Method for laser marking an electronic module for a smart card

Abstract

The invention relates to a method for marking an electronic module (5) for a smart card by means of a laser beam, characterised in that it consists in marking the surface of the electronic module with a laser beam (16) that has a wavelength in the ultraviolet spectrum.

Description

Laser marking method for an electronic module for a smart card

[0001] The present invention relates to a new method of security marking on a smart card module, in particular for the purpose of pairing between an electronic module and a security document such as a bank smart card, a passport or an identity card. STATE OF THE ART

[0002] Law enforcement agencies in various countries where smart cards or security documents incorporating electronic modules are used frequently request the ability to easily verify that a module containing an electronic chip has not been swapped with one from another card or document for fraudulent purposes. This demand for simplified verification will increase with the growing use of microelectronic chips, particularly in the context of digital identity based on certificates embedded in the electronic module's chip.

[0003] To verify that an electronic module on a smart card has not been removed from another product, methods already exist for applying security markings to the modules, but these are done mechanically, notably by material ablation. These known marking solutions using ablation techniques are relatively crude, in that they do not provide sufficient marking resolution for markings that are easily legible by simple visual inspection by law enforcement. For example, document EP 2 533 175 B1 describes a smart card with a module whose upper surface bears a printed image, notably by laser printing or laser ablation, without specifying the characteristics of the laser used.

[0004] Document EP 2 720 175 A1 also describes a smart card module whose metallic surface has an area exposing the dielectric backing film, which is then customized with graphics. This document advises against laser engraving the metal, as the resulting engraved design has low contrast. Therefore, the document recommends using graphic customization by printing or applying the design to the exposed dielectric film in the area without metal.

[0005] Furthermore, known marking methods only allow for fixed markings on a set of modules. These methods therefore cannot incorporate personalization data from one module to another based on the end user's database.

[0006] Ultimately, existing marking solutions therefore do not allow for the creation of a high-resolution security mark, such as a serial number of the electronic module or a clearly recognizable photograph of the smart card holder, nor do they allow for confirmation or denial that the module thus marked corresponds to the smart card or more generally to the security document that bears it and has not been previously exchanged.

[0007] Therefore, there is a need for a new security marking solution for the electronic module intended for a smart card or other security document. PURPOSE OF THE INVENTION

[0008] The invention therefore has the general aim of proposing a new marking process to overcome the drawbacks of the security markings already used on electronic modules for smart cards or equivalent.

[0009] A particular objective of the process according to the invention is to enable the creation of a high-resolution marking, sufficient so that the mark produced allows for clear identification by simple visual examination with the naked eye of a mark in the form of a string of alphanumeric characters, symbols, or even an image, such as a greyscale photograph of the smart card holder.

[0010] Another specific objective of the invention is to provide a method for marking the electronic module towards the end of the smart card manufacturing process, so as to personalize the marking according to data relating to the future smart cardholder. This amounts to marking the electronic module not only with fixed markings (such as an identification of the smart card issuer), but also with variable markings from one smart card to another. This will also allow for visual matching of the electronic module carrier, which typically bears a marking or serial number, with the module itself, which will bear a corresponding marking. PRINCIPLE OF THE INVENTION

[0011] In principle, the process according to the invention consists of implementing an engraving solution using a laser with a short wavelength located in the ultraviolet spectrum, allowing a very fine laser beam to be obtained and consequently a much higher resolution of the engraved pattern, compared with the resolution obtained with conventional laser marking processes.

[0012] The laser used is chosen in such a way as to limit the marking depth and also in such a way as to avoid too much localized heat release in order to avoid damage to the chip.

[0013] This engraving, performed by a specific low-wavelength laser, is placed on the superficial metallic layer of the module, which it ablates very superficially without altering the functionality of the module or its appearance outside strictly the marked area.

[0014] In the version of the process comprising a variable data marking phase, the process according to the invention can be supplemented by an image processing module prior to its engraving, so as to precisely adjust the parameters affecting the readability of the marking, such as its contrast. SUBJECT OF THE INVENTION

[0015] The invention therefore relates to a method of marking an electronic module for a smart card using a laser beam, consisting of marking the surface of the electronic module using a laser beam having a wavelength in the ultraviolet spectrum, characterized in that the ultraviolet laser beam is generated from an infrared laser beam with a wavelength of 1064 nm passing through crystals chosen to obtain a laser beam of ultraviolet wavelength.

[0016] According to a preferred embodiment, the marking process uses a laser with a wavelength between 300 and 355 nm.

[0017] In the marking process according to the invention, the UV laser beam is used to mark the apparent metallic surface of the electronic module with a fixed mark, a variable mark, or a combination of fixed and variable marks.

[0018] In the case of a variable brand marking, this marking contains, among other things, information relating to the smart card holder. The variable brand marking is applied at the end of the smart card manufacturing process, between the chip insertion stage and the graphic and electronic personalization of the smart card.

[0019] In the case of marking with a fixed mark, this is carried out either before the module insertion stage, or at the end of the smart card manufacturing process, between the chip insertion stage and the graphic and electronic personalization of the smart card.

[0020] The invention also relates to an electronic module for security documents, characterized in that it includes marking carried out by laser engraving using a marking process as described above. DETAILED DESCRIPTION

[0021] The invention will be described in more detail with reference to the following detailed description, in conjunction with the figures, in which: Figure 1 represents a schematic diagram of the steps in the marking process according to the invention. Figure 2 represents the calculation of the diameter of a laser beam configured to strike the metallic surface of the electronic module. Figure 3 represents a diagram of the process for obtaining an ultraviolet laser beam from an infrared laser source. Figure 4 represents a graph of the absorption spectrum of laser beams at different wavelengths by certain metals used on the surface of the electronic module. Figure 5 represents an example of a top view and a cross-sectional view of a smart card module.

[0022] We refer to the. Unlike the laser marking processes commonly used for marking electronic modules for smart cards, the invention provides for obtaining and using a laser beam, not at an infrared wavelength (typically 1064 nm), but at an ultraviolet wavelength, denoted UV, allowing for a particularly legible and high-quality marking without damaging the structure of the module and the microelectronic chip it contains.

[0023] The marking may contain personal data of the smart card holder, such as their name, or even a good quality greyscale photograph of the smart card holder, which will allow it to be quickly verified visually and without special tools that the module corresponds to the smart card holder.

[0024] According to a preferred variant of the process, a digital photograph of the cardholder, for example a color portrait 1, is first processed in 2 before the marking phase, to improve its characteristics and compatibility with the subsequent UV laser marking. This yields a black and white image 3, for example a portrait of the cardholder, optimized for the subsequent phase 4 of UV laser engraving of the metallic surface of the electronic module 5. A high-resolution laser marking 6, reproducing all or part of the black and white image 3, is then obtained on the surface of the electronic module 5, preferably in an area of ​​the module not targeted by the reading pins of a smart card reader.

[0025] Laest is a diagram explaining the technical reason for choosing a UV wavelength laser beam to perform the marking according to the invention. Indeed, the diameter d of the laser beam or spot at the output of the laser equipment is known to be given by the following formula:

[0026] [Math 1] d = (4 x λ x M 2 x F) / (π x D)

[0027] where λ represents the wavelength of the laser beam, M 2 represents a beam quality factor, F represents the focal distance between the laser output lens and the surface to be engraved, and D represents the diameter of the beam incident on the output lens.

[0028] It can therefore be seen that the diameter of the laser spot that strikes the surface to be engraved is proportional to the wavelength λ. Consequently, to increase the fineness of the marking, it is necessary to use a laser beam with a wavelength much lower than the 1064 nm of the infrared lasers typically available and used in the prior art.

[0029] The invention therefore proposes to use a laser beam in the UV wavelength spectrum. Preferably, the target wavelength will be in the range of 300 to 355 nm.

[0030] Lasers with such a wavelength are not commonly available or used in the smart card industry. As schematically illustrated, the invention therefore provides for starting from a commonly available infrared laser source 11 using a wavelength of 1064 nm, and obtaining a laser beam 16 of UV wavelength by means of a treatment in a laser chamber 10, consisting of passing the infrared laser beam 12 from the laser source 11 through a first crystal 13 allowing to obtain a laser beam 14 of green wavelength of the order of 532 nm, which is sent through a second crystal 15 allowing to obtain an output laser beam 16 of wavelength located in the UV spectrum, for example 355 nm, intended to etch the surface of an electronic module.

[0031] Generally, the active medium of a solid-state laser consists of a glass or crystalline "host" material, to which a "dopant" such as neodymium, chromium, erbium, thulium, or ytterbium is added. Most common dopants are rare-earth ions, because the excited states of these ions are not strongly coupled to the thermal vibrations of their crystal lattices (phonons), and their operating thresholds can be reached with relatively low optical pumping intensities.

[0032] There are several hundred solid-state gain media in which the laser effect has been achieved, but only a few types are in common use. Among these, the most common is probably neodymium-doped yttrium aluminum garnet (Nd:YAG). These Nd:YAG lasers emit light with a typical wavelength of 1064 nm, in the infrared.

[0033] To obtain a UV laser beam from this infrared laser, a diode-pumped solid-state infrared laser is used, in which the gain medium consists of one or more crystals used to achieve a wavelength in the UV range. Other types of UV lasers potentially usable for etching electronic modules are excimer lasers and metal vapor lasers. These two types of lasers allow the emission of UV radiation at even shorter wavelengths, some below 300 nm.

[0034] As examples of realization, LBO [LiB3O5], CBO [CsB3O5], BABF [BaAlBO3F2] and CBF [Ca5(BO3) 3F] crystals allow the production of UV laser sources around 355 nm by third harmonic generation of Nd or Yb based laser sources.

[0035] The graph represents the absorption rate of laser beam energy by various metals as a function of the laser beam's wavelength. As can be seen, absorption is highest for copper, silver, and nickel at UV wavelengths between 300 and approximately 355 nm. These metals are typically used in the surface structure of smart card modules.

[0036] Absorption rates are then around 60%, significantly higher than the absorption levels of infrared lasers by the same metals. The emitted photons are therefore more efficiently absorbed by the surface to be marked. Consequently, high power is not required for marking, thus avoiding deep penetration of the electronic module and the risk of damaging the chip it contains.

[0037] The image shows a top view and a cross-section of the well-known structure of an electronic module 5 for a smart card. The surface of the module 5 has electrically insulated metallic areas, namely the standardized contacts C i according to ISO 7816. The module comprises a glass epoxy substrate 20, overlaid by several layers of metal 21, 22, 23, containing gold and nickel, and optimized for their mechanical strength and electrical conductivity. As is known, the laser beam directed at the metallic surface of the electronic module 5 degrades the surface layer 23 of the module. This involves material removal or surface ablation of the module's surface, creating a pattern. This pattern can be fixed, such as a state coat of arms, or variable, such as the photograph of the smart card holder, or a combination of both.

[0038] It should be noted that engraving a fixed pattern on the module can be done before the module is inserted into the body of a smart card, i.e., the module integration step. However, it can also be done after the insertion step.

[0039] Engraving a variable pattern will preferably take place after the inserting stage, during the personalization stage of the smart card with biographical and biometric data of the cardholder. ADVANTAGES OF THE INVENTION

[0040] The invention achieves the stated objectives and provides several advantages over previously used marking techniques. It allows for the easy creation of a very fine marking of a fixed or variable pattern identifiable to the naked eye by law enforcement, thus enabling simple verification of the correspondence between the smart card body and the marked module it contains.

[0041] The implementation of the invention does not require significant modifications to the smart card production equipment; the additional production cost is zero or negligible.

Claims

Method of marking an electronic module (5) for a smart card using a laser beam, consisting of marking the surface of the electronic module (5) using a laser beam (16) having a wavelength in the ultraviolet spectrum, characterized in that the ultraviolet laser beam (16) is generated from an infrared laser beam (12) with a wavelength of 1064 nm passing through crystals (13, 15) chosen to obtain a laser beam (16) of ultraviolet wavelength. Marking method according to claim 1, characterized in that a laser with a wavelength between 300 and 355 nm is used. A marking method according to any one of the preceding claims, characterized in that the UV laser beam (16) is used to mark the apparent metallic surface (17) of the electronic module (5) with a fixed or variable mark (6). Marking method according to claim 3, characterized in that the variable mark (6) contains information relating to the smart card holder. Marking method according to claim 4, characterized in that the marking with a variable mark is carried out at the end of the manufacturing of the smart card, between the chip insertion step and the graphic and electronic personalization of the smart card. Marking method according to claim 3, characterized in that the marking with a fixed mark is carried out either before the module insertion step, or at the end of the smart card manufacturing process, between the chip insertion step and the graphic and electronic personalization of the smart card. Electronic module (5) for security document, characterized in that it comprises a marking made by laser engraving using a marking process according to any one of claims 1 to 6.

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