WO2007068280A1

WO2007068280A1 - Crimping method and device manufactured thereby

Info

Publication number: WO2007068280A1
Application number: PCT/EP2005/014221
Authority: WO
Inventors: Yves Stricot; Christophe Mathieu; Bogdan Rosinski
Original assignee: Fci
Priority date: 2005-12-16
Filing date: 2005-12-16
Publication date: 2007-06-21
Also published as: CN101361231A; EP1969678A1

Abstract

A method for crimping two thin elements together, while connecting ther electrically, comprising the step of: a) providing a dielectric substrate (5) with a conductive layer; b) providing a metallic strap with at least one work hardened piercing toot) (10a, 10b, 10c, 10d, 10'a, 10'b, 10'c, 10'd); c) piercing both the dielectric substrate and the conductive layer with the at least one piercing tooth; and d) bending the at least one piercing tooth on the conductive layer so as tc clamp at least the conductive layer and the dielectric substrate between the a least one piercing tooth and the metallic strap. A device manufactured with such a method.

Description

CRIMPING METHOD^AND DEVICE MANUFACTURED THEREBY

The present invention generally relates to crimping methods and devices manufactured thereby. More specifically, such methods apply for crimping two thin elements together, while connecting them electrically.

For instance, such methods may be applied for attaching bridges or straps on antennas in RFID (Radio Frequency IDentifier) tags, over the antenna spiral turns. The use of a tag having an RFID antenna for identifying and monitoring objects is well known in the art. With no self source of energy, the tag comprises an antenna 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 magnetic field, the RFID antenna will become energized and the electronic circuit can transmit a coded signal towards the reader or a separate receiving antenna.

An example of RFID layout is shown on Figs. 1a to 1c. This layout includes an antenna 1. An integrated circuit (IC) chip (not shown on Figs. 1a to 1c) is connected to this antenna. The antenna loop 1 , also called later on antenna tracks, generally comprises a plurality of turns that spiral around on a planar dielectric substrate. The antenna tracks 1 may be either formed before being laid on the substrate or formed directly upon it (by printing and/or etching techniques for example), among known techniques. When the antenna pattern requires more than one turn, the antenna terminals 2 and 2' as seen in Figs. 1a to 1c are separated by the plurality of turns, and an electrical bridge must be formed over these spiral turns to close the antenna loop. Different techniques are known to form and connect this bridge, also called later on a strap or a conductive strap, to the antenna, while keeping this bridge electrically isolated from the tracks. The PCT application WO 2005/041121 discloses a RFID device with a strap and an antenna electrically coupled together via crimped connections.

The applicant looked for a simple, straightforward, efficient and improved method for making such connections. Accordingly, the present invention provides an assembly method according to claim 1. The present invention further provides a device according to claim 8.

The invention takes advantage of the improved crimping technique that allows :

- a large contact area between the piercing teeth formed on the conductive strap and the conductive layer;

- a reliable piercing and crimping thanks to the work hardened tooth or teeth, - a strong strain resistance thanks to the bending of the hardened tooth or teeth against the conductive layer.

Other embodiments and/or implementation of the invention correspond to claims 2-7 and 9-11, considered either independently or as twofold or manifold combined. Other features and advantages of this invention will further appear in the hereafter description when considered in connection to the accompanying drawings, wherein:

FIG. 1a - 1c illustrate different configurations of antenna terminals when a bridge or strap is required, FIG. 2 illustrates a view of a bridge or strap with the cut piercing teeth for attachment to an RFID antenna in an exemplary implementation of the method according to the present invention;

FIG. 3 illustrates a view of a first carrier carrying straps used in the antenna circuit according to the invention; FIG. 4 illustrates a view of a second carrier carrying straps used in the antenna circuit according to the invention;

FIG. 5 illustrates a sectional view of a bridge that is crimped to the antenna terminals of an RFID antenna according to the exemplary implementation of the method according to the present invention; FIG. 6a-c illustrates the different steps of the exemplary implementation of the method according to the present invention.

For illustrating purposes, the invention is described below as an RFID tag manufacturing method. Such a RFID tag generally comprises a dielectric substrate (not shown in FIGs. 1a to 1c) that carries an antenna. On the example shown, several turns 1 form the antenna loop of a spiral antenna. This antenna comprises first and second antenna terminals 2 and 2'. A chip (not shown in FIGs. 1a to 1c) is generally attached to the antenna tracks, so as to form a RFID antenna. The chip is either attached in the region inside the turns 1 to the chip terminals 3 and 3' (FIG. 1b), or outside the turns 1 to the chip terminals 3 and 3' (FIG. 1c). The chip may also be provided on the bridge (not shown in FIGs. 1a to 1c) that closes the antenna loop (FIG. 1a). In all three instances, a bridge or conductive strap has to be attached to the antenna terminals 2 and 2' to close the antenna loop. The antenna circuit may be provided without a chip, e.g. in the case of a capacitive antenna which may be similar to the antenna of FIG. 1a.

The antenna is carried by a dielectric substrate. This substrate is made of a suitable material for ISO contactless RFID cards. This dielectric substrate may be made for example of PVC, polyester, PET (polyethylene terephthalate),

PEN (polyethylene naphthalate), polyimides, epoxy-glass, etc. Substrates such as paper may also be used. The substrate is rigid as well as flexible. For instance, the substrate thickness is in a 100-300 microns range and is preferably about 200 μm thick.

The RFID tag presents an upper face 6 carrying the tracks 1 , and a lower face 7 corresponding to the face of the dielectric substrate 5 free of antenna terminals.

The antenna is made by plating a conductive layer on the substrate and possibly etching it according to a pattern corresponding to the turn's tracks.

The conductive layer may be made of copper, gold, platinum, aluminum, brass, tin, silver or any other suitable conductive metal or alloy. The conductive layer may also be laminated over the dielectric substrate using an adhesive laid over the substrate beforehand if necessary. The thickness of the tracks is generally in the 9 to 50 microns range, but may also be thinner or thicker depending on the antenna circuit specifications. Preferably they are about 35 μm thick.

The substrate and the antenna are covered with a glue layer 10-30 μm, for instanceiδ μm, thick. After an antenna circuit with antenna terminals 2 and 2' is formed on the dielectric substrate 5, an additional attachment step is performed: a conductive strap 10 is attached to said the antenna terminals so as to form a bridge crossing over the antenna turns, as seen in FIGs. 5 and 6. The bridge or strap is formed through stamping of a thin metal sheet as seen on FIGS 3 and 4. The strap may also carry an insulating material as seen later on.

This strap material is for instance phosphor bronze, or another copper alloy, or any other alloy having a mechanical resistance high enough. The strap thickness is for instance in a 50-100 microns range and is preferably about 80 μm thick

An example of embodiment of the strap is shown in FIG. 2. The ends of strap 10 comprise a first and a second enlarged terminal portions 115 and 115' respectively, which are to be attached to the antenna terminals 2 and 2' respectively. The strap 10 further comprises a central narrow portion 110 which helps reduce the stray capacity of the strap when attached to the antenna circuit. The visual aspect of the antenna circuit is also improved.

Each end of strap 10 comprises at least one piercing tooth or petal, such as 10a, 10b, 10c and 10d for terminal portion 115 and 10'a, 10'b, 10'c and 10'd for terminals portion 115'. This piercing tooth may be part of a ring of teeth as seen in FIG. 2 to 4, for example 4 teeth.

The piercing teeth are obtained by means of cutting, i.e. stamping, through the whole conductive strap thickness. A cutting following a cross pattern may be carried out on the terminals portions 115 and 115' of the strap 10 as seen on FIG. 2. The resulting piercing teeth can be seen on FIG. 4. During the cutting step, the teeth are elongated, for instance of more than 50%, so as to be work hardened. After the teeth 10a to 10d are cut, said teeth are bent along their basis, i.e. along the line linking the piercing teeth to the terminal portion. The teeth are preferably bent so as to be substantially perpendicular to the main plane defined by the strap. As seen on FIG. 2, the teeth may present a triangular shape, with a sharp tip. They may also present a rounded tip as seen in FIG. 4, provided an different cut is performed for obtaining the appropriate shape. The tip of the teeth may also present a flat profile.

The bent piercing teeth define openings 15 and 15' on the terminal portions 115 and 115' respectively, as seen in FIG. 4. FIG. 5 illustrates a view of an RFID antenna according to an exemplary implementation of the invention, with its antenna terminals 2 and 2' and a bridge 10 connecting said terminals to each other. The antenna circuit corresponds to the antenna of Fig. 1 b or 1c with the chip provided outside the conductive strap 10. Antenna turns 1 are formed over a dielectric material 5. As described before for FIG. 1 b and 1c, antenna terminals 2 and 2' are spaced apart from each other with turns 1 in between, so that a bridge or conductive strap 10 is necessary to electrically link these terminals together.

The strap 10 is applied directly opposite the antenna terminals 2 and 2' on the face of the dielectric substrate free of antenna terminals. The dielectric substrate 5 is locally used as the insulating layer separating the antenna tracks 1 from said strap. Adding an insulating layer on the strap is therefore not needed. This allows avoiding stray capacity between the strap and the antenna tracks. This allows avoiding creating a specific isolating layer between the strap and the antenna tracks. The method to attach strap 10 through crimping to the RFID tag will be described in details hereafter. Such a method is illustrated on FIGS. 6a to 6c. After the piercing teeth 10a and 10c are formed on the strap ends as explained before, the strap is placed facing the RFID lower face 7. The strap is then pressed against this face 7. The RFID tag is torn by means of the piercing teeth that cut through dielectric substrate 5, the antenna terminal 2 and the glue layer 20, until said piercing teeth arises on the RFID tag opposite side as seen in FIG. 6b. The tearing from the lower side 7 of the RFID tag is performed into the direction shown by arrows F on FIG. 6a.

As shown in FIG. 6b piercing teeth have passed through the dielectric substrate 5, antenna terminal 2 and the glue layer 20 successively. Direction F is substantially perpendicular to strap 10 main plane. Piercing by means of teeth 10a to 10d through the RFID tag may be facilitated thanks to the respective teeth tips 10e to 10h. Each piercing teeth 10a to 10d comes into contact with antenna terminal 2 along a first portion 18 of each teeth. The length of this first portion 18 depends upon antenna terminal thickness 20.

After antenna terminal 2 has been cut through, each teeth 10a to 10d is crimped over the RFID tag upper face 6 as seen in FIG. 6c. The bending direction of this crimping is shown on FIG. 6b thanks to arrows F'. By crimping teeth 10a to 10d on the upper face 6 of RFID tag, one may understand that the piercing teeth are actually bent towards the RFID tag upper face 6, and away from each others. Thus, piercing teeth 10a to 10d are bent away from central opening 15, and/or the ring of piercing teeth. A punching tool may be used to bend the piercing teeth.

FIG. 5, as well as FIG. 6c, shows conductive strap 10 and antenna circuit 1 after crimping of strap 10 with the method according to the invention. Only piercing teeth 10a and 10c are visible on these section views. Strap 10 has been brought into contact with the lower face 7, and piercing teeth 10a to 10d, and 10'a to 10'd have cut firstly through dielectric 5, secondly antenna terminals 2 and 2' rand third through the glue layer 20. Piercing teeth have been bent against the upper side 6, i.e. the side opposite the side of insertion of the teeth. Piercing teeth 10a and 10c are bent till they come into contact with antenna terminal 2, while piercing teeth 10'a and 10'c are bent till they come into contact with antenna terminal 2'. Consequently, the electrical path between the antenna terminals and the strap 10 passes both through the portions 18 and through the contact areas between the teeth tips and the antenna tracks.

Each piercing teeth is characterised by a height 17 at least higher than thickness 18 of the RFID tag in the antenna terminal region as seen in FIG. 6a. Height 17 is measured along a direction perpendicular to strap 10, between the tip of the piercing teeth, and its base where it bents away from strap 10. As an example the RFID tag thickness may be of 200 (substrate) +35 (conductive track layer) +18 (glue layer)=253 μm around the antenna terminal region, and the piercing teeth height may be at least greater than this height and preferably a few hundred microns long in order to bend said piercing teeth towards the RFID tag.

In an alternative implementation of the RFID tag according to the invention, the strap 10 may also be attached on the upper face 6 of the RFID tag (not shown). An insulation layer is needed to electrically isolate said strap from the antenna tracks 1. The steps described above with regard to FIG. 6a to 6c are transposed to a strap piercing through the antenna terminals 2 and 2' before piercing through dielectric substrate. The conductive strap is provided with an insulating layer, so as to insulate the strap from the antenna turns. The piercing teeth then tear the antenna terminals before tearing the dielectric substrate till the insulating layer comes into contact with the antenna turns. As seen in FIG. 3, strap 10 may cut out in a carrier 200. An insulting layer 70 may be laid upon the straps. Strap 10 may also be formed through stamping of a sheet of suitable conductive material as seen in FIG. 4.

Strap 10 comprises a narrow central section 110 and enlarged terminal portions 115 and 115, on which piercing teeth 10a to 10d, and 10'a to 10'd have been cut out respectively. Considering the dimensions of the straps 10, and specifically the high length to width ratio, carrier strip may comprises lateral guiding portions 120 and 120' - provided with guiding holes 121 and 121' respectively - guiding portions to which all straps are attached by means of narrowed portions 120a and 120'a respectively. Thus the integrity of straps 10 is improved, and guiding holes may also be used as markers for an improved positioning of the stamping tools.

Piercing teeth may be cut out either before or after the strap 10 is cut out. On FIG. 4, piercing teeth are shown after their first bending so as to be substantially perpendicular to the strap, and in this example to the carrier strip. As mentioned before, if such a stamped strap is to be attached on the upper face of an RFID tag, an insulating layer (not shown on FIG. 4) ought to be added on top of the strap. Straps 10 are then severed from carrier strip

(straps 10' on FIG. 4) before being crimped to an RFID tag or at the same time.

An alternative solution to the insulating layer added to the strap can be found in adding selectively an insulating layer to the RFID tag upper side, while leaving antenna terminals free of insulating material.

When the strap is attached on the substrate upper face, the piercing teeth, after having passed through the substrate once are bent against the lower face 7 so that the tips of the piercing teeth pierce again the dielectric substrate 5 to come close to or into contact with antenna terminals. The dielectric substrate may be locally heated thanks to heating rods positioned next to the tip of the teeth. The heating results in a local weakening of the dielectric substrate so that a welded joint can be formed between the tip of piercing teeth and the antenna terminals.

The length of the piercing teeth is preferably comprised between 0.8 mm to 1. 5 mm and preferably 1.2 mm. Tests have shown that the strap thickness does not influence the piercing step, while a shorter tooth may result in difficulties during the bending step. The 4 teeth configuration appears particularly well suited to crimp the bridge as the resulting crimped bridge is stable against the RFID tag and ensures a good electrical and mechanical contact with the antenna terminals.

Once the strap is attached to the substrate, it is laminated at 130⁰C with a 20 bars pressure. Thank to the method according to the invention the electrical contact and the mechanical attachment remain efficient.

Claims

1. A method for crimping two thin elements together, while connecting them electrically, comprising the step of: a) providing a dielectric substrate (5) with a conductive layer; b) providing a metallic strap with at least one work hardened piercing tooth (10a, 10b, 10c, 10d, 10'a, 10'b, 10'c, 10'd); c) piercing both the dielectric substrate and the conductive layer with the at least one piercing tooth; and d) bending the at least one piercing tooth on the conductive layer so as to clamp at least the conductive layer and the dielectric substrate between the at least one piercing tooth and the metallic strap.

2. A method according to claim 1 , wherein the metallic strap comprises at least four piercing teeth that are work hardened in cutting them out of the metallic strap in a star shape.

3. A method according to claim 1 or claim 2, wherein the metallic strap comprises at least four piercing teeth that are work hardened in elongating of at least 50%.

4. A method according to any one of the previous claims, wherein the dielectric substrate is made of one of the following plastic materials: PVC, polyester and any plastic material having equivalent structural properties.

5. A method according to any one of the previous claims, wherein the metallic strap is made of out of one of the following materials: phosphor bronze and any other conductive alloy, such as copper alloy, having equivalent structural properties.

6. A method according to any one of the previous claims, wherein at least one piercing tooth tears the dielectric substrate before tearing the conductive layer.

7. A method according to any one of the previous claims, wherein the conductive layer comprises an antenna loop made of a metallic layer plated and etched on the dielectric substrate.

8. A device made according to any one of the previous claims, comprising - a dielectric substrate (5) with a conductive layer;

- a metallic strap with at least one work hardened piercing tooth (10a, 10b,

10c, 10d, 10'a, 10'b, 10'c, 10'd); this piercing tooth piercing both the dielectric substrate and the conductive layer and being bent on the conductive layer so as to clamp at least the conductive layer and the dielectric substrate between the at least one piercing tooth and the metallic strap.

9. A device according to claim 8, wherein the dielectric substrate is at least 100 μm thick and is made of one of the following plastic materials: PVC, polyester and any plastic material having equivalent structural properties.

10. A device according to claim 8 or claim 9, wherein the metallic strap is between 50 and 100 μm thick and is made of out of one of the following materials: phosphor bronze and any other conductive alloy, such as copper alloy, having equivalent structural properties.

11. A device according to any one of claims 8-10, wherein the conductive layer comprises an antenna loop made of a metallic layer between 20 and 50 μm thick, plated and etched on the dielectric substrate.