Metallic chip card and method for its manufacture

Abstract

The present invention relates to a smart card comprising: - a metallic layer including an RF antenna disposed within or in front of a recessed area; - a module including an RF chip; - a pattern of conductive material disposed within or in front of the recessed area and comprising: - a central area; - at least two separate and distant traces of conductive material, 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 is configured to form a capacitance electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern combined with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency.

Description

Technical Field

[0001] The invention relates to the field of smart cards and more particularly to metallic smart cards capable of operating in contactless mode. Previous technique

[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 forms depending on their respective uses. Smart cards can be designed to perform various types of functions, including carrying out transactions such as banking transactions (payments, transfers, etc.), authentication transactions, and so on.

[0003] As is well known, a smart card typically consists of a card body equipped with an electronic chip configured to exchange signals with the outside world and perform various functions depending on the card's intended use. To achieve this, smart cards are equipped with communication means that allow them to interact with the outside world, typically with an NFC reader or external reader.

[0004] Traditionally, a smart card is designed to cooperate with an external NFC reader via external contacts accessible on the card's surface. An external NFC reader can then position appropriate contact pins on the card's external contacts to establish contact communication.

[0005] More recently, contactless smart cards have seen increasing growth due to the speed and simplicity of contactless transactions. To achieve this, contactless cards incorporate a radio frequency (RF) antenna that allows the exchange of RF signals with an external NFC reader (for example, using NFC, or Near Field Communication). This RF antenna is typically composed of multiple conductive coils extending into the card's body.

[0006] The structure and appearance of smart cards can vary. Metallic smart cards, in particular, are experiencing growing interest due to their attractive aesthetics (metallic sheen, brushed surface effect, etc.), the high-quality impression they can provide (the substantial weight of the metal, high-end aesthetic), and the prestige they confer upon users. Because of their significant weight and high-quality impression, these cards are preferred by some users as a status symbol and a way to distinguish themselves.

[0007] However, it has been observed that the presence of metal in the body of a smart card poses significant difficulties when the card incorporates an RF antenna for contactless operation. The metal acts as electromagnetic shielding and blocks or interferes with the RF signals exchanged by the RF antenna with the outside world. The metal present in the card body can therefore disrupt contactless communication between a smart card and an external NFC reader, hindering, for example, the completion of a contactless transaction (payment or otherwise).

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

[0009] US patent 2023 / 067229 A1 describes a metallic smart card capable of operating in contactless mode, comprising a plurality of metallic layers with at least one upper metallic layer and one lower metallic layer, and an RF antenna comprising at least one conductive loop, disposed in an internal cavity formed between the upper and lower metallic layers. The upper and lower metallic layers each comprise a partial recess area Z1, Z2 opposite the at least one loop, each partial recess area having at least one opening through the thickness of the metallic layer, and each partial recess area being partially covered by at least one metallic protrusion extending from an edge of the partial recess area so as to define the outline of said at least one opening.The RF antenna coils are partially covered by the metallic protrusions, allowing a connection between the RF antenna coils and the metallic protrusions.

[0010] US patent application 2023 / 237305 A1 describes a contactless metallic smart card with an integrated "mini relay antenna." The relay antenna is embedded in a metallic insert and works in tandem with the card's RFID module, which has its own antenna. This relay antenna can be configured as nested spirals and "have a total surface area equal to 6 or 7 times the surface area of ​​the module's antenna."

[0011] US Patent 2018 / 232617 A1 describes a metallic smart card capable of operating in contactless mode, designed to improve contactless communication through a slot in the metal that channels the current induced by the magnetic field. The card in this patent has a metallic layer in which a cavity is formed. A module (RFIC chip) is embedded in this cavity, and an inlay is located in a recess within the cavity. The inlay has two coiled antennas on either side of the inlay, connected to each other by a via. The first antenna has a broad portion, and the second antenna has islands. By varying the number of islands, the size of the effective capacitor formed by the broad portion and the plurality of islands can be adjusted. Impedance matching can therefore be facilitated by adjusting the overall capacitance.

[0012] Another viable solution involves using a small antenna inserted inside or superimposed on a cavity (without metal) made in a metal sheet, with the cavity 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 the antenna itself, typically occupying the entire size of the card.

[0013] Since the magnetic field lines are closed lines, the interrogation magnetic field incident on the surrounding metallic 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 near the cavity will be diverted inwards, thus passing through the area of ​​the antenna and adding to the normal magnetic flux passing through the antenna, making its effective area larger than if it had been used without this surrounding metal.

[0014] Although the technique described above exhibits good NFC performance, it can suffer from a major technical problem. Since the antenna insert consists of a printed circuit board, this circuit is implemented using conventional printed circuit board technology on a dielectric substrate such as, for example, FR4 material. The antenna traces are produced in this case by a conventional subtractive PCB process (mechanical or chemical etching) with optional electrodeposited metal growth or without electrolysis to achieve a certain thickness. The conventional board manufacturing process then includes at least one filling process for the cavity area above the antenna to ensure a seal between these two mechanically distinct elements: the printed circuit board substrate and the surrounding metal strip.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 different folding cycles throughout the product's life cycle.

[0015] A major problem arises for this sealing / resin process to be successful and fulfill the role described above: because the NFC antenna is routed in typical closed loops, the central area of ​​the printed circuit board antenna is completely free of metal, while the antenna towers at the periphery bear the weight of the metal. This creates a structural asymmetry on the PCB surface on both sides of the circuit. This lack of homogeneity leads to poor adhesion and, consequently, a lack of the intended monolithic appearance, ultimately resulting in fragility of the entire board. Furthermore, the larger the cavity, the more severe this problem becomes.

[0016] There is therefore a need for high-performance metallic smart cards (e.g., RFID) that are simple to manufacture and capable of cooperating effectively in contactless mode with an external terminal. Description of the invention

[0017] The present invention relates to a smart card comprising: a card body formed at least in part by a metallic layer comprising a recessed area and at least two plastic layers on either side of the metallic layer; at least one RF antenna disposed in or opposite the recessed area; a module comprising an RF chip, the module being positioned in a through-hole 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 disposed in or opposite the recessed area and comprising a central area whose conductive surface is less than or equal to 20% of the surface area of ​​a central area circumscribed by said antenna; at least two traces of conductive material (Ti) separated from each other and extending from said central area of ​​said pattern,said at least two traces of conductive material being spaced apart 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 combined with the capacitance of said antenna allows the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency.

[0018] Inserting a pattern of conductive material into a central area of ​​the antenna can improve the robustness of the metallic smart card by adding a metal layer to a cavity that previously lacked metal, creating a region with a different structure than the existing metallic layer outside the cavity. The conductive material of the pattern also provides additional capacitance.

[0019] According to some embodiments, said antenna comprises two RF windings (AT1, AT2) electrically connected to each other and located respectively on either side of said recessed area, two patterns of conductive material being located respectively on either side of said recessed area and each connected to one of the RF windings.

[0020] The two patterns in conductive material can thus form a parallel capacitance and can improve the capacitive value of the entire resonant circuit formed by the pattern and the antenna.

[0021] According to some embodiments, the said determined communication frequency is 13.56 MHz and conforms to ISO 14443-2 or ISO 10373-6.

[0022] According to certain embodiments, at least one antenna comprises a plurality of turns, the central area of ​​said pattern is round 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 central round area of ​​the pattern, the traces being separated from each other by first circular non-conductive areas extending between each of the circular traces and a second straight area connecting said first circular non-conductive areas and cutting each of the circular conductive traces of said pattern so as not to form a closed loop to avoid the formation of eddy currents on said card, the first circular non-conductive areas being each open so as to ensure conductive continuity between the central area and the traces of said pattern.

[0023] According to certain embodiments, 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 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.

[0024] According to certain embodiments, 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 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.

[0025] According to some embodiments, the traces in conductive material are distributed uniformly around the central round surface.

[0026] According to some embodiments, the number of conductive traces depends on the value of the connected capacitance.

[0027] According to some embodiments, the traces have a width configured to reduce the eddy currents present on said smart card.

[0028] According to another aspect, the present invention relates to a method for manufacturing a smart card (CD1) formed at least in part by a card body comprising a metallic layer (103), said metallic layer comprising a recessed area (104), the method comprising: a) formation (S4) on or in the card body of at least one first RF antenna (AT1, AT2) in or opposite the recess area of ​​the metallic layer; b) formation (S6) of at least one pattern of conductive material at the center of at least one antenna connected in parallel to said at least one antenna and disposed in or opposite the recess area, the metallic pattern comprising a central area whose conductive surface is less than or equal to 20% of the area of ​​a central area circumscribed by said antenna, at least two traces of conductive material (T i ) separated from each other and extending from said central area of ​​said pattern, said at least two metallic traces being spaced apart 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 such that the capacitance formed by said pattern combined with the capacitance of said antenna enables the resonant circuit formed by the antenna and said pattern to resonate at a determined communication frequency; c) assembly (S8) of an RF chip such that said RF chip is electrically connected to said at least one antenna; d) deposition (S10) of a resin layer to seal the metallic layer and the recess area comprising said at least one antenna and said at least one metallic pattern.

[0029] Other features and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings which illustrate an example of an embodiment without any limiting character. Brief description of the drawings

[0030] There figure 1a represents a view of the front face of a smart card according to certain embodiments of the invention, The figure 1b represents a view of the back face of a smart card according to certain embodiments of the invention, The figure 2a represents a profile view of the layers of a smart card not assembled according to certain embodiments of the invention, the figure 2b represents a profile view of the layers of a smart card assembled according to certain embodiments of the invention, The figure 3 represents an example of a motif according to a first embodiment of the invention, The figure 4 represents an example of a motif according to a second embodiment of the invention, The figure 5 represents an example of a motif according to a third embodiment of the invention, The figure 6 represents an electrical diagram equivalent to the antenna according to certain embodiments of the invention, The figure 7 represents a comparison between a response curve obtained according to the prior art and according to an embodiment of the present invention, The figure 8 represents an embodiment giving an example of the dimensions that can be used for the motif, The figure 9 represents a method for manufacturing a smart card according to certain embodiments of the invention. Description of the implementation methods

[0031] As previously stated, the invention relates to metallic smart cards configured to operate in contactless mode, and also concerns a method for manufacturing such smart cards. In this document, a "metallic smart card" means a smart card comprising a metal or a combination (alloy) of metals, for example in the form of a metallic layer or a plurality of metallic layers.

[0032] As mentioned previously, a contactless smart card is inherently designed to communicate wirelessly with external devices, specifically with an external NFC reader. To this end, a contactless smart card incorporates a radio frequency (RF) antenna to exchange (receive and / or transmit) RF signals with an external NFC reader. Such a smart card may also be capable of operating in contact mode, using external contacts designed for this purpose on the card's surface: these are known as "dual-interface" cards, which are thus capable of functioning in both contactless and contact modes.

[0033] Today, there is strong user demand for metallic smart cards, particularly for the reasons mentioned previously (aesthetics, high-quality printing, prestige, etc.). It is especially desirable to produce smart cards where the majority (or a significant portion) of the card body is made of metal, or at least where the card body includes a metallic plate (or metallic layer), in order to achieve a certain uniformity and quality in the visual and aesthetic appearance of the card.

[0034] As mentioned previously, when the antenna has a central area devoid of metal, the board surface exhibits structural asymmetry due to the uneven distribution of metal across the board. The central area of ​​the antenna on the printed circuit board is completely metal-free, while the antenna coils at the periphery bear the metal. This creates a structural asymmetry on the printed circuit board surface on both sides of the circuit. To better understand the problem, in some embodiments, the antenna coils are typically thicker than 30 µm and can reach 90 µm, which can disrupt the homogeneity of the sealing material on the printed circuit board surface.

[0035] In the present exposition, examples of implementations of the invention are described in relation to a "dual" type smart card, that is to say, a card with a dual communication interface, capable of communicating both in contact mode (via external contacts) and in contactless mode (via an RF antenna structure). It should 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 also has the capacity to operate in contact mode.

[0036] Furthermore, in the following examples, the smart card is considered to be a bank card, such as a payment card. This smart card may conform to ISO 7816 and may operate according to the EMV standard, although neither of these aspects is mandatory for implementing the invention. More generally, the invention applies to any metallic smart card configured to implement a contactless transaction, 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"). In general, the smart card of the invention can be configured to perform any type of transaction, such as banking transactions (payment, transfer, debit transactions, etc.), authentication transactions, and so on.

[0037] 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.

[0038] The terms "first(s)", "second(s)", etc.) are used in this document by arbitrary convention to allow identification and distinction of different elements (such as keys, devices, etc.) implemented in the embodiments described below.

[0039] THE figures 1a et 1b represent a front view and a rear view of a CD1 smart card according to an embodiment of the present invention. If the figure 1a represents a view of the front face, the figure 1b represents a view of the rear face and vice versa. The method of implementation of figures 1a et 1b is described in more detail later in the figures 2a et 2b and in the figure 3 .

[0040] The CD1 smart card as shown in the embodiment of figures 1a et 1b The CD1 board includes a metallic layer 103, a first antenna winding AT1, and a second antenna winding AT2. The two antenna windings AT1 and AT2 are electrically connected using metallic vias or perforations. The CD1 board also includes a pattern M1 and a pattern M2 located at the center of the antenna. The two patterns M1 and M2 are electrically connected using metallic vias or perforations. These two patterns are also each electrically connected to the antenna.

[0041] The AT1 and AT2 antenna windings, as well as the M1 and M2 patterns, are located in a substrate itself situated in a recess in the metal area. The various layers of the CD1 board are illustrated in more detail in the... figures 2a et 2b One or more transparent layers, for protection for example, may also be present on the metallic layer, as shown in figure 2a et 2b .

[0042] The patterns M1 and M2 comprise circular metallic traces centered on the center of the antenna windings. The pattern further includes a central, round portion C1 made of conductive material (respectively C'1 on the other side). Each of the traces T11, T12, and T13 (respectively T'11, T'12, and T'13 on the other side) is isolated from the neighboring trace by a gap of non-conductive material, such as the substrate comprising the antenna and the pattern. Moreover, each trace does not form a closed circular surface and is open via a gap P2 connecting the center C1 to the substrate between the pattern and the antenna. Thus, the traces of conductive material are spaced apart to allow a magnetic field to pass through the antenna and are configured so as not to form a closed loop, thereby preventing the formation of eddy currents on the CD1 board. The pattern of conductive material forms a capacitive circuit.It is configured so that the capacitance formed by the pattern combined with the capacitance of said antenna allows the resonant circuit formed by the antenna and the pattern to resonate at a determined communication frequency.

[0043] According to some embodiments, on one side of the card, the radius of the circle formed by the innermost turn of winding AT1 is 11.51 mm and that of the outermost turn is 12.12 mm. On a second side, these radii, for winding AT2, are respectively 11.31 mm and 12.32 mm. The area located inside the inner turn of winding AT1 or AT2 can be approximately equal to 387 mm².

[0044] Thus the two windings AT1 and AT2 may not overlap exactly, each on one side of the card, but be slightly offset.

[0045] THE figures 2a et 2b represent respectively an exploded view and an assembled view of a smart card 1 according to an embodiment of the invention.

[0046] In the examples given, the smart card is in the ID1 format of a credit card, although other forms are possible to implement the invention.

[0047] On the figure 2a We observe a first layer of plastic material 101a and a second plastic layer 101b, one of whose objectives is to protect the internal layers of the CD1 smart card. The optional layers 101a and 101b are for example made of polycarbonate and preferably transparent.

[0048] Under layers 101a and 101b, resin layers 102a and 102b are deposited respectively. One of the objectives of the resin layers is to seal the internal layers of the CD1 smart card.

[0049] The CD1 smart card is formed or comprises a metallic layer 103 including a recessed area 104 in which a substrate 105 is housed (inserted). The recessed area 104 is an opening or through-area provided in the metallic layer 103 to allow the positioning of the AT1 antenna and possibly the AT2 antenna (the AT2 antenna being connected to the AT1 antenna).

[0050] The shape and dimensions of this recessed area 104 can be adapted as needed. For example, the recessed area 104 is rectangular. This metallic layer 103 can be made of a single metal, such as stainless steel or aluminum, or an alloy of several different metals. The metallic layer 103 may comprise a plurality of metallic sublayers.

[0051] As a particular example, the 100 card body and more generally the CD1 smart card is ferrite-free, which simplifies the manufacture of the card.

[0052] An AT1 antenna and a conductive material motif M1, as disclosed by embodiments of the present invention, for example with reference to Figures w3, 4 and 5, are arranged on a substrate 105. As illustrated in the figure 2a The CD1 card can be equipped with an antenna comprising a first winding, designated AT1, and a second winding, designated AT2. One winding is present on each side of the substrate, and therefore on each face of the CD1 smart card. The two windings are physically connected by a via (or a metallic perforation). Two motifs, M1 and M2, made of conductive material, are also included, with one motif physically connected to each winding. The presence of a winding on each face allows for optimal use of the available surface area on the substrate, thus maximizing the energy captured from ambient electromagnetic radiation. The number of turns on each face of the substrate is advantageously between two and five, which means that only a modest fraction of the substrate surface is occupied near its perimeter, typically between 5 and 10% of this surface.

[0053] On the figure 2b , we observe a profile view of the CD1 smart card, the layers mentioned in reference to the figure 2a being assembled to form the smart card. During the assembly of the CD1 card, the resin 102a comes to conform to the surface between the assembly formed of the metal layer 103 and the substrate 105 and the plastic layer 101a.

[0054] It can be seen that the conductive material pattern placed at the center of the antenna fills the gap that would otherwise exist, thus improving layer adhesion, for example, during resin application. This results in a board with improved structural homogeneity, making it more robust. In other words, the pattern allows for better filling of the central part of the antenna on both sides of the PCB, leading to greater homogeneity during resin application and therefore preventing these structural problems.

[0055] Of course, the CD1 smart card may include other elements or layers not shown in the figures. In particular, the CD1 smart card may include an RF chip, RF standing for radio frequency throughout this 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 AT1 antenna (and to the AT2 antenna, if present).

[0056] Thus, the present invention relates to a smart card comprising: a card body formed at least in part by a metallic layer comprising a recessed area and at least two plastic layers on either side of the metallic layer; at least one RF antenna disposed in or opposite the recessed area; a module comprising an RF chip, the module being positioned in a through-hole 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 disposed in or opposite the recess area and comprising a central area whose conductive surface is less than or equal to 20% of the surface area of ​​a central area 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 metallic traces being spaced apart 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 in 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.

[0057] Preferably, all traces of a pattern are located in the same horizontal plane with respect to the faces of the smart card.

[0058] On the figures 2a et 2b We observe that the pattern in conductive material (each pattern in conductive material on each side of the card) is positioned at the center of the antenna and consists of at least two metallic traces. We note on the figures 2a et 2b that the pattern in conductive material includes, for example, four traces in conductive material.

[0059] The formation of the pattern in the form of traces can help to avoid disturbing the magnetic field and thus to avoid altering the operation of the antenna.

[0060] Les figures 3, 4 , et 5 allow us to illustrate examples of patterns in 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.

[0061] The reasons for figures 3, 4 et 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 loop of the antenna.

[0062] The pattern consists of at least two conductive traces, separated by at least one space and with at least one space from the innermost / nearest loop of the antenna, on each side of the substrate. More than two traces may be used, provided that each pair is separated by a space. All traces on each side of the substrate form a continuous galvanic surface. The conductive traces of each pattern are configured to avoid forming loops, thus preventing the formation of eddy currents in the metallic form facing the incident magnetic field.

[0063] Furthermore, the central part of the motif, depicted on the figures 3, 4 et 5 respectively by references C 1 , C 2 and C 3 occupies an area less than or equal to 20% of the area delimited by the inner loop of the antenna and contained within this loop.

[0064] The central part of each pattern may consist of a continuous metallic patch (or surface) having an area of ​​less than 20% of the internal area defined by the area contained within the innermost loop of the antenna to make eddy current losses negligible.

[0065] By forming the pattern in conductive material with separate, interlacing conductive traces, the induced magnetic field lines can pass through the antenna without altering the magnetic field, thus preserving the antenna's behavior. Furthermore, using patterns where the conductive traces do not form a closed loop can reduce the effects of eddy currents, rendering them negligible.

[0066] The conductive material pattern adds additional capacitance to the antenna, increasing its overall capacitance. Thus, for the same desired resonant frequency, the diameter of the innermost loop of the antenna is larger, with a reduced number of turns and the same antenna pitch, than for a state-of-the-art antenna without this conductive material pattern, while maintaining low resistance.

[0067] The characteristics of the added capacitance, including the spacing between 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 resonant frequency, chosen according to the needs of the card and in particular the standards with which the card must comply.

[0068] For the sake of clarity, figures 3, 4 et 5The patterns represent the antenna design on one side of the CD1 board. The pattern can easily be reproduced on the other side, as the two patterns are opposite each other on each side. Furthermore, it is understood that the two patterns are electrically connected, for example, using vias and / or by the electrical connection to the antenna, with the turns of antenna AT1 connected to the turns of antenna AT2 vias. The patterns are connected to the antenna by terminals La and Lb, which are illustrated in the diagram. figure 6 on the electrical diagram equivalent to the antenna.

[0069] La figure 3 This represents a first example of a pattern made of conductive material positioned at the center of the antenna, on each side of the substrate. Only one face is shown, therefore only one of the two patterns is represented.

[0070] In accordance with the implementation method of the figure 3 , at least one antenna comprises a plurality of turns, the central area of ​​the pattern is round 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 circular non-conductive areas extending between each of the circular traces and a second straight area connecting the first circular non-conductive areas and cutting each of the circular conductive traces of the pattern so as not to form a closed loop to avoid the formation of eddy currents on the board, the first circular non-conductive areas being each open so as to ensure conductive continuity between the central area and the traces of the pattern.

[0071] The pattern comprises three conductive metallic traces T11, T12, and T13. These three metallic traces are circular in shape, conforming to the shape of the antenna turns; that is, the center of each trace is the same, or nearly the same, as the center of the antenna turns. Trace T11, the outermost trace of the pattern and closest to the turns, is preferably located at a distance D from the innermost antenna turn. The minimum distance D may depend on the technology used and can be calculated to avoid short-circuiting the pattern with the antenna turn.

[0072] According to some embodiments, the distance D is between 200 µm and 1 mm.

[0073] The three traces are connected to each other and to the center C1. They are separated by a gap of non-conductive material, called an insulating gap (such as the substrate), except for a portion of their circumference. This allows for galvanic continuity between the traces and the center. The gap of non-conductive material partially separating them connects the spaces 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 gap that follows the circumference of the traces, except for a portion of its circumference, leaving an opening connecting the traces to each other and to the center of the pattern. This opening could, for example, have a width d2 of 200 µm.

[0074] The conductive opening left between the traces and the center of the pattern can, for example, be located diametrically opposite to the insulating space joining the center of the pattern to the non-conductive area located between the antenna (its innermost winding) and the outermost trace of the pattern.

[0075] It can be noted that this opening can be different for each trace.

[0076] In some embodiments, the distance d2 is determined to maintain an open circuit. The distances d2, d3, and d4 can be equal or all different. Using identical distances d2, d3, and d4 helps improve mechanical strength because the symmetry is better and can also facilitate the printed circuit board manufacturing process, particularly during chemical etching baths.

[0077] Trace T11, the outermost trace, is connected to a terminal La of the antenna. When the other side of the board includes 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 antenna winding present on this second side of the CD1 board.

[0078] La figure 4 This represents a second example of a pattern made of conductive material positioned at the center of the antenna, on each side of the substrate. Only one face is shown, therefore only one of the two patterns is represented.

[0079] According to this embodiment, the pattern comprises at least twelve conductive traces or conductive traces T21, T22, T23, T24, T25, T26, T27, T28, T29, T30, T31, T32. The twelve conductive traces are connected to each other at one end by means of a central conductive surface C2, which may be a round surface, the area of ​​which is at most 20% of the size of the area delimited by the inner loop of the antenna and contained within that loop. According to other embodiments, this central surface may be of a shape other than round, for example, elliptical, square, or rectangular. This central surface C2 may be metallic.

[0080] The distances d21, d22, d23... to d32 are equal or different and represent the spacing between the traces. In some embodiments, the distances d21 to d32 are equal, and in others, they are different. Using identical distances d21 to d32 helps improve mechanical strength because the symmetry is better and can also facilitate the printed circuit board manufacturing process, particularly during chemical etching baths.

[0081] It is advantageous to use thin traces (also called strands), on the order of 200 µm. This can help reduce eddy currents in each strand. However, the thinner the strands, the greater the number of strands needed to achieve a desired capacitance value. Thus, the size and number of strands can be determined based on the required capacitance value.

[0082] The twelve traces T 21, T 22, T 23, T 24, T 25, T 26, T 27, T 28, T 29, T 30, T 31, T 32 can be of the same length or of different lengths. When the traces are of the same length, the resin flow is advantageously improved by making it more homogeneous.

[0083] The twelve traces are rectangular in shape. They are configured to form a surface based on a target capacity value.

[0084] The end of the traces not connected to the central surface is free and located at a distance D' from the inner loop of the antenna. The minimum distance D' may depend on the technology used and can be calculated to avoid a short circuit between the pattern and the antenna loop.

[0085] La figure 5 This represents a third example of a pattern made of conductive material positioned at the center of the antenna, on each side of the substrate. Only one face is shown, therefore only one of the two patterns is represented.

[0086] According to this embodiment, the conductive material pattern comprises at least eight conductive traces T40, T41, T42, T43, T44, T45, T46, and T47. These eight conductive traces are connected at one end by a central conductive surface C3, which may be a round surface with a surface area not exceeding 20% ​​of the size of the area enclosed within the inner loop of the antenna. In other embodiments, this central surface may be of a shape other than round, for example, elliptical, square, or rectangular. This central surface C3 may be metallic.

[0087] The distances d40, d42, d42... to d47 are equal or different and represent the spacing between the traces. In some embodiments, the distances d31 to d38 are equal, and in others, they are different. Using identical distances d40 to d47 helps improve mechanical strength because the symmetry is better and can also facilitate the printed circuit board manufacturing process, particularly during chemical etching baths.

[0088] It is advantageous to use thin traces (also called strands), on the order of 200 µm. This can help reduce eddy currents in each strand. However, the thinner the strands, the greater the number of strands needed to achieve a desired capacitance value. Thus, the size and number of strands can be determined based on the required capacitance value.

[0089] The eight conductive traces T40, T41, T42, T43, T44, T45, T46, and T47 can be of the same or different lengths. When the traces are of the same length, resin flow is advantageously improved by making it more homogeneous.

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

[0091] The end of the traces not connected to the central surface is free and located at a distance D" from the inner loop of the antenna. The minimum distance D" may depend on the technology used and can be calculated so as to avoid a short circuit of the pattern with the loop of the antenna.

[0092] La figure 6 represents an example of an electrical diagram equivalent to the antenna as proposed according to the different embodiments of the invention.

[0093] The inductance La and capacitance Ca of the antenna can be seen, along with an additional capacitance Cmotif corresponding to the capacitor formed by the metallic traces of the pattern. The resonant RLC circuit thus formed, consisting of the resistance Ra, the impedance La, and the capacitances Ca and Cmotif, allows the antenna's resonant frequency to be adapted so that it is, for example, equal to 13.56 MHz, enabling contactless communication of the RFID type with an external reader, according to one of the standards ISO 14443, ISO 10373, ISO 18745, ISO 15693, or EMVCo. La figure 6 allows us to understand that the patterns in conductive material are connected to L a and L b.

[0094] Advantageously, as mentioned previously, the antenna can consist of turns arranged on each face of the substrate, and vias allow the turns to be connected from one face to the other. In this case, we can speak of two antennas, AT1 and AT2. This ensures continuity in the loops formed by these turns. The connection points La and Lb can therefore be located on either side of the substrate.

[0095] To obtain a resonant frequency of 13.75 MHz, one can choose an inductance value for LA of 1.29 µH, a resistance value for RA of 4.76 Ohms, a capacitance value for CA of 1 to 2 pF and a capacitance value for C motif of 54.23 pF. The capacitance of the RF chip, on the order of 50 pF, is added to these two capacitances.

[0096] La figure 7 represents a comparison between a response curve obtained according to the prior art and according to an embodiment of the present invention. More specifically, 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 pattern in conductive material implemented in figure 3 (curves C3 and C4). An ISO reference curve representing the reference values ​​required by ISO 14443-2 is also shown 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 lies.

[0097] It can therefore be seen that the conductive material pattern can improve the reaction time. Thus, the charge modulation amplitude required by ISO 14443-2 is achieved. for a magnetic field of 1.1 Amperes per meter, represented by point A on the curve for a CD1 card according to the embodiment of la figure 3 and for a magnetic field of 1.5 Amperes per meter, represented by point B on the curve for a map that does not implement the present invention.

[0098] It can therefore be observed that the card implementing an embodiment of the present invention can, on the one hand, trigger an activation of the card more quickly and, on the other hand, with a greater amplitude of charge modulation, than when the present invention is not implemented.

[0099] There figure 8 represents an embodiment of motifs M1 and M2, each located on one face of card CD1, and illustrates orders of magnitude of dimensions that can be used for motifs M1 and M2 according to certain embodiments of the invention, motifs M1 and M2 being motifs such as those represented in figure 3 . Examples of dimensions of pattern M1

[0100] Note 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 gap between the traces can be 0.2 mm. The solid surface of center C1 has an area of ​​162.94 mm², and the value of p2 is 0.20 mm. The outer radius of the last trace is 7.54 mm. Examples of dimensions of pattern M2

[0101] Note 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 C1 has an area of ​​148.03 mm², and the value of p2 is 0.20 mm. The outer radius of the last trace is 7.47 mm.

[0102] The fabrication of a printed circuit board has a certain tolerance depending on the technology used. Since the capacitance provided by the pattern synthesizes its capacitive value as a function of the substrate's permittivity, its thickness, and the surface area of ​​the opposing electrical plates, the dimensions of the pattern are chosen to be slightly larger on one layer than on the other (i.e., the dimensions of M1 relative to M2) in order to ensure a precise surface area of ​​the capacitor plates and thus to overcome the effect of the tolerance and precision of the technology used for the printed circuit board.

[0103] La figure 9 schematically represents a manufacturing process for 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 refers to figures 2 à 5 applies by analogy to the manufacturing process illustrated in figure 9 .

[0104] During a supply step S2, a card body 100 is formed (or supplied) comprising a metallic layer 103 as previously described. In particular, this card body 6 is formed at least in part by a metallic layer 103, this metallic layer 103 comprising a recessed area 104, as already described.

[0105] During a forming step S4, an RF antenna is formed (or assembled) on or within the card body 100 in or opposite the recess 104 of the metal layer 103, as previously described. In some 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. Since the antenna insert is a printed circuit board, it is manufactured using conventional printed circuit board technology on a dielectric substrate such as, for example, FR4 material. The antenna traces are produced in this case by a conventional subtractive printed circuit board process (mechanical or chemical etching) with optional electrodeposited metal growth or without electrolysis to achieve a specific thickness.

[0106] During step S6, a pattern of conductive material is formed at the center of the antenna, or more precisely, within a surface located at the center of the antenna. When the antenna comprises two windings, a first and second pattern are deposited opposite each other on either side of the substrate 105, in an area located at the center of the antenna windings. The innermost turn of the winding defines a central circle without a turn. The traces of the pattern in conductive material are produced in this case by a conventional subtractive printed circuit board process (mechanical or chemical etching) with optional electrodeposited metal growth, or without electrolysis, to achieve a certain thickness.

[0107] During an S8 step, an RF chip is assembled so that the RF chip is electrically connected to the RF antenna.

[0108] The conventional manufacturing process for the CD1 card includes at least one resin deposition or filling step, S10, of the cavity area above the antenna to ensure a seal between these two mechanically distinct elements: the printed circuit board substrate and the surrounding metal layer. This sealing step is essential to give the entire product a monolithic appearance for aesthetic purposes, but more importantly, to provide mechanical stability to the card, preventing it from tearing during the various folding cycles throughout the product's lifecycle. This is achieved, in particular, by the presence of the conductive material pattern according to any one of the embodiments of the invention, which reduces the open area at the center of the antenna.

[0109] The process may further include an additional step (not shown) of depositing a protective plastic layer on the card, represented by layer(s) 101a and 101b on les figures 2a et 2b . This layer is, for example, a polycarbonate layer. In other embodiments, this layer can be PVC, PETF, or other polymers.

[0110] A person skilled in the art will understand that the embodiments and variations described above are merely non-limiting examples of how the invention can be implemented. In particular, a person skilled in the art may consider any adaptation or combination of the embodiments and variations described above to meet a specific need in accordance with the claims set forth below.

Claims

1. Smartcard (CD1) comprising: - a card body (100) formed at least in part by a metal layer (103) comprising a recess region (104) and at least two plastics layers on either side of the metal layer; - at least one RF antenna (AT1, AT2) arranged in or opposite the recess region (104); - a module comprising an RF chip, the module being positioned in a cavity that passes through a plastics layer and being electrically connected to the RF antenna (AT1); - a conductive-material pattern that is connected in parallel with said at least one antenna (AT1) and arranged in or opposite the recess region (104) and comprises - a central region, the conductive surface area of which is less than or equal to 20% of the surface area of a central region contained by said antenna - at least two conductive-material traces (Ti) that are separated from one another and extend from said central region of said pattern, said at least two conductive-material traces being remote from one another in order to allow a magnetic field to pass through said antenna and being configured so as not to form a closed loop, in order to prevent the formation of Foucault currents on said card, said conductive-material pattern being configured to form a capacitance that is electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern, which is 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. Smartcard according to Claim 1, wherein said antenna comprises two RF windings (AT1, AT2) that are electrically connected to one another and respectively situated on either side of said recess region, two conductive-material patterns being respectively situated on either side of said recess region and each connected to one of the RF windings.

3. Smartcard according to either of the preceding claims, wherein said determined communication frequency is 13.56 MHz and conforms to the standard ISO 14443-2 or ISO 10373-6.

4. Smartcard according to one of the preceding claims, wherein - the at least one antenna comprises a plurality of coils, - the central region of said pattern is round and centred on the centre of the coils of the antenna, and - the traces of said pattern are circular traces centred on the centre of the coils and forming rings around the round central region of the pattern, the traces each being separated from one another by first nonconductive circular regions extending between each of the circular traces and a second rectilinear region connecting said first nonconductive circular regions and interrupting each of the conductive circular traces of said pattern so as not to form a closed loop, in order to prevent the formation of Foucault currents on said card, - the first nonconductive circular regions each being open so as to ensure a conductive continuity between the central region and the traces of said pattern.

5. Smartcard according to either of Claims 1 and 2, wherein - the at least one antenna comprises a plurality of coils, - said conductive-material pattern comprises a round conductive central surface centred on the centre of the coils of the antenna and interconnecting a plurality of said pairs of conductive-material traces, - said conductive-material traces being rectangular, connected to said conductive central surface by one of their ends, the other end being free, and uniformly distributed around said central region of the pattern.

6. Smartcard according to either of Claims 1 and 2, wherein - the at least one antenna comprises a plurality of coils, - said conductive-material pattern comprises a round conductive central surface centred on the centre of the coils of the antenna and interconnecting a plurality of said pairs of conductive-material traces, - said conductive-material traces being helical, connected to said conductive central surface by one of their ends, the other end being free, and uniformly distributed around said central region of the pattern.

7. Smartcard according to either of Claims 5 and 6, wherein the conductive-material traces are uniformly distributed around the round central surface.

8. Smartcard according to one of the preceding claims, wherein the number of conductive traces depends on the value of the connected capacitance.

9. Smartcard according to one of the preceding claims, wherein the traces have a width that is configured to reduce the Foucault currents present on said smartcard.

10. Method for manufacturing a smartcard (CD1) that is formed at least in part by a card body comprising a metal layer (103), said metal layer comprising a recess region (104), the method comprising: a) forming (S4), on or in the card body, at least one first RF antenna (AT1, AT2) in or opposite the recess region of the metal layer; b) forming (S6) at least one conductive-material pattern at the centre of the at least one antenna connected in parallel with said at least one antenna and arranged in or opposite the recess region, the metal pattern comprising - a central region, the conductive surface area of which is less than or equal to 20% of the surface area of a central region contained by said antenna - at least two conductive-material traces (Ti) that are separated from one another and extend from said central region of said pattern, said at least two metal traces being remote from one another in order to allow a magnetic field to pass through said antenna and being configured so as not to form a closed loop, in order to prevent the formation of Foucault currents on said card, said conductive-material pattern being configured to form a capacitance that is electrically connected to the antenna, the value of which is determined so that the capacitance formed by said pattern, which is 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 (S10) a layer of resin in order to seal the metal layer and the recess region comprising said at least one antenna and said at least one metal pattern.

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