Abstract:
Methods, systems, and apparatuses for antenna designs for radio frequency identification (RFID) tags are described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. application Ser. No. 10/866,151, filed Jun. 14, 2004, now U.S. Pat. No. 7,404,199, which claims the benefit of U.S. Provisional Application No. 60/477,735, filed Jun. 12, 2003, both of which are herein incorporated by reference in their entireties. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to antenna designs for radio frequency identification (RFID) tags. 
   2. Related Art 
   Pick and place techniques are often used to assemble electronic devices. Such techniques involve a manipulator, such as a robot arm, to remove integrated circuit (IC) dies from a wafer and place them into a die carrier. The dies are subsequently mounted onto a substrate with other electronic components, such as antennas, capacitors, resistors, and inductors to form an electronic device. 
   Pick and place techniques involve complex robotic components and control systems that handle only one die at a time. This has a drawback of limiting throughput volume. Furthermore, pick and place techniques have limited placement accuracy, and have a minimum die size requirement 
   One type of electronic device that may be assembled using pick and place techniques is an RFID “tag.” An RFID tag may be affixed to an item whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored by devices known as “readers.” 
   As market demand increases for products such as RFID tags, and as die sizes shrink, high assembly throughput rates for very small die, and low production costs are crucial in providing commercially-viable products. Accordingly, what is needed is an electronic device, such as an RFID tag, that overcomes these limitations. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to methods, systems, and apparatuses for producing one or more electronic devices, such as RFID tags, that each include a die having one or more electrically conductive contact pads that provide electrical connections to related electronics on a substrate. 
   According to the present invention, electronic devices are formed at much greater rates than conventionally possible. In one aspect, large quantities of dies can be transferred directly from a wafer to corresponding substrates of a web of substrates. In another aspect, large quantities of dies can be transferred from a support surface to corresponding substrates of a web of substrates. In another aspect, large quantities of dies can be transferred from a wafer or support surface to an intermediate surface, such as a die plate. The die plate may have cells formed in a surface thereof in which the dies reside. Otherwise, the dies can reside on a surface of the die plate. The dies of the die plate can then be transferred to corresponding substrates of a web of substrates. 
   In an aspect, a punch plate, punch roller or cylinder, or expandable material can be used to transfer dies from the die plate to substrates. 
   Large quantities of dies can be transferred. For example, 10s, 100s, 1000s, or more dies, or even all dies of a wafer, support surface, or die plate, can be simultaneously transferred to corresponding substrates of a web. 
   In one aspect, dies may be transferred between surfaces in a “pads up” orientation. When dies are transferred to a substrate in a “pads up” orientation, related electronics can be printed or otherwise formed to couple contact pads of the die to related electronics of the tag substrate. 
   In an alternative aspect, the dies may be transferred between surfaces in a “pads down” orientation. When dies are transferred to a substrate in a “pads down” orientation, related electronics can be pre-printed or otherwise pre-deposited on the tag substrate. 
   In an aspect of the present invention, a radio frequency identification (RFID) tag antenna is formed. The antenna includes a first, a second, a third, and a fourth arm. Each of the arms is affixed to a substrate and extends radially from a central location to form a X-shaped structure. The antenna further includes a fifth, a sixth, a seventh, and an eighth arm. The fifth and sixth arms oppositely extend from the third arm. The seventh and eighth arms oppositely extend from the fourth arm. In this way, two smaller X-shaped structures are formed on two legs of the larger X-shaped structure. 
   Any number of one or more such antennas may be formed in an array in a web of tags. 
   These and other advantages and features will become readily apparent in view of the following detailed description of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
     The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
       FIG. 1  shows a block diagram of an exemplary RFID tag, according to an embodiment of the present invention. 
       FIGS. 2A and 2B  show plan and side views of an exemplary die, respectively. 
       FIGS. 2C and 2D  show portions of a substrate with a die attached thereto, according to example embodiments of the present invention. 
       FIGS. 3-5  illustrate antenna and web configurations according to exemplary embodiments of the present invention. 
   

   The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides improved processes and systems for assembling electronic devices, including RFID tags. The present invention provides improvements over current processes. Conventional techniques include vision-based systems that pick and place dies one at a time onto substrates. The present invention can transfer multiple dies simultaneously. Vision-based systems are limited as far as the size of dies that may be handled, such as being limited to dies larger than 600 microns square. The present invention is applicable to dies 100 microns square and even smaller. Furthermore, yield is poor in conventional systems, where two or more dies may be accidentally picked up at a time, causing losses of additional dies. The present invention allows for improved yield values. Badmash 
   The present invention provides an advantage of simplicity. Conventional die transfer tape mechanisms may be used by the present invention. Furthermore, much higher fabrication rates are possible. Current techniques process 5-8 thousand units per hour. The present invention can provide improvements in these rates by a factor of N. For example, embodiments of the present invention can process dies 5 times as fast as conventional techniques, at 100 times as fast as conventional techniques, and at even faster rates. Furthermore, because the present invention allows for flip-chip die attachment techniques, wire bonds are not necessary. 
   Elements of the embodiments described herein may be combined in any manner. Example RFID tags are described in the section below. Assembly embodiments for RFID tags are described in the next section. Example applications for tags and tag assembly techniques are then described, followed by a description of example substrate webs and antenna layouts. 
   The present invention is directed to techniques for producing electronic devices, such as RFID tags. For illustrative purposes, the description herein primarily relates to the production of RFID tags. However, the description is also adaptable to the production of further electronic device types, as would be understood by persons skilled in the relevant art(s) from the teachings herein. 
     FIG. 1  shows a block diagram of an exemplary RFID tag  100 , according to an embodiment of the present invention. As shown in  FIG. 1 , RFID tag  100  includes a die  104  and related electronics  106  located on a tag substrate  116 . Related electronics  106  includes an antenna  114  in the present example. As is further described elsewhere herein, die  104  may be mounted in either a pads up or pads down orientation. 
   RFID tag  100  may be located in an area having a large number, population, or pool of RFID tags present. RFID tag  100  receives interrogation signals transmitted by one or more tag readers. According to interrogation protocols, RFID tag  100  responds to these signals. Each response includes information that identifies the corresponding RFID tag  100  of the potential pool of RFID tags present. Upon reception of a response, the tag reader determines the identity of the responding tag, thereby ascertaining the existence of the tag within a coverage area defined by the tag reader. 
   RFID tag  100  may be used in various applications, such as inventory control, airport baggage monitoring, as well as security and surveillance applications. Thus, RFID tag  100  can be affixed to items such as airline baggage, retail inventory, warehouse inventory, automobiles, compact discs (CDs), digital video discs (DVDs), video tapes, and other objects. RFID tag  100  enables location monitoring and real time tracking of such items. 
   In the present embodiment, die  104  is an integrated circuit that performs RFID operations, such as communicating with one or more tag readers (not shown) according to various interrogation protocols. Exemplary interrogation protocols are described in U.S. Pat. No. 6,002,344 issued Dec. 14, 1999 to Bandy et al. entitled System and Method for Electronic Inventory, and U.S. patent application Ser. No. 10/072,885, filed on Feb. 12, 2002, both of which are incorporated by reference herein in its entirety. Die  104  includes a plurality of contact pads that each provide an electrical connection with related electronics  106 . 
   Related electronics  106  are connected to die  104  through a plurality of contact pads of IC die  104 . In embodiments, related electronics  106  provide one or more capabilities, including RF reception and transmission capabilities, sensor functionality, power reception and storage functionality, as well as additional capabilities. The components of related electronics  106  can be printed onto a tag substrate  116  with materials, such as conductive inks. Examples of conductive inks include silver conductors 5000, 5021, and 5025, produced by DuPont Electronic Materials of Research Triangle Park, N.C. Other materials or means suitable for printing related electronics  106  onto tag substrate  116  include polymeric dielectric composition 5018 and carbon-based PTC resistor paste 7282, which are also produced by DuPont Electronic Materials of Research Triangle Park, N.C. Other materials or means that may be used to deposit the component material onto the substrate would be apparent to persons skilled in the relevant art(s) from the teachings herein. 
   As shown in  FIG. 1 , tag substrate  116  has a first surface that accommodates die  104 , related electronics  106 , as well as further components of tag  100 . Tag substrate  116  also has a second surface that is opposite the first surface. An adhesive material or backing can be included on the second surface. When present, the adhesive backing enables tag  100  to be attached to objects, such as books and consumer products. Tag substrate  116  is made from a material, such as polyester, paper, plastic, fabrics such as cloth, and/or other materials such as commercially available Tyvec®. 
   In some implementations of tags  100 , tag substrate  116  can include an indentation, “cavity,” or “cell” (not shown in  FIG. 1 ) that accommodates die  104 . An example of such an implementation is included in a “pads up” orientation of die  104 . 
     FIGS. 2A and 2B  show plan and side views of an example die  104 . Die  104  includes four contact pads  204   a - d  that provide electrical connections between related electronics  106  and internal circuitry of die  104 . Note that although four contact pads  204   a - d  are shown, any number of contact pads may be used, depending on a particular application. Contact pads  204  are made of an electrically conductive material during fabrication of the die. Contact pads  204  can be further built up if required by the assembly process, by the deposition of additional and/or other materials, such as gold and solder flux. Such post processing, or “bumping,” will be known to persons skilled in the relevant art(s). 
     FIG. 2C  shows a portion of a substrate  116  with die  104  attached thereto, according to an example embodiment of the present invention. As shown in  FIG. 2C , contact pads  204   a - d  of die  104  are coupled to respective contact areas  210   a - d  of substrate  116 . Contact areas  210   a - d  provide electrical connections to related electronics  106 . The arrangement of contact pads  204   a - d  in a rectangular (e.g., square) shape allows for flexibility in attachment of die  104  to substrate  116 , and good mechanical adherement. This arrangement allows for a range of tolerance for imperfect placement of IC die  104  on substrate  116 , while still achieving acceptable electrical coupling between contact pads  204   a - d  and contact areas  210   a - d . For example,  FIG. 2D  shows an imperfect placement of IC die  104  on substrate  116 . However, even though IC die  104  has been improperly placed, acceptable electrical coupling is achieved between contact pads  204   a - d  and contact areas  210   a - d.    
   Note that although  FIGS. 2A-2D  show the layout of four contact pads  204   a - d  collectively forming a rectangular shape, greater or lesser numbers of contact pads  204  may be used. Furthermore, contact pads  204   a - d  may be laid out in other shapes in embodiments of the present invention. 
     FIG. 3  illustrates an antenna array or web  300  that includes a four by five array of antennas  305   a - 305   t , although other sized arrays are also possible. Web  300  may be a complete web sheet, or may be a portion of a larger web. Antennas  305  can be made in any size. For example, a die pitch or spacing of antennas  305  can be 100 mm, or other amounts. 
   As shown in  FIG. 4 , antenna  305  is disposed on a rectangular substrate portion. Antenna  305  has first and second bar-shaped patterns  402   a  and  402   b . The first and second bar-shaped patterns  402   a - b  intersect orthogonally to form a first X-shaped structure for antenna  305 . Antenna  305  includes a third bar-shaped pattern  418 . Third bar-shaped pattern  418  intersects first bar-shaped pattern  402   a  to form a second X-shaped pattern  408   a . A location where pattern  418  intersects pattern  402   a  is at less than half the distance from an end  412   c  of pattern  402   a  to a central location in a central portion  425  of the first X-shaped structure. Antenna  305  includes a fourth bar-shaped pattern  420 . Fourth bar-shaped pattern  420  intersects second bar-shaped pattern  402   b  to form a third X-shaped pattern  408   b . A location where pattern  420  intersects pattern  402   b  is at less than half the distance from an end  412   d  of pattern  402   b  to the central location of the first X-shaped structure. 
   From another perspective, antenna  305  can be viewed as having four arms  410   a - d  radially extending from a center portion  425  of antenna  305  to form the first X-shaped structure for antenna  305 . Two of the arms that are adjacent to each other each further includes two smaller arms extending therefrom. Specifically, in the example of  FIG. 4 , arm  410   c  includes an arm  404   a  extending from a first side  406   a , and an arm  404   b  extending from a second opposing side  406   b  to form the third X-shaped pattern  408   b . Arms  404   a  and  404   b  form third bar-shaped pattern  418 . Similarly, arm  410   d  includes an arm  404   c  extending from a first side  406   c  and an arm  404   d  extending from a second opposing side  406   d  to form the second X-shaped pattern  408   a . Arms  404   c  and  404   d  form fourth bar-shaped pattern  420 . In this way, two smaller X-shaped structures  408   a - b  are formed in the third and fourth arms  410   c - d  of the first X-shaped structure formed by arms  410   a - b.    
   As shown in  FIG. 4 , arms  410   c  and  410   d  both include a pair of parallel slots  430   a - b  and  432   a - b  extending along or portion of their respective lengths. In an embodiment, the pair of slots  430   a - b  begin from near a center location of the first X-shaped structure, where arms  410   a - d  intersect, and stop approximately at the start of a junction where arms  404   a - b  extend from arm  410   c . Similarly, the pair of slots  432   a - b  start from near a center location of the first X-shaped structure, where arms  410   a - d  intersect, and end approximately at the start of a junction where arms  404   c - d  extend from arm  410   d . Any number and length of slots may be present in one or more arms of antenna  305  as desired for a particular application. 
   As shown in  FIG. 4 , arms  410   a - d  have ends  412   a - d , respectively. Ends  412   a - d  are shown as squared in  FIG. 4 , although they can have other shapes. Arms  404   a - d  have ends  416   a - d , respectively. Ends  416   a - d  are shown as triangular shaped or pointed, in  FIG. 4 , but can have other shapes. 
   Arms  410   a - d  and  404   a - d  are elongated patterns made from an electrically conductive material suitable for use as an antenna material, such as conductive ink, or any other suitable material disclosed elsewhere herein or otherwise known to persons skilled in the relevant art(s). 
     FIG. 5  illustrates a detailed view of center portion  425  shown in  FIG. 4 . Center portion  425  of antenna  305  has a die mounting position  502 , for a die having four contact pads. When a die is present, each contact pad of the die is coupled to a respective pad coupled to one of arms  410   a - d  of antenna  305 . Die mounting position  502  includes a first pad  504   a , a second pad  504   b , a third pad  504   c , and a fourth pad  504   d . As shown in  FIG. 5 , first pad  504   a  is located most closely to and is coupled to arm  410   a . Second pad  504   b  is located most closely to and is coupled to arm  410   b . A slot  506  separates first pad  504   a  and second pad  504   b . Third pad  504   c  is coupled to a first end of an elongated pattern  506  of arm  410   c  located between slots  430   a  and  430   b  of arm  410   c . Similarly, fourth pad  504   d  is coupled to a first end of an elongated pattern  508  of arm  410   d  located between slots  432   a  and  432   b  of arm  410   c . A slot  508  is open between slot  430   a  and slot  432   a , and separates first pad  504   a  from fourth pad  504   d , and separates second pad  504   b  from third pad  504   c . A slot  510  is open between a central location of slot  508  and an intersection of slots  430   b  and  432   b.    
   As shown in  FIG. 5 , one or more of pads  504   a - d  may each have one or more openings. The openings allow UV light to pass through the respective pad(s) to cure an adhesive material that is used to attached a die to pads  504   a - d.    
   CONCLUSION 
   While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.