Abstract:
The present invention provides an RFID (Radio_Frequency_IDentification) tag which exchanges information with external equipment on a non-contact basis and which can both reduce the bending stress and improve reliability under temperature changes. An RFID has a base; an antenna pattern which, being installed on the base, forms a communications antenna; a circuit chip which, being electrically connected to the antenna pattern and fixed to the base, conducts wireless communications via the antenna; and a first reinforcement body which covers the circuit chip, being fixed to the base at a location away from the circuit chip without being fixed to the circuit chip.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an RFID (Radio_Frequency_IDentification) tag which exchanges information with external equipment on a non-contact basis as well as to its manufacturing method. Incidentally, the RFID tag referred to herein is also known as an “RFID tag inlay” among those skilled in the art, meaning a component laid into the RFID tag. Also, the RFID tag is sometimes called a “wireless IC tag.” Besides, the RFID tags include a noncontact IC card.  
         [0003]     2. Description of the Related Art  
         [0004]     Recently, various types of RFID tag have been proposed to exchange information with external equipment typified by reader-writers on a non-contact basis by radio. A configuration in which an antenna pattern for wireless communications and an IC chip are mounted on a base sheet made of plastics or paper has been proposed as a type of RFID tag. One possible application for RFID tags of this type is to affix them to goods and identify the goods by exchanging information about the goods with external equipment.  
         [0005]     The RFID tag has a wide range of possible applications including the one described above. For example, when affixing the RFID tag to easily deformable goods such as clothing, bending stress is exerted on the IC chip, which is hard to bend whereas the base sheet is flexible. Breakage of the IC chip, separation of the IC chip, and the like which can result from the bending stress poses a major problem and various attempts are made to reduce the bending stress acting on the IC chip.  
         [0006]      FIG. 1  is a side view of a conventional RFID tag. However, the side view here shows internal structure seen through a flank of the RFID tag. Hereinafter, all side views are of the same nature.  
         [0007]     The RFID tag  1  shown in  FIG. 1  consists of an antenna  12  mounted on a sheet-type base  13  made of PET film, polyimide film, or the like, an IC chip  11  connected to the antenna  12  via bumps (metal protrusions)  14 , an adhesive which bonds the IC chip  11  to the base  13 , and a reinforcement body  16  which buries the entire IC chip  11  and part of the antenna  12 .  
         [0008]     The reinforcement body  16  spreads out bending stress over where the reinforcement body  16  exists, and thereby helps reduce the bending stress acting on the IC chip  11 .  
         [0009]     To further reduce bending stress, it has also been proposed to install a reinforcement plate stronger than the reinforcement body  16  on or in the reinforcement body  16  or on the opposite side of the base  13  from the reinforcement body  16  (see, for example, Japanese Patent Laid-Open Nos. 2001-319211 (p. 6 and  FIG. 1 ), 2003-288576 (p. 6 and  FIG. 2 ), 2005-4429 (p. 10 and  FIG. 1 ), and 2005-4430 (p. 10 and  FIG. 1 )).  
         [0010]     If the IC chip is protected firmly with a reinforcement body or reinforcement plate as is the case with the conventional techniques, although bending stress is reduced, temperature changes in the operating environment of the RFID tag can cause stress on the IC chip because of difference in thermal expansion (or contraction) between the IC chip and the hard reinforcement body or reinforcement plate. This can result in breakage or separation of the IC chip, presenting a problem of low reliability under temperature changes.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention has been made in view of the above circumstances and provides an RFID tag which can both reduce the bending stress and improve reliability under temperature changes.  
         [0012]     The present invention provides an RFID tag having:  
         [0013]     a base;  
         [0014]     an antenna pattern which, being installed on the base, forms a communications antenna;  
         [0015]     a circuit chip which, being electrically connected to the antenna pattern and fixed to the base, conducts wireless communications via the antenna; and  
         [0016]     a first reinforcement body which covers the circuit chip, being fixed to the base at a location away from the circuit chip without being fixed to the circuit chip.  
         [0017]     With the RFID tag according to the present invention, since the circuit chip and first reinforcement body are not fixed to each other and fixed at locations apart from each other even, in the case of thermal expansion (or contraction) resulting from temperature changes, any difference in thermal expansion between the circuit chip and first reinforcement body is absorbed by that part of the base which is located between the circuit chip and first reinforcement body, avoiding breakage of the circuit chip. Also, the bending stress acting on the circuit chip is reduced by the first reinforcement body. Thus, the RFID tag according to the present invention can both reduce the bending stress and improve reliability under temperature changes.  
         [0018]     Preferably, the RFID tag according to the present invention has a second reinforcement body located across the base from the first reinforcement body without being fixed to the base right behind the circuit chip.  
         [0019]     The second reinforcement body makes it possible to further reduce the bending stress acting on the circuit chip while maintaining the capability of the base to absorb the difference in thermal expansion.  
         [0020]     Preferably, in the RFID tag according to the present invention, the first reinforcement body is fixed to the base, but is not fixed to the base right behind the circuit chip where the first reinforcement body covers the base.  
         [0021]     The first reinforcement body covering the base also serves as the second reinforcement body in a way. Also, it improves the durability of the RFID tag by giving it watertightness.  
         [0022]     Preferably, the RFID tag according to the present invention has an auxiliary body which, being more flexible than the first reinforcement body, fills at least a boundary between the first reinforcement body and the base.  
         [0023]     The auxiliary body allows the RFID tag to spread out the bending stress acting on the boundary between the first reinforcement body and the base, thereby avoiding breaks in the antenna pattern.  
         [0024]     Preferably, the RFID tag according to the present invention has an auxiliary body which, being more flexible than the first reinforcement body, fills a boundary between the first reinforcement body and the base while covering the base.  
         [0025]     The auxiliary body which covers the base not only allows the RFID tag to avoid breaks in the antenna pattern as above, but also improves the durability of the RFID tag by giving it watertightness.  
         [0026]     The present invention provides an RFID tag manufacturing method having:  
         [0027]     a first adhesive-application step of applying an adhesive to a semi-finished product at a location away from a circuit chip, where the semi-finished product has a base, an antenna pattern which, being installed on the base, forms a communications antenna, and the circuit chip which, being electrically connected to the antenna pattern and fixed to the base, conducts wireless communications via the antenna; and  
         [0028]     a first fixing step of fixing a first reinforcement body which covers the circuit chip to the semi-finished product using the adhesive applied in the first adhesive-application step.  
         [0029]     The RFID tag manufacturing method according to the present invention makes it possible to manufacture the RFID tag according to the present invention easily.  
         [0030]     Preferably, the RFID tag manufacturing method according to the present invention has:  
         [0031]     a second adhesive-application step of applying an adhesive to the semi-finished product on the side, which is opposite the side where the first reinforcement body is fixed, by avoiding a location right behind the circuit chip; and  
         [0032]     a second fixing step of fixing a second reinforcement body located across the base from the first reinforcement body using the adhesive applied in the second adhesive-application step.  
         [0033]     This preferred RFID tag manufacturing method makes it easy to manufacture a preferable RFID tag equipped with a reinforcement body even on the reverse side of the base.  
         [0034]     As described above, the present invention provides an RFID tag which can both reduce the bending stress and improve reliability under temperature changes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIG. 1  is a side view of a conventional RFID tag;  
         [0036]      FIG. 2  is a side view of an RFID tag according to a first embodiment of the present invention;  
         [0037]      FIG. 3  is a side view of an RFID tag according to a second embodiment of the present invention;  
         [0038]      FIG. 4  is a side view of an RFID tag according to a third embodiment of the present invention;  
         [0039]      FIG. 5  is a side view of an RFID tag according to a fourth embodiment of the present invention;  
         [0040]      FIG. 6  is a side view of an RFID tag according to a fifth embodiment of the present invention;  
         [0041]      FIG. 7  is a side view of an RFID tag according to a sixth embodiment of the present invention;  
         [0042]      FIG. 8  is a sideview of an RFID tag according to a seventh embodiment of the present invention;  
         [0043]      FIG. 9  is a process chart showing a process of fixing a reinforcement body to an inlay;  
         [0044]      FIG. 10  is a process chart showing a process of forming an auxiliary body around a reinforcement body;  
         [0045]      FIG. 11  is a process chart showing a process of forming a reinforcement body which entirely covers an inlay; and  
         [0046]      FIG. 12  is a process chart showing a process of forming an auxiliary body which entirely covers an inlay. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]     Embodiments of the present invention will be described below with reference to the drawings.  
         [0048]      FIG. 2  is a side view of an RFID tag according to a first embodiment of the present invention.  
         [0049]     The RFID tag  100  shown in  FIG. 2  consists of a sheet-type base  113  made of PET film, an antenna  112  made of thin copper film and mounted on the base  113 , an IC chip  111  mainly made of Si and connected to the antenna  112  via bumps (metal protrusions)  114 , an adhesive  115  made of thermosetting epoxy resin and bonding the IC chip  111  to the base  113 , and a reinforcement body  116  which, being made of polyphenylene sulfide and fixed to the base  113 , covers the entire IC chip  111  and part of the antenna  112 .  
         [0050]     Besides the polyphenylene sulfide, possible materials for the reinforcement body  116  include other plastic resins, which are as hard as PPS, such as ABS (acrylonitrile-butadiene-styrene copolymer) and polycarbonate, ceramic, and metal. In addition to the PET film described above, a wide range of materials are available for the base  113  including other polyester resins such as PET-G (noncrystal polyester resins), polyvinyl chloride, ABS (acrylonitrile-butadiene-styrene copolymer), cellulosic resins, vinyl acetate resins, polystyrene resins, and polyolefin resins. Possible materials for the antenna  112  include, in addition to the thin copper film described above, thin film of other metals such as aluminum, iron, and nickel; and paste material of epoxy or other resins mixed with metal filler (generally, Ag) to give electrical conductivity.  
         [0051]     The reinforcement body  116  is an example of the first reinforcement body according to the present invention. It is shaped like a cap with a wide inner wall  116   a  formed in such a way as to provide a clearance between itself and the IC chip  111 . The base  113  is free of hard structure in a portion d between fixing positions of the reinforcement body  116  and IC chip  111 . Although the base  113  is shown as being thicker in  FIG. 2  than it really is for purposes of illustration, actually the base  113  is thin, and thus it deforms and extends easily in the portion d. Consequently, even if temperature changes in the operating environment of the RFID tag  100  cause differences in expansion or contraction between the reinforcement body  116  made of polyphenylene sulfide and IC chip  111  mainly made of Si, the differences are absorbed by the portion d of the base  113 , preventing breakage or separation of the IC chip  111 . This increases reliability of the RFID tag  100  under temperature changes.  
         [0052]     Also, since the reinforcement body  116  is fixed to the base  113  while covering the IC chip  111 , any bending stress caused by bending of the base  113  is received and spread by the reinforcement body  116 , which thus reduces the bending stress acting on the IC chip  111 .  
         [0053]     This concludes description of the first embodiment. Various other embodiments different from the first embodiment will be described below, wherein the same components as those of the first embodiment will be denoted by the same reference numerals as corresponding components of the first embodiment and description thereof will be omitted to avoid redundancy. The following description of the embodiments will focus on differences from the first embodiment.  
         [0054]      FIG. 3  is a side view of an RFID tag according to a second embodiment of the present invention.  
         [0055]     In addition to the reinforcement body  116  which covers the IC chip  111 , the RFID tag  200  according to the second embodiment is equipped with another reinforcement body  117  located on the opposite side of the base  113  from the reinforcement body  116 . The reinforcement body  117  is an example of the second reinforcement body according to the present invention. It has the same shape as there reinforcement body  116  which covers the IC chip  111 . Consequently, absorption of the differences in expansion or contraction by the portion d shown in  FIG. 2  is not obstructed. Thus, the RFID tag  200  according to the second embodiment also has high reliability under temperature changes. Also, the existence of the second reinforcement body  117  further reduces the bending stress caused by bending of the base  113  because the bending stress is spread out by the two reinforcement bodies  116  and  117 .  
         [0056]      FIG. 4  is a side view of an RFID tag according to a third embodiment of the present invention.  
         [0057]     The RFID tag  300  according to the third embodiment has an auxiliary body  118  which is more flexible (i.e., lower in bending strength or Young&#39;s modulus) than the reinforcement body  116  along the boundary between the reinforcement body  116  and base  113 . Incidentally, although the auxiliary body  118  is shown as riding the antenna  112  in  FIG. 3  for the convenience of illustration, the antenna  112  is provided only in part of the periphery of the reinforcement body  116  while the auxiliary body  118  is provided in a wide area along the periphery of the reinforcement body  116 .  
         [0058]     The auxiliary body  118  is an example of the auxiliary body according to the present invention. Possible materials for the auxiliary body  118  include rubber materials such as urethane rubber and silicone rubber as well as epoxy adhesives, thermosetting silicone resins, and ultraviolet-curing acrylic resins.  
         [0059]     With the RFID tag  300  according to the third embodiment, the bending stress caused by bending of the base  113  is spread out by the auxiliary body  118 , reducing stress concentration on the boundary between the reinforcement body  116  and base  113 , and thereby preventing breakage of the antenna  112 .  
         [0060]      FIG. 5  is a side view of an RFID tag according to a fourth embodiment of the present invention.  
         [0061]     Instead of the reinforcement body  116  shown in  FIG. 2 , the RFID tag  400  according to the fourth embodiment is equipped with a reinforcement body  116 _ 1  covering the entire base  113 . Although the reinforcement body  116 _ 1  is fixed to the base  113 , that part P of the reinforcement body  116 _ 1  which is right behind the IC chip  111  is not fixed to the base  113 . Consequently, according to the fourth embodiment again, the differences in expansion or contraction is absorbed by the portion d shown in  FIG. 2 , resulting in high reliability under temperature changes. Also, the structure in which the reinforcement body  116 _ 1  covers the entire base  113  further increases strength against bending stress. Furthermore, the reinforcement body  116 _ 1  according to the fourth embodiment has a watertight structure which gives the RFID tag  400  high durability and makes it serviceable in a wide range of use environments.  
         [0062]      FIG. 6  is a side view of an RFID tag according to a fifth embodiment of the present invention.  
         [0063]     The RFID tag  500  according to the fifth embodiment is equipped with a reinforcement body  116 _ 2  slightly different from the reinforcement body  116 _ 1  according to the fourth embodiment. The reinforcement body  116 _ 2  has an inner wall b at a location corresponding to the part P right behind the IC chip  111  in  FIG. 5 . Thus, the reinforcement body  116 _ 2  is not only unfixed to the part P, but also free from contact with it. Consequently, any pinching force acting in the up-and-down direction in the drawing on the RFID tag  500  at a location around the IC chip  111  is hard to be transmitted to the IC chip  111 . This increases the safety of the IC chip  111  and reliability of the RFID tag  500 .  
         [0064]      FIG. 7  is a side view of an RFID tag according to a sixth embodiment of the present invention.  
         [0065]     Instead of the auxiliary body  118  according to the third embodiment, the RFID tag  600  according to the sixth embodiment is equipped with an auxiliary body  118 _ 1  which entirely covers the reinforcement body  116  and base  113  and has a watertight structure.  
         [0066]     Since the auxiliary body  118 _ 1  is flexible, the RFID tag  600  is bendable as a whole. The stress produced when the RFID tag  600  bends is spread out as in the case of the third embodiment and the like. Consequently, the RFID tag  600  according to the sixth embodiment is effective for applications which assume that the RFID tag will be bent, including applications where the RFID tag  600  is affixed to bendable goods such as clothing.  
         [0067]      FIG. 8  is a side view of an RFID tag according to a seventh embodiment of the present invention.  
         [0068]     The RFID tag  700  according to the seventh embodiment of the present invention has reinforcement bodies  116  and  117  on both sides of the base as in the case of the second embodiment shown in  FIG. 3  as well as an auxiliary body  118 _ 2  which entirely covers the reinforcement bodies  116  and  117  and base  113 . Again, the auxiliary body  118 _ 2  has a watertight structure.  
         [0069]     Since the bending stress is spread out by the two reinforcement bodies  116  and  117 , the RFID tag  700  is more effective for applications which assume that the RFID tag will be bent.  
         [0070]     This concludes the description of structures according to various embodiments. Now description will be given of manufacturing methods for the embodiments described above, but instead of describing a manufacturing method for each embodiment redundantly, description will be given of elemental processes used as appropriate in the manufacture of individual embodiments. The embodiments described above are manufactured using the following processes as appropriate.  
         [0071]     A group of the components (from the IC chip  111  to the adhesive  115 ) shown in  FIG. 2  excluding the reinforcement body  116  will be referred to as an “inlay” without any reference character. Regarding manufacturing processes of the inlay, known manufacturing processes can be used as appropriate, and thus description thereof will be omitted.  
         [0072]     First, a process of fixing a reinforcement body to an inlay will be described.  
         [0073]      FIG. 9  is a process chart showing a process of fixing a reinforcement body to an inlay.  
         [0074]     In this process, a bonding adhesive  120  made of thermosetting epoxy resin is applied to the inlay in such a way as to surround the IC chip  111  as shown in part (A) of  FIG. 9 , then the reinforcement body  116  is placed on the adhesive  120  in alignment with the IC chip  111  and the like as shown in part (B) of  FIG. 9 , and the adhesive is cured by heating. The step shown in part (A) is an example of the first adhesive-application step according to the present invention while the step shown in part (B) is an example of the first fixing step according to the present invention.  
         [0075]     When the reinforcement bodies  116  and  117  are installed on both sides of the inlay as in the case of the second and seventh embodiments, the adhesive  120  is applied to the surface opposite to the surface to which the reinforcement body  116  is fixed as shown in part (C), the other reinforcement body  117  is placed in alignment on the adhesive  120  as shown in part (D), and the adhesive is cured by heating. The step shown in part (C) is an example of the second adhesive-application step according to the present invention while the step shown in part (D) is an example of the second fixing step according to the present invention.  
         [0076]     Through the above process, the reinforcement bodies  116  and  117  are fixed to the inlay.  
         [0077]     Next, a process of forming an auxiliary body around a reinforcement body will be described.  
         [0078]      FIG. 10  is a process chart showing a process of forming an auxiliary body around a reinforcement body.  
         [0079]     This process uses an assembly consisting of the reinforcement bodies fixed to the inlay in the process shown in  FIG. 9 . Part (A) of  FIG. 10  shows an assembly consisting of the reinforcement body  116  fixed to one side of the inlay as an example while part (B) shows the inlay in the same state as viewed from above the reinforcement body  116 . The antenna  112  is installed on the base  113  and the reinforcement body  116  covering part of the base  113  is fixed to the antenna  112 . Thus, edges of the reinforcement body  116  cross the antenna  112  at some locations and an auxiliary body is provided to prevent the antenna from being broken at these locations.  
         [0080]     A fluid  122  such as thermosetting silicone resin or ultraviolet-curing acrylic resin which is an ingredient of an auxiliary body is applied around the reinforcement body  116  along the boundary between the reinforcement body  116  and base  113  by a dispenser  121  as shown in part (C) of  FIG. 10  and the fluid  122  is cured by heating or ultraviolet irradiation, thereby forming the auxiliary body  118  around the reinforcement body  116  as shown in part (D).  
         [0081]     The process described above can be used as it is even when providing an auxiliary body on a reinforcement body installed on the opposite side of the inlay from the IC chip  111 .  
         [0082]     Next, a process of forming a reinforcement body which entirely covers an inlay will be described.  
         [0083]      FIG. 11  is a process chart showing a process of forming a reinforcement body which entirely covers an inlay.  
         [0084]     It is assumed here that the reinforcement body has a block construction. As shown in part (A) of  FIG. 11 , a lower cover  116 _ 1   a  of the reinforcement body has a recess into which the inlay fits snugly. A bonding adhesive  123  made of ultraviolet-curing acrylic resin is applied to the inner part of the recess. In so doing, the adhesive  123  is applied by avoiding the part P right behind the IC chip  111  in  FIG. 5 .  
         [0085]     Next, as shown in part (B) of  Fig. 11 , the inlay is aligned with and fitted in the recess of the lower cover  116 _ 1   a  and ultraviolet rays are emitted from the inlay to cure the adhesive  123 , thereby fixing the inlay and the lower cover  116 _ 1   a  together. Incidentally, although an ultraviolet-curing resin is used for the bonding adhesive assuming that the base  113  of the inlay is made of PET or similar material transparent to ultraviolet rays, a thermosetting resin may be used for the bonding adhesive if the base  113  is not transparent to ultraviolet rays.  
         [0086]     Next, the adhesive  120  is applied to a peripheral part of the lower cover  116 _ 1   a  as shown in part (C) of  FIG. 11 , an upper cover  116 _ 1   b  is mounted on the lower cover  116 _ 1   a  in alignment with the latter as shown in part (D), and the adhesive  120  is cured by heating, thereby forming the reinforcement body  116 _ 1 .  
         [0087]     Incidentally although  FIG. 11  illustrates, as an example, how to form the reinforcement body  116 _ 1  according to the fourth embodiment, the process shown in  FIG. 11  also applies as it is to the reinforcement body  116 _ 2  according to the fifth embodiment.  
         [0088]     Finally, a process of forming an auxiliary body which entirely covers an inlay will be described.  
         [0089]      FIG. 12  is a process chart showing a process of forming an auxiliary body which entirely covers an inlay.  
         [0090]     Again, this process uses an assembly consisting of the reinforcement bodies fixed to the inlay in the process shown in  FIG. 9 . Part (A) of  FIG. 12  shows an assembly consisting of the reinforcement body  116  fixed to one side of the inlay as an example. It is assumed here that the auxiliary body has a block construction. As shown in part (B) of  FIG. 12 , a lower cover  118 _ 1   a  of the auxiliary body in which the auxiliary body is divided has a recess into which the inlay fits snugly. The inlay is aligned with and fitted in the recess.  
         [0091]     Next, as shown in part (C) of  FIG. 12 , an upper cover  118 _ 1   b  of the auxiliary body in which the auxiliary body is divided is mounted on the lower cover  118 _ 1   a  in alignment with the latter. The upper cover  118 _ 1   b  has a recess to accept the reinforcement body  116 .  
         [0092]     Next, as shown in part (D), areas around the inlay are heated under pressure by a heating fixture  124  with a built-in heater  124   a . Consequently, a peripheral part of the lower cover  118 _ 1   a  and peripheral part of the upper cover  118 _ 1   b  are fused together, thereby forming the auxiliary body  118 _ 1  which covers the inlay.  
         [0093]     Incidentally, although  FIG. 12  illustrates,.as an example, how the auxiliary body  118 _ 1  according to the sixth embodiment is formed, the process shown in  FIG. 12  also applies as it is to the auxiliary body  118 _ 2  according to the seventh embodiment.  
         [0094]     Each of the embodiments described above are manufactured using an appropriate selection or combination of the processes described above.  
         [0095]     Incidentally, although a reinforcement body free from contact with the IC chip has been described as an example of the first reinforcement body according to the present invention, the first reinforcement body according to the present invention may be placed in contact with the IC chip as long as it is not fixed to the IC chip.