FI3643149T3

FI3643149T3 - Through connection in a support film which is printed on both sides

Info

Publication number: FI3643149T3
Application number: FIEP18746566.1T
Authority: FI
Inventors: Alexander Ferber
Original assignee: Bundesdruckerei Gmbh
Priority date: 2017-06-20
Filing date: 2018-06-20
Publication date: 2023-11-20
Also published as: PL3643149T3; DE102017210217A1; PT3643149T; ES2963297T3; WO2018233768A1; DE112018003136A5; EP3643149A1; EP4114149A1; EP3643149B1

Claims

1 18746566.1 THROUGH CONNECTION IN A SUPPORT FILM WHICH IS PRINTED ON BOTH SIDES

The invention relates to a method for producing a through-contact in a carrier film printed on both sides.

Carrier films printed with conductor tracks are known in the state of the art.

For example, RFID labels ("radio frequency identification" labels or labels for identification using electromagnetic waves) comprise an antenna in the form of a conductor track printed on a film, which is connected to an RFID chip and serves both for energy supply and for communication with an RFID reader.

The conductor track is often designed coil-

shaped and is connected to the corresponding contacts of the RFID chip at two antenna taps located at a distance from one another.

With sufficiently large RFID chips, it is possible to connect the two antenna taps directly to the RFID chip by placing the RFID chip directly on the coil-shaped conductor track, whereby two contacts of the RFID chip arranged at a distance from one another are connected to the antenna taps.

The RFID chip in this regard acts as a bridge between the two antenna taps via the further windings of the antenna located between the antenna taps.

DE 10 2011 016512 Al describes a method for producing a through-contact in a substrate, on both sides of which electrically conductive structures are printed, in which conductive structures are first printed on one side of the substrate in a first step.

DE 699 19 008 T2 teaches a contactless chip card having an antenna in the form of a conductor track applied to one side of a carrier material, which is short-circuited via two through-contacts and a bridge connecting the through-contacts on the other side of the carrier material.

From US 6 353 420 B1, the manufacture of contactless devices is known, such as RFID tags or chip cards, comprising through-contacts for connection of an antenna formed as a conductor track on one side of the carrier material.

US 5 266 904 A is directed to the provision of contact points by means of which a directly neighbouring through-contact can be tested with suitable measuring devices.

The object of the present invention is to introduce an improved method for manufacturing a carrier film for an RFID chip.

This object is solved by a method according to the independent claim.

Advantageous further embodiments are the subject of the dependent claims.

2 18746566.1

The invention is based on and includes the realization that, due to the progressive miniaturization of RFID chips, it is becoming increasingly difficult to bridge the antenna windings since the distance between the contacts of the RFID chips is often smaller than the minimum distance between the two antenna taps of the conductor track that can be manufactured with reasonable effort.

Accordingly, the invention relates to a method for producing a through-contact in a carrier film, on both sides of which conductor tracks are printed and the two sides of which are printed with electrically conductive material in the region of the intended through-contact in two printing steps, wherein, after the first printing step and at the latest before the second printing step, a through-hole, which is filled with electrically conductive material during the one or more following printing steps for the purpose of through-contact, is made in the carrier film, wherein the printing steps take place one after another, and the through-hole extends through the electrically conductive material applied in the first printing step.

A carrier film is further disclosed, on both sides of which conductor tracks are printed and having at least one through-contact produced according to the invention.

The invention has recognized that, in the case of a carrier film printed on both sides, the electrically conductive material applied during the two printing steps is sufficient to provide a secure electrically conductive connection between the two sides of the carrier film in the form of a through-contact, under the condition that at least one suitable through-hole is created for this purpose before one of the printing steps.

The through- hole is advantageously designed such that it is filled solely by the electrically conductive material applied in a single printing step such that the electrically conductive material in the through-hole remains electrically connected to the material applied neighbouring to the through-hole in the same printing step.

This can be ensured by appropriately dimensioning the through-hole, the depth of which corresponds to the thickness of the carrier film.

The dimensions of the through-hole can be suitably selected by the person skilled in the art responsible for the implementation depending on the thickness of the carrier film and the viscosity of the printed electrically conductive material.

The through-hole in the carrier film can in principle be made before or after the first printing step, whereby it is then filled with electrically conductive material in either the first or the second printing step.

According to the invention, the through-hole is made in the carrier film after the first printing step.

The method can therefore be flexibly

3 18746566.1 integrated into existing processes.

According to the invention, the two printing steps are carried out one after another, i.e. conductive tracks are first applied to one side of the carrier film in a first printing step before conductive tracks are applied to the other side of the carrier film in a second printing step after completion of the first printing step.

However, it is also possible for the printing steps to be carried out simultaneously or overlapping.

If the through-hole is made after the first printing step, it may be preferable, according to one aspect of the description, that the electrically conductive material applied in the first printing step is retained during the process.

The material from the first printing step thus forms an electrically conductive termination of the through-hole, which ensures a good electrical connection with the electrically conductive material made in the through-hole in the second printing step.

Making the through-hole must be done so precisely that, on the one hand, the carrier film is completely removed in the region of the through-hole, but at the same time the electrically conductive material applied in the first printing step is retained as completely as possible so that the desired through-contact can be achieved by subsequently filling the through-hole with electrically conductive material.

According to the invention, the through-hole, when it is made after the first printing step, also extends through the already applied electrically conductive material.

In this case, there are no special requirements for the accuracy of the depth of the through-hole.

It has also been shown that a through-hole can be filled more reliably with the electrically conductive material applied in the subsequent second printing step than with a cavity sealed by the electrically conductive material applied in the first printing step.

If the through-hole is made before the first printing step or if the through-hole,

when it is made after the first printing step, also extends through the electrically conductive material already applied, it is preferable if the through-hole is dimensioned such that the electrically conductive material applied in the subsequent first or second printing step does not penetrate the through-hole.

In other words, the electrically conductive material printed on one side of the carrier film should not substantially pass through the through-hole and emerge freely on the other side; rather, it should remain in the through-hole to fill it.

This can regularly be achieved by a sufficiently small cross- section of the through-hole, adapted to the flow properties of the electrically conductive material during the printing process, as a whole or at least on the other side.

For example,

4 18746566.1 the through-hole can be shaped like a truncated cone with a cross-section decreasing towards the other side.

The diameter of the through-hole can be 50 micrometres to 5000 micrometres.

In particular, if the through-hole is made after the first printing step while retaining the electrically conductive material applied in the process, it is preferable if the diameter of the through-hole is 100 micrometres to 500 micrometres, more preferably 200 micrometres to 400 micrometres.

An appropriate diameter ensures dependable through- contact with high electrical conductivity value.

In this case, there is no risk of penetration by the material applied in the second printing step.

The diameter of the through-hole is preferably 50 micrometres to 200 micrometres, especially in cases where penetration is possible in principle.

With the usual electrically conductive materials used for printing methods, this can prevent the material from penetrating.

The thickness of the carrier film is preferably 20 micrometres to 500 micrometres, more preferably 20 micrometres to 250 micrometres, more preferably 50 micrometres to 150 micrometres, more preferably 50 micrometres to 100 micrometres, so that the through-hole is filled as extensively as possible to completely by electrically conductive material applied in a printing step.

The thickness of the layer of electrically conductive material applied in a printing step is preferably 5 to 50 micrometres, more preferably 5 to 20 micrometres.

Even if dimensions for the diameter of the through-hole are given above, the shape of the through-hole is not limited to the preferred circular design.

In the case of a non-circular through-hole, the cross-sectional area of the through- hole directly linked to the diameter specifications is to be used, i.e. preferably 0.002 square millimetres to 20.0 square millimetres, further preferably 0.008 square millimetres to 0.2 square millimetres or 0.002 square millimetres to 0.03 square millimetres.

Ultimately, the geometry of the through-hole must be selected such that any changes to the geometry of the through-hole and/or the through-contact in subsequent process steps - such as, for example, hot lamination - are taken into account in advance such that the through-contact and/or the desired electrical conductivity value is still reliably achieved after the corresponding process steps.

The through-hole can be made by punching, drilling or lasering, preferably CO2 lasering, for example, wherein lasering is preferred due to the accuracy that can regularly be achieved.

In particular, if the electrically conductive material applied in the first printing step is to be retained as far as possible during making, the through-hole should

18746566.1 preferably be made by lasering, as the required accuracy with regard to the depth of the through-hole can also be easily maintained.

When the through-hole is made by means of lasering, it is also advantageous if the process parameters are selected such that the laser selectively removes the material from

5 the carrier film with high precision without unintentionally destroying any electrically conductive material that has already been applied or changing its electrical properties.

In addition, the through-hole should be sufficiently clean immediately after making so that it can be filled with electrically conductive material without additional process steps.

Last but not least, it is advantageous if the above reguirements can also be achieved in a fast process for effective production.

It has been shown that percussion drilling with a CO2 laser is a good way of meeting these reguirements.

A CO2 laser beam preformed according to the desired geometry of the through-hole to be created - such as a circular beam with a diameter corresponding to the desired diameter of the through-hole - is pulsed several times onto the location of the through-hole to be created on the carrier film until the desired through-hole is created.

A wobbling or trepanning of a laser beam that is smaller than the desired geometry of the through-hole is dispensed with in the process.

The power, the repetition rate, the number of shots and the timing of the pulse should preferably be selected so that the material of the carrier film vaporizes without the resulting heat leading to undesirably large ablation ejection in the edge region of the through-hole to be created and/or leading to undesirably high mechanical stress on any electrically conductive material already applied to the carrier film.

It has proven to be advantageous if, for making the through-hole, at least one process parameter is selected from the group consisting of: wavelength of the laser 1 to 100 micrometres, preferably 10 to 11 micrometres, beam diameter 100 to 500 micrometres, preferably 200 to 400 micrometres, laser power 50 to 500 watts, preferably 100 to 200 watts, pulse width 3 to 10 microseconds, preferably 5 to 7 microseconds, number of shots 5 to 100, preferably 10 to 30, repetition freguency 1 to 100 kilohertz, preferably 4 to 8 kilohertz, rise and fall time per pulse less than 70 microseconds.

The combination of the process parameters of the number of shots and the pulse width in the aforementioned ranges is particularly relevant and preferred, as the corresponding combination directly results in the making of the through-hole taking place in a large number of small steps, in each of which only a small part of the material is removed.

The repetition freguency is also preferably selected

6 18746566.1 within the specified range. The thermal load on the material of the carrier film can be kept low by a corresponding repetition frequency at the preferred pulse width, In order to achieve permanently consistent results, while a through-hole is being made by means of a laser, it is preferable that the carrier film rests on a metal surface,

e.g. a metal table, in order to ensure uniform and reproducible heat dissipation. In order to prevent vapours or smoke generated by the laser from being deposited on the carrier film as contamination, it is also preferable if air or another gas, e.g. an inert gas, is made to flow over the carrier film when a through-hole is made, with which any vapours or smoke generated are immediately transported out of the machining zone. It is preferable if the electrically conductive material is conductive silver paste. Conductive silver paste is well suited for printing conductor tracks. In particular, if the through-hole is made by a CO2 laser, the use of conductive silver paste as an electrically conductive material offers the advantage that it does not cause any damage when the laser hits it as due to the usual wavelength of CO2 lasers, it is only slightly oxidized and, if at all, only barely ablated. The carrier film is preferably made from polycarbonate. A carrier film made from polycarbonate can be laminated with other layers of polycarbonate to form a laminated RFID security document without an increased risk of delamination due to incompatible materials in the layers of the layer bonding. The disclosed carrier film, on both sides of which conductor tracks are printed, has at least one through-contact manufactured according to the invention. Reference is made to the explanations above for further details. Since the electrical conductivity value of a through-contact may be too low for an intended use due to the dimensions of the through-hole required for the method according to the invention, it is possible to electrically connect a conductor track on different sides of the carrier film to one another by an array of at least two through- contacts. The through-contacts, which are preferably arranged in close neighbourhood to one another, thus create parallel connections between the two conductor tracks, resulting in an increased cumulative electrical conductivity value between the two conductor tracks. In addition, there is a redundancy of the through-contacts, whereby an insufficient contact in one through-contact is compensated for by a successful contact in another through-contact.

7 18746566.1

It is further preferred if two conductor tracks on the carrier film connected by at least one through-contact comprise contact points for checking the one or more through- contacts.

Test probes of a measuring device can be applied to the contact points for checking the basic existence of an electrical connection via the one or more through-

contacts and/or the electrical resistance or electrical conductivity value of the one or more through-contacts.

The invention will now be described by way of example using advantageous embodiments with reference to the accompanying drawings.

What is shown is:

Figure 1: —a schematic representation of an example embodiment of an RFID inlay with a disclosed carrier film;

Figure 2a: a schematic detailed representation of the carrier film from Figure 1;

Figure 2b: a schematic detailed representation of an embodiment variant of Figure 23; and

Figures 3a-c:schematic representations of various embodiments of the method according to the invention (Figure 3c) and of methods according to aspects of the description outside the protective scope of the claims for producing a through-contact in a carrier film, on both sides of which conductor tracks are printed.

In Figure 1, a RFID inlay 1, as used in security documents (e.g. passports) is represented.

The RFID inlay 1 comprises a disclosed carrier film 10, on both sides of which conductor tracks 11 are printed.

In Figure 1, the conductor tracks 11 on the directly visible front of the carrier film 10 are shown in solid lines, while the conductor tracks 11 on the back of the carrier film 10 are shown in dashed lines.

The RFID inlay 1 further comprises the RFID chip 2, which is merely indicated by a dotted line and is arranged on the back of the carrier film 10.

The RFID chip 2 of the RFID inlay 1 is, via feed lines 3, connected to antenna taps 4 of an antenna 5, whereby the latter also serves as a power supply in addition to communication purposes.

The feed lines 3, the antenna taps 4 and the antenna 5 itself are formed by the conductor tracks 11 printed on the carrier film 10. On the front of the carrier film 10, the conductor track 11 for forming the antenna 3 is designed coil-shaped and is extended at the antenna taps 4 to form arrays that, merely by way of example, are formed in circular shape.

On the back, the conductor tracks 11 are designed as two separate feed lines 3, each of which has circular arrays at one end (concealed by the

8 18746566.1 antenna taps 4 in Figure 1) analogous to the antenna taps 4 on the front side.

In the example embodiment shown, the two feed lines 3 are designed to converge towards one another at their other ends on a common axis.

This optional but preferred design allows the carrier film 10 to be flexibly equipped with different RFID chips 2, since the layout of the conductor tracks 11 does not specify a spacing for the contacts of the RFID chip 2, but RFID chips 2 with different contact spacings can be arranged on the carrier film 10 such that one contact is connected to a feed line 3 in each case.

For connection of the conductor tracks 11 on the front and back of the carrier film 10, arrays of through-contacts 12 are intended in the region of the antenna taps 4, with which the antenna taps 4 are electrically connected to the feed lines 3 and thus the antenna 5 to the RFID chip 2.

Figures 2a and b show two different embodiment variants for the array of through- contacts 12 in schematic detail views, with the variant in Figure 2a corresponding to the representation in Figure 1. The through-contacts 12, which are concealed by the conductor track 11 on the front, are indicated by dotted lines.

In the embodiment variant shown in Figure 2a, 21 through-contacts 12 are intended in the region of each antenna tap 4, with each through-contact 12 having a diameter of approximately 140 micrometres.

In the embodiment variant shown in Figure 2b, only five through-contacts 12 are intended in the region of each antenna tap 4.

However, since these each have a diameter of approximately 285 micrometres, the cumulative electrical conductivity value of a respective field of through-contacts 12 is practically identical for both embodiment variants, assuming identical materials and thickness of the carrier film 10. The invention is not limited to the numbers of through- contacts 12 shown and can be realized in individual cases with different constellations.

The through-contacts 12 of the carrier film 10 of the RFID chip from Figures 1 and 2a, b have been produced in a method according to the invention, as explained with reference to Figure 3c.

Two different implementation variants of a method according to an aspect of the description outside the scope of protection of the claims are explained with reference to Figures 3a and b.

In the method shown in Figure 3a, a first side of the carrier film 10 is printed with an electrically conductive material 13 to form conductor tracks 11 in a first step, with electrically conductive material 13 being printed in particular in the region intended for through-contacting (Figure 3a.1). A through-hole 14 is then made in the carrier film 10,

9 18746566.1 although the previously applied electrically conductive material 13 is retained at least almost completely {Figure 3a.2). The through-hole 14 can be made via a CO2 laser and has proven to be sufficiently accurate.

The second side of the carrier film 10 is subsequently printed with an electrically conductive material 13 to form conductor tracks 11, with the material application also extending in particular over the through-hole 14. By applying the electrically conductive material 13 in the second printing process, the through-hole 14 is filled as extensively as possible, preferably completely, with electrically conductive material 13, so that an electrical connection is created between the conductor tracks 11 on both sides of the carrier film (Figure 3a.3).

Since the through-hole 14 is closed on one side by the electrically conductive material 13 already applied before it is made, the only thing that needs to be taken into account when dimensioning the through-hole 14 is that it can be sufficiently filled by the electrically conductive material 13 applied in the second printing step and that a good electrical connection between the through-hole 12 created in this way and the neighbouring conductor tracks 11 is ensured.

The diameter of the through-hole 14 in Figure 3a is approximately 285 micrometres (see Figure 2b). Provided that the through- hole 14 is filled with electrically conductive material 13 in a printing step, this method can also be used to realize any other diameter, e.g. also about 140 micrometres (see Figure 2a).

In Figure 3b, an alternative implementation of the method for producing a through- contact 12 in a carrier film 10, on both sides of which conductor tracks 11 are printed, is represented.

In the first step, a through-hole 14 is made in the carrier film 10 before any electrically conductive material 13 is applied (Figure 3b.1). The through-hole 14 can be made by laser cutting, drilling, or punching.

In particular, the through-hole 14 can also be created using a CO2 laser in this method.

The first side of the carrier film 10 is subsequently printed with electrically conductive material 13, wherein the through-hole 14 is also filling with this material 13 (Figure 3b.2). In order to prevent the electrically conductive material 13 applied in this step from immediately emerging again on the second side of the carrier film 10 - thus penetrating the through-hole 14 - the through- hole 14 is dimensioned accordingly.

In particular, the diameter of the through-hole 14 on the second side of the carrier film 10 is suitably adapted to the flow properties of the electrically conductive material 13 during the printing process and the thickness of the

10 18746566.1 carrier film.

Finally, the second side of the carrier film 10 is printed with electrically conductive material in a second printing process, resulting in the desired through- contact (Figure 3b.3).

In the implementation variant of the method according to the invention shown in Figure 3c, electrically conductive material 13 is first printed onto the first side of the carrier film 10 in a first step (Figure 3c.1). A through-hole 14 is subsequently made, wherein this through-hole 14 extends not only through the carrier film 10 but also through the previously applied electrically conductive material 13 (Figure 3c.2). Here too, the through-hole 14 can be created by means of a CO2 laser, although different process parameters may have to be selected than in the above embodiment variants in order to penetrate the previously applied electrically conductive material 13. In a second printing process, electrically conductive material 13 is then printed onto the second side of the carrier film 10, wherein the through-hole 14 is also being filled (Figure 3c.3). Since the through-hole 14 is open on the first side of the carrier film 10 during the second printing step, penetration of the electrically conductive material 13 is prevented by appropriately dimensioning the through-hole 14. Reference is made to the relevant explanations for Figure 3b.

2. In all the example embodiments described above, the carrier film 10 is preferably made of polycarbonate and has a thickness of around 100 micrometres.

The electrically conductive material 13 is preferably conductive silver paste, which is applied with a layer thickness of approx. 20 micrometres.

Under these conditions, penetration of the electrically conductive material 13 through the through-hole 14 can be avoided, for example, if the diameter of the through-hole 14 is between 100 and 200 micrometres, for example about 140 micrometres.

As a result, the implementations of the method shown in Figures 3b and 3c are particularly suitable for the design variant of an array of through- contacts 12 shown in Figure 2a.

In the design variant shown in Figure 2b, the risk of penetration of electrically conductive material 13 through the through-hole 14 is significantly higher due to its larger diameter.

A CO2 laser with the following process parameters is preferably used for making the through-holes 14: Wavelength of the laser 10 to 11 micrometres Beam diameter = diameter of through-hole 14 Laser power 100 to 200 watts

11 18746566.1

Pulse width 5 to 7 microseconds

Number of shots 10 to 30

Repetition frequency 4 to 8 kilohertz

Rise and fall time < 70 microseconds per pulse

A higher number of shots is required to pierce through even the electrically conductive material 13 in the implementation variant shown in Figure 3c than in the two other implementation variants shown in Figures 3a, b, in which the through-hole 14 only has to be made in the carrier film 10.

Irrespective of the embodiment variant for the field of through-contacts 12 (Figure 2a, b) and the final implementation of the method according to the invention for producing the through-contacts 12 (Figure 3c), the conductor tracks 11 of the carrier film 10 shown in Figure 1 comprise advantageous, but in the context of the invention optional, contact points 6 for the test probes of a measuring device (not shown). By suitably applying the two test probes of a measuring device, the electrical connection between two of these contact points 6 and thus - depending on the choice of contact points 6 - also an array of through-contacts 12 can be checked.

In addition to determining the existence of an electrical connection through the through-contacts 12, the electrical conductivity value for an array of through-contacts 12 can also be determined if required.

12 18746566.1 List of reference numerals 1 RFID inlay 2 RFID chip 3 feed line

4 antenna tap 5 antenna 6 contact points carrier film

10 11 — conductor track 12 — through-contact 13 electrically conductive material 14 through-hole