Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-06-21
2002-06-04
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S895000
Reexamination Certificate
active
06400323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna coil for an IC card and to the method of manufacturing the same. More specifically, the present invention relates to an antenna coil for an IC card in which a circuit pattern layer of the antenna coil for the IC card is formed of an aluminum foil, as well as to the method of manufacturing the same. Here, the aluminum foil is not limited to a pure aluminum foil but it also includes an aluminum alloy foil.
2. Description of the Related Art
Recently, IC cards have been developed remarkably, and the use of the IC cards is widening to telephone cards, credit cards, pre-paid cards, cash cards, ID cards and card keys. As a base material for the conventional IC cards, resin film such as a polyimide film, a general purpose polyethylene terephthalate (PET) film or the like has been used. A copper foil or a high-purity aluminum foil is laminated on each side of the resin film and subjected to etching, whereby a circuit pattern layer of copper or aluminum is formed on a surface of the base material, providing an antenna coil for the IC card.
The process of etching the copper foil for forming the circuit pattern layer takes too much time, and therefore production efficiency is low. Further, after the etching process of the copper foil, an oxidizing reaction tends to occur at the surface of the copper foil, making instable the electrical resistance value of the surface of the circuit pattern.
When such a resin as described above is used as a base material of the antenna coil for IC cards and copper foils are to be laminated on both surfaces of the base material, it is necessary to attain electrical conduction between the circuit pattern layers of the copper foils formed on opposing surfaces of the base material. For this purpose, a plating layer of a through hole is formed between the circuit pattern layers of the copper foil, or printing with silver paste is performed. Such process steps lead to increased cost for manufacturing the antenna coil for IC cards and lowers production efficiency.
When a high-purity aluminum foil (having the purity of at least 99.8 mass %) is used as the material for forming the circuit pattern layer, superior oxidation resistance can be attained. Etching, however, takes longer time, resulting in low production efficiency. An IC card having the circuit pattern layer formed by using the high-purity aluminum foil is susceptible to possible disconnection of the circuit caused by emboss processing or imprinting such as inscription provided on the final product, thus reliability is not very high.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an antenna coil for an IC card having superior processability and allowing higher efficiency of production.
The antenna coil for an IC card in accordance with the present invention includes a base material containing resin and having a thickness of at least 15 &mgr;m and at most 70 &mgr;m, and a circuit pattern layer formed on a surface of the base material and having the thickness of at least 7 &mgr;m and at most 60 &mgr;m formed of a foil containing aluminum of at least 97.5 mass % and at most 99.7 mass %.
In the antenna coil for an IC card in accordance with the present invention, the foil constituting the circuit pattern layer has low aluminum purity, and therefore etch rate to form the circuit pattern layer can be improved, and hence production efficiency can be improved. Further, as the circuit pattern layer contains aluminum of the limited purity as mentioned above, it is possible to maintain electrical resistance value of the surface stable over a long time. Thus, an antenna coil for an IC card having higher stability over a long period of time can be attained.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the foil constituting the circuit pattern layer includes iron by at least 0.7 mass % and at most 1.8 mass %.
Here, as the aluminum foil constituting the circuit pattern layer contains iron by a limited content, it has such strength and elongation that lead to superior processability. Therefore, during the steps of manufacturing the antenna coil for an IC card or during emboss processing of the final product, possible tearing of the aluminum foil or disconnection of the circuits can be prevented. Further, as the etch rate for forming the circuit pattern layer can be improved, production efficiency can be improved.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the aluminum foil constituting the circuit pattern layer contains silicon by at least 0.03 mass % and at most 0.5 mass %.
Preferably, in the antenna coil for an IC card in accordance with the present invention, the aluminum foil constituting the circuit pattern layer contains silicon by at least 0.03 mass % and at most 0.5 mass % and copper by at most 0.3 mass %.
The polyimide film used as the base material of the antenna coil for an IC card is expensive, and in addition it absorbs much moisture, resulting in variation in electrical characteristic of the antenna coil during use of the IC card, possibly causing a malfunction. When a general purpose PET film is used as the base material of the antenna coil for an IC card, there would be an undesirable shrinkage as the base material is heated when an IC chip is mounted on the surface of the circuit pattern layer, for example. Therefore, dimensional accuracy of the circuit pattern layer formed on the base material of general purpose PET file becomes instable, and in addition, smoothness of the base material deteriorates.
Therefore, it is preferred that the base material includes a resin of which thermal contraction when held at 150° C. for 30 minutes is at most 0.3%.
Here, as the base material includes the resin having such a limited thermal contraction coefficient, contraction can be effectively prevented in the step of thermal processing at the time of mounting the IC chip, for example. Hence, dimensional accuracy of the circuit pattern layer can be maintained stable and the smoothness of the base material can also be maintained satisfactorily.
Preferably, the resin used as the base material of the antenna coil for an IC card in accordance with the present invention is at least one selected from the group consisting of low profile polyethylene terephthalate (PET) and low profile polyethylene naphthalate (PEN).
Preferably, in the antenna coil for an IC card in accordance with the present invention, the circuit pattern layer includes a first circuit pattern formed on one surface of the base material, and a second circuit pattern layer formed on the other surface of the base material. Here, it is preferred that at least a part of the first circuit pattern layer is in contact with at least a part of the second circuit pattern, penetrating through the base material. This enables electrical conduction between the first and second circuit pattern layers. Contact between the first and second circuit pattern layers can be attained easily by a crimping process.
Preferably, the antenna coil for an IC card in accordance with the present invention further includes an adhesive layer interposed between the circuit pattern layer and the base material for bonding therebetween. It is preferred that the adhesive layer includes a polyurethane based adhesive containing an epoxy resin.
There is a problem that when the manufactured antenna coils for the IC cards are stacked on one another or wound as a belt-shaped roll for shipping or storage, overlapping portions are adhered with each other (hereinafter referred to as blocking). Therefore, when an IC card is to be manufactured using the antenna coil, separation of the adhered portions of the antenna coils is expected to be difficult, possibly stopping the manufacturing line.
In order to prevent the blocking, excessive adhesive on the resin film as the base material should be removed, or a released paper should be inserted to overlapping portions of the antenna coil. Perfect removal
Kubota Tadashi
Sakamoto Hiroyuki
Tada Hiroshi
Takano Toshinori
Yasukawa Hidenori
Fasse W. F.
Fasse W. G.
Ho Tan
Toyo Aluminium Kabushiki Kaisha
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