EP2633744A1

EP2633744A1 - Flexible printed circuits

Info

Publication number: EP2633744A1
Application number: EP11767442.4A
Authority: EP
Inventors: François LECHLEITER; Laurent Berdalle
Original assignee: Linxens Holding SAS
Current assignee: Linxens Holding SAS
Priority date: 2010-10-29
Filing date: 2011-10-10
Publication date: 2013-09-04
Also published as: WO2012055696A1

Abstract

A flexible printed circuit for a contact- communication device, comprises: -a flexible substrate (6) having opposed first and second faces (6a, 6b), -electrical contacts (7a-7h) patterned on the first face (6a), electrical zones (13a-13h) patterned also on the first face (6a), the zones being associated to contacts, -an electrical path (14a-14h) patterned on the second face (6b) and electrically connected both to a zone and an associated contact.

Description

FLEXIBLE PRINTED CIRCUI TS

FIELD OF THE INVENTION

The instant invention relates to flexible printed circuits .

BACKGROUND OF THE INVENTION

Contact cards are used every day. Such cards usually comprise a body and a module. Such a module comprises a flexible printed circuit, which has a flexible substrate on which are formed electrical contacts. These contacts are to be connected to an integrated circuit (or ^λοηίρ' ) of the card. The contacts serve to be connected to an external card reader. Using the card reader, it is possible to access data of the card, for example.

An example of such a flexible printed circuit can for example be found in WO 2005/027,020.

Such flexible printed circuits could be used in other kinds of applications.

Recently, it has been intended to enable these cards to be permanently installed in proximity to their card reader. The flexible printed circuit was provided with electrical zones, remote from the electrical contacts, but electrically connected there to. The electrical zone is to be welded to an electrical track of the card-receiving support. In this way,

the card is fixed to the card-receiving support, the information can be accessed by the card- receiving support through the electrical zone which is electrically connected to the contact and hence to the chip,

in other applications, such cards can still be removably used in conventional card-readers, where the contacts will be contacted to the card-reader .

However, an accurate fixation of the flexible printed circuit to its card-receiving support, while ensuring the above three functions, has proven difficult. This is because it was witnessed that, during welding, the solder paste used to weld the electrical zone to the support flows. Thus, the accuracy of the welding is worsened, and its repeatability is difficult.

The instant invention has notably for object to improve such fixation.

SUMMARY OF THE INVENTION

To this aim, it is provided a flexible printed circuit for a contact-communication device. The flexible printed circuit comprises a flexible electrically- insulating substrate having opposed first and second faces.

Electrical contacts are patterned on the first face. These contacts are designed to be placed in electrical contact with an electrical card-reading device. These electrical contacts are to be electrically connected to an integrated circuit of the contact-communication device .

Electrical zones are also patterned on the first face. Each zone is associated to a respective contact.

An electrical path is electrically connected both to a zone and an associated contact. At least part of the electrical path is patterned on the second face.

With these features, the area where the solder paste is placed is circumscribed. Thus, the flow of the solder paste is more limited, and accuracy and repeatability of the fixation is enhanced, while ensuring all the functions of the device.

In some embodiments, one might also use one or more of the features as defined in the dependant claims.

According to another independent aspect, the invention relates to a longer lasting flexible printed circuit .

Since such cards may now be permanently installed, it is necessary to improve their life expectancy. In particular, the range of operating temperatures of such cards can be quite large, depending on the final use of the product. Due to its composite nature, mechanical stresses will be generated at the interface between the substrate and the electrically-conducting contacts in case of thermal variations. This is due to the differential dilatation properties of these two materials. Such stresses may even cause failure of the flexible printed circuit.

Therefore, it is another aim of the invention to improve the capacity of the flexible printed circuit to stand large temperature variations.

To this effect, it is provided a flexible printed circuit for a contact-communication device. This flexible printed circuit comprises a flexible electrically- insulating substrate having a face.

This flexible printed circuit further comprises a plurality of electrical contacts patterned on this face of the substrate. These electrical contacts are designed to be placed in electrical contact with an electrical card- reading device.

The electrical contacts are also to be electrically connected to an integrated circuit of the contact- communication device.

A plurality of electrical zones are patterned on a face of the substrate, each zone being associated to a respective contact.

The electrical contact and associated zone together form a shape which is elongated along a respective direction.

An electrical path electrically connects the zone to the associated contact. The electrical path is formed on a face of the substrate. It has a leg angled by at least 30° with respect to said direction.

In such way, the electrical path does not extend along the direction of main stress due to the differential dilatation of the materials. Hence, the stresses encountered in the electrical path are lower, and the risk of failure lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will readily appear from the following description of one of its embodiments, provided as a non- limitative examples, and of the accompanying drawings.

On the drawings :

- Fig. 1 is a partial perspective exploded view of a system according to a first embodiment,

- Fig. 2 is a partial top view of a flexible printed circuit for the system of Fig. 1,

- Fig. 3 is a view corresponding to Fig. 2 also showing in dotted lines the bottom face of the flexible printed circuit,

- Fig. 4 is a view similar to Figs. 2 and 3 only showing the bottom face of the flexible printed circuit,

- Fig. 5 is a cross-sectional partial view along line V-V of Fig. 3,

- Fig. 6 is a lateral view of a system according to a second embodiment,

- Fig. 7 is an enlarged view designated by sign 7 on Fig. 3,

- Fig. 8 is a top view of a band used for the manufacture of flexible printed circuit,

- Fig. 9a and 9b are schematic side views illustrating differential thermal dilatation, respectively at rest and dilated, and

- Fig. 9c is a schematic top view corresponding to

Fig. 9b.

On the different figures, the same reference signs designate like or similar elements. DETAILED DESCRIPTION

Fig. 1 shows a system according to a first embodiment. The system comprises a connector (or card reader) 1 and a contact card 2 which is to be read in the card reader. In order to ease the description, the card is shown upside down with respect to the card reader. In use, the card 2 will be turned upside down, relative to the drawing of Fig. 1 to be placed in the card reader 1.

The card 2 comprises a body 3 and a module 4 fixed to the body 3 by any suitable means. Details of the module 4 are not visible on Fig. 1. However, such a module 4 will at least comprise a flexible printed circuit 5. The flexible printed circuit will at least comprise a flexible substrate 6 on which are formed electrical contacts 7a-7h, which are to be described later in more details. The contacts 7a-7h are in electrical connection with an integrated circuit, or chip (not visible on Fig. 1) of the card. The chip is for example provided in the module 4, or elsewhere in the card 2.

Turning to the card reader 1, it may comprise a housing 8 of electrically insulating material, which receives electrical contacts 9a-9h, electrically insulated from one another. Each of these contacts comprise a contacting portion which will be placed in electrical contact with a respective electrical contact 7a-7h of the flexible printed circuit 5 when the card 2 is inserted in the card reader 1.

For example, one part of each of the contacts 9a-9h of the card reader 1 is electrically connected to an electrical device (not shown) which needs to access to the data contained in the chip of the card, and/or write data therein. By way of example, the card reader 1 can be connected to a printed circuit board 10 of this electrical device. The printed circuit board 10 may comprise tracks lla-lld which will each correspond to a respective one of the contacts 9a-9h (in the present case, where there are eight contacts, eight tracks may be provided, although only four are shown on the drawings) . The tracks lla-lld end with respective connection surfaces 11a' -lid'.

The card 2 may be removably placed in the card reader 1. For example, one may use elastic clips 12 on each side of the card reader, which will be deformable so as to enable introduction of the card in the reader, maintain the card therein, and/or remove the card therefrom.

Turning back to the flexible printed circuit 5, it comprises a substrate 6 made of an electrically insulating material such as glass-epoxy of a suitable thickness, or other suitable materials. The substrate is provided as a thin plate having two opposed main faces 6a, 6b. The main face 6a is to be turned toward the contacts of the card reader in use. The main face 6b is globally parallel to the main face 6a. The main face 6a carries the electrical contacts 7a-7h of the flexible printed circuit 5. These contacts are electrically insulated from one another. These contacts are for example provided by electro- deposition and lamination processes.

As visible on Fig. 2, one of the electrical contacts, for example the contact 7e, can be provided with a shape differing from that of the other contacts, so as to define the orientation of the flexible printed circuit with respect to the card.

As can be seen on Fig. 1, and more precisely on Fig. 2, an electrical zone 13a-13h is associated, respectively, to each electrical contact 7a-7h. Each electrical zone 13a-13h is provided on the first main face 6a of the substrate. On this face, each zone 13a-13h, is separated from its associated electrical contact 7a-7h by a respective gap, so that there is no direct electrical connection between a zone and its associated contact on the first main face 6a. As visible, the zones 13a-13h are also electrically insulated from one another. For example, the zones 13a-13h are provided during the same manufacturing process as the electrical contacts 7a-7h.

Fig. 4 now shows a bottom face 6b of the substrate.

As will appear from Fig. 3, Fig. 4 is shown along the same orientation as Fig. 2, i.e. seen from over the substrate 6 and through it. Electrical paths 14a-14h are provided on the second face 6b. Each electrical path 14a-14h is associated both to a respective electrical contact 7a-7h, respectively, and to its associated electrical zone 13a- 13h, respectively. The electrical path 14a-14h are electrically insulated from one another on the second main face 6b. There are for example manufactured according to the same process as the contacts 7a-7h and the zones 13a- 13h. As can be seen in particular on Fig. 3, the electrical path 14c comprises a first region 15 which overlies the associated electrical contact 7c, and a second region 16 which overlies the associated zone 13c. The two regions 15 and 16 are electrically connected to one another on the second face. This description also applies to the other electrical paths in relation to their associated contact and zone.

In the following, the description will focus on one 14e of the electrical paths, and its associated contact and zone. A similar description could be applied to the other ones. The first region 15 of the electrical path is electrically connected to the associated electrical contact 7e. This electrical connection is performed through the substrate 7. For example, a through hole 17 is provided in the substrate, extending between the two main faces 6a, 6b. Electrical connection occurs for example by metallisation of this through hole 17. For example, a blind plated through hole is provided. A similar method can be used to electrically connect the second region 16 to the electrical zone 13e through the substrate 6 by way of a through hole 18. The electrical connection between the two regions 15 and 16 of the electrical path 14 is performed out of the plane of Fig. 5. The chip 19 is also partly shown on Fig. 5. The chip 19 has an electrical connection terminal 19e which is electrically connected to the electrical contact 7e. In the present example, the terminal 19e of the chip is electrically connected to the electrical path 14e, in particular its first region 15 which, itself, is electrically connected to the contact 7e. However, other connections are possible. In the illustrative embodiment, this connection is performed using an electrical conductor (wire 20) extending from the terminal 19e to the electrical path 14. However, this embodiment is illustrative only. The assembly of the flexible printed circuit 5 and of the chip 19 shown on Fig. 5 provides a module 4. For example, the chip 19 is provided on the second main face 6b of the flexible printed circuit 6. It is fixed thereto by any suitable way.

Fig. 1 shows an embodiment where the card 2 is removably inserted into a card reader 1. According to another embodiment, shown on Fig. 6, the card 2 is permanently fixed to the printed circuit board 10 of the electrical device. On Fig. 6, the tracks 11a, lie of the printed circuit board 10 are shown. These tracks are electrically connected by welding to a respective electrical zone 13a, 13e, directly overlying the respective track. The respective welds are shown as 21a, 21e on Fig. 6. Because the surface of the zones 13a-13h is relatively small, and is restricted, the weld has no risk of flowing along a metallisation of the first face 6a of the flexible printed circuit during soldering. Thus, the volume of necessary solder paste can be precisely controlled. Further, thanks to this method, no solder resist is used, so that the problems associated with solder resist are prevented .

In the embodiment of Fig. 6, the electrical device will be able to access to the information of the chip of the card, since the track 11a, which is electrically connected through the soldering 21a with the zone 13a which, itself, is in electrical connection with the respective terminal area of the chip 19 through the flexible printed circuit.

Hence, the same card 2 can be used either removably in a card reader 1, as shown on Fig. 1, or permanently as shown on Fig. 6.

According to another aspect, the geometry of an electrical path will be described, in relation to Fig. 7. This description is applied to the electrical path 14a, and its associated zone 13a and contact 7a, but could be transposed to the other electrical paths of the embodiment. As can be seen on Fig. 7, the electrical contact 7a and its associated zone 13a together form an elongated shape along an axis X. The axis X can be defined as the main stress axis, when considering stress occurring in the device due to differential thermal dilatation of the two materials of the flexible printed circuit. Accordingly, the axis X can be considered as a main geometrical axis of the considered shape .

Fig. 9a is a schematic cross-section of a composite comprising a material Ml and a material M2 assembled along an assembly surface S. As shown on Fig. 9b, whenever thermal dilatation occurs, material M2 will tend to expand more than material Ml while still being constrained by its fixation thereto. This will result in high shearing stress and strain at the interface between Ml and M2 which may, ultimately, lead to failure. In particular, if the metallic material fails, its ability to conduct electrical current will be impaired. Such failure need not be global but may be provided as micro-cracks, which will worsen current flow. Further, these cracks may propagate when the card is submitted to repeated thermal stress (such as entering/leaving heated or air-conditioned buildings, ...) .

Fig. 9c is a schematic top view showing that, for an elongated part, its dilatation will be maximal in its direction of main elongation ( i.e. its length increase will be greater than its width increase) .

Now, turning back to Fig. 7, the electrical path is designed so as to withstand high stresses due to differential dilatation of the material of the substrate 6 and that (or those) of the electrical path 14a. In particular, no leg of the electrical path 14a is aligned with the direction X . In the present embodiment, the electrical path is sensibly V-shaped or U-shaped. It has a first leg 22 which extends sensibly along a first direction Xi . It has a second leg 23 which extends sensibly along a second direction X₂. It has a third leg 24 which extends sensibly along a third direction X₃ . The second leg 23 may extend along a direction X₂ which is parallel to the direction X but offset with respect thereto along a direction (V) which is normal to the direction X and defines therewith the plane 6a of the substrate first face (in the present embodiment, this axis is of course also offset along the thickness direction of the substrate, since the path is not located on the same surface as the contact 7a and associated zone 13a) . The direction Xi extends between a point P_i2 corresponding to the intersection of the first and second directions Xi , X₂ , and a center 25 of the connection region of the electrical path 14a with the electrical zone 13a. Projected in the plane of the drawing, the angle θι can be measured between the axis X and the direction Xi .

Similarly, the third direction X₃ extends from a first point P₂₃ corresponding to the intersection of the second and third directions X₂ , X₃ and a center 26 of the connection region of the electrical path 14a to the electrical contact 7a. An angle θ₂ is defined between the axis X and the direction X₃.

It was determined that, taking into account the properties of the material and the geometry of the connection, an angle of θι of 30 degrees was enough to sufficiently improve the ability of the system to withstand stresses due to differential dilatation. An angle of θ₂ of at least 30 degrees also provided good results. If the angle was lower, the system may not be able to sufficiently withstand stresses due to differential thermal dilatation. In addition, with an angle of about 30 degrees, the length of the electrical path 14a would still be short, so that its cost will still be maintained reduced. Greater angles, such as angles of 60 degrees, as shown, or more, will further improve the ability to withstand these stresses, but to the additional cost of increasing the length of the electrical path 23 and thereby increasing its cost.

In particular, in the present embodiment, the points 25 and 26 are aligned along the direction X.

Fig. 8 now shows an example of an embodiment for the manufacture of such flexible printed circuits. Fig. 8 shows a part of a band 27 made of the material of the substrate, which is continuously processed in a roll-to- roll process. The band is driven by driven patterns 28 through a plurality of handling stations which each perform one step of the manufacturing process, such as patterning the contacts, zones and/or paths. The band can be virtually divided in a plurality of areas 29 each corresponding to a flexible printed circuit to be manufactured. The areas are arranged in an array of rows and columns. Each zone or contact to be metallised is in electrical connection (not visible) with a part which is at a given potential, so that metallisation of these contacts or zones can be performed. This is for example the role of the tails 30 which can be seen on Fig. 3 and 4.

At the end of the manufacturing process, each formed flexible printed circuit will be separated from the band, for example by cutting along the dotted line 31 which is also visible on Fig. 3. This cutting will also insulate from one another the areas which have to be isolated from one another.

Claims

1. A flexible printed circuit for a contact- communication device, comprising:

- a flexible electrically-insulating substrate (6) having opposed first (6a) and second (6b) faces,

a plurality of electrical contacts (7a-7h) patterned on said first face (6a), and designed to be placed in electrical contact with an electrical card- reading device, said electrical contacts being further adapted to be electrically connected to an integrated circuit (19) of the contact-communication device,

a plurality of electrical zones (13a-13h) patterned also on said first face (6a), each zone being associated to a respective contact (7a-7h),

an electrical path (14a-14h) electrically connected both to a zone and an associated contact, wherein at least part of said electrical path is patterned on the second face ( 6b) .

2. A flexible printed circuit according to claim 1, comprising a first hole (18) through said substrate (6), said hole being metalized so as to electrically connect the electrical path to the zone.

3. A flexible printed circuit according to claim 1 or 2, comprising a second hole (17) through said substrate, said hole being metalized so as to electrically connect the electrical path to the contact.

4. A flexible printed circuit for a contact- communication device, comprising:

an electrical path (14a-14h) electrically connected both to a zone and an associated contact, wherein at least part of said electrical path is patterned on the second face ( 6b) ,

- a first hole (18) through said substrate (6), said hole being metalized so as to electrically connect the electrical path to the zone,

a second hole (17) through said substrate, said hole being metalized so as to electrically connect the electrical path to the contact.

5. A flexible printed circuit according to any of claims 1-4, wherein said electrical contact and associated zone together form a shape which is elongated along a respective direction (X) , and wherein at least part of said electrical path (14a-14h) is angled by at least 30° with respect to said direction.

6. A flexible printed circuit according to any of claims 1-5, wherein said electrical contact and associated zone are insulated from one another on said first face (6a) .

7. A flexible printed circuit for a contact- communication device, comprising:

a flexible electrically-insulating substrate (6) having a face,

- a plurality of electrical contacts (7a-7h) patterned on said face of said substrate, and designed to be placed in electrical contact with an electrical card- reading device, said electrical contacts being further adapted to be electrically connected to an integrated circuit (19) of the contact-communication device, a plurality of electrical zones (13a-13h) patterned on a face of said substrate, each zone being associated to a respective contact,

said electrical contact and associated zone together forming a shape which is elongated along a respective direction (X) ,

an electrical path (14a-14h) electrically connected both to a zone and an associated contact, wherein said electrical path is formed on a face of said substrate and comprises at least a leg (22;24) angled by at least 30° with respect to said direction (X) .

8. A flexible printed circuit according to claim 7, wherein said electrical path (14a-14h) has a shape of at least a V or a U, wherein said leg is a first leg (22), wherein the electrical path comprises a second leg (24) angled by at least 30° with respect to said direction.

9. A flexible printed circuit according to claim 7 or 8, wherein said direction (X) is a main axis of said shape .

10. A flexible printed circuit according to claim 9, wherein said main axis (X) is a main axis of stress due to differential strain of the substrate (6) and the contacts (7a-7h) in case of thermal changes.

11. A flexible printed circuit for a contact- communication device, comprising :

a flexible electrically-insulating substrate (6) having a face,

a plurality of electrical contacts (7a-7h) patterned on said face of said substrate, and designed to be placed in electrical contact with an electrical card- reading device, said electrical contacts being further adapted to be electrically connected to an integrated circuit (19) of the contact-communication device,

a plurality of electrical zones (13a-13h) patterned on a face of said substrate, each zone being associated to a respective contact,

said electrical contact and associated zone together forming a shape which is elongated along a respective direction (X) , being a main axis of stress due to differential strain of the substrate (6) and the contacts (7a-7h) in case of thermal changes,

an electrical path electrically connected both to a zone and an associated contact, wherein said electrical path is formed on a face of said substrate, wherein said electrical path (14a-14h) has a shape of at least a V or a U, and comprises at least a first leg (22;24) angled by at least 30° with respect to said direction (X), and a second leg (24) angled by at least 30° with respect to said direction (X) .

12. A flexible printed circuit according to any of claims 7-11, wherein the electrical path (14a-14h) comprises no portion aligned with said direction (X) .

13. A flexible printed circuit according to any of claims 7-12 wherein the electrical path (14a-14h) comprises a first end at said zone, a second end at said associated contact, and wherein an arbitrary straight line joining said first and second ends is aligned with said direction (X) .

14. A flexible printed circuit according to any of claims 7-13 wherein said contact and associated zone are provided on a first face (6a) of said substrate, wherein the substrate comprises a second face (6b) opposed to said first face, wherein the electrical path (14a-14h) extends on said second face (6b) .

15. A flexible printed circuit according to claim 14 wherein the electrical path (14a-14h) is connected to the zone through a first metallised through hole (18) provided through said substrate, wherein the electrical path is connected to the contact through a second metallised through hole (17) provided through said substrate, wherein an arbitrary straight line joining said first and second through holes is aligned with said direction (X) .

16. A module (4) comprising a flexible printed circuit according to any of claims 1 to 15, and an integrated circuit (19) having a plurality of electrical contacts having an electrical connexion to a respective electrical contact of the flexible printed circuit.

17. A module according to claim 16, wherein said electrical connexion comprises an electrical conductor (20) connected at one end to said integrated circuit and at another end to said path.

18. A card (2) comprising a module according to claim 16 or 17.

19. A system comprising:

a printed circuit board (10) having electrical connexion surfaces (lla'-lle'),

a card (2) according to claim 18,

wherein the electrical connexion surfaces are electrically connected to a respective electrical contact.

20. A system according to claim 19, wherein the electrical connexion surfaces of the printed circuit board are welded to respective electrical zones of the flexible printed circuit.

21. A system comprising:

a printed circuit board (10) having electrical connexion surfaces (lla'-lle'),

a card (2) comprising a module (2), said module comprising a flexible printed circuit for a contact- communication device, said flexible printed circuit comprising :

.a flexible electrically-insulating substrate (6) having opposed first (6a) and second (6b) faces,

.a plurality of electrical contacts (7a-7h) patterned on said first face (6a), and designed to be placed in electrical contact with an electrical card- reading device, said electrical contacts being further adapted to be electrically connected to an integrated circuit (19) of the contact-communication device,

.a plurality of electrical zones (13a-13h) patterned also on said first face (6a), each zone being associated to a respective contact (7a-7h),

.an electrical path (14a-14h) electrically connected both to a zone and an associated contact, wherein at least part of said electrical path is patterned on the second face ( 6b) ,

the module further comprising an integrated circuit (19) having a plurality of electrical contacts having an electrical connection to a respective electrical contact of the flexible printed circuit,

wherein the electrical connection surfaces of the printed circuit board are welded to respective electrical zones of the flexible printed circuit.

22. A system comprising :

- a printed circuit board (10) having electrical connection surfaces (11a', lie'),

a card comprising a module (2), said module comprising a flexible printed circuit for a contact- communication device, said flexible printed circuit comprising:

.a flexible electrically-insulating substrate (6) having a face,

.a plurality of electrical zones (13a-13h) patterned on a face of said substrate, each zone being associated to a respective contact,

.an electrical path (14a-14h) electrically connected both to a zone and an associated contact, wherein said electrical path is formed on a face of said substrate and comprises at least a leg (22;24) angled by at least 30° with respect to said direction (X) ,

the module further comprising an integrated circuit

(19) having a plurality of electrical contacts having an electrical connection to a respective electrical contact of the flexible printed circuit,

23. A system according to claim 19, further comprising a connector (1) fixed to the printed circuit board, and wherein the card (2) is removably mounted in the connector.

24. A system according to claim 23, wherein the connector has electrical contacts (9a-9h) each having a first portion connected to an electrical connexion surface of the printed circuit board, and a second portion in contact with a respective electrical contact of the flexible printed circuit.

25. A band (27) comprising a plurality of similar flexible printed circuits according to any of claims 1 to 15, arranged in rows and columns, and sharing a common substrate ( 6) .