Metallic antenna insert for smart cards and smart cards incorporating such an antenna insert

Abstract

The invention relates to an antenna insert (1) for a smart card with a contactless communication interface or a dual contact and contactless communication interface, characterized in that it is devoid of a plastic layer and essentially consists of a metal foil (2) having conductive turns (3, 4, 5) delimited by areas (6) rendered non-conductive by anodizing. Figure for the Abstract: Figure 5B

Description

Title of the invention: Metallic antenna insert for smart card and smart card incorporating such an antenna insert

[0001] The present invention relates to a new antenna insert structure for contactless or mixed contact / contactless smart cards, as well as a new method for manufacturing such an antenna insert. PRIOR TECHNOLOGY

[0002] For contactless or mixed contact / contactless smart cards, it is necessary to incorporate an antenna within the card body. Antenna inserts, primarily made of plastic, have long been used for this purpose to ensure good radio frequency communication performance. These inserts typically consist of a PET substrate with an aluminum antenna layer on each side, featuring turns formed by etching the aluminum layer. This substrate is then surrounded by other plastic layers, the whole assembly being bonded by lamination, to form an antenna insert ready to be integrated between the outer layers of a card body. Such a structure is described, in particular, in document FR 2 944 122 Bl.

[0003] However, in the field of smart cards, particularly those used for banking applications, some demand has recently shifted towards heavier, more premium-looking cards than traditional plastic-bodied smart cards, due to concerns about improved handling and increased differentiation. A frequently sought-after aspect is the noise such a smart card makes when placed on a surface, which must be significantly different from the noise generated by a card made primarily of plastic.

[0004] However, the majority of metallic smart cards currently on the market still contain a plastic component to ensure adequate radio frequency communication performance. The only smart cards with a predominantly metallic structure do not meet the criteria of banking sector standards, such as the so-called EMVCo standards.

[0005] It is therefore necessary to propose a new contactless smart card or dual communication interface card with increased differentiation and higher value, in particular a higher weight than known smart cards, but while retaining its communication properties and ability to be graphically personalized. PURPOSE OF THE INVENTION

[0006] The invention aims to provide a new smart card structure capable of satisfying the conflicting requirements of a structure that is more valuable than the material plastic, while exhibiting a contactless communication capability that complies with the requirements of EMVCo type specifications.

[0007] Another objective of the invention is to offer such a smart card while maintaining a simple structure that is easy to mass-produce at a reduced cost and with very high reliability.

[0008] In particular, the invention aims to provide a 100% metallic antenna insert, capable of being integrated with a card body that is also metallic or made of a heavy, durable and valuable material, while exhibiting radio frequency performance compatible with bank card standards. SUBJECT OF THE INVENTION

[0009] In principle, the invention consists of producing antenna coils by anodizing in a sheet or block entirely of metal, and then assembling this entirely metal insert with a card body that is also metallic, or a card body formed by layers of a more noble material than plastic, such as wood, leather, glass, porcelain, etc.

[0010] Anodizing is a surface treatment often used with aluminum, which consists of creating, by electrolysis, a uniform and highly resistant layer of aluminum oxide. Anodizing also has the property of making the anodized layer electrically insulating. Thanks to this property, the invention provides for selectively anodizing the aluminum insert in order to delineate conductive zones corresponding to the turns of an antenna, and insulating zones located between and below the turns, which remain conductive.

[0011] From this all-metal insert composed of antenna coil zones and electrically insulating zones, a new type of smart card can then be constructed, composed either of a metallic card body and ferrite layers interposed between the metallic insert and the metallic card body, or of a card body composed of noble non-metallic materials such as leather, glass, porcelain, assembled with the all-metal antenna insert.

[0012] The invention therefore relates to an antenna insert for a smart card with a contactless communication interface or with a dual contact and contactless communication interface, characterized in that it is devoid of a layer of plastic material and in that it essentially consists of a metal sheet having conductive turns delimited by areas made non-conductive by anodizing.

[0013] According to one embodiment of the antenna insert, the metal sheet is an aluminum or copper sheet, 20 to 100 micrometers thick, and whose anodizing depth from one or both of its faces is between 10 and 50 micrometers.

[0014] According to an advantageous embodiment, the antenna insert further comprises on at least one of its faces a capacitor connected to the terminals of the antenna turns, said capacitor being made by a first armature made up of a non-anodized area of ​​the antenna insert, a second armature made up of a metallic pellet, and between the two armatures, a dielectric made up of an anodized area of ​​the antenna insert.

[0015] According to one embodiment, the antenna insert has conductive turns on both sides, interconnected by means of a via passing through the metal sheet.

[0016] According to one embodiment, all the faces of the insert are anodized to a shallow depth (on the order of 10 micrometers), so as to harmonize the cosmetic appearance of the faces of the antenna insert and to make the surface of the insert electrically insulating and to electrically insulate the conductive turns from the surface of the insert.

[0017] The invention also relates to a method for manufacturing an antenna insert as described above, characterized in that it comprises steps consisting of: - Mask one side of the antenna insert using a protective mask reproducing the shape of the antenna loops to be made on that side; - Immerse the antenna insert in an anodizing bath for a sufficient time initially to anodize said face to a first depth corresponding to the desired thickness of the conductive turns; - Remove the antenna insert from the anodizing bath and remove the protective mask over the conductive turns.

[0018] According to a variant of the method adapted to an insert having antenna turns on both its faces, it comprises steps consisting of: - Mask both sides of the antenna insert using a protective mask reproducing the shape of the turns to be made on each side; - Immerse the antenna insert in an anodizing bath for a sufficient time initially to anodize each face to a depth corresponding to the desired thickness of the conductive turns; - Remove the antenna insert from the anodizing bath and remove the protective mask over the conductive turns.

[0019] According to a preferred embodiment of the method according to the invention, it comprises a step consisting, after initial anodizing to delineate the conductive turns, of re-immersing the antenna insert in the anodizing bath for a second, shorter time than the first, so as to superficially anodize and electrically insulate the surface of the antenna insert overlying the antenna turns. In this way, the turns are encapsulated and protected under an anodized layer, and the cosmetic appearance of the insert faces is uniform.

[0020] The invention also relates to a smart card, characterized in that it includes at least one antenna insert as described above.

[0021] According to one embodiment, the smart card comprises a metallic body, and on at least one of the faces of said metallic body, an antenna insert as described above, as well as a ferrite layer interposed between the antenna insert and the corresponding face of the metallic body.

[0022] According to one embodiment, the smart card comprises a body formed by two outer layers of a non-metallic and electrically insulating material, and an antenna insert as described above, interposed and fixed between said two outer non-metallic layers.

[0023] According to another embodiment, the smart card comprises a body formed by a central layer of a non-metallic and electrically insulating material, interposed between two all-metallic antenna inserts as described above. DETAILED DESCRIPTION

[0024] The invention will be described in more detail with reference to the drawings, in which: - Figures IA, IB represent the two faces of the metallic antenna insert according to the invention comprising an antenna and an anodized area on one face only; - Fig. 2 represents a view along a cross-section AA of the antenna insert of Fig. 1B after anodizing one face; - Fig. 3 represents the second face of the metallic antenna insert according to the invention comprising an antenna and an anodizing on this second face; - Fig. 4 represents a cross-sectional view BB of the antenna insert of Fig. 3; - Fig. 5A represents a view of the other side of the antenna insert of Fig. 3, with the representation of the elements of a capacitor; - Fig. 5B represents a CC cross-sectional view of the antenna insert of Fig. 5A; - Fig. 6 represents a cross-sectional view of a first embodiment of a smart card incorporating two antenna inserts according to the invention; - Fig. 7 represents a cross-sectional view of a second embodiment of a smart card incorporating two antenna inserts according to the invention; - Fig. 8 represents a cross-sectional view of a third embodiment of a smart card incorporating a single antenna insert according to the invention;

[0025] It is recalled that to produce the metallic antenna insert 1 according to the invention, the principle of anodizing a metallic layer, in particular aluminium, is used.

[0026] Aluminum naturally has a surface layer of alumina that protects it from oxidation. However, this natural layer is only a few nanometers thick and is subject to deterioration. In order to create conductive tracks in an aluminum sheet, it is necessary to create non-conductive areas that are thicker and more stable than a natural alumina layer, around areas left in a non-anodized, and therefore conductive, state.

[0027] For this purpose, selective anodizing can be used, only in certain areas of the aluminum layer, so as to leave only conductive areas forming antenna loops.

[0028] To carry out the anodizing of aluminum itself, electrolysis in an acidic medium can be performed using a known method. In this case, the insulating layer is not created by adding material but by controlled oxidation of the substrate in order to passivate it. The nature of the anodizing baths and the cathode can easily be adapted if a metal other than aluminum is used to manufacture the antenna insert, but the manufacturing process of an aluminum insert will be described below, without limiting the invention.

[0029] In a tank filled with an acidic medium such as sulfuric acid, the part to be anodized is placed at the anode of a direct current generator. The cathode of the system is generally made of lead. During electrolysis, the oxide layer forms from the outer surface of the aluminum layer towards the core of the metal. This results in the formation of an alumina layer of controlled thickness, which has electrical insulating properties.

[0030] Several types of anodizing can be distinguished, depending on the bath composition. Chromic anodizing allows for a deposit of a few microns. Anodizing with a sulfuric acid bath is the most suitable for the intended application. It allows for insulating thicknesses ranging from 10 to 100 µm. Anodizing is accompanied by a change in appearance. Its color varies from gray to black.

[0031] Reference is made to Figure 1. In [Fig. 1A] one face of the metallic antenna insert 1 according to the invention is shown. This is a single-sided antenna insert, all the antenna tracks 3 being located on the same face of the insert 1. In this case, the antenna turns 3 are distributed between large outer turns, close to the periphery of the insert 1, and smaller turns, corresponding to a concentrator antenna or “booster”, which in a future smart card using the insert 1 will be located opposite and coupled with the turns of a contactless electronic module.

[0032] In order to delimit conductive antenna turns 3, selective anodizing of the metal sheet 2 of the insert 1 is carried out, in order to make the entire metal face of the insert, with the exception of the areas corresponding to the antenna turns 3, non-conductive.

[0033] To this end, the face of the antenna insert 1 bearing the turns 3 is first masked with a protective mask such as a plastic film resistant to the anodizing bath, or a printed protective resin, and whose geometry corresponds to the geometry of the future antenna tracks 3. Then the antenna insert 1 is immersed in an anodizing bath for a sufficient time to anodize the unmasked part to a predetermined depth, in this case approximately 50 micrometers maximum, or roughly half the thickness of an antenna insert. Next, the antenna insert 1 is removed from the anodizing bath and the protective mask is removed, in particular by peeling or washing, which reveals on the previously masked face the antenna tracks 3 which have remained conductive, as can be seen in [Fig.[2], on which a cross-sectional view AA of a portion of the insert 1 is shown after the anodizing phase of the first face (upper face). It can be seen that a passivated zone 6 (hatched area) has been obtained over approximately the upper half of the thickness of the metal sheet 2, i.e. approximately 50 micrometers out of the 100 micrometers thickness of the insert 1. Only the areas corresponding to the turns 3 of the single-sided antennas of the insert remain conductive on the upper face of the insert 1.

[0034] If it is planned to make an antenna insert 1 with a double-sided antenna 3,4,5 as shown in figures 3 and 4, it will be necessary to also mask the second side of the insert as shown in [Fig.3], in order to be able to make conductive tracks 4, 5 on this second side either in a second step, or simultaneously, in the same way as the tracks 3 of the first side were made in the example of figure 1.

[0035] In [Fig.4] the metal insert 1 of [Fig.3] is shown in cross-sectional view BB after selective anodizing of both faces. This results in an insert with a double-sided antenna, with tracks 3, 4, 5 offset between the two faces, or which can be locally interconnected by a via 8 ([Fig.3]).

[0036] Tracks 3, 4, and 5 of the antenna correspond to the inductive and resistive parts of the antenna in insert 1. To adjust the antenna's resonance characteristics, it may be necessary to add a capacitor 7 to the circuit formed by the turns. For this purpose, the invention provides, as schematically shown in Figures 5A and 5B, for arranging a metal disc 10 on at least one anodized portion of one face of the insert to form a capacitor 7 whose capacitance depends on the surface area of ​​the metal disc 10.

[0037] As is known, a capacitor is a passive electronic component consisting of two conductive plates separated by a dielectric.

[0038] As shown in [Fig.5B], in the context of the present invention, to form the necessary capacitor 7, the following procedure is used to obtain a double-sided metallic antenna insert 1 having antenna tracks 3,4,5 on its two faces.

[0039] First antenna tracks 4,5 are formed on a first face of the insert, as well as a first plate 9 of the future capacitor, by a first selective anodization of a first face of the insert 1 (upper part of the [Fig.5B]).

[0040] Then we form second antenna tracks 3 on the second face of the insert (lower part of [Fig.5B]), as well as a dielectric zone 11 made of anodized aluminum and therefore insulating.

[0041] Next, a metal pellet 10 is placed opposite the dielectric zone 11 and fixed, for example, to the dielectric zone 11 using a layer of conductive glue 12. The stacking of the layers 9, 11, 10 thus obtained forms the structure of a capacitor 7. The plate 10 of the capacitor protrudes slightly beyond the dielectric zone 11 to come opposite an antenna track 3, to which it is electrically connected at 15 by the layer of conductive glue 12.

[0042] Since anodizing has the effect of changing the color of the aluminum, it may be useful for cosmetic purposes to carry out a final light anodizing step on the face 13 of the insert 1 which will remain visible on the final product, which will form a thin layer 14 of anodized aluminum making it possible to uniform the appearance of this face 13 and to isolate the antenna from the outside of the card by encapsulating it under the thin layer of anodized aluminum 14. This will also have the effect of preventing any potential short circuit between the antenna tracks 4,5 in case of contact with an external metallic object.

[0043] It would also be possible to perform the final anodizing of both faces during the same dipping operation, each face having its own mask. The depth of the vias can be checked by testing the electrical conductivity.

[0044] Once a metallic antenna insert 1 has been made as described above, it can be used to assemble it with the layers of a card body, as shown by way of non-exhaustive examples in Figures 6 to 8, in which the thicknesses of the layers of the smart card have been greatly exaggerated compared to those of a real smart card, for the sake of clarity of representation.

[0045] The smart card 20 of [Fig. 6] comprises a metallic card body 30 and two inserts 1 according to the invention, positioned on the two faces of the metallic card body 30. In order to limit the influence of the metallic card body 30 on the operation of the antennas of the metallic inserts 1 (not shown), a ferrite layer 31 is interposed between each antenna insert 1 and the metallic card body 30. The various elements 1, 30 are bonded together using thin layers of adhesive 32. An electronic module 33 is positioned in a known manner within a cavity 34 of the metal card body 30. This is a known contactless module and is also equipped with an antenna (not shown). Since, as shown, metallic antenna inserts 1 are positioned on both sides of the smart card 20, the cavity 34 extends under the electronic module 33 to the insert 1 on the opposite side, so that the contactless electronic module 33 can communicate with a remote contactless reader via the antennas of each of the inserts 1 located on the upper or lower face of the smart card 20. Of course, a simpler smart card structure with a metallic antenna insert 1 on only one of its faces is also conceivable within the scope of the invention.

[0046] In the smart card 21 of [Fig. 7], a metallic antenna insert 1 according to the invention is interposed between two layers 35 of a non-metallic material, such as glass, porcelain, or other high-quality non-metallic material. This material does not impede good inductive coupling between the antenna (not shown) of the electronic module 33 and the antenna(s) (not shown) of the antenna insert 1. No ferrite layer is necessary in this configuration, resulting in a particularly simple, economical, and high-value smart card structure, depending on the material used for the layers 35.

[0047] In the smart card 22 shown schematically in [Fig. 8], two metallic antenna inserts 1 according to the invention are used, surrounding a non-metallic card body 36, for example made of glass, porcelain, or other non-conductive and valuable material. Again, no ferrite layer is necessary; the antenna of the electronic module 33 (not shown) can be coupled to the antennas of the antenna inserts 1 through the material of the card body 36. ADVANTAGES OF THE INVENTION

[0048] The invention achieves the stated objectives. Tests have shown that radio frequency communication with a contactless reader is of good quality regardless of the card's orientation, and remains compliant with EMVCo specifications.

[0049] The anodized metallic faces of the smart card according to the invention are solid, without compromising the quality of radio frequency communication. They give the smart card an attractive metallic appearance, which can be customized later, and a weight that meets the requirements of the premium card market, as well as a good grip.

[0050] The manufacture of monolithic metal antenna inserts is very simple and economical, and the assembly with the board body and an electronic module uses standardized and low-cost processes.

[0051] In conclusion, the metallic antenna insert according to the invention and the smart cards which integrate it function in the same way as PET core inserts, but they are of much higher quality while respecting the imposed radio frequency communication standards.

Claims

Demands

1. Antenna insert (1) for smart card (20, 21, 22), characterized in that it is devoid of a plastic layer and in that it essentially consists of a metal foil (2) having conductive turns (3; 4,5) delimited by areas (6) made non-conductive by anodizing.

2. Antenna insert (1) according to claim 1, characterized in that the metal sheet (2) is an aluminum or copper sheet, 50 to 100 micrometers thick, and whose anodizing depth from one or both of its faces is between 10 and 50 micrometers.

3. Antenna insert (1) according to any one of the preceding claims, characterized in that it further comprises on at least one of its faces a capacitor (7) connected to terminals of the antenna turns, said capacitor (7) being made by a first armature (9) made up of a non-anodized area of ​​the antenna insert (1), a second armature (10) made up of a metal pellet, and between the two armatures (9,10), a dielectric (11) made up of an anodized area of ​​the antenna insert (1).

4. Antenna insert (1) according to any one of the preceding claims, characterized in that it comprises conductive antenna turns (3; 4, 5) on both its faces, interconnected by means of a via (8) passing through the metal sheet (2).

5. Antenna insert (1) according to any one of the preceding claims, characterized in that the entirety of the faces of the antenna insert (1) is anodized to a shallow depth of the order of 10 micrometers so as to harmonize the cosmetic appearance of the faces of the antenna insert (1) and to make the surface electrically insulating and to electrically isolate the conductive antenna turns (3; 4,5) from the surface of the insert.

6. Method of making an antenna insert (1) according to any one of the preceding claims, characterized in that it comprises steps consisting of: - Masking a first face of the antenna insert (1) with a protective mask reproducing the shape of the conductive antenna turns (3; 4,5) to be made on this face; - Mask the opposite face of the antenna insert if a second antenna is planned; - Immerse the antenna insert (1) in an anodizing bath for a sufficient time to anodize said first face to a first depth corresponding to the desired thickness of the conductive antenna turns (3; 4, 5); - Remove the antenna insert (1) from the anodizing bath and remove the protective mask above the conductive turns (3; 4, 5);

7. A method for making an antenna insert (1) according to any one of claims 1 to 5, comprising conductive antenna loops (3; 4, 5) on its two faces, characterized in that it comprises steps consisting of: - Masking the two faces of the antenna insert (1) with a protective mask reproducing the shape of the conductive antenna loops (3; 4, 5) to be made on each face; - Immersing the antenna insert (1) in an anodizing bath for a first time sufficient to anodize each face of the antenna insert to a depth corresponding to the desired thickness of the conductive antenna loops (3; 4, 5); - Removing the antenna insert (1) from the anodizing bath and removing the protective mask above the conductive antenna loops (3; 4, 5).

8. Method according to claim 6 or claim 7, characterized in that it comprises a step consisting of re-dipping the antenna insert (1) in the anodizing bath for a second time shorter than the first time so as to superficially anodize and electrically insulate the surface of the antenna insert (1) overhanging the conductive antenna turns (3; 4, 5).

9. Smart card (20, 21, 22) with a contactless communication interface or with a dual contact and contactless communication interface, characterized in that it comprises at least one antenna insert (1) according to any one of claims 1 to 5.

10. Smart card (20) according to claim 9, characterized in that it comprises a metallic body (30), and on at least one of the faces of said metallic body (30), an antenna insert (1) and a ferrite layer (31) interposed between the antenna insert (1) and the corresponding face of the metallic body (30).

11. Smart card (21) according to claim 9, characterized in that it comprises a body formed by two outer layers (35) of a non-metallic and electrically insulating material, and an antenna insert (1) interposed and fixed between said two outer layers (35).

12. Smart card (22) according to claim 9, characterized in that it comprises a body formed by a central layer (36) of a non-metallic and electrically insulating material, interposed between two antenna inserts (1).

Images