  606 , structural ablation is performed. Which laser performs the structural ablation, and in what sequence, will depend upon the specific embodiment of the invention. For example, for the embodiment shown in  FIG. 2 , the course laser  214  may perform wide area ablation, then the fine laser  224  may perform narrow area ablation. Alternatively, the fine laser  224  may perform narrow area ablation, then the course laser  214  may perform wide area ablation. Or alternatively, the course laser  214  may perform a portion of the wide area ablation, the fine laser  224  may perform narrow area ablation, then the course laser  214  may perform another portion of the wide area ablation. Or alternatively, the fine laser  224  may perform a portion of the narrow area ablation, the course laser  224  may perform wide area ablation, then the fine laser  224  may perform another portion of the narrow area ablation. 
         [0071]    As discussed above with reference to  FIGS. 5A-5E , the thermal isolation ablation and the structural ablation may be performed sequentially or in alternation. According to one embodiment of the present invention, structural ablation is performed on a segment after the segment has been thermally isolated. (See  FIGS. 5B-5C  and related discussion.) According to another embodiment of the present invention, a sequence of thermal isolation ablations are performed (see  FIG. 5D  and related discussion), then a sequence of structural ablations are performed (see  FIG. 5E  and related discussion). The exact sequence of thermal isolation ablations and structural ablations may vary according to various factors, such as the desired use of the laser(s), the structures that controls the movement of the laser or the laser beam, the specifics of the circuits to be etched, etc. 
         [0072]    In step  608 , recycling of the ablated metal is performed. The recycling process is as described above. 
         [0073]      FIG. 7  is a block diagram of a control system  700  for controlling laser ablation according to an embodiment of the present invention. The control system  700  includes a master control block  702 , beam control A block  704 , optional beam control B block  706 , position control X block  708 , and position control Y block  710 . The control system  700  generally controls the operation of the laser etching system according to the various embodiments of the present invention. The control system  700  may be implemented in hardware, software, or a combination of hardware and software. 
         [0074]    The master control block  702  generally coordinates the other components of the control system  700 . The master control block may store a program or other set of instructions for performing a specific set of ablations, and may then instruct the other components of the control system to in accordance with the program or other instructions. 
         [0075]    The beam control A block  704  controls the operation of a laser in an embodiment of the present invention (for example, laser  114  in  FIG. 1 ) via control signals. The control signals may indicate the activation of the laser, the power of the laser, or other controllable attributes of the laser in accordance with the specifics of the ablation desired. 
         [0076]    The beam control B block  706  is optional in that it controls the operation of a second laser, when present, in an embodiment of the present invention (for example, fine laser  224  in  FIG. 2 ) via control signals. The control signals may indicate the activation of the laser, the power of the laser, or other controllable attributes of the laser in accordance with the specifics of the ablation desired. In systems having only a single laser, the beam control B block  706  is not required. 
         [0077]    The position control X block  708  controls, via control signals, the relative position between the laser and the coated sheet in an embodiment of the present invention. For example, in the laser etching system  100  of  FIG. 1 , the position control X block  708  controls the movement of the coated film  104  from one reel to another. The movement may be from the reel  108  to the reel  106 , or vice versa. As another example, in the laser etching system  400  of  FIG. 4 , the position control X block instructs the patterning control  422 , for example, to move the laser  402  along an x-axis, along a y-axis, or in a combination of x-axis and y-axis movement. 
         [0078]    The position control Y block  710  controls, via control signals, other aspects of the relative position between the laser and the coated sheet not otherwise controlled by the position control X block  708  in an embodiment of the present invention. For example, in the laser etching system  100  of  FIG. 1 , the position control Y block  710  controls the mirror  116 . In such manner, the movement of the coated film  104  and the mirror  116  can be coordinated so that the laser beam  118  ablates at the desired location on the coated film  104 . 
         [0079]    As discussed above, the systems and methods according to various embodiments of the present invention are suitable for flexible circuit manufacturing techniques. Flexible circuits may be used in many different applications, including RFID antennas, RFID tag circuitry, membrane switches, flexible heaters and printed circuits, data compact disks, and data video disks. 
         [0080]    The above description illustrates various embodiments of the present invention along with examples of how aspects of the present invention may be implemented. The above examples and embodiments should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the present invention as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents will be evident to those skilled in the art and may be employed without departing from the spirit and scope of the invention as defined by the claims. The terms and expressions that have been employed here are used to describe the various embodiments and examples. These terms and expressions are not to be construed as excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the appended claims.