WO2010081967A1

WO2010081967A1 - Method of fabricating an electronic module, especially for electronic chip-based identification device

Info

Publication number: WO2010081967A1
Application number: PCT/FR2010/000030
Authority: WO
Inventors: Halim Bousmaha; Bernard Calvas
Original assignee: Smart Packaging Solutions (Sps)
Priority date: 2009-01-16
Filing date: 2010-01-14
Publication date: 2010-07-22
Also published as: FR2941316A1

Abstract

The method of fabrication according to the invention comprises steps consisting in: - making an electronic circuit (27) on a fine and flexible substrate (21); - disposing on said substrate (21) a layer of material acting as a spacer (22) and comprising at least one cavity (23) in its thickness; - depositing in each cavity (23) of said spacer layer (22) a microelectronic chip (24) and electrically connecting the output pads (25) of the microelectronic chip (24) to the corresponding terminals (26) of the electronic circuit (27); - protecting the microelectronic chip (24) thus connected, by shutting off the cavity (23) enclosing the microelectronic chip (24) with the aid of an electrically insulating material. The method is characterized in that in order to form the spacer layer (22), a layer of photosensitive resin (31) is deposited on the substrate (21), and in that in order to form said cavity (23), said photosensitive resin is locally removed.

Description

Method of manufacturing an electronic module, in particular for an electronic chip identification device

The invention relates to an improvement to a method for manufacturing an electronic chip identification device, in particular a device operating by a contactless or contactless communication or both, with a reader of the identification device.

The invention also relates to the structure of the identification device obtained by the implementation of the method. The invention further relates to the use of the identification device for the manufacture of security identification and tamper-proof documents, such as for example electronic passports.

Radiofrequency identification devices are already known in the state of the art, according to which radiofrequency electronics constituted by a microelectronic chip connected to an antenna are arranged on an insulating substrate, and then laminated on top of them. the substrate provided with the electronics formed by the chip and the antenna, one or more layers of more or less compressible materials, intended to protect and integrate the electronics.

Also known from FR 2 882 174-A of the Applicant, an improved manufacturing process compared to the prior art. This method makes it possible in particular to manufacture contactless electronic modules, having a small calibrated thickness, and capable of being reported in identification documents provided with a receiving cavity of the electronic module. Thus, it is possible to economically manufacture identification documents, such as electronic passports, by inserting the modules into said cavities, without the modules inserted do not produce extra thickness incompatible with the functioning or durability of the identification document.

The method according to FR 2 882 174-A and the resulting electronic modules nevertheless have certain residual disadvantages revealed by the use, related to the thickness of the module, to the precision required for the relative positioning of its components, to the formation of air bubbles between the layers of the module, and the possibility of delamination of these layers. These disadvantages will be described in more detail in connection with FIG.

A general object of the invention is therefore to provide a method of manufacturing electronic modules, in particular for identification devices or for electronic modules for smart cards, which is able to solve the residual technical problems mentioned above.

A more specific object of the invention is to provide an improved manufacturing method which leads to a high reliability over time of the devices obtained.

Another object of the invention is to provide a method of manufacturing electronic modules to prevent the formation of air bubbles between the substrate and the spacer, during lamination.

. Another object of the invention is to provide a manufacturing method capable of eliminating the need for a baking step to solidify the encapsulation resin of the chip of the module.

Another object of the invention is to propose a manufacturing method for achieving a resolution in thickness of the order of 10 microns for a total thickness of the order of 300 to 400 microns for the stacking of the substrate and of the layer acting as a spacer. Another object of the invention is to propose a method for manufacturing electronic modules, making it possible to produce particularly economical radiofrequency identification devices that are suitable for a large number of applications, so as to take advantage of manufacturing volumes. very high, and therefore lower unit costs. Indeed, given the large quantities of identification and communication devices to be delivered to security organizations such as those of certain states, it is essential to have a manufacturing technique that is very simple, allowing manufacturing cost low compared to the intended application, while having sufficient reliability to ensure the life in question.

For this purpose, the subject of the invention is a method for manufacturing electronic devices of very small thickness, as defined in the claims. More precisely, the subject of the invention is thus a method for manufacturing an electronic module (20) capable of interacting by contact or without contact with a reader, this method comprising the steps of: producing an electronic circuit on a substrate fine and flexible; disposing on said substrate a layer of material acting as a spacer and comprising at least one cavity in its thickness; depositing in each cavity of said spacer layer a microelectronic chip and electrically connecting the output pads of the microelectronic chip to the corresponding terminals of the electronic circuit; protecting the microelectronic chip thus connected, by closing the cavity enclosing the microelectronic chip with an electrically insulating material; characterized in that to form the spacer layer is deposited on the substrate a layer of photoresist, and in that to form said cavity is locally removed said photoresist. Thus, the. electronic module is particularly innovative insofar as the spacer layer is no longer made of kapton laminated with the substrate and only available in a multiple thickness of 100 microns, but the layer above the substrate is made by depositing a varnish or a resin whose thickness may vary continuously depending on the amount deposited on the substrate. In addition, the varnish being photosensitive, it can be cured by UV type radiation in particular, and some areas of its surface can be insolated and then processed by photogravure, in particular to make the cavities. In addition, the technology for depositing a varnish, instead of lamination of a perforated layer, makes it possible to obtain a much better positioning accuracy of the cavity relative to the substrate, compared with the technique of rolling together a substrate and a kapton spacer layer.

Preferably, the resin or varnish layer has a thickness of a few micrometers to a few tens of micrometers, which makes it possible to produce particularly thin electronic modules.

Thus, the flexible substrate and the resin layer are each of substantially uniform thickness, and the sum of their thicknesses is less than about 350 micrometers, but the thickness of the resin layer is slightly greater than the thickness of the chip microelectronics to form a spacer for subsequent encapsulation of the chip. As an example of a practical embodiment, a product known under the name "Liquid Photoimageable solder mask PSR-4000 AUS21 / CA-40 AUS21" or a resin known under the reference DELO 4696/4670 will be used for the photoresist.

In a preferred variant of the process according to the invention, it also comprises a step of depositing a varnish compatible with the polyimide substrate, on the bottom of each cavity, before insertion. of the chip. This solves the possible problem of compatibility failure typically between the polyimide and an ultraviolet sensitive (UV-rated) encapsulation resin. Indeed, all types of electronic modules based on a polyimide substrate, for reasons of chemical incompatibility, can not be encapsulated with a resin sensitive to UV rays. Thus, this variant of the invention provides for depositing a thin layer of the aforementioned varnish, as interface between the polyimide of the substrate and the UV-sensitive encapsulation resin. The flexible polyimide substrate being typically continuous and roll-conditioned, a plurality of electronic identification devices are then assembled by continuous deposition of photosensitive resin on the substrate and photogravure the resin, then the photosensitive resin is frozen and individualized. electronic devices thus formed, making a transverse cut between two contiguous electronic devices.

According to a subsequent step of the method, for closing the cavity enclosing the chip, a liquid and photosensitive encapsulation resin is deposited in the cavity, above the microelectronic chip and connections at the terminals of the circuit, so as to substantially fill the free volume of the cavity, and then polymerizes the resin of the cavity by UV irradiation.

The invention also relates to an electronic module, characterized in that it is obtained using the manufacturing method as described above.

The invention further relates to the use of this electronic module for the manufacture of a passport comprising one or more sheets coated with identification information of its holder, one of the sheets of the passport comprising a recess suitable for receive the electronic module. Other characteristics and advantages of the invention will appear on reading the detailed description of the appended drawings in which:

- Figure 1 illustrates a top view of a substrate strip surmounted by a spacer layer laminated according to the manufacturing method according to the state of the art;

- Figure 2 illustrates in sectional view an electronic module obtained according to the manufacturing method according to the state of the art; FIG. 3 is a cross-sectional view of an electronic module obtained according to the method of the invention;

- Figure 4 illustrates in sectional view an electronic module obtained according to another variant of the method according to the invention.

Referring to Figures 1 and 2 which respectively illustrate in top view and in section a substrate strip 21 surmounted by a layer of laminated spacer 22, according to the manufacturing method known in the state of the art.

Thus, after individualization by cutting as shown schematically by the broken line 33 in FIG. 1, each radiofrequency identification device 20 comprises a substrate 21 on which a kapton sheet 22, of small and calibrated thickness, has been placed, contributing in the manner of a spacer, to obtain a thin and calibrated thickness for the device 20. The spacer terminology is that, during the transfer of the electronic module 20 in an identification device, such as an electronic passport, the chip will be protected during the passport manufacturing steps, by the sheet 22 acting with regard to the passport sheets as a spacer. This sheet 22 comprises in its thickness one or more perforations forming reservations or cavities 23, at the place intended to receive a microelectronic chip 24 from a sawed chipboard. The substrate sheet 21 is configured as a strip, for example 35 mm wide, wound in a roll, and surmounted by the perforated sheet 22 also available in strips. The substrate strip 21 comprises on its sides driving holes 32 intended to cooperate with the pins of a machine (not shown) for rolling, so as to drive the substrate strip 21. The strip of material of the perforated sheet 22 has cavities 23 regularly spaced in which it is expected to have a microelectronic chip 24 and the resin 29 as described above. We can see at the bottom of each cavity 23, the terminals

26 of each antenna made on the substrate strip 21 by one of the known techniques, for example the deposition of conductive material.

The substrate 21 is relatively flexible. Made in particular of polyimide or polyepoxy, it is originally continuous and packaged in roll and is coated on at least one of its faces with a very thin adhesive film, shown in FIG. 2 by the reference 30.

A first problem with this known manufacturing process is that the material of the substrate and the spacer, both supplied in rolls, exist commercially only with thicknesses available in steps of 100 micrometers. Thus, there are materials 100 or 200 micrometers thick, but there are no substrates or spacers having, for example, 120 or 140 micrometers thick. However, some market demands require that thickness resolutions of up to 10 micrometers can be achieved in order to better control the final thickness of the electronic module integrating the substrate and spacer layers.

A second problem lies in the fact that with the lamination assembly method of the substrate 21 and the spacer layer 22, the accuracy of the relative positioning between the substrate layer and the spacer layer can only be done with a accuracy of the order of +/- 150 micrometers, while recent market demands require a positioning accuracy of +/- 75 micrometers.

Another problem that has been observed is that of the appearance of air bubbles during the lamination of the substrate 21 of polyimide and the spacer 22 kapton. Indeed, given the nature of these materials, it is expected in the state of the art to use a very thin adhesive interface 30 of a few microns between the two layers. During lamination, air bubbles can form and remain trapped in certain areas of the interface, which can weaken the strength of the final product compared to the delamination of the layers, or even generate slight unevenness at the surface. surface of the rolled product.

Moreover, as described in detail in the previous document already cited, the kapton spacer has holes which form cavities 23 adapted to receive a microelectronic chip 24. As shown in FIG. 2, the chip once in place and electrically connected to an electrical circuit such as an antenna for example, is covered with an encapsulation resin 29, also called "potting" resin in English terminology. It is a thermal resin that to solidify must go to the oven, which is a long step that weighs down and increases the manufacturing process.

In addition, after the cavity 23 has been filled with the resin and after the resin has hardened, the mechanical strength at the side walls of the cavity is ensured only by the cohesive force between the hardened resin and the material. This cohesion can be reduced over time, in particular when the final product incorporating the electronic module is subjected to mechanical flexing, which is often the case for smart cards or electronic passports, for example. The combination of the problems and disadvantages mentioned above can also quickly become troublesome when the electronic modules are incorporated in the new electronic passports, which provide very restrictive specifications with regard to their mechanical strength, or their lifetime which must to be several years, especially ten years in Europe.

Referring now to Figure 3 which illustrates in sectional view a microelectronic module 40 obtained according to the method of the invention. According to the invention, instead of laminating a kapton spacer sheet on the substrate, an adhesive resin 31 is deposited on the substrate, with a desired thickness, which is not limited by steps of 100 micrometers. The resin layer 31 therefore has a thickness of a few. micrometers to a few tens of micrometers. The resin 31 is a photoimageable resin, in particular sensitive to UV rays. Thus, to then make the cavities 23, the corresponding parts of the surface of the deposited resin are insulated, then the cavities 23 are photogravured.

This procedure also significantly increases the position accuracy of the cavities, since it is no longer necessary to continuously adjust the relative position of two strips of material, namely a substrate strip and a spacer strip.

Once the cavities 23 have been made in the varnish layer 31, an electronic chip 24 is deposited in a conventional manner in each cavity 23 and bonded to the substrate 21 by means of an adhesive that can be electrically conductive or electrically insulating (a process known as The name of "die attach" in English terminology provides the active face of the chip so that its output pads 25 are oriented towards the opening of the cavity 23. The output pads 25 of the chip are then electrically connected to the corresponding terminals 26 of the electrical circuit or the antenna 27 by using a technique of micro wiring known in itself, called "wire-bonding" in English terminology, which consists in producing by conductors son 28 and welds, the connection of the output pads 25 of the chip 24 with the contact terminal block 26 of the printed circuit board.

When the electrical connections 28 are made, the wired chip is encapsulated in a package (so-called "potting" operation), which consists in protecting the chip 24 and the soldered connection wires 28, or the protuberances conductive, where appropriate, by filling the remainder of the cavity 23 with the liquid encapsulation resin 29, and then polymerizing the resin to cure it. In this way, the cavity 23 is filled and closed and an electronic module device 40 is obtained which is particularly thin and of particularly calibrated thickness.

According to one aspect of the invention, the encapsulation resin 29 is no longer a thermosetting resin as known in the state of the art, but a resin curable by exposure to radiation, in particular UV radiation. This avoids the passage to the oven, and can accelerate very significantly the manufacturing process.

Reference is now made to FIG. 4 to describe a preferred embodiment of the invention. Indeed, the photosensitive resins that can be used as encapsulation resin 29 are typically not chemically compatible with the substrate 21 of polyimide, which can adversely affect the good resistance of the device in case repeated bending, which can therefore cause delamination of the device.

In order to remedy this problem, the method according to the invention furthermore provides a step of depositing a thin layer of varnish 34 compatible with the polyimide substrate 21, on the bottom of each cavity 23, before the insertion of the chip 24. This varnish 34 may advantageously have the same composition as the resin 31 mentioned above and used for producing the spacer layer. As regards the dimensions of the radiofrequency identification device 40 according to the invention, they may depend on the final applications, and in particular on the desired range which determines the size of the antenna 27. In practice, the identification devices 40 intended to communicate at short range and to be incorporated in passports or similar supports, may have dimensions quite reduced, for example a length of between about 14 mm and about 25 mm, a width of between about 13 mm and about 19 mm, and a thickness less than about 350 micrometers.

The invention meets the stated goals. Indeed, the manufacturing method does not use a laminated adhesive between the substrate and the spacer layer, which prevents the formation of air bubbles between the substrate and the spacer. In addition, by using a photosensitive encapsulation resin in place of the usual thermal resin, it is no longer necessary to use a baking step to solidify the encapsulation resin. , which significantly speeds up the manufacturing time. The mechanical strength of the varnish on the surface of the substrate and on the cavities containing the chips is much greater than that of the known device, which contributes to a better durability of the device in normal use. In addition, from the point of view of safety, it should be noted that because of the strong resistance of the varnish, any attempt at delamination will result in the destruction of the electronic module, which reduces the possibility of fraud on the product.

. In addition, the use of a resin deposit to obtain the spacer layer, instead of the lamination of a kapton strip, makes it possible to very finely choose the thickness of the spacer layer, which makes it possible to adapt to the required thickness, other than in steps 100 micrometers. Consequently, a total thickness of the order of 300 to 400 micrometers is easy to achieve for the stacking of the substrate and the spacer layer. Subsequently, it is sufficient to individualize the unit modules by cutting from the flexible strip formed by the substrate and its varnish, to obtain electronic modules in the form of pellets of reduced dimensions and very small thickness and calibrated. These pellets can then be reported, in particular not gluing, rolling or other known techniques, in media such as smart card bodies, or sheets for the manufacture of passports, or any other identification document.

Claims

1. A method of manufacturing an electronic module (40) capable of interacting by contact or without contact with a reader, this method comprising the steps of: - producing an electronic circuit (27) on a thin substrate (21) and flexible ;

placing on said substrate (21) a layer of spacer material (22) and having at least one cavity (23) in its thickness; depositing in each cavity (23) of said spacer layer (22) a microelectronic chip (24) and electrically connecting the output pads (25) of the microelectronic chip (24) to the corresponding terminals (26) of the electronic circuit ( 27); - protecting the microelectronic chip (24) thus connected, by closing the cavity (23) enclosing the microelectronic chip (24) with an electrically insulating material; characterized in that to form the spacer layer (22) is deposited on the substrate (21) a photoresist layer (31), and in that said cavity (23) is locally removed said photosensitive resin .

2. The manufacturing method according to claim 1, characterized in that the localized removal of the photoresist (31) at the cavity (23) is carried out by photoetching.

3. The manufacturing method according to claim 1, characterized in that the resin layer (31) has a thickness of a few micrometers to a few tens of micrometers.

4. The manufacturing method according to claim 1, characterized in that the photoresist (31) is a resin sensitive to UV rays.

5. Manufacturing process according to any one of the preceding claims, characterized in that it further comprises a step of depositing a varnish (34) chemically compatible with the substrate (21) polyimide, on the bottom of each cavity (23) before insertion of the microelectronic chip (24).

6. Manufacturing method according to one of the preceding claims, characterized in that the flexible substrate (21) and the resin layer (31) are each of substantially uniform thickness, the sum of their thickness being less than about 350 micrometers and the thickness of the resin layer (31) being constant and slightly greater than the thickness of the microelectronic chip (24) so as to form a spacer for encapsulation of the chip.

7. The manufacturing method according to claim 6, characterized in that the flexible substrate (21) being continuous and roll-conditioned, assembling a plurality of electronic modules (40) by continuously depositing photoresist (31) on the substrate followed by a photogravure step of the resin (31), and then the individual electronic modules (40) thus formed are individualized, making a transverse cut (33) between two adjacent electronic devices (40).

8. Manufacturing method according to any one of the preceding claims, characterized in that for closing the cavity (23) enclosing the microelectronic chip (24), is deposited in the cavity (23), above the microelectronic chip ( 24) and connections (28) to the terminals of the antenna, a liquid encapsulation resin (29) and photosensitive, so as to substantially fill the free volume of the cavity (23), and then polymerizes the resin by UV insolation .

9. The manufacturing method according to claim 8, characterized in that the electronic circuit (27) is an antenna connected to the terminals of the microelectronic chip so as to allow for the electronic module (40) a radiofrequency communication with a remote reader.

10. Electronic module (40), characterized in that it is obtained using the manufacturing method according to any one of the preceding claims.

11. Use of an electronic module (40) according to claim 10, for the manufacture of a passport comprising one or more sheets of material coated with identification information of its holder, one of the sheets of the passport comprising a recess adapted to receive the electronic module (40).