METHOD FOR PRODUCEING A THROUGH-CONTACT IN A DOUBLE-SIDED PRINTED CARRIER FILM

Description

[0001] The invention relates to a method for creating a through-hole in a double-sided printed carrier film and to a double-sided printed carrier film with a through-hole.

[0002] Carrier films printed with conductive traces are known in the prior art. For example, RFID labels (radio frequency identification labels or labels for identification using electromagnetic waves) comprise an antenna in the form of a conductive trace printed on a film, which is connected to an RFID chip and serves both for power supply and communication with an RFID reader. The conductive trace is often coil-shaped and is connected to corresponding contacts of the RFID chip at two widely separated antenna taps.

[0003] With sufficiently large RFID chips, it is possible to connect the two antenna contacts directly to the RFID chip by placing the RFID chip directly onto the coil-shaped conductor track. This connects two widely separated contacts of the RFID chip to the antenna contacts. The RFID chip acts as a bridge between the two antenna contacts via the additional windings of the antenna located between them.

[0004] Document DE 10 2011 016 512 A1 describes a method for creating a via in a carrier film printed with conductive traces on both sides, in which conductive traces are first printed on one side of the carrier film.

[0005] Document DE 699 19 008 T2 proposes a contactless chip card with an antenna applied to one side of a substrate material in the form of a conductor track, which is short-circuited via two vias and a bridge connecting the vias on the other side of the substrate material.

[0006] Document US 6,353,420 B1 deals with the manufacture of contactless devices, such as RFID tags or chip cards, including vias for connecting an antenna formed as a conductor track on one side of the substrate material.

[0007] Document US 5,266,904 A concerns the provision of contact points immediately adjacent to a via for the purpose of verifying the via using appropriate measuring instruments.

[0008] The document Venkat S: "Laser drilled Microvias Present and Future Laser drilling promises even faster, more flexible and economical microvia manufacturing in the future" is a compilation of methods for manufacturing through-hole vias in printed circuit boards.

[0009] Document US 2012 / 0111841 A1 mentions percussion drilling with pulsed CO2 lasers as a method for producing through-hole vias.

[0010] The object of the present invention is to introduce an improved method for manufacturing a carrier film for an RFID chip.

[0011] This problem is solved by a method according to the main claim and a carrier film according to the dependent claim. Advantageous further developments are the subject of the dependent claims.

[0012] The invention is based on and includes the realization that, due to the progressive miniaturization of RFID chips, bridging the antenna windings is becoming increasingly difficult, since the distance between the contacts of the RFID chips is often less than the minimum distance between the two antenna taps of the conductor track that can be produced with reasonable effort.

[0013] The invention relates to a method for creating a through-hole in a carrier film printed on both sides with conductive traces, the two sides of which are printed in two printing steps with electrically conductive material in the area of ​​the intended through-hole, wherein after the first printing step and at the latest before the second printing step, a through-hole is introduced into the carrier film, which is filled with electrically conductive material in the subsequent printing step(s) for the through-hole, whereby the already applied electrically conductive material is retained, wherein the printing steps are carried out sequentially and the introduction of the through-hole is carried out by percussion drilling with a CO2 laser, wherein the following process parameters are selected for the introduction of the through-hole: wavelength of the laser 1 to 100 micrometers, beam diameter 100 to 500 micrometers, laser power 50 to 500 watts, pulse width 3 to 10 microseconds.Number of shots: 5 to 100; repetition rate: 1 to 100 kilohertz; and rise and fall time per pulse: less than 70 microseconds.

[0014] Furthermore, a carrier film is disclosed which is printed on both sides with conductive traces and has at least one via produced according to the invention.

[0015] The invention recognizes that, in the case of a double-sided printed carrier film, the electrically conductive material applied during the two printing steps is sufficient to create a reliable electrically conductive connection between the two sides of the carrier film in the form of a via, provided that at least one suitable through-hole is created before one of the printing steps. Advantageously, the through-hole is designed such that it is filled solely by the electrically conductive material applied in a single printing step, ensuring that the electrically conductive material within the through-hole remains electrically connected to the material applied adjacent to the through-hole in the same printing step. This can be achieved by appropriately dimensioning the through-hole, the depth of which corresponds to the thickness of the carrier film.The dimensioning of the through-hole can be appropriately selected by the specialist responsible for the execution, depending on the thickness of the carrier film and the viscosity of the printed electrically conductive material.

[0016] The insertion of the through-hole into the carrier film can generally take place before or after the first printing step, in which case it is filled with electrically conductive material in either the first or the second printing step. According to the invention, the insertion of the through-hole into the carrier film takes place after the first printing step. This allows the method to be flexibly integrated into existing processes. According to the invention, the two printing steps are carried out sequentially; that is, in a first printing step, conductive traces are applied to one side of the carrier film, before, after completion of the first printing step, conductive traces are applied to the other side of the carrier film in a second printing step. However, it is also possible for the printing steps to be carried out simultaneously or overlapping in time.

[0017] If the through-hole is created after the first printing step, the electrically conductive material applied in the first printing step is retained according to the invention. The material from the first printing step thus forms an electrically conductive seal of the through-hole, ensuring a good electrical connection with the electrically conductive material introduced into the through-hole in the second printing step. The creation of the through-hole must be carried out with such precision that, on the one hand, the carrier film in the area of ​​the through-hole is completely removed, while on the other hand, the electrically conductive material applied in the first printing step is retained as completely as possible, so that the desired via can be achieved by subsequently filling the through-hole with electrically conductive material.

[0018] Alternatively, according to one aspect of the description, it is possible if the through-hole, when inserted after the first printing step, also extends through the already applied electrically conductive material. In this case, there are no special requirements regarding the accuracy of the through-hole's depth. 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 a cavity sealed by the electrically conductive material applied in the first printing step.

[0019] If the through-hole is created before the first printing step, or if, when created after the first printing step, the through-hole extends through the already applied electrically conductive material, it is preferred that the through-hole be dimensioned such that the electrically conductive material applied in the subsequent first or second printing step does not pass through the through-hole. In other words, the electrically conductive material printed on one side of the carrier film should not essentially pass through the through-hole and exit 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, either overall or at least on the other side.For example, the through-hole can be shaped like a frustocone with a cross-section that decreases towards the other side.

[0020] The diameter of the through-hole can range from 50 micrometers to 5000 micrometers. Particularly when the through-hole is created after the first printing step, preserving the electrically conductive material applied during that step, a diameter of 100 micrometers to 500 micrometers, and more preferably 200 micrometers to 400 micrometers, is preferred. A corresponding diameter ensures reliable through-hole contact with high electrical conductivity. In this case, there is no risk of material being blown through the through-hole after being applied in the second printing step. Especially in cases where blow-through is fundamentally possible, the diameter of the through-hole is preferably 50 micrometers to 200 micrometers. With conventional electrically conductive materials used in printing processes, this prevents material blow-through.The thickness of the carrier film is preferably 20 to 500 micrometers, more preferably 20 to 250 micrometers, more preferably 50 to 150 micrometers, and more preferably 50 to 100 micrometers, so that the through-hole is filled as completely as possible by the electrically conductive material applied in a single printing step. The thickness of the layer of electrically conductive material applied in a single printing step is preferably 5 to 50 micrometers, and more preferably 5 to 20 micrometers.

[0021] Even though 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.

[0022] In the case of a non-circular through-hole, the cross-sectional area of ​​the through-hole, which is directly linked to the diameter specifications, is to be taken into account, i.e. preferably 0.002 square millimeters to 20.0 square millimeters, further preferably 0.008 square millimeters to 0.2 square millimeters or 0.002 square millimeters to 0.03 square millimeters.

[0023] Ultimately, the geometry of the through-hole must be chosen in such a way that any changes to the geometry of the through-hole and / or the via in subsequent process steps - such as hot lamination - are taken into account in such a way that the via and / or the desired electrical conductivity is still reliably achieved even after the corresponding process steps.

[0024] The through-hole can be created, for example, by punching, drilling, or laser cutting, preferably with a CO2 laser, with laser cutting being preferred due to the accuracy that can be regularly achieved. In particular, if the electrically conductive material applied in the first printing step is to be preserved as much as possible, the through-hole is preferably created by laser cutting, since the required accuracy regarding the depth of the through-hole can also be easily maintained in this way.

[0025] When creating the through-hole using lasers, it is advantageous to select the process parameters such that the laser selectively removes the carrier film material with high precision, without unintentionally damaging or altering the electrical properties of any previously applied electrically conductive material. Furthermore, the through-hole should be sufficiently clean immediately after creation to allow for subsequent filling with electrically conductive material without additional processing steps. Finally, it is advantageous if the aforementioned requirements can be met even with a fast process for efficient manufacturing.

[0026] It has been shown that the aforementioned requirements can be effectively met by percussion drilling with a CO2 laser. In this process, a CO2 laser beam, pre-shaped according to the desired geometry of the through-hole to be created—for example, a circular beam with a diameter corresponding to the desired diameter of the through-hole—is pulsed repeatedly onto the location of the through-hole on the substrate until the desired through-hole is formed. Wobbling or trepanning of a laser beam smaller than the desired geometry of the through-hole is avoided.

[0027] The power, repetition rate, number of shots and the temporal profile of the pulse are preferably selected such that the material of the carrier film evaporates without the resulting heat leading to undesirably large ablation ejection in the edge area of ​​the through-hole to be created and / or undesirably high mechanical stress on any electrically conductive material already applied to the carrier film.

[0028] According to the invention, the through-hole is created by percussion drilling with a CO2 laser. The following process parameters are selected for creating the through-hole: laser wavelength 1 to 100 micrometers, beam diameter 100 to 500 micrometers, laser power 50 to 500 watts, pulse width 3 to 10 microseconds, number of shots 5 to 100, repetition frequency 1 to 100 kilohertz, and rise and fall time per pulse less than 70 microseconds.

[0029] It has proven further advantageous if at least one process parameter for creating the through-hole is selected from the group consisting of: laser wavelength 10 to 11 micrometers, beam diameter 200 to 400 micrometers, laser power 100 to 200 watts, pulse width preferably 5 to 7 microseconds, number of shots 10 to 30, repetition rate 4 to 8 kilohertz. The combination of the process parameters number of shots and pulse width in the aforementioned ranges is particularly relevant and preferred, since the corresponding combination directly results in the creation of the through-hole in a multitude of small steps, in each of which only a small portion of the material is removed. A repetition rate within the aforementioned range is also preferably selected.By using an appropriate repetition frequency at the preferred pulse width, the thermal stress on the carrier film material can be kept low.

[0030] To achieve consistently uniform results, it is preferred that the carrier film rests on a metal surface, e.g., a metal table, during the laser cutting process to ensure uniform and reproducible heat dissipation. To prevent laser-generated vapors or smoke from settling on the carrier film, it is further preferred that the carrier film be flushed with air or another gas, e.g., an inert gas, during the cutting process, so that any vapors or smoke that may be generated are immediately carried away from the processing zone.

[0031] It is preferable to use silver conductive paste as the electrically conductive material. Silver conductive paste is well-suited for printing conductive traces. In particular, when the through-hole is created using a CO2 laser, the use of silver conductive paste as the electrically conductive material offers the advantage that, due to the typical wavelength of CO2 lasers, it oxidizes very little and, if at all, is only minimally ablated when struck by the laser.

[0032] The carrier film is preferably made of polycarbonate. A polycarbonate carrier film can be bonded to further layers of polycarbonate by lamination to form a layered RFID security document without increasing the risk of delamination due to incompatible materials in the layers of the composite.

[0033] The disclosed carrier film, printed on both sides with conductive traces, has at least one through-hole produced according to the invention. For further explanation, reference is made to the preceding statements.

[0034] Since the electrical conductivity of a via may be too low for a given application due to the required dimensions of the through-hole for the inventive method, it is possible to electrically connect two conductor tracks on opposite sides of the substrate film using an array of at least two vias. The vias, which are preferably arranged close to each other, thus establish parallel connections between the two conductor tracks, resulting in an increased cumulative electrical conductivity between the two conductor tracks. Furthermore, redundancy of the vias is achieved, whereby an insufficient connection in one via is compensated for by a successful connection in another.

[0035] It is further preferred if two conductor tracks connected by at least one via on the substrate include contact points for checking the via(s). Test probes of a measuring instrument can be applied to the contact points to verify the existence of an electrical connection via the via(s) and / or the electrical resistance or conductance of the via(s).

[0036] The invention will now be described by way of example with reference to advantageous embodiments and the accompanying drawings. These show: Figure 1: a schematic representation of an embodiment of an RFID inlay with a disclosed carrier film; Figure 2a: a schematic detail representation of the carrier film made of Figure 1 Figure 2b: a schematic detail representation of a variant design. Figure 2a; and Figures 3a-c: schematic representations of various implementations of the method according to the invention ( Figure 3a ) as well as methods according to aspects of the description for creating a through-hole in a carrier film printed with conductor tracks on both sides.

[0037] In Figure 1 Figure 1 shows an RFID inlay 1, as used in security documents (e.g., passports). The RFID inlay 1 comprises a disclosed carrier film 10, printed on both sides with conductive traces 11. Figure 1 The conductor tracks 11 on the directly visible front side of the carrier film 10 are shown in solid lines, while the conductor tracks 11 on the back side of the carrier film 10 are shown in dashed lines. The RFID inlay 1 also includes the RFID chip 2, indicated only by a dash-dot line, which is located on the back side of the carrier film 10.

[0038] The RFID chip 2 of the RFID inlay 1 is connected via leads 3 to antenna taps 4 of an antenna 5, the latter serving both communication purposes and power supply. The leads 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 side of the carrier film 10, the conductor track 11 is coiled to form the antenna 3 and extended at the antenna taps 4 into circular fields (for illustrative purposes only). On the back side, the conductor tracks 11 are configured as two separate leads 3, each with a terminal at one end (in Figure 1The antenna taps 4 (concealed by the antenna taps 4) have circular fields analogous to the antenna taps 4 on the front side. In the illustrated embodiment, the two supply lines 3 are configured to converge on a common axis at their other ends. This optional, but preferred, configuration allows the carrier film 10 to be flexibly equipped with different RFID chips 2, since the layout of the conductor tracks 11 does not prescribe a specific spacing for the contacts of the RFID chip 2, but rather RFID chips 2 with different contact spacings can be arranged on the carrier film 10 such that each contact is connected to a supply line 3.

[0039] To connect the conductor tracks 11 on the front and back of the carrier film 10, 4 fields of vias 12 are provided in the area of ​​the antenna taps, with which the antenna taps 4 are electrically connected to the supply lines 3 and thus the antenna 5 to the RFID chip 2.

[0040] In Figures 2a and b Two different design variants for the field of vias 12 are shown in schematic detail views, with the variant made of Figure 2a the representation from Figure 1 This corresponds to the vias 12, which are normally concealed by the conductor track 11 on the front side, indicated by dotted lines.

[0041] In the version according to Figure 2a In the area of ​​each antenna tap 4, 21 vias 12 are provided, each via having a diameter of approximately 140 micrometers. In the embodiment according to Figure 2bIn the area of ​​each antenna tap 4, only five vias 12 are provided. However, since these each have a diameter of approximately 285 micrometers, the cumulative electrical conductance of a respective field of vias 12 is practically identical in both embodiments, assuming identical materials and thickness of the substrate film 10. The invention is not limited to the number of vias 12 shown and can be implemented with different configurations in individual cases.

[0042] The vias 12 of the carrier film 10 of the RFID chip made of Figure 1 and 2a, b are in a method according to the invention, as shown by the Figure 3a explained, generated. Two different implementation variants of a procedure according to one aspect of the description are presented based on the Figures 3b and c explained.

[0043] At the in Figure 3aIn the described method, in a first step a first side of the carrier film 10 is printed with an electrically conductive material 13 to form conductor tracks 11, wherein in particular electrically conductive material 13 is printed in the area intended for through-hole plating ( Figure 3a .1). Subsequently, a through hole 14 is made in the carrier film 10, whereby the previously applied electrically conductive material 13 remains at least almost completely intact ( Figure 3a.2) The creation of the through-hole 14 can be carried out using a CO2 laser and has proven to be sufficiently accurate. Subsequently, the second side of the carrier film 10 is printed with an electrically conductive material 13 to form conductor tracks 11, the material application extending in particular also over the through-hole 14. By applying the electrically conductive material 13 in the second printing process, the through-hole 14 is filled as completely as possible, preferably entirely, 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).

[0044] Since the through-hole 14 is closed on one side by the electrically conductive material 13 applied prior to its insertion, the only consideration required for 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 resulting via 12 and the adjacent conductor tracks 11 is ensured. The diameter of the through-hole 14 in Figure 3a is approximately 285 micrometers (see below). Figure 2b ). With this method, provided that the through-hole 14 is filled with electrically conductive material 13 in one printing step, any other diameter can also be achieved, e.g., approximately 140 micrometers (see below). Figure 2a ).

[0045] In Figure 3bAn alternative implementation of the method for creating a via 12 in a carrier film 10 printed on both sides with conductor tracks 11 is shown.

[0046] In the first step, before any electrically conductive material 13 is applied, a through hole 14 is made in the carrier film 10 ( Figure 3b .1) The through-hole 14 can be created by laser cutting, drilling, or punching. In particular, the through-hole 14 can also be created using a CO2 laser in this process. Subsequently, the first side of the carrier film 10 is printed with electrically conductive material 13, whereby the through-hole 14 is also filled with this material 13 ( Figure 3b.2) To prevent the electrically conductive material 13 applied in this step from immediately emerging again on the second side of the carrier film 10 – i.e., from shooting through 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 appropriately adapted to the flow properties of the electrically conductive material 13 during the printing process and the thickness of the carrier film. Finally, the second side of the carrier film 10 is printed with electrically conductive material in a second printing step, resulting in the desired through-hole ( Figure 3b .3).

[0047] At the in Figure 3c In the illustrated implementation variant of the process, electrically conductive material 13 is first printed onto the first side of the carrier film 10 in a first step ( Figure 3c.1). Subsequently, a through hole 14 is made, whereby 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 using a CO2 laser, whereby different process parameters than in the above embodiment variants may need to be selected to penetrate the previously applied electrically conductive material 13. In a second printing step, electrically conductive material 13 is then printed onto the second side of the carrier film 10, thereby also filling the through-hole 14 ( 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 appropriate dimensioning of the through-hole 14. Reference is made to the relevant explanations for Figure 3b.2.

[0048] In all the embodiments described above, the carrier film 10 is preferably made of polycarbonate and has a thickness of approximately 100 micrometers. The electrically conductive material 13 is preferably silver conductive paste applied with a layer thickness of approximately 20 micrometers. 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 micrometers, for example, approximately 140 micrometers. Consequently, the embodiments described above are suitable for use in Figures 3b and 3c demonstrated implementations of the procedure, especially for the in Figure 2a The illustrated design variant of an array of vias 12. In the design variant according to Figure 2bThe risk of electrically conductive material 13 being shot through the through hole 14 is significantly higher due to its larger diameter.

[0049] A CO2 laser with the following process parameters is preferably used to create the through holes 14: wavelength of the laser 10 to 11 micrometers Beam diameter = Diameter of through hole 14 Laser power 100 to 200 watts Pulse width 5 to 7 microseconds Number of shots 10 to 30 Repetition rate 4 to 8 kilohertz Rise / fall time < 70 microseconds per pulse

[0050] For penetrating even the electrically conductive material 13 during the in Figure 3c The depicted execution variant requires a higher number of shots than the other two execution variants according to Figures 3a , b , in which the through hole 14 only needs to be inserted into the carrier film 10.

[0051] Regardless of the design variant for the field of vias 12 ( Figure 2a, b) and the final implementation of the inventive method for generating the vias 12 ( Figure 3a ) comprise the conductor tracks 11 of the in Figure 1 The illustrated carrier film 10 provides advantageous, but within the scope of the invention optional, contact points 6 for the test probes of a measuring instrument (not shown). By appropriately applying the two test probes of a measuring instrument, the electrical connection between any two of these contact points 6, and thus – depending on the choice of contact points 6 – also an array of vias 12, can be checked. In addition to determining the existence of an electrical connection through the vias 12, the electrical conductance for an array of vias 12 can also be determined if required. Reference symbol list

[0052] 1 RFID inlay 2 RFID chip 3 Lead wire 4 Antenna tap 5 Antenna 6 Contact points 10 Carrier foil 11 Conductor track 12 Via 13 Electrically conductive material 14 Through hole

Claims

1. Method for producing a through connection (12) in a carrier film (10) which is printed on both sides with conductor tracks (11) and the two sides of which are printed in one of two printing steps with electrically conductive material (13) in the area where the through connection (12) is provided, wherein, after the first printing step and at the latest before the second printing step, a through hole (14) is introduced into the carrier film (10) and, in the subsequent printing step(s), the hole is filled with an electrically conductive material (13) for the through connection, while the electrically conductive material (13) already applied is retained, characterized in that the printing steps are performed one after the other and the introduction of the through hole (14) takes place by means of percussion drilling with a CO2 laser, with the following being chosen as process parameters for the introduction of the through hole: wavelength of the laser 1 to 100 micrometres, beam diameter 100 to 500 micrometres, laser power 50 to 500 watts, pulse width 3 to 10 microseconds, number of shots 5 to 100, repetition frequency 1 to 100 kilohertz, and rise and fall time per pulse less than 70 microseconds.

2. Method according to Claim 1, characterized in that a conductor track (11) on one side of the carrier film (10) is electrically connected to one on the other side in each case by an array of at least two through connections (12).

3. Method according to one of the preceding claims, characterized in that the diameter of the through hole (14) is 50 micrometres to 5000 micrometres, preferably 50 micrometres to 200 micrometres or 100 micrometres to 500 micrometres, and / or the diameter of the through hole (14) corresponds to the beam diameter, and / or in that the thickness of the carrier film (10) is 20 micrometres to 250 micrometres, preferably 75 micrometres to 125 micrometres.

4. Method according to one of the preceding claims, characterized in that at least one process parameter from the following group is chosen for the introduction of the through hole: wavelength of the laser 10 to 11 micrometres, beam diameter 200 to 400 micrometres, laser power 100 to 200 watts, pulse width 5 to 7 microseconds, number of shots 10 to 30, repetition frequency 4 to 8 kilohertz.

5. Method according to one of the preceding claims, characterized in that during the introduction of the through hole (14), the carrier film (10) rests on a metal surface and / or is flowed over by air or gas.

6. Method according to one of the preceding claims, characterized in that the electrically conductive material (13) is silver conductive paste.

7. Method according to one of the preceding claims, characterized in that the carrier film (10) is made of polycarbonate.

8. Method according to one of the preceding claims, characterized in that a conductor track (11) on one side of the carrier film (10) is electrically connected to one on the other side in each case by an array of at least two through connections (12).

9. Method according to one of the preceding claims, characterized in that 21 through connections (12) are provided, wherein each through connection (12) has a diameter of approximately 140 micrometres, or in that five through connections (12) are provided, wherein each through connection (12) has a diameter of approximately 285 micrometres.

10. Method according to one of the preceding claims, characterized in that two conductor tracks (11) connected by at least one through connection (12) comprise contact points (6) for testing the through connection(s) (12).