metal smart card and method of manufacturing a metal smart card

Abstract

Metal smart card and method for manufacturing a metal smart card The present invention relates to a smart card comprising: - a metal layer comprising an RF antenna arranged in or facing a recess area; - a module comprising an RF chip, - a pattern of conductive material arranged in or facing the recess area and comprising - a central area - at least two traces of conductive material separated and spaced apart from each other, to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency. Figure for abstract: Fig. 2a.

Description

Title of the invention: metal smart card and method for manufacturing a metal smart card Technical field

[0001] The invention relates to the field of smart cards and relates more particularly to metal smart cards capable of operating in contactless mode. Prior art

[0002] The use of smart cards (or microcircuit cards) is now widespread in everyday life. Such cards are used, for example, as bank cards, loyalty cards, access cards, etc., and can take various formats depending on their respective uses. Smart cards can be designed to perform various types of functions, in particular to carry out transactions, such as banking transactions (payment transactions, transfer transactions, etc.), authentication transactions, etc.

[0003] As is known, a smart card generally comprises a card body which is equipped with an electronic chip configured to exchange signals with the outside and perform various functions depending on the desired use of the card. To do this, smart cards are provided with communication means allowing interaction with the outside, typically with an NFC reader or external reader.

[0004] Traditionally, a smart card is designed to cooperate with an external NFC reader by means of external contacts accessible on the surface of the card. An external NFC reader can thus position appropriate contact pins on the external contacts of the card in order to establish contact communication.

[0005] More recently, contactless smart cards have experienced increasing popularity due to the increased speed and simplicity of contactless transactions. To achieve this, contactless cards incorporate a radio frequency (RF) antenna enabling the exchange of RF signals with an external NFC reader (for example, in near field NFC for "Near Field Communication" in English). This RF antenna is generally composed of a plurality of conductive turns which extend into the body of the card.

[0006] The structure and appearance of smart cards can vary depending on the case. Metal smart cards are particularly enjoying growing interest due in particular to the attractive aesthetic appearance of these cards (metallic reflections, brushed surface effect, etc.), the quality impression that they can provide (appreciable weight of the metal, high-end aesthetics), or the connotation of prestige associated with them for their users. Due in particular to their significant weight and the printing Due to the high quality they give off, these cards are favored by some users to serve as a social marker and a differentiating element.

[0007] However, it has been observed that the presence of metal in the body of a smart card poses major difficulties when the card incorporates an RF antenna to operate in contactless mode. The metal acts as electromagnetic shielding and blocks or interferes with the RF signals exchanged by the RF antenna with the outside. The metal present in the card body can thus disrupt the contactless communications of a smart card with an external NFC reader and, for example, interfere with the completion of a contactless transaction (payment or other).

[0008] A known solution is to use a ferrite layer between the antenna and the metal sheet. Although simple, this solution makes the card manufacturing complex and the card can only communicate with the interrogating reader from one side.

[0009] Another relevant solution is to use a reduced-size antenna inserted inside or superimposed with a cavity (absence of metal) made in a metal sheet, the cavity being connected to the outer edge of the metal layer by means of a slot. In this configuration, the metal layer surrounds the NFC antenna and therefore has a larger physical surface area than that of the antenna and generally occupies the entire size of the card.

[0010] Since the magnetic field lines are closed lines, the interrogating magnetic field incident on the surrounding metal layer, in such a topology, will therefore be diverted away from the metal: the magnetic field lines at the periphery of the metal will be diverted outwards while the lines close to the cavity will be diverted inwards, thus crossing the area of ​​the antenna and adding to the normal magnetic flux crossing the antenna, making its effective area larger than if it had been used without this surrounding metal.

[0011] Although the technique described above exhibits good NFC behavior, it may suffer from a major technical problem. Since the antenna insert consists of a printed circuit, this circuit is implemented by conventional printed circuit technology on a dielectric substrate such as, for example, FR4 material. The antenna traces are made in this case by a conventional subtractive PCB process (mechanical or chemical etching) with optional electroplated or electroless metal growth to achieve a certain thickness. The conventional card manufacturing process then includes at least one process of filling the cavity area above the antenna, in order to ensure sealing between these two mechanically different elements, i.e. the printed circuit substrate and the surrounding metal strip.This sealing step is essential to give the entire product a monolithic appearance for . to satisfy a certain aesthetic aspect, but above all to give mechanical stability to the card by preventing it from tearing during the different folding cycles throughout the product life cycle.

[0012] A major problem arises for this sealing / resin process to be successful and play the role described above: since the NFC antenna is routed in the form of typical closed loops, the central antenna area of ​​the PCB is perfectly free of metal while the antenna turns at the periphery carry the antenna turns. This creates a structural asymmetry on the PCB surface on both sides of the circuit. This lack of homogeneity leads to a lack of adhesion and, consequently, a lack of the intended monolithic appearance and, finally, brittleness of the entire board. Furthermore, the larger the cavity, the more serious this problem is.

[0013] There is therefore a need for high-performance metal chip cards (RFID type for example) that are easy to manufacture and capable of cooperating effectively without contact with an external terminal. Statement of the invention

[0014] The present invention relates to a smart card comprising: - a card body formed at least in part by a metal layer comprising a recessed area and at least two plastic layers on either side of the metal layer; - at least one RF antenna arranged in or facing the recess area; - a module comprising an RF chip, the module being positioned in a through cavity of a plastic layer and being electrically connected to the RF antenna; - a pattern of conductive material connected in parallel to said at least one antenna and arranged in or opposite the recess area and comprising - a central zone whose conductive surface is less than or equal to 20% of the surface of a central zone circumscribed by said antenna - at least two traces of conductive material (T;) separated from each other and extending from said central area of ​​said pattern, said at least two traces of conductive material being distant from each other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on said card, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency.

[0015] Inserting a pattern made of conductive material into an area included in the center of the antenna can make it possible to improve the robustness of the metal chip card by adding a metal area into a cavity that did not contain any and which therefore constituted an area whose structure was different from the structure provided by the metal layer present outside the cavity. The pattern being made of conductive material, it also makes it possible to provide additional capacity.

[0016] According to certain embodiments, said antenna comprises two RF windings (ATI, AT2) electrically connected to each other and located respectively on either side of said recess area, two patterns made of conductive material being located respectively on either side of said recess area and each connected to one of the RF windings.

[0017] The two patterns made of conductive material can thus form a parallel capacitance and can make it possible to improve the capacitive value of the entire resonant circuit formed by the pattern and the antenna.

[0018] According to certain embodiments, said determined communication frequency is 13.56 MHz and complies with the ISO 14443-2 or ISO 10373-6 standard.

[0019] According to certain embodiments, - the at least one antenna comprises a plurality of turns, - the central area of ​​said pattern is round in shape and centered on the center of the turns of the antenna, and - the traces of said pattern are circular traces centered on the center of the turns and forming rings around the round central area of ​​the pattern, the traces being separated from each other each by first non-conductive circular areas extending between each of the circular traces and a second rectilinear area connecting said first non-conductive circular areas and intersecting each of the conductive circular traces of said pattern so as not to form a closed loop to avoid the formation of eddy currents on said card, - the first non-conductive circular zones each being open so as to ensure conductive continuity between the central zone and the traces of said pattern.

[0020] According to certain embodiments, - the at least one antenna comprises a plurality of turns, - said conductive material pattern comprises a central conductive surface of round shape centered on the center of the turns of the antenna and interconnecting a plurality of said pairs of traces of conductive material, - said traces of conductive material being rectangular in shape and connected to said central conductive surface by one of their ends, the other end being free, and distributed uniformly around said central area of ​​the pattern.

[0021] According to certain embodiments, - the at least one antenna comprises a plurality of turns, - said conductive material pattern comprises a central conductive surface of round shape centered on the center of the turns of the antenna and interconnecting a plurality of said pairs of traces of conductive material, - said traces of conductive material being helical in shape and connected to said central conductive surface by one of their ends, the other end being free, and distributed uniformly around said central area of ​​the pattern.

[0022] According to certain embodiments, the conductive material traces are distributed uniformly around the round central surface.

[0023] According to certain embodiments, the number of conductive traces depends on the value of the connected capacitance.

[0024] According to certain embodiments, the traces have a width configured to reduce the eddy currents present on said smart card.

[0025] According to another aspect, the present invention relates to a method of manufacturing a smart card (CD1) formed at least in part by a card body comprising a metal layer (103), said metal layer comprising a recess area (104), the method comprising: a) formation (S4) on or in the card body of at least one first RF antenna (ATI, AT2) in or opposite the recess area of ​​the metal layer; b) formation (S6) of at least one pattern of conductive material in the center of the at least one antenna connected in parallel to said at least one antenna and arranged in or opposite the recess zone, the metal pattern comprising - a central zone whose conductive surface is less than or equal to 20% of the surface of a central zone circumscribed by said antenna - at least two traces of conductive material (TO) separated from each other and extending from said central area of ​​said pattern, said at least two metal traces being distant from each other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on said card, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency c) assembling (S8) an RF chip such that said RF chip is electrically connected to said at least one antenna, d) depositing (S 10) a layer of resin to seal the metal layer and the recess area comprising said at least one antenna and said at least one metal pattern metal.

[0026] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an exemplary embodiment thereof without any limiting character. Brief description of the drawings

[0027] [Fig. 1a] [Fig. 1a] represents a view of the front face of a smart card according to certain embodiments of the invention,

[0028] [Fig.lb] [Fig.lb] represents a view of the rear face of a smart card according to certain embodiments of the invention,

[0029] [Fig.2a] [Fig.2a] represents a side view of the layers of a chip card not assembled according to certain embodiments of the invention,

[0030] [Fig.2b] [Fig.2b] represents a side view of the layers of a smart card assembled according to certain embodiments of the invention,

[0031] [Fig.3] [Fig.3] represents an example of a pattern according to a first embodiment of the invention,

[0032] [Fig.4] [Fig.4] represents an example of a pattern according to a second embodiment of the invention,

[0033] [Fig.5] [Fig.5] represents an example of a pattern according to a third embodiment of the invention,

[0034] [Fig.6] [Fig.6] represents an electrical diagram equivalent to the antenna according to certain embodiments of the invention,

[0035] [Fig.7] [Fig.7] represents a comparison between a response curve obtained according to the prior art and according to an embodiment of the present invention,

[0036] [Fig.8] [Fig.8] represents an embodiment giving an example of the dimensions which can be used for the pattern,

[0037] [Fig.9] [Fig.9] represents a method of manufacturing a smart card according to certain embodiments of the invention. Description of the embodiments

[0038] As previously indicated, the invention relates to metal smart cards configured to operate in contactless mode, and also relates to a method of manufacturing such smart cards. A "metal smart card" refers herein to a smart card comprising a metal or a combination (alloy) of metals, for example in the form of a metal layer or a plurality of metal layers.

[0039] As previously indicated, a contactless smart card is configured by nature to communicate contactlessly with the outside world, more particularly with an external NFC reader. For this purpose, a contactless smart card incorporates a radio frequency (RF) antenna for exchanging (receiving and / or transmitting) RF signals with an external NFC reader. Such a smart card may also have the ability to operate in contact mode, using external contacts provided for this purpose on the surface of the card: these are then referred to as “dual” cards (or cards with a dual communication interface), these cards being capable of operating in contactless mode and in contact mode.

[0040] There is currently a strong demand among users for metal smart cards, particularly for the reasons mentioned above (aesthetic aspects, quality printing, prestige, etc.). It is particularly desirable to produce smart cards in which the majority (or a significant part) of the card body is made of metal, or at least in which the card body includes a metal plate (or metal layer), in order to obtain a certain uniformity and quality in the visual and aesthetic appearance of the card.

[0041] As mentioned previously, when the antenna has a central area devoid of metal, the surface of the board has a structural asymmetry, due to a non-homogeneous distribution of metal on the board, the central area of ​​the antenna of the printed circuit being perfectly devoid of metal while the turns of the antenna at the periphery carry the turns of the antenna. This creates a structural asymmetry on the surface of the printed circuit on both sides of the circuit. To better understand the problem, according to certain embodiments, the antenna turns generally have a thickness greater than 30 pm and can reach 90 pm, this can therefore disturb the homogeneity of the sealing material on the surface of the printed circuit.

[0042] In the present disclosure, examples of implementations of the invention are described in relation to a “dual” type smart card, i.e. a card with a dual communication interface, having the capacity to communicate both in contact mode (via external contacts) and in contactless mode (via an RF antenna structure). It will be noted, however, that the invention can be applied more generally to any smart card configured to communicate in contactless mode, whether or not it has the capacity to also operate in contact mode.

[0043] Furthermore, it is considered in the following examples that the smart card is a bank card, such as a payment card for example. This smart card may comply with the ISO 7816 standard and may operate according to the EMV standard, although neither of these aspects is mandatory to implement the invention. More generally, the invention applies to any metal smart card configured to implement a transaction in contactless mode, including EMV cards or smart cards using another transaction standard, for example the NFC standard (according to for example ISO 14443-2, ISO 10373-6, “EMV Contactless Certification”). Generally speaking, the smart card of the invention can be configured to carry out a transaction of any type, such as banking transactions (payment, transfer, debit transactions, etc.), authentication transactions, etc.

[0044] Unless otherwise indicated, elements common or similar to several figures bear the same reference signs and have identical or similar characteristics, so that these common or similar elements are generally not described again for the sake of simplicity.

[0045] The terms "first(s)", "second(s)", etc.) are used in this document by arbitrary convention to enable different elements (such as keys, devices, etc.) implemented in the embodiments described below to be identified and distinguished.

[0046] Figures 1a and 1b show a view of the front face and a view of the rear face of a smart card CD1 according to an embodiment of the present invention. If [Fig.1a] shows a view of the front face, [Fig.1b] shows a view of the rear face and vice versa. The embodiment of Figures 1a and 1b is described later in more detail in Figures 2a and 2b and in [Fig.3].

[0047] The smart card CD1 as shown in the embodiment of Figures 1a and 1b comprises a metal layer 103, a first antenna winding ATI and a second antenna winding AT2. The two antenna windings ATI and AT2 are electrically connected using metal vias or perforations. The card CD1 also comprises a pattern M1 and a pattern M2 located in the center of the antenna. The two patterns M1 and M2 are electrically connected using metal vias or perforations. These two patterns are also each electrically connected to the antenna.

[0048] The windings ATI and AT2 of the antenna as well as the patterns M1 and M2 are located in a substrate itself located in a recess of the metal zone. The different layers of the card CD1 are illustrated in more detail in Figures 2a and 2b. One or more transparent layers, for example protective layers, may also be present on the metal layer, as shown in [Fig.2a] and 2b.

[0049] The patterns M1 and M2 comprise circular metal traces centered on the center of the antenna windings. The pattern further comprises a central portion Ci of round shape, made of conductive material (respectively C'i on the other face). Each of the traces Tu, Ti2 and Tn (respectively T'n, T'i2 and T'n on the other face) is isolated from the neighboring trace by a space made of non-conductive material, such as the substrate comprising the antenna and the pattern. In addition, each of the traces does not form a closed circular surface and is open by a space P2 connecting the center Ci to the substrate comprised between the pattern and the antenna. Thus, the traces made of conductive material are distant from each other on the other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on the CD1 card. The pattern made of conductive material forms a capacitive circuit. It is configured so that the capacitance formed by the pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and the pattern to resonate at a determined communication frequency.

[0050] According to certain embodiments, on a first face of the card, the radius of the circle formed by the innermost turn of the ATI winding is 11.51 mm and that of the outermost turn is 12.12 mm. On a second face, these radii, for the AT2 winding, are respectively 11.31 mm and 12.32 mm. The area located inside the inner turn of the ATI or AT2 winding may be substantially equal to 387 mm2.

[0051] Thus the two windings ATI and AT2 may not overlap exactly, each on one side of the card but be slightly offset.

[0052] Figures 2a and 2b respectively represent an exploded view and an assembled view of a smart card 1 according to an embodiment of the invention.

[0053] In the examples given, the smart card is in the ID1 format of a credit card, although other shapes are possible for implementing the invention.

[0054] In [Fig.2a], we observe a first layer of plastic material 101a and a second plastic layer 101b, one of the objectives of which is to protect the internal layers of the smart card CD1. The layers 101a and 101b, optional, are for example made of polycarbonate and preferably transparent.

[0055] Under the layers 101a and 101b, resin layers 102a and 102b are deposited respectively. One of the purposes of the resin layers is to seal the internal layers of the smart card CD1.

[0056] The smart card CD1 is formed or comprises a metal layer 103 comprising a recess area 104 in which a substrate 105 is housed (inserted). The recess area 104 is an opening or through area provided in the metal layer 103 to allow the positioning of the antenna ATI and possibly the antenna AT2 (the antenna AT2 being connected to the antenna ATI).

[0057] The shape and dimensions of this recess area 104 may be adapted as appropriate. For example, the recess area 104 is rectangular. This metal layer 103 may be made of a single metal, such as stainless steel or aluminum for example, or of an alloy of several different metals. The metal layer 103 may comprise a plurality of metal sub-layers.

[0058] According to a particular example, the card body 100 and more generally the smart card CD1 is devoid of ferrite, which makes it possible to simplify the manufacture of the card.

[0059] An antenna ATI as well as a pattern M1 made of conductive material such as disclosed by the embodiments of the present invention, for example with reference to figures w3, 4 and 5, are arranged on a substrate 105. As illustrated in [Fig.2a], the card CD1 can be equipped with an antenna comprising a first winding denoted ATI and a second winding denoted AT2, a winding being present on each side of the substrate and therefore on each face of the smart card CD1, the two windings being physically connected by a via (or a metal perforation) and two patterns M1 and M2 made of conductive material, a pattern being respectively physically connected to each winding.The presence of a winding on each of the faces makes it possible to make the best use of the surface available on the substrate and therefore to optimize the energy captured in the ambient electromagnetic radiation; the number of turns on each of the faces of the substrate is advantageously between two and five, which amounts to occupying only a modest fraction of the surface of the support near its contour, typically between 5 and 10% of this surface.

[0060] In [Fig.2b], a side view of the smart card CD1 is observed, the layers mentioned with reference to [Fig.2a] being assembled to form the smart card. During the assembly of the card CD1, the resin 102a comes to fit the surface between the assembly formed by the metal layer 103 and the substrate 105 and the plastic layer 101a.

[0061] It can thus be seen that the pattern of conductive material placed in the center of the antenna can fill the space that would exist in its absence in the center of the antenna and thus can allow better adhesion of the layers, for example when applying a layer of resin. Thus, the card has a surface whose structural homogeneity is improved, thus making it more robust. In other words, the pattern allows better filling of the central part of the antenna on each side of the PCB, providing more homogeneity when applying the resin and therefore making it possible to avoid these structural problems.

[0062] Of course, the smart card CD1 may comprise other elements or layers, not shown in the figures. The smart card CD1 may in particular comprise an RF chip, RF meaning radio frequency throughout the description. The RF chip is configured to establish contactless communication with an external terminal (not shown) using the antenna included in the smart card. To do this, the RF chip is electrically connected to the antenna ATI (and to the antenna AT2 if present).

[0063] Thus, the present invention relates to a smart card comprising: - a card body formed at least in part by a metal layer comprising a recessed area and at least two plastic layers on either side of the metal layer; - at least one RF antenna arranged in or facing the recess area; - a module comprising an RF chip, the module being positioned in a through cavity of a plastic layer and being electrically connected to the RF antenna; - a pattern of conductive material connected in parallel to said at least one antenna and arranged in or opposite the recess area and comprising - a central zone whose conductive surface is less than or equal to 20% of the surface of a central zone circumscribed by said antenna - at least two traces of conductive material separated from each other and extending from said central area of ​​said pattern, said at least two metal traces being distant from each other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on said card, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency.

[0064] Preferably, all the traces of a pattern are located in the same horizontal plane relative to the faces of the smart card.

[0065] In Figures 2a and 2b, it can be seen that the conductive material pattern (each conductive material pattern on each side of the card) is positioned in the center of the antenna, and consists of at least two metal traces. It can be seen in Figures 2a and 2b that the conductive material pattern comprises, for example, four conductive material traces.

[0066] Forming the pattern in the form of traces can help not to disturb the magnetic field and thus not to modify the operation of the antenna

[0067] Figures 3, 4, and 5 illustrate examples of patterns made of conductive material, M1 or M2, whose characteristics can ensure better homogeneity of the card while not disturbing, or even improving, the performance of the antenna.

[0068] The patterns of figures 3, 4 and 5 are such that they occupy between 60 and 90% of the surface created at the center of the antenna, that is to say of the surface delimited by the internal turn of the antenna.

[0069] The pattern consists of at least two conductive traces having at least one gap between them and at least one gap to the innermost / nearest turn of the antenna, on each side of the substrate. More than two traces may be used, provided that each pair is separated by a gap. All traces on each side of the substrate represent a continuous galvanic surface. The conductive traces of each pattern are configured to avoid forming a loop to avoid the formation of eddy currents in this metallic form facing the incident magnetic field.

[0070] Furthermore, the central part of the pattern, represented in Figures 3, 4 and 5 respectively by the references Ch C2 and C3, occupies a surface less than or equal to 20% of the surface delimited by the internal turn of the antenna and included inside this turn.

[0071] The central portion of each pattern may consist of a continuous metal patch (or surface) having a surface area of ​​less than 20% of the internal surface area defined by the surface area included within the innermost turn of the antenna to make eddy current losses negligible.

[0072] By forming the conductive material pattern by separate conductive traces, which can be interlaced, the induced magnetic field lines can pass through the antenna without modifying the magnetic field, and thus the behavior of the antenna is not modified. In addition, the use of patterns whose conductive traces do not form a closed loop can reduce the effects of eddy currents, the effects of which will be negligible.

[0073] The conductive material pattern provides additional capacity to the antenna's capacity, increasing the total capacity of the antenna. Thus, for the same desired resonant frequency, the diameter of the innermost turn of the antenna is larger, with a reduced number of turns and the same antenna pitch, than for an antenna without this state-of-the-art conductive material pattern, while maintaining low resistance.

[0074] The characteristics of the capacitance thus added, in particular the spacing between the traces, the shape of the pattern (width, length, shape and number of traces) are chosen so that this capacitance defines, with the antenna and the chip, a given resonance frequency, chosen according to the needs of the card and in particular the standards with which the card must comply.

[0075] For reasons of clarity, figures 3, 4 and 5 represent the pattern of the antenna on a single face of the card CD1. The pattern can easily be reproduced on the other face, the two patterns being opposite each other on each of the faces. Furthermore, it is understood that the two patterns are connected to each other electrically, for example using vias and / or by the electrical connection with the antenna, the turns of the antenna ATI being connected to the turns of the antenna AT2, by vias. The patterns are connected to the antenna by the terminals La and Lb, which are illustrated in [Fig.6] on the electrical diagram equivalent to the antenna.

[0076] [Fig.3] represents a first example of a pattern in conductive material positioned in the center of the antenna, on each side of the substrate. Only one face is represented, therefore only one of the two patterns is represented.

[0077] According to the embodiment of [Fig.3], - the at least one antenna comprises a plurality of turns, - the central area of ​​the pattern is round in shape and centered on the center of the antenna turns, and - the traces of the pattern are circular traces centered on the center of the turns and forming rings around the central round area of ​​the pattern, the traces being separated from each other by first non-conductive circular areas extending between each of the circular traces and a second rectilinear area connecting the first non-conductive circular areas and intersecting each of the conductive circular traces of the pattern so as not to form a closed loop to avoid the formation of eddy currents on the card, - the first non-conductive circular zones each being open so as to ensure conductive continuity between the central zone and the traces of the pattern.

[0078] The pattern comprises three conductive metal traces Tu, T[2, Tn. The three metal traces are circular shaped traces, which follow the shape of the antenna turns, i.e. the center of the traces is the same or almost the same as the center of the antenna turns. The trace Tu, which represents the outer trace of the pattern, closest to the turns, is preferably located at a distance D from the innermost turn of the antenna. The minimum distance D may be dependent on the technology used and may be calculated so as to avoid a short circuit of the pattern with the antenna turn.

[0079] According to certain embodiments, the distance D is between 200 pm and 1 mm.

[0080] The three traces are connected to each other and connected to the center Cp. They are separated by a space made of non-conductive material, called an insulating space (such as the substrate), except on a part of their circumference, this to allow galvanic continuity between the traces and the center. The space made of non-conductive material partially separating them connects the spaces present between all the traces to the non-conductive zone located between the antenna (its innermost winding) and the outermost trace of the pattern. In other words, a circular trace is separated from the adjacent trace(s) by a circular insulating space matching the circumference of the traces, except on a part of its circumference, leaving an opening connecting the traces to each other and connecting them with the center of the pattern. This opening can for example have a width d2 of 200 pm.

[0081] The conductive opening left between the traces and the center of the pattern may, for example, be located diametrically opposite the insulating space joining the center of the pattern to the non-conductive zone located between the antenna (its innermost winding) and the outermost trace of the pattern.

[0082] It can be noted that this opening can be different for each trace.

[0083] According to certain embodiments, the distance d2 is determined to allow an open circuit to be maintained. The distances d2, d3, d4 may be equal or all different. Taking identical distances d2, d3 and d4 helps to improve the mechanical strength because the symmetry is better and can also facilitate the manufacturing process of the printed circuit, in particular during chemical etching baths.

[0084] Trace Tu, the outermost trace, is connected to a terminal La of the antenna. When the other face of the card comprises a second pattern opposite the pattern as described, this second pattern is similar to the pattern described and connected to a second terminal Lb of the antenna, more precisely of the winding of the antenna present on this second face of the card CD1.

[0085] [Fig.4] shows a second example of a conductive material pattern positioned in the center of the antenna, on each side of the substrate. Only one face is shown, so only one of the two patterns is shown.

[0086] According to this embodiment, the pattern comprises at least twelve traces made of conductive material or conductive traces T2b T22, T23, T24, T25, T26, T27, T28, T29, T30, T3b T32. The twelve conductive traces are connected to each other, at one of their ends, by means of a central conductive surface C2, this being able to be a round surface, the surface of which is at most equal to 20% of the size of the surface delimited by the internal turn of the antenna and included inside this turn. According to other embodiments, this central surface can be of a shape other than round, for example elliptical, square, rectangle. This central surface C2 can be metallic.

[0087] The distances d2b d22, d23.. .to d32 are equal or different and represent the spacing between the traces. According to certain embodiments, the distances d2[ to d32 , are equal and according to certain embodiments, they are different. Taking identical distances d2i to d32 helps to improve the mechanical strength because the symmetry is better and can also facilitate the manufacturing process of the printed circuit, in particular during chemical etching baths.

[0088] It is advantageous to take thin traces (also called strands), of an order of magnitude of 200 pm. This can help to reduce the eddy currents in each strand. However, the thinner the strands, the higher the number of strands must be in order to achieve a desired capacitance value. Thus, the size and number of strands can be determined according to the capacitance value to be obtained.

[0089] The twelve traces T2b T22, T23, T24, T25, T26, T27, T28, T29, T30, T3b T32 can be of the same length or of different lengths. When the traces are of the same length, the resin finishing is advantageously improved by making it more homogeneous.

[0090] The twelve traces are rectangular in shape. They are configured to form a surface depending on a target capacitance value.

[0091] The end of the traces not connected to the central surface is free and located at a distance D' from the internal turn of the antenna. The minimum distance D' may be dependent on the technology used and can be calculated to avoid short-circuiting the pattern with the turn of the antenna.

[0092] [Fig.5] shows a third example of a conductive material pattern positioned in the center of the antenna, on each side of the substrate. Only one face is shown, so only one of the two patterns is shown.

[0093] According to this embodiment, the pattern made of conductive material comprises at least 8 conductive traces T40, T4b T42, T43, T44, T45, T46, T47. The eight conductive traces are connected to each other, at one of their ends, by means of a central conductive surface C3, this being able to be a round surface, the surface of which is at most equal to 20% of the size of the surface delimited by the internal turn of the antenna and included inside this turn. According to other embodiments, this central surface can be of a shape other than round, for example elliptical, square, rectangle. This central surface C3 can be metallic.

[0094] The distances d40, d42, d42.. .to d47 are equal or different and represent the spacing between the traces. According to certain embodiments, the distances d3[ to d38 , are equal and according to certain embodiments, they are different. Taking identical distances d40 to d47 helps to improve the mechanical strength because the symmetry is better and can also facilitate the manufacturing process of the printed circuit, in particular during chemical etching baths.

[0095] It is advantageous to take thin traces (also called strands), of an order of magnitude of 200 pm. This can help to reduce the eddy currents in each strand. However, the thinner the strands, the higher the number of strands must be in order to achieve a desired capacitance value. Thus, the size and number of strands can be determined according to the capacitance value to be obtained.

[0096] The at least 8 conductive traces T40, T4b T42, T43, T44, T45, T46, T47 can be of the same length or of different lengths. When the traces are of the same length, the resin finishing is advantageously improved by making it more homogeneous.

[0097] The twelve traces are rectangular in shape. They are configured to form a surface depending on a target capacitance value.

[0098] The end of the traces not connected to the central surface is free and located at a distance D” from the internal turn of the antenna. The minimum distance D” can be dependent on the technology used and can be calculated so as to avoid a short circuit of the pattern with the turn of the antenna.

[0099] [Fig.6] represents an example of an electrical diagram equivalent to the antenna as proposed according to the different embodiments of the invention.

[0100] We can see the inductance La and the capacitance Ca of the antenna and an additional capacitance Cmotif corresponding to the capacitor formed by the metal traces of the pattern. The resonant RLC circuit thus constituted by the resistance Ra, the impedance La and the capacitances Ca and Cmotif, makes it possible to adapt the resonant frequency of the antenna so that it is, for example, equal to 13.56 MHz, which allows communication in contactless mode of the RFID type with an external reader, according to one of the standards ISO 14443, ISO 10373, ISO 18745, ISO 15693, EMVCo. [Fig.6] makes it possible to understand that the patterns in conductive material are connected to La and Lb.

[0101] Advantageously, as mentioned previously, the antenna can comprise turns arranged on each face of the substrate and therefore, vias allow the connection of the turns from one face to the other, in this case we can speak of two antennas ATI and AT2. This allows continuity in the loops formed by these turns. The connection points La and Lb can therefore be located on either side of the substrate.

[0102] To obtain a resonance frequency of 13.75 Mhz, one can choose an inductance value for LA of 1.29 pH, a resistance value RA of 4.76 Ohms, a capacitance value CA of 1 to 2 pF and a capacitance value Cmotif of 54.23 pF. The capacitance of the RF chip, of the order of 50 pF, is also added to these two capacitances.

[0103] [Fig.7] represents a comparison between a response curve obtained according to the prior art and according to an embodiment of the present invention. More precisely, the curves represent a comparison between the reaction time of the card without the invention (curves C1 and C2) and with the embodiment of the conductive material pattern implemented in [Fig.3] (curves C3 and C4). An ISO reference curve representing the reference values ​​required by the ISO 14443-2 standard is also represented in the figure. A high curve (C1 or C3) and a low curve (C2 or C4) respectively illustrate the high and low limits between which the load modulation amplitude is located.

[0104] It is therefore noted that the conductive material pattern can improve the reaction time. Thus, it is noted that the charge modulation amplitude required by the ISO 14443-2 standard is achieved: - for a magnetic field of 1.1 Ampere per meter, represented by point A on the curve for a CD1 card according to the embodiment of [Fig.3] and - for a magnetic field of 1.5 Amperes per meter, represented by point B on the curve for a card which does not implement the present invention.

[0105] It can therefore be seen that the card implementing an embodiment of the present invention can make it possible on the one hand to trigger an activation of the card more quickly and on the other hand with a greater load modulation amplitude, than when the present invention is not implemented.

[0106] [Fig.8] represents an embodiment of the patterns M1 and M2 each located on one side of the CD card 1 and illustrates orders of magnitude of dimensions which can be used for the patterns M1 and M2 according to certain embodiments of the invention, the patterns M1 and M2 being able to be patterns such as represented in [Fig.3].

[0107] Examples of dimensions of the pattern Ml

[0108] It can be noted that the distance d2 (as well as d3 and d4) can be 0.5 mm. The width of the traces can be 1.65 mm and the width of the space between the traces can be 0.2 mm. The solid surface of the center C has an area of ​​162.94 mm2 and the value of p2 is 0.20 mm. The external radius of the last trace is 7.54 mm.

[0109] Examples of dimensions of the M2 pattern

[0110] It can be noted that the distance d2 (as well as d3 and d4) can be 0.35 mm. The width of the traces can be 1.50 mm and the width of the space between the traces can be 0.35 mm. The solid surface of the center C has an area of ​​148.03 mm2 and the value of p2 is 0.20 mm. The external radius of the last trace is 7.47 mm.

[0111] The production of a printed circuit has a certain tolerance depending on the technology used. As the capacitance provided by the pattern synthesizes its capacitive value as a function of the permittivity of the substrate, its thickness and the surface of the electrical armatures opposite, the dimensions of the pattern are chosen to be slightly larger on one layer than on the other (i.e. the dimensions of M1 compared to M2) in order to ensure a precise surface of the armatures of the capacitance and therefore to be able to circumvent the effect of the tolerance and the precision of the technology used for the printed circuit.

[0112] [Fig. 9] schematically represents a method of manufacturing one of the CD1 smart cards described above, according to at least one particular embodiment. The above description of the CD1 smart card according to various embodiments with reference to Figures 2 to 5 applies by analogy to the manufacturing method illustrated in [Fig. 9].

[0113] During a supply step S2, a card body 100 is formed (or supplied) comprising a metal layer 103 as previously described. In particular, this card body 6 is formed at least in part by a metal layer 103, this metal layer 103 comprising a recess zone 104, as already described.

[0114] During a forming step S4, an RF antenna is formed (or assembled) on or in the card body 100 in or opposite the recess area 104 of the metal layer 103, as already described. According to certain embodiments, the RF antenna may comprise a first winding of turns and a second winding of turns, the two windings being formed (or assembled) opposite each other. The antenna insert being made of a printed circuit, this is produced by conventional printed circuit technology on a dielectric substrate such as, for example, FR4 material. The antenna traces are produced in this case by a classic subtractive printed circuit board process (mechanical or chemical etching) with optional electroplated or electroless metal growth to achieve a certain thickness.

[0115] During a step S6, a pattern made of conductive material is formed in the center of the antenna or more precisely in a surface located in the center of the antenna. When the antenna comprises two windings of turns, a first and a second pattern are deposited facing each other on either side of the substrate 105, in an area located in the center of the antenna windings, the innermost turn of the winding defining a central circle without turns. The traces of the pattern made of conductive material are produced in this case by a conventional subtractive printed circuit process (mechanical or chemical etching) with optional electroplated or electroless metal growth to obtain a certain thickness.

[0116] In a step S8, an RF chip is assembled such that the RF chip is electrically connected to the RF antenna.

[0117] The conventional process for manufacturing the CD1 card then comprises at least one process of depositing a layer of resin or filling, step S10, the area of ​​the cavity located above the antenna, in order to ensure sealing between these two mechanically different elements, i.e. the substrate of the printed circuit and the metal layer which surrounds it. This sealing step is essential to give the entire product a monolithic appearance in order to satisfy a certain aesthetic aspect, but above all to give mechanical stability to the card by preventing it from tearing during the various folding cycles throughout the life cycle of the product. This is notably obtained thanks to the presence of the pattern made of conductive material according to any one of the embodiments of the invention, making it possible to reduce the surface area left empty in the center of the antenna.

[0118] The method may further comprise an additional step (not shown) of depositing a plastic layer for protecting the card, represented by the layer(s) 101a and 101b in FIGS. 2a and 2b. This layer is for example a polycarbonate layer. In other embodiments, this layer may be PVC, PETF or other polymers.

[0119] A person skilled in the art will understand that the embodiments and variants described above constitute only non-limiting examples of implementation of the invention. In particular, a person skilled in the art may envisage any adaptation or combination of the embodiments and variants described above, in order to meet a very specific need in accordance with the claims presented below.

Claims

Claims

1. Smart card (CD1) comprising: - a card body (100) formed at least in part by a metal layer (103) comprising a recess area (104) and at least two plastic layers on either side of the metal layer; - at least one RF antenna (ATI, AT2) arranged in or opposite the recess area (104); - a module comprising an RF chip, the module being positioned in a through cavity of a plastic layer and being electrically connected to the RF antenna (ATI); - a pattern of conductive material connected in parallel to said at least one antenna (ATI) and arranged in or opposite the recess zone (104) and comprising - a central zone whose conductive surface is less than or equal to 20% of the surface of a central zone circumscribed by said antenna - at least two traces of conductive material (TO separated from each other and extending from said central zone of said pattern,said at least two traces of conductive material being distant from each other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on said card, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency.,

2. Smart card according to claim 1 wherein said antenna comprises two RF windings (ATI, AT2) electrically connected to each other and located respectively on either side of said recess area, two patterns of conductive material being located respectively on either side of said recess area and each connected to one of the RF windings.

3. Smart card according to one of the preceding claims in which said determined communication frequency is 13.56 MHz and complies with the ISO 14443-2 or ISO 10373-6 standard.

4. Smart card according to one of the preceding claims in which - the at least one antenna comprises a plurality of turns, - the central area of ​​said pattern is round in shape and centered on the center of the turns of the antenna, and - the traces of said pattern are circular traces centered on the center of the turns and forming rings around the round central area of ​​the pattern, the traces being separated from each other each by first non-conductive circular areas extending between each of the circular traces and a second rectilinear area connecting said first non-conductive circular areas and intersecting each of the conductive circular traces of said pattern so as not to form a closed loop to avoid the formation of eddy currents on said card, - the first non-conductive circular areas each being open so as to ensure conductive continuity between the central area and the traces of said pattern.

5. Smart card according to one of claims 1 or 2 wherein - the at least one antenna comprises a plurality of turns, - said pattern of conductive material comprises a central conductive surface of round shape centered on the center of the turns of the antenna and interconnecting a plurality of said pairs of traces of conductive material, - said traces of conductive material being of rectangular shape and connected to said central conductive surface by one of their ends, the other end being free, and distributed uniformly around said central area of ​​the pattern.

6. Smart card according to one of claims 1 or 2 wherein - the at least one antenna comprises a plurality of turns, - said pattern of conductive material comprises a central conductive surface of round shape centered on the center of the turns of the antenna and interconnecting a plurality of said pairs of traces of conductive material, - said traces of conductive material being of helical shape and connected to said central conductive surface by one of their ends, the other end being free, and distributed uniformly around said central area of ​​the pattern.

7. Smart card according to one of claims 5 or 6 in which the traces of conductive material are distributed uniformly around the round central surface.

8. Smart card according to one of the preceding claims in which the number of conductive traces depends on the value of the connected capacitance.

9. A smart card according to any preceding claim wherein the traces have a width configured to reduce eddy currents present on said smart card.

10. A method of manufacturing a smart card (CD1) formed at least in part by a card body comprising a metal layer (103), said metal layer comprising a recess area (104), the method comprising: a) forming (S4) on or in the card body at least one first RF antenna (ATI, AT2) in or facing the recess area of ​​the metal layer; b) forming (S6) at least one pattern of conductive material in the center of the at least one antenna connected in parallel to said at least one antenna and arranged in or facing the recess area, the metal pattern comprising - a central area whose conductive surface is less than or equal to 20% of the surface of a central area circumscribed by said antenna - at least two traces of conductive material (T;) separated from each other and extending from said central area of ​​said pattern,said at least two metal traces being spaced apart from each other in order to allow a magnetic field to pass through said antenna and configured so as not to form a closed loop to avoid the formation of eddy currents on said card, said pattern of conductive material being configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern associated with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency c) assembling (S8) an RF chip so that said RF chip is electrically connected to said at least one antenna, d) depositing (S 10) a layer of resin to seal the metal layer and the recess area comprising said at least one antenna and said at least one metal pattern.,

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