The invention relates to a double-sided integrated circuit designed for a hybrid contact-contactless smart card and specifically concerns a double-sided electronic module for a hybrid smart card.
Contactless smart cards are currently widely used in many fields such as the transport sector and the banking sector as well as for identifying persons and objects. Contactless smart cards feature an antenna embedded in the card connected to an electronic chip inserted in the card which is used for developing, storing and processing the information.
Such cards allow the exchange of information with the outside by remote, and therefore contactless, electromagnetic coupling, between the antenna and a second antenna located in the associated reader. Hybrid contact-contactless smart cards have a group of contacts flush with the card surface so that the exchange of information can be accomplished by electrical transmission of data between the flush contacts of the card's electronic module as well as the contacts of a reader's reading head into which the card is inserted.
The chip of hybrid smart cards must therefore be connected to the group of flush contacts, on the one hand, and to the antenna's bonding pads, on the other hand. Several solutions are used to achieve this double connection of chips in hybrid smart cards.
A first solution illustrated in cross-section in
As shown in
The next step consists in inserting the module using a glue enabling the module to be fixed on the external part of the cavity and a conductive glue enabling the module to be connected to the antenna's bonding pads moved apart thanks to the two pits 36. The small surface of the external cavity 34 due to the size of the chip encased in the resin 24 does not allow the glue to be applied over the entire perimeter. As a result, only two locations 40 and 42, shown shaded in the figure, are covered with glue. For this reason, the connections made with conductive glue between the contacts 14 of the module and the antenna pads located at the bottom of the pits 36 are subjected to maximum mechanical bending stresses when the card is folded along its width in particular. The welding of gold connecting wires 22 between the chip 16 and the antenna contacts 14 are also subjected to mechanical bending stress when the card is folded. The electronic module is thus subjected to stresses that may alter the connection with the antenna and therefore the card's reliability. Furthermore, the cavities milled in the card body weaken the card, considering its small thickness of 0.76 mm which is required by the standard. The location of contacts 14 placed very close to the module edges because of the large size of the encased chip also represents a problem when installing the module in the cavity, since conductive glue may move back up and create short-circuits with the flush contacts.
In addition to these technical problems of mechanical strength and reliability, the production cost of such modules must also be taken into account. Double-sided circuits are about three times as expensive as single-sided circuits, and making the connections with gold wires further increases the card's cost price.
Connecting the electronic module with the antenna being one of the problems of manufacturing such smart cards, another solution consists in not using a double-sided circuit. This solution described in detail in the patent application FR 2 810 768 consists in transferring and connecting the chip directly onto the antenna before laminating together the various layers that constitute the card. A very thin cavity is then milled in the card body suitable for receiving a single-sided circuit made up of the group of flush contacts. The connections between the chip and the group of contacts are made by a set of connecting pits and routing traces created beforehand on the antenna support and connected to the chip. This solution enables the use of a single-sided circuit and helps relocate the chip in the card body at a place where stresses are the lowest, i.e. at mid-thickness and preferably in a corner. The main problem with such a solution comes from cards intended to be scrapped. The chip is actually inserted right at the start of the card's fabrication process and is discarded with the card if lamination or printing problems occur thereafter, which represents a significant cost in the card's cost price.
This is why an object of the invention is to solve the problems of mechanical stresses exerted on the connections between the antenna and the electronic module of a hybrid contact-contactless smart card without increasing the card's cost price.
Another object of the invention is to particularly propose a fabrication process of a hybrid contact-contactless smart card where the connection between the antenna and the electronic module withstands the mechanical bending stresses applied to the card.
The purpose of the invention is thus a double-sided electronic module of a hybrid contact-contactless smart card made on a support that is non-conductive and designed to be lodged in a cavity of the card and to be connected to the bonding pads of the antenna embedded in the card, the cavity including an internal portion for lodging the chip and an external portion whose thickness is lower than that of the internal portion, the module including a group of contacts on one side, some of the contacts each covering a through hole in the support, the group being adapted so that the contacts are flush with the card surface. According to a main characteristic of the invention, on the second side of the module are screen printed first routing traces connected by their first end to the through holes and by the other end to the chip's bonding pads, and second routing traces each connected respectively to a screen printed bonding pad on one side and to two of the chip's bonding pads on the other side, the bonding pads being positioned so that, when inserting the module in the cavity, they are opposite the antenna's bonding pads and allow the module to be bonded along its whole periphery in the external portion provided to this end.
The purposes, objects and characteristics of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which:
The electronic module which makes the subject of the invention is manufactured from a single-sided circuit as shown in
With reference to
In reference to
The smart card body 61 in standard format 85.6 mm×54 mm shown in
The internal cavity 62 designed to house the chip is small in relation to a cavity made to house an encased electronic module as shown in
The electronic module made in this manner has the advantage of being thin which presents a number of advantages in relation to a traditional module where the chip is encased. The maximum thickness of the cavity milled in the card body is in the order of 400 μm instead of 600 μm in the case of an encased electronic module.
Advantageously, the electrical connection between the antenna's bonding pads and the module is made thanks to silver particles contained in the conductive material cast into the card's connecting pits 66 and in the screen printed ink to create routing traces 55 and 56 and the bonding pads 57 and 58 on the second side of the module and the antenna pads.
Due to the advantages provided by the electronic module according to the invention and its means for connecting to the antenna, the mechanical stresses exerted on the connections between the antenna and the chip are reduced.
However, it is possible to make these connections even more resistant to mechanical stresses by using a conductive glue consisting of a product that has a flexible and semi-rigid consistency, such as silicone or polyurethane, in order to create the electrical junction in the card's cavities 66. As for epoxy type ink, silicone or polyurethane is loaded with silver or carbon to make it conductive. Silver particles represent between 40% and 65% in weight of the final product and have a dimension of 30 to 230 μm, considering that 80% of particles have a size which is 55 μm or less. The silicone or polyurethane-based conductive glue is placed in the card's connecting pits 66 in order to form an electrical junction between the antenna and the module, and it polymerises at ambient temperature without interacting with the cyanoacrylate type glue used to attach the module as silicone and polyurethane do not present any incompatibility with cyanoacrylate type glue. Furthermore, since silicone and polyurethane remain somewhat soft once polymerised, the electrical junction is more resistant to mechanical shear stresses. Break test type mechanical tests performed on cards equipped with this type of electrical connection between the module and the antenna have shown that the card is capable of withstanding 25% more break tests than cards equipped with epoxy type electrical junctions loaded with silver.
Number | Date | Country | Kind |
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0413951 | Dec 2004 | FR | national |