Patent Publication Number: US-6666379-B2

Title: Method of fabricating a wireless radio frequency identification device

Description:
RELATED PATENT DATA 
     This patent resulted from a continuation application of U.S. patent application Ser. No. 09/383,589, filed Aug. 26, 1999 now U.S. Pat. No. 6,471,129, entitled “Methods of Processing Liquids, Epoxy Fabrication Method, Method of Fabricating a Radio Frequency Intelligent Communication Device, and Method Involving a Mixture of Different Liquids”, naming Rickie C. Lake as inventor, which was a divisional application of U.S. patent application Ser. No. 08/953,030, filed Oct. 17, 1997 now U.S. Pat. No. 6,089,459, entitled “Methods of Processing Liquids, Epoxy Fabrication Method, Method of Fabricating a Radio Frequency Intelligent Communication Device, and Method Involving a Mixture of Different Liquids”, naming Rickie C. Lake as inventor, the disclosures of which are incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to methods of fabricating radio frequency remote intelligent communications devices. The invention has applicability to methods of processing liquids, epoxy fabrication methods and processes involving a mixture of different liquids. 
     BACKGROUND OF THE INVENTION 
     Electronic identification systems typically comprise two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems are operable to provide such communications via a wireless medium. 
     One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee of the present application and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system including communication devices. The communication devices include an interrogator and a transponder such as a tag or card. 
     The communication system can be used in various identification and other applications. The interrogator is configured to output a polling signal which may comprise a radio frequency signal including a predefined code. The transponders of such a communication system are operable to transmit an identification signal responsive to receiving an appropriate command or polling signal. More specifically, the appropriate transponders are configured to recognize the predefined code. The transponders receiving the code subsequently output a particular identification signal which is associated with the transmitting transponder. Following transmission of the polling signal, the interrogator is configured to receive the identification signals enabling detection of the presence of corresponding transponders. 
     Such communication systems are useable in identification applications such as inventory or other object monitoring. For example, a remote identification device is attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output an identification signal. Generating the identification signal identifies the presence or location of the identification device and article or object attached thereto. 
     SUMMARY 
     In but one aspect, the invention comprises a method of fabricating a radio frequency intelligent communications device. A substrate is formed to have conductive lines, at least a portion of which comprise an antenna. An integrated circuit chip and a battery are conductively bonded to the conductive lines on the substrate. A visible spectrum colored liquid resin and a visible spectrum substantially colorless liquid hardener are combined into an epoxy mixture. The liquid hardener has a fluorescent material received therein. Radiation is impinged onto the epoxy mixture effective to cause the fluorescent material to fluoresce. From the fluorescing fluorescent material, degree of homogeneity in the epoxy mixture can be determined. Upon achieving desired homogeneity, the substrate with chip and battery are encapsulated in the epoxy mixture, with the epoxy mixture being cured. 
     The invention also has applicability to epoxy systems and other liquid mixtures having at least two liquid components. The invention also comprises providing first and second liquids where one of said liquids has an invisible component therein. The first and second liquids are combined together into a mixture. The invisible component remains invisible in the mixture upon the combining. After the combining, the component is rendered visible, for example by exposure to ultraviolet radiation. Degree of homogeneity in the mixture is determined while the component has been rendered visible. After the determining, the component is rendered invisible, for example by removing the ultraviolet light source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
     FIG. 1 is a block diagram of a wireless communication system including an interrogator and a wireless communication device embodying the invention. 
     FIG. 2 is a front elevational view of the wireless communication device. 
     FIG. 3 is a front elevational view of the wireless communication device at an intermediate processing step. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
     This description of the present invention discloses embodiments of various wireless communication devices. The wireless communication devices are fabricated in card configurations (which include tags or stamps) according to some aspects of the present invention. Certain embodiments of invention are methods for producing wireless communication devices such and remote intelligent communication devices (RIC) including radio frequency identification devices (RFID). The embodiments are illustrative only and other configurations in accordance with the invention are of course possible, with the invention only being limited by the accompanying claims appropriately interpreted in accordance with the Doctrine Of Equivalents. 
     Referring to FIG. 1, a remote intelligent communication device or wireless communication device  10  comprises part of a communication system  12 . The remote intelligent communication device is capable of functions other than the identifying function of a radio frequency identification device. A preferred embodiment of the remote intelligent communication device includes a processor. 
     The communication system  12  includes an interrogator unit  14 . An exemplary interrogator  14  is described in U.S. patent application Ser. No. 08/806,158, filed Feb. 25, 1997, assigned to the assignee of the present application and incorporated herein by reference. The wireless communication device  10  communicates via wireless electronic signals, such as radio frequency (RF) signals, with the interrogator unit  14 . Radio frequency signals including microwave signals are utilized for communications in a preferred embodiment of communication system  12 . The communication system  12  includes an antenna  16  coupled to the interrogator unit  14 . 
     Referring to FIG. 2, the wireless communication device  10  includes an insulative substrate or layer of supportive material  18 . The term “substrate” as used herein refers to any supporting or supportive structure, including but not limited to, a supportive single layer of material or multiple layer constructions. Example materials for the substrate  18  comprise polyester, polyethylene or polyimide film having a thickness of 3-10 mils (thousandths of an inch). 
     Substrate  18  provides a first or lower portion of a housing for the wireless communication device  10  and defines an outer periphery  21  of the device  10 . Substrate  18  includes a plurality of peripheral edges  17 . 
     Referring to FIG. 3, at least one ink layer  19  is applied to substrate  18  in preferred embodiments of the invention. Ink layer  19  enhances the appearance of the device  10  and conceals internal components and circuitry provided therein. A portion of ink layer  19  has been peeled away in FIG. 3 to reveal a portion of an upper surface  25  of substrate  18 . In other embodiments, plural ink layers are provided upon upper surface  25 . 
     A support surface  20  is provided to support components and circuitry formed in later processing steps upon substrate  18 . In embodiments wherein at least one ink layer  19  is provided, support surface  20  comprises an upper surface thereof as shown in FIG.  3 . Alternatively, upper surface  25  of substrate  18  operates as the support surface if ink is not applied to substrate  18 . 
     A patterned conductive trace  30  is formed or applied over the substrate  18  and atop the support surface  20 . Conductive trace  30  is formed upon ink layer  19 , if present, or upon substrate  18  if no ink layer is provided. A preferred conductive trace  30  comprises printed thick film (PTF). The printed thick film comprises silver and polyester dissolved into a solvent. One manner of forming or applying the conductive trace  30  is to screen or stencil print the ink on the support surface  20  through conventional screen printing techniques. The printed thick film is preferably heat cured to flash off the solvent and UV cured to react UV materials present in the printed thick film. 
     The conductive trace  30  forms desired electrical connections with and between electronic components which will be described below. In one embodiment, substrate  18  forms a portion of a larger roll of polyester film material used to manufacture multiple devices  10 . In such an embodiment, the printing of conductive trace  30  can take place simultaneously for a number of the to-be-formed wireless communication devices. 
     The illustrated conductive trace  30  includes conductive lines and patterns, such as an electrical connection  28 , a first connection terminal  53  (shown in phantom in FIG. 3) and a second connection terminal  58 . Conductive trace  30  additionally defines transmit and receive antennas  32 ,  34  in one embodiment of the invention. Antennas  32 ,  34  are suitable for respectively transmitting and receiving wireless signals or RF energy. Transmit antenna  32  constitutes a loop antenna having outer peripheral edges  37 . Receive antenna  34  constitutes two elongated portions individually having horizontal peripheral edges  38   a , which extend in opposing directions, and substantially parallel vertical peripheral edges  38   b.    
     Other antenna constructions are of course possible. In particular, both transmit and receive operations are implemented with a single antenna in alternative embodiments of the present invention. Both antennas  32 ,  34  preferably extend or lie within the confines of peripheral edges  17  and outer periphery  21  and define a plane (shown in FIG.  4 ). 
     One embodiment of a wireless communication device  10  includes a power source  52 , an integrated circuit chip  54 , and capacitor  55 . Power source  52 , capacitor  55 , and integrated circuit chip  54  are provided and mounted on support surface  20  and supported by substrate  18 . The depicted power source  52  is disposed within transmit antenna  32  of wireless communication device  10 . Capacitor  55  is electrically coupled with loop antenna  32  and integrated circuit  54  in the illustrated embodiment. 
     Power source  52  provides operational power to the wireless communication device  10  and selected components therein, including integrated circuit  54 . In the illustrated embodiment, power source  52  comprises a battery. In particular, power source  52  is preferably a thin profile battery which includes first and second terminals of opposite polarity. More particularly, the battery has a lid or negative (i.e., ground) terminal or electrode, and a can or positive (i.e., power) terminal or electrode. 
     Conductive epoxy is applied over desired areas of support surface  20  using conventional printing techniques, such as stencil or screen printing, to assist in component attachment described just below. Alternately, solder or another conductive material is employed instead of conductive epoxy. The power source  52  is provided and mounted on support surface  20  using the conductive epoxy. Integrated circuit  54  and capacitor  55  are also provided and mounted or conductively bonded on the support surface  20  using the conductive epoxy. Integrated circuit  54  can be mounted either before or after the power source  52  is mounted on the support surface  20 . 
     Integrated circuit chip  54  includes suitable circuitry for providing wireless communications. For example, in one embodiment, integrated circuit chip  54  includes a processor  62 , memory  63 , and wireless communication circuitry or transponder circuitry  64  (components  62 ,  63 ,  64  are shown in phantom in FIG. 3) for providing wireless communications with interrogator unit  14 . An exemplary and preferred integrated circuit  54  is described in U.S. patent application Ser. No. 08/705,043, incorporated by reference above. 
     One embodiment of transponder circuitry  64  includes a transmitter and a receiver respectively operable to transmit and receive wireless electronic signals. In particular, transponder circuitry  64  is operable to transmit an identification signal responsive to receiving a polling signal from interrogator  14 . In the described embodiment, processor  62  is configured to process the received polling signal to detect a predefined code within the polling signal. Responsive to the detection of an appropriate polling signal, processor  62  instructs transponder circuitry  64  to output an identification signal. The identification signal contains an appropriate code to identify the particular device  10  transmitting the identification signal in certain embodiments. The identification and polling signals are respectively transmitted and received via antennas  32 ,  34  of the device  10 . 
     First and second connection terminals  53 ,  58  are coupled to the integrated circuit  54  by conductive epoxy in accordance with a preferred embodiment of the invention. The conductive epoxy also electrically connects the first terminal of the power source  52  to the first connection terminal  53 . In the illustrated embodiment, power source  52  is placed lid down such that the conductive epoxy makes electrical contact between the negative terminal of the power source  52  and the first connection terminal  53 . 
     Power source  52  has a perimetral edge  56 , defining the second power source terminal, which is provided adjacent second connection terminal  58 . In the illustrated embodiment, perimetral edge  56  of the power source  52  is cylindrical, and the connection terminal  58  is arcuate and has a radius slightly greater than the radius of the power source  52 , so that connection terminal  58  is closely spaced apart from the edge  56  of power source  52 . 
     Subsequently, conductive epoxy is dispensed relative to perimetral edge  56  and electrically connects perimetral edge  56  with connection terminal  58 . In the illustrated embodiment, perimetral edge  56  defines the can of the power source  52 . The conductive epoxy connects the positive terminal of the power source  52  to connection terminal  58 . The conductive epoxy is then cured. Thus, the integrated circuit and battery are conductively bonded relative to the substrate and to the conductive lines of trace  30 . 
     An encapsulant, such as encapsulating epoxy material, is subsequently formed following component attachment. In one embodiment, the encapsulant is provided over the entire support surface  20 . Such encapsulates or envelopes the antennas  32 ,  34 , integrated circuit  54 , power source  52 , conductive circuitry  30 , capacitor  55 , and at least a portion of the support surface  20  of substrate  18 . Such operates to insulate and protect the components (i.e., antennas  32 ,  34 , integrated circuit  54 , power source  52 , conductive circuitry  30  and capacitor  55 ). 
     An exemplary encapsulant is a flowable encapsulant. The flowable encapsulant is applied over substrate  18  and subsequently cured following the appropriate covering of the desired components. In the preferred embodiment, such encapsulant constitutes a two-part epoxy perhaps including fillers such as silicon and calcium carbonate. The preferred two-part epoxy is sufficient to provide a desired degree of flexible rigidity. Such encapsulation of wireless communication device  10  is described in U.S. patent application Ser. No. 08/800,037, filed Feb. 13, 1997, assigned to the assignee of the present application, and incorporated herein by reference. Other encapsulant materials of insulative layer  60  can be used in accordance with the present invention. Encapsulation would preferably occur from fabrication of multiple device patterns  10  formed on a single substrate sheet, and then cutting individual devices  10  from the sheet after encapsulation and cure. 
     Fabrication of the epoxy encapsulant material presents some challenges. Specifically, the preferred epoxy comprises a two-component system having a liquid resin material and a liquid hardener material. A presently preferred resultant color for the cured encapsulant is light grey. The resin typically constitutes three times the volume of the hardener within the liquid mixture from which the two-part system cures. In the preferred embodiment, the liquid resin is fabricated to be grey in color in light within the visible electromagnetic radiation spectrum. The hardener is clear or colorless in light within the visible spectrum. It is highly desirable that adequate and complete mixing of the resin/hardener two-component epoxy system occur prior to dispensing or otherwise providing the liquid encapsulant atop the substrate, chip, and battery. This is difficult to discern visually where one of the liquid mixing components is clear and the other is not. 
     A color-changing phenomenon might be utilized, but may also adversely affect the desired finished color of the product. For example, consider provision of a yellowish-colored hardener and a bluish-colored resin. The combination of these two natural colors produces green. Complete homogeneity in the mix of two such components could be determined quite easily visually by verifying uniform green coloring throughout the mix. However where the desired finished product is to be some color other than green, an obviously less than desirable result occurs. 
     In accordance with one aspect of the invention, at least one of the liquid resin and the liquid hardener is provided to have a fluorescent material therein. An example would be any of the T-700 Series, T-1020 Series, T-100-OS Series aqueous or oil soluble fluorescent tracers available from Shannon Luminous Materials, Inc., of Santa Ana, Calif. Such materials are understood to have been utilized in the prior art as additives to liquid coatings to assure complete coating of a substrate covered by the coating. Preferably, the other of the liquid resin or liquid hardener is provided to have no fluorescent material therein, or less preferably have some other distinguishing fluorescent material therein. 
     The liquid resin and the liquid hardener are then combined into an epoxy mixture, and ideally stirred to achieve desired complete mixing. Thereafter or during mixing, radiation of suitable wave length is impinged onto the epoxy mixture effective to cause the fluorescent material to fluoresce. From the fluorescing fluorescent material, degree of homogeneity in the epoxy mixture can be determined. Such determination could occur simply by the human eye, or by more automated spectrographic means. For example, where the fluorescing material was fluorescent in ultraviolet light, ultraviolet radiation could be impinged upon the mixture with the results being viewed by a human eye. If the mixture glowed uniformly throughout, complete mixing has occurred such that the mixture is substantially homogenous. If on the other hand the mixture has specs or streaks of fluorescence and lack of fluorescence or uniform fluorescence, such would evidence that complete mixing has not yet occurred. Such can also be used to determine if the hardener has even been added to the mixture. 
     In the preferred embodiment, the fluorescent material is preferably placed within the hardener, which is also the lower volume component of the mixture and also in this embodiment a component which is colorless in light within the visible spectrum or substantially clear. Also preferably, the liquid resin is provided to be substantially void of any fluorescent material. Ideally, the epoxy mixture has substantially the same color and light within the visible spectrum as would exist if the fluorescent material, when not fluorescing, were not present in the epoxy mixture. 
     Once desired homogeneity was achieved as evidenced by examination of the fluorescent material, the substrate with chip and battery would be encapsulated within the epoxy mixture. After such encapsulating, the epoxy mixture would then essentially cure into a solidified mass. 
     Although specifically motivated for epoxy fabrication methods, and for use of such methods in remote intelligent communication devices, the invention is believed to have applicability in other methods of processing liquid mixtures comprising at least two different liquids. For example, the invention is seen to have applicability for any two mixture combinations of two liquids whereby a fluorescent material is provided into at least one of the liquids prior to combination with a second liquid to form a mixture. Degree of homogeneity in the mixture can be determined qualitatively or quantitatively by causing the fluorescent material to fluoresce and analyzing its presence throughout the mixture. Preferably, where the volume of liquids within the mixture is different, the fluorescent material is provided in the lower volume component. 
     Liquid mixture systems involving three or more different liquids could of course also be utilized in combination with a fluorescent material in preferably only one of the liquids to determine a degree of homogeneity in a resultant mixture of such liquids. 
     In accordance with the above-described preferred embodiments, the fluorescent material ideally comprises an invisible component which is provided in at least one of the first and second liquids. Such component ideally remains invisible in a mixture of the liquids. After forming the mixture, the invisible component in the mixture is rendered visible, in the above example by impinging ultraviolet radiation, and the degree of homogeneity in the mixture is determined therefrom. After such determination, and if desired further mixing, the invisible component is returned to its invisible state, in the above example, by removing the impinging radiation source. Thus, resultant color in the finished and solidified product is not impacted by the component from which homogeneity is determined. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.