Metal working – Method of mechanical manufacture – Electrical device making
Patent
1999-10-25
2000-12-19
Hall, Carl E.
Metal working
Method of mechanical manufacture
Electrical device making
29849, 336200, 342 51, H01F 4104
Patent
active
061612766
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for producing transponder coils and to a transponder comprising a coil produced according to this method. More specifically, the present invention relates to a method of producing coils for transponders, for example for chip cards.
PRIOR ART
In the technology of transponders, and in particular of chip cards of the transponder type, it is often desired to connect an induction coil to an electronic circuit, such as, for example, an integrated circuit mounted on a printed circuit board. Such a configuration is described, for example, in WO-91/19302. The coil is generally produced by winding a wire around a core. Such coils are complex to make, and therefore relatively costly. Moreover the connection between the printed circuit and the coil gives rise to certain additional problems relating to mounting and poses problems of reliability, in particular when these elements are integrated in a chip card not offering adequate protection against deformation and mechanical stresses. Furthermore the thickness of the coil makes it difficult to integrate the coil into a chip card of standard 0.76 mm thickness.
Coils are also known in which the turns of the coil are formed directly by the conducting tracks of a printed circuit, thus making it possible to avoid any soldering. The tracks of the printed circuit are generally produced by photo-chemical means, which entails numerous costly operations and the use of polluting products.
U.S. Pat. No. 4,555,291 describes an essentially mechanical method of producing a coil. A fine metallic film is cut beforehand in the shape of a spiral. In order to make the cut spiral rigid, the various turns are not completely separated. The spiral is then fixed on a sheet of dielectric material, and a second cutting device is set in operation to remove the interconnections between turns to produce a circuit of inductive nature.
This solution is complex to apply and entails, in particular, two distinct cutting operations. The thickness of the pre-cut metallic film must be sufficient to allow it to be transported without becoming deformed or torn; the width of the turns and of the gaps which have been cut between the turns must likewise be sufficient to provide the film with a minimum of rigidity prior to stratification on the dielectric substrate.
Other methods of producing coils starting from a synthetic film covered with a superficial conducting layer are known, and in these methods the various turns are demarcated by mechanical stamping of the said conducting layer carried out by means of a stamping die. U.S. Pat. No. 2,622,054, EP 0 096 516 or GB 610 058, for example, describe variants of such a method. It is difficult to obtain tracks of very narrow width with these stamping techniques. Moreover, the synthetic film must have a sufficient thickness to withstand the stamping pressure and remain sufficiently rigid even in the regions stamped by the stamping die.
DE 2 758 204 describes a method of producing a printed circuit, in particular an inductance circuit, in which the various tracks that form the turns of the coil are demarcated by thermo-mechanical machining of a synthetic film covered with a superficial metallic layer. A heated metallic spike (3) passes through the superficial metallic layer and simultaneously causes part of the synthetic layer to melt beneath the metal.
The method described in the DE 2 758 204 document is more specifically suited to the production of various kinds of devices or to coils whose thickness is not crucial. The thickness of the synthetic layer (1) must be sufficiently thick to be indented by the metallic spike (3) and at the same time be heated without being passed through completely. Control of the temperature of the spike (3) poses additional difficulties; moreover, the metallic spike (3) must be moved slowly enough for the synthetic material to have time to melt. This method is thus unsuitable for producing coils which must, for example, be integrated into chip cards and whose thickness as w
REFERENCES:
patent: 2622054 (1952-12-01), Franklin
patent: 4023998 (1977-05-01), Cederberg et al.
patent: 5184111 (1993-02-01), Pichl
Browing Clifford W.
Hall Carl E.
NagraID S.A.
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