METHOD FOR MANUFACTURING AN ANTENNA IN A PLASTIC BODY

Description

[0001] The invention relates to a method for manufacturing an antenna, in particular an RF antenna, in a plastic body, in particular in a plastic security document.

[0002] Particularly in the field of security documents, flat, miniature data storage devices such as RFID (radio-frequency identification) chips are state-of-the-art for storing and making information readable. This information can also be used as a security feature to increase the document's resistance to counterfeiting. The RFID chips are embedded in a plastic body, which then serves as the card-shaped document.

[0003] RFID chips do not have their own independent power supply, but instead have antennas, so-called RF (high-frequency) antennas, which convert the electromagnetic radiation from a reader of the RFID chip into a current sufficient to power the passive storage medium (the RFID chip) and thus enable access to the stored information. Such an arrangement is disclosed, for example, in publication JP 2001 92 936 A. The antenna is spirally embedded in the card body and has an inner and an outer end. To ensure a power supply to the RFID chip, both ends must be connected to it. Consequently, it is necessary that one of the two ends is routed through windings of the antenna without creating a short circuit.

[0004] There are several methods for incorporating an RF antenna structure into the card body. One option is to lay an insulated copper wire on a substrate using a high-frequency oscillating tapping motion. Alternatively, a pre-existing antenna structure can be applied to the substrate, either etched or milled from aluminum foil. Another possibility is to incorporate the antenna onto the substrate, for example, using screen printing and liquid, electrically conductive ink. Conductive ink contains a high proportion of nanoparticles of a conductive material such as copper, carbon, or silver. The present invention relates to the latter method for manufacturing an antenna in a plastic body. Such a method is known from US 2012,175,422 A1.The ends of the spiral antenna structure are connected to each other by an insulated bridge that extends over the conductors of the antenna structure.

[0005] US patent 2004,082,189 A1 discloses a manufacturing process for a printed circuit board (PCB) in which a conductive paste is introduced into cavities of a resin substrate and covered by a lamination layer. The lamination of the resin layer and the sintering of the conductive paste within the cavity occur simultaneously. US patent 2005,072,595 A1 also discloses a manufacturing process for a PCB.

[0006] Document DE 10 2009 050 199 A1 explicitly describes this combined method as the core of its teaching for improving the electrical conductivity of conductor structures on temperature-sensitive films. However, the connection between different conductor layers is achieved through vias ("contact windows") and not through a planar, printed bridge structure.

[0007] Document DE 10 2006 059 454 A1 also mentions simultaneous sintering and lamination, but only in the specific context of electrically contacting a thin silicon chip with the antenna connections. Here, it serves as an alternative method to bonding and not for manufacturing the antenna coil itself. A printed bridge structure for crossing conductor tracks is not disclosed in D6; instead, the chip itself acts as a bridge, or the antenna runs beneath the chip.

[0008] Against the background of the prior art described above, the object of the present invention is to provide a time- and cost-efficient method for manufacturing an antenna in a plastic body, as well as a plastic body for use in a security document and a security document with an antenna manufactured by the method according to the invention.

[0009] This problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are contained in the dependent claims.

[0010] The inventive method for manufacturing an antenna in a plastic body comprises several steps. First, a conductive ink, preferably applied by a screen printing process, is deposited onto a substrate such that it forms a spiral antenna structure with an inner and an outer end, wherein the inner end is located inside and the outer end outside of conductive traces of the spiral antenna structure. In a next step, a bridge, consisting of an insulating element, preferably made of a thermoset, and a conductive element, is deposited onto the substrate, wherein the bridge is arranged such that the conductive element electrically connects one end of the antenna structure to a point on the other side of the conductive traces via at least a portion of them, and the conductive element is electrically insulated from the conductive traces by the insulating element.Finally, the substrate is laminated with at least one laminate layer that completely covers the antenna structure. The temperature and duration of the lamination are selected such that the antenna is sintered during the process. The laminate layer and the substrate together form the plastic body. This process sinters the antenna structure into the finished antenna.

[0011] During the sintering process of the ink applied to the antenna structure, the nanoparticles bond together, thereby increasing conductivity and forming the antenna. This applies particularly to the connection points between the bridge's conductor element and the antenna structure provided by the conductive ink. Preferably, the bridge's conductor element has the same conductive material as the conductive ink to enable the two elements to bond during the sintering process. The bridge ensures that both ends of the antenna are located on the same side of the conductor tracks (conductor windings) and can thus both be connected to an electrical component, such as an RFID element.The installation of an RFID chip and its connection to the antenna structure preferably takes place before laminating the laminate layer onto the substrate, so that the RFID chip can also be completely covered and thus protected by the laminate layer and the electrical connection between the chip and the ends of the antenna can be ensured.

[0012] The ink applied to the substrate to form the antenna structure preferably has a paste-like consistency. This prevents the desired antenna structure from being damaged by ink runoff. A paste-like consistency is particularly advantageous when applying the ink using screen printing.

[0013] In an advantageous embodiment of the invention, the bridge is applied by both applying the insulating element and subsequently applying the conductor element to the insulating element using a printing process, preferably a screen printing process. This allows both the insulating element and the conductor element to be applied with precise positioning, preventing a short circuit between the conductor element and the conductor tracks of the antenna structure. The insulating element is preferably applied after the antenna structure has at least partially dried. Preferably, the same material is used to manufacture both the insulating element and the antenna structure. This ensures that the antenna structure and the conductor element bond well during the subsequent sintering process.

[0014] Generally, the application of ink to a substrate to form a spiral antenna structure and the application of a bridge (consisting of an insulating element and a conductor element) are preferably carried out using separate printing processes. This means that these are preferably printing processes that are separated in time, and more preferably screen printing processes that are separated in time.

[0015] In an alternative advantageous embodiment for mounting the bridge on the support, a prefabricated insulating element is provided, which has two connection openings. A conductor element is then applied to the insulating element, preferably by printing, and particularly preferably by screen printing, such that it can form electrical contact points through the connection openings. If an RFID chip is connected to these electrical contact points, a current flow between the antenna and the chip can be ensured. The electrical contact points thus define the positions at which the bridge can transmit the current flow generated in the antenna.

[0016] Another alternative embodiment for mounting the bridge on the support involves the use of an insulated conductor element. The insulated conductor element is defined by the fact that an insulating element is arranged around the conductor element in its cross-section, providing radial insulation. This insulated conductor element is placed over the conductor tracks and connected to the antenna structure at one axial endpoint using a thermal process such as welding. The current flow generated by the antenna can be tapped at the other axial endpoint.

[0017] Preferably, the insulated conductor element is applied to the support by means of an oscillating impact load. The heat energy generated thereby leads to a deformation of the insulating element, thus forming a force-fit connection between the bridge and the support or the conductor tracks.

[0018] In an advantageous embodiment of the invention, the bridge consisting of an insulating element and a conductor element is first prefabricated and then mounted on the support in its prefabricated state. The prefabricated state is characterized in that the insulating element and the conductor element are already connected to each other before they are applied to the support.

[0019] In a further advantageous embodiment of the invention, the lamination of the substrate and the laminate layer is carried out according to a lamination curve, wherein the substrate and the laminate layer are heated to a defined target temperature, in particular 190 °C, within 30 minutes and then cooled uniformly again within 30 minutes. In this way, clean results can be ensured for both the lamination process and the sintering process for forming the antenna. A lamination curve in which the temperature is kept constant for a defined period, for example 7 minutes, is also preferred.

[0020] Preferably, the lamination is carried out at least partially under the additional application of pressure to the lamination partners, i.e. at least the substrate and the laminate layer.

[0021] A plastic body produced by the process has a spiral antenna arranged between a substrate and at least one laminate layer. The antenna has an inner end and an outer end, with the inner end located inside and the outer end outside of conductive traces of the spiral antenna structure. The plastic body further comprises a bridge with an insulating element and a conductive element, the insulating element having two connecting openings which are connected by the conductive element. The bridge is arranged such that the conductive element is connected to one end of the antenna in one connecting opening, and the other connecting opening is located on the opposite side of the conductive traces. The conductive element is further insulated from the conductive traces by the insulating element.Such a plastic body provides an antenna for use in a security element in conjunction with an RFID chip and can therefore be used in a security element.

[0022] The security document according to the invention includes at least one antenna produced by the method according to the invention.

[0023] The embodiments and positive aspects of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows the application of an antenna structure 10 to a support 20 according to an embodiment of the method according to the invention. Fig. 2a shows a first step for applying a bridge 70 in a first embodiment. Fig. 2b shows a second step for applying a bridge 70 in the first embodiment. Fig. 3 schematically shows the lamination of the support 20 with two lamination layers 60 according to the method according to the invention. Fig. 4a shows a second embodiment according to the invention for applying a bridge 70 within the framework of the method according to the invention. Fig. 4b shows an example of a cross-section of an insulated conductor which can be used as a bridge 70 within the framework of the method according to the invention. Fig. 5a shows a third embodiment of a bridge 70 which is applied to the support 20 within the framework of the method according to the invention. Fig. 5b shows a cross-section of the Fig. 5a Bridge shown 70

[0024] Fig. 1 Figure 1 shows the application of an antenna structure 10 made of conductive ink to a substrate 20 and thus represents the first step of the method according to the invention. The conductive ink has nanoparticles of a conductive material that enable the flow of current. The substrate 20 is made of plastic and serves as a base for the antenna structure 10. The antenna structure 10 is produced by a screen printing process, wherein liquid conductive ink, in particular with a pasty, i.e., viscous, consistency, is forced through a screen opening 31 of a screen 30 by means of a preferably elastic squeegee 40. The screen 30 is placed on the substrate 20 and the ink is forced through a screen opening 31 indicated by the arrow. Fig. 1 The depicted movement of the squeegee 40 across the screen 30. The ink remains in the screen openings 31 and is pressed onto the carrier 20, leaving the pattern of the screen openings 31 on the carrier 20 as an antenna structure 10.

[0025] This creates the spiral antenna structure 10 from the conductive ink on the substrate 20. In the illustrated embodiment, the spiral structure is also arranged as a rectangle, which corresponds to a typical geometry of an antenna structure 10. The antenna structure 10 has several conductor turns or conductor tracks 13 as well as an outer end 11 and an inner end 12, which is angled inwards, i.e., towards the center of the antenna structure 12. The outer end 11 is located outside the conductor tracks 13 and the inner end 12 inside them.

[0026] In order to use the antenna for the application described above in conjunction with an RFID chip, both ends 11, 12 of the antenna structure 10 must be connectable to an RFID chip to allow current to flow to the RFID chip. For this purpose, either the inner end 12 must be routed to the outside via the conductor tracks 13, or the outer end 11 must be routed to the inside. No electrical connection may be established between the ends and the conductor tracks 13, as this would cause a short circuit and prevent current flow to the RFID chip. Therefore, a jumper 70 must be placed across the conductor tracks 13 to ensure electrical insulation.

[0027] A first embodiment for manufacturing a bridge 70 is described in the Figs. 2a and 2b shown. The bridge 70 consists of an insulating element 71 and a conductor element 72. In a first step, during the in Fig. 2a In the illustrated embodiment, the insulating element 71 is printed over the conductor tracks 13 of the antenna structure 10 using a screen printing process. The insulating element 71 consists of an electrically insulating material, which is preferably also printed in a paste-like consistency. The screen printing is carried out analogously to the previously described method for applying the antenna structure 10. The material of the insulating element 71 is pressed onto the substrate 20 through a suitably shaped opening 31 of a screen 30 using a squeegee 40. It is important to note that the antenna structure 10 must preferably be at least partially dry to ensure that the conductor tracks 13 are not severed by the application of the insulating element 71, which would interrupt the current flow in the conductor tracks 13. Likewise, they should not deform in such a way that they touch each other, in order to prevent a short circuit.

[0028] In a further step, a conductor element 72 is applied in the illustrated embodiment, with this element running precisely on the insulating element 71. The conductor element 72 is also applied by means of screen printing and, in the illustrated embodiment, establishes an electrical connection with the outer end 11 of the antenna structure 10. It preferably consists of the same material as the antenna structure 10. The conductor element 72 is thus able to conduct a current flowing in the antenna to be produced from the antenna structure 10 into the interior of the antenna structure 10, thereby enabling an RFID chip 50 arranged inside the antenna structure 10 to be connected to both ends 11, 12. Between the process steps, at least partial drying of the elements already applied to the carrier 20 is preferred. For reasons of time, this is preferably carried out actively using a corresponding airflow or...hardening radiation or similar.

[0029] The inner end 12 and the outer end 11 of the antenna structure 10, which is also directed inwards by means of the bridge 70, can now be connected to an RFID chip 50.

[0030] To produce a plastic body, the process according to the invention is carried out as described in Fig. 3 The carrier 20 is shown laminated with at least one laminate layer 60. In the illustrated embodiment, a laminate layer 60 is provided on both sides of the carrier 20. The antenna structure 10 is completely covered by a laminate layer 60, and the carrier 20 is bonded to the laminate layers 60 in a material-bonded manner.

[0031] During the lamination of the carrier 20 with at least one laminate layer 60, sufficient energy is simultaneously supplied for a sintering process of the antenna structure 10. In this process, the nanoparticles of the conductive ink are fused to increase or establish conductivity. In particular, the contact points to the conductor element 72 of the bridge 70 and the RFID chip 50 are strengthened by this fusion of the material. The sintering process transforms the antenna structure 10 into the actual RF antenna.

[0032] The plastic body produced in this way can be used directly as a card-shaped security document or as an inlay for insertion into a corresponding document. A complete security document typically has many different layers, while an inlay has fewer layers and can be incorporated into a final product, such as a security document, for further processing.

[0033] The method according to the invention thus allows a large number of different layers to be bonded together during the lamination process. The lamination process preferably follows a lamination curve, which defines the temperature and / or pressure during lamination. If a large number of different layers are to be bonded together, a different lamination curve is generally required than when bonding only a few layers.

[0034] According to a preferred lamination curve for bonding a large number of layers, the elements to be bonded are first heated from a temperature of preferably 20 °C to a temperature of preferably 190 °C over 30 minutes and then cooled again at a constant temperature over 30 minutes. This lamination curve ensures a high-quality sintering and lamination process even with many layers. When bonding only a few layers, the heating and cooling phases can be significantly shorter. However, a certain sintering time at a specific temperature level is required for a high-quality antenna sintering process. For this purpose, a phase of constant temperature, for example 7 minutes at 190 °C, can preferably be included in the lamination curve.

[0035] Preferably, during the lamination process, area pressure is applied at least temporarily to the partners to be laminated, i.e., the substrate 20 and the laminate layers 60, in order to bond the laminate layers 60 and the substrate 20 together. In the plane of the drawing Fig. 3 Accordingly, the printing is applied from above and below.

[0036] The conductor tracks 13 of the antenna structure 10 are preferably coated with a thickness (height of the applied paint) of 100 µm misprinted, with the thickness after the sintering process only 50 µm A typical RFID 50 chip, which is suitable for use in security documents, for example, has a thickness of approximately 180 mm. µm The distance between the conductor tracks 13 is preferably 300 µm , to prevent a short circuit between the conductor tracks 13 or a flowing of the conductor tracks 13 during the printing and sintering process.

[0037] The Figs. 4a und 4b Figure 1 shows a further embodiment of a method for applying the bridge 70 to the support 20. In this embodiment, the bridge 70 is connected to the support 20 or the conductor tracks 13 by means of an oscillating impact load in a force-fit and / or form-fit manner.

[0038] The bridge 70, in the embodiment shown, consists as in Fig. 4b The bridge 70 is represented by a conductor element 72 with a round cross-section, which is radially insulated by the insulating element 71, preferably made of a thermoset. Within the scope of this application, the bridge 70 constructed in this manner is also referred to as the insulated conductor element 71. The oscillating impact load introduces heat energy into the insulating element 72, thereby creating a force-fit connection with the support 20 or the conductor tracks 13.

[0039] The conductor element 71 is electrically connected to the outer end 11, or the RFID chip, at its axial ends. This is preferably done by a thermal process such as soldering or welding at the relevant points. In this process, the insulating element 72 can be melted at the electrical contact points, creating a metallurgical bond between the conductor element 71 and the corresponding connection partner, thus ensuring a reliable electrical connection.

[0040] The Figs. 5a und 5b Figure 1 shows a further embodiment of a method for applying the bridge 70 to the support 20. For this purpose, an insulating element 71 is first provided, which serves as an insulating base. The insulating element 71 is designed as a flat plate made of an electrically non-conductive material and has two connecting openings 74. Subsequently, a conductor element 72 is applied to the insulating element 71 such that it is positioned between the two connecting openings 74 and at least partially fills them, so that electrical contact points 73 are formed in the connecting openings 74.

[0041] Fig. 5a This shows one possibility of applying the conductor element 72 to the insulating element 71 using a screen printing process. For this purpose, as with regard to applying the antenna structure 10 to the support 20, the following is used: Fig. 1 As described, a conductive ink, preferably of paste consistency, is pressed through a sieve opening 31 of a sieve 30 by means of a squeegee 40 in order to produce the desired geometry of the conductor element 72 on the insulating element 71. Preferably, the same material is used for forming the conductor element 72 as for forming the antenna structure 10.

[0042] The prefabricated bridge can then be placed on the support 20 (see e.g. Fig. 1The contact points 73 are arranged such that one of them is located on the end of the antenna structure 10 that is to be conductive via the conductor tracks 13. The electrically non-conductive insulating element 71 rests on the conductor tracks 13 and thus insulates the conductor element 72. To ensure the electrical connection between the contact points 73 and the corresponding connection partners, a thermal process, in particular a welding or soldering process, is preferably used.

[0043] The bridge 70 can be laid on both a wet and a dry antenna structure 10 and does not necessarily require intermediate drying of the antenna structure 10. Preferably, after connecting the bridge 70 to the antenna structure 10, the antenna structure 10 and the conductor element 72 of the bridge 70 are dried and then laminated.

Claims

1. Method for producing an antenna in a plastics body, comprising the following steps, applying a conductive ink to a carrier (20) in a first step such that it forms a spiral antenna structure (10) having an inner end (12) and an outer end (11), wherein the inner end (12) is arranged inside and the outer end (11) is arranged outside conductor tracks (13) of the spiral antenna structure (10), applying a bridge (70) consisting of an insulating element (71) and a conductor element (72) in a next step, wherein the bridge (70) is arranged such that the conductor element (72) electrically connects one of the ends of the antenna structure (10) via at least a part of the conductor tracks (13) of the spiral antenna structure (10) to a point on the other side of the conductor tracks (13) and the conductor element (72) is electrically insulated from the conductor tracks (13) by the insulating element (73), and laminating the carrier (20) with at least one laminate layer (60) which completely covers the antenna structure (10), wherein the temperature and duration of the lamination are selected such that the antenna structure (10) is sintered during the lamination.

2. Method according to the preceding claim, wherein the conductive ink has a pasty consistency.

3. Method according to either of the preceding claims, wherein the ink is applied by means of a screen printing method.

4. Method according to any of the preceding claims, wherein the application of the bridge (70) is carried out by application of the insulating element (71) and a subsequent application of the conductor element (72) on the insulating element (71) by means of a printing method, in particular by means of a screen printing method.

5. Method according to any of the preceding claims 1 to 3, wherein the bridge (70) is formed by a prefabricated insulating element (71) having two connection openings (74), to which a conductor element (72) is applied by means of screen printing in such a way that the conductor element (72) can form electrical contact points (73) through the connection opening (74).

6. Method according to any of the preceding claims 1 to 3, wherein the bridge (70) is applied in the form of an insulated conductor element (72), wherein in particular the conductor element (72) is connected to the antenna structure by means of welding.

7. Method according to the preceding claim, wherein the insulated conductor element (72) is applied to the carrier (20) by means of an oscillating impact load.

8. Method according to any of the preceding claims, wherein the bridge (70) is first prefabricated and is mounted on the carrier (20) in the prefabricated state.

9. Method according to any of the preceding claims, wherein in order to laminate the carrier (20) with the laminate layer, both are heated to a specified target temperature, in particular 190°C, within a specified period of time, in particular within 30 minutes, and are then cooled again uniformly within a further specified period of time, in particular within 30 minutes.

10. Security document comprising at least one antenna manufactured by a method according to one of claims 1 to 9.