Abstract:
A process is disclosed for attaching an RFID tag such as an AK module or QFP package to a flexible surface such as textile or fabric. The process comprises providing a heat fusible label including at least a first layer having a first adhesive layer, a substrate layer including a secondary antenna structure, a heat activated second adhesive layer and a pressure sensitive adhesive (PSA) layer for holding the RFID tag. The process further includes positioning the RFID tag on the PSA layer, pressing the tag against the PSA layer such that the PSA layer holds the tag against the heat fusible label at least temporarily, positioning the heat fusible label with the RFID tag on the flexible surface and applying heat and pressure to the heat fusible label to melt the heat activated layer and to fuse the label to the flexible surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/AU2013/001106 filed Sep. 30, 2013, published in English, which claims priority from Australian Patent Application No. 2012904291 filed Oct. 1, 2012. The present invention is related to the following international patent applications assigned to the present applicant the disclosures of which are incorporated herein by cross reference: PCT/AU2010/000373 —RFID TAG ASSEMBLY AND METHOD and PCT/AU2012/000305 —RFID TAG ASSEMBLY AND LABEL PROCESS. 
     TECHNICAL FIELD 
     The present invention relates to a tag assembly for attaching an RFID tag to a surface including a flexible surface such as textile or fabric and a process for producing an RFID tag assembly and/or label. 
     BACKGROUND OF THE INVENTION 
     Use of a generic RFID tag on a flexible surface such as textile or fabric typically involves stitching or bonding the tag directly to the fabric or enclosing it within a patch to provide an enclosure for the tag. However this often leads to cumbersome and inflexible solutions particularly with a clothing garment that may be uncomfortable to wear. 
     In one prior art solution, a conductive thread is used to provide a secondary antenna and a plastics encapsulated RFID tag in the form of a traditional clothing button is stitched to the fabric in order to couple to the secondary antenna to form a larger overall tag system. While this solution is flexible and comfortable the thread link holding the button to the fabric loosens over time with repeated washing cycles and the button can rock about or tilt, deteriorating electromagnetic coupling between a primary antenna on the RFID tag and the secondary antenna associated the fabric. 
     An object of the present invention is to at least alleviate the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a process for attaching an RFID tag including a surface mount integrated package such as an AK module or Quad Flat Package (QFP) to a flexible surface such as textile or fabric, said process comprising: providing a heat fusible label including at least: a) a first layer having a first adhesive layer; b) a substrate layer including a secondary antenna structure; c) a heat activated second adhesive layer; and d) a pressure sensitive adhesive (PSA) layer for holding said RFID tag; positioning said RFID tag on said PSA layer; pressing said tag against said PSA layer such that said PSA layer holds said tag against said heat fusible label at least temporarily; positioning said heat fusible label with said RFID tag on said flexible surface; and applying heat and pressure to said heat fusible label to melt said heat activated layer and to fuse said label to said flexible surface. 
     The PSA layer may be relatively thin and may provide tack at room temperature. The heat fusible label may include markings to facilitate accurate placement of the RFID tag relative to the secondary antenna structure. The heat fusible label may further include a printable layer applied over the first layer. The printable layer may comprise a coating of white varnish and thermal transfer ink. 
     The first layer may include a woven polymeric or synthetic material. The secondary antenna structure may be provided by weaving, knitting and/or stitching conductive wire in association with said substrate layer. The substrate layer may include a polymeric layer such as Polyethylene Naphthalate (PEN), Polyimide (PI) or Polyethylene Terephthalate (PET) or a knitted or woven layer. The RFID tag may include an AK module or QFP package. 
     The secondary antenna may include a dipole antenna. The surface may be flexible such as fabric or textile or it may be relatively rigid such as cardboard. The surface may include an item of clothing. 
     According to a further aspect of the present invention there is provided a heat fusible RFID label assembly suitable for attachment to a flexible surface such as textile or fabric, said label comprising: a first layer including a first adhesive layer; a substrate layer including a secondary antenna structure; a heat activated second adhesive layer; a pressure sensitive adhesive (PSA) layer for holding said RFID tag at least temporarily; and an RFID tag. 
     The PSA layer may be relatively thin and may provide tack at room temperature. The heat fusible RFID label assembly may include markings to facilitate placement of the RFID tag relative to the secondary antenna structure. The heat fusible RFID label assembly may further include a printable layer applied over the first layer. 
     The printable layer may comprise a coating of white varnish and thermal transfer ink. The first layer may include a woven polymeric or synthetic material. The secondary antenna structure may be provided by weaving, knitting and/or stitching conductive wire in association with the substrate layer. The substrate layer may include a polymeric layer (PEN or PI) or a knitted or woven layer. The RFID tag may include an AK module or QFP package. 
     According to a still further aspect of the present invention there is provided a process for producing an RFID label including an RFID tag, such as an AK module or QFP package, for attaching to a flexible surface such as textile or fabric, said process including forming a label substrate, providing a secondary antenna structure in association with the label substrate, projecting a spot of glue on said label substrate for receiving said RFID tag, locating said RFID tag on said substrate and sealing said cavity and RFID tag with a cover. 
     The cover may include clear or opaque film or ribbon. The secondary antenna structure may be provided by weaving, knitting and/or stitching conductive wire in association with said label substrate. The process may include monitoring the antenna structure via a fast video camera to determine a position for the spot of glue. The step of locating may be performed via a pick and place machine. 
     According to a still further aspect of the present invention there is provided a process for producing an RFID tag assembly comprising:
     providing a peripheral frame including antenna parts for an associated or primary antenna;   connecting the antenna parts to form said associated antenna having a desired resonant frequency;   connecting an RFID chip to the associated antenna;   encapsulating the RFID chip and associated antenna; and trimming the peripheral frame;   wherein said step of connecting the antenna parts includes adjusting effective area or inductance of said associated or primary antenna to obtain the desired resonant frequency.   

     The step of connecting the antenna parts may include placing conductive connections such as wire-bonds between the antenna parts such as lands or zones. 
     The effective area or inductance of the primary antenna may be adjusted up or down by placing the conductive connections between defined positions on the antenna parts. The defined positions for the conductive connections may be determined by means of a modeling simulator such as ANSYS HFSS. 
     The associated or primary antenna may include a nested loop antenna. The peripheral frame and antenna parts may be provided by die stamping conductive strip material. The process may include forming the peripheral frame with a plurality of like frames by die stamping from a roll of conductive material. The conductive material may include stainless steel. The RFID tag assembly may include a QFP, LQFP or TQFP package. 
     In industrial laundries, wear and tear of linen or the like may be reduced by avoiding relatively sharp edges associated with a QFP package. Therefore in some embodiments the epoxy package outer casing may be formed with rounded corners or a substantially round package. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-3  show a heat fusible label assembly and process for producing an RFID label; 
         FIGS. 4-7  show a process for producing an RFID label; 
         FIGS. 8-9  show a further process for producing an RFID label; 
         FIGS. 10-11  show details of a process for producing an RFID tag assembly/QFP kernel; and 
         FIG. 12  shows a graph of minimum power levels to initiate communication for various RFID tag assemblies. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A tag assembly method is described below with reference to  FIG. 1 .  FIG. 1  shows a thermo patch assembly  10  comprising at least the following layers:
     1. a top woven polymeric sheet or synthetic layer  11 ;   2. an adhesive layer  12  for a secondary antenna layer;   3. a secondary antenna layer  13 ;   4. a heat activated adhesive layer  14 ; and   5. a relatively thin pressure sensitive adhesive (PSA) layer  15 .   

     Top woven polymeric sheet or synthetic layer  11  may include a PI, PEN or PET substrate that is relatively resistant to high temperatures including temperatures that may be at least 200° C. or more. In one form the top layer  11  may include a PI layer that is 30 μm to 100 μm in thickness. Secondary antenna layer  13  may be provided on a woven (textile or fabric) or plastics (PEN) substrate. Secondary antenna layer  13  may include a 17 μm-35 μm thick etched copper layer to provide the radiating loop of the secondary antenna. 
     An optional over-layer  16  such as polycarbonate sheet or polyester fiber and a polyurethane primer layer  17  may be applied over top layer  11  to make the thermo patch assembly  10  printable and/or waterproof. Primer layer  17  may include a 30 to 40 μm thick white printable polymeric varnish, or a white PET/PEN laminated overlay. 
     Heat activated adhesive layer  14  may include a 50 μm thick polyurethane adhesive layer such as a layer of hot melt glue. PSA layer  15  may include a 20 μm acrylic layer with room temperature tack to hold in place RFID tag  18 . 
     A plurality of thermo patch assemblies  10  may be optionally applied to a carrier reel or tape including a “siliconized” or release layer or liner. The release layer or liner (not shown) may allow for easy peeling of thermo patch assembly  10  with a small force and should provide a clean release that does not retain any traces of PSA layer  15  on its surface. The main function of the optional carrier reel or tape is to carry a plurality of cut-out patch assemblies  10  on a “reel” or “roll” for transport and delivery where the patch assemblies may be peeled off manually or automatically using dedicated equipment. 
     The thermo patch assembly  10  may be used to apply an RFID tag  18  to a garment or fabric as described below with reference to  FIG. 3 . The PSA layer  15  may facilitate alignment of RFID tag  18  relative to secondary antenna layer  13  as described below. 
     A further tag assembly method is described below with reference to  FIG. 2 .  FIG. 2  shows a thermo patch assembly  20  comprising at least the following layers:
     1. a top woven polymeric sheet (PI/PEN/PET) or synthetic layer  21 ;   2. an adhesive layer  22  for a secondary antenna layer;   3. a secondary antenna layer  23 ;   4. a heat activated adhesive layer  24  such as a polyurethane adhesive layer; and   5. a relatively thin PSA layer  25  with room temperature tack.   

     Polymeric sheet  21  may include a Polyimide, PEN, PET substrate that is relatively resistant to high temperatures (200° C. minimum) and 20-50 μm thick. Secondary antenna layer  23  may be provided on a woven (textile or fabric) or plastics (PEN) substrate. An optional over-layer  26  comprising printable white varnish with thermo transfer ink on top may be applied over top layer  21  to make the patch assembly  20  printable and/or waterproof. The thermo patch assembly  20  may be used to apply an RFID tag  27  to a garment or fabric as described below with reference to  FIG. 3 . Optional overlayer  26  may be omitted in low cost versions of the thermo patch assembly  20 . 
     Referring to  FIG. 3  an RFID tag  18  or  27  (QFP/TQFP) may be sandwiched between a flexible surface  30  such as fabric, textile or a garment and an opaque and printable thermo patch  10  or  20  as described above. As described, thermo patch  10  or  20  includes a layer of heat activated adhesive layer  14  or  24  on its underside that is adapted to hold antenna layer  13  or  23 . Antenna layer  13  or  23  comprises a polymeric substrate such as polyethylene napthalate (PEN) with an antenna pattern  31  applied thereto. Antenna pattern  31  comprises a laminate of a conductor such as copper or aluminium that may be about  10 - 17  um in thickness. Heat activated adhesive layer  14  or  24  is interposed between antenna layer  13  or  23  and a garment or fabric surface  30  for heat sealing patch  10  or  20  to hold antenna layer  13  or  23  and RFID tag  18  or  27  in position against garment or fabric surface  30 . It is desirable that each RFID tag  18  or  27  be placed accurately relative to antenna pattern  31  to facilitate close electromagnetic coupling to a primary antenna (not shown) that is associated with RFID tag  18  or  27 . 
     The method of attaching thermo patch  10  or  20  to a surface  30  may be performed manually using heat sealing equipment set at around 170-200° to press and activate the adhesive. The patch assembly  10  or  20  may then be resistant to washers and driers. The process may use a conventional etched aluminium or copper conductive antenna on a PEN substrate (the latter may withstand higher temperatures than PET) which is adhered to a thermo sealing patch. Printable patches  10  with secondary antenna already attached and covered with heat activated adhesive such as hot melt glue may be supplied to an operator ready for attachment to garment/fabric surface  30  or the like. 
     The operator may initially peel off from a reel a precut label assembly and turn it upside down to view a marked antenna pattern including a central tag receiving part. The operator may then place RFID tag  18  or  27  (QFP/TQFP) against the tag receiving part of the label which may hold the tag  18  or  27  via the thin PSA layer  15  with room temperature tack. The operator may then turn the thermo patch assembly  10  or  20  upside down and place the RFID tag  18  or  27  (QFP/TQFP) and thermo patch assembly  10  or  20  on top of garment or fabric surface  30 . Thermal sealing equipment may then be used to press and heat the thermo patch  10  or  20  on top of garment or fabric surface  30  causing the thermo patch  10  or  20  and RFID tag  18  or  27  to be attached to the garment or fabric surface  30 . 
       FIG. 4  shows tape substrate  40  being woven or knitted on a loom (not shown). Tape substrate  40  comprises a plurality of yarns including synthetic yarns such as polyester nylon, polyamide and carbon and conductive yarns such as stainless steel suitable for industrial washing liquids. The conductive yarns may be woven, knitted and/or stitched in association with tape substrate  40  to form an antenna pattern  41 . The antenna pattern  41  may form plural separate antennas after tape substrate  40  is singulated into individual labels. Each label may be attached to an article such as an item of clothing. The tape substrate may include a printed logo. The logo may be laser printed or applied using industrial means such as inkjet, thermal transfer or sublimation onto the singulated label during assembly or it may be printed onto a reel of tape substrate before assembly. 
       FIG. 5  shows a production line process for attaching RFID tags  50  to tape substrate  40  such as by means of a multi-step online machine. The process includes supplying individual tags  50  via a bowl feeder or the like and testing and programming each tag  50  at a testing station  51  prior to attaching the tags  50  to tape substrate  40 . Each tag  50  is attached to tape substrate  40  via a layer or spot of adhesive  52  which may be precisely projected or applied to tape substrate  40 . This may be followed by accurate positioning of each tag  50  relative to antenna pattern  41  (refer  FIG. 4 ) using a pick and place machine. Accurate placement may ensure good electromagnetic coupling to a primary antenna associated with tag  50 . Adhesive  52  may be applied or projected with assistance of a monitoring station (not shown). The monitoring station may accurately monitor the secondary antenna pattern  41  using a fast video camera or the like. 
       FIG. 6  shows a fusing station  60  which follows a tape folding station (not shown) for folding tape substrate  40  in half over tags  50 . Fusing station  60  includes fusing tool  61  including four sonotrodes (raised portions). The sonotrodes cooperate with an anvil (not shown) to make four spot welds around each RFID tag  50 . The four spot welds create a pocket between the folded layers of tape substrate  40  for locating RFID tag  50  in the pocket.  FIG. 6  includes an ultrasonic welding station  62  for continuously sealing the open seam comprising folded layers of tape substrate  40 . This is followed by testing of each label with tag  50  at testing station  63 . Labels that do not pass the test may be marked with a black dot or punched with a hole for identification.  FIG. 6  includes a winding station  64  for winding the tested labels onto roll  65  suitable for subsequent automatic deposition of labels. 
     The singulation station may include a punching tool or laser.  FIG. 7  shows a modification of the process shown in  FIG. 6  including singulation station  70  for cutting tape substrate  40  into individual labels  71  via a punch or laser and a testing station  72  for testing isolated ribbon antenna following singulation. The process in  FIG. 7  is suitable for manual deposition of individual labels  71 . 
       FIGS. 8 and 9  show a modification to the production line process in  FIGS. 5 to 7 . 
       FIG. 8  shows tape substrate  40  formed with an antenna pattern  41  passing around RFID tag  80  after testing and positioned over tape substrate  40 .  FIG. 8  also shows a polyester film cover  81  comprising clear or opaque ribbon positioned over tape substrate  40  and RFID tag  80 . Film cover  81  comprises polyester film. Film cover  81  may be formed from extensible material to facilitate stretching over RFID tag  90  as it is ultrasonically welded to tape substrate  40  via seams  90  as shown in  FIG. 9 . 
       FIG. 10  shows inline steps for producing an RFID tag assembly  100  including a primary antenna  101  and IC (integrated circuit) chip  102 . Primary antenna  101  comprises planar nested loops to reduce the overall dimensions of the RFID assembly while still being able to resonate at a desired frequency such as 860 MHz to 900 MHz. The production steps include steps  103 - 108  which may be carried out at respective production stations (not shown). 
     A ribbon of stainless steel material may be die stamped at step  103  to provide a strip of peripheral frames  109 , each containing antenna parts joined to frame  109  via narrow strips of material  109   a.    
     IC chip or die  102  is bonded at step  104  to a chip receiving land  101   a  via a non-conductive adhesive. IC chip or die  102  is electrically connected to primary antenna  101  at wire bonding step  105 . IC chip  102  is electrically connected to pads or lands of antenna  101  via wires  102   a ,  102   b  as is known in the art. 
     Because the input impedance of each chip  102  may vary even when it comes from the same batch of a specific manufacturer, it is desirable to accurately match the inductance of each primary antenna  101  to the input impedance of associated IC chip  102 . 
     The input impedance of IC chip  102  may be represented via a capacitor/resistor equivalent circuit. The primary antenna loop creates an inductance (L) which compensates for on chip capacitance (C) at the resonant frequency (Fr=1/(2×π×√{square root over (L×C)})), which may be near 860 MHz to 900 MHz. The parameter that may be adjusted easily is the inductance L, while on chip capacitance C may be in the range of 0.8 pF to 1.2 pF. 
     The parts of antenna  101  are joined together at wire bonding step  106  to produce a primary antenna  101  as described below. The resonant frequency of primary antenna  101  depends on the effective area or inductance of the antenna loop. The effective area or inductance of the antenna loop may be adjusted up or down by joining the antenna parts via carefully positioned wire bonds  110 ,  113 . Wire bonds  110 ,  113  may be placed in defined positions on the antenna parts such as pads or lands  111 ,  112 ,  114 ,  115  (refer  FIG. 11 ). 
     The position of each wire bond  110 ,  113  may determine the effective area and inductance of primary antenna  101 . Minute changes to positions of bonds  110 ,  113  may be used to finely tune the resonant frequency of primary antenna  101  to RFID chip  102  regardless of the manufacturer used to supply RFID chip  102 . Fine tuning of the resonant frequency of the primary antenna is desirable to guarantee performance of an RFID tag assembly in the face of variations in input impedance of each RFID chip. Examples of wire bonding step  106  are described below with reference to  FIGS. 11A to 11D . 
     The resonant frequency of antenna  101  may additionally be adjusted to compensate for a detuning effect or frequency shift that occurs when an RFID tag including a primary antenna is electromagnetically coupled to a secondary antenna when the primary and secondary antennas are brought together. Both antennas frequencies are shifted towards each other such that the lower frequency of the primary antenna shifts upwards nearer to a 900 MHz optimum (happy medium between EU and US Bands) and the higher frequency of the secondary antenna shifts downwards. Critical or optimum coupling may see both frequencies very close to each other at 900 MHz to match the frequency of an interrogating carrier wave. 
     Hence the relevant performance criterion is the one for a complete RFID assembly including the RFID tag assembly or primary kernel coupled to a secondary antenna. The coupling shift for the primary resonant frequency may be determined by experience/modelling and/or via a trial and error method. 
     Frequency compensation may go even further and may also be used to adjust resonant frequency of the primary antenna to specific applications in which detuning or frequency shifting may be experienced in some environments such as water, rubber, etc. due to a high level of dielectric constant of an environment. In such an environment a deliberate frequency shift may be required to compensate for a detuning effect due to a higher dielectric constant. 
     Step  107  includes encapsulating the antenna  101  and chip  102  by surrounding the RFID tag assembly via a dedicated mold and injecting epoxy resin material into the mold. An advantage of using a standard QFP casing is that it may enable reuse of existing standard size molds. 
     However, as noted above wear and tear of linen or the like may be reduced in industrial laundries by avoiding relatively sharp edges associated with a QFP package. Therefore it is desirable in some embodiments to produce the epoxy package outer casing rounded in shape rather than square. A round shape is not standard although a dedicated mold can be made to accommodate a package of any shape, size and form from 5 mm to 50 mm dimensions and is readily available from the micro-packaging industry. 
     Step  108  includes trimming the peripheral frame  109  to obtain a singulated RFID tag assembly  100 . 
       FIG. 11A  shows an example of a standard wiring (V 1 ) for a MONZA 5 chip wherein the top wire bond  110  is near the tops of upper lands  111 , 112  and the bottom wire bond  113  is near the tops of lower lands  114 ,  115 . 
       FIG. 11B  shows an example of a long wiring (V 2 ) for a MONZA 5 chip wherein the top wire bond  110  is near the bottom of upper lands  111 , 112  and the bottom wire bond  113  is near the bottoms of lower lands  114 ,  115 . 
       FIG. 11C  shows a standard wiring for a G2iL chip wherein the top wire bond  110  is near the bottoms of upper lands  111 , 112  and the bottom wire bond  113  is near the bottom of lower land  114  and near the middle of lower land  115 . 
       FIG. 11D  shows a standard wiring for an EM4124 chip wherein the top wire bond  110  is near the bottom of upper lands  111 , 112  and the bottom wire bond  113  is near the bottom of lower land  114  and near the middle of lower land  115 . 
     The positions of wire bonds  110 ,  113  may be accurately determined by means of a 3D electromagnetic field simulation tool such as ANSYS HFSS. The simulation tool may allow the position of each wire bond  110 ,  113  to be accurately defined since as noted above the performance of an RFID tag assembly depends in part on the impedance of primary antenna  101  matching RFID chip  102 . 
       FIG. 12  shows dips in power levels to initiate communication for various RFID tag assemblies including the four tag assemblies shown in  FIG. 11A-11D , wherein the curves for the four tag assemblies are labeled M5 std, M5 Long, G2IL and EM 4124 respectively. 
     The curve represented by uTrak V 1  is an older design with a single turn design and with no frequency adjustment possible using Monza 4D older generation RFID chips. It may be seen that the curve for uTrak V 1  is positioned high in the graph denoting a lower sensitivity since the Y-axis denotes power levels necessary to communicate with the chip in dBm. The higher power levels necessary to initiate communication with a chip imply a lower sensitivity and thus read range performance criteria. According to  FIG. 12  the M5 long wiring chip (Monza 5 series) provides the best performance as far as frequency and sensitivity are concerned. 
     Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.