WO2013037762A1

WO2013037762A1 - Rfid antenna

Info

Publication number: WO2013037762A1
Application number: PCT/EP2012/067718
Authority: WO
Inventors: Christophe Mathieu; Yean Wei Yeap
Original assignee: Linxens Holding
Priority date: 2011-09-14
Filing date: 2012-09-11
Publication date: 2013-03-21
Also published as: EP2756547B1; CN108695595A; CN103947040A; EP2756547A1; MY166125A; JP6126188B2; KR20140060358A; JP6095070B2; JP2016034151A; JP2014527375A

Abstract

The present invention relates to a method for manufacturing an antenna which comprises the following steps : • providing a magnetic sheet made of composite material including magnetic particles and a synthetic resin, said magnetic sheet having a first surface; • forming directly on the first surface of the magnetic sheet an electrically conductive planar track having at least one turn.

Description

RFID ANTENNA

Field of the invention

The invention relates to a method for manufacturing an antenna and to an antenna obtainable by the method.

Description of prior art

The use of a tag having an RFID antenna to identify and monitor objects is well known in the art. Such a tag comprises for instance an antenna circuit formed with conductive tracks which is electrically connected to 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 for a sufficient time, the RFID antenna will become energized and the electronic circuit can transmit a signal towards the reader or a separate receiving antenna.

Such a mode for contactless communication between an IC tag and a reader/writer is expected to become more diversified in the future. For example, in order to further increase the level of convenience, portable communication terminals, such as mobile phones will be equipped with a tag function and a reader/writer function.

For example, by providing a mobile phone with a tag function, the mobile phone can be used to pay train fares by holding the phone up against the station gate.

In recent RFID systems (e.g. NFC standard) that operate at a frequency of 13.56 MHz, a proper operating environment is required. For example, with regard to communication properties, a longer communication distance is desired, or if the reader/writer and the IC tag are opposed to each other, a wide planar communication range is desired . However when such a tag is mounted on an article whose surface is made of conductive material or is located in an environment surrounded by electromagnetic fields, e.g. in a phone casing or over the battery, the resonance frequency of the antenna is shifted with respect to the nominal resonance frequency. This shifting of resonance frequency affects the information exchange between the transponder and the reader/writer device and even results in no communication at all (de-tuning of the whole RFID system) .

Furthermore, to be applicable, such antenna also has to meet space consumption requirement, in particular the antenna should have a thickness as thin as possible and should be as easy as possible to manufacture and is compatible with mass production specification. Thickness issue is particularly important when the antenna is intended to be cased in a mobile phone, especially new generation of slim smart phones, where space is quite limited .

Summary of the invention

An object of the present invention is to provide a method for manufacturing an antenna of reduced thickness and cost and which is operative when it is mounted on a metallic device and/or placed in an environment surrounded by electromagnetic fields.

To this end, it is provided a method according to claim 1.

Indeed with the claimed features, it is possible to make a reduced thickness (as low as 150 ym) antenna since the antenna conductive track is directly formed onto the ferrite sheet which acts as a supporting substrate in addition to its primary function as a shielding member. Thus, it is not necessary to make use of any additional intermediate supporting substrate for the antenna and therefore this also helps reduce manufacturing tolerance stack .

Short description of the drawings

These and further aspects of the invention will be explained in greater detail by way of example and with reference to the accompanying drawings, in which:

Fig.l shows a first embodiment of an antenna according to the invention;

Fig.2 shows a second embodiment of an antenna according to the invention;

Fig.3 shows a cross-sectional view of the antenna of along the arrow of Fig. 2.

The figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the figures.

Detailed description of preferred embodiments

Fig.l show a first embodiment of a planar RFID antenna which comprises a supporting substrate 2 on which an electrically conductive track 4 has been formed. The substrate 2 is, in the context of the invention, made of a magnetic flexible sheet which comprises magnetic particles (such as a powder or a flake of magnetic ferrite) dispersed in a resin binder. An example of such a ferrite sheet is Liqualloy^(TM) Flexible Film sold by Alps Electric Co., LTD. Such type of ferrite sheets are also easily available by ferrite material suppliers, such as for example Japanese ferrite material suppliers. The conductive track has been directly formed on a first main surface of the ferrite sheet, such that the conductive track extends in a plane parallel to the first main surface. The conductive track is for instance made of copper. As visible on Fig.l, the antenna track comprises a plurality of turns (here there are four turns) in the form of a spiral. The outer turns comprises a connection end which is connected to a connection end of the inner turn via an electrical bridge.

In the context of the invention, the verb "form" and its conjugations encompass the non-exhaustive below-listed methods :

• lamination of a conductive foil and selective chemical etching of the conductive foil after selective masking of the conductive foil, with e.g. a photo resist resin;

• lamination of a conductive foil already patterned by mechanical stamping;

• screen or gravure or inkjet or offset printing of an electrically conductive ink;

• laying a conductive wire onto the first surface of the magnetic sheet;

• chemical vapour deposition of electrically conductive particles .

From manufacturing standpoint, the method will be advantageously chosen such that it can be carried out via a reel-to-reel process, which allows high production rate. Methods particularly adapted for reel-to-reel implementation are the first three above-mentioned methods.

The antenna track can be designed such that its resonance frequency lies in the range of 13.56 MHz in order to meet, for instance NFC specification. In order to tune the inductance, one may vary the distance gap between two adjacent turns and/or the width of each turn and/or the number of turns.

Fig. 2 represents a second embodiment of the antenna and differs from the first one in that the two connection ends of the antenna conductive track are not bridged.

With reference of Fig. 3, which is a cross-sectional view in a line A-A of Fig. 2, one may observe that the copper ferrite laminate is provided with two blind holes, located at the level of the two antenna connection ends. These blind holes provide an easy access for electrically connecting the antenna to a device. The antenna connection ends may be mechanically embossed for getting a reliable electrical connection with the device.

Now it will be described a preferred process for manufacturing an antenna according to the second embodiment .

The process comprises:

a) providing a ferrite sheet;

b) applying an adhesive layer on a first surface of the ferrite sheet;

c) punching two through-holes in the ferrite sheet ;

d) laminating a copper foil onto the adhesive layer;

e) masking the copper layer with a masking material so as to define the antenna pattern;

f) removing the un-masked area of the copper foil;

g) removing the masking material so as to expose the copper track.

Optionally, after step g) , one may proceed with an additional plating step on the exposed copper track and on the bottom surface of the blind holes, for instance with a nickel and gold coating; alternatively one may carry out passivation step of the antenna tracks for corrosion protection .

Alternatively, steps b) and d) to g) can be replaced by printing techniques, as described e.g. in US 7,060,418 which is incorporated by reference.

The applicant has then succeeded in obtaining antennas of thickness ranging between 150 to 200ym with a layered structure as schematically drawn in Fig. 4.

The layered structure so called single-sided with blind holes comprises the ferrite sheet, an adhesive layer on top of the first surface of the ferrite sheet and eventually a laminated copper layer. Typically the ferrite sheet, the adhesive layer and the conductive track thicknesses are about lOOym, 20ym and 35ym, respectively.

Optionally, a second sheet of magnetic material is placed on a second surface of the above described composite magnetic sheet, i.e. on an opposite surface of the first magnetic sheet to the surface onto which the conductive track is formed or to be formed.

In this embodiment of the invention two types of ferrite materials are used for the first and second sheet.

The first sheet is preferably chosen with a value of the imaginary part μ' ' of the permeability which is lower than 5 H/m. "lower" will be understood as "lower or equal". Due to low value of μ' ' of such a composite ferrite material which is typically polymer based, this first magnetic sheet will typically have a value of the real part ] ' of the permeability which is low i.e. a value which is between 40 and 50 H/m.

Such a low value of μ' ' allows to minimize ohmic loss of the eventually realised antenna. The second sheet of ferrite material is chosen with a high value of μ' , i.e. a value higher than 100 H/m. "Higher" will be understood as "higher or equal". The choice of the value of μ' ' is not important.

A second sheet of ferrite material with such a high value of μ' allows to obtain an antenna with an enhanced quality factor Q.

Such a second magnetic sheet can be made of a composite material including magnetic particles and a synthetic resin, a sintered type of magnetic material or can be a plain ferrite sheet.

By using a combination of such first and second magnetic sheets the obtained antenna has excellent behaviour in particular as to reduced ohmic loss and quality factor Q.

Such first and second magnetic sheets are in particular easily available by ferrite material suppliers, such as for example Japanese ferrite material suppliers.

In known antenna structure, the layered structure usually comprises:

• a dielectric substrate (e.g. epoxy glass or PET or polyimide) ;

• electrically conductive tracks formed on a first surface of the dielectric substrate;

· a ferrite sheet laminated on the opposite side second surface of the dielectric substrate.

Main limitations of the known antenna structure are the high total thickness and the high distance between antenna conductive tracks and the ferrite sheet.

Although the described embodiments relate to a single sided antenna, the skilled person in the art may conceive that it is also possible to manufacture double sided antenna with conductive holes according to the above- described method .

Claims

1. Method for manufacturing an antenna comprising the following steps:

· providing a magnetic sheet made of composite material including magnetic particles and a synthetic resin, said magnetic sheet having a first surface;

• forming directly on the first surface of the magnetic sheet an electrically conductive antenna track having at least one turn.

2. Method according to claim 1, wherein the step of forming the antenna conductive track includes the following steps :

• applying an electrically conductive layer on the first surface so as the conductive layer adheres to the first surface;

• applying a masking pattern on the electrically conductive layer to selectively protect the conductive layer;

· chemically etching the electrically conductive layer so as to remove the un-protected conductive layer; and

• removing the masking pattern to expose the conductive track .

3. Method according to claim 2, further comprising a step of plating or passivating the exposed conductive track .

4. Method according to claim 1, wherein the step of forming the antenna track includes the step of:

• applying an electrically conductive patterned layer on the first surface so as the patterned conductive layer adheres to the first surface.

5. Method according to any one of preceding claims, wherein the electrically conductive layer is selected from copper, silver, aluminium, palladium and graphite.

6. Method according to any one of preceding claims, wherein the application of the conductive layer is carried out by laminating the conductive layer on the first surface of the ferrite sheet.

7. Method according to claim 1, wherein the step of forming the antenna conductive track comprises the following step:

• applying an electrically conductive ink to provide the antenna conductive track.

8. Method according to claim 7, further comprising the step of plating the circuit track pattern with an electrically conductive coating.

9. Method according to claims 7 or 8, wherein the conductive ink is applied by screen or gravure or inkjet or offset printing.

10. Method according to claim 1, wherein the step of forming the antenna conductive track comprises the step of mounting a metallic wire onto the first surface of the magnetic sheet.

11. Method according to anyone of the preceding claims, wherein it comprises the step of placing a second magnetic sheet on a second surface of said magnetic sheet made of composite material including magnetic particles and a synthetic resin, said second surface being opposite to said first surface, the said magnetic sheet made of composite material including magnetic particles and a synthetic resin having a permeability with a value of imaginary part μ' ' which is lower than 5 H/m and the said second magnetic sheet having a permeability with a real part μ' which is higher than 100 H/m.

12. An antenna obtainable by a process according any one of preceding claims.