Title of Invention	'METHOD OF PRODUCING A TRANSPONDER'
Abstract	Method of producing a transponder (20) comprising the following steps: - Demarcation of different turns (8) of a coil in a sheet (1) including a dielectric substrate covered by at least one conducting layer (2) by stamping said conducting layer by means of a stamping die (5) having cutting surfaces of contact (6) with the superficial conducting layer (2), - Connection of at least one electronic component (25) with the said turns (8), - Mounting of at least one protective sheet (22; 27) covering said coil and said electronic component (25). To facilitate the stamping and to obtain clean incisions, the conducting layer is covered before stamping with a synthetic film. To prevent short circuits from becoming established over the incisions, the latter are preferably filled in with adhesive, varnish or lacquer.

Title of Invention

'METHOD OF PRODUCING A TRANSPONDER'

Abstract

Method of producing a transponder (20) comprising the following steps: - Demarcation of different turns (8) of a coil in a sheet (1) including a dielectric substrate covered by at least one conducting layer (2) by stamping said conducting layer by means of a stamping die (5) having cutting surfaces of contact (6) with the superficial conducting layer (2), - Connection of at least one electronic component (25) with the said turns (8), - Mounting of at least one protective sheet (22; 27) covering said coil and said electronic component (25). To facilitate the stamping and to obtain clean incisions, the conducting layer is covered before stamping with a synthetic film. To prevent short circuits from becoming established over the incisions, the latter are preferably filled in with adhesive, varnish or lacquer.

Full Text	Technical Field This invention concerns a method for producing transponders according to the preamble of claim 1 and a transponder produced according to said method. More specifically, the present invention concerns a method of producing transponders, for example smart cards, including at least one coil and at least one electronic component. Prior Art In the technology of transponders, in particular of chip cards - also called smart cards - of the transponder type, it is often desired to associate 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 renders difficult its integration in a chip card of standard 0.76 mm thickness. Coils are also known in which the turns are constituted directly by the conducting paths of the printed circuit, thus making it possible to avoid any soldering. The paths of the printed circuit are generally realised by photochemical means, which necessitates numerous costly operations and the use of polluting substances. US 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. 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 to allow it to 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 substrate. Other methods of producing coils are known starting from a synthetic film covered by a superficial conducting layer in which the different turns are demarcated by mechanical stamping of the said conducting layer carried out by means of a stamping die. US 2,622,054, EP 0 096 516 of GB 610,058, for example, describe variants of such a method. It is difficult to obtain paths of very narrow width with these stamping techniques. Moreover, the synthetic filrr must have a sufficient thickness to support the stamping pressure and remain sufficiently rigid even in the regions impressed by the stamping die. DE-2 758 204 describes a method of producing a printed circuit, in particular an inductance, 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 metallic layer and simultaneously causes part of the synthetic layer to melt beneath the metal. The method described in the aforementioned document is more specifically adapted for producing different kinds of devices or for coils whose thickness is not critical. 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 production must be kept at a minimum. One object of the present invention is thus to propose an improved method of producing a coil for a transponder, in particular a method allowing further increase of the density of the turns of the coil on a transponder and/or reduction of the thickness of the coil. 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. A preferred variant embodiment is indicated in claim 12, and is based on the observation that it is difficult for clean and precise incisions to be made which delimit the turns of a coil. The difficulty stems from the ductility of metals used for the conducting layer. The stamping die, when it is lowered, tends to sink into and deform the conducting layer without immediately cutting it. When the pressure is sufficient, the conducting layer tears roughly under the die. The edges at the rim of the incision stamped using this method are not very clean and may include burrs; fine and relatively shallow incisions are consequently difficult to achieve, especially when the stamping die is not perfectly sharpened. To reduce the risk of short circuit between the turns on each side of the incision, it is necessary to replace the die frequently and to stamp incisions having a relatively large width, for example by pressing the die down more, which runs counter to the aim of maximising the density of the turns and of limiting the thickness of the coil. Moreover it is difficult to laminate a protective coating on the chip card, generally of PVC, on top of the conducting layer, generally of aluminium. The problem is particularly critical when the sheet of aluminum is not absolutely flat. According to the invention, these difficulties are eliminated by covering beforehand the conducting layer to be stamped with a superficial film, for example with a synthetic film. Tests have shown that this superficial film allows stamping of incisions to be greatly facilitated, and allows much cleaner edges to be obtained at the rim of incisions with the same depth of penetration, using the same die. This method thus allows the mentioned drawbacks of the prior art to be avoided. Accordingly, the present invention relates to method of producing a transponder comprising the following steps: supplying a printed circuit which is made of a dielectric film covered by at least one superficial conducting layer demarcation of different conducting paths in said printed circuit, connection of at least one electronic component on said conducting paths mounting of at least one sheet of protection on said printed circuit characterised in that, said demarcation is realized by mechanical machining said superficial conducting layer by means of a sharp edged cutting tool allowing incisions to be cut separating said conducting paths, without removal or depthwise indentation of conducting material from said conducting layer. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Other aspects and advantages of the invention follow from the description, given by way of example and illustrated by the attached figures which show: Figures 1 to 6, a cutaway view of a portion of coil during six successive stages of manufacture; Figure 7, a perspective view of a chip card including a printed circuit according to a first embodiment of the connection between the coil and the electronic component, both depicted as if the card were transparent; Figure 8, a perspective view of a chip card including a printed circuit according to a second embodiment of the connection between the coil and the electronic component, both depicted as if the card were transparent; and Figure 9, a perspective view of a printed circuit before bending, realised according to a variant embodiment of the invention which includes a bending step. Figure 1 shows a cutaway view of a sheet 1, 4, 2. The sheet 1, 4, 2 is preferably composed of any dielectric substrate 1, for example a synthetic material of the PVC type or of cardboard, covered by a superficial conducting layer 2. Depending upon the application, a flexible film a more rigid substrate is chosen. The substrate 1 can also be composed of a composite or multi-layered material, for example a stratified material comprising a plurality of layers of material, or including local reinforcements, for example of epoxy, fibreglass, carbon fibre, etc., for example, in the zone intended to receive the electronic component. The superficial conducting layer 2 is applied to the layer 1 using a known method and is maintained, for example, by soldering or by means of adhesive 4. The adhesive 4 can, for example be a hot-setting adhesive, a cold-setting adhesive or an adhesive hardening by exposure to UV; it is also possible to use, instead of adhesive, a double-faced adhesive sheet or a thermo-adhesive film. The layer 2 is made of an appropriate metal, for example copper, aluminium, silver or a conducting alloy, or by means of a conductive ink. Optionally, the dielectric substrate 1 can be provided with through holes which will be filled in by the metal of the layer 2 upon lamination under pressure. Points of electrical contact on the lower face of the sheet 1, 4, 2 can thus be realised economically. The upper face (opposite the substrate) of the conducting layer 2 is preferably covered beforehand by a film 3, for example with a film of synthetic material. Metallic sheets, for example sheets of aluminium, covered with a thin, synthetic protective coating, are widely available commercially. The function of this film 3, as will be seen, is mainly to facilitate the stamping of incisions, separating the paths, and thus improves the quality of the incisions obtained. It is also possible to deposit the film 3 on the conductive layer 2 after lamination of the layer 2 and of the substrate 1, for example just before stamping. Figure 2 shows a cutaway view of a stamping die 5 on top of a portion of sheet 1,2,3, 4, before separation of conducting paths. The stamping die 5 has cutting surfaces of contact with the superficial layer 3. The stamping die 5 is lowered, by means not shown, with a pressure just sufficient so that the sharp-edged surfaces of contact 6 perforate and cut the superficial metallic layer 2. Mechanical stops can be used to control the lowering. The profile of the surfaces 6 is sufficiently sharpened that the die cuts fine incisions in the coating 2 without removing conducting material as in the methods of milling and without compression in depth as in the stamping methods of the type described in GB 1,138,628. Here, according to the present invention, the metallic material is incised by surfaces 6. Figure 3 shows a cutaway view of the portion of sheet 1, 2, 3, 4 covered with a metallic layer 2 after demarcation of conducting paths 8. It can be seen that the incisions 7 are just deep enough to pass through the film 3, the metallic layer 2, the adhesive layer 4 and possibly graze the dielectric, synthetic layer 1. In a variant, the incisions completely pass through the film 3 and the superficial metallic layer only, the bottom of the incisions being in the vicinity of the adhesive layer 4. In this way the synthetic film 1 is made as weak as is necessary by machining demarcations between conducting paths 8, and can have a minimal thickness. In a variant embodiment of the invention (not shown) the film 3 intended to facilitate machining of clean incisions is removed after the stamping operation in order to reduce maximally the thickness of the card. To this end, the film 3 is not necessarily pasted on the metallic layer 2, or at least not by means of a permanent adhesive. The stamping causes a lateral compression of the material in the incisions 7. This compression of material causes a bending of the sheet 1, 2, 3, 4, greatly exaggerated in Figure 3, so that the incisions 7 gape widely. To optimise the density of the conducting paths 8 on the printed circuit, the width of the incisions 7 is as fine as possible. The superficial layer 3 allows a very clear cutting of incisions to be obtained so that the risk of short circuit between conducting paths 8, caused by burrs, is greatly reduced. The stamping die has a spiral cutting surface 6 and cuts an inductive element (coil) in the conducting layer 2, the turns of which are constituted by the conducting paths of the printed circuit. Usual supplementary machining operations, for example, boring and soldering, can then be carried out to fix discrete components on the printed circuit thus produced. During the subsequent manufacturing step, which is not illustrated here, certain pre-cut zones of the conducting layer 2 are preferably detached and removed in such a way as to preserve only useful portions of the conducting layer 2. The detached zones can include, for example, the metallic zone A (figures 7 and 8) inside the coil between the turns, the zone C on the exterior of the coil, or a segment of said turns. By doing away with the portions A and C on the inside or outside, respectively, of the turns, these portions of poorly controlled shape can be kept from disturbing the lines of magnetic field of the coil and from modifying the characteristics of the coil in a way difficult to foresee. By detaching a portion B of the turns, the inductance of the coil, for example, can be adjusted. To facilitate the detachment, a non-permanent adhesive 4 is preferably used between the conducting layer 2 and the substrate 1, permitting easy detachment by peeling off of the desired portions A, B, C. In another embodiment, it is also possible to spread adhesive beforehand only on the portions of the metallic layer 2 intended to be maintained on the substrate 1, and leave unglued the residual portions intended to be removed. The dielectric layer, for example of PVC, must be apparent in the portions of the card A, B, C, where the metallic layer 2 has been detached, with the two associated layers 3 and/or 4. The lamination (described further on) of a protective layer 22 on top of the card is thus greatly facilitated since the protective layer is generally chosen in the same dielectric material as the layer 1. In particular, if the portion C of the conducting layer is detached, the adhesion of layers 1 and 22 is ensured on the edges of the card. After the cutting of incisions 7, the method according to the invention preferably includes a step of inserting insulating material in the incisions 7 in order to prevent the incisions from closing up again if the card undergoes deformation. In Figure 4, the incisions are filled with a varnish or a lacquer 9, for example, applied by spraying on the surface of the sheet 1, 2, 3, 4, or applied by serigraphy. The incisions could also be filled and insulated, however, with any insulating material. For example, the surface of the sheet 1, 2, 3, 4, could be coated with a cold-setting or hot-setting adhesive sufficiently fluid to also penetrate to the bottom of the incisions 7, and permitting an upper layer of protection to be adhered on the surface of the cut coil. On account of the maximal spacing of incisions, due to the bending of the sheet, the chosen material 9 easily penetrates to the bottom of the incisions 7. The material 9 allows the irregularities in height of the cut sheet 1, 2, 3, 4, to be amply compensated for. The following manufacturing step, which is optional and is not illustrated here, consists in straightening out the sheet 1, 2, 3, 4, by compressing it between two plates, possibly at high temperature, in such a way as to compensate for the bending. In a first embodiment, the pressure applied during this operation of correction of the bending is sufficient to press down the non-detached portions of the conducting layer 2, 3, 4 into the thickness of the dielectric 1. It is possible to push down the layer 2 until it becomes flush with the upper surface of the dielectric layer 1, thus improving substantially the surface evenness of the layered arrangement. In a second embodiment, the difference in height resulting from detachment of portions A, B and/or C of the conducting layer 2 is compensated for by laminating over the dielectric layer 1 an intermediate dielectric sheet (not shown) having substantially the thickness of the layers 2, 3, and, if applicable, 9, and whose shape corresponds to that of the detached portions A, B, C. In a third embodiment, this difference in height is compensated for beforehand by laminating over the dielectric 1, before the actual application of the layer 2, 3, a dielectric sheet (not shown) having substantially the thickness of the layers 2, 3, 9, and whose shape corresponds to that of the portions without paths A, B, C. In this case, the conducting layer 2, 3, is cut in the desired shape even before its actual lamination on the layer 1. The following manufacturing step, which is not illustrated here, involves the mounting of at least one electric or electronic component on the sheet 1, 2, 3, 4. This component can be fixed on the sheet by any means, for example by gluing or by bonding. In another embodiment, discussed in more detail further below, the component is simply placed at the appropriate place on the sheet and is maintained only by the upper protective coating. Depending upon the thickness of the component, it could be necessary to provide a recess in the sheet 1, 2, 3, 4 to accommodate the component so that no bulging on the surface of the card is created. The accommodation can be machined in one or more layers of the sheet 1, 2, 3, 4, for example by stamping, before, during or after the lamination of these layers. It is also possible to machine this recess by means of the stamping die 5 which in this case has one or more portions allowing the material of the sheet 1, 2, 3, 4 to be pressed in or pushed back depth-wise in the zone intended to accommodate the component or in any zone likely to have an excessive thickness, for example in the zone of the bridge between the coil and the electric component. Figure 5 illustrates the following step of manufacture of the transponder according to the invention. During this step, the sheet 1, 2, 3, 4 according to the invention, covered by the layer 9 filling in at least partially the incisions 7, is laminated between (at least) one upper protective sheet 22 and (at least) one lower protective sheet 27. Each sheet of protection is mounted preferably under pressure, for example by means of a layer of adhesive 220, respectively 270. The layer of adhesive 220 allowing mounting of the upper protective sheet 22 is preferably sufficiently thick and fluid to compensate for irregularities in the thickness of the surface of the card, in particular at the level of the coil and of the electronic component or components, and to fill in the residual gaps in the incisions 7. The protective sheets 22, 27 can also be laminated by hot pressing without the adhesive layer 220, 270. In this case the melted material of the sheets also contributes to compensating for the irregularities in thickness. Moreover, in a known way, windows, for example for the electrical contacts, and recesses to accommodate the components in the card can be provided in the sheet 22 and/or 27. The external face of sheets 22 and 27 is sufficiently smooth to allow printing of the finished card in the case where the sheets 22, 27 have not been printed beforehand. In another embodiment of the invention, the lower protective sheet 27 is omitted. In this case, the lower external surface of the card is directly constituted by the surface of the dielectric layer 1 which must have sufficient surface qualities to allow printing and, if need be, reliable functioning in the automatic machines. In another embodiment, the chip card is made by placing the sheet 1, 2, 3, 4 in a mould and by injecting material around this sheet (moulding over). In this embodiment it can be advantageous to laminate a supplementary dielectric sheet 1 over the assembly 1, 2, 3, 4 in such a way that the result is a sheet moulded over as symmetrically as possible. In any case, the compensation of the bending of the sheet is less critical in this embodiment. Figure 6 shows a section through a portion of the finished card. It can be noted that under the joint effect of the pressure applied upon lamination of the protective sheets 22, 27 and of the rigidity of these sheets, bending of the card is stopped so that the method allows absolutely flat cards to be obtained. The mentioned step of straightening out the sheet by compression before the lamination of the sheets 22, 27 is not generally necessary in the case where the sheets 22, 27 undergo cold lamination. It can be noted that in the portions A, B, C without conducting paths 2, 3, 4, 9, the layer 220 can be laminated directly on the dielectric layer 1, or, where the case arises, on the layer mentioned to compensate height. Optimal adherence is thus ensured. Several chip cards are preferably made from a single sheet 1, 2, 3, 4. It is possible, for example, to distribute a large number of coils, disposed in a matrix, on a single sheet of sufficient size or on a continuous strip. The different coils on the sheet can be machined simultaneously, by means of a single stamping die of large dimension, or successively by means of the same die placed between each cut (stepper). In both cases, an operation of fractionation (not shown) of the sheet and of cutting of the individual cards is necessary after lamination of the various layers. Above we discussed only briefly the connection of the electronic component or components with the turns 8 of the coil thus machined. Figures 7 to 9 illustrate three embodiments of this connection, in the case where the transponder is constituted by a chip card having an integrated circuit 25 and a coil 8. The integrated circuit 25, which can be accommodated in a recess (not shown) in one or more layers of the card, is connected to two ends of the inductive element 8. The connection between the circuit 25 and the internal turn of the coil can be made directly in the case, shown in Figure 7, where the circuit 25 is disposed between the turns of the coil. The connection with the external turn of the coil 8 must be made, on the other hand, by the way of a bridge 80 over the turns 8. The bridge can, for example, be constituted by a simple wire soldered over or under the conducting paths 8. In the case of a circuit with several conducting layers, it is also possible to use one of the metallised layers to make the bridge, or to integrate the bridge into the substrate 1 before lamination of the conducting layers 2. In Figure 7, the bridge has been made very simply by detaching (after, if the case applies, atomising the insulating material) an appropriate length of the last turn of the coil and by bending back, if necessary, this length over the other turns, or possibly under the other turns by passing through a through hole provided for this purpose. The electrical insulation between the length 80 and the other turns is achieved solely by means of the atomised layer 9 and/or by the layer 3. The end of the length 80 can be glued between the turns or simply maintained owing to the rigidity of the metallic material 2. A connection pin 250 of the component 25 is thus put in electrical contact with this portion 80, respectively with the internal turn of the coil. In Figure 8, the integrated circuit 25 is mounted straddling over the turns 8. This arrangement makes the bridge 80 superfluous; a connection pin 250 of the circuit 25 is connected electrically directly to the external turn of the coil 8 whereas another pin 250 is connected directly to the internal turn of this coil. This variant is especially simple to achieve, but limits the choice of circuits 25 which can be used and has the drawback of adding the thickness of the coil to that of the circuit 25 or of necessitating provision of a recess or a lowering of the turns at that spot. Figure 9 shows a printed circuit in an intermediate stage of manufacture, according to a variant of the method of connection between the circuit 25 and the external portion 26 of the inductive element 23. This variant is intended, for example, for security tags for merchandise but can also be applied to chip cards or to, other devices. A printed circuit including a portion in the shape of an inductiv^ element 23 is machined in the way described above on a flexible substrate 1, for example on a support of cardboard. The inductive element 23 occupies only about half of the total surface of the substrate 1. One of the ends 26 of the inductive element 23 extends on the other half of the sheet 21. This end can, for example, be constituted by a discrete wire soldered to the external portion of the inductive element 23. In a variant, this end 26 is machined by stamping the superficial conducting layer 2, in the way described above. The rest of the superficial layer 2 on this half of the sheet 21 can then be detached by leaving only the end 26 remaining. The component 25 is mounted in a zone of the sheet not occupied by the conducting paths, in this example on the inside of the inductive element 23. The component 25 can be, for example, an integrated circuit or a fuse. It is connected to the internal portion of the inductive element 23 by way of a zone of conductive contact 51. In addition, the component is connected to a second zone of conductive contact 52 intended to establish the connection with the end 26 of the inductive element 23. After machining of conducting paths constituting the coil and the assembly of the element 25, the half of the sheet 21 occupied by the conducting paths is covered with an insulating layer (not shown). To do this, the inductive element 23 can, for example, be covered with a layer of insulating lacquer or an insulating adhesive sheet. The zone of contact 52, however, is not covered by the insulating layer. The sheet 21 is then folded over on itself along a folding axis 53 so that the two halves formed are superimposed. The end 26 of the inductive element 23 is thus put into electrical contact with the zone of contact 52. A connection is thus formed very simply between the external portion of the inductive element 23 and the element 25. The two folded halves of the sheet 21 can be fixed with respect to one another, for example by gluing. The connection pins 250 of the circuit 25 (figures 7 and 8) can be glued, soldered or fixed by bonding with the turns 8. It has been observed in conventional transponders, however, that such soldering sometimes breaks when the card is folded or deformed a large number of times. To lessen this risk, in a preferred embodiment of the invention the connection pins 250 are simply disposed over the turns 8, without soldering or any particular fixing. The integrated circuit is thus maintained pressed against the paths 8 by the protective layer 22. This arrangement allows the pins to slide slightly over the paths 8 when the card is bent and to return to their initial position when the card regains its shape. Owing to the elasticity of the upper protective layer 22, the pins 25 remain continuously pressed with a certain pressure against the contact portion of the turns 8, which enables an electrical contact of good quality to be ensured even after the card has been bent a number of times or has been deformed. Of course it is important to ensure that the zone of paths 8 intended to come into contact with the pins of the circuit 25 are not covered by insulating material 3 or 9. To this end, this zone can, for example, be protected during the lamination of film 2 or the spraying of material 9. It is also possible to remove locally these layers 3, 9 before mounting of the circuit 25. One skilled in the art will note that this supplementary aspect of the invention is independent from the manufacture of the coil and can be used to connect any type of wound or machined coil to any type of electronic component. Depending upon the desired application and the available space remaining on the card, components other than the integrated circuit 25 and the coil 8 can be integrated on the printed circuit 21. It is possible, for example, to place on the circuit a battery (not shown) which could be recharged from the outside by means of an inductive element, for example by means of element 23. Ideally these other components would be mutually connected and also connected to the elements 8 and 25 by means of conducting paths machined in the superficial conducting layer or layers 2 in the way described above. One skilled in the art will note here that, contrary to the majority of known prior art techniques, the manufacture of conducting paths 8 on the printed circuit by the method according to the invention creates remarkably few irregularities in the surface, which irregularities are moreover compensated for by the adhesive or upon fusion of the upper layers. It is thus relatively easy to mount the upper sheet 22 while obtaining an external surface which is absolutely flat. Other methods of lamination of chip cards can be used with the coils according to the invention, for example the methods which are the subject matter of the patent application W094/22111, the text of which is incorporated here by reference, or prior art methods mentioned in said document. The method according to the invention can be extended to the production of double face circuits. The incisions 7 delimiting the paths 8 on each face are preferably made in a single operation. To do this, the dielectric film 1, covered on each face with a conducting layer 2, is pressed between two stamping dies (not shown), each of which has cutting surfaces of contact 6 with the metallic surface. It is nevertheless also possible to achieve the incisions 7 on the two faces in two operations, one face and then the other. Since the method according to the invention can be used even with dielectric films 1 of very fine thickness, this variant allows capacitive elements to be made very easily whose plates are formed by the metallic paths superimposed on each face. These components can, for example, be combined with inductive elements to constitute LC resonant circuits of reduced volume. If the capacitive coupling between the paths on the two faces must be reduced, topographies of conducting paths on the two faces having a minimum of overlapping are chosen instead. The method according to the invention can be extended to the production of transponders with multi-layer circuits, that is having a plurality of layers of conducting material 2 superimposed and machined so as to define a plurality of levels of paths. In this case, the dielectric film 1 is covered with a plurality of conducting layers 2 insulated by a plurality of layers of adhesive or by a supplementary layer of insulation between the two metallic layers, for example a supplementary synthetic layer. The cutting tool used to separate the conducting paths 8 is designed to cut the incisions deep enough to pass through all the metallic layers 2 in a single operation. The topography constituted by the conducting paths 8 on the different conducting layers is thus identical. By connecting the different layers to one another at appropriate places, for example with metallised holes, this arrangement allows circuits of high inductance to be achieved. It is of course possible to produce multi-layered circuits with variable topographies on the different layers by using a die machining incisions 7 of variable depth, certain incisions passing through all the superimposed metallised layers, whereas others only pass through the top layer, and still others pass through a plurality of layers but not all layers. In this way topologies having different paths on different layers can be achieved. By laminating the layers after demarcation of paths by machining, a very great amount of freedom can be attained with respect to the configuration of the different layers. For example, it is possible to use one or more intermediate layers as connection layers, allowing bridges for the upper layers to be achieved. It is also possible to dispose a plurality of layers of paths back to back, and thus to obtain, for example, double face circuits by lamination of two simple circuits face to face. One skilled in the art will of course understand that it is possible to combine freely the variants mentioned above. For example, it is possible to achieve circuits covered with a plurality of superficial conducting coatings on each face. Besides manufacture of chip cards, the method can also be used to produce any type of transponder, for example used for tagging objects or animals or for surveillance of articles in a shop. Depending upon the application, the shape and the characteristics of the coil could be quite different. In the case of a chip card for applications of the banking transaction or payment type, a chip card provided with a coil permitting communication with the outside at high frequency is preferred, preferably with a frequency of more than 50 kHz, for example 10 MHz. The method according to the invention is also perfectly suitable for production of flexible printed circuits. Such circuits are used, for example, to manufacture flexible plug connectors. Moreover the method is perfectly adapted to any case where a maximal density of paths on the surface of a printed circuit is required. One skilled in the art will realise moreover that the method can also be used in combination with any other known method of printed circuit production. It is possible, for example, to make cards on which part of the conducting paths are obtained or separated by electrochemical means, the rest being machined in the way specified in the claims. One skilled in the art will realise that the term "printed circuit" has been used in this specification and in the claims even though the invention applies particularly to circuits and to cards produced without the step of printing in the usual sense. WE CLAIM: 1. Method of producing a transponder (20) comprising the following steps: supplying a printed circuit (21; 31) which is made of a dielectric film (1) covered by at least one superficial conducting layer (2) demarcation of different conducting paths (8) in said printed circuit (21; 31), connection of at least one electronic component (25) on said conducting paths (8) mounting of at least one sheet of protection (22, 27) on said printed circuit (21; 31) characterised in that, said demarcation is realized by mechanical machining said superficial conducting layer (2) by means of a sharp edged cutting tool (5, 10) allowing incisions (7) to be cut separating said conducting paths, without removal or depthwise indentation of conducting material from said conducting layer (2). 2. Method as claimed in claim 1, wherein said dielectric film (1) is covered by a plurality of mutually insulated, superimposed conducting layers (2), and wherein said incisions (7) separating the conducting paths (8) are machined so as to traverse said plurality of superimposed conducting layers. 3. Method as claimed in claim 1, wherein each face of said dielectric film (1) is covered by one or more superimposed superficial conducting layers (2), different conducting paths (8) being demarcated on each face by machining of incisions (7) in said conducting layers. 4. Method as claimed in claim 1, wherein said cutting tool is a stamping die (5) having sharp-edged surfaces of contact (6) with the superficial conducting layer (2). 5. Method as claimed in claim 1, wherein said cutting tool is a knife or a blade (10) cutting sequentially incisions (7) separating the conducting paths (8) according to a pattern recorded beforehand in an electronic memory. 6. Method as claimed in claim 1, wherein said method comprises a step of machining in said film at least one accommodation (24) intended to accommodate said at least one electronic component (25) connected to said conducting paths (8). 7. Method as claimed in claim 1, wherein said comprises a step of covering part of the conducting paths (8) by an insulating layer and a step of folding said dielectric film along a folding axis (53) in such a way as to create at least one electrical bridge (26) between portions (26, 52) of electric paths (8) not covered by said insulating layer. 8. Method as claimed in claim 1, wherein said at least one sheet of protection (22; 27) is mounted by gluing on said printed circuit (21, 31). 9. Method as claimed in claim 1, wherein it comprises a step of insertion of at least one material (9, 22) in said incisions (7) to ensure an electrical isolation of different conducting paths (8). 10. Method as claimed in claim 8 or 9, wherein said at least one sheet of protection (22; 27) is mounted by hot setting adhesive on said printed circuit (21; 31). 11. Method as claimed in claim 1, wherein a step of preparation in said at least one sheet of protection of a window allowing access from the exterior of the transponder to the electronic component or to contacts connected to said electronic component. 12. Method as claimed in claim 1, wherein said conducting layer (2) is covered, before stamping, with a superficial film (3) intended to facilitate stamping. 13. Method as claimed in claim 1, wherein said dielectric substrate has local reinforcements in the zone of the electronic component. 14. Method as claimed in claim 1, wherein said dielectric film (1) has at least one through hole which will fill the material of said conducting layer. 15. Method as claimed in claim 9, wherein said material (9) comprises a lacquer or a varnish applied on said conducting path after stamping said incisions (7). 16. Method as claimed in claim 9, wherein said material (220) comprises an adhesive for mounting a sheet of protection (22), glued on said sheet after stamping. 17. Method as claimed in claim 9, wherein said sheet (1, 2,3, 4) is bent so as to eliminate said incisions (7) upon insertion of said material (9, 220). 18. Method as claimed in claim 1, wherein it comprises a step of flattening said sheet (1, 2, 3, 4) by compression. 19. Method as claimed in claim 1, wherein it comprises a step of folding at least a portion (80) of said paths in such a way to create at least one electrical bridge (80) over said paths. 20. Method as claimed in claim 1, wherein said conducting layer (2) is mounted on said dielectric film (1) by means of a non- permanent glue (4) and wherein it comprises a step of peeling off at least one portion (A, B, C) of said conducting layer after said step of stamping incisions. 21. Method as claimed in claim 20, wherein said at least one peeled-off portion has at least the portion (A) of said conducting layer inside said turns of the coil. 22. Method as claimed in any one of the claims 20 or 21, wherein said at least one peeled-off portion has at least the portion (C) of said conducting layer outside said turns of the coil. 23. Method as claimed in any one of the claims 20 to 22, wherein said at least one peeled-off portion has at least a segment (80) of said turns. 24. Method as claimed in claim 23, wherein the inductance of the coil is adjusted by peeling off an appropriate length of said turns of the coil. 25. Method as claimed in any one of the claims 23 or 24, wherein, after peeling off of a segment (80) of said turns (8) previously covered with an insulating layer, said segment is used to constitute an electrical bridge (80). 26. Method as claimed in claim 1, wherein said conducting layer is glued on said dielectric substrate only on certain portions in such a way as to facilitate the subsequent peeling off of residual portions (A, B, C). 27. Method as claimed in claim 1, wherein it comprises a step of indenting said conducting layer (2, 3, 4) in the thickness of the dielectric film (1) to improve the surface evenness. 28. Method as claimed in any one of the claims 20 to 27, wherein it comprises a step of lamination of an intermediate sheet of dielectric having the thickness of said conducting layer (2, 3, 9) and whose shape corresponds to that of the portions (A, B, C) without paths in order to improve the surface evenness. 29. Method as claimed in claim 1, wherein it comprises a step of mounting at least one electronic component (25) straddling the said turns of the coil. 30. Method as claimed in claim 1, wherein at least one of said electronic components (25) is directly positioned, without soldering, on the portions of contact of the turns of the coil (8). 31. Method as claimed in claim 1, wherein it comprises a step of mounting a second sheet of protection (27) on the face opposite that provided with the first sheet of protection. 32. Method of producing a transponder (20), substantially as herein described with reference to and as illustrated in the accompanying drawings.

Full Text

Technical Field
This invention concerns a method for producing transponders according to the preamble of claim 1 and a transponder produced according to said method. More specifically, the present invention concerns a method of producing transponders, for example smart cards, including at least one coil and at least one electronic component.
Prior Art
In the technology of transponders, in particular of chip cards - also called smart cards - of the transponder type, it is often desired to associate 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 renders difficult its integration in a chip card of standard 0.76 mm thickness.
Coils are also known in which the turns are constituted directly by the conducting paths of the printed circuit, thus making it possible to avoid any soldering. The paths of the printed circuit are generally realised by photochemical means, which necessitates numerous costly operations and the use of polluting substances.
US 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. 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 to allow it to 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 substrate.
Other methods of producing coils are known starting from a synthetic film covered by a superficial conducting layer in which the different turns are demarcated by mechanical stamping of the said conducting layer carried out by means of a stamping die. US 2,622,054, EP 0 096 516 of GB 610,058, for example, describe variants of such a method. It is difficult to obtain paths of very narrow width with these stamping techniques. Moreover, the synthetic filrr must have a sufficient thickness to support the stamping pressure and remain sufficiently rigid even in the regions impressed by the stamping die.
DE-2 758 204 describes a method of producing a printed circuit, in particular an inductance, 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 metallic layer and simultaneously causes part of the synthetic layer to melt beneath the metal.
The method described in the aforementioned document is more specifically adapted for producing different kinds of devices or for coils whose thickness is not critical. 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 production must be kept at a minimum.
One object of the present invention is thus to propose an improved method of producing a coil for a transponder, in particular a method allowing further increase of the density of the turns of the coil on a transponder and/or reduction of the thickness of the coil.
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.
A preferred variant embodiment is indicated in claim 12, and is based on the observation that it is difficult for clean and precise incisions to be made which delimit the turns of a coil. The difficulty stems from the ductility of metals used for the conducting layer. The stamping die, when it is lowered, tends to sink into and deform the conducting layer without immediately cutting it. When the pressure is sufficient, the conducting layer tears roughly under the die. The edges at the rim of the incision stamped using this method are not very clean and may include burrs; fine and relatively shallow incisions are consequently difficult to achieve, especially when the stamping die is not perfectly sharpened. To reduce the risk of short circuit between the turns on each side of the incision, it is necessary to replace the die frequently and to stamp incisions having a relatively large width, for example by pressing the die down more, which runs counter to the aim of maximising the density of the turns and of limiting the thickness of the coil.
Moreover it is difficult to laminate a protective coating on the chip card, generally of PVC, on top of the conducting layer, generally of aluminium. The
problem is particularly critical when the sheet of aluminum is not absolutely flat.
According to the invention, these difficulties are eliminated by covering beforehand the conducting layer to be stamped with a superficial film, for example with a synthetic film.
Tests have shown that this superficial film allows stamping of incisions to be greatly facilitated, and allows much cleaner edges to be obtained at the rim of incisions with the same depth of penetration, using the same die.
This method thus allows the mentioned drawbacks of the prior art to be avoided.
Accordingly, the present invention relates to method of producing a transponder comprising the following steps: supplying a printed circuit which is made of a dielectric film covered by at least one superficial conducting layer demarcation of different conducting paths in said printed circuit, connection of at least one electronic component on said conducting paths mounting of at least one sheet of protection on said printed circuit characterised in that, said demarcation is realized by mechanical machining said superficial conducting layer by means of a sharp edged cutting tool allowing incisions to be cut separating said conducting paths, without removal or depthwise indentation of conducting material from said conducting layer.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other aspects and advantages of the invention follow from the description, given by way of example and illustrated by the attached figures which show:
Figures 1 to 6, a cutaway view of a portion of coil during six successive stages of manufacture;
Figure 7, a perspective view of a chip card including a printed circuit according to a first embodiment of the connection between the coil and the electronic component, both depicted as if the card were transparent;
Figure 8, a perspective view of a chip card including a printed circuit according to a second embodiment of the connection between the coil and the electronic component, both depicted as if the card were transparent; and
Figure 9, a perspective view of a printed circuit before bending, realised according to a variant embodiment of the invention which includes a bending step.
Figure 1 shows a cutaway view of a sheet 1, 4, 2. The sheet 1, 4, 2 is preferably composed of any dielectric substrate 1, for example a synthetic material of the PVC type or of cardboard, covered by a superficial conducting layer 2. Depending upon the application, a flexible film a more rigid substrate
is chosen. The substrate 1 can also be composed of a composite or multi-layered material, for example a stratified material comprising a plurality of layers of material, or including local reinforcements, for example of epoxy, fibreglass, carbon fibre, etc., for example, in the zone intended to receive the electronic component.
The superficial conducting layer 2 is applied to the layer 1 using a known method and is maintained, for example, by soldering or by means of adhesive 4. The adhesive 4 can, for example be a hot-setting adhesive, a cold-setting adhesive or an adhesive hardening by exposure to UV; it is also possible to use, instead of adhesive, a double-faced adhesive sheet or a thermo-adhesive film. The layer 2 is made of an appropriate metal, for example copper, aluminium, silver or a conducting alloy, or by means of a conductive ink.
Optionally, the dielectric substrate 1 can be provided with through holes which will be filled in by the metal of the layer 2 upon lamination under pressure. Points of electrical contact on the lower face of the sheet 1, 4, 2 can thus be realised economically.
The upper face (opposite the substrate) of the conducting layer 2 is preferably covered beforehand by a film 3, for example with a film of synthetic material. Metallic sheets, for example sheets of aluminium, covered with a thin, synthetic protective coating, are widely available commercially. The function of this film 3, as will be seen, is mainly to facilitate the stamping of incisions, separating the paths, and thus improves the quality of the incisions obtained. It is also possible to deposit the film 3 on the conductive layer 2 after lamination of the layer 2 and of the substrate 1, for example just before stamping.
Figure 2 shows a cutaway view of a stamping die 5 on top of a portion of sheet 1,2,3, 4, before separation of conducting paths. The stamping die 5 has cutting surfaces of contact with the superficial layer 3.
The stamping die 5 is lowered, by means not shown, with a pressure just sufficient so that the sharp-edged surfaces of contact 6 perforate and cut the superficial metallic layer 2. Mechanical stops can be used to control the
lowering. The profile of the surfaces 6 is sufficiently sharpened that the die cuts fine incisions in the coating 2 without removing conducting material as in the methods of milling and without compression in depth as in the stamping methods of the type described in GB 1,138,628. Here, according to the present invention, the metallic material is incised by surfaces 6.
Figure 3 shows a cutaway view of the portion of sheet 1, 2, 3, 4 covered with a metallic layer 2 after demarcation of conducting paths 8. It can be seen that the incisions 7 are just deep enough to pass through the film 3, the metallic layer 2, the adhesive layer 4 and possibly graze the dielectric, synthetic layer 1. In a variant, the incisions completely pass through the film 3 and the superficial metallic layer only, the bottom of the incisions being in the vicinity of the adhesive layer 4. In this way the synthetic film 1 is made as weak as is necessary by machining demarcations between conducting paths 8, and can have a minimal thickness.
In a variant embodiment of the invention (not shown) the film 3 intended to facilitate machining of clean incisions is removed after the stamping operation in order to reduce maximally the thickness of the card. To this end, the film 3 is not necessarily pasted on the metallic layer 2, or at least not by means of a permanent adhesive.
The stamping causes a lateral compression of the material in the incisions 7. This compression of material causes a bending of the sheet 1, 2, 3, 4, greatly exaggerated in Figure 3, so that the incisions 7 gape widely.
To optimise the density of the conducting paths 8 on the printed circuit, the width of the incisions 7 is as fine as possible. The superficial layer 3 allows a very clear cutting of incisions to be obtained so that the risk of short circuit between conducting paths 8, caused by burrs, is greatly reduced.
The stamping die has a spiral cutting surface 6 and cuts an inductive element (coil) in the conducting layer 2, the turns of which are constituted by the conducting paths of the printed circuit. Usual supplementary machining
operations, for example, boring and soldering, can then be carried out to fix discrete components on the printed circuit thus produced.
During the subsequent manufacturing step, which is not illustrated here, certain pre-cut zones of the conducting layer 2 are preferably detached and removed in such a way as to preserve only useful portions of the conducting layer 2. The detached zones can include, for example, the metallic zone A (figures 7 and 8) inside the coil between the turns, the zone C on the exterior of the coil, or a segment of said turns. By doing away with the portions A and C on the inside or outside, respectively, of the turns, these portions of poorly controlled shape can be kept from disturbing the lines of magnetic field of the coil and from modifying the characteristics of the coil in a way difficult to foresee. By detaching a portion B of the turns, the inductance of the coil, for example, can be adjusted. To facilitate the detachment, a non-permanent adhesive 4 is preferably used between the conducting layer 2 and the substrate 1, permitting easy detachment by peeling off of the desired portions A, B, C. In another embodiment, it is also possible to spread adhesive beforehand only on the portions of the metallic layer 2 intended to be maintained on the substrate 1, and leave unglued the residual portions intended to be removed.
The dielectric layer, for example of PVC, must be apparent in the portions of the card A, B, C, where the metallic layer 2 has been detached, with the two associated layers 3 and/or 4. The lamination (described further on) of a protective layer 22 on top of the card is thus greatly facilitated since the protective layer is generally chosen in the same dielectric material as the layer 1. In particular, if the portion C of the conducting layer is detached, the adhesion of layers 1 and 22 is ensured on the edges of the card.
After the cutting of incisions 7, the method according to the invention preferably includes a step of inserting insulating material in the incisions 7 in order to prevent the incisions from closing up again if the card undergoes deformation. In Figure 4, the incisions are filled with a varnish or a lacquer 9,

for example, applied by spraying on the surface of the sheet 1, 2, 3, 4, or applied by serigraphy. The incisions could also be filled and insulated, however, with any insulating material. For example, the surface of the sheet 1, 2, 3, 4, could be coated with a cold-setting or hot-setting adhesive sufficiently fluid to also penetrate to the bottom of the incisions 7, and permitting an upper layer of protection to be adhered on the surface of the cut coil. On account of the maximal spacing of incisions, due to the bending of the sheet, the chosen material 9 easily penetrates to the bottom of the incisions 7. The material 9 allows the irregularities in height of the cut sheet 1, 2, 3, 4, to be amply compensated for.
The following manufacturing step, which is optional and is not illustrated here, consists in straightening out the sheet 1, 2, 3, 4, by compressing it between two plates, possibly at high temperature, in such a way as to compensate for the bending.
In a first embodiment, the pressure applied during this operation of correction of the bending is sufficient to press down the non-detached portions of the conducting layer 2, 3, 4 into the thickness of the dielectric 1. It is possible to push down the layer 2 until it becomes flush with the upper surface of the dielectric layer 1, thus improving substantially the surface evenness of the layered arrangement.
In a second embodiment, the difference in height resulting from detachment of portions A, B and/or C of the conducting layer 2 is compensated for by laminating over the dielectric layer 1 an intermediate dielectric sheet (not shown) having substantially the thickness of the layers 2, 3, and, if applicable, 9, and whose shape corresponds to that of the detached portions A, B, C.
In a third embodiment, this difference in height is compensated for beforehand by laminating over the dielectric 1, before the actual application of the layer 2, 3, a dielectric sheet (not shown) having substantially the thickness of the layers 2, 3, 9, and whose shape corresponds to that of the portions
without paths A, B, C. In this case, the conducting layer 2, 3, is cut in the desired shape even before its actual lamination on the layer 1.
The following manufacturing step, which is not illustrated here, involves the mounting of at least one electric or electronic component on the sheet 1, 2, 3, 4. This component can be fixed on the sheet by any means, for example by gluing or by bonding. In another embodiment, discussed in more detail further below, the component is simply placed at the appropriate place on the sheet and is maintained only by the upper protective coating. Depending upon the thickness of the component, it could be necessary to provide a recess in the sheet 1, 2, 3, 4 to accommodate the component so that no bulging on the surface of the card is created. The accommodation can be machined in one or more layers of the sheet 1, 2, 3, 4, for example by stamping, before, during or after the lamination of these layers. It is also possible to machine this recess by means of the stamping die 5 which in this case has one or more portions allowing the material of the sheet 1, 2, 3, 4 to be pressed in or pushed back depth-wise in the zone intended to accommodate the component or in any zone likely to have an excessive thickness, for example in the zone of the bridge between the coil and the electric component.
Figure 5 illustrates the following step of manufacture of the transponder according to the invention. During this step, the sheet 1, 2, 3, 4 according to the invention, covered by the layer 9 filling in at least partially the incisions 7, is laminated between (at least) one upper protective sheet 22 and (at least) one lower protective sheet 27. Each sheet of protection is mounted preferably under pressure, for example by means of a layer of adhesive 220, respectively 270. The layer of adhesive 220 allowing mounting of the upper protective sheet 22 is preferably sufficiently thick and fluid to compensate for irregularities in the thickness of the surface of the card, in particular at the level of the coil and of the electronic component or components, and to fill in the residual gaps in the incisions 7. The protective sheets 22, 27 can also be laminated by hot pressing without the adhesive layer 220, 270. In this case the melted material
of the sheets also contributes to compensating for the irregularities in thickness. Moreover, in a known way, windows, for example for the electrical contacts, and recesses to accommodate the components in the card can be provided in the sheet 22 and/or 27. The external face of sheets 22 and 27 is sufficiently smooth to allow printing of the finished card in the case where the sheets 22, 27 have not been printed beforehand.
In another embodiment of the invention, the lower protective sheet 27 is omitted. In this case, the lower external surface of the card is directly constituted by the surface of the dielectric layer 1 which must have sufficient surface qualities to allow printing and, if need be, reliable functioning in the automatic machines.
In another embodiment, the chip card is made by placing the sheet 1, 2,
3, 4 in a mould and by injecting material around this sheet (moulding over). In
this embodiment it can be advantageous to laminate a supplementary dielectric
sheet 1 over the assembly 1, 2, 3, 4 in such a way that the result is a sheet
moulded over as symmetrically as possible. In any case, the compensation of
the bending of the sheet is less critical in this embodiment.
Figure 6 shows a section through a portion of the finished card. It can be noted that under the joint effect of the pressure applied upon lamination of the protective sheets 22, 27 and of the rigidity of these sheets, bending of the card is stopped so that the method allows absolutely flat cards to be obtained. The mentioned step of straightening out the sheet by compression before the lamination of the sheets 22, 27 is not generally necessary in the case where the sheets 22, 27 undergo cold lamination.
It can be noted that in the portions A, B, C without conducting paths 2, 3,
4, 9, the layer 220 can be laminated directly on the dielectric layer 1, or, where
the case arises, on the layer mentioned to compensate height. Optimal
adherence is thus ensured.
Several chip cards are preferably made from a single sheet 1, 2, 3, 4. It is possible, for example, to distribute a large number of coils, disposed in a
matrix, on a single sheet of sufficient size or on a continuous strip. The different coils on the sheet can be machined simultaneously, by means of a single stamping die of large dimension, or successively by means of the same die placed between each cut (stepper). In both cases, an operation of fractionation (not shown) of the sheet and of cutting of the individual cards is necessary after lamination of the various layers.
Above we discussed only briefly the connection of the electronic component or components with the turns 8 of the coil thus machined. Figures 7 to 9 illustrate three embodiments of this connection, in the case where the transponder is constituted by a chip card having an integrated circuit 25 and a coil 8.
The integrated circuit 25, which can be accommodated in a recess (not shown) in one or more layers of the card, is connected to two ends of the inductive element 8. The connection between the circuit 25 and the internal turn of the coil can be made directly in the case, shown in Figure 7, where the circuit 25 is disposed between the turns of the coil. The connection with the external turn of the coil 8 must be made, on the other hand, by the way of a bridge 80 over the turns 8. The bridge can, for example, be constituted by a simple wire soldered over or under the conducting paths 8. In the case of a circuit with several conducting layers, it is also possible to use one of the metallised layers to make the bridge, or to integrate the bridge into the substrate 1 before lamination of the conducting layers 2.
In Figure 7, the bridge has been made very simply by detaching (after, if the case applies, atomising the insulating material) an appropriate length of the last turn of the coil and by bending back, if necessary, this length over the other turns, or possibly under the other turns by passing through a through hole provided for this purpose. The electrical insulation between the length 80 and the other turns is achieved solely by means of the atomised layer 9 and/or by the layer 3. The end of the length 80 can be glued between the turns or simply maintained owing to the rigidity of the metallic material 2. A connection pin 250
of the component 25 is thus put in electrical contact with this portion 80, respectively with the internal turn of the coil.
In Figure 8, the integrated circuit 25 is mounted straddling over the turns 8. This arrangement makes the bridge 80 superfluous; a connection pin 250 of the circuit 25 is connected electrically directly to the external turn of the coil 8 whereas another pin 250 is connected directly to the internal turn of this coil. This variant is especially simple to achieve, but limits the choice of circuits 25 which can be used and has the drawback of adding the thickness of the coil to that of the circuit 25 or of necessitating provision of a recess or a lowering of the turns at that spot.
Figure 9 shows a printed circuit in an intermediate stage of manufacture, according to a variant of the method of connection between the circuit 25 and the external portion 26 of the inductive element 23. This variant is intended, for example, for security tags for merchandise but can also be applied to chip cards or to, other devices. A printed circuit including a portion in the shape of an inductiv^ element 23 is machined in the way described above on a flexible substrate 1, for example on a support of cardboard. The inductive element 23 occupies only about half of the total surface of the substrate 1. One of the ends 26 of the inductive element 23 extends on the other half of the sheet 21. This end can, for example, be constituted by a discrete wire soldered to the external portion of the inductive element 23. In a variant, this end 26 is machined by stamping the superficial conducting layer 2, in the way described above. The rest of the superficial layer 2 on this half of the sheet 21 can then be detached by leaving only the end 26 remaining.
The component 25 is mounted in a zone of the sheet not occupied by the conducting paths, in this example on the inside of the inductive element 23. The component 25 can be, for example, an integrated circuit or a fuse. It is connected to the internal portion of the inductive element 23 by way of a zone of conductive contact 51. In addition, the component is connected to a second
zone of conductive contact 52 intended to establish the connection with the end 26 of the inductive element 23.
After machining of conducting paths constituting the coil and the assembly of the element 25, the half of the sheet 21 occupied by the conducting paths is covered with an insulating layer (not shown). To do this, the inductive element 23 can, for example, be covered with a layer of insulating lacquer or an insulating adhesive sheet. The zone of contact 52, however, is not covered by the insulating layer.
The sheet 21 is then folded over on itself along a folding axis 53 so that the two halves formed are superimposed. The end 26 of the inductive element 23 is thus put into electrical contact with the zone of contact 52. A connection is thus formed very simply between the external portion of the inductive element 23 and the element 25. The two folded halves of the sheet 21 can be fixed with respect to one another, for example by gluing.
The connection pins 250 of the circuit 25 (figures 7 and 8) can be glued, soldered or fixed by bonding with the turns 8. It has been observed in conventional transponders, however, that such soldering sometimes breaks when the card is folded or deformed a large number of times. To lessen this risk, in a preferred embodiment of the invention the connection pins 250 are simply disposed over the turns 8, without soldering or any particular fixing. The integrated circuit is thus maintained pressed against the paths 8 by the protective layer 22. This arrangement allows the pins to slide slightly over the paths 8 when the card is bent and to return to their initial position when the card regains its shape. Owing to the elasticity of the upper protective layer 22, the pins 25 remain continuously pressed with a certain pressure against the contact portion of the turns 8, which enables an electrical contact of good quality to be ensured even after the card has been bent a number of times or has been deformed.
Of course it is important to ensure that the zone of paths 8 intended to come into contact with the pins of the circuit 25 are not covered by insulating
material 3 or 9. To this end, this zone can, for example, be protected during the lamination of film 2 or the spraying of material 9. It is also possible to remove locally these layers 3, 9 before mounting of the circuit 25.
One skilled in the art will note that this supplementary aspect of the invention is independent from the manufacture of the coil and can be used to connect any type of wound or machined coil to any type of electronic component.
Depending upon the desired application and the available space remaining on the card, components other than the integrated circuit 25 and the coil 8 can be integrated on the printed circuit 21. It is possible, for example, to place on the circuit a battery (not shown) which could be recharged from the outside by means of an inductive element, for example by means of element 23. Ideally these other components would be mutually connected and also connected to the elements 8 and 25 by means of conducting paths machined in the superficial conducting layer or layers 2 in the way described above.
One skilled in the art will note here that, contrary to the majority of known prior art techniques, the manufacture of conducting paths 8 on the printed circuit by the method according to the invention creates remarkably few irregularities in the surface, which irregularities are moreover compensated for by the adhesive or upon fusion of the upper layers. It is thus relatively easy to mount the upper sheet 22 while obtaining an external surface which is absolutely flat.
Other methods of lamination of chip cards can be used with the coils according to the invention, for example the methods which are the subject matter of the patent application W094/22111, the text of which is incorporated here by reference, or prior art methods mentioned in said document.
The method according to the invention can be extended to the production of double face circuits. The incisions 7 delimiting the paths 8 on each face are preferably made in a single operation. To do this, the dielectric film 1, covered on each face with a conducting layer 2, is pressed between two
stamping dies (not shown), each of which has cutting surfaces of contact 6 with the metallic surface. It is nevertheless also possible to achieve the incisions 7 on the two faces in two operations, one face and then the other.
Since the method according to the invention can be used even with dielectric films 1 of very fine thickness, this variant allows capacitive elements to be made very easily whose plates are formed by the metallic paths superimposed on each face. These components can, for example, be combined with inductive elements to constitute LC resonant circuits of reduced volume. If the capacitive coupling between the paths on the two faces must be reduced, topographies of conducting paths on the two faces having a minimum of overlapping are chosen instead.
The method according to the invention can be extended to the production of transponders with multi-layer circuits, that is having a plurality of layers of conducting material 2 superimposed and machined so as to define a plurality of levels of paths. In this case, the dielectric film 1 is covered with a plurality of conducting layers 2 insulated by a plurality of layers of adhesive or by a supplementary layer of insulation between the two metallic layers, for example a supplementary synthetic layer. The cutting tool used to separate the conducting paths 8 is designed to cut the incisions deep enough to pass through all the metallic layers 2 in a single operation. The topography constituted by the conducting paths 8 on the different conducting layers is thus identical. By connecting the different layers to one another at appropriate places, for example with metallised holes, this arrangement allows circuits of high inductance to be achieved.
It is of course possible to produce multi-layered circuits with variable topographies on the different layers by using a die machining incisions 7 of variable depth, certain incisions passing through all the superimposed metallised layers, whereas others only pass through the top layer, and still others pass through a plurality of layers but not all layers. In this way topologies having different paths on different layers can be achieved. By
laminating the layers after demarcation of paths by machining, a very great amount of freedom can be attained with respect to the configuration of the different layers. For example, it is possible to use one or more intermediate layers as connection layers, allowing bridges for the upper layers to be achieved. It is also possible to dispose a plurality of layers of paths back to back, and thus to obtain, for example, double face circuits by lamination of two simple circuits face to face.
One skilled in the art will of course understand that it is possible to combine freely the variants mentioned above. For example, it is possible to achieve circuits covered with a plurality of superficial conducting coatings on each face.
Besides manufacture of chip cards, the method can also be used to produce any type of transponder, for example used for tagging objects or animals or for surveillance of articles in a shop. Depending upon the application, the shape and the characteristics of the coil could be quite different. In the case of a chip card for applications of the banking transaction or payment type, a chip card provided with a coil permitting communication with the outside at high frequency is preferred, preferably with a frequency of more than 50 kHz, for example 10 MHz.
The method according to the invention is also perfectly suitable for production of flexible printed circuits. Such circuits are used, for example, to manufacture flexible plug connectors. Moreover the method is perfectly adapted to any case where a maximal density of paths on the surface of a printed circuit is required.
One skilled in the art will realise moreover that the method can also be used in combination with any other known method of printed circuit production. It is possible, for example, to make cards on which part of the conducting paths are obtained or separated by electrochemical means, the rest being machined
in the way specified in the claims.
One skilled in the art will realise that the term "printed circuit" has been used in this specification and in the claims even though the invention applies particularly to circuits and to cards produced without the step of printing in the usual sense.

WE CLAIM:
1. Method of producing a transponder (20) comprising the following
steps:
supplying a printed circuit (21; 31) which is made of a dielectric film (1) covered by at least one superficial conducting layer (2)
demarcation of different conducting paths (8) in said printed circuit (21; 31), connection of at least one electronic component (25) on said conducting paths (8) mounting of at least one sheet of protection (22, 27) on said printed circuit (21; 31)
characterised in that, said demarcation is realized by mechanical machining said superficial conducting layer (2) by means of a sharp edged cutting tool (5, 10) allowing incisions (7) to be cut separating said conducting paths, without removal or depthwise indentation of conducting material from said conducting layer (2).
2. Method as claimed in claim 1, wherein said dielectric film (1) is
covered by a plurality of mutually insulated, superimposed conducting
layers (2), and wherein said incisions (7) separating the conducting paths
(8) are machined so as to traverse said plurality of superimposed
conducting layers.
3. Method as claimed in claim 1, wherein each face of said dielectric
film (1) is covered by one or more superimposed superficial conducting
layers (2), different conducting paths (8) being demarcated on each face by
machining of incisions (7) in said conducting layers.
4. Method as claimed in claim 1, wherein said cutting tool is a
stamping die (5) having sharp-edged surfaces of contact (6) with the
superficial conducting layer (2).
5. Method as claimed in claim 1, wherein said cutting tool is a knife or
a blade (10) cutting sequentially incisions (7) separating the conducting
paths (8) according to a pattern recorded beforehand in an electronic
memory.
6. Method as claimed in claim 1, wherein said method comprises a
step of machining in said film at least one accommodation (24) intended to
accommodate said at least one electronic component (25) connected to
said conducting paths (8).
7. Method as claimed in claim 1, wherein said comprises a step of
covering part of the conducting paths (8) by an insulating layer and a step
of folding said dielectric film along a folding axis (53) in such a way as to
create at least one electrical bridge (26) between portions (26, 52) of
electric paths (8) not covered by said insulating layer.
8. Method as claimed in claim 1, wherein said at least one sheet of
protection (22; 27) is mounted by gluing on said printed circuit (21, 31).
9. Method as claimed in claim 1, wherein it comprises a step of
insertion of at least one material (9, 22) in said incisions (7) to ensure an
electrical isolation of different conducting paths (8).
10. Method as claimed in claim 8 or 9, wherein said at least one sheet
of protection (22; 27) is mounted by hot setting adhesive on said printed
circuit (21; 31).
11. Method as claimed in claim 1, wherein a step of preparation in said
at least one sheet of protection of a window allowing access from the
exterior of the transponder to the electronic component or to contacts
connected to said electronic component.
12. Method as claimed in claim 1, wherein said conducting layer (2) is
covered, before stamping, with a superficial film (3) intended to facilitate
stamping.
13. Method as claimed in claim 1, wherein said dielectric substrate has
local reinforcements in the zone of the electronic component.
14. Method as claimed in claim 1, wherein said dielectric film (1) has at
least one through hole which will fill the material of said conducting layer.
15. Method as claimed in claim 9, wherein said material (9) comprises a
lacquer or a varnish applied on said conducting path after stamping said
incisions (7).
16. Method as claimed in claim 9, wherein said material (220)
comprises an adhesive for mounting a sheet of protection (22), glued on
said sheet after stamping.
17. Method as claimed in claim 9, wherein said sheet (1, 2,3, 4) is bent
so as to eliminate said incisions (7) upon insertion of said material (9,
220).
18. Method as claimed in claim 1, wherein it comprises a step of
flattening said sheet (1, 2, 3, 4) by compression.
19. Method as claimed in claim 1, wherein it comprises a step of folding
at least a portion (80) of said paths in such a way to create at least one
electrical bridge (80) over said paths.
20. Method as claimed in claim 1, wherein said conducting layer (2) is
mounted on said dielectric film (1) by means of a non- permanent glue (4)
and wherein it comprises a step of peeling off at least one portion (A, B, C) of said conducting layer after said step of stamping incisions.
21. Method as claimed in claim 20, wherein said at least one peeled-off
portion has at least the portion (A) of said conducting layer inside said
turns of the coil.
22. Method as claimed in any one of the claims 20 or 21, wherein said
at least one peeled-off portion has at least the portion (C) of said
conducting layer outside said turns of the coil.
23. Method as claimed in any one of the claims 20 to 22, wherein said
at least one peeled-off portion has at least a segment (80) of said turns.
24. Method as claimed in claim 23, wherein the inductance of the coil is
adjusted by peeling off an appropriate length of said turns of the coil.
25. Method as claimed in any one of the claims 23 or 24, wherein, after
peeling off of a segment (80) of said turns (8) previously covered with an
insulating layer, said segment is used to constitute an electrical bridge
(80).
26. Method as claimed in claim 1, wherein said conducting layer is
glued on said dielectric substrate only on certain portions in such a way
as to facilitate the subsequent peeling off of residual portions (A, B, C).
27. Method as claimed in claim 1, wherein it comprises a step of
indenting said conducting layer (2, 3, 4) in the thickness of the dielectric
film (1) to improve the surface evenness.
28. Method as claimed in any one of the claims 20 to 27, wherein it
comprises a step of lamination of an intermediate sheet of dielectric
having the thickness of said conducting layer (2, 3, 9) and whose shape corresponds to that of the portions (A, B, C) without paths in order to improve the surface evenness.
29. Method as claimed in claim 1, wherein it comprises a step of
mounting at least one electronic component (25) straddling the said turns
of the coil.
30. Method as claimed in claim 1, wherein at least one of said
electronic components (25) is directly positioned, without soldering, on the
portions of contact of the turns of the coil (8).
31. Method as claimed in claim 1, wherein it comprises a step of
mounting a second sheet of protection (27) on the face opposite that
provided with the first sheet of protection.
32. Method of producing a transponder (20), substantially as herein
described with reference to and as illustrated in the accompanying
drawings.

Documents:

2003-del-1997-abstract.pdf

2003-del-1997-claims.pdf

2003-del-1997-correspondence-others.pdf

2003-del-1997-correspondence-po.pdf

2003-del-1997-description (complete).pdf

2003-del-1997-drawings.pdf

2003-del-1997-form-1.pdf

2003-del-1997-form-13.pdf

2003-del-1997-form-19.pdf

2003-del-1997-form-2.pdf

2003-del-1997-form-3.pdf

2003-del-1997-form-4.pdf

2003-del-1997-form-6.pdf

2003-del-1997-gpa.pdf

2003-del-1997-petition-137.pdf

2003-del-1997-petition-138.pdf

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Patent Number

214885

Indian Patent Application Number

2003/DEL/1997

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

18-Feb-2008

Date of Filing

17-Jul-1997

Name of Patentee

NAGRAID S.A.

Applicant Address

RUE DES CHAMPS 12, 2301 LA CHAUX-DE-FONDS, SWITZERLAND.

Inventors:

#	Inventor's Name	Inventor's Address
1	FRANCOIS DROZ,	PRAIRIE 46,, 2300 LA CHAUX-DE-FONDS, SWITZERLAND.

PCT International Classification Number

H045K 3/30

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA