Abstract:
A radio frequency identification tag is provided. The radio frequency identification tag includes a base, an antenna formed on the base, an integrated circuit chip electrically connected to the antenna, and a bonding layer bonding the integrated circuit chip to the base. The bonding layer includes a conductive filler. The base is configured to bend away from a surface on which the integrated circuit chip is bonded.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-83758, filed on Mar. 30, 2009, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a radio frequency identification (RFID) tag and a method for manufacturing the RFID tag. 
       BACKGROUND 
       [0003]    In recent years, RFID tags configured to receive power supply and data from external devices, such as reader/writers, and to transmit data to the external devices by using electric waves in a non-contact manner have been available. 
         [0004]    A RFID tag includes a transmitting/receiving antenna and an integrated circuit (IC) chip disposed on a substrate composed of plastic, paper, or the like. The antenna and a capacitor inside the IC chip form a resonant circuit so that the RFID tag can communicate wirelessly with external devices through the antenna. 
         [0005]    The outline of a method for manufacturing a common RFID tag will now be described with reference to  FIGS. 11 to 16 .  FIGS. 11 to 16  are diagrams illustrating a typical method for manufacturing a common RFID tag. 
         [0006]    As illustrated in  FIG. 11 , first, a base  3 , on which an antenna  4  is disposed, is placed on a stage  2  functioning as a working table. An adhesive  7  is discharged from a nozzle  6  to cover an upper surface of the base  3  and regions near an opening  5  in the antenna  4 . The adhesive  7  covering the upper surface of the base  3  and the regions near the opening  5  in the antenna  4  will form a bonding layer that bonds the base  3  to an IC chip  10 . 
         [0007]    Next, as illustrated in  FIG. 12 , the IC chip  10  including a pair of electrodes  11  is placed above the base  3 . The upper surface (the upper surface in  FIG. 12 ) of the IC chip  10  is pressed downward and heated with a bonding device  12  to press-bond the IC chip  10  onto the base  3 . 
         [0008]    During this operation, as illustrated in  FIG. 13 , the inner portion of the antenna  4  on the base  3  may be fixed while being bent downward due to the heat and pressure applied by the bonding device  12 . As illustrated in  FIG. 14 , the IC chip  10  is bonded to the base  3  with a bonding layer composed of an adhesive thermally cured by application of heat and pressure by the bonding device  12 . 
         [0009]    Next, as illustrated in  FIG. 15 , an elastomer member  13  and a reinforcing plate  14  are disposed in that order above the base  3  bonded with the IC chip  10 , and another elastomer member  13  and another reinforcing plate  14  are disposed in that order under the base  3  bonded with the IC chip  10 . While the base  3  is being surrounded by packages  2 ′, heat and pressure are applied to the packages  2 ′ by the bonding device  12  ( FIG. 12 ) to enclose the base  3 , the IC chip  10 , and the reinforcing plates  14  inside the packages  2 ′. 
         [0010]    As a result of performing the steps illustrated in  FIGS. 11 to 15  described above, a RFID tag  1 ′ including the base  3  provided with the antenna  4 , the IC chip  10  bonded to the base  3 , and the two reinforcing plates  14  respectively disposed above and under the base  3  can be produced, as illustrated in  FIG. 16 . 
         [0011]    RFID tags may be employed in a distribution field to manage linen goods such as uniforms, for example. In order to use RFID tags for linen management, a quantity of RFID tags equal to the number of uniforms are necessary, and thus the unit price of the RFID tag should be low. 
         [0012]    However, RFID tags for apparel or linen goods cannot withstand external force applied during washing or the like unless the nearby regions of IC chips are protected with reinforcing plates. As illustrated in  FIG. 16 , a pair of reinforcing plates  14  must be formed inside the RFID tag  1 ′ (above the IC chip  10  and below the base  3 ), which increases the cost because more components are required. 
         [0013]    Japanese Laid-open Patent Publication No. 6-204654 (“JP 6-204654”) discloses a printed board, which is one structure of a RFID tag of this type that has been used before. According to the disclosure of JP 6-204654, thermal press-bonding is performed while having a lead tip of a tape carrier package mounted on a conductive pad on the printed board, and a reinforcing plate is bonded and fixed on the rear surface of the printed board at a position corresponding to the conductive pad. 
         [0014]    However, according to the RFID tag  1 ′ in related art, the antenna  4  is pressed downward by the electrodes  11  of the IC chip  10  due to the heat and pressure applied by the bonding device  12 . Since the antenna  4  bends inward as a result of the applied heat and pressure by the bonding device  12 , a conductive filler  8  may become trapped (i.e., “a” in  FIG. 13 ) or the antenna  4  may contact an edge of the IC chip  10  (i.e., “b” in  FIG. 13 ), resulting in a short-circuit between the base  3  and the IC chip  10 . 
         [0015]    Furthermore, when press-bonding is carried out with the bonding device  12 , a filler attack (i.e., “c” in  FIG. 13 ), i.e., a phenomenon in which the conductive filler  8  containing a nickel material is brought into contact with an electric pattern formed on the rear surface of the IC chip  10 , may occur. This causes problems such as scraping of an electric pattern of the IC chip  10 . 
         [0016]    As further described in JP 6-204654, deflection of the base  3  may cause the antenna  4  to contact the IC chip  10 , which may result in a short-circuit between the base  3  and the IC chip  10 . 
       SUMMARY 
       [0017]    According to an embodiment of the invention, there is provided a radio frequency identification tag. The radio frequency identification tag includes a base, an antenna formed on the base, an integrated circuit chip electrically connected to the antenna, and a bonding layer bonding the integrated circuit chip to the base. The bonding layer includes a conductive filler. The base is configured to bend away from a surface on which the integrated circuit chip is bonded. 
         [0018]    The object and advantages of the invention will be realized and achieved by means of the elements and combinations particularly pointed out in the claims. 
         [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]    The above and other features and advantages of the invention will become apparent from the following description of the embodiments in conjunction with the accompanying drawings, wherein: 
           [0021]      FIG. 1  is a vertical cross-sectional view illustrating a RFID tag in accordance with an embodiment of the invention. 
           [0022]      FIG. 2  is a plan view illustrating a surface of an IC chip in accordance with an embodiment of the invention. 
           [0023]      FIG. 3  is a plan view illustrating a rear surface of the IC chip in accordance with an embodiment of the invention. 
           [0024]      FIG. 4  is a flowchart of a method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0025]      FIG. 5  is a diagram illustrating the method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0026]      FIG. 6  is a diagram illustrating the method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0027]      FIG. 7  is a diagram illustrating the method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0028]      FIG. 8  is a diagram illustrating the method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0029]      FIG. 9  is a diagram illustrating the method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0030]      FIG. 10  is a diagram illustrating a method for manufacturing a RFID tag in accordance with an embodiment of the invention. 
           [0031]      FIG. 11  is a diagram illustrating a method for manufacturing a RFID tag. 
           [0032]      FIG. 12  is a diagram illustrating the method for manufacturing a RFID tag. 
           [0033]      FIG. 13  is a diagram illustrating the method for manufacturing a RFID tag. 
           [0034]      FIG. 14  is a diagram illustrating the method for manufacturing a RFID tag. 
           [0035]      FIG. 15  is a diagram illustrating the method for manufacturing a RFID tag. 
           [0036]      FIG. 16  is a diagram illustrating the method for manufacturing a RFID tag. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]    Embodiments of a RFID tag and a method for manufacturing the RFID tag to be disclosed by this application will now be described with reference to the attached drawings. 
         [0038]    First, the overall configuration of a RFID tag  1  of an embodiment of the invention is described.  FIG. 1  is a vertical cross-sectional view of a RFID tag of an embodiment of the invention.  FIG. 2  is a plan view illustrating a mounting surface of an IC chip in accordance with an embodiment of the invention.  FIG. 3  is a plan view illustrating the rear surface of the IC chip in accordance with an embodiment of the invention. 
         [0039]    As illustrated in  FIG. 1 , the RFID tag  1  of can include a package main body  20  including a rectangular shape and a base  33  configured inside the package main body  20 . The base  33  can include a surface on which an antenna  35  is disposed. 
         [0040]    The RFID tag  1  can also include an IC chip  38  disposed on an upper surface of the base  33  and a reinforcing plate  50  disposed above the IC chip  38 . The reinforcing plate  50  can be a glass epoxy plate in which a glass material and an epoxy material are combined. As described below, the reinforcing plate  50  can be configured to reinforce the upper part of the RFID tag  1 . 
         [0041]    As illustrated in  FIG. 1 , the base  33  including the antenna  35  can include a curved shape allowing it to bend away (downward in  FIG. 1 ) from the surface on which the IC chip  38  above the base  33  can be bonded. 
         [0042]    When the IC chip  38  is bonded onto the base  33  with an adhesive serving as a thermosetting material, a bonding layer  33   b  can be formed. A space (curved part) below the lower surface of the base  33  can also be filled with the adhesive. In particular, the adhesive filling a space  33   a  below the lower surface (curved part) of the base  33  can be cured by applying heat and pressure so that the lower part of the base  33  can be reinforced by the cured adhesive filling the space  33   a.    
         [0043]    In other words, according to the RFID tag  1  illustrated in  FIG. 1  to  FIG. 3 , the upper part of the RFID tag  1  can be configured to retain strength by the reinforcing plate  50  and the lower part of the RFID tag  1  by being reinforced by curing the adhesive filling the space  33   a  below the lower surface of the base  33  under application of heat and pressure so as to retain the strength of the RFID tag  1 . 
         [0044]    For the base  33 , a substrate, such as a polyethylene terephthalate (PET) film or a polyethylene naphthalate (PEN) film, that has high strength, high heat resistance, and high hydrolysis resistance can be used. 
         [0045]    The antenna  35  can be formed of a conductor foil and can be mounted on a surface portion of the base  33  by a flip-chip technique. A pair of protrusions  37  can be disposed on the rear surface of the base  33 . 
         [0046]    Thus, the pair of protrusions  37  on the lower surface of the main body of the base  33  can allow the base  33  to bend away from (downward from in  FIG. 1 ) the surface on which the IC chip  38  disposed above the base  33  is bonded. The space  33   a  below the lower surface of the base  33  created thereby can be filled with the adhesive which is cured to function as a reinforcing plate. 
         [0047]    As illustrated in  FIG. 3 , the protrusions  37  attached to the base  33  can be positioned within the IC chip-mounted area. The protrusions  37  can be symmetric with respect to a line connecting the mount center point of the mounted IC chip  38  and the position that divides a chip side into equal lengths. 
         [0048]    In other words, the pair of protrusions  37  can be provided so that a portion of the base  33  that extends over the size of the IC chip  38  bends away from the chip-mounting surface when the IC chip  38  is mounted. According to this structure of this embodiment, the short-circuit between the IC chip  38  and the base  33  can be prevented. 
         [0049]    A through hole  34  can be formed at a center portion where the IC chip  38  is mounted on the base  33 . An opening can be formed at the center of the antenna  35 . The portion below the rear surface of the base  33  can be filled with an adhesive injected through the through hole  34  and cured by heat (thermally cured adhesive). 
         [0050]    The IC chip  38  can include a communication circuit, a memory, and a controller circuit configured to record and read data without a manufacturing contact. The IC chip  38  can also include a pair of electrodes  39  configured to provide electrical connections to the antenna  35 , and dummy posts  39   a , as illustrated in  FIG. 2 , that are configured to adjust the height of the IC chip  38 . 
         [0051]    As described above, according to the RFID tag  1  illustrated in  FIG. 1  to  FIG. 3 , since the base  33  of the RFID tag  1  can be configured to bend away from the surface on which the IC chip  38  is bonded, the contact between the base  33  and the IC chip  38  can be avoided, and the short-circuit between the IC chip  38  and the base  33  can be prevented. 
         [0052]    Since the base  33  of the RFID tag  1  can be configured to bend away from the surface on which the IC chip  38  is bonded, failures, such as trapping of the conductive filler  8  (“a” in  FIG. 13 ) and scraping of the electric pattern of the IC chip  38  by a filler attack, i.e., contact with the conductive filler  8 , can be avoided. 
         [0053]    Since the RFID tag  1  can include the bonding layer  33   b  that bonds the IC chip  38  to the base  33  and the reinforcing layer that can be made of a thermosetting material (adhesive), and furthermore can function as a reinforcing plate disposed below the lower surface, i.e., the curved surface, of the base  33 , the number of reinforcing plates  50  required can be reduced and the cost of the RFID tag  1  can be lowered. 
         [0054]    A method for manufacturing the RFID tag  1  will now be described with reference to  FIGS. 4 to 9 .  FIG. 4  is a flowchart illustrating a process for manufacturing the RFID tag  1  in accordance with an embodiment of the invention. 
         [0055]      FIGS. 5 to 9  are diagrams illustrating a process for manufacturing the RFID tag  1  in accordance with an embodiment of the invention. In the description below describing the method for manufacturing the RFID tag  1 , a production system, such as bonding equipment, can be used. 
         [0056]    As illustrated in the flowchart of  FIG. 4 , according to the method for manufacturing the RFID tag  1  in accordance with an embodiment of the invention, a protrusion forming step, a through hole forming step, a substrate forming step, an adhesive filling step, a first heating and pressurizing step, and a second heating and pressurizing step are performed sequentially in that order by the production system. 
         [0057]    First, a protrusion-forming step (step S 1 ) of forming the protrusions  37  on the lower surface (rear surface) of the base  33  ( FIG. 5 ) can be conducted. In this protrusion-forming step, the pair of protrusions  37  can be formed on the rear surface of the base  33  by bonding or etching. Forming the protrusions  37  on the rear surface of the base  33  allows the base  33  to bend in a particular direction (downward in  FIG. 1 ). 
         [0058]    Next, a through hole forming step (step S 2 ) for forming the through hole  34  ( FIG. 5 ) in the rear surface of the base  33  can be performed. In this through hole forming step, the through hole  34  that allows an adhesive to pass through can be formed so that the adhesive injected from the nozzle  6  can fill the portion below the rear surface of the base  33 . Thus, because of the through hole  34  in the base  33 , the portion below the back surface of the substrate can be filled with the adhesive. In particular, the through hole  34  can be formed by punching to allow the adhesive to enter the space  33   a  below the rear surface of the base  33  during mounting of the IC chip  38  on the base  33 . 
         [0059]    Next, a substrate forming step (step S 3 ) of forming a base that functions as a substrate of the RFID tag  1  can be performed. In this substrate forming step, a particular shape can be imparted to the base  33  to be placed inside the RFID tag  1  (see the lower part of the  FIG. 1 ). 
         [0060]    To be more specific, according to the production system for the RFID tag  1  in accordance with an embodiment of the invention, as illustrated in  FIG. 5 , a stage  30  including a pair of through holes  31  formed in the respective end portions (left and right portions in  FIG. 1 ) of the stage main body can be prepared. The base  33  including the antenna  35  can be placed on the upper surface of the stage  30 . The parts of the stage  30  that make contact with the adhesive can be coated with Teflon (trade name) or the like to prevent adhesion of the adhesive. 
         [0061]    Then, as illustrated in  FIG. 5 , the entire base  33  can be suctioned through the through holes  31  by using a suction device (not shown) from the rear surface of the stage  30 . Since the pair of protrusions  37  can be disposed on the rear surface of the base  33 , the base  33  can be deformed downward by the suction using the suction device. Since the base  33  can be configured to bend away from the surface on which the IC chip  38  is to be bonded, a short-circuit between the IC chip  38  and the base  33  can be prevented. 
         [0062]    Next, the adhesive-filling step (step S 4 ) for filling the portion below the base  33  with the adhesive can be performed. This adhesive-filling step is a step of forming a reinforcing layer under the base  33  with the adhesive. 
         [0063]    To be more specific, as illustrated in  FIG. 6 , the adhesive, i.e., a thermosetting material, can be injected from the nozzle  6  through the opening  36  in the antenna  35  and the through hole  34  in the base  33 . The adhesive injected through the opening  36  in the antenna  35  can form the bonding layer  33   b  that bonds the rear surface of the IC chip  38  onto the upper surface of the base  33 . The adhesive injected from the nozzle  6  through the through hole  34  in the base  33  can fill the space  33   a  below the lower surface of the base  33 . 
         [0064]    Next, a first heating and pressurizing step (step S 5 ) of heating and pressurizing the base  33  can be performed. The first heating and pressurizing step can be a step of heating and pressurizing the IC chip  38  disposed above the base  33  by using a bonding device  40 . 
         [0065]    In particular, as illustrated in  FIG. 7 , the IC chip  38  can be placed above the base  33  and the upper surface (upper surface in  FIG. 7 ) of the IC chip  38  can be pressurized and heated with the bonding device  40  so that the IC chip  38  is press-bonded onto the base  33 . 
         [0066]    During this operation, as illustrated in  FIG. 8 , the base  33  can be bonded to the IC chip  38  with the bonding layer  33   b  formed of the adhesive thermally cured by the heat and pressure applied from the bonding device  40 . The adhesive filling the space  33   a  below the lower surface of the base  33  can be thermally cured and thereby can form a reinforcing layer  33   c.    
         [0067]    Next, a second heating and pressurizing step (step S 6 ) for disposing an elastomer member  41  and the reinforcing plate  50  above the base  33  can be performed. This second heating and pressurizing step can be a step of heating and pressurizing the elastomer member  41  and the reinforcing plate  50  disposed above the base  33 . 
         [0068]    In particular, as illustrated in  FIG. 9 , the elastomer member  41  and then the reinforcing plate  50  can be placed above the base  33  bonded with the IC chip  38 . Then while surrounding the base  33  with a package (not shown in the drawing), heat and pressure can be applied by the bonding device  40  from above and below the base  33  so that the base  33 , the IC chip  38 , and the reinforcing plate  50  are press-bonded inside the package. 
         [0069]    By performing the steps illustrated in  FIGS. 5 to 9 , the RFID tag  1  can be made which can include the base  33  including the antenna  35 , the IC chip  38  bonded to the base  33 , the reinforcing plate  50  arranged above the base  33 , and the reinforcing layer disposed below the curved surface of the base  33 , the reinforcing layer being formed of a thermosetting material (adhesive) and serving as a reinforcing plate. 
         [0070]    A method for manufacturing the RFID tag  1  in accordance with an embodiment of the invention will now be described.  FIG. 10  is a diagram illustrating a method for manufacturing the RFID tag  1  in accordance with an embodiment of the invention. In the description below, the detailed description of the steps identical to the steps described in a previous embodiment is omitted. 
         [0071]    According to the method for manufacturing the RFID tag in accordance with an embodiment of the invention, the base can be produced by using a stage  30   a  including a pair of protrusions  32  on which the base can be placed. That is, as illustrated in  FIG. 10 , the stage  30   a  that can include the pair of protrusions  32  on which the base  33  can be placed and a pair of through holes  31  respectively formed in the two end portions (left and right portions in  FIG. 10 ) of the stage main body can be used. 
         [0072]    According to the method for manufacturing the RFID tag in accordance with an embodiment of the invention, the pair of protrusions  32  fixed on the stage  30   a  can allow the base  33  to bend away from the IC chip  38  to be formed as in the method described above for another embodiment of the invention. In this manner, a short-circuit between the IC chip  38  and the base  33  can be prevented. The RFID tag can be reinforced by the thermosetting material (adhesive) filling the portion below the base, and thus the cost for an additional reinforcing plate can be cut. Since the step of forming the pair of protrusions  37  on the lower surface of the base  33  performed in a previously described embodiment can be omitted, the production steps can be streamlined. 
         [0073]    For example, although the base  33  including the antenna  35  can be formed by manufacturing it to bend away from the surface on which the IC chip  38  is bonded, as previously described, a base that has been imparted a curved shape in advance so as to allow the portion below the base to be filled with the adhesive may be used. 
         [0074]    All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventors to further the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the invention have been described in detail, it will be understood by those of ordinary skill in the relevant art that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention as set forth in the claims.