The present invention relates to a flexible, electronic card including a fingerprint sensor, and to a method of manufacturing such an electronic card.

US 2015/049925 describes an example of a prior art technique for manufacturing a flexible, electronic "smart" card 2 including a fingerprint sensor 10. In that method, the electronic card 2 is manufactured by first forming a card body 4 with an embedded circuit 6 that includes connection pads 8 for connection to a fingerprint sensor 10, and then removing material from the card body 4 to form a cavity that exposes the pads 8. The walls of the cavity are coated with an adhesive epoxy, and contacts 12 on the underside of the fingerprint sensor 10 are connected to the connection pads 8 of the circuit 6 using a conductive epoxy. An electronic card 2 manufactured in accordance with this technique is illustrated in Figures 1A and 1 B.

It is desirable for such electronic cards to be highly flexible, preferably of similar flexibility to conventional smart cards or credit cards. However, fingerprint sensors are relatively weak and can be easily damaged by such movements. This has proved to be an impediment to wide implementation of fingerprint sensors in electronic cards.

It has been proposed in WO 2009/140968 to reinforce the fingerprint sensor against damage due to bending by using a thickened printed circuit board within the body of the card. However, this has been found to undesirably increase the overall stiffness of the card, making it difficult for the card to meet various flexibility requirements.

The present invention provides, in a first aspect, a flexible electronic card comprising a fingerprint sensor having a sensing area, and a reinforced electrode adjacent the sensing area, wherein the reinforced electrode is adapted to act as a reinforcement member to protect the fingerprint sensor against bending.

This configuration synergistically uses a single component to provide both an electrode for the fingerprint sensor, as well as to provide reinforcement for to the relatively weak fingerprint sensor. Bending forces in particular can result in large strains at the surface of the sensor, which can damage the sensor.

In the present context, flexible is intended to mean that the electronic card complies with the bending stiffness requirements of the relevant standard for electronic smart cards, for example ISO 7816, or similar. The electronic card preferably has a thickness less than 0.84 mm, and preferably of about 0.76 mm (e.g. ± 0.08 mm), which are the thickness of a normal smart card. The electronic card preferably has a width of between 85.47 mm and 85.72 mm, and a height of between 53.92 mm and 54.03 mm. More generally, the electronic card preferably complies with ISO 7816.

In various embodiments, the card body is formed from PVC. The card may include a circuit substrate having one or more electronic components formed thereon. The circuit substrate is preferably a flexible circuit substrate, and may be flexible printed circuit board , for example having a circuit etched thereon. The term "flexible substrate" is intended to include any substrate that is at least sufficiently flexible such that the card can comply with the bending requirements of ISO 7816. The flexible circuit substrate preferably has a thickness of less than 0.20mm, more preferably less than 0.15mm and preferably less than 0.10mm. That is to say, the flexible circuit preferably does not provide a significant degree of reinforcement against bending of the smartcard.

The reinforced electrode may provide an increase of at least 25%, more preferably at least 35% and most preferably at least 50% to the stiffness of the electronic card at the sensor (e.g. compared to the stiffness of the electronic card if the reinforced electrode was not present). This increase in stiffness of the card at the sensor means that the degree of bending at this point decreases, reducing the likelihood of sensor damage.

Preferably the fingerprint sensor is an active capacitance fingerprint sensor (also known as an RF fingerprint sensor). Thus, the reinforced electrode may be for applying a voltage to a finger presented to the sensing area in use whilst the sensor performing a fingerprint scan of the finger.

The fingerprint sensor may be an area-type fingerprint sensor. That is to say, the fingerprint sensor is configured such that a fingerprint is detected by placing the finger on the sensing area in a static manner, i.e. as opposed to a swipe-type fingerprint sensor. The fingerprint sensing area preferably has a length of at least 6mm, optionally at least 8mm and optionally at least 10mm. The fingerprint sensing area preferably has a width of at least 6mm, optionally at least 8mm and optionally at least 10mm. In one embodiment, the sensing area is approximately square, e.g. having a length and a width within 10%.

The reinforced electrode may be made of metal, such as steel (e.g.

stainless steel) or copper. The reinforced electrode preferably comprises a conductive surface on the front face of the card for contact with the finger, which provides the electrode function. Compared to normal electrodes, the reinforced electrode may be thicker in cross-section, or may surround a greater amount of the sensor in order to provide the reinforcement effect.

In preferred embodiments, the reinforced electrode completely surrounds a sensing area of the fingerprint sensor. Preferably the reinforced electrode comprises at least a continuous electrode element circumscribing the sensing area of the fingerprint sensor. The planar portion preferably provides an electrode contact surface having a width of at least 1 mm, more preferably at least 1 .5mm, on each side of the fingerprint sensor. The electrode contact surfaces preferably extend along the full length of each side of the sensing area of the fingerprint sensor.

The reinforced electrode may comprise a planar portion adjacent a front face of the fingerprint sensor and surrounding adjacent the sensing area of the fingerprint sensor. The planar portion may form a rectangular plate, and in one configuration has a central hole for the sensing area to be exposed, for example a rectangular hole.

The thickness of the planar portion is preferably at least 0.05 mm, more preferably at least 0.10mm, more preferably at least 0.20mm and most preferably between 0.30mm and 0.50mm. In a preferred embodiment, the thickness of the planar portion may be between 0.375mm and 0.425mm.

The planar portion is preferably substantially flat, for example having a flatness of less than 50μηι per mm, more preferably less than 25μηι per mm, more preferably less than 10μηι per mm and most preferably less than 5μηι per mm.

In one embodiment, the reinforced electrode may comprise only the planar portion. That is to say, the electrode may be a planar electrode.

The reinforced electrode may comprise an edge portion adjacent the sides of the fingerprint sensor. The edge portion may form a closed shape around all sides of the fingerprint sensor. For example, the edge portion may have a tubular, rectangular shape.

In one embodiment the reinforced electrode comprises both the planar portion and the edge portion, with the edge portion extending away from the plane of the planar portion. These portions may be integrally connected such that the reinforced electrode has an open, box-like structure. The reinforced electrode, in one example takes the form of an open frame. Optionally, one or more sides of the frame may have an inverted, L-shape section (i.e. with the bottom of the L-shape at the front of the card), preferably with the planar portion forming a horizontal of the inverted L-shape and the edge portion forming a vertical of the inverted L-shape. This shape has been found to be highly effective at protecting the fingerprint sensor against damage from bending strains.

The thickness of the, or each, of the planar portion and/or the edge portion may be at least 0.05 mm, more preferably at least 0.10mm, more preferably at least 0.20mm and most preferably between 0.30mm and 0.50mm.

The electronic card may further comprise a transition member adjacent the fingerprint sensor. The transition member may comprise electrical connections, such as a wire-bonded connection, to the fingerprint sensor in the plane of the card, and preferably in the length-ways direction of the card. The transition member may also connect to an electronic circuit embedded within a body of the card.

The reinforced electrode preferably also protects and reinforces the transition member against bending strains, and particularly may protect the electrical connections (such as fine wires or the like) between the transition member and the fingerprint sensor. These connections may be close to the face of the card, and thus bending of the card in certain directions could put high strain on these connections. The reinforcement from the reinforced electrode reduces such forces, by stiffening the card at this location, reducing the bending strains that could otherwise pull the fingerprint sensor away from the transition member, damaging the delicate connections between these components.

The electronic card may be any one of: an access card; a credit card; a debit card; a pre-pay card; a loyalty card; an identity card; and a cryptographic card. The electronic card is preferably arranged to be inoperable if the biometric sensor does not provide an indication of an authorised user.

The present invention also provides, in a second aspect, a method of manufacturing a flexible, electronic card, the method comprising: providing a fingerprint sensor having a sensing area; and mounting a reinforced electrode adjacent the sensing area of the fingerprint sensor, wherein the reinforced electrode is adapted to act as a reinforcement member to protect the fingerprint sensor against bending.

This method of manufacture results in a fingerprint sensor having improved resistance to bending at the sensor compared to prior art techniques. In various embodiments, the card being manufactured is a card according to the first aspect. Thus, the card being manufactured may optionally include any or all of the optional features above, and the method may include providing such features.

In one embodiment, the method may comprise mounting the reinforced electrode to the fingerprint sensor, and subsequently installing the fingerprint sensor and electrode into a card body.

In another embodiment, the method may comprise mounting the reinforced electrode to the fingerprint sensor after installing the fingerprint sensor in a card body.

The method may include mounting the fingerprint sensor and electrode into a cavity in a card body.

Preferably walls of the cavity are coated with an adhesive (e.g. an epoxy) prior to the fingerprint sensor and reinforced electrode being installed into the cavity. The adhesive seals the fingerprint sensor in place to prevent it becoming dislodged.

The method may comprise forming the cavity, preferably by removing material from a preformed card body to form the cavity. Particularly, the cavity may be milled using a precision end mill or, more preferably, a laser mill. A laser milling machine is very precise and can be adjusted to remove just the right amount of material, which is more difficult with conventional mechanical milling.

The card body may be formed by a method comprising: providing a first plastic layer; providing a circuit substrate on the first plastic layer; providing a second plastic layer on the first plastic layer with the circuit substrate interposed between the first plastic layer and the second plastic layer; and laminating the first plastic layer and the second plastic layer to form the card. The laminating may be performed at a temperature of at least 135°C and/or a pressure of at least 5 MPa, and is preferably performed at a temperature of at least 150°C and a pressure of at least 6.5 MPa. In some embodiments, additional layers may be provided above and/or below the first and second layers prior to lamination.

The lamination process above allows for materials such PVC to be used for the card body. With this method, it is possible for such a lamination technique to be used to provide an electronic card including heat sensitive parts. Additionally, by pre-forming the card body in this manner, known card forming techniques may be used to manufacture the card body allowing the manufacturing method of the present aspect to be compatible with existing techniques. The method of the above aspect may be used to manufacture electronic cards for a number of purposes where it is necessary for the identity of the bearer of the electronic card to be verified. For example, the electronic card manufactured in accordance with the above aspect may be any one of: an access card; a credit card; a debit card; a pre-pay card; a loyalty card; an identity card; and a

cryptographic card. As discussed above, the electronic card is preferably arranged to be inoperable if the biometric sensor does not provide an indication of an authorised user. Thus, the electronic card may provide its desired function only when the biometric information confirms that the user is authorised. For example, where the electronic card is an access card, the access card may provide access only when the user is authorised. Further, the method of the above aspect may be used to manufacture electronic cards which use any one or more of: an RFID circuit and/or an electrical contact pad.

Certain preferred embodiments of the present invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which:

Figures 1A and 1 B illustrate a first electronic card manufactured in accordance with a prior art method;

Figures 2A and 2B illustrate a second electronic card having reduced thickness compared to the cards shown in Figure 1 ;

Figures 3A and 3B shows a variation of the second electronic card including a reinforcement member;

Figure 4 shows a detail view of a first reinforcement member;

Figure 5 shows a detail view of a second reinforcement member; and Figure 6 shows a detail view of a third reinforcement member; and

Figure 7 shows a smartcard incorporating the third reinforcement member.

In the card 2 illustrated in Figures 1 A and 1 B, the fingerprint sensor module 4 has rows of contacts 12 on the rear surface (the side opposite to the scanning side) designed to be connected to a circuit 6 embedded in the smartcard 2. This configuration results in two sets of contacts 8, 12 (one set on the card circuit 6 and one set on the sensor module 10) being present between the circuit layer 6 of the card 2 and the sensor 10. These contacts 8, 12 have a considerable thickness, relative to the thickness of the card body 4, and have been found to result in an undesirable thick card 2, as a whole. Figures 2A and 2B illustrate an alternative configuration for a card 20 that reduces this problem. In this configuration, the sensor module 22 has contacts formed on the front surface of the module 22, i.e. the side one on which the finger is to be placed to be scanned. In order to connect the contacts of the sensor module 22 to contacts 24 of the circuit 26 embedded within the body 28 of the card 20, a transition member 30 is provided. The transition member 30 is fitted into the cavity, adjacent the module 22. The transition member 30 connects to the contacts of the sensor module 22 by wire bonding, and provides contact pads 32 on its rear surface that correspond to contact pads 24 on the flex circuit 26.

The rear face of the transition member 30 is offset with respect to the rear face of the sensor module 22 such that the rear surface of the sensor module 22 just touches the circuit substrate 26 of the card 20 when the contact pads 32 of the transmission member 30 are in contact with the pads 24 of the circuit.

Thus, in Figures 2A and 2B, the bond pads 32 that connect to the circuit 26 are formed on the offset transition member 30, and therefore card thickness can be reduced compared to the configuration of Figures 1 A and 1 B.

In a preferred embodiment, the fingerprint sensor 22 applies a high frequency AC voltage signal to the skin when a measurement takes place. The individual pixels of the sensor 22 are excited by this signal and have a voltage impressed upon them that is a function of the closeness of the finger to the sensor 22. In other words the variable profile of the fingerprint is impressed on the sensor 22 and can be read out to form an image of the fingerprint. Such fingerprint sensors are known as active capacitance fingerprint sensors (sometimes also known as an AC or RF fingerprint sensors). An example of such fingerprint sensors include the FPC1025 and FPC1055 sensors manufactured by Fingerprint Cards AB.

It is necessary, for the correct function of this type of fingerprint sensor 22, to provide an electrode 42 at the periphery of the sensor face that is in contact with the finger. This electrode 42 carries the electrical signal which causes the voltage signal to be imparted to the finger.

In the card 40 shown in Figures 3A and 3B, this electrode 42 has been shaped to form an enclosure, whereby the whole sensor face is surrounded (see Figure 3B). More specifically, the electrode 42 is shaped like a box and provides strength to the otherwise very vulnerable sensor module 22. As illustrated in Figure 3A, the box of the electrode 42 also encloses the transition member 30. A box-like shape is relatively hard to bend. The box-shape of the electrode 42 has a cross sectional thickness sufficient to provide the desired reinforcement. This configuration provides structural integrity for the fingerprint sensor 22 and transition member 30, which may be relatively weak and could be damaged or pulled apart when the card is bend, as well as a useful electrode for active capacitance fingerprint detection.

Figures 4 and 5 show details of two alternative, exemplary reinforcement members 42' 42". Both exemplary reinforcement members 42' 42" are shaped for use with a swipe-type fingerprint sensor 22, such as illustrated in Figures 1 to 3, but it will be appreciated that the sensor opening 47 in the reinforcement members 42' 42" could be modified to accommodate an area-type fingerprint sensor 64.

The reinforcement members 42', 42" each comprise an edge portion 44 that fits adjacent the sides of the biometric sensor module 22 and the transition member 30. The edge portion 44 has a tubular, rectangular shape, although it is envisaged that, in some embodiment, it may not form a complete tube. For example, the edge portion 44 could be present only around the corners of the reinforcement member, or could be only present along the sides and not at the corners.

The reinforcement members 42', 42" further comprise a planar portion 46 that is formed integrally with the side portion 44, and fits adjacent a front face of the biometric sensor module 22. Thus a rectangular hole 47 for exposing the sensing area is formed that is bounded on one side by the planar portion 46 and on the other three by the side portion 44.

In the first reinforcement member 42', the planar portion 46' is strip-shaped and serves as the electrode for the sensor module 22. As can be seen from Figure 3A, the planar portion 46' covers the transition member 30, protecting the delicate wire-bonding between the transition member 30 and the sensor module 22 from being damaged as the card 40 flexes.

In this example, the reinforcement member 42' is in the shape of a rectangular frame having a generally inverted L-shape cross-section along one side, and a generally planar cross-section along the other sides.

In the second reinforcement member 42", the planar portion 46" extends around the entire reinforcement member 42". Thus, it surrounds a scanning area of the biometric sensor module 22. The planar portion 46" is thus shaped as a rectangular plate with a rectangular hole 47 exposing the sensing area. In this example, the reinforcement member 42' is in the shape of a rectangular frame having a generally inverted L-shape cross-section along all of its sides.

These shapes have been found to be highly effective at protecting the biometric sensor module 22, and also the electrical connections to the transition member 30, against damage.

Figure 6 shows details of a further alternative, exemplary reinforcement member 48. This third reinforcement member 48 is shaped for use with an area- type fingerprint sensor 64, but it will again be appreciated that the sensor opening 52 in the reinforcement member 48 could be modified to accommodate a swipe- type fingerprint sensor 22.

The third reinforcement member 48 does not comprise an edge portion to fit adjacent the sides of the biometric sensor module and the transition member.

Instead, the third reinforcement member 48 comprises only a planar portion 50 that fits adjacent a front face of the biometric sensor module.

In the third reinforcement member 48, the planar portion 50 extends around the entire reinforcement member 48. Thus, it surrounds a scanning area of the biometric sensor module. The planar portion 50 is thus shaped as a rectangular plate with a square hole 52 exposing the sensing area.

The planar portion 50 has an outer length and width of 16.31 mm ± 0.05mm and the rectangular hole 52 has a length and width of 12.64 mm ± 0.05mm. The corners of the rectangular hole 52 are curved at a radius of 0.25mm.

Thus, the planar portion 46"' defines a conductive strip having a width of 1.82mm extending all the way around the rectangular hole 52, and hence around the sensing area. It will be appreciated that the width of the planar portion 50 could be enlarged on one side, similar to the first and second reinforcement members 42', 42", to also reinforce a transition member or the like.

The planar portion 50 has a thickness of 0.40mm ± 0.025mm and has a flatness of less than 5μηι per mm.

This shape has also been found to be highly effective at protecting the biometric sensor module against damage from bending.

An electronic payment card 60 having a card body 62 and an area-type fingerprint sensor 64 is illustrated in Figure 7. The card 60 is shown incorporating the third reinforcement member 48 circumscribing a sensor area of the fingerprint sensor 64. Further features of the cards 20, 40, 60 are discussed below.

The smart card 20, 40, 60 comprise the card body 28, 62 and a circuit substrate 26 enclosed within the card body. The circuit substrate 26 is in the form of a flexible printed circuit 26, which is preferably made from polyamide or FR-4 grade glass-reinforced epoxy laminate, with an etched, copper circuit formed on the surface.

The circuit substrate 26 is laminated between at least two layers of plastic. The at least two layers of plastic include an first layer of plastic and a second layer of plastic with the circuit 26 sandwiched between the first and second layers. The layers of plastic are made of PVC; however, other plastics may be used. Examples of other suitable plastics include polyester, acrylonitrile-butadiene-styrene (ABS), and any other suitable plastic. Additionally, plasticisers or dyes may be added to the plastic to achieve a desired look and feel.

An antenna 30 is connected to the circuit substrate 26 and is also embedded within the card body 28, 62. The antenna 30 is used to communicate with a card reader, which is external to card 20, 40. The antenna 30 may be formed by etching a suitable pattern onto a copper cladding of the printed circuit 26.

A number of additional components are also mounted to the circuit substrate 26. These include a processor and a memory. The memory is arranged to store biometric information relating to a bearer of the smart card 20, 40 and the processor is arranged to compare the biometric information stored on the memory to biometric information acquired by the biometric sensor module 22, 64 and communicated via the contacts 24 of the circuit substrate 26. The processor is therefore arranged to determine if the user is an authorised user based on an indication provided by the biometric sensor.

Furthermore, subject to verification of the bearer of the smart card 20, 40, the processor is arranged to communicate the data stored on the memory to a card reader, for example using the antenna 30.

The additional components 36 may, in some embodiments, also include a battery which is configured to power the memory and processor. Alternatively, or in addition to the battery, the card 20, 40 may be arranged to be powered via a contact pad (not shown) that couples to a power source, such as a contact card reader, or the card 20, 40 may be arranged to draw power from the antenna 34 when it is energised by a contactless card reader. The cards 20, 40 shown in Figures 2 and 3 may be manufactured using a suitably modified version of the method described in US 2015/049925.

For example, an exemplary method of manufacturing the cards 20, 40 includes:

forming a card body 28, 62 including a circuit substrate 26 on which is formed a circuit having contacts 24 for connection to a biometric sensor 22, 64, the contacts 24 being embedded within the card body 28, 62;

forming a cavity in the card body 28, 62 to expose the contacts 24 and to receive the biometric sensor module 22, 64 and transition member 30;

connecting the contacts of the biometric sensor module 22, 64 to the transition member 30;

installing the biometric sensor module 22, 64 and the transition member 30 into the cavity; and

connecting the contacts 32 of the transition member 30 to the contacts 24 of the circuit 26 using a conductive epoxy.

The electrode 42, if desired, may be fitted to the biometric sensor 22, 64 and transition member 30 before installation into the cavity, or may be installed around the biometric sensor 22, 64 and transition member 30 after their installation into the cavity.

The card body 28, 62 may be produced by a hot lamination method, for example as described in US 6,586,078 B2. A suitable hot lamination method could comprise the following steps:

forming a core by providing first and second layers of plastic and positioning the circuit substrate 26 between the first and second layers of plastic to thus form the core;

placing the core in a laminator;

applying a heat cycle to the core in the laminator to liquefying or partially liquefying the layers of plastic, the heat cycle operating at a temperature of between 135°C and 250°C;

increasing a laminator ram pressure in combination with the heat to a pressure of approximately 6.5 MPa;

applying a cooling cycle to the core in the laminator with an associated increase in ram pressure of approximately 25% until the core has cooled to approximately 5°C to 20°C; and

removing the core from the laminator. Conventional processing techniques, that would be well known to the person skilled in the art, may then be applied to the core to form the card body 28, 62. Such processing techniques may include inking, the formation of an overlaminate film, or the like.

The cavity is then milled into the surface of the card body 28, 62. This may be done using a precision end mill or, more preferably, a laser mill. The depth of the milling is set so that the base of the cavity is at the level of the circuit substrate 26 within the card body 28, 62, such that the contacts 24 are exposed.

A conductive epoxy is then applied to the surface of the contacts 24 of the circuit prior to the biometric sensor module 22, 64 and transition member 30 being inserted. A suitable conductive epoxy is type SEC1222 epoxy, manufactured by Resinlab, LLC of Wisconsin USA, which cures at room temperatures (approx. 25°C).

A conductive epoxy having a strongly anisotropic characteristic may be used. This is beneficial when the contacts 24 on the transition member 30 are very close together because it provides the required conductivity between the respective contacts 24, 32, whilst ensuring that the epoxy does not form any appreciable conductive path between adjacent contacts, even if the conductive epoxy flows between them.

Interior walls of the cavity are coated with an adhesive epoxy prior to the biometric sensor module 22, 64 and transition member 30 being inserted. The adhesive epoxy seals the biometric sensor module 22, 64 and transition member 30 in place to prevent them from becoming dislodged and becoming disconnected from the contacts 24 of the circuit substrate 26.

The biometric sensor 22, 64 and transition member 30 are then electrically connected and bonded to one another, aligned with the cavity and pushed into the cavity such that the contacts 32 on the transition member 30 and the contacts 24 in the circuit substrate 24 are brought into electrical contact through the conductive epoxy. Preferably, the rear surface of the sensor module 22, 64 is flush against the circuit substrate, thus minimising the projection of the module 22, 64 from the card body 28, 62.

The conductive epoxy and adhesive epoxy preferably cure without heating. However, alternatively, one or both of the conductive epoxy and adhesive epoxy may require heat curing where the curing temperature of the conductive epoxy and/or adhesive epoxy is below a safe temperature of the biometric sensor module 22, 64, for example below 60°C. Higher temperatures may be possible for short time periods and/or for different sensor types.