WO2006008167A1

WO2006008167A1 - Method to manufacture an electrical bridge for an rfid antenna

Info

Publication number: WO2006008167A1
Application number: PCT/EP2005/007982
Authority: WO
Inventors: Jean-Jacques Mischler; Jean-Pierre Radenne; Stéphane BARLERIN
Original assignee: Fci
Priority date: 2004-07-21
Filing date: 2005-07-21
Publication date: 2006-01-26
Also published as: FR2873470A1; EP1771815A1

Abstract

The invention relates to a method of making an RFID tag comprising the steps of: a) providing a dielectric substrate (502); b) forming on said substrate an antenna circuit (515), said antenna circuit comprising more than one turn (515) and a first (521) and second (522) antenna terminals, said first terminal comprising an arm portion (5211) and a terminal end (5212), c) cutting out said dielectric substrate to form a dielectric tongue (540), d) bending said dielectric tongue so that a portion of said dielectric tongue is used as an insulating layer between said more than one turn and a conductive path between said first and second.

Description

METHOD TO MANUFACTURE AN ELECTRICAL BRIDGE FOR

AN RFID ANTENNA

The present invention generally relates to RFID (Radio Frequency IDentifier) manufacturing methods, and more specifically to a method to manufacture a bridge or strap over the antenna spiral turns.

The use of a tag having an RFID tag to identify and monitor objects is well known in the art. With no self source of energy, the tag comprises an antenna circuit formed with conductive tracks, and an integrated circuit (IC) chip that includes a memory. It uses electromagnetic field produced by an RFID reader. If such a tag enters the electromagnetic field, the RFID antenna will become energized and the electronic circuit can transmit a coded signal towards the reader or a separate receiving antenna.

A typical RFID tag, or inlay, generally includes an antenna and an integrated circuit (IC) chip connected to the antenna. The antenna pattern, also called later on antenna tracks, generally comprises a plurality of turns that spiral around on a planar dielectric substrate and two turn ends, i.e. the antenna terminals as seen on Fig. 5. The antenna tracks can be either formed before being laid on the substrate or formed directly upon it (by printing techniques for example), among known techniques. When the antenna pattern requires more than one turn, an electrical bridge must be formed over the spiral turns of the antenna to prolong one of the antenna terminals up to the vicinity of the other one so as to facilitate the electrical connection of the IC chip or any other device.

A bridge can also be used to connect distant tracks in a circuit that are separated from each other by other tracks on the circuit. The bridge can therefore be considered as a tracks connecting device.

Different techniques are known to form this bridge. For example, a separate electrical conductor can be used as a bridge laid over the antenna tracks with a dielectric material in between. The IC chip can also be used as the bridge. The connection of the IC chip and/or the separate conductor can be positioned on the same side of the substrate on which the antenna is mounted or on the opposite side. These methods result in additional manufacturing stages to attach the bridge, causing longer processes and higher production costs.

Therefore, the purpose of the present invention is to offer a simplified manufacturing method for an RFID antenna, that allows an easy construction of the bridge and that is compatible with the mass production specifications.

Accordingly, the present invention provides an assembly method according to claim 1. The present invention further provides an RFID antenna according to claim 7.

The invention takes advantage of the available dielectric material provided by the dielectric substrate and uses it as an insulation material. After a dielectric tongue is cut out in the dielectric substrate, the tongue is bent across the tracks, This portion of the dielectric tongue is used then as an insulating layer between said the antenna tracks and a electrically conductive path linking inner and outer antenna ends. Thus no additional, i.e. distinct, insulating material is needed .

Thus a simplified manufacturing method is provided, requiring only cutting and bending operations carried out on the same support comprising the dielectric material and the antenna track.

Other features and advantages of this invention will further appear in the hereafter description when considered in connection to the accompanying drawings, wherein:

FIG. 1 illustrates a perspective view of a first exemplary embodiment of an antenna according to the invention, with a dielectric tongue foldable over the dielectric substrate,

FIG. 2. a and 2.b are detailed view of FIG. 1 , showing the different folding stages of the dielectric tongue,

FIG. 3 illustrates a perspective view of a second exemplary embodiment of an antenna according to the invention, with a dielectric tongue laterally foldable over the dielectric substrate,

FIG. 4.a and 4.b are detailed view of FIG. 3, showing the different folding stages of the dielectric tongue, FIG. 5 illustrates a perspective view of an RFID antenna in accordance with a third exemplary embodiment of the present invention;

FIG. 6.1 to 6.3 are detailed views illustrating around the antenna first terminal the different steps of the third exemplary embodiment of the present invention;

FIG. 7 illustrates the final step of the third exemplary embodiment of the present invention;

FIG. 8 illustrates a view of the third exemplary embodiment of the present invention applied on a reel;

FIG. 9.1 and 9.2 illustrate detailed views of a fourth embodiment of the present invention; and,

FIG. 10 illustrates a perspective view of a fifth embodiment of the present invention.

As mentioned here before, a bridge, or a tracks connecting device for a circuit comprising a dielectric substrate carrying conductive tracks, allows to connect distant tracks that are separated from each other by other tracks, while avoiding any short-circuit of the tracks coming in between the distant tracks.

The following embodiments will refer to the example of an RFID antenna, but the principles of this invention can also be applied to a connecting device for tracks of a circuit, as long as it can be taken advantage of the flexibility of the dielectric substrate.

FIGS. 1 and 2.a-2.b illustrate a method of constructing an RFID antenna in accordance with a first exemplary embodiment of the present invention. The RFID antenna can be used as an RFID tag when connected to an IC chip.

In the following description, the term dielectric will be used as a synonym to insulating material, insulator or insulant.

The RFID antenna as seen on FIG. 1 comprises a substrate 1 made of dielectric material, that is preferably a transparent polyamide or polyester, a plastic material, paper or cardboard, or any other dielectric material relevant for that matter. The antenna pattern, or tracks, comprising the antenna turns 2 in the form of a spiral, can be either printed (serigraphy or any other suitable printing technique), chemically plated or etched onto the substrate 1. The whole manufacturing process, including the hereafter method according to the invention, can be carried out on a reel as seen in FIG. 8. The turns are spaced apart from each other by a certain gap or distance, either of a constant value, or varying depending on the antenna characteristics.

On said substrate 1 are also provided IC contact ends 15, 16, in the form of small plates, for the connection of an IC (not shown) to the antenna. Both IC contact ends can also be connected to each other through a conductive wire. Thanks to an appropriate choice of a conductive material and/or the width of the wire, the conductive wire can then be used as a fuse for RFID tags applied to detect unpaid objects at the exit of a store.

According to the first embodiment of the present invention shown on FIG. 1 , substrate 1 comprises peripheral tracks 2 with the shape of plane turns, thus forming an antenna and a connecting zone for an IC through IC contact ends 15 and 16, provided to connect the IC wirings outside the turns. As mentioned before, to connect the antenna to an IC, both turn ends, i.e. the antenna terminals, ought to be electrically linked to the IC so as to close the loop formed by the antenna.

The outer antenna terminal that ends the outer antenna turns comprises an arm portion and a terminal end 8. The arm portion further comprises a discontinuity corresponding to the IC contact ends 15 and 16. The terminal end 8 is connected to the IC contact end 16. The connection of the inner antenna terminal 2a (which ends the inner antenna turns) to the outer antenna terminal requires crossing the tracks, either on top or below said tracks, that are laid out between the two antenna terminals. The inner antenna terminal 2a further comprises an arm portion 6 and a terminal end 7.

To cross the tracks, a dielectric tongue 3, provided with a folding section and a conductive section, is cut out on the inner surface defined by the inner antenna turns. The conductive section of dielectric tongue 3 corresponds to arm portion 6, i.e. to a conductive strand that links the inner antenna turns to a terminal end 7 provided at the free end of the dielectric tongue 3. The antenna terminal 2a is to be laid out over the conductive turns 2 towards a distant section of the substrate 1 after bending the dielectric tongue 3 so as to make an electrical bridge crossing over the antenna turns. The distant section corresponds to the outer antenna terminal, and more precisely the outer terminal end 8.

A precut 9 is carried out on substrate 1 to delimit the dielectric tongue. This precut 9 which silhouettes out dielectric tongue 3 is carried out so as to leave between the dielectric substrate 1 and said dielectric tongue 3 at least a bridge connection 10 that connects the antenna terminal 2a to the antenna turns 2 through conductive strand 6. The bridge connection 10 forms a hinge for the dielectric tongue 3. In the first embodiment as seen on FIG. 2b, conductive strand 6 is doubled around the connection with antenna turns 2, and is carried by two bridge connections 10, to link the terminal end 7 to the inner antenna turns.

To maintain a mechanical reliability of the whole dielectric tongue 3 and antenna turns 2, as long as the tongue is not bent, at least one bridge connection 11 , to mechanically maintain the dielectric tongue 3 attached to the dielectric substrate, is kept during the cut out between the tongue and the substrate. This bridge connection 11 is adapted to be cut to allow the folding of said dielectric tongue, by for example, pushing onto dielectric tongue 3 and breaking the bridge connection 10. A bridge connection 11 of smaller width than the bridge connection 10 would allow such a break.

According to the first embodiment of the present invention, the dielectric tongue 3 is 180° foldable over the substrate side carrying the tracks 2. The dielectric tongue further comprises a dielectric flap 12, foldable over said dielectric tongue to mask a portion of the conductive strand 6 and/or the terminal end 7. The dielectric flap 12 depends on the tongue configuration, and the tracks position with regard to the folded dielectric tongue 3, as its face carrying the conductive strand 6 and the terminal end 7 is laid after bending upon, and more precisely against, the dielectric substrate side carrying the tracks 2, with said dielectric flap 12 interposed in between as an insulation layer. More specifically, for this first embodiment wherein the dielectric tongue 3 is 180° fordable over the conductive tracks 2, the dielectric flap 12 is integral with said dielectric tongue 3, and provided laterally on said tongue and facing a portion of the arm portion 6, i.e. the conductive section of the tongue. The flap 12 is preferably attached to the dielectric tongue through connection bridges 13 used as hinges.

In an alternate embodiment, the flap 12 can be separate and dissociated from the dielectric tongue 3, and turned down over tracks 2 through bending onto the bending zone of tongue 3.

Terminal end 8 from the outer antenna turns is positioned so that terminal end 7 lays out over it after bending dielectric tongue 3. Bending steps are described in FIG. 2a and 2b.

On FIG. 2a, the first 3 steps are illustrated. The first step on the left hand-side corresponding to the cutting out of the precut, the second and third steps corresponding to the breaking of a bridge connection that links the dielectric flap 12 to the dielectric substrate 1 , followed by the bending of the flap 12 over the arm portion 6 to mask said arm portion.

On FIG. 2b, the following bending steps are illustrated. In the fourth step, on the left hand-side of the drawing, the connection bridge 11 linking the dielectric tongue 3 to the substrate 1 is broken. In the fifth step in the middle of FIG. 2b, the bridge is 180° bent over the tracks 2 thanks to the connection bridges 10 behaving as hinges. In the last step on the right hand-side of FIG. 2b, terminal end 7 is connected to terminal end 8 through electrical connection means of said first and second terminal ends 7, 8. In the present example, clamping or stapling means 14 can be used.

The IC can be attached to IC contact ends 15, 16 at any steps in this first embodiment of the method according to the invention.

In the second embodiment of the present invention illustrated on FIG. 3 and 4a-4b, the dielectric tongue 5 is provided with a folding section as well as a conductive section, and comprises a conductive strand 6 that links the inner antenna turns to a terminal end 7 provided at the free end of the dielectric tongue 5, both conductive strand 6 and terminal end 7 forming the antenna terminal 2a. The antenna terminal 2a is to be laid out over the turns 2 towards a distant section of the substrate 1 after bending the dielectric tongue 5 so as to make an electrical bridge crossing over the antenna turns. In this embodiment, the dielectric tongue 5 is lifted of the substrate 1 , in the direction of the substrate side carrying the tracks 2, and bent laterally.

A precut 9 is carried out on substrate 1 to delimit the dielectric tongue 5, so as to leave a connection bridge 10 between the tongue 5 and the substrate 1 that connects the antenna terminal 2a to the antenna turns 2 through conductive strand 6. As in the first embodiment, a terminal end 8 of the outer antenna turns can be provided so that terminal end 7 is laid upon terminal end 8 after bending laterally the dielectric tongue 5 over the turns 2. Thus a portion of the dielectric tongue 5 is used as an insulation layer between the turns 2 and the arm portion 6 so as to make an electrical bridge crossing over the turns 2. As in the previous embodiment, no insulation means are necessary in between the turns and the conductive strand 6, the dielectric carrying the dielectric tongue 5 forming the desired insulation layer.

In the illustration of FIG. 5, IC contact ends are not provided on the antenna terminal of the outer turns, but are split over the terminal end 15 of the outer antenna terminal, and additional terminal end 16' provided on the dielectric tongue 5 and electrically connected to the terminal end 7.

The bending steps are illustrated on FIG. 4a and 4b. The first step in FIG. 4a corresponds to the cutting out of the dielectric tongue 5, while the second step of FIG. 4b corresponds to the lift off of the tongue 5, followed by pivoting said tongue 5 around the connection bridge 10, i.e. bending laterally said tongue, so that the antenna terminal 2a is laid upon the turns in the direction of the outer antenna terminal, with a portion of said dielectric tongue 5 used as an insulation layer between the turns 2 and the arm portion 6 so as to make an electrical bridge crossing over the turns 2. Electrical connection means can be used to attach the dielectric tongue 5 as in the first embodiment. Complementary fastening means can also be provided, such as holes 17 on the substrate 1 and hole 18 on the tongue, coming into alignment when the dielectric tongue is positioned, clamping or stapling means being used to attach both tongue and substrate. Reinforcement means can also be used to reinforce the connection bridge 10 to avoid any unwanted breaking.

A third exemplary embodiment according to the invention is illustrated through FIG 5 to 8.

The turns, at least more than one, are terminated on their extremities by first and second terminal 521 and 522 respectively as seen in FIG. 5, these terminals 521 and 522 being integrally connected to the turns extremities. In the different embodiments described hereafter, the second terminal is connected to the inner most spiral turn, or inner turn, while the first terminal is connected at the periphery of the antenna pattern to the outermost spiral turn, or outer turn. The person skilled in the art shall easily apply the teaching of the present invention to the second terminal 522 being folded over the tracks of the antenna.

The second terminal 522 comprises an arm portion 5221 and a terminal end 5222. The first terminal 521 also comprises an arm portion 5211 and a terminal end 5212, but slightly defers from the second terminal. Indeed the arm portion 5211 further comprises a discontinuity consisting of a pair of chip contact ends 5215 and 5216 respectively, provided to connect the IC chip 530 as seen on FIG. 6.1.

After the antenna tracks are manufactured as seen in FIG. 5, in a next step represented in FIG. 6.1 , the IC chip 530 is attached to the antenna on the chip contact ends 5215 and 5216 through a binding process (for example soldering, resin bonding, using anisotropic conductive films, ...).

In a further step of the third embodiment of the method according to the invention, as seen in FIG. 6, the substrate 502 is cut out or punched out, around the first terminal 521 to form a dielectric tongue, using stamping for example, or any other cutting techniques suitable for that matter. The dielectric tongue 540, also call cut out in the following and formed around the terminal 521 comprises a dielectric flap 545 adapted to cover or mask the arm portion 5211 of the first terminal 521 when folded over it. The dielectric flap 545 is preferably provided laterally to the dielectric tongue 540, and facing the arm portion 5211. The dielectric tongue 540 comprises the flap 545 along with the dielectric portion that carries the first terminal 521. In order to facilitate the operation, enough substrate ought to be available around the first terminal 521. Therefore the flap can either be cut out outwardly from the spiral turns, in the free portion of the substrate 502 close to its edges, or, provided the gap between the first terminal and the neighboring spiral turn going inwardly is sufficiently large, inwardly towards this neighboring spiral turn.

In its folded position, the dielectric flap 45 ought to cover the whole width of the arm portion 5211 to ensure proper electrical insulation from the antenna tracks after the first terminal is folded as described later on. To that effect, the dielectric flap 545 presents a width slightly larger than the width of the arm portion 211 of the first terminal 521. The width of the arm portion 5211 is defined as the width of its track portion in the region of the arm portion 5211 , or as the width of the chip contact ends 5215 and 5216 when provided on the first terminal 521. The bending line 550, along which the flap 545 is folded over the arm portion 5211 and shown in dotted line on FIG. 6.2, is defined parallel to the straight portion of the first terminal 21. When folded over the arm portion 5211 , the flap 545 can cover completely its width of the arm portion. When the first terminal 521 as seen on FIG 5 or 6.1 presents a substantially straight shape, the flap 545 is of a rectangular shape.

The IC chip may also be attached after the here above step instead of before performing the cut out 540.

In an additional step of the third embodiment, as seen in FIG. 7, the first terminal 521 is folded over the turns 2 to make a bridge crossing the antenna turns 515, with a portion of the dielectric tongue 540, here the flap 545, the flap 545 interposed in between the tracks and the arm portion. In order to fold the first terminal inwardly over the antenna tracks, the dielectric tongue 540 ought to be long enough along the first terminal 521 to provide a foldable bridge. Therefore as seen in FIG. 6.2, the dielectric tongue 540 is defined along the first terminal edges, including the terminal end 5212, except in the flap region attached to the dielectric substrate carrying the first terminal. The dielectric tongue 540 has a generally U shaped form that extends around the first terminal so that the first terminal is left attached to the antenna tracks in a region 548 where the first terminal is to be folded to make the bridge.

As seen in FIG. 6.2, during the cut out step, openings are defined next to the flap 545. A first opening 546 is defined on the flap side next to the terminal end 5212 so that when the flap is folded over the arm portion 5211 , the terminal end 5212 is left free as seen in FIG. 6.3. A second opening 547 is defined next to the region 48 to facilitate the folding of the first terminal.

The length of the flap 545, and consequently the length of the dielectric tongue 540 measured along the arm portion 5211 of the first terminal 521 , depend upon the tracks width measured along the bridge direction (actually defined by the direction of the folded first terminal when the terminal ends 5212 and 5222 come into contact). When the first terminal 521 is folded over the tracks towards the second terminal 522 so that their respective terminal ends 5212 and 5222 can be electrically bonded to each other, the arm portion 5211 of the first terminal is laid out upon the tracks 515 of the antenna. Therefore the flap 545, interposed between the tracks and the first terminal, needs to be long enough to isolate all the tracks that the first terminal 521 may come into contact with. Hence the flap portion length is as long or longer than the tracks widths measure along the bridge direction.

Furthermore, the length of the dielectric tongue 540 around the first terminal 521 , that defines the foldable length of the first terminal over the spiral turns 515, is adapted to allow both terminal ends 5212 and 2522 to come into contact with each other when the first terminal is folded over the tracks towards the terminal end 5222 of the second terminal 522. Therefore, the first terminal is long enough to bridge, when cut out, the tracks and connect with the second terminal end.

A soldering technique or any other electrically conductive bonding techniques may be used to attach the terminals ends 5212 and 5222 together to close the antenna.

Unless mentioned otherwise, the different steps and characteristics of the following alternative embodiments of the invention are similar to the third embodiment. A fourth alternative embodiment of the invention is illustrated in FIG. 9.1 and 9.2. In this embodiment, the first terminal 521 does not present any electrical discontinuity. A dielectric tongue 540 is punched around the first terminal 521 with a dielectric flap 545 defined as before. The parameters width wf and length L of the flap 545 are defined as before. Either before the cut out step, before the folding of the flap step, or right after it, the chip is soldered to either terminal ends 5212 or 5222, which act as chip contact ends. In this embodiment, an IC chip with its contact ends on its opposite sides is used so that the IC chip can be connected to the second terminal end after bending the first terminal 521. The terminal ends are actually connected to each other through the IC chip sandwiched or interposed in between. Any soldering or bonding techniques can be used to attach the IC chip to the antenna terminals ends.

In a fifth alternative embodiment of the invention shown FIG. 10, the chip contact ends 5225 and 5226 are provided on the arm portion 5221 of the second terminal 522. The first terminal 521 is similar to the first terminal of the fourth embodiment as seen in FIG. 9.1 As the chip contact ends are not carried by the first terminal that acts as the bridge, the IC chip can be soldered, contrary to the third embodiment, at any time during the process of constructing the bridge. This embodiment even presents the advantage of manufacturing the antenna with its bridge alone, the IC chip attachment being postponed to a later step that can take place in a different location.

As seen in FIG. 8, the method according to the invention may be implemented on a reel or carrier 1 , on which the antenna is constructed in steps 5301 to 5307 corresponding to the different steps described here before.

It has to be noted that the invention is not limited to embodiments wherein the conductive path between first and second terminal ends is supported by the same dielectric bridge than the flap used as insulating bridge. Indeed, a flap may be cut out in the dielectric substrate and bent over the tracks, while a conductive path either cut out, or not, and consequently either supported, or not, by the same dielectric substrate is folded or transferred on the flap. For instance, a conductive strap supporting or not a chip provides the electrical link between inner and outer ends of the antenna.

Claims

1. A method of making an RFID tag comprising the steps of: a) providing a dielectric substrate (1 , 502); b) forming on said substrate an antenna circuit (2, 515), said antenna circuit comprising more than one turn (2, 515) and a first (2a, 521 ) and second (522) antenna terminals, said first terminal comprising an arm portion (6, 5211 ) and a terminal end (7, 5212), c) cutting out said dielectric substrate to form a dielectric tongue (3, 5, 540), d) bending said dielectric tongue so that a portion of said dielectric tongue is used as an insulating layer between said more than one turn and a conductive path between said first and second.

2. A method according to claim 1 , wherein the dielectric tongue comprises a dielectric flap (12, 545) being foldable over said dielectric tongue so as to mask a portion of said arm portion and/or terminal end of the first terminal, and wherein after step c), said dielectric flap is folded over said arm portion.

3. A method according to the previous claim, wherein the second terminal comprises a terminal end (15, 5222), and in step d) the first terminal is folded towards said terminal end of said second terminal,

4. A method according to claim 1 , wherein in step d) the dielectric tongue is laterally bent so that the dielectric portion of the dielectric tongue carrying the terminal portion is interposed between said terminal portion and the more than one turn.

5. A method according to any of the previous claims, wherein in step c) the dielectric tongue is delimited through at least a precut (9) carried out in the dielectric substrate so as to leave between said dielectric substrate and said dielectric tongue a bridge connection (10) that connects the first terminal to the more than one turn, said bridge connection forming a hinge for said dielectric tongue.

6. A method according to any of the previous claims, wherein at least one bridge connection (11 ) is formed on the dielectric substrate to mechanically maintain the dielectric tongue attached to said dielectric substrate, said bridge connection being adapted to be cut to allow the folding of said dielectric tongue.

7. An RFID antenna comprising: a dielectric substrate (1 , 502), an antenna circuit (2, 515), said antenna circuit comprising more than one turn (2, 515), a first (2a, 521) and second (522) antenna terminals , and a bridge between said first and second antenna terminals wherein said electrical bridge comprises a dielectric tongue (3, 5, 540) integrally formed in said dielectric substrate, said tongue being bent over said more than one turn with a portion of said dielectric tongue used as an insulation layer between said more than one turn and a conductive path linking first and second terminals.

8. An antenna according to claim 7, wherein first terminal is connected to said more than one turn and makes an electrical bridge crossing over said more than one turn,

9. An RFID antenna according to the previous claim, wherein the dielectric tongue comprises a dielectric flap (12, 545) folded over said dielectric tongue so as to mask a portion of an arm portion of the first terminal and/or a terminal end of the first terminal.

10. An RFID antenna according to the previous claim, wherein the second antenna terminal comprises a terminal end (5222), and the first terminal is folded towards said terminal end of said second terminal.

11. An RFID antenna according to claim 7, wherein the dielectric tongue is laterally bent so that the dielectric portion of the dielectric tongue carrying the terminal portion is interposed between said conductive path and the more than one turn.

12. An RFID antenna according to any of the previous claims 7 to 11 , wherein the dielectric tongue is delimited through at least a precut (9) carried out in the dielectric substrate so as to leave between said dielectric substrate and said dielectric tongue a bridge connection (10) that connects the first terminal to the more than one turn, said bridge connection forming a hinge for said dielectric tongue.

13. An RFID antenna according to one of the previous claims 7 to 12, wherein at least one bridge connection (11 ) is formed on the dielectric substrate to mechanically maintain the dielectric tongue attached to said dielectric substrate, said bridge connection being adapted to be cut to allow the folding of said dielectric tongue.