Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-01-15
2001-01-23
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S841000, C029S846000, C029S600000, C174S250000, C174S261000
Reexamination Certificate
active
06176010
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method for producing printed circuits according to the preamble of claim
1
. Moreover the invention likewise concerns a printed circuit, for example an inductance coil whose turns are constituted by the paths of the printed circuit, made according to this method.
PRIOR ART
In the technology of chip cards and of transponders, it is often desired to connect an induction coil with an electronic circuit, 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, thus relatively costly. Moreover the connection between the printed circuit and the coil gives rise to certain additional problems of 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 often poses a problem as well when it has to be integrated into a miniaturised device or in a chip card in which one hopes to keep the standard thickness of 0.76 mm.
To reduce these difficulties, devices are also known in which the turns of the inductance are constituted directly by the conducting paths of the printed circuit. The paths of the printed circuit are generally realised by photochemical means, which necessitates numerous costly operations and the use of polluting substances.
U.S. Pat. No. 4,555,291 describes an essentially mechanical method of producing a printed circuit. A fine metallic film is cut beforehand in spiral shape. The different turns are not totally separated in order to make the cut spiral rigid. The spiral is then fixed to a sheet of dielectric material, and a second cutting device is set in operation to block the interconnections between turns, a circuit of inductive nature remaining.
This solution is complex to apply and necessitates, in particular, two distinct cutting operations. The thickness of the pre-cut metallic film must be sufficient so that it can be transported without becoming deformed or torn. The width of the turns and of the intervals which have been cut between the turns must likewise be sufficient to ensure a minimum of rigidity of the film before stratification on the dielectric support.
Other methods of producing a printed circuit are known starting from a synthetic film covered by a superficial conducting layer in which the different conducting paths are demarcated by mechanical stamping of the said conducting layer carried out by means of a stamping die. FR-2 674 724, GB-1138628, or U.S. Pat. No. 4,356,627, for example, describe variants of such a method. It is difficult to obtain paths of very reduced width with these stamping techniques. Moreover, the synthetic film must have a sufficient thickness to support the stamping pressure and remain sufficiently rigid even in the regions stamped in by the stamping die.
The other known methods of producing a printed circuit starting with a synthetic film covered by a superficial conducting layer comprise an operation of demarcation of different conducting paths constituting the printed circuit by cutting of the superficial layer of the printed circuit (cf. DE-3 330 738 and U.S. Pat. No. 4,138,924). The interstices between conducting paths thus necessarily have a sufficiently large width corresponding to at least the width of the milling tool. It is therefore not possible to obtain an optimal density of paths. Moreover, the cutting produces slivers which must be carefully removed to prevent possible short circuits between paths. When the superficial metallic layer is made of a costly material, for example of silver, there is waste of material.
DE-2 758 204 describes a method of producing a circuit, in particular of inductance in the form of a printed circuit, in which the different paths constituting the turns of the coil are demarcated by thermo-mechanical machining of a synthetic film covered by a superficial metallic layer. A heated metallic point (
3
) passes through the superficial layer of metal and simultaneously causes part of the synthetic layer to melt beneath the metal.
This method is more specifically adapted to producing different kinds of devices or to coils whose thickness is not crucial. The synthetic layer (
1
) must be thick enough for an incision to be made with the point (
3
) and be heated at the same time without being completely cut through. Control of the temperature of the point poses additional difficulties; moreover, the metallic point (
3
) must be moved slowly enough for the synthetic material to have the melting temperature. This method is thus unsuitable for producing coils which must be integrated, for example, in smart cards and whose thickness as well as cost and time of manufacture must be kept at a minimum.
One object of the present invention is thus to propose an improved method of producing a printed circuit, in particular when it is used to make inductance coils for a chip card whose turns are constituted by the conducting paths of the printed circuit.
DESCRIPTION OF THE INVENTION
According to one aspect of the invention, this object is attained by means of a method of manufacture of a printed circuit such as is specified in claim
1
.
This method allows the mentioned drawbacks of the prior art to be avoided.
Moreover, this method permits a printed circuit of remarkable surface evenness to be obtained. When the printed circuit is integrated in a chip card it is therefore easier to obtain absolutely flat external faces which notably facilitates the printing of possible motifs.
The invention also concerns printed circuits produced by this method, in particular coils or connectors made by this method. The invention concerns in addition chip cards incorporating a coil made by this method and/or a printed circuit made by this method.
Variants of the invention, in particular those specified by the dependent claims, allow, moreover, the density of the circuits obtained and/or of the inductance of the coils obtained to be further increased.
REFERENCES:
patent: 2622054 (1952-12-01), Franklin
patent: 3911716 (1975-10-01), Weglin
patent: 4138924 (1979-02-01), Seebach
patent: 4356627 (1982-11-01), Hoffman
patent: 4555291 (1985-11-01), Tait et al.
patent: 4694283 (1987-09-01), Reeb
patent: 4970495 (1990-11-01), Matsumoto et al.
patent: 4990891 (1991-02-01), Reeb
patent: 5649352 (1997-07-01), Gustafson
patent: 5671525 (1997-09-01), Fidalgo
patent: 5809633 (1998-09-01), Mundigl et al.
patent: 3330738A1 (1985-07-01), None
patent: 2137991 (1972-12-01), None
patent: 26 74724 (1992-02-01), None
patent: 1138628 (1969-01-01), None
patent: 9119302 (1991-12-01), None
Arbes Carl J.
Browning Clifford W.
NagraID S.A.
Woodard Emhardt Naughton Moriarty & McNett
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