MXPA97005524A

MXPA97005524A - Method for connecting electrically an integrated circuit to a ultraflexi substrate

Info

Publication number: MXPA97005524A
Application number: MXPA/A/1997/005524A
Authority: MX
Inventors: R Isaacson Mark; F Piccoli Anthony; Holloway Michael
Original assignee: Checkpoint Systems Inc
Priority date: 1996-07-22
Filing date: 1997-07-21
Publication date: 1998-02-01

Abstract

The present invention relates to a method for electrically connecting an integrated circuit (IC) to at least one electrical conductor on a flexible substrate comprising the steps of: (a) providing a flexible dielectric substrate having a localized IC fixing area on one of a first main surface and a second opposing main surface of the substrate and at least one resonant circuit comprising a first conductor pattern disposed on the first main surface and a second conductor pattern disposed on the second main surface, wherein the first The conductor pattern is electrically connected to the second conductor pattern so that the first and second conductor patterns form an inductor and a capacitor, where the inductor functions as a wavehead, (b) clean an area of IC binding attachment from the substrate, comprising the area IC bonding fixation area of the substrate and circuit resonate close to, and including the IC fixing area, (c) securing the flexible substrate in a fixed position to prevent substantial movement of the substrate, (d) securing the CI to the IC fixing area of the flexible substrate to minimize the movement of the IC in relation to the flexible substrate, (e) electrically connect the IC to the resonant circuit, thereby electrically connecting the IC to the resonant circuit with at least one wire junction, and (f) applying a protective cover over the at least one wire joint to protect the at least one wire joint from being damaged by external forces

Description

METHOD FOR ELECTRICALLY CONNECTING A CIRCUIT INTEGRATED TO A ULTRAFLEXIBLE SUBSTRATE FIELD OF THE INVENTION The present invention relates to the electrical connection of an integrated circuit to an ultra-flexible substrate and, more particularly, to an integrated circuit mounted on a radio frequency identification label.

BACKGROUND OF THE INVENTION Printed circuit boards (PCBs) and integrated circuits (ICs) are well known and commonly used in many different applications. Integrated circuits provide large amounts of electronic functionality in a small area. Typically, a PCB comprises a plurality of layers alternating between electrically conductive layers and insulating layers, and includes a plurality of holes or passageways for interconnecting the conductive layers. One or more ICs are mounted to the PCB by placing pins that extend from the IC into predetermined holes in the PCB and then welding the pins to one or more of the conductive layers of the PCB. The insulating layers of the PCB are generally composed of epoxy resin and glass, and the conductive layers are generally copper. Consequently, PCBs comprise very rigid structures capable of withstanding high temperatures and it is a relatively simple task to mechanically secure and electrically connect an IC to the PCB. However, there are situations in which it would be advantageous to fix an IC to a flexible or non-rigid substrate which generally can not be subjected to high temperatures, such as the temperature required to carry out the welding procedures. Moreover, it would be desirable to also fix an IC to an ultra-flexible substrate. An ultra-flexible substrate comprises a substrate that is even more flexible (and less rigid) than current "flexible" substrates, such as kapton. Accordingly, as used herein, the term "flexible" refers to substrates that are more flexible than commercially available Kapton substrates. Attempts to electrically connect ICs to such flexible substrates have had limited success due to the difficulties in transferring ultrasonic energy only to the electrical junction area. That is, due to the flexible nature of the substrate, much of the ultrasonic energy required for the electrical bonding process is lost with the movement of the substrate caused by the ultrasonic energy. The present invention provides a flexible substrate having a mechanically fixed integrated circuit and electrically connected thereto. The present invention also provides a method for electrically connecting an IC to such a flexible substrate.

BRIEF DESCRIPTION OF THE INVENTION Briefly mentioned, the present invention comprises a method for electrically connecting an integrated circuit (IC) to at least one electrical conductor on a flexible substratum. The method comprises the steps of: (a) providing a flexible dielectric substrate having an IC fixation area located on one of a first major surface and a second opposing major surface of the substrate and at least one resonant circuit comprising a first conductor pattern disposed on the first main surface and a second conductor pattern disposed on the second main surface, wherein the first conductor pattern is electrically connected to the second conductor pattern so that the first and second conductor patterns form an inductor and a capacitor, where the inductor works with an antenna; b) cleaning an IC junction fixing area of the substrate, the IC junction binding area comprising an area of the substrate and the resonant circuit close to and including the IC fixation area; c) securing the flexible substrate in a fixed position to prevent substantial movement of the substrate; d) securing the CI to the CI fixation area of the flexible substrate to minimize the movement of the IC in relation to the flexible substrate; e) electrically connecting the IC to the resonant circuit, thus electrically connecting the IC to the resonant circuit with at least one electrical connection; and f) applying a protective cover on the at least one electrical connection to protect the at least one electrical connection from being damaged by external forces. The present invention also provides a radio frequency identification (RFID) tag for use with a communication system having means to detect the presence of an RFID tag within a monitored area using electromagnetic energy at a frequency within a scale of predetermined frequency and means for receiving digitally encoded information transmitted from the RFID tag. The RFID tag comprises a flexible dielectric substrate, at least one resonant circuit comprising a first conductive pattern disposed on a first main surface of the flexible substrate, a second conductive pattern disposed on a second opposing main surface of the flexible substrate, wherein the The first conductor pattern is electrically connected to the second conductor pattern such that the first and second conductor patterns form an inductor and a capacitor, wherein the inductor functions as an antenna, an area of fixation of IC on the substrate, an integrated circuit ( IC) fixed to the IC fixing area and electrically connected to the resonant circuit, storing the IC digitally encoded information, where the detection by means of the antenna of a signal at a predetermined frequency causes the antenna to provide power to the IC so that the digitally encoded information is emitted from it and t Transmitted by the antenna at a predetermined frequency scale, and an encapsulating layer covering the IC and the electrical connections between the IC and the resonant circuit.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description, as well as the following detailed description of the preferred embodiments of the invention, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustration of the invention, embodiments which are currently preferred are shown in the drawings, it being understood, however, that the invention is not limited to the precise and described arrangements and instrumentalities. In the drawings: Figure 1 is a schematic diagram of an equivalent electrical circuit of a resonant frequency identification (RFID) tag according to a preferred embodiment of the present invention; Figure 2 is an elongated plan view of one side of a flexible printed circuit RFTD tag according to a first embodiment of the present invention; Figure 3 is an elongated plan view of one side of a flexible printed circuit RFID tag according to a second embodiment of the present invention; Figure 4 is an elongated plan view of a portion of the flexible printed circuit RFID tag of Figure 3; Figure 5 is a broadly elongated plan view of a portion of the flexible printed circuit RFID tag of Figure 3, including an integrated circuit mounted thereon. Figure 6 is an elongated plan view of a portion of the flexible printed circuit RFID tag of Figure 3, which includes an integrated circuit assembled and electrically connected thereto; Figure 7 is a flow chart of a method for constructing a resonant frequency identification tag according to a preferred embodiment of the present invention; Figure 8 is an exploded view of a resonant frequency identification tag according to a preferred embodiment of the present invention; and Figure 9 is a sectional side view of a portion of a housing of the resonant frequency identification tag of Figure 8.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Some terminology is used in the following description solely as a convenience and is not limiting. The words "upper" and "lower" designate directions in the drawings to which reference is made. The term "flexible" means substrates "ultraflexibl.es", which are substrates that are more flexible than substrates constructed of kapton, as is known to those skilled in the art. The terminology includes the words mentioned specifically above, derived from them and words of similar importance. The present invention is directed to the manufacture of a flexible and thin resonant circuit with a custom made integrated circuit (IC) and provides a method for electrically linking the IC to the flexible substrate of the resonant circuit. Although the invention is described with reference to resonant circuit tags and in particular radio frequency identification (RFID) tags, which are activated by a radio frequency interrogation signal, it will be recognized by those skilled in the art. that the inventive concepts described are applicable to other devices that would benefit from having an integrated circuit fixed and connected to a flexible substrate. Accordingly, it is not intended that the present invention be limited to RFID tags.

RFID tags are generally known and applicable to a wide variety of uses. The patent of E.U.A. No.5, 430, 41 discloses a response tag that transmits a digital encoded signal in response to an interrogation signal. The label comprises a rigid substrate constituted by a plurality of dielectric layers and conductive layers and includes an integrated circuit completely embedded within a hole in the substrate and joined by tongue-to-trace tab conductive metal. Another RFID tag is described in the US patent. 5, 444,223 to Blama. Blarna recognizes the advantage of manufacturing a label from flexible, low-cost materials such as paper. However, instead of storing a predetermined identification code in a single integrated circuit, Blarna manufactured a label that uses a plurality of circuits, each circuit representing a single bit of information. According to the present invention, RFID tags thin flexible are manufactured using a very thin substrate of a dielectric material such horn polyethylene, laminated on both sides with a very thin layer of conductive material such as aluminum foil , which is photo-printed and subsequently recorded to form a two-sided circuit consisting of at least one inductor-connected to one or more capacitors, thus forming a resonant circuit. One of the layers of conductive material also includes a fixing area for receiving an IC. The IC is fixed to the fixing area and is electrically connected to the resonant circuit, thus electrically connecting the IC to the resonant circuit. Referring now to the drawings, in which the same reference number designations are applied to corresponding elements along several figures, it is shown in FIG. 1 a schematic diagram of an equivalent electrical circuit of a resonant frequency identification tag 10 according to a preferred embodiment of the present invention. The tag 10 comprises a resonant circuit 12 electrically connected to an integrated circuit (IC) 14. The resonant circuit 12 may comprise one or more inductor elements electrically connected to one or more capacitor elements. In a preferred embodiment, the resonant circuit 12 is formed by the combination of a single inductor element, an inductor or coil L electrically connected to a capacitor element or capacitance CANT in a loop in series. As is well known to those skilled in the art, the frequency of the resonant circuit 12 depends on the values of the inductor coil L and the capacitor CANT -such resonant circuit is shown and described in detail in Patent U.S.A. No. 5,276,431, which is incorporated herein by reference. The size of the inductor L and the value of the capacitor-CANT are determined based on the desired resonant frequency of the resonant circuit 12 and the need to maintain a low induced voltage across the capacitor plates. In one embodiment of the invention, tags 10 are constructed which operate at 13.56 MHz. Although the tag 10 includes a single inductor L and a single capacitor element CANT element, they can be used multiple inductors and capacitors elements alternately. For example, resonant circuits of multiple elements are well known in the art of electronic security and surveillance, such as those described in the U.S. patent. No. 5,103,210 entitled "Activatable / Deactivatable Security Tag for Use with an Electronic Security System", which is incorporated herein by reference. The IC 14 stores a predetermined digital value, which can be used for a variety of purposes, such as to identify a particular object or person associated with the tag 10. The stored digital value can be unique for each tag 10, or in In some cases, it may be desirable for two or more labels to have the same stored digital value. In addition to identifying an object, IC 14 could be used to store product warranty information. A proximity reader or interrogator device (not shown) is used to read information stored in the IC 14. In operation, the proximity reader creates an electromagnetic field at the resonant frequency of the resonant circuit 12. When the label 10 is placed near the reader and in the electromagnetic field, a voltage is induced on the inductor coil Lides power to IC 14 at the ANT input of IC 14. IC 14 internally rectifies the AC voltage induced at the ANT input to provide an internal source of DC voltage. When the internal DC voltage reaches a level which ensures the proper operation of the IC 14, the TC 14 operates to output the digital value stored therein to the MOD output of the IC 14. A CMOD modulation capacitor is connected to the MOD output of the IC 14 and the resonant circuit 12. The IC output pulses switch the CMOD capacitor inside and outside the resonant circuit 12 creating and breaking ground connections to change the total capacitance of the resonant circuit 12 according to the stored data, which changes the resonant frequency of the resonant circuit 12, detuning it from the main operational frequency up to a predetermined higher frequency. The reader detects the energy consumption within its electromagnetic field. The data pulses of the tag 10 are created by the tuning and detuning of the resonant circuit 12. The reader detects changes in the power consumption to determine the digital data value output emitted from the TC 14. The TC 14 includes also a power return or GND output and one or more additional inputs 16 that are used to program the IC 14 (ie, store or alter the digital-value therein). In the currently preferred embodiment, the IC 14 comprises 64 bits of non-volatile memory and the reader and label 10 operate at 13.56 MHz. Of course, it will be apparent to those skilled in the art that memory chips having a capacity can be used. of storage, whether larger or smaller, so that the IC 14 stores more or fewer memory bits. In addition, it will be apparent to those skilled in the art that the resonant circuit 12 and the reader can operate at radio frequencies other than 13.56 MHz. Referring now to FIG. 2, a side or main surface of a first embodiment of an RFID tag 20 is shown. TAG_20_, like tag 10, includes a resonant circuit comprising an inductor in the form of a coil 22 and a capacitor 24. The capacitor 24 comprises two plates located on opposite sides or main surfaces of a substrate 26. The inductor coil 22 is located on one of the main surfaces of the sub-substrate 26 and comprises a coil extending close to, and around an edge peripheral outer 28 of the substrate 26. Since only one side of the label 20 is shown, only one capacitor plate 24 is shown in FIG. 2. The capacitor plate 24 includes a plurality of fingers or extensions 30, which are provided to tune the resonant circuit. That is, the fingers 30 can be cut, engraved or trimmed and otherwise removed to change the value of the capacitor 24 and thus the resonant frequency of the resonant circuit 12. In the first preferred embodiment, the substrate 26 comprises a material dielectric or flat and generally rectangular insulator, which is preferably flexible, such a paper or a polymeric material. In the currently preferred embodiment, substrate 26 comprises full polyethylene. However, it will be apparent to those skilled in the art that the substrate 26 may be made from other materials, such as any solid material or mixed structures of materials, as long as the substrate 26 is insulating and can be used as a dielectric. The elements and circuit components of the resonant circuit 12 are formed on both main surfaces of the substrate 26 by means of pattern-conducting material on the surfaces of the substrate 26. A first conductor pattern is imposed on the first side or surface of substrate 26, which surface is selected albitrapamente like the upper surface of the label 20, and a second conductor pattern is imposed on the second surface or opposite side (not shown) of the substrate 26, sometimes called the back or bottom surface. The conductive patterns can be formed on the surfaces of the substrate with electrically conductive materials of a known type and in a form that is well known in the art electronic article surveillance. The conductive material preferably has patterns formed by a subtraction (i.e. engraving) procedure, wherein the unwanted material is removed by chemical etching after the desired material has been protected, typically printed on etch-resistant ink. In the preferred embodiment, the conductive material comprises a thin sheet of aluminum. However, other conductive materials (eg, thin foils or conductive inks, gold, nickel, copper, phosphor bronzes, brass, solder, high density graphite or conductive epoxy resins filled with silver) can be replaced by aluminum without change the nature of the resonant circuit or its operation. The first and second conductive patterns establish at least one resonant circuit, such as the resonant circuit 12, having a resonant frequency within a predetermined operational frequency scale, such as the aforementioned preferred frequency of 13.56 MHz. As mentioned above in relation to fig. .1, the resonant circuit 1.2 is formed by the combination of a single element, inductor, or coil L electrically connected to a single capacitor element or capacitance CANT in a series laso. The inductor element L formed by the coil portion 22 of the first conductor pattern is formed as a spiral coil of conductive material on a first main surface of the substrate 26 and the capacitor element CANT, as mentioned above, is comprised of a first plate formed by a generally rectangular plate (shown at 24) of the first conductive pattern and a second plate formed by a corresponding generally rectangular and aligned plate of the second conductive pattern (not shown). As will be appreciated by those skilled in the art, the first and second plates are generally in register and are separated by the dielectric substrate 26. The first plate of the QANT capacitor element is electrically connected to one end of the inductor 22. Similarly , the second plate of the QANT capacitor element is electrically connected by means of a soldered connection (not shown) extending through the substrate 26 to connect the second plate to the other end of the inductor 22, thereby connecting the inductor element L to the Capacitor element CANT in a well-known way. In the presently preferred embodiment, the substrate 26 and the first and second conductor patterns are approximately 3.3 microns thick, the substrate 26 having approximately 1.0 micron thickness, the first conductive pattern (i.e., the coil layer or side shown in FIGS. Figures 2 and 3) is approximately 2.0 microns thick and the second conductive pattern is approximately 0.3 microns thick. Since the substrate 26 is relatively thin and very flexible, it has been found that the substrate 26 does not provide, in itself, adequate support to receive the IC 14 and keep the IC 14 in a firm or stable position to be able to form electrical connections. between the IC 14 and the resonant circuit .14 that are resistant and do not break or compromise easily. Accordingly, the present invention provides an IC fixing or receiving area 32 for receiving and supporting the IC 14.

The IC fixing area 32 is located on a surface of the substrate 26 and is made of a material suitable to sufficiently support the IC 14. The IC fixing area 32 provides a stable surface to which the. IC 14 can be fixed or secured such that the IC. 14 does not move relative to the substrate 26 and the resonant circuit 12 during an ultrasonic electrical bonding operation. In the currently preferred embodiment, the IC fixing area 32 has the same general dimensions as the IC 14 (e.g., generally rectangular in shape) but is somewhat larger in size than the IC 14 so that it is not difficult place the IC 14 in the IC fixing area 32. Preferably, in order to keep the manufacturing process efficient and cost-effective, the fixation area of IC 14 is made of the same material as the first conductive pattern and is formed on the substrate 26 at the same time that the re-energizing circuit 12 is formed on the substrate 26. The IC fixing area 32 should be located as close as possible to those areas or terminal areas to which the IC 14 will be electrically connected, in such a way that the electrical connections do not have an excessive length. As shown in Figure 2, in a first preferred embodiment, the IC fixation area 32 is located on an upper right side of the euperior surface of the substrate 26 close to, but not in contact with, the coil 22 or the capacitor 24 so that the fixing area 32 is physically and electrically isolated from the other components. This location is adequate because it allows the IC 14 to be positioned or located near each of the terminal areas or areas to which it will be electrically connected. Referring now to Figure 3, one side of a second preferred embodiment of an RFID tag 34 is shown. Like the tag 20, the tag 34 comprises a substrate 26, an inductor coil 22 that functions as an antenna and a capacitor 24 having fingers or extensions 30 to allow adjustment of the value of capacitor 24. Preferably sub-substrate 26 comprises polyethylene, which is formed into sheets and inductor 22 and capacitor-24 comprise a thin sheet of etched aluminum , as previously described. The tag 34 also includes an IC fixation area 36 comprising a filler shoulder or corner of the inductor coil 22. In contrast to the isolated or floating IC fixation area 32 (FIG. 2), forming the area 36 of FIG. IC fixation as an integral portion of the conductive pattern-on one side of the surface of the substrate 26 provides a more stable support surface for the IC 14, because the movement of the substrate 26 is absorbed over a larger area (e.g. The vibration of the IC fixing area 36 caused by the ultrasonic energy during the electrical connection is absorbed not only by the IC fixing area 36, but also by the coil 22). Providing a more stable or rigid support area for the IC 14 is important, since it makes possible the proper electrical connection of the IC 14 to the resonant circuit 12, as described hereinabove. Referring now to FIGS. 2 and 3, a plurality of joint end areas are also formed on the first side of the substrate 26 to which the IC 14 is electrically connected. A first terminal junction area 38 is designed to connect to the input ANT of IC 14. A second terminal junction zone 40 is provided for connecting to the MOD output of IC 14 and a plurality of junction terminal zones 42 are provided for connecting to additional inputs 16 of IC 14 used to program IC 14 as described above. Each of the terminal junction zones 38, 40, 42 are formed of a conductive material - and are preferably made of the same material as the first conductive pattern and are formed on the substrate 26 at the same time that the resonant circuit is formed on the substrate 26. The GND output of IC 14 is connected to coil 22 at a location on coil 22 that is close to IC 14. Referring now to Figures 4-6 and 7, in accordance with the present invention, IC 14 is connected electrically to the terminal connecting zones 38, 40, 42 and to the coil 22 with wires 44 (Figure 6) using an ultrasonic welding process. In the preferred ultrasonic welding process, a wire fastener with a vacuum plenum table is used to interconnect an input / output terminal zone on the IC 14 to a corresponding joint end zone 38/40/42 on the substrate 26. using a conductive wire, such as 0.032 mm aluminum wire. Figure 7 is a flowchart of the electrical joining method 50. In order to overcome the difficulties of the electrical connection of the IC 14 on the flexible substrate 26, it has been determined that the proper cleaning of the terminal connecting areas 38, 40, 42, by adhesively securing the IC 14 to the fixing area 32/36 of IC 14 and securely holding the subassembly 26 in a fixed pointer during the welding or electrical bonding process, are important steps to ensure that a suitable electrical connection is made between the IC 14 and the junction terminals 38, 40, 42. Starting with step 52, the resonant circuit 12 is die cut from a core formed as part of the manufacturing process having a plurality of resonant circuits individual 12 formed on it. Before the IC 14 is fixed to the IC fixing area 36, an area of the substrate 26 and the resonant circuit 12 close to, and including the IC fixing area 36, generally referred to as the IC fixing junction area 46 (FIG. 4), is chemically cleaned in step 54 to remove any photoresist material remaining on the IC attachment fixation area 46 after the formation of the resonant circuit 12. In the preferred embodiment, the joint fixation area 46 of IC is cleaned with acetone using a cotton swab. In step 56, the resonant circuit 12 is placed in a plenum or holder designed to receive and sustain the resonant circuit 12 securely. Preferably the plenum includes a recess having a size and shape adapted to receive the resonant circuit 12. Although it is known that the spatially available plenums supporting a workpiece inside the plenum by means of vacuum pressure, it has been found that using only vacuum pressure to hold the resonant circuit 12 within the plenum is not sufficient to keep the substrate flexible. 26 in it and carry out the electrical connection operation in it. Consequently, in the preferred manufacturing process, the resonant circuit 12 is maintained within the gap of the plenum both by vacuum pressure and by placing an adhesive medium in the plenum circuit reception area. It has been found that the combination of vacuum pressure and adhesive securely and adequately supports the resonant circuit 12 within the. full so that an ultrasonic welding or electrical bonding operation can be carried out. In the currently preferred embodiment, the adhesive means for fixing the resonant circuit 12 to the plenum is strong enough to hold the resonant circuit 12 in place on the plenum, but also allows the resonant circuit 12 to be removed from the plenum without breaking or damaging the resonant circuit 12. In step 58, an adhesive, preferably an epoxy resin, is applied to the IC fixing area 32/36 to secure or fix the IC to the IC fixing area 32/36. The IC 14 is fixed to the IC fixing area 32/36 with such an adhesive to keep the IC 14 in position and to ensure that the IC 14 does not move during the electrical bonding operation. In accordance with the present invention, it is preferred that more than one small epoxy resin point be placed on the IC fixing area 32/36 and that a large amount of epoxy resin be used instead to make or form a base more stable and rigid for the IC 14. I mean, that the epoxy resin must expand at least 2 microns beyond a perimeter of IC 14 after IC 14 has been placed. Preferably, the IC 14 is fixed to the IC fixing area 32/36 with an ultraviolet (UV) curable adhesive, such as a UV-curable epoxy resin. In step 60, the IC 14 is placed in the center of the IC fixing area 32/36. A vacuum-assisted lifting tool can be used to lift and position the IC 14 over the IC fixing area 32/36. Care should be taken to ensure that the IC 14 is properly oriented and seated and that there is a sufficient strip of epoxy resin around the IC 14. Coated clamps or wooden pallets can be used to assist in the alignment of the IC 14. You have also careful to avoid scratching or staining an upper side of the IC 14 or the terminal junction zones 38, 40, 42 with epoxy resin. After the IC 14 has been fixed to the IC fixing area 32/36 with epoxy resin, in step 62 the epoxy resin is cured by placing the resonant circuit 12 through a UV curing conveyor furnace. The UV curing conveyor furnace uses ultraviolet light to cure the epoxy resin at a temperature of about 60 ° C. It is preferred to cure the epoxy resin at 60 ° C, because higher temperatures could destroy or damage the substrate 26 and the flexible circuit 12. In step 64, those areas of the connecting terminal zones 38, 40, 42 to which the wires 44 will be joined, called the wire joining area 48 (Figure 5), cleaned to remove oxidation (e.g., AIO2) and also to provide texture to the wire bonding area 48 of the conductive material. The addition of texture to the wire bonding area 48 acts as an energy director and provides extra conductive material that is conductive for welding the wires 44 to the junction terminals 38, 40, 42. Accordingly, the cleaning step 34 is carried out with a soft abrasive, such as a synthetic steel wool scouring pad or a pencil eraser. It is also preferred that the cleaning step 64 be carried out just before the electrical bonding step to ensure that there is minimal or no oxidation on the conductive material during the electrical bonding step. In step 66, the wires 44 are attached to the IC 14 and to the joint end regions 38, 40, 42 (Figure 6). Preferably, the wire 44 is an 0.032 mm thick aluminum wire having a breaking strength of 18-20 g. The wire 44 is attached to the terminal junction zones 38, 40, 42 and to the IC 14 using a joining apparatus and an ultrasonic generator of a type that is commercially available today. Preferably, the bond strength is greater than 6 gm and the wire loop height does not exceed 0.381 mm. As mentioned above, since the resonant circuit 12 is made using a flexible substrate 26, it is important that the resonant circuit 12 be held firmly during the electrical bonding procedure. Thus, as also previously described, it is currently preferred that the resonant circuit 12 be held either adhesively in the plenum or by vacuum pressure to ensure that the ultrasonic energy generated by the electrical junction apparatus and directed to the IC 14 and to the terminal junction zones 38, 40, 42 are not lost by the movement or vibration of IC 14 and / or substrate 26. Electrical bonding apparatus uses sonic vibration to partially melt portions of wire 44 and join wire 44 to areas junction terminals, 38, 40, 42, respectively. The combination of adhesively securing the resonant circuit 12 to the electrical junction machine using vacuum pressure to secure the resonant circuit 12 to the electrical junction machine and fix the IC 14 to the resonant circuit 12 using epoxy resin, suitably supports the resonant circuit 12 and IC 14 so that effective electrical connections are formed. After the IC 14 has been electrically connected to the resonant circuit 12, a cover or protective encapsulant 45 (Figure 9) is placed on at least the wire joints in step 68. Preferably, the encapsulant 45 covers the entire IC 14, the wires 44 and the wire joints. The encapsulant 45 is applied using a pneumatic encapsulant dispenser, as is known to those skilled in the art. It is currently preferred that the encapsulant 45 be a curing resin with light and that the finished height of the encapsulant 45 over the bound IC 14 does not exceed 0.635 mrn and that the diameter of the encapsulant 45 does not exceed 6.35 mrn for the encapsulated IC 14 to fit within of a recess of a polymeric housing, as described hereinabove. In step 70, the encapsulant 45 is cured by placing the circuit 12 in a UV cure conveyor furnace. Preferably, the encapsulant 45 is cured using ultraviolet light at a temperature of about 60 ° C. The encapsulant 45 is not cured by cooking because the preferred polyethylene substrate 26 melts at about 75 ° C. In such a case, the cooking would damage or destroy the substratum 26. In step 72, the frequency of the resonant circuit 12 is measured using a spectrum analyzer or a test facility using a frequency generator and a presentation monitor. The capacitor 40 is trimmed by cutting and removing one or more of the fingers 30 of the capacitor, if necessary, to assure that the resonant circuit 12 operates at a predetermined resonant frequency, which in the preferred embodiment is between 13.6 MHz to 13.8 MHz. In step 74, the IC 14 is programmed to store the desired data in the IC 14 in a manner well known in the art, preferably by attaching leads from a computer to the terminal programming zones 42. Now that the formation of the label 10 including resonant circuit 12 and IC 14 has been completed, label 10 can be used for a variety of purposes and in a variety of different environments. Such a use of the tag 10 is in a proximity card of the type used for access control. Referring now to FIG. 8, an exploded view of a proximity card 90 is shown. The proximity card 90 comprises the RFID tag 10, a housing 92, a double-sided adhesive tape 94 and a label or cover reinforcement 96. As shown in Figure 9, the housing 92 includes a recess 98 located and configured to receive the encapsulated IC 14 of the label 10. The transfer adhesive label 94 also includes a cutting area 100 in a corner thereof. corresponds to the recess 98 and the IC 14 so that the IC 14 can be received within the recess 98. In step 76 (Figure 7), the double-sided transfer adhesive tape 94 is applied to the lower surface of the recess 92 in a orientation such that the cutting area 100 corresponds to the recess 98. In step 78, the label 10 is attached to the transfer adhesive tape 94 on the housing 92 and the IC 14 is received within the recess 98 of the housing 92. Final At step 80, the cover label 96 is applied to the label 10 with an adhesive (not shown). The cover label 96 may include indexes printed on its outer surface for advertising or identification purposes. The proximity card 90 preferably has a rectangular shape to simulate a credit card in both size and shape, which is convenient for human handling. A sequence number and a date code for the card 90 can be stamped on an outer surface of the housing 92 or on the cover label 96. The housing 92 is preferably made of a polymeric material, such as polyvinyl chloride and formed by injection molding or otherwise, as is known in the art. The adhesive transfer tape 94 is preferably a double-sided double-sided double-sided adhesive tape., which is commercially available generally in packaged rolls. The proximity card 90 can be used as an access control card as is known to those skilled in the art. Alternatively, the tag 10 can be used as a security tag, which is placed on a counter item to be used for security or product warranty purposes. It will also be apparent to those skilled in the art that the label 10 can be used in other commercial applications. From the above description it can be seen that the present embodiment comprises a method of electrical connection of an IC to a flexible substrate composed of a material that can not withstand the high temperatures required for the welding processes. It will be recognized by those skilled in the art that changes can be made to the embodiment of the invention described above without departing from the inventive concepts thereof. Therefore, it is understood that this invention is not limited to the particular embodiment described, but is intended to cover any modifications that are within the scope and spirit of the invention as defined by the appended claims.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - A method for electrically connecting an integrated circuit (IC) to at least one electrical conductor on a flexible substrate comprising the steps of: (a) providing a flexible dielectric substrate having an IC fixing area located on a of a first main surface and a second opposing main surface of the substrate and at least one resonant circuit comprising a first conductor pattern disposed on the first main surface and a second conductor pattern disposed on the second main surface, wherein the first conductor pattern it is electrically connected to the second conductor pattern so that the first and second conductor patterns form an inductor and a capacitor, where the inductor operates with an antenna; (b) cleaning an IC junction fixing area from the substrate, the IC junction binding area comprising an area of the substrate and resonant circuit close to, and including the IC fixation area; (c) securing the flexible substrate in a fixed position to prevent substantial movement of the substrate; (d) securing the IC to the CI fixation area of the flexible substrate to minimize the movement of the IC relative to the flexible substrate; (e) electrically joining the IC to the resonant circuit, thereby electrically connecting the IC to the resonant circuit with at least one wire junction; and (f) applying a protective cover over at least one wire joint to protect the at least one wire joint from being damaged by external forces.

2. The method according to claim 1, wherein the flexible substrate comprises a polyethylene layer.

3. The method according to claim 2, wherein the conductive patterns comprise aluminum.

4. The method according to claim 1, wherein the IC is secured to the flexible substrate in step (d) with an epoxy resin, and where the epoxy resin expands beyond a perimeter of the IC, forming a rigid region on the subetrato near the IC.

5. The method according to claim 4, further comprising the step of curing the epoxy resin before electrically bonding the IC to the substrate in step (e).

6. The method according to claim 5, wherein the epoxy resin is cured with ultraviolet light.

7. The method according to claim 1, wherein the IC attachment fixation area is cleaned in step (b) with acetone.

8. The method according to claim 7, further comprising the step of abrasively cleaning at least a portion of the resonant circuit near the IC fixing area to remove the oxidation thereof before carrying out the step of electrical union (e).

9. The method according to claim 1, wherein the protective cover comprises an encapsulant. 10.- The method according to the claim 9, which further comprises, after step i f), the step of curing the encapsulant with ultraviolet light. 11. The method according to claim 1, further comprising the step of positioning the IC in a predetermined orientation with respect to the. flexible substrate. 12. The method according to claim 1, wherein the IC is electrically connected to the resonant circuit by means of ultrasonic welding, wherein the IC is secured to the IC fixing area and the substrate is held in a secure manner in a Fixed position avoids substantial movement of both the substrate and the IC, thus preventing excessive dissipation of energy during the welding process. 13. The method according to claim 1, wherein the substrate is held in a secure manner in the fixed position in the hole (c) a plenum using vacuum pressure and an adhesive. 14. The method according to claim 1, further comprising after the p >; aso i f), the step of adhesively securing the flexible subassembly to the flexible housing having a recess to receive the IC. 15. The method according to claim 1, further comprising after step (f), the step of programming the IC with predetermined information digitally encoded. 16. The method according to claim 1, wherein the IC fixing area comprises a portion of one of the first and second conductive patterns wherein the first conductive pattern provides a rigid region to which the IC is secured. . 17. A radio frequency identification (RFID) tag for use with a communication system having means to detect the presence of an RFID tag within a monitored area using electromagnetic energy at a frequency within a frequency scale predetermined and means for receiving digital encoded information transmitted from the RFID tag, the RFID tag comprising: a flexible dielectric substrate; at least one resonant circuit comprising a first conductor pattern disposed on a first main surface of the flexible substrate and a second conductor pattern disposed on a second opposite major surface of the flexible substrate, wherein the first conductor pattern is electrically connected to the second conductor pattern so that the first and second conductive patterns form an inductor and a capacitor, where the inductor functions as an antenna; an IC fixation area on one of the first and second major surfaces of the substrate; an integrated circuit (IC) fixed to the IC fixing area and electrically connected to the resonant circuit, the IC storing digitally encoded information, wherein the detection by means of the antenna of a signal at a predetermined frequency causes the antenna to provide power to the IC so that the digitally encoded information is emitted therefrom and transmitted by the antenna at a predetermined frequency scale; and an encapsulant that covers the IC and the electrical connections between the IC and the resonant circuit. 18. The security tag according to claim 17, wherein the IC fixing area comprises an inductor shoulder formed by one of the first and second conductive patterns. 19. The security tag according to claim 17, wherein the IC is adhesively fixed to the IC fixing area. 20. The security tag according to claim 17, wherein the first and second conductive patterns comprise engraved aluminum. 21. The security tag according to claim 17, further comprising a polymeric housing cover covering the first conductive pattern and the IC, wherein the housing includes a recess for receiving the IC therein.