Wet Strap Attach Process
Field of the Disclosure
[001] The present subject matter relates to a method to produce radio frequency identification (“RFID”) devices and the devices made by the method. More particularly, the present subject matter relates to self-adhesive RFID straps and techniques for mounting such RFID straps to antennas.
Background
[002] RFID tags and labels have a combination of antennas and analog and/or digital electronics, which may include, for example, communications electronics, data memory, and control logic. RFID tags and labels are widely used to associate an object with an identification code. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,692.
[003] Methods for manufacturing RFID labels are disclosed in PCT Publication No. WO 2001/61646 by Moore North America, Inc. The method disclosed in PCT Publication No. WO 2001/61646 uses a number of different sources of RFID inlets, each inlet including an antenna and a chip. A plurality of webs are matched together and RFID labels are die cut from the webs, to produce RFID labels with liners. Alternatively, linerless RFID labels are produced from a composite web with a release material on one face and pressure-sensitive adhesive on the other, where the labels are formed by perforations in the web. Various alternatives are possible.
[004] Still other RFID devices and methods for manufacturing RFID labels are disclosed in U.S. Patent Application Publication No. US2001/0053675 by Plettner. The devices include a transponder comprising a chip having contact pads and at least two coupling elements, which are conductively connected with the contact pads. The coupling elements are touch-free relative to each other and formed in a self-supported as well as a free-standing way and are essentially extended parallel to the chip plane. The total mounting height of the transponder corresponds essentially to the mounting height of the chip. The size and geometry of the coupling elements are adapted for acting as a dipole antenna or in conjunction with an evaluation unit as a plate capacitor. Typically, the transponders are produced at the wafer level. The coupling elements can be contacted with the contact pads of the chip directly at the wafer level, i.e., before the chips are extracted from the grouping given by the wafer.
[005] In many applications, it is desirable to reduce the size of the electronics as small as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “straps”, “interposers”, and “carriers” to facilitate inlay manufacture. Straps include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads provide a larger effective electrical contact area than Integrated Circuits (“ICs”) precisely aligned for direct placement onto the antenna without a strap. The larger area reduces the accuracy required for placement of ICs during manufacture while still providing effective electrical connection. IC placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or strap structures, typically using a flexible substrate that carries the strap's contact pads or leads.
[006] One type of prior art RFID inlet manufacturing process using straps is disclosed in European Patent Application EP 1039543 A2 to Morgan Adhesives Company (“Morgan”). This patent application discloses a method of mounting an integrated circuit chip (IC) using a strap that is connected across a gap between two thin conductive film sections of a conductive film antenna. The strap comprises a thin substrate having two printed conductive ink pads. This method is said to be suitable for mass production of RFIDs by mounting ICs on straps that are then physically and electrically connected to the antenna sections using a pressure sensitive conductive adhesive. The pressure sensitive conductive adhesive provides a direct electrical connection between the strap contact pads and the antenna sections.
[007] Another type of prior art RFID inlet manufacture using straps is based on a technique for manufacturing microelectronic elements as small electronic blocks, associated with Alien Technology Corporation (“Alien”). Alien has developed techniques to manufacture small electronic blocks and then deposit the small electronic blocks into recesses on an underlying substrate. To receive the small electronic blocks, a planar substrate is embossed with numerous receptor wells. The receptor wells are typically formed in a pattern on the substrate. For instance, the receptor wells may form a simple matrix pattern that may extend over only a predefined portion of the substrate or may extend across substantially the entire width and length of the substrate, as desired. Alien has a number of patents on its technique, including U.S. Pat. Nos. 5,783,856;
5,824,186; 5,904,545; 5,545,291 ; 6,274,508; and 6,281 ,038. Further information can be found in Alien's Patent Cooperation Treaty publications, including WO 00/49421 ; WO 00/49658; WO 00/55915; WO 00/55916; WO 00/46854 and WO 01/33621.
[008] As noted above, RFID inlets using straps provide an inherent advantage in high speed manufacture by facilitating effective mechanical and electrical connection of ICs to antennas.
[009] Faster production is often also associated with lower costs. More recently, IC chips have been getting smaller, and adhesives have been developed that cure faster than ever. To take advantage of these developments, production methods must be adapted.
Summary
[0010] There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as may be set forth in the claims appended hereto.
[0011] The present disclosure introduces a method of assembling RFID devices. An embodiment involves multiple antennas made from an electrically conductive material on a lead frame carrier substrate. This may be a thin metal foil attached to a carrier substrate, usually PET or paper , but other substrates are possible. Another possibility may involve printed structures that are printed with conductive inks. Said lead frame carrier substrates are moved along a planar axis. This may be realized by some conveyor belt or by using an endless substrate and separating the antennas later. [0012] A plurality of RFID straps are then provided, said straps each comprising an IC chip attached to a conductor from an electrically conductive material on an IC-bearing side. The conductor will typically be a very thin material such as a metal foil or conductive ink on a thin stabilizing carrier substrate, so that the thickness of the material is very small in comparison to its dimensions in the other two directions of the three- dimensional room. Thus, the conductor has, ignoring the thickness of the material, basically two sides. The side the IC is attached to is called the “IC-baring side” herein. The other, planar side is assigned the term “second planar side” herein. This is typically the side of the stabilizing substrate, also called the carrier or the lead frame carrier. The carrier may be a continuous material, so as to create a line of consecutive structures. The carrier may also be a sheet, with multiple conductor structures after and next to each other.
[0013] The IC bearing side of said multitude of RFID straps may be covered with a pressure sensitive adhesive and a common (continuous) liner material. This way a ribbon or tape is created with RFID straps between two continuous tapes of liner. This ribbon may also be rolled-up on a reel after preparing the ribbon. Said antennas and said ribbon of RFID straps are then delivered to a connecting area. In some embodiments, this is a planar surface, where the feeding (delivery) speed of said antennas and said RFID straps coordinated, so that each RFID strap is associated with one antenna. The disclosed embodiments describe means to peel off the liner from the IC-bearing side, thereby exposing the pressure sensitive adhesive, which covers the IC- bearing side. The peeled-off liner is then rolled up on a roll, reel or the like. In some embodiments, the liner can be re-used, which would constitute an improvement to the sustainability of the process. Further, the disclosed embodiments describe providing means to separate the RFID straps from the ribbon, belt, tape or the like. Thereby, single RFID straps are created, that can be attached, one RFID strap to each antenna, on said planar axis by means of the pressure sensitive adhesive, so that RFID straps are electrically connected to the antenna. [0014] Another embodiment discloses the means to separate or “singulate” the RFID straps is a wheel with cutting edges that rotates as the ribbon, belt, tape, etc. is delivered beneath it. In such an embodiment, the cutting edges are distanced so that the wheel cuts the ribbon in regular pieces, containing one RFID strap each.
[0015] In yet another embodiment, the means to separate the RFID straps is a wedge and a cutting device, in particular a knife, wherein the cutting device is calibrated to cut through ribbon between two RFID straps, but not through the liner covering the pressure sensitive adhesive, so the liner can be peeled off as a tape. As an alternative, the cutting device can also be located on the planar axis, but after the point at which the RFID strap is attached to the antenna.
[0016] In another embodiment the wedge has a sharp edge, which works as means to peel off the liner which then may be taken up by a reel or otherwise collected. The wedge may be designed and positioned so that the peeled off liner is pulled around the sharp edge, thereby placing the RFID strap onto the antenna. The delivery speeds of the ribbon with RFID straps and the antennas have to be adapted to enable a precise attachment.
[0017] In another embodiment, a tamp applicator is provided, which tamps or presses the separated and peeled-off RFID straps onto the antennas, so that the pressure sensitive adhesive is activated.
[0018] In a further embodiment the peeled-off liner is made of a reusable material. This may improve the environmental sustainability of the disclosed method.
[0019] In another embodiment, the ribbon is wound up on a reel and delivered to the connection area from said reel. This embodiment may be advantageous for reel-to-reel production setups.
[0020] An embodiment also discloses a system for assembling an RFID device, comprising an antenna creation station configured to form a multitude of antennas defining a gap; a strap creation station, providing RFID straps comprising an IC-bearing side and a second planar side each, wherein an adhesive and a continuous liner are applied to both sides, so that a ribbon of consecutive RFID straps covered with adhesive and liner on both sides is created; and a strap attach station with a planar strap attach area, wherein the ribbon of RFID straps and the RFID antennas are transported to the strap attach area so that each RFID strap matches up with one antenna, wherein the strap attach station comprises means to peel off the liner from the IC-bearing side and means to cut the ribbon to separate the RFID straps from each other.
Brief Description of the Drawings
[0021] Fig. 1 is a flowchart of an example production workflow in accordance with an embodiment.
[0022] Fig. 2A is a schematic drawing of the construction of an illustrative RFID strap; [0023] Fig. 2B is a schematic drawing of the different layers on one side of the RFID strap;
[0024] Fig. 3 is a schematic drawing of RFID device assembly in accordance with an embodiment;
[0025] Fig. 4 is a schematic drawing of RFID device assembly in accordance with an embodiment;
[0026] Fig. 5 is a schematic drawing of aRFID device assembly in accordance with an embodiment.
Description of the Illustrated Embodiments
[0027] Fig. 1 shows a flowchart of an example of a production workflow 100 using an embodiment of the disclosed invention. The workflow 100 starts after the production of the ribbon or tape of RFID straps, which has a liner disposed on both sides of the RFID straps and is rolled onto a reel. Also, the antennas are connected by a common substrate and are rolled up on a second reel. Both antennas 102 and RFID straps 101 are unwound from their respective reels. The RFD straps are singulated 103 and transferred to the planar attaching area, where each RFID strap is attached to one antenna 104 each by means of the adhesive. The liner covering the adhesive may be peeled off either before or after the singulation of the RFID straps. The antennas with the attached RFID straps are then inspected and measured 105 to determine if the alignment of antenna and RFID straps is acceptable (e.g. within one or more predetermined parameters. The RFID devices are then converted 106, which may involve being covered with paper to make the RFID devices printable. A final testing 107 ensures the full functionality of the RFID device. In case the final test is failed, a feedback loop can adjust the attachment process 108. The finished product is then rewound onto another reel 109.
[0028] Fig. 2A shows a schematic drawing of the construction of an RFID strap 200. Conductive structures 204 are attached to a stabilizing carrier material or substrate 201 . The carrier material 201 may for example be sheets or tapes of paper or PET. The sheets or tapes may be very long, so the material can be wound up on a reel. To form the conductive structures 204, thin metal foils, conductive inks or the like may be used. The IC chips 202 are attached to the conductive structures 204 using a conductive adhesive 203, e.g. Anisotropic Conductive Paste (ACP). After that, an adhesive tape 205 is applied. The inside liner 206 of the adhesive tape 205 is removed, while the outside liner 207 will only be removed to attach the RFID strap 200 to the antenna during the inventive method of production.
[0029] Fig. 2B shows the schematic drawing of the different layers on one side of an RFID strap. The lowest layer is showing the conductive structures 204 with the attached IC chip 202 on the carrier substrate 201 . Layer 205 is the adhesive, covered by the liner 207.
[0030] Fig. 3 shows a schematic drawing of RFID device assemby 300 oin accordance with an embodiment. A ribbon of RFID straps, produced as described in Fig. 2A and Fig. 2B, is delivered to a pulley 310. At the pulley 310, the liner 307 is peeled off from the adhesive layer 305 and transported away. It may, for example, be wound up on a reel and re-used. The ribbon is then transported over another pulley 313, with the exposed adhesive 305 on the outside. A wheel 311 with cutting edges 312 or rotating blades is singulating the RFID straps from each other by cutting the carrier material 301 . The separated RFID straps are then attached to the antennas 309, which are transported on a substrate 308 along the planar attachment area. The delivery speeds of the pulley 313 delivering the RFID straps and the transportation of the antennas 309 are matched, so that each RFID strap gets attached precisely over the gap 309a in the antenna 309, defining the strap landing zone. [0031] Fig. 4 is a schematic drawing of RFID device assembly in accordance with another embodiment. From a reel 414 the RFID strap ribbon or tape is delivered towards a wedge 415. The tip of the wedge serves as attachment device and peel-off device for the liner, exposing the adhesive 405. The adhesive 405 may be a pressure sensitive adhesive and a wheel (not shown) may apply pressure to the attached RFID strip following the application area, where the RFID straps are applied to the antenna structures 409 defining a gap 409a as the antennas 409 are transported on a substrate 408. The RFID straps may be aligned so that the IC chip 402 fits in the gap 409a defined by the antenna structure 409. A cutting device 412 is cutting the carrier material and singulating the RFID straps. The waste liner is wound up on a reel 416 and may be reused.
[0032] Fig. 5 is a schematic drawing of RFID device assembly in accordance with yet another embodiment. Again the RFID strap produced as described above are delivered from a reel 514. The wedge 515 helps in peeling the liner, which is then wound up on a reel 516. A cutting device 512 singulates the RFID straps. In contrast to the embodiment shown in Fig. 4, the tip of the wedge 515 does not deliver the singulated RFID straps directly to the antennas 509, which are defining a gap 509a, but instead to a tamping device 517. The tamping device 517 tamps one RFID strap at a time onto one antenna structure 509 as the antennas 509 are transported on a substrate 508. The pressure sensitive adhesive is activated by the tamping. This way any further device for activating the adhesive isn’t necessary. The delivery speeds of RFID straps, antennas and the tamping frequency are calibrated, so that the RFID strap is placed exactly over the gap 509a in the antenna 509.