Radio frequency IC device and method of manufacturing the same

A radio frequency IC device that prevents variations in the value of capacitive coupling between a radio frequency IC element and a radiation electrode and has good signal transmission efficiency includes a radio frequency IC element including input/output electrodes and, a first base including intermediate electrodes that are capacitively coupled to the input/output electrodes and have capacitance values C1a and C1b, respectively, and a second base including radiation electrodes and that are capacitively coupled to the intermediate electrodes and have capacitance values C2a and C2b, respectively. A capacitance C1 obtained by combining C1a and C1b is smaller than a capacitance C2 obtained by combining C2a and C2b.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to radio frequency IC devices and methods of manufacturing the same, and, more particularly, to a radio frequency IC device preferably for use in an RFID (Radio Frequency Identification) system and a method of manufacturing the radio frequency IC device.

2. Description of the Related Art

In recent years, as a product management system, an RFID system has been developed in which a reader/writer for generating an induction field communicates with an IC tag (hereinafter referred to as a radio frequency IC device) attached to a product in a non-contact manner so as to obtain predetermined information stored in the IC tag. For example, Japanese Unexamined Patent Application Publication No. 2008-160874 discloses a radio frequency IC device used in an RFID system.

In a radio frequency IC device disclosed in Japanese Unexamined Patent Application Publication No. 2008-160874 (for example, see FIG. 5 in Japanese Unexamined Patent Application Publication No. 2008-160874), a flexible sheet including a feeding circuit provided thereon and a radio frequency IC chip mounted on the feeding circuit and another flexible sheet on which a radiation plate is disposed are bonded so that the feeding circuit and the radiation plate are capacitively coupled.

However, in this radio frequency IC device, high accuracy is required when bonding these flexible sheets. The accuracy is low, variations in the value of capacitive coupling between the radio frequency IC chip and the radiation plate occur and an impedance deviates from a set value. As a result, signal emission/reception performed by the radiation plate becomes unstable and signal transmission efficiency is reduced.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a radio frequency IC device that prevents variations in the value of capacitive coupling between a radio frequency IC element and a radiation electrode and has good signal transmission efficiency, and also provide a method of manufacturing the radio frequency IC device.

A radio frequency IC device according to a first preferred embodiment of the present invention includes a radio frequency IC element including an input/output electrode, a first base including an intermediate electrode capacitively coupled to the input/output electrode with a capacitance value C1, and a second base including a radiation electrode capacitively coupled to the intermediate electrode with a capacitance value C2that is greater than C1.

A radio frequency IC device manufacturing method according to a second preferred embodiment of the present invention includes a step of mounting a radio frequency IC element including an input/output electrode on a first base including an intermediate electrode and capacitively coupling the input/output electrode and the intermediate electrode with a capacitance value C and a step of mounting the first base on which the radio frequency IC element is mounted on a second base including a radiation electrode and capacitively coupling the intermediate electrode and the radiation electrode with a capacitance value C2that is greater than C1.

In the radio frequency IC device, the radio frequency IC element and the radiation electrode are coupled via a capacitor having the capacitance value C1and a capacitor having the capacitance value C2which are connected in series between the radio frequency IC element and the radiation electrode. That is, C1and C2are connected in series on a transmission path of a radio frequency signal. Here, the relationship between C1and C2is C1<C2. In this case, the total capacitance value C between the radio frequency IC element and the radiation electrode is controlled by the capacitance value C1that is the smaller one. The capacitance value C1is obtained between the input/output electrode included in the radio frequency IC element and the intermediate electrode included in the first base. The radio frequency IC element can be accurately mounted on the first base using an IC installation apparatus in the related art, and variations in the capacitance value C1rarely occur. On the other hand, the capacitance value C2is obtained between the intermediate electrode and the radiation electrode. Even if the first base is inaccurately mounted on the second base and variations in the capacitance value C2occur, the capacitance value C2has little effect on the capacitance value C between the radio frequency IC element and the radiation electrode. Accordingly, the occurrence of variations in the capacitance value C between the radio frequency IC element and the radiation electrode is suppressed and minimized, and the reduction in signal transmission efficiency can be prevented.

According to preferred embodiments of the present invention, variations in the value of capacitive coupling between a radio frequency IC element and a radiation electrode can be prevented, signal emission/reception performed by the radiation electrode becomes stable, and signal transmission efficiency is not reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A radio frequency IC device according to various preferred embodiments of the present invention and a method of manufacturing the radio frequency IC device will be described below with reference to the accompanying drawings. In the drawings, the same reference numeral is used to represent the same component or the same element so as to avoid repeated explanation.

First Preferred Embodiment

As illustrated inFIGS. 1A and 1B, a radio frequency IC device according to the first preferred embodiment includes a radio frequency IC element1obtained by mounting a radio frequency IC chip5(seeFIG. 4) on a feeding circuit board4and covering the radio frequency IC chip5with a resin layer3, a first base11including intermediate electrodes12aand12b, and a second base16including radiation electrodes15aand15b.

As illustrated inFIG. 4, the radio frequency IC chip5is connected to a feeding circuit (not illustrated) in the feeding circuit board4via solder bumps7, and input/output electrodes2aand2bare disposed on the surface of the feeding circuit board4. The radio frequency IC element1is attached to the first base11via an insulating adhesive layer13so that the input/output electrodes2aand2bface the intermediate electrodes12aand12b, respectively. The input/output electrodes2aand2bare capacitively coupled to the intermediate electrodes12aand12bwith capacitance values C1aand C1b, respectively. Thus, the unit in which the radio frequency IC element1and the first base11are integrated is called a basic module8.

The first base11is attached to the second base16via an insulating adhesive layer14so that the intermediate electrodes12aand12bface the radiation electrodes15aand15b, respectively. The intermediate electrodes12aand12bare capacitively coupled to the radiation electrodes15aand15bwith capacitance values C2aand C2b, respectively.

The first base11and the second base16are preferably made of an insulating material (dielectric) such as a PET film or paper, for example. Various electrodes are preferably formed of an evaporated metal film such as an Au or Ag film, an applied film, or a thin metal film such as aluminum foil, for example. The insulating adhesive layers13and14are preferably formed of, for example, an epoxy resin. The radio frequency IC chip5includes a clock circuit, a logic circuit, and a memory circuit, stores necessary information as is known, and can transmit/receive a predetermined high-frequency signal.

In a radio frequency IC device having the above-described configuration, the radiation electrodes15aand15breceive a high-frequency signal (for example, in the UHF or HF frequency band) emitted from a reader/writer (not illustrated), a feeding circuit (not illustrated) in the feeding circuit board4that is capacitively coupled to the radiation electrodes15aand15bresonates, and energy obtained by the resonance is supplied to the radio frequency IC chip5. On the other hand, predetermined energy is extracted from the received signal, the feeding circuit makes information stored in the radio frequency IC chip5conform to a predetermined frequency using the energy, and a transmission signal is transmitted to the radiation electrodes15aand15bvia the above-described capacitive coupling and is transmitted to the reader/writer from the radiation electrodes15aand15b.

FIG. 1Cillustrates an equivalent circuit of a radio frequency IC device according to the first preferred embodiment. The radio frequency IC element1and the radiation electrode15aare coupled via a capacitor having the capacitance value C1aand a capacitor having the capacitance value C2awhich are connected in series between the radio frequency IC element1and the radiation electrode15a. The radio frequency IC element1and the radiation electrode15bare coupled via a capacitor having the capacitance value C1band a capacitor having the capacitance value C2bwhich are connected in series between the radio frequency IC element1and the radiation electrode15b. Here, C1a, C1b<C2a, C2bis set. For example, a capacitance obtained by combining the capacitance values C1aand C1bis about 2 pF, and a capacitance obtained by combining the capacitance values C2aand C2bis about 20 pF.

In this case, a capacitance value C between the radio frequency IC chip5and each of the radiation electrodes15aand15bis controlled by the very small capacitance values C1aand C1b. When C1aand C1bare set as C1and C2aand C2bare set as C2, the following equation is obtained.

When the capacitance value C1is much smaller than the capacitance value C2(C2>>C1), the value of (C1/C2) is close to zero. Accordingly, the capacitance value C is controlled by the capacitance value C1. The capacitance value C2can be easily increased by increasing areas of an overlapping portion of the intermediate electrode12aand the radiation electrode15aand an overlapping portion of the intermediate electrode12band the radiation electrode15b. The capacitance value C1ais obtained between the input/output electrode2aof the radio frequency IC element1and the intermediate electrode12aon the first base11, and the capacitance value C1bis obtained between the input/output electrode2bof the radio frequency IC element1and the intermediate electrode12bon the first base11. The radio frequency IC element1can be accurately mounted on the first base11using an IC installation apparatus in the related art, and variations in the capacitance value C1(C1aand C1b) rarely occur. On the other hand, the capacitance value C2ais obtained between the intermediate electrode12aand the radiation electrode15a, and the capacitance value C2bis obtained between the intermediate electrode12band the radiation electrode15b. Even if the first base11is inaccurately mounted on the second base16and variations in the capacitance value C2(C2aand C2b) occur, the capacitance value C2(C2aand C2b) has little effect on the capacitance value C between the radio frequency IC element1and each of the radiation electrodes15aand15b. Accordingly, the occurrence of variations in the capacitance value C between the radio frequency IC element1and each of the radiation electrodes15aand15bis suppressed and minimized, and the reduction in signal transmission efficiency caused by impedance mismatching can be prevented. It is desired that C2be about 5 to about 10 times C1, for example.

The size of the second base16is preferably larger than that of the first base11in the first preferred embodiment. The first base11includes the small-sized radio frequency IC chip5, and is small in size. By using the large-sized second base16, the small-sized first base11can be easily attached to the second base16. In this case, installation is more accurately performed as compared with a case in which the radio frequency IC element1is mounted on the large-sized second base16.

The first base11and the intermediate electrodes12aand12bhave flexibility. Therefore, the basic module8can be easily handled, and the first base11can be easily attached to the second base16. It is desired that the second base16and the radiation electrodes15aand15bhave flexibility so as to attach the radio frequency IC device to variously-shaped surfaces of products.

Next, a method of manufacturing a radio frequency IC device will be described with reference toFIGS. 2A-2Dand3A-3C. First, the intermediate electrodes12aand12bare formed on the first base11functioning as a substrate using the ink jet method or the screen printing method (seeFIG. 2A). Subsequently, a double-side tape is attached to the first base11as the insulating adhesive layer13so that the double-side tape covers the intermediate electrodes12aand12bon the first base11(seeFIG. 2B). Subsequently, the radio frequency IC elements1are disposed at predetermined positions on the insulating adhesive layer13(seeFIG. 2C). At that time, the radio frequency IC element1is accurately disposed so that the input/output electrodes2aand2bface the intermediate electrodes12aand12b, respectively, at predetermined positions.

Subsequently, a double-side tape is attached to the first base11as the insulating adhesive layer14so that the double-side tape covers the radio frequency IC elements1. As a result, the group of the basic modules8is obtained (seeFIG. 2D). Subsequently, as illustrated inFIG. 3A, the group is cut into the separate basic modules8and the basic modules8are attached to a base film18via an adhesive layer19(seeFIG. 3B). Subsequently, the base film18is turned upside down, the basic modules8are separated from the base film18one by one, and the basic module8is attached to the second base16on which the radiation electrodes15aand15bare formed via the insulating adhesive layer14(seeFIG. 3C). At that time, the attachment of the basic module8is performed so that the intermediate electrodes12aand12bface the radiation electrodes15aand15b, respectively, at predetermined positions, and high attachment position accuracy is not required as described previously.

Modification of Basic Module8

Various types of the basic modules8can be used. A first modification of the basic module8is illustrated in FIG.5A. The basic module8is preferably the same as the basic module8illustrated inFIG. 4except that the input/output electrodes2aand2bare disposed in the feeding circuit board4. In the basic module8, the input/output electrodes2aand2bare capacitively coupled to the intermediate electrodes12aand12b, respectively, via the insulating adhesive layer13and a dielectric layer of the feeding circuit board4.

In a second modification of the basic module8, as illustrated inFIG. 5B, a feeding circuit board is not disposed and the input/output electrodes2aand2bdisposed on the undersurface of the radio frequency IC chip5surface and are capacitively coupled to the intermediate electrodes12aand12b, respectively, via the insulating adhesive layer13.

Modification of Manufacturing Process

The manufacturing method illustrated inFIGS. 2 and 3can be variously changed. A modification of the manufacturing method is illustrated inFIGS. 6A and 6B. After the process illustrated inFIG. 2Dhas been performed, a cover sheet20is attached to the surface of the insulating adhesive layer14(seeFIG. 6A). Subsequently, the cover sheet20is removed and the basic module8is attached to the second base16(seeFIG. 6B). The process illustrated inFIG. 6Bcorresponds to the process illustrated inFIG. 3C. Thus, by attaching the cover sheet20in the middle of the manufacturing process, it is possible to avoid adherence of dust or the like to the surface of the insulating adhesive layer14. Any material can be used for the cover sheet20.

Second Preferred Embodiment

As illustrated inFIG. 7C, in a radio frequency IC device according to the second preferred embodiment, a single input/output electrode22is disposed on the surface of the feeding circuit board4. The input/output electrode22faces and is capacitively coupled to an intermediate electrode21. Except this point, the second preferred embodiment is preferably the same as the first preferred embodiment.FIG. 7Billustrates an equivalent circuit of a radio frequency IC device according to the second preferred embodiment. The input/output electrode22and the intermediate electrode21are capacitively coupled with the capacitance value C1. The capacitance value C1is, for example, about 4 pF, and a capacitance value obtained by combining the capacitance value C2abetween the intermediate electrode21and the radiation electrode15aand the capacitance value C2bbetween the intermediate electrode21and the radiation electrode15bis, for example, about 20 pF.

In the second preferred embodiment, the insulating adhesive layer14is not formed, and the radio frequency IC element1is in contact with the second base16.

Third Preferred Embodiment

As illustrated inFIG. 8A, in a radio frequency IC device according to the third preferred embodiment, a single radiation electrode30is disposed on the second base16. Like in the second preferred embodiment, the input/output electrode22is capacitively coupled to the intermediate electrode21.FIG. 8Billustrates an equivalent circuit of a radio frequency IC device according to the third preferred embodiment. The input/output electrode22and the intermediate electrode21are capacitively coupled with the capacitance value C1, and the intermediate electrode21and the radiation electrode30are capacitively coupled with the capacitance value C2. The capacitance value C1is, for example, about 3 pF, and the capacitance value C2is, for example, about 20 pF.

In the third preferred embodiment, the radiation electrode30may have a large area (for use in the UHF frequency band), or have a loop shape (for use in the HF frequency band).

Fourth Preferred Embodiment

As illustrated inFIG. 9, in a radio frequency IC device according to the fourth preferred embodiment, the radio frequency IC element1mounted on the first base11is covered with an insulating adhesive layer41(formed of, for example, an epoxy resin) and the intermediate electrode21is attached to the insulating adhesive layer41. As a result, the basic module8is formed. The basic module8is attached to the second base16including the radiation electrode30via an insulating adhesive layer42(formed of, for example, an epoxy resin). As a result, a radio frequency IC device is formed. An equivalent circuit of a radio frequency IC device according to the fourth preferred embodiment is the same as that illustrated inFIG. 8B.

Fifth Preferred Embodiment

As illustrated inFIG. 10, in a radio frequency IC device according to the fifth preferred embodiment, the radio frequency IC element1is embedded in a soft insulating adhesive layer43(for example, an epoxy resin layer of B stage), and the intermediate electrode21is attached to the insulating adhesive layer43. As a result, the basic module8is formed. The basic module8is attached to the second base16including the radiation electrode30via the insulating adhesive layer42. As a result a radio frequency IC device is formed. An equivalent circuit of a radio frequency IC device according to the fifth preferred embodiment is the same as that illustrated inFIG. 8B. In the fifth preferred embodiment, the insulating adhesive layer43functions as a first base.

Sixth Preferred Embodiment

As illustrated inFIG. 11, in a radio frequency IC device according to the sixth preferred embodiment, the radio frequency IC element1is embedded in the soft insulating adhesive layer43, and the insulating adhesive layer43is attached to the intermediate electrode21located on the first base11. As a result, the basic module8is formed. The basic module8is attached to the second base16including the radiation electrode30via the insulating adhesive layer42. As a result, a radio frequency IC device is formed. An equivalent circuit of a radio frequency IC device according to the sixth preferred embodiment is the same as that illustrated inFIG. 8B.

Seventh Preferred Embodiment

As illustrated inFIG. 12A, the configuration of a radio frequency IC device according to the seventh preferred embodiment is basically the same as that of a radio frequency IC device according to the first preferred embodiment except that the insulating adhesive layer14is not formed. Accordingly, immediately after the process illustrated inFIG. 2C, the basic modules8are separated one by one, and each of the basic modules8is attached to the second base16including the radiation electrodes15aand15b(seeFIG. 12B).

Eighth Preferred Embodiment

A process of manufacturing a radio frequency IC device according to the eighth preferred embodiment will be described. First, a plurality of radio frequency IC elements1are mounted on the first base11at predetermined intervals (seeFIG. 13A), and are covered with the insulating adhesive layer41(see FIG.13B). Subsequently, the intermediate electrodes12aand the intermediate electrodes12bare disposed on the insulating adhesive layer41(seeFIG. 13C). The intermediate electrodes12aand12bmay be obtained by forming an electrode film on the entire surface of the insulating adhesive layer41and patterning the insulating adhesive layer41into a predetermined shape. Subsequently, the insulating adhesive layer42is formed on the insulating adhesive layer41so that the insulating adhesive layer41covers the intermediate electrodes12aand12b(seeFIG. 13D). Subsequently, the basic modules8are cut one by one, and are each attached to the base film18via the adhesive layer19(seeFIG. 14A). Subsequently, the base film18is turned upside down, the basic modules8are separated from the base film18one by one, and the basic module8is attached to the second base16on which the radiation electrodes15aand15bare formed (seeFIG. 14B).

An equivalent circuit of a radio frequency IC device according to the eighth preferred embodiment is the same as that illustrated inFIG. 1C, and an operational effect of the eighth preferred embodiment is also the same as that of the first preferred embodiment.

Ninth Preferred Embodiment

A process of manufacturing a radio frequency IC device according to the ninth preferred embodiment will be described. First, a plurality of radio frequency IC elements1are embedded in the soft insulating adhesive layer43at predetermined intervals (seeFIGS. 15A and 15B). The intermediate electrodes12aand the intermediate electrodes12bare formed on the insulating adhesive layer43(seeFIG. 15C). Subsequently, the insulating adhesive layer42is formed on the insulating adhesive layer43so that the insulating adhesive layer42covers the intermediate electrodes12aand12b(seeFIG. 15D). Subsequently, the basic modules8are cut one by one, and are each attached to the second base16on which the radiation electrodes15aand15bare formed (seeFIG. 15E).

An equivalent circuit of a radio frequency IC device according to the ninth preferred embodiment is the same as that illustrated inFIG. 1C, and an operational effect of the ninth preferred embodiment is also the same as that of the first preferred embodiment.

Other Preferred Embodiments

A radio frequency IC device according to the present invention and a method of manufacturing the radio frequency IC device are not limited to the above-described preferred embodiments, and various changes can be made thereto without departing from the scope and spirit of the present invention.

As described previously, preferred embodiments of the present invention are useful for a radio frequency IC device and a method of manufacturing the radio frequency IC device, and provide significant advantages to prevent variations in the value of capacitive coupling between a radio frequency IC element and a radiation electrode and having good signal transmission efficiency.