JP2001118041A - Id tag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an epoxy resin for coil sealing from cracking even if a large temperature difference between low temperature and high temperature is applied to an ID tag. SOLUTION: When a large difference exists between the coefficient of thermal expansion of epoxy resin for sealing an antenna coil and that of the antenna coil, the epoxy resin cracks if a large temperature difference is applied to the ID tag. If the amount of a filler that the epoxy resin contains is increased, the coefficient of thermal expansion of the epoxy resin decreases to approximate the coefficient of thermal expansion of the antenna coil. In this case, the viscosity of the epoxy resin increases in proportion to the increase of the amount of the filler in the epoxy resin and then it becomes difficult to cast the resin. Therefore, the amount of the filler is set to 50% (wt.%). Consequently, the epoxy resin is prevented from cracking while keeping the castability of the epoxy resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ID tag in which a coil housed in a case is sealed with epoxy resin.

[0002]

2. Description of the Related Art For example, as a system for identifying a moving object,
There is a remote ID system using high frequency radio waves.
In this method, communication is performed between the controller and the ID tag by radio waves to read data of an ID tag at a remote position or write data to the ID tag. Such a remote ID system is considered to be applied to various systems such as a delivery system, an inventory management system, and a sales system.

[0003]

By the way, this kind of I
The D tag is configured so that the IC chip module and the coil are sealed with an epoxy resin casting in a state where the IC chip module and the coil are electrically connected and housed in a molded case. Is common.

However, in such a structure, when an ID tag is used in an environment where a temperature difference between a low temperature and a high temperature is large, a large stress acts on the epoxy resin, and the epoxy resin may be broken. There is a disadvantage that the product life is shortened.

The present invention has been made in view of the above circumstances, and an object thereof is to cause cracks in a coil sealing epoxy resin even when a large temperature difference between a low temperature and a high temperature is applied. An object of the present invention is to provide an ID tag capable of preventing the above.

[0006]

According to the first aspect of the present invention, even if a large temperature difference between a low temperature and a high temperature is applied to the ID tag, the epoxy resin for coil encapsulation has a thermal expansion coefficient of the filler. By doing so, the coefficient of thermal expansion of the coil is close to that of the coil, so that a large stress does not act on the epoxy resin, and it is possible to effectively prevent the epoxy resin from cracking.

According to the second aspect of the present invention, the larger the filler amount, the higher the viscosity of the epoxy resin and the worse the moldability. However, when the content ratio of the filler in the epoxy resin is set to about 50%, Further, it is possible to prevent the epoxy resin from cracking while ensuring the moldability of the epoxy resin.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a cross section of the ID tag. In FIG. 2, the ID tag 1 is formed by casting an epoxy resin 5 in a state where an IC chip module 2 and an antenna coil 3 that are electrically connected in advance are housed in a case 4. The IC chip module 2 is formed by molding a resin with the IC chip 7 mounted on the printed wiring board 6.

FIG. 3 shows an electrical configuration of the ID tag 1. In FIG. 3, an ID tag 1 includes an antenna coil 3 for transmitting and receiving a radio signal, and a resonance capacitor 8.
, An IC chip 7 and a smoothing section 9, and the resonance capacitor 8, the IC chip 7 and the smoothing section 9 are mounted on the printed wiring board 6.

The IC chip 7 includes an MPU (microprocessor unit) 10, a rectifier 11, and a modem 1.
2. The semiconductor elements constituting the memory unit 13 and the like are integrated into one chip. Although not shown, the smoothing unit 9 has a smoothing capacitor, a Zener diode, and the like.

The antenna coil 3 is connected in parallel with the resonance capacitor 8 to form a resonance circuit 14, and when a predetermined high frequency power radio signal is transmitted from an interrogator as an external device. , Receiving this, rectifying unit 1
Send to 1. The rectifying unit 11 constitutes an operation power supply circuit 15 together with the smoothing unit 9. The rectifying unit 11 rectifies the power radio wave signal transmitted from the resonance circuit 14, smoothes the power radio wave signal using the smoothing unit 9, and performs a constant voltage DC power Power) and MP
Supply to U10 etc.

A signal such as data transmitted from the interrogator is transmitted while being superimposed on a radio wave signal for electric power.
It is given to PU10. The MPU 10 operates according to an operation program stored in a ROM included in the memory unit 13, executes a process corresponding to a signal input from the modem unit 12, and deletes received data from the EEPROM or the like included in the memory unit 13. The data is written to a possible non-volatile memory, or data is read from the memory unit 13, modulated by the modulation / demodulation unit 12, and transmitted as a radio signal from the antenna coil 3.

When a large temperature difference (cold thermal shock) between a low temperature and a high temperature is applied to the ID tag 1 having the above structure, the epoxy resin 5 may be cracked. Thus, the portion where the epoxy resin 5 cracks is a boundary portion with the antenna coil 3 (see FIG. 2), and it has been found that a stress exceeding the strength of the epoxy resin 5 is generated here. The cause of the cracks in the epoxy resin 5 is when a large temperature difference (cold thermal shock) between the low temperature and the high temperature is applied, and the mechanical properties depending on the temperature, that is, the antenna coil 3 and the epoxy It was assumed that the difference was due to the difference in the coefficient of thermal expansion of the resin 5. In this case, the antenna coil 3 is mainly composed of copper and has a coefficient of thermal expansion of 18 ppm, whereas the epoxy resin 5 has a large coefficient of thermal expansion.
8 ppm, and the difference between the two is 50 ppm.

Here, the stress acting on the epoxy resin 5 can be obtained by the difference of thermal expansion coefficient × temperature difference × Young's modulus. It was found that the stress generated according to the temperature difference exceeded the strength of the epoxy resin 5.

In order to reduce the stress acting on the epoxy resin 5, there is a method of reducing the difference in thermal expansion coefficient, the temperature difference, or the Young's modulus. The purpose is to reduce the difference between the coefficients of thermal expansion of the resin 5.

Therefore, in the present embodiment, by causing the thermal expansion coefficient of the epoxy resin 5 to approach the thermal expansion coefficient of the antenna coil 3, it is possible to prevent a large stress from being generated in the epoxy resin 5 due to thermal shock. I made it.

That is, from the experimental results of the inventor, it was found that, as shown in FIG. 1, when filler was mixed into the epoxy resin 5, the thermal expansion coefficient of the epoxy resin 5 decreased as the filler amount increased. Was. In this case, when the coefficient of thermal expansion of the epoxy resin 5 is reduced to the coefficient of thermal expansion of the antenna coil 3, the two expand and contract together, so that the stress acting on the epoxy resin 5 can be reduced to zero. Although it is possible, as the amount of filler contained in the epoxy resin increases, the viscosity of the epoxy resin 5 increases and casting becomes difficult.
% (% By weight). At this time, since the thermal expansion coefficient of the epoxy resin is 35 ppm, the difference between the thermal expansion coefficient of the epoxy resin 5 and the thermal expansion coefficient of the antenna coil 3 is 17 p.
pm.

With the thermal expansion coefficient of the epoxy resin 5 approaching the thermal expansion coefficient of the antenna coil 3 as described above, the same measurement as described above was performed, and it was confirmed that the generated stress was smaller than the strength of the epoxy resin 5. After that, at 20 ° C for 30 minutes,
A thermal shock test was performed at 180 ° C. for 30 minutes. As a result of this experiment, the conventional epoxy resin containing no filler was 6
While cracks occurred in four cycles, it was confirmed that the epoxy resin 5 of the present embodiment did not crack even after 900 cycles.

According to this embodiment, the filler of the epoxy resin 5 is mixed with the epoxy resin 5 so that the coefficient of thermal expansion of the epoxy resin 5 approaches the coefficient of thermal expansion of the antenna coil 3. Unlike the conventional example in which the antenna coil is simply sealed with epoxy resin, even when a large temperature difference between the low temperature and the high temperature is applied to the ID tag 1, the epoxy resin 5 is cracked. Can be effectively prevented. In this case, it is only necessary to mix the filler into the epoxy resin 5, so that it can be easily implemented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a filler amount and a thermal expansion coefficient according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an ID tag.

FIG. 3 is a block diagram showing an electrical configuration of the ID tag.

[Explanation of symbols]

1 is an ID tag, 3 is an antenna coil, 4 is a case, 5
Denotes an epoxy resin, and 7 denotes an IC chip.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 23/31

Claims (2)

[Claims] 1. An ID tag in which a coil housed in a case is sealed with epoxy resin, wherein a filler is included in the epoxy resin so that a thermal expansion coefficient of the epoxy resin is close to a thermal expansion coefficient of the coil. ID tag to do. 2. The ID tag according to claim 1, wherein the content weight ratio of the filler in the epoxy resin is set to approximately 50%.