Device for the metallisation of printed forms which are equipped with electrically conductive tracks and associated metallisation method

Abstract

The invention relates to a printed circuit which is equipped with electrically conductive tracks and which can be obtained by means of gravure printing. Gravure printing can be used to obtain conductive tracks of a very small thickness, such that said tracks have a high electrical resistance. In order to reduce the electrical resistance of the tracks (30) thus obtained, the invention consists in connecting at least two first electrodes (9, 8) to opposite portions (17, 18) of the same track while the middle (19) of said track is immersed in an electrolytic bath (7). Moreover, the bath is connected to a second electrode (26) which is in turn connected to a second potential (15) having an opposite polarity to that of a first potential (14) connecting the first electrodes.

Description

The invention concerns a metallization device for printed forms which are equipped with electrically conductive tracks and an associated metallization method. The invention more particularly concerns a metallization device for a succession of patterns of electrically conductive tracks having a low electrical conductivity and printed on a dielectric support. In one example, the pattern particularly represents a planar antenna. The invention also concerns the field of printed circuits obtained by any technique for printing electrically conductive tracks, such as, for example, by a heliogravure technique, offset printing, serigraphy, etc.

In document EP-A-0839,667, D1, a process is known for printing with electrically conductive ink or the heliogravure printing technique. This printing technique uses an engraved cylinder and a counter-pressure cylinder between which a thin dielectric support is placed in order to be printed. The engraved cylinder is designed to be partially immersed in a vat containing an electrically-conductive ink while rotating around an axis of rotation of this same cylinder. The counter-pressure cylinder is designed to press the dielectric support onto the engraved cylinder while also rotating around another axis of rotation of this cylinder. The engraved cylinder and the counter-pressure cylinder are designed to cooperate such that the engraved cylinder prints electrically-conductive ink tracks onto the dielectric support.

This heliogravure printing technique is particularly interesting since it permits obtaining precise conductive tracks. The heliogravure printing technique also permits obtaining conductive tracks of very small thickness (of the order of 1 μm, for example). The tracks obtained by the heliogravure printing technique nevertheless have a high electrical resistance.

Document U.S. Pat. No. 4,119,516, D2 describes an electrolytic device permitting metal to be deposited on the different conductive tracks by an electrolytic technique. This device can be used after the printed circuit has been printed with conductive tracks. The electrolytic device, which is described in document D2, has a cathode and a pair of anodes, the cathode being designed to be in contact with the conductive tracks and the pair of anodes being designed to be immersed in an electrolytic vat containing an electrolytic bath. The cathode is connected to a negative potential and the anode pair is connected to a positive potential, by means of a direct current voltage generator, to deposit the electrolytic metal onto the conductive tracks.

However, this metallization technique has the disadvantage of obtaining a metallization that is disrupted by a low electrical conductivity of the printed conductive tracks obtained by the previously-mentioned printing techniques. The consequence of this is a poor distribution of metal thicknesses deposited on the tracks. Sometimes, the metallization process can even be stopped.

As a result, the metallized printed circuits obtained by this metallization technique cannot be sufficiently functional, and this is incompatible with an efficacious transmission or detection of electromagnetic signals from or by the printed circuit relative to an integrated circuit of a smart card or an electronic tag, for example.

In order to resolve this problem while keeping the same printing techniques for electrically conductive tracks, notably a heliogravure printing technique, the invention provides a device for metallization in which at least two first electrodes connected to a first potential are positioned at two opposite track sections with the same pattern, and said pattern is designed to be partially immersed in an electrolytic bath between these two first electrodes. These two first electrodes are made in such a way that they are separated from one another by a distance less than or equal to one dimension of a pattern, which dimension is measured relative to the direction of movement of the support in the bath. More precisely, the two first electrodes are separated from one another by a distance less than or equal to a length of a pattern measured along the support between the two first electrodes with regard to the direction of movement of the support in the bath. The positioning of these two first electrodes with regard to one another permits assuring a metallization of all the tracks of the same pattern by putting these same tracks at equipotential by means of these first electrodes in contact with the pattern. These two first electrodes are connected to a first potential with a polarity that is opposite to a second potential, which second potential is connected to a second electrode designed to supply the electrolytic bath with the second potential.

The subject of the invention is a metallization device for a dielectric support coated with patterns of electrically conductive tracks, and comprising

an electrolytic station,

this electrolytic station comprises an electrolytic bath, first electrodes connected to a source of a first electrical potential with a polarity opposite to that of the second electrical potential, the bath being subjected to the second electrical potential by one or more second electrodes of the electrolytic station, characterized in that

the dielectric support is immersed in the electrolytic bath so that the tracks of the same pattern are connected in short-circuit to the first potential and to the second potential, and

at least two first electrodes are connected to opposite pattern sections of the same pattern while the middle section of this same pattern is immersed in the bath.

The subject of the invention is also a metallization method for a dielectric support coated with patterns of electrically conductive tracks, characterized in that

a—at least one conductive track pattern is subjected to an electrolytic bath by immersing the dielectric support in this bath, and by connecting the tracks in short-circuit to a source of a first electrical potential with a polarity opposite that of a second potential to which the electrolytic bath is subjected, and

b—opposite pattern sections of the same pattern are subjected to the first potential by means of at least two electrodes, while a middle section of the pattern is immersed in the bath.

The invention will be better understood upon reading the description that follows and examining the figures that accompany it. These figures are only shown by way of indication and do not at all limit the invention. The figures show:

FIG. 1: A schematic diagram of a metallization device according to the invention,

FIG. 2: A schematic diagram of a dielectric support according to the invention,

FIG. 3: A schematic diagram of a variant of embodiment of the metallization device according to the invention,

FIG. 1 shows a metallization device 1 for a dielectric support 2, according to the invention. Dielectric support 2 can be, for example, a dielectric substrate manufactured of PET, PVC, polycarbonate, ABS, impregnated or non-impregnated paper, epoxy glass, polyimide, LCP, etc. This dielectric support 2 is formed by elements 3 (see FIG. 2), each coated with a pattern 4 of electrically conductive tracks. Each of the patterns can be connected together by means of at least one linking track such as 37. Pattern 4 of the conductive tracks can represent a planar antenna, as shown in FIG. 2, or a printed circuit of any other form. A planar antenna can be integrated in a simple manner in smart cards or electronic tags, being connected with the integrated circuit by the usual processes, such as wire soldering, flip-chip mounting or the like. A planar antenna, as shown in FIG. 2, is formed by a succession of concentric whorls, each of the whorls forming an electrically conductive track 30.

The pattern of conductive tracks can be obtained by a heliogravure printing technique using a gravure printing station 5, FIG. 1. Or the pattern of the conductive tracks can be obtained by other techniques such as, for example, serigraphy or offset printing techniques, such as previously mentioned. In one example, the heliogravure printing technique permits obtaining a track 1 μm thick, therefore very thin and allowing a high track density.

According to the invention, metallization device 1 comprises an electrolytic station 6, and this station 6 can be placed downstream of heliogravure printing station 5. This electrolytic station 6 comprises an electrolyte bath 7 to bathe dielectric support 2. This electrolytic station 6 also comprises first electrodes and at least one second electrode. In the preferred example of FIG. 1, the electrolytic station comprises five first electrodes 8, 9, 10, 11, 12, all connected together, and a second electrode 13. The first electrodes place the tracks in short-circuit and, by permitting these tracks to be connected to a first electrical potential source 14, permit putting the tracks at equipotential. The second electrode permits subjecting electrolytic bath 7 to a second electrical potential source 15. The differences between the potentials are such that it can be said that the first electrodes are connected to the first potential 14 with a polarity opposite to the second electrical potential 15 connecting the second electrode. The first potential and the second potential, for example, are produced by a voltage rectifier 16 or by a voltage generator.

Electrolytic bath 7 can preferably be formed by a formulation based on copper sulfate in acid medium, or by any other solution that can release metals during electrolysis. The polarity of the first electrodes and the polarity of the second electrode depend on the nature of the solution contained in the electrolytic bath. In the case of a solution formed by copper sulfate, the first electrodes are connected to the first potential 14 of negative polarity so as to draw copper ions towards these first electrodes and therefore towards the tracks during electrolysis, while the second electrode is connected to positive-polarity potential 15. Thus, the first electrodes designed to be in contact with the tracks permit these tracks then to form cathodes designed to attract the cations while the second electrode forms an anode designed to attract the anions.

The first electrodes are positioned here so that they are situated outside the bath. Then an electrolysis is conducted between two first electrodes and the electrolytic bath, followed by contact of at least one first electrode 8 (or 9) onto pattern 4 of conductive tracks, and then followed by the immersion of at least a part of this conductive track pattern in the bath 7.

The two first electrodes 8 and 9 are separated from one another for a distance less than or equal to a length 21 of a pattern 4, length 21 being measured along the support or insulating sheet relative to the direction of movement of the support, as shown by the arrow in FIGS. 1 and 2. In particular, at least two first electrodes 8 and 9 are connected to opposite pattern sections 17 and 18 of the same pattern 4, FIG. 2. A pattern 4 comprises a first pattern section 17 and a second pattern section 18, each of the sections or ends being opposite one another. These two opposite sections are separated by an intermediate or middle pattern section 19. During movement of support 2, the first section 17 of pattern 4 is electrolyzed first by connection to electrode 8 and immersed in bath 7 while the second section 18 of pattern 4 is electrolyzed last. When section 18 is electrolyzed by means of electrode 8, section 17 comes to be electrolyzed by electrode 9.

The metallization device also has a drive means 22 for sheet 2 and a succession of bath sections which sheet 2 goes in and out of. This succession of bath sections permits improving the deposition of metal onto the tracks in conjunction with the movement of the pattern in the bath.

According to a first preferred embodiment of the invention shown by FIG. 1, drive means 22 can be formed by a series of first rollers such as 8 to 11 situated outside the bath, and by a series of second rollers 26 situated in the bath. In the example of FIG. 1, the drive means is formed by four second rollers such as 26. In this preferred embodiment of the invention, the first rollers are metal and form first electrodes 8, 9, 10, 11 and 12. The second rollers are preferably insulating and assure the immersion of the sheet between at least two first electrodes during movement of the sheet. All of these rollers can be supported by the same crossbar (not shown). Sheet 2 is driven by successive passages from a first roller to a second roller and so on. These successive passages from a first roller to a second roller and so on permit improving the metal deposition on the tracks as the support moves in the electrolytic bath. If the sheet is subjected to a tension that is too high and that might deform it, these rollers can be mounted on bearings and/or motorized so as to reduce the tension between each of the rollers.

In a variant of this, the drive means could comprise a first series of first rollers 8, 9, 10, 11, 12 and a second series of first rollers 27 mounted in correspondence and supported against the rollers of the first series of first rollers. The first series of first rollers corresponds to the first rollers previously described while the second series of first rollers is shown by the dashed circles in FIG. 1. These two series of first rollers would permit a first face 24 and/or a second face 25 of printed insulating sheet 2 to be subjected to electrolysis, the first face and the second face each being coated with at least one pattern of electrically conductive tracks. The first series of first rollers would be positioned in such a way that first face 24 would be in contact with these first rollers and the second series of first rollers would be made up in such a way that second face 25 would be in contact with these latter first rollers.

The first rollers are supplied with first potential 14 and the second rollers are preferably insulating. The second rollers can also be supplied with the first potential as shown by the dashed line in FIG. 1. It would then suffice to regularly replace these second rollers, which, during electrolysis, could become progressively covered with metal.

In order to drive the sheet, the rollers are motorized. Nevertheless, only a few rollers need be motorized for the sheet to move sufficiently. The rate of rotation of the rollers is regulated so that the total passage duration is sufficient to form the desired thickness.

The metallization process of insulating sheet 2 in view of obtaining a dielectric support printed with patterns of electrically conductive tracks is obtained by carrying out the following steps. First of all, patterns of conductive tracks, interconnected or not, are printed onto the sheet by the heliogravure printing technique. In order to do this, heliogravure printing station 5, as previously mentioned, comprises an engraved cylinder 31 and a counter-pressure cylinder 32. Engraved cylinder 31 comprises openings 33 designed to print the conductive tracks onto support 2. The engraved cylinder and the counter-pressure cylinder are supported against one another with the dielectric support in between. The engraved cylinder and the counter-pressure cylinder rotate around their respective axes, while permitting obtaining a precise printing of tracks onto the insulating sheet. A scraper 34 is provided to obtain a precise printing of tracks onto the dielectric support. Scraper 34 then permits removing the excess ink situated outside the openings of the engraved cylinder before the counter-pressure cylinder prints the pattern of conductive tracks onto the support pressed by the counter-pressure cylinder.

Once printed, the conductive tracks are then subjected to electrolyte bath 7 by immersing the dielectric support in this bath connected to the second electrical potential of positive polarity, and by connecting the tracks in short-circuit to the first electrical potential source of negative polarity. The continuity of electrolysis on the same pattern is assured during movement of the sheet between the rollers by means of a previous calibration of the distance between at least two first rollers corresponding to two first electrodes, which distance between these two first rollers is such that it corresponds to a length less than or equal to a length 21 of a pattern 4 of the support measured along sheet 2 relative to the direction of movement of the support in the bath.

The rollers forming the first electrodes are also made so that they comprise a length measured relative to a direction perpendicular to the direction of movement of the support in the bath at least equal to a width 38 of a pattern 4, which width of a pattern 4 is measured on the support relative to the same direction perpendicular to the direction of movement of the support in the bath. More precisely, the first rollers or first electrodes comprise a length permitting covering all the tracks of at least the same pattern 4 relative to a direction perpendicular to the direction of movement of the support in the bath. The first rollers or first electrodes could comprise a length dependent on the number of patterns present on support 2.

In the example, the electrolysis steps are repeated as many times as there are elements 3 immersed in station 6, in particular because the distance between the first rollers 8 and 9, or 9 and 10, or 10 and 11, or 11 and 12, measured along support 2, is less than or equal to the dimension of a pattern 4.

According to the preferred embodiment of the invention of FIG. 1, the steps are repeated in the same electrolytic bath since rollers such as 26 are immersed in the same bath.

As a variant, it is possible to use a series of compartments 28, each comprising an electrolytic bath, FIG. 4. In this example, the metallization device according to this variant has a series of three compartments, such as 28. These compartments are created in such a way that they permit the passage of dielectric support 2 through a slot. Each compartment, according to the invention, has a dimension less than a pattern 4. Tracks 30 of each support element are connected to at least two first cylindrical electrodes 29 and 35. These first electrodes 29 and 35 are in contact with each of the tracks by blocks situated outside compartment 28. In one example, the blocks can be replaced by rollers. Electrodes 29 and 35 connected to each other are in contact with sections 18 and 17, respectively. A similar mounting is adapted for the other compartments. Contact with the bath is assured by an electrode 36 during passage of the support into each compartment.

A sensor C of the level of the electrolytic bath can be positioned so as to prevent a possible lowering of the level that could impede correct electrolysis of patterns 4, FIG. 1.

Printing step 5 and electrolysis step 6 that permit ending up at the correct metallization are preferably performed one after the other without stopping in between, so as to prevent detachments of print that could result infallibly from an intermediate wrapping up. The movement speed of the sheet during the printing step can be different from the movement speed of the sheet during the electrolysis step; an adapter 39 for the movement speed of the sheet could be provided, which adapter can be placed between the heliogravure printing station 5 and electrolytic station 6, as shown very schematically in FIG. 1. In one example, the movement speed of the sheet during the step of printing by heliogravure is 50 to 100 meters per minute and the movement speed of the sheet during the electrolysis step is 1 to 10 meters per minute.

In practice, electrolysis step 6 that permits arriving at the correct metallization is conducted at rates comprised between 1 and 10 meters per minute.

Claims

1. A metallization device for a dielectric support coated with patterns of electrically conductive tracks, and comprising an electrolytic station, this electrolytic station comprises an electrolytic bath, first electrodes connected to a source of a first electrical potential, with a polarity opposite to that of a second electrical potential, the bath being subjected to the second electrical potential by one or more second electrodes of the electrolytic station, characterized in that the dielectric support is immersed in the electrolytic bath so that the tracks of the same pattern are connected in short-circuit to the first potential and to the second potential, and at least two first electrodes are connected to opposite pattern sections of the same pattern while the middle section of this same pattern is immersed in the bath.

2. The device according to claim 1, further characterized in that two first electrodes are separated from one another by a distance less than a length of a pattern measured along the support relative to the direction of movement of the support in the bath.

3. The device according to claim 1, further characterized in that it comprises a drive means for the dielectric support, and a succession of bath sections into and out of which the support is passed.

4. The device according to claim 3, further characterized in that it comprises a series of first rollers situated outside the bath, and a series of second rollers situated in the bath, the dielectric support passing alternatively from a first roller to a second roller and so on, the first rollers being supplied at the first potential, the second rollers preferably being insulating.

5. The device according to claim 4, further characterized in that the rollers are motorized.

6. The device according to claim 1, further characterized in that the electrolytic bath is a formulation based on copper sulfate in acid medium.

7. The device according to claim 1, further characterized in that the dielectric support is positioned between a first series of first electrodes and a second series of first electrodes.

8. The device according to claim 1, further characterized in that each of these patterns are connected together by at least one connection track.

9. A metallization method for a dielectric support coated with patterns of electrically conductive tracks, characterized in that a—at least one conductive track pattern is subjected to an electrolytic bath by immersing the dielectric support in this bath, and by connecting the tracks in short-circuit to a source of a first electrical potential with a polarity opposite to that of a second potential to which the electrolytic bath is subjected, and b—opposite pattern sections of the same pattern are subjected to the first potential by means of at least two electrodes, while a middle section of the pattern is immersed in the bath.

10. The method according to claim 9, further characterized in that steps a and b are repeated.

11. The method according to claim 10, further characterized in that for the repetition, the same bath is used.

12. The method according to claim 9, further characterized in that the electrolytic bath is a formulation based on copper sulfate in acid medium.

13. The method according to claim 9, further characterized in that the steps a and b are successive in time at a rate comprised between 1 to 10 meters per minute.