Patent Application
20050133375
The present invention relates to a method of producing a structured metal layer. More particularly, structured metal layers of this type can be used, for example, as antennas for RF ID tags.
Modem transponder technology permits contactless reading out and storing of data from and onto a microchip by means of electromagnetic carrier waves as the transporting medium. For this purpose, the microchip is connected to an antenna, which receives and sends the electromagnetic radiation required for writing to or reading from the microchip. It is then possible to communicate with the microchip by means of an external transmitting or receiving unit. In general, the microchip does not have an energy supply of its own, so that the electromagnetic radiation used for writing to or reading from the microchip is also used for supplying energy to the microchip. However, the production of the RF ID tags comprising the antenna and the microchip was previously relatively expensive. For this reason, transponder technology has so far only been used for relatively high-value or durable articles. For example, transponder technology is used for finding buried pipelines or for quickly detecting animals in large herds.
For example, in large herds of cattle, the animals have a microchip implanted under the skin. If these animals are driven past a transmitting and receiving station, the correspondingly prepared cattle can be identified without any problem by the data stored on the microchip, since the data are read out without making contact with the animal. Apart from this application, other areas of use are also conceivable, such as for example the monitoring and observation of endangered species of animals in the wild for research purposes or behavioral studies, since the corresponding investigations can be conducted without significantly disturbing the animal's habitat.
Apart from this, there are further application areas, such as for example electronic protection against theft of expensive luxury items such as fur coats, perfumes, CD-ROMs, etc. For this, however, retailers have to be equipped with corresponding devices for reading the microchips.
Transponder technology has so far been used in particular for items which are very durable or are of very high value. Introduction of transponder technology on a broad base has been prevented by the comparatively high costs. If the costs for the production of the RF ID tag can be drastically lowered, this would open up the path to many applications which are subject to high cost pressure.
There is for instance a conceivable application serving for bureaucratic purposes, such as for example the monitoring of important documents and file records in government or administrative buildings, the files being electronically registered at the individual processing stations. The path followed by the file can be traced in a simple way and the file easily relocated if need be. In the simplest case, for this purpose the corresponding transmitting or receiving station is installed in the door frame, so that the file is electronically registered when it enters or leaves the room.
A further application example is the administration and loading of items of baggage at airports, ports, railroad stations or other item-redistributing stations, the item of baggage having to be directed to a specific location. In this case, a relatively small unit price for the RF ID tag, which comprises a memory chip and a transmitting and receiving unit, is considered just about profitable for these applications.
There is great interest in a variant of this technology in many areas in which a considerable number of data are to be reliably registered in short time periods. Many examples from everyday life can be found for this, such as for example the electronic postage stamp or the use of electronic labels marking products in the retail trade. In this case, the products located in a shopping cart can be contactlessly registered at an electronic cash register and a bill produced for these items. Furthermore, this also opens up the possibility of transmitting the data on to stockkeeping and of automatically re-ordering the products purchased.
However, the consumer articles referred to generally have a minimal market value, so that the costs for the electronic tags must be reduced considerably to allow them to be introduced on the market.
To be able to lower the production costs of an RF ID tag, various approaches are available. The costs of the microchip may be lowered, but on the other hand so too may be the costs which are incurred for the transmitting and receiving unit, in particular the antenna structure.
In cards used, for example, for controlling access to sensitive areas in research facilities or production works, a simple wire coil is used as the antenna structure. However, this form of antenna structure is far too expensive for the applications described above. In addition, antennas which are produced from metal foils are also known, for it then to be applied subsequently to a separate carrier.
The antenna structure may in this case be produced by various techniques.
One possibility is to laminate a metal foil onto the support over its full surface area and subsequently carry out structuring subtractively by selective etching. The antenna structure may, however, also first be punched out from metal foil and subsequently laminated onto the carrier.
In the case of these methods, the antenna structure is created subtractively, i.e. a full-area copper layer is first created and subsequently has to be structured. This produces a considerable amount of copper waste, which has to be recovered.
If the preparation of macroscopic starting materials is to be avoided because of the complex processing, the antenna structure may also be printed or sprayed onto the carrier using electrically conductive pastes. For this purpose, however, the copper must first be correspondingly prepared. The copper must be comminuted into adequately small particles, to allow a paste suitable for printing to be produced. What is more, corresponding accompanying substances, such as binders or solvents, must be added.
Finally, conventional semiconductor technology is also suitable, with a mask first being defined on the carrier by photolithography, for example using a photoresist. Subsequently, the intermediate spaces not covered by the mask on the carrier are currentlessly metallized. The method consequently requires working steps in which the photoresist is applied and structured. Furthermore, costs are incurred for the photoresist itself. This method is therefore also not suitable for the low-cost production of antenna structures for RF ID tags.
In the case of conventional methods of producing copper layers, it has previously been customary to create the copper layers by electrodeposition on a high-grade steel drum connected as a cathode. The adherence of copper on high-grade steel is relatively low, so that the copper foil created can simply be detached from the high-grade steel matrix and laminated onto a corresponding carrier in the further course of the method. To facilitate the detachment of the copper from the high-grade steel matrix, additives may be initially applied to the high-grade steel drum, such as graphite or molybdenum sulfide for example, which further reduces the adherence of the copper on the high-grade steel surface.
Also decisive for processing at lowest possible cost is that the copper material to be deposited is deposited on the cathode as efficiently as possible. For the RF ID tags under discussion, about 100 mg of copper are required per tag. This means that, given an efficient production procedure, approximately 10,000 antennas can be produced with an amount of material of 1 kg of copper. However, in the case of the subtractive structuring methods described further above, the offcut copper waste generated as scrap must be recycled, since the price of copper is relatively high.
The object of the invention is therefore to provide a method of producing a structured metal layer as used, for example, as an antenna structure in RF ID tags which can be carried out simply and inexpensively.
An aspect of the present invention is achieved by a method of producing a structured metal layer which comprises at least the following steps: provision of a cathode, conducting and nonconducting regions which form a mask structure being defined on the surface of the cathode and of an anode, the cathode and the anode being arranged in an electrolyte which contains a substrate metal, application of a voltage between the cathode and the anode, depositing of the substrate metal onto the conducting regions of the cathode, provision of a carrier layer and bringing the carrier layer into contact with the surface of the cathode, transfer of the substrate metal deposited onto the cathode to the carrier layer, and the structured metal layer being obtained.
The predetermined mask structure on the cathode has the effect that the desired structure of the metal layer is already obtained when the substrate metal is electrodeposited. The metal layer consequently does not have to be subsequently structured and there is consequently also no offcut waste as scrap. The mask structure defined on the cathode is formed in a thickness which corresponds at least to the layer thickness of the metal layer to be created. The conditions for the electrodeposition are chosen such that only the substrate metal is selectively deposited and the structured metal layer is produced in the desired layer thickness, that is to say, for example, no overfilling of the regions predetermined by the mask structure takes place. The substrate metal is in ionic form in the electrolyte and is reduced on the cathode to form the substrate metal.
After the electrodeposition, the structured metal layer, for example an antenna structure for an RF ID tag, is transferred directly to the desired carrier layer. Further transfer, printing and etching costs do not arise. The price of producing an antenna structure for RF ID tags is essentially determined in the case of the method according to the invention by the pure material costs and therefore permits low-cost production of high numbers of units.
In a preferred embodiment of the method according to the invention, the cathode has a cylindrical geometry. The cathode is consequently in the form of a roll, drum or rollers. With such a cathode, the method according to the invention can be carried out continuously. The cylindrical cathode is immersed with its lower portion into the electrolyte and continuously rotated. A specific portion of the circumferential surface consequently enters the electrolyte and is moved through it. As this happens, the substrate metal is deposited on the conducting regions of the portion. The rotatioal speed of the cylinder is set such that the portion of the circumferential surface remains in the electrolyte sufficiently long for the structured metal layer to be deposited in the desired layer thickness. The portion of the circumferential surface is moved out of the electrolyte again by further rotation of the cylinder. A carrier material is then continuously fed to the circumferential surface, so that the structured metal layer deposited on the portion of the circumferential surface is transferred to the carrier layer. By further rotation of the cylindrical cathode, the portion of the circumferential surface is immersed once again into the electrolyte and the cycle begins once again.
The continuous depositing of the copper layer and the continuous transfer of the deposited structured metal layer to the carrier layer consequently permits a continuous working mode. This eliminates the unproductive times inevitably occurring in the case of a discontinuous method, thereby permitting an increase in throughput.
It is advantageous if at least the conducting regions of the cathode are constructed from high-grade steel. High-grade steel has, on the one hand, an adequately high conductivity and is, on the other hand, adequately corrosion-resistant. The high conductivity of the high-grade steel permits efficient depositing of the substrate metal. The corrosion resistance of high-grade steel provides the cathodes with a long service life, even under extreme galvanic conditions. Therefore, exchange of the cathode is required relatively rarely. As a result, the service life and degree of utilization of the device used for electrodepositing the substrate metal are increased.
Furthermore, high-grade steel can be produced and processed at relatively low cost, meaning that the financial expenditure for producing the corresponding cathode drums also remains within restricted limits.
It is also advantageous if the nonconducting regions on the surface of the cathode consist of a plastic and/or a ceramic. These materials are, on the one hand, very inexpensive and, in addition, have a high specific resistance. The high specific resistance produces sharp contouring of the mask structure with respect to the conducting regions. Ceramics and plastics can by now be produced at very low cost and exhibit good potential for deformability, this giving rise to possible application to a wide variety of cathode geometries. A further advantage is also the relatively low density of these materials, which results in a weight saving and easy transportability of the cathode objects used.
In a preferred embodiment of the method according to the invention, the conducting regions of the cathode surface have the form of an antenna structure. The method according to the invention permits the extremely low-cost production of antenna structures for RF ID tags. Consequently, the costs for the production of such RF ID tags can be significantly lowered, so that they can also be used for applications which are under high cost pressure.
The anode preferably contains the substrate metal. Apart from its property as a charge pole, the anode also acts as a reservoir for the substrate material. Consequently, in this case there is no need for the otherwise required continuous feeding of the substrate metal into the electrolyte. There is no need for complex preparation of the substrate metal, since the substrate metal can also be used in the form of an unpurified crude metal. The selectivity for the deposition in this case takes place by means of a suitable voltage difference between the anode and the cathode. In this way, troublesome or even harmful or toxic intermediate products can be avoided during the production of the antenna structure. Furthermore, the anode slurries occurring during electrochemical depositing can be used for obtaining valuable precious metals and contribute to reducing overall costs. Considered electrochemically, these metals are of a higher grade than the substrate metal, and accordingly have a higher oxidation potential.
It is advantageous if the substrate metal is copper. Copper has a very high conductivity and is relatively inexpensive to obtain. The price of copper is currently relatively low. The high conductivity of copper is surpassed only by very few metals, these metals being much more expensive in costs of procurement. The ratio of conductivity to price in the case of copper is optimal. A high conductivity of the substrate metal guarantees high efficiency of the energy input of the electromagnetic radiation into the antenna structure and consequently high efficiency for the exchange of information. At the same time, the response times are relatively short and consequently a high flow of information can be achieved with low susceptibility to interference.
In a preferred embodiment of the method according to the invention, the depositing of the substrate metal is controlled in such a way that the layer thickness of the structured metal layer is less than the depth of the mask structure, so that a residual volume is formed. A residual volume refers to the space which is defined between a plane which passes through the surface of the nonconducting regions of the mask structure and a plane which passes through the exposed surface of the deposited structured metal layer. The layer thickness of the structured metal layer can in this case be controlled by means of the applied current density or else by means of the dwell time of the cathode or the conducting portions of the mask structure in the electrolyte.
Consequently, various layer thicknesses can be realized by the same depositing device with low expenditure. Various auxiliary materials can be filled into the residual volume formed.
In a particularly preferred embodiment, an adhesive is applied to the structured metal layer in the residual volume.
The adhesive allows the structured metal layer to be easily removed from the mask structure, since adequate adherence with respect to the carrier layer is created. Furthermore, the adhesive produces permanent fixing of the structured metal layer, preferably an antenna structure, on the carrier layer.
The adhesive is preferably selected such that it adheres on the deposited structured metal layer, but not on the nonconducting regions of the mask structure. After applying the adhesive and applying the carrier layer, the latter with the structured metal layer fixed on it can be readily lifted off again. Furthermore, the adhesives should not contain any toxic accompanying substances, to avoid endangering the environment.
It is particularly advantageous if the adhesive is a thermoplastic adhesive or a reaction adhesive. A thermally or photochemically curable adhesive may be used, for example, as the reaction adhesive. Examples of reaction adhesives are polyether sulfones, cyanurates, epoxy compounds and similar classes of compounds. A precondition here is that the corresponding adhesives permit a solid bond between the structured metal layer and the carrier layer, but at the same time do not impair the structure of the structured metal layer with respect to the surface and dimensional stability.
If copper is used as the substrate metal, it is advantageous if the electrolyte contains sulfuric acid and copper sulfate as the copper-containing salt. Because of its high degree of dissociation, sulfuric acid increases the conductivity of the electrolyte and improves the depositing quality of the copper layer. Copper sulfate has a high solubility in aqueous systems, so that a relatively high copper ion concentration can be achieved in the electrolyte.
In addition, further optimizing additives may be added to the electrolyte, such as triisopropranolamine, gelatin, glue, thiourea, cellulose ether or chloride ions. The effect of these additives is either an improvement in the fluid-dynamic properties of the electrolyte solution (e.g. increase in the viscosity) or an increase in the conductivity, which leads to an improvement in the depositing quality. The conductivity-improving additives include, for example, copper fluoroborate electrolyte (e.g. copper(II)tetrafluoroborate, borofluoric acid, boric acid).
For the copper deposition, a bath temperature of up to 75° C. and flow rates of up to 7 m/s with a current density of up to 150 A/dm2 have proven to be suitable.
After the transfer of the structured metal layer formed as an antenna structure to the carrier layer, the antenna structure can be supplemented by a microchip to form an RF ID tag.
The above and still further aspects, features and advantages of the present invention will become apparent upon consideration of the following definitions, descriptions and descriptive figures of specific embodiments thereof wherein like reference numerals in the various figures are utilized to designate like components. While these descriptions go into specific details of the invention, it should be understood that variations may and do exist and would be apparent to those skilled in the art based on the descriptions herein.
The invention is explained in more detail with reference to the accompanying figures, in which:
As represented in
In order, for example, to deposit a copper layer 10 μm thick, the depth of the mask structure is chosen to be 10.5 μm. The areas exposed by the isolating mask structure are galvanically coated with a copper layer 10 μm thick. In the remaining residual depth of 0.5 μm, the adhesive is then introduced in a gravure printing process. A specific portion on the circumferential surface is consequently introduced into the electrolyte 15 by rotation of the high-grade steel drum 14 and moved through it. As this happens, copper is continuously deposited on the electrically conductive exposed regions until this portion is moved out of the electrolyte 15 again by further rotation of the high-grade steel drum 14. In this case, the depositing of the copper is set such that a residual volume for the adhesive still remains in the electrically conducting regions. Once the portion of the circumferential surface 19 of the high-grade steel drum 14 has been moved out of the electrolyte 15, it is initially taken past a rinsing device 20 and a drying device 21. Subsequently, adhesive is applied to the circumferential surface 19 of the high-grade steel drum 14 by a roll 22 provided with an adhesive. Excess adhesive is removed by a stripping device 23, so that the adhesive remains essentially only in the residual volumes on the previously deposited copper. The portion of the circumferential surface 19 provided with the adhesive is moved further by rotation of the high-grade steel drum 14 and reaches a printing roll 24. A carrier layer 25, for example a sheet of paper or sheet of plastic film, is fed to the circumferential surface 19 and pressed against it by means of the printing roll 24. The antenna structure provided with the adhesive layer is transferred from the circumferential surface 19 to the carrier layer 25. The carrier layer 25 with the antenna structure (not represented) applied on it is continuously transported away by the printing roll 24.
Further auxiliary devices may be built into the overall installation, in order to facilitate the lifting of the antenna structures out of the structured belt.
Having described preferred embodiments of a new and improved method of producing electrodeposited antennas for RF ID tags by means of selectively introduced adhesive, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by the appended claims. Although specific terms are employed herein, they are used in generic and descriptive sense only and not for purposes of limitation.
List of Designations
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 29 166.7 | Jun 2002 | DE | national |
This application is a continuation of PCT Application No. PCT/DE03/01376, filed on Apr. 29, 2003, and titled “Method for Producing Galvanically Deposited Antennae for RFID Labels Using an Adhesive that is Selectively Applied,” which claims priority under 35 U.S.C. §119 from German Patent Application No. DE 102 29 166.7, filed on Jun. 28, 2002, and titled “Method of Producing Electrodeposited Antennas for RF ID Tags by Means of Selectively Introduced Adhesive,” the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/DE03/01376 | Apr 2003 | US |
| Child | 11017793 | Dec 2004 | US |
