BIOMETRIC SENSOR MODULE FOR A CHIP CARD AND METHOD FOR MANUFACTURING SUCH A MODULE

Description

technical field

[0001] The invention relates to the field of smart cards. State of the art

[0002] In the field of smart cards, and particularly smart cards used as a payment method, manufacturers are constantly striving to offer users ever-greater security. For example, it has been proposed to integrate biometric sensors for fingerprint reading into smart cards. See, for instance, patent applications WO2018066857A1 and WO2019058259A1 for examples of such cards.

[0003] For example, for cards with both contact and contactless reading modes, a module integrated into the card and containing a biometric sensor can authorize a transaction only if the cardholder's fingerprint is detected. This type of card is described, for instance, in patent document EP 3 336 759 A1. To create such a card, a cavity is milled into the card to expose an electrical circuit previously integrated into the card body, and the module is housed within this cavity. The module, once housed in this cavity, is also electrically connected to the circuit.

[0004] It has been observed that the detection zone, on which a finger must be placed for the fingerprint to be recognized, is subject to a number of factors (humidity, perspiration, mechanical abrasion, UV aging, temperature, etc.) that can deteriorate and / or prematurely wear down this detection zone. Covering this detection surface with a protective layer could be considered. However, a material must then be found that simultaneously increases resistance to the aggressive factors to which the detection zone is subjected, does not interfere with fingerprint detection, and is also compatible with all other manufacturing, processing, and encapsulation stages of the biometric module.

[0005] The invention aims to find a solution to improve at least partially the protection of the detection zone. Summary of the invention

[0006] Thus, according to the invention, a biometric sensor module for smart cards is proposed, comprising a dielectric support comprising a front face and a rear face, both forming principal faces of the support, and a biometric sensor for fingerprint detection attached to the rear face and extending under the rear face over a detection area.

[0007] In addition, this module includes, on the front face, on a detection area extending opposite the detection area and on a surface corresponding at least to that of the detection area, at least one protective layer comprising a photoimageable coverlay material, i.e. a photosensitive material.

[0008] Thus, thanks to this layer of photoimageable coating material, it is possible to protect the substrate with a relatively mechanically and chemically resistant material, the use of which can be easily integrated into an industrial process, particularly a roll-to-roll process, and is compatible with the heating steps necessary for a possible solder connection of the module to the circuit already integrated into the body of a board. Its photoimageable nature also makes it compatible with the implementation of industrially controllable photolithography steps that allow for high yields.

[0009] Preferably, the protective layer comprising the photoimageable covering material is based on epoxy-acrylate resins whose physicochemical properties, particularly in terms of hardness and abrasion resistance, are superior after UV or thermal curing to those obtainable with pure acrylates, for example. Similarly, epoxy-acrylate resins are easier to process than epoxy resins.

[0010] This smart card module may include one or more of the following features, each considered independently of the other, or each in combination with one or more others: the protective layer has a thickness of between 5 and 100 micrometers, and more preferably a thickness close to 25 micrometers; the protective layer is deposited on a layer of epoxy resin-based adhesive; a bezel is formed on the front face and the protective layer covers an area located inside the bezel; it includes on the rear face, electrically conductive connection pads, these connection pads being placed essentially opposite an area of ​​the front face covered by the bezel and at least one conductive via being made in the thickness of the support, this via electrically connecting the bezel to the connection pads;at least some of the connection pads each have at least one drop of solder material, this drop of solder material being deposited before or after the assembly of the biometric sensor onto the dielectric support, and preferably after the assembly of the biometric sensor onto the dielectric support.

[0011] In another aspect, the invention relates to a smart card comprising a biometric sensor module according to the invention. This smart card comprises a card body with an electrical circuit integrated within the card body. The module and the circuit are electrically connected to each other using a solder material.

[0012] According to yet another aspect, the invention relates to a method for manufacturing a biometric sensor module for a smart card, comprising steps in which a dielectric support is provided having a front face and a rear face, both forming principal faces of the support, a biometric sensor for fingerprint detection is attached to the rear face, a detection area covered by the sensor on the rear face being placed opposite a detection area on the front face.

[0013] According to this process, a protective layer of a photoimageable covering material is also created on the detection area.

[0014] This process may include one or more of the following characteristics, considered independently of each other or each in combination with one or more others: The dielectric support is a flexible support of the polyimide family; the front face is coated with an electrically conductive layer, in which a bezel is formed, the protective layer covering on the front face a surface located inside the bezel; at least one conductive via is made in the thickness of the support to electrically connect the bezel to the rear face; the support is provided with a first electrically conductive layer on the rear face, then the front face is coated with an adhesive layer, at least one hole is made to form the via, this hole passing through the first conductive layer, the support and the adhesive layer; a second electrically conductive layer is laminated on the rear face, this second conductive layer at least partially covering the hole to form the via;The bezel is etched into the second conductive layer, leaving the hole intended to form the via at least partially covered by the second conductive layer; the protective layer is deposited inside the bezel onto the adhesive layer exposed during the etching of the bezel; connection pads are etched into the first conductive layer, so that at least some of them are positioned essentially opposite an area of ​​the front face covered by the bezel; the biometric sensor is attached to the rear face of the support using a die-attach adhesive that cures at temperatures between 100°C and 150°C; at least one drop of solder is deposited on at least some of the connection pads. Brief description of the drawings

[0015] Other aspects, purposes and advantages of the invention will become apparent from the detailed description that follows, as well as from the accompanying drawings, which are given by way of non-limiting examples and on which: [ Fig.1 ] schematically represents in perspective a smart card conforming to a first example of an embodiment of the invention; [ Fig. 2 ] schematically represents in perspective a smart card conforming to a second example of an embodiment of the invention; [ Fig.3 ] schematically represents, in cross-section, different stages of an example of a manufacturing process for a biometric sensor module such as the one integrated into the card shown on the figure 2 ; Fig. 4 [This schematically represents, in cross-section, the integration into a circuit board of a biometric sensor module obtained using a process such as that illustrated by the] figure 3 ; Fig. 5] schematically represents different possible variants for the shape of the connection pads placed on the rear face of a biometric sensor module obtained using a process such as that illustrated on the figure 3 ; And [ Fig. 6 ] schematically represents yet other possible variants for the shape of the connection pads placed on the rear face of a biometric sensor module obtained using a process such as that illustrated on the figure 3 . Detailed description

[0016] An example of a smart card 1 according to the invention is shown on the figure 1 In this example, card 1 is an ID-1 format bank card. This card 1 has a first module 2 comprising a connector 3 and an electronic chip (under the connector). Connector 3 allows the electronic chip to be electrically connected to a card reader, to exchange data between the chip and the card reader.

[0017] In the case of dual-interface cards, meaning those that allow both contact and contactless reading, this card 1 also includes an antenna integrated into its body. This antenna is connected, for example, to the chip located in the first module 2. This antenna enables contactless data exchange between the chip and a contactless card reader. This antenna, or another part of an electrical circuit located within the body of card 1, is also electrically connected to a second module 4 integrated into card 1. The second module 4 is a biometric module. This biometric module 4 includes a sensor for fingerprint recognition. The second module 4 determines whether the fingerprint read by the sensor matches that of a user authorized to use this card 1. In this case, contactless communication between the chip and a reader can be authorized.

[0018] The example of how to implement map 1 shown on the figure 2 differs from the one depicted on the figure 1 , essentially by the fact that the second module 4 has a conductive contour 5 (a "bezel" 5), which may or may not be continuous. The bezel 5 is electrically connected to the biometric sensor located on the back of the second module 4. It allows for the dissipation of any electrostatic charges that could damage the sensor or prevent the sensor from reading a fingerprint. On the figure 2 The bezel 5 has a continuous annular shape. According to variants, the bezel 5 may consist of several conductive segments, or points, arranged around the area on which a finger must be placed to read the corresponding fingerprint.

[0019] The manufacturing process for a module of the type illustrated on the figure 2 is described below.

[0020] This process includes: The supply of a complex material 100 comprising a support 101 of dielectric material onto which is laminated a foil consisting of a first electrically conductive material 102 (see figure 3a ); for example, the dielectric material is a polyimide with a thickness between 25 and 75 micrometers, and preferably 50 micrometers, and the first electrically conductive material 102 is a copper alloy with a thickness between 12 and 35 micrometers, and preferably 18 micrometers; for an industrially efficient implementation of the process according to the invention, this complex material 100 ("copper clad") is advantageously supplied in rolls and the process is carried out reel-to-reel; The coating, with an adhesive material 103, of the face of the dielectric material opposite to that onto which the first electrically conductive material is laminated (see figure 3b ); the adhesive material 103 is, for example, an epoxy resin, possibly modified with resins and mineral fillers; the adhesive material 103 is thus deposited to a thickness of between 10 and 25 micrometers; the adhesive material 103 may optionally undergo a continuous drying process to remove solvents present in the formulation at the time of its deposition; The perforation of holes 104 through the new complex material comprising the dielectric support 101, the layer of the first electrically conductive material 102 and the layer of adhesive material 103 (see figure 3c) ; The lamination of a layer of a second electrically conductive material 105; for example, this second electrically conductive material is a copper alloy with a thickness of between 12 and 35 micrometers, preferably this thickness is equal to 18 micrometers; this layer made of the second electrically conductive material 105 seals the holes 104 (see figure 3d ); the adhesive material 103 may undergo a crosslinking step according to a defined cycle with temperature plateaus adapted to the chemistry of the adhesive material 103; the lamination of a dry film of photosensitive resin 106 onto each of the two main faces of the complex obtained at the end of the previous step (see figure 3e), then exposure through a mask, and development of the photosensitive resin to form patterns used in subsequent steps: etching on certain areas of the layers of the first 102 and second 105 electrically conductive materials; electrolytic deposition of metal layers 107 (copper, nickel, gold, palladium, silver for example) intended to facilitate the soldering of connecting wires on the second conductive material and / or to create conductive vias between the first 102 and the second 105 conductive material at the holes 104; deposition of a layer of a protective material 108 on a detection area; this protective material 108 is, for example, a photosensitive covering material; for example, the layer of protective material 108 has a thickness between 15 and 50 micrometers, and is, for example, equal to 25 micrometers;For example, the protective material layer 108 is deposited as a laminated film on the front face of the support 101; for example, the protective material layer 108 is deposited as an epoxy-acrylate film (for example, this is the product marketed under the reference by the company Ethernal (www.eternal-group.com); alternatively, the protective material layer 108 is deposited using a screen printing technique; alternatively again, the protective material layer 108 is deposited by a technique similar to inkjet printing; alternatively still, the protective material layer 108 is deposited by a coating technique; the protective layer 108 extends on the front face over a surface corresponding to a detection zone;and _ in cases where the deposition of the protective material layer 108 is carried out by a non-selective deposition technique, after deposition of the protective material layer 108, it may be necessary to carry out a step of exposure to appropriate radiation through a mask, followed by a chemical development step; _ a thermal crosslinking step of the protective layer. ;

[0021] According to a particular embodiment of the process according to the invention, a solder material 6 is deposited onto connecting pads 7 formed in the previous steps within the layer of the first conductive material 102. For example, the solder material 6 is a tin-bismuth or tin-bismuth-silver alloy; for example, the solder material 6 is deposited by screen printing or by jetting. Furthermore, instead of making the holes 104 conductive by means of electrolytic deposits of metal layers 107, this step of depositing a solder material 6 can also be used to deposit the material in the holes 104, thus making them conductive between the layers of the first 102 and the second 105 conductive materials.

[0022] The welding material 6 can be deposited onto connecting pads 7 of different shapes (see figure 5). For example, these shapes have an essentially continuous outline that delimits a rectangular, diamond, square, oval, or round shape.

[0023] Alternatively, instead of depositing solder material 6 onto the connection pads 7, they are left undisturbed until the module 4 is inserted into the board 1. Then, during the insertion operation, prior to placing the module 4 into the cavity 208 formed (for example, by milling) in the board body, solder material 6, an anisotropic conductive paste or film 6' is deposited onto the connection pads 7 in order to establish a connection with the circuit 200 housed in the board body (see figures 3 And 4 ). When an anisotropic conductive paste or film 6' is used, the connecting pads 7 may have a shape such as those described above in relation to the figure 5or they may have a shape with extensions 10 allowing better adhesion of the paste or better performance in terms of electrical conductivity of the anisotropic conductive film 6' on the connection pads 7.

[0024] More advantageously, the connecting pads 7 have a shape compatible with the use of both a soldering material 6 and an anisotropic conductive paste or film 6'. To this end, the connecting pads 7 can have shapes including a rectangle, a rhombus, a square, an oval, or a disc, as well as lateral extensions 10 (see figure 6 ).

[0025] Following the steps above, a roll is obtained that supports 200 biometric sensor mounts for smart cards. Each of these 200 mounts has a structure corresponding, for example, to that shown in the figure 3f1 or the figure 3f2depending on whether the biometric sensor is assembled after or before the solder paste 6 is applied to the pads 7. Each support 200 therefore includes: A front face, with a bezel 5 formed in the layer of the second conductive material 105, a protective layer 108 deposited on the layer of adhesive material 103, at the level of a detection area located inside the ring formed by the bezel 5; A rear face with connection pads 7, optionally with a drop of a solder material 6 deposited on at least some of these connection pads 7 in order to be able to subsequently connect a module 4 to a circuit 200 integrated in the card body.

[0026] For use and integration into a smart card, each support 200 is equipped with a biometric fingerprint sensor 300. This biometric sensor 300 is attached to the back, for example, using a known chip attachment technology ("die attach"). For example, the biometric sensor 300 is attached to the back of the support 101 using a thermosetting adhesive that can be cured at temperatures between 100°C and 150°C and has the characteristic of migrating by capillary action under the entire surface of the sensor without generating voids or bubbles ("underfill").

[0027] The deposition of a solder material 6 on connection pads 7 is carried out before or after assembly of the biometric sensor 300, but preferably after to avoid the biometric sensor 300 undergoing thermal shock during the remelting operation of the solder paste forming the solder material 6.

[0028] Similarly, the welding material 6 is deposited by screen printing or by jet printing.

[0029] Preferably, the deposition of the welding material 6 onto the connection pads 7 is carried out by jet if the biometric sensor 300 is already assembled on the dielectric support 101.

[0030] The biometric sensor 300 occupies, on the rear face, a surface essentially corresponding to a detection area located opposite the detection zone on which the protective layer 108 is deposited. This biometric sensor 300 is connected to the connection pads 7 and the bezel 5 using a known technology, such as flip chip technology or wire bonding 11. Advantageously, the biometric sensor 300 and its optional wires 11 are protected in an encapsulation resin 12. A hot melt adhesive 10 is optionally also disposed on the rear face on, or next to, the connection pads 7. This hot melt adhesive 10 is intended to fix the biometric sensor module 4 in the cavity 208 provided in the body of a smart card.

[0031] When inserting module 4 into a circuit board, several options are available to establish a connection between the module's connection pads 7 and the circuit 200 integrated into the board. For example, the connection pads 7 can be soldered directly to the circuit 200 using the solder material 6 applied to the connection pads 7 (see figure 4Alternatively, drops 206 of a solder material can be deposited onto the circuit 200, and a connection can be made between the solder pads 7 and the circuit 200 by melting one, the other, or both of the solder materials previously deposited, respectively, onto the connection pads 7 and onto the circuit 200. More specifically, for example, a first solder material 6 can be deposited onto the connection pads 7 and a second solder material 206 onto the circuit 200. The first solder material 6 is then advantageously a solder material having a low melting point (for example, a melting point less than or equal to 140°C), the second solder material 206 having a higher melting point, close to or the same as that of the first solder material 6.Advantageously, the use of a second welding material 206 with a higher melting temperature helps to limit the risk of creep of the welding material(s) into and towards the edge of the cavity 208, or even outside of it.

[0032] For example, to connect the connection pads 7 with the circuit 200, a thermode 400 is placed on the bezel 5. The bezel 5 being advantageously opposite the connection pads 7 on either side of the support 101, thermal conduction is thus particularly well carried out between the two faces of the support 101.

[0033] Using a first solder material 6 with a low melting temperature (less than or equal to 140°C) on the connection pads 7 and a second solder material 206 with a higher temperature on the circuit 200, the thermode 400, heated for example to a temperature of 230°C, is applied for 2.5 seconds. The heat supplied by the thermode 400 also diffuses to the hot-melt adhesive 10 to bond the module 4 to the board 1.

[0034] By using a first solder material 6 with a low melting temperature (less than or equal to 140°C) on the connection pads 7 and a second solder material 206 on the circuit 200, having a melting temperature equal to, close to, or lower than that of the first solder material 6, the thermode 400, heated for example to a temperature of 230°C, is applied for 1.5 seconds. The process described is therefore faster in this case. Furthermore, the use of solder materials 6 and 206 with low melting temperatures allows for the use of a thermode 400 with a smaller bearing surface, which can help to better control creep and limit the risk of deformation of the board 1 and / or the module 4.

[0035] Generally, to connect module 4 to circuit 200, one can use an electrically conductive adhesive or paste 6', an anisotropic conductive film, or a soldering material 6. However, in all cases, advantageously, one uses the method described above or variants thereof, by creating connection pads 7 with a shape compatible with the use of both a soldering material 6 and an anisotropic conductive paste or film 6', this shape being rectangular, diamond-shaped, square, oval, or disc-shaped, with additional lateral extensions 10 (see figure 6 The module 4 according to the invention is therefore the same whether it is connected by soldering or using a conductive adhesive. This allows the module 4 to be manufactured in larger series while giving the inserter the option of choosing either connection technology.

[0036] It has been described in relation to the figures 2 ,3 And 4 , the production and insertion of a module 4 including a bezel 5 on the front panel. In the case, for example, where the biometric sensor 300 is not or only slightly sensitive to electrostatic charges, the bezel 5 can be omitted (see figure 1 ). The process described above is then easily simplified. It is indeed possible to dispense with making holes 104. It is also possible to use only a single sheet of conductive material 102 (thus eliminating, in particular, the steps illustrated by the figures 3c and 3dThe conductive material 102 is then placed only on the rear face of the support 101 to form the connection pads 7. The protective layer 108 is designed to cover at least the detection area opposite the detection area of ​​the sensor 300. In addition to its function of protecting the support 101, the protective layer 108 indicates where to place the finger to detect its fingerprint. The protective layer 108 can be tinted in different colors to, for example, match the color of the card 1.

[0037] The protective layer 108 may consist of or contain an ink. For example, it may be an epoxy-acrylate based ink. For example, this is the product marketed under the reference SD 2444 NB-M by the company Peters (www.peters.de).

Claims

1. A biometric sensor module for a smart card, comprising: • a dielectric support (101) having a front face and a rear face, both forming main faces of the support (101), • a biometric sensor (300) for detecting fingerprints, attached to the rear face and extending under the rear face over a detection area located opposite a detection zone situated on the front face of the support (101), characterised in that it comprises, on the front face, on a detection zone extending opposite the detection area and over a surface corresponding at least to that of the detection area, at least one protective layer (108) comprising a photoimageable coverlay material.

2. The module according to Claim 1, wherein the photoimageable coverlay material is based on epoxyacrylate resins.

3. The module according to Claim 1 or 2, wherein the protective layer (108) has a thickness of between 5 and 100 micrometres, and more preferably has a thickness of about 25 micrometres.

4. The module according to any one of Claims 1 to 3, wherein the protective layer (108) is deposited on an adhesive layer (103) based on epoxy resin.

5. The module according to any one of the preceding claims, wherein a bezel (5) is formed on the front face and the protective layer (108) covers an area located inside the bezel (5).

6. The module according to Claim 5, comprising, on the rear face, electrically conductive connection pads (7), said connection pads (7) being placed substantially opposite an area of the front face covered by the bezel (5), and at least one conductive via (104) being formed in the thickness of the support (101), said via (104) electrically connecting the bezel (5) to the connection pads (7).

7. The module according to Claim 6, wherein at least some of the connection pads (7) each comprise at least one droplet of solder material (6).

8. A smart card comprising a card body with an electrical circuit (200) integrated in the card body and a module (4) according to any one of the preceding claims, the module (4) and the circuit (200) being electrically connected by means of a solder material (6).

9. A method for manufacturing a biometric sensor module (4) for a smart card, comprising the steps of: • providing a dielectric support (101) having a front face and a rear face, both forming main faces of the support (101), • attaching a biometric sensor (300) for detecting fingerprints to the rear face, a detection area covered by the sensor on the rear face being placed opposite a detection zone situated on the front face of the support (101), characterised in that a protective layer (108) of a photoimageable coverlay material is formed on the detection zone.

10. The method according to Claim 9, wherein the dielectric support (101) is a flexible support of the polyimide family.

11. The method according to Claim 9 or 10, wherein: • the front face is coated with an electrically conductive layer (105), in which a bezel (5) is formed, the protective layer (108) covering on the front face a surface located inside the bezel, and • at least one conductive via (104) is formed in the thickness of the support (101) to electrically connect the bezel (5) to the rear face.

12. The method according to Claim 11, wherein: • the support (101) is provided with a said other electrically conductive layer (102) on the rear face, then the front face is coated with an adhesive layer (103), • at least one hole (104) intended to form the via is formed, said hole (104) passing through said other conductive layer (102), the support (101) and the adhesive layer (103), • said electrically conductive layer (105) is laminated onto the rear face, said conductive layer (105) at least partially covering the hole (104) intended to form the via, • the bezel (5) is etched in said conductive layer (105), leaving the hole (104) intended to form the via at least partially covered by said conductive layer (105), • the protective layer (108) is deposited, inside the bezel (5), on the adhesive layer (103) exposed during the etching of the bezel (5).

13. The method according to Claim 12, wherein connection pads (7) are etched in said other conductive layer (102), such that at least some of them are placed substantially opposite an area of the front face covered by the bezel (5).

14. The method according to any one of Claims 9 to 13, wherein the biometric sensor (300) is attached to the rear face of the support (101) by means of a die-attach adhesive curing at temperatures of between 100°C and 150°C.

15. The method according to Claim 14, wherein at least one droplet of solder (6) is deposited on at least some of the connection pads (7).