Memory card and method for producing same

The invention relates to a memory card of the type comprising a card body (1) having an integrated circuit (2) embedded in one face thereof, with said face carrying a conductor pattern (3) made up of a plurality of conductive areas (4) and of associated conductive tracks (5). According to the invention, a reinforcing element (10) implemented in the form of a closed ring is disposed in the thickness of the card body (1), in register with the zone occupied by the integrated circuit (2) so as to stiffen locally the zone of the card which carries the integrated circuit.

The invention relates to a memory card having an integrated circuit, and
 more particularly to a memory card of the type comprising a card body
 having a face in which (or more precisely through which) an integrated
 circuit is embedded directly, and having on said face a conductor pattern
 constituted by a plurality of conductive areas and of associated
 read/write conductive tracks connecting said areas to the integrated
 circuit.
 BACKGROUND OF THE INVENTION
 By way of example, reference can be made to documents FR-A-2 671 461 and
 FR-A-2 684 471 in the name of the Applicant, which describe a memory card
 of the above-specified type.
 This type of memory card having an integrated circuit embedded in the bulk
 of the card body is sometimes insufficiently reliable because of the
 stresses exerted on the edges of the integrated circuit when the card is
 subjected to bending or flexing. If a high degree of flexing is applied,
 then the curving of the card body runs the risk of destabilizing retention
 of the integrated circuit in the card body, and this can go as far as
 leading to said integrated circuit being expelled. In practice, it is
 commonplace to cover the conductor pattern, e.g. by means of a varnish
 that is usually transparent, while leaving the conductive areas of the
 conductor pattern uncovered. This protective layer participates in holding
 the integrated circuit in the card body in the event of said card body
 being flexed, however this holding is of limited effectiveness.
 Consequently, there exists a need to improve the retention of an integrated
 circuit in a card body in order to obtain better resistance to the flexing
 that may be applied to the card.
 This technical problem is already known for laminated cards, i.e. cards of
 the type comprising a hot-softenable core layer, two covering layers
 disposed on either side of the core layer, and a module integrated in the
 core layer and in one of the covering layers by hot-rolling after the
 various elements making up the card have been stacked on one another. For
 cards of that type, proposals have thus been made to put into place a belt
 surrounding the module and extending in the core layer so as to limit the
 bending forces to which the resin mass constituting the module is
 subjected, consequently reducing the risk of link members breaking
 (reference can be made in particular to document WO-A-92/01533 and EP-A-0
 466 557).
 Nevertheless, it is not possible to use those techniques with an integrated
 circuit that is embedded directly into the bulk of the card body since it
 would be quite impossible to place a belt around the integrated circuit.
 Proposals have also been made to place a reinforcing plate in the bottom of
 a housing made in the card body for the purpose of stiffening the zone in
 which the integrated circuit is installed, as illustrated in document
 JP-A-61 095 486. Nevertheless, the reinforcement provided thereby is
 limited since neither the reinforcing plate nor the integrated circuit is
 embedded directly in the body of the card.
 Document EP-A-0 189 039 describes a laminated card in which the integrated
 card is housed in a recess formed in a hard core disposed in the core
 layer of the card so as to provide a degree of protection to the
 integrated circuit when the card is subjected to deformation.
 Document EP-A-0 311 434 describes a laminated card having an integrated
 circuit, in which a reinforcing element in the form of a star is disposed
 on each of the two faces of the card, on either side of the integrated
 circuit.
 Finally, document EP-A-0 331 316 describes a laminated card in which the
 integrated circuit is surrounded by a deformable tubular element made of
 rubber which serves to absorb shocks and deformation when the card is
 handled.
 Furthermore, document EP-A-0 128 822 describes a hot-pressing method of
 assembling an integrated circuit module in a card body. It should be
 observed that no reinforcing element is provided in the zone occupied by
 the integrated circuit.
 OBJECTS AND SUMMARY OF THE INVENTION
 An object of the invention is to solve the above-specified problem, by
 designing a memory card of the type having an integrated circuit embedded
 in the body of the card, in which the structure thereof serves to improve
 the reliability with which the integrated circuit is held in the card
 body.
 According to the invention, this problem is solved by a memory card of the
 type comprising a card body having a face in which an integrated circuit
 is embedded directly, and having on said face a conductor pattern
 constituted by a plurality of conductive areas and of associated
 conductive tracks connecting said areas to the integrated circuit, wherein
 a reinforcing element implemented in the form of a closed ring, is buried
 in the material of the card body in register with the zone occupied by the
 integrated circuit, the ring extending in a plane to be substantially
 parallel to the above-specified face of the card body.
 The closed reinforcing ring whose function is to stiffen locally the zone
 of the card which contains the integrated circuit and its electrical
 connections, thus achieves local stiffening of the card body, thereby
 enabling stresses in the zone concerned to be considerably reduced at the
 surfaces of the integrated circuit, and thus improving the reliability of
 the electrical connections.
 Preferably, the closed ring forming the reinforcing element is disposed in
 register with the conductive areas of the conductor pattern. The stiffened
 zone thus extends beyond the zone which is in register with the conductive
 tracks, thereby providing the electrical connections with very
 satisfactory levels of reliability.
 Preferably, the closed ring forming the reinforcing element is disposed
 substantially at half-thickness within the card body.
 In a particular implementation, the closed ring forming the reinforcing
 element is a body of revolution about an axis, and the integrated circuit
 is essentially centered on said axis. The circular ring may also have a
 section that is rounded or quadrangular in shape: such a section
 facilitates embedding of the ring in the card body, by encouraging body
 material to creep around the side walls of said ring.
 The closed ring forming the reinforcing element may be made of a rigid
 material, being made of an injected rigid plastics material, e.g.
 injectable polyacrylic or homopolymer polyoxymethylene, or a metal, e.g.
 steel or copper.
 The invention also provides a method of fabricating a memory card having at
 least one of the above-specified characteristics, said method being
 remarkable in that it comprises the following successive steps:
 a) a rigid closed ring is placed on a top face of a first sheet of
 thermoplastic plastics material;
 b) said rigid ring is pressed hot into the first sheet;
 c) a second sheet of thermoplastic plastics material is placed on the first
 sheet fitted with the rigid ring, and the first and second sheets are
 assembled together by hot pressing so as to constitute an assembly of
 thickness corresponding to the card body thickness required for the card
 that is to be made;
 d) an integrated circuit is hot-pressed into the free top face of the
 second sheet until said integrated circuit is completely embedded therein,
 at a location such that the rigid ring is in register with the zone
 occupied by the integrated circuit; and
 e) a conductor pattern having conducive areas and associated conductive
 tracks is made in conventional manner on said free top face.
 Preferably, step b) of hot-pressing the rigid ring is continued until said
 ring is partially embedded in the first sheet, and step c) is performed
 simultaneously with said rigid ring being simultaneously embedded in part
 in the second sheet. This ensures that the rigid ring is anchored in
 highly satisfactory manner in the bulk of the card body.
 Preferably, the first and second sheets used are of substantially the same
 thickness, such that the location of the rigid ring lies substantially at
 mid-thickness within the card body, i.e. it lies in the midplane of said
 body (i.e. the plane containing its neutral fiber).
 Finally, and preferably, step e) is followed by a conventional step f) in
 which the conductor pattern is covered by a protective layer leaving
 uncovered the conductive areas of said pattern.

MORE DETAILED DESCRIPTION
 FIGS. 1 and 2 show a memory card C of the invention, said card being of the
 type comprising a card body 1 of insulating material, e.g. polycarbonate,
 having a face (referenced F) in which an integrated circuit 2 is embedded,
 with said face F carrying a conductor pattern 3 constituted by a plurality
 of read/write conductive areas 4 and associated conductive tracks 5
 connecting said areas to the integrated circuit 2. Specifically, a
 conductor pattern 3 is shown that is made up of a set of six conductive
 areas 4, each of which is connected to the integrated circuit 2 via an
 associated conductive track 5. Nevertheless, such an organization for the
 conductive track 3 naturally constitutes merely one possible example, and
 the invention should not be considered under any circumstances as being
 limited to one such particular conductor pattern.
 According to an essential characteristic of the invention, a reinforcing
 element 10 organized as a closed ring is disposed in the thickness of the
 card body 1, in register with the zone occupied by the integrated circuit
 2, the ring lying in a plane (referenced PM) extending substantially
 parallel to the above-specified face F of the card body 1. The zone
 concerned may be a zone directly beneath the integrated circuit 2 (the
 face F being seen from above), but said zone is preferably enlarged so as
 to include the zone underlying the conductive areas of the conductor
 pattern 3, so that the local stiffening of the card body applies to all of
 the conductive tracks of the conductor pattern, thereby optimizing
 electrical connection reliability.
 In the plan view of FIG. 1, there can thus be seen such a reinforcing ring
 10 which in the present case is circularly symmetrical about an axis X,
 with the integrated circuit 2 being essentially centered on said axis X.
 The inside diameter of the ring 10 is not smaller than the largest
 dimension of the integrated circuit, i.e. its diagonal if the integrated
 circuit is rectangular as in the present case. The outside diameter of
 said ring preferably corresponds to the largest dimension of the outline
 containing the conductive tracks of the conductor pattern. In FIG. 2, it
 can be seen that the closed ring 10 is disposed substantially halfway
 through the thickness of the card body 1, occupying the plane PM. The
 plane PM is thus the midplane of the card body 1, which plane contains the
 neutral fiber parallel to the longitudinal direction of the card and
 serving as the reference for deformation of said card body in the event of
 bending.
 Specifically, the circular ring 10 is of a section that constitutes a
 quadrangle, in this case a diamond-shape with its tips pointing upwards
 and downwards. This particular embodiment facilitates implanting the
 closed ring 10 in the bulk of the card body, by enhancing creep of the
 plastics material over the side walls of the ring, as described in greater
 detail below with reference to FIG. 3 which shows the steps of the method
 of fabricating this memory card C. In a variant, it is possible to provide
 a section of different shape, in particular a section of rounded shape.
 The closed ring 10 can be made of any rigid material that provides the
 reinforcement desired for the integrated circuit zone, and it is possible,
 for example, to use a plastics material such as an injectable polyacrylic
 (e.g. a polymethacrylate such as Plexiglass.RTM.) or a homopolymer
 polyoxymethylene (e.g. polyacetal), or indeed a metal, such as steel or
 copper.
 FIGS. 1 and 2 also show a covering layer 6, e.g. made in the form of a
 transparent protective varnish, extending in part over the conductor
 pattern 3, while leaving the conductive areas 4 of said pattern uncovered.
 FIG. 1 shows a rectangular outline for said protective layer 6, but this
 naturally constitutes only one particular example.
 The various successive steps of a method of fabricating a memory card of
 the above-described type are described below with reference to FIG. 3. The
 various successive steps of the method are referenced a) to f), with the
 characteristic steps being steps a) to c) since those are the steps that
 relate to implanting the above-mentioned reinforcing rigid ring in the
 card body.
 In step a), a rigid closed ring 10 is disposed on a top face referenced F.1
 of a first sheet 1.1 of thermoplastic material, the axis X of the ring
 being disposed at a point which corresponds to the center of the
 integrated circuit that is subsequently to be implanted in the card body
 by being embedded directly therein.
 In step b), a punch PO exerts sufficient pressure on the top edge of the
 rigid ring 10 to cause said rigid ring to be pressed hot into the first
 sheet 1.1, with the downward movement of the punch PO as represented by
 arrow 100. Specifically, this step b) of hot pressing the rigid ring 10 is
 continued until said ring has been embedded partially (e.g. to half depth)
 in the first sheet 1.1. Small bulges are shown diagrammatically on either
 side of the middle portion of the rigid ring 10 to represent the
 thermoplastic material that is pushed back against the walls of the rigid
 ring while said rigid ring is being pressed in hot.
 In step c), a second sheet 1.2 of thermoplastic plastics material is placed
 on the first sheet 1.1 fitted with the rigid ring 10, and the first and
 second sheets 1.1 and 1.2 are assembled together hot and under pressure so
 as to constitute an assembly of thickness corresponding to the thickness
 that is required of the card body that is to be made. Specifically, the
 figure shows assembly by applying pressure while hot as implemented by
 compression between two plates PL of a press, in which the top plate
 presses against the top face referenced F.2 of the second thermoplastic
 sheet 1.1. The urging together of the plates PL is represented by arrows
 101. Such adhesion under pressure while hot can occur naturally by the
 thermoplastic material melting without there being any need to provide
 additional adhesive. In a variant, the hot press assembly operation could
 be performed by passing the sandwich constituted by the two superposed
 sheets between two rollers, using a well-known technique already in use
 for making laminated memory cards of the type mentioned above. Passing
 between two rollers makes it possible to perform hot pressure assembly on
 a continuous basis on thermoplastic sheets of great length, which
 assembled sheets can subsequently merely be cut up to constitute
 individual card bodies. The two sheets 1.1 and 1.2 are preferably made out
 of the same thermoplastic material, so that spontaneous adhesion between
 them is intimate and reliable. It will be observed that the adhesion
 between the two sheets takes place in the midplane of the resulting card
 body. Because the rigid ring 10 is embedded in part in the first sheet 1.1
 during step b), step c) simultaneously causes said rigid ring 10 to be
 embedded in part in the second sheet 1.2. This guarantees extremely
 reliable bonding of the rigid ring 10 at an accurately determined
 location.
 Subsequently implemented steps d), e), and f) are well known in the art in
 question for one-piece cards, and are therefore summarized only briefly
 below.
 In step d), an integrated circuit 2 is pressed hot into the free top face
 F.2 of the second sheet 1.2 until said integrated circuit is fully
 embedded therein, with the circuit being embedded in a location such that
 the rigid ring 10 is in register with the zone occupied by the integrated
 circuit 2. This pressing operation is represented by arrow 102. As shown,
 steps are taken to ensure that the center of the integrated circuit 2 is
 disposed as accurately as possible on the axis X of the rigid ring 10. The
 pads of the integrated circuit 2 are referenced 9, which pads face
 outwards as is conventional in the technique for embedding an integrated
 circuit directly in a card body.
 In step e), the conductor pattern 3 is made including its conductive areas
 4 and the associated conductive tracks 5 which connect the areas 4 to the
 pads of the integrated circuit 2. This is preferably performed by
 depositing a conductive polymer on the top face F.2, in particular by
 using a silkscreen printing technique.
 In step f), the conductor pattern 3 is covered by a protective layer 6,
 e.g. of transparent varnish, while leaving the conductive areas 4 of said
 pattern uncovered.
 This provides a memory card that is of locally-reinforced stiffness in the
 zone that includes the integrated circuit and the electrical connections.
 This stiffening serves to protect the electric connections in the event of
 the card body being subjected to flexing.
 The invention is not limited to the embodiment described, but on the
 contrary covers any variant that uses equivalent means to reproduce the
 essential characteristics specified above.