WO2005125290A1

WO2005125290A1 - A method for processing an electrically conductive pattern

Info

Publication number: WO2005125290A1
Application number: PCT/FI2005/000293
Authority: WO
Inventors: Lauri Huhtasalo; Juha-Pekka Alho
Original assignee: Upm-Kymmene Corporation
Priority date: 2004-06-22
Filing date: 2005-06-21
Publication date: 2005-12-29
Also published as: FI20045235A0; FI20045235A

Abstract

The present invention relates to a method for processing an electrically conductive pattern comprising a process step in which the electrically conductive pattern is transferred to an application substrate when the electrically conductive pattern is brought into contact with the application substrate (1). Before the electrically conductive pattern is transferred, the electrically conductive pattern is heated, and the application substrate comprises material, which softens when the electrically conductive pattern is brought into contact with the application substrate, thus causing the electrically conductive pattern to adhere to the application substrate (1).

Description

A method for processing an electrically conductive pattern

The present invention relates to two methods belonging to the same inventive concept. The first method is a method for processing an electrically conductive pattern comprising forming the electrically conductive pattern on a non-adhesive surface of a carrier substrate, or forming the electrically conductive pattern by separating the electrically conductive pattern from a carrier substrate consisting of a metallic foil; heating the electrically conductive pattern; and transferring the electrically conductive pattern to an application substrate, which comprises material, which softens when the heated electrically conductive pattern is brought into contact with the application substrate, thus causing the electrically conductive pattern to adhere to the application substrate.

The second method is a method for processing an electrically conductive pattern comprising forming the electrically conductive pattern by cutting a metal foil forming the outmost layer of an application substrate, which is a laminate comprising the metal foil, an adhesive and a non-metallic web, the adhesive being of material which softens when heated; heating the application substrate and removing the rest of the metal foil.

The transponders refer in this application to products, which comprise an RF-ID (radio frequency identification) circuit comprising a circuitry pattern and an integrated circuit on a chip. The circuitry pattern is located on a substrate, and the integrated circuit on the chip is electrically connected to the circuitry pattern. The chip can be attached to the circuitry pattern as a single chip without any substrate, or it can be attached to the circuitry pattern with a module comprising the chip and necessary leads on a substrate. The circuitry pattern can be a coil, or an antenna based on the dipole-antenna technique.

The electrically conductive pattern means in this application mainly the circuitry pattern but also the leads forming the electrical connection between the circuitry pattern and the chip include in the scope of the invention, as well as capacitor plates, which can be formed on the same substrate as the circuitry pattern. Also multi-layer structures belong to this context.

The principle of the present invention is that the electrically conductive pattern is first formed on a surface of a carrier substrate or separated from a metal foil, and then heated by a suitable energy source in such a manner that the electrically conductive pattern becomes adherent to the application substrate when the heated pattern softens thermoplastic material on the surface of the application substrate when the electrically conductive pattern and the application substrate are brought into contact with each other. When the thermoplastic material cools the electrically conductive pattern and the application substrate are firmly attached together. Alternatively, when the electrically conductive pattern is separated from the metal foil backed with a non- conductive web the electrically conductive pattern can remain in its place on the application substrate, and the excess foil is removed by heating at least those parts which are due to be removed. The temperature in which the thermoplastic material becomes adherent is the glass transition temperature of the thermoplastic material. Usually the temperature range to which the electrically conductive pattern is heated in order to make it adhere to another surface is between 30 and 150°C, preferably between 30 and 60°C. The adhesive is preferably based on ethylene vinyl acetate (EVA) but other adhesives may be suitable as well. The melting point of EVA can be adjusted by adjusting the amount of ethylene.

In the both methods of the invention it is possible that the electrically conductive pattern is heated selectively in such a manner that the electrically conductive pattern is in a different temperature compared to the materials surrounding it but it is as well possible that the electrically conductive pattern is after heating substantially in the same temperature as the materials surrounding it. Besides the temperature difference the detachment of the electrically conductive pattern may be based on differences e.g. in the porosity of materials or surface roughness. Generally at least the application substrate is in a web form but also the carrier substrate or the first substrate is often in a web form. In other words, the present method is mainly used in continuous processes. The heating process can be based on heat convection, heat conduction, electromagnetic radiation, or magnetic or electric field induced heating, such as induction heating. The means for heating may comprise an electric resistor, a hot-air blower, or a device emitting electromagnetic radiation. The electromagnetic radiation can be infrared radiation, radio frequency radiation (for example varied frequency microwaves), or ultraviolet radiation.

In the first embodiment of the invention, an electrically conductive pattern is first formed on a surface of a heat resisting carrier substrate and reduced to metal, and after that transferred to an application substrate. In this context, metal refers to any metal or mixture of metals. Copper oxide is the preferred starting material, which is reduced to copper. Also silver-, aluminium-, or carbon-based starting materials can be used. All starting materials are not necessarily reduced but high temperatures may be required for drying the pattern.

Fine-grained copper oxide powder having a grain size of the order of 10 μm or less is provided for the formation of a paste; a paste is formed from copper oxide powder, a binding agent and possible alloying elements and additives; using the paste, an electrically conductive pattern of desired shape is formed on the surface of a carrier substrate; the electrically conductive pattern on the surface of the carrier substrate is metallized and sintered at an elevated temperature to form a continuous and electrically conductive copper foil.

The carrier substrate, which has a substantially non-adhesive surface made of a material capable of withstanding the elevated temperature used for the metallization and/or sintering and non-reacting with the substances contained in the paste, is arranged to allow the copper foil to be detached from the carrier substrate. After the metallization and sintering, the copper foil is detached from the carrier substrate and transferred onto the surface of an application substrate.

The copper oxide powder comprises copper(l)oxide, which is prepared from a water solution by precipitating at a controlled temperature, solution strength and other conditions controlling the properties and by drying to produce active, fine-grained, pure and homogeneous copper oxide powder. By precipitating from a water solution, sufficiently finegrained and homogeneous powder is obtained. Correspondingly, the paste comprises fine-grained copper oxide powder having a grain size of the order of 10 μm or less and a binding agent. It is possible that the paste comprises also alloying elements and additives. The alloying element may be mixed in the copper oxide powder to form a homogeneous alloy, said alloying element being selected from the following group: silver, gold, platinum, palladium, oxides of silver, gold, platinum and palladium, halogenides of silver, gold, platinum, palladium or mixtures of these. By using alloying elements, the properties of the alloy can be improved.

The binding agent can be an organic binding agent, such as polyvinylbutyral (PVB) or dibutylphtalate (DBP), which is mixed in the paste. In addition, alloying elements serving to control the rheology, creep and/or adhesion may be mixed in the paste. The printability of the paste can be adjusted by using intermediate agents like these, which may be resins, various dispersing agents, solvents, etc.

The manufacturing line of the electrically conductive pattern comprises a forming device for forming the paste into a blank of an electrically conductive pattern having the shape of a desired electrically conductive pattern on the surface of the carrier substrate. In addition, the line comprises a metallizing and sintering device for metallizing and sintering the blank of the electrically conductive pattern on the surface of the carrier substrate at an elevated temperature to form a continuous and electrically conductive copper foil. The shape of the electrically conductive pattern is first formed on a carrier substrate. The carrier substrate has a substantially non- adhesive surface of a material capable of withstanding the elevated temperature used for the metallization and/or sintering and non- reacting with the substances contained in the paste so that the electrically conductive pattern, i.e. the copper foil, can be detached from the carrier substrate. The carrier substrate may have a polished smooth substantially non-adhesive surface, which is made of graphite or ceramic material. The graphite surface, which is the preferred choice, has preferably a surface roughness R_a of the order of 0.5 μm or less. Graphite is a cheap material having a good heat resistance. It is soft and can be easily polished by a simple technique to make it smooth enough to allow the copper foil to be readily detached from it, and it is regenerable for reuse so that it can be used multiple times.

To mention a few alternatives, the carrier substrate can be a plate for a single pattern, an endless conveyor comprising sequential plates, a smooth endless band, or a plate for multiple patterns. A preferred method for forming the blank of the electrically conductive pattern is silk printing. The blank of the electrically conductive pattern can be formed also by another impression printing technique in which case the forming device of the blank of the electrically conductive pattern a printing device. The blank of the electrically conductive pattern can also be formed by an output printing technique known from computer output technology in which case individual electrically conductive patterns of widely varying shapes can be easily created by a computer-aided method. In general, the printing method can be selected amongst silk, tampo, inkjet, laser, flexo, gravure and litho printing. Typically, the blank of the electrically conductive pattern has a thickness of about 5 - 100 μm.

The graphite substrate bearing the blank of the electrically conductive pattern is led to an oven to be reduced to elementary metal, i.e. to become the electrically conductive pattern. The metallization and sintering of the blank of the electrically conductive pattern to form a copper foil are performed in a hydrogen atmosphere in a chamber hermetically isolated from the environment. The chamber is provided with a heater, by means of which the electrically conductive pattern to be metallized and sintered is brought to a temperature exceeding 500 °C, preferably of the order of 1000 °C. When the copper oxide is reduced to copper, a porous spongy structure is formed, which has to be sintered to make it coherent. Since the spongy metal structure has a large area, even as large as hundreds of square meters in a gram of material, it would tend to oxidize unless a hydrogen atmosphere was provided in the chamber. In addition to hydrogen, the atmosphere may contain other gaseous substances, such as nitrogen. The other gaseous substances shall be inert. At a temperature of the order of 1000 °C, thorough sintering takes place so that the spongy metal becomes sintered, i.e. solidified so as to form a continuous metal layer, which is simultaneously deactivated and will not oxidize again. When a temperature as mentioned above is used, the metallization and sintering take place quickly, in a few minutes, so the manufacturing process is fast and can be implemented on a continuous production line. To promote the reduction process, the copper oxide powder may be treated with an organic intermediate agent to form a reducing compound on the surfaces of the copper oxide particles of the powder. As an organic intermediate agent, e.g. acetic acid, oxalic acid and/or formic acid may be used. Metallization takes place by the aid and influence of these because they are reducing compounds. As it breaks down, such as an organic intermediate agent reduces the copper oxide next to it. The reducing intermediate agent added to the paste allows the metallization to be effected at a lower temperature. However, an organic intermediate agent alone is not sufficient without metallization performed at a high temperature, but it makes it possible to significantly reduce the temperature to be used, e.g. to 500°C. The electrically conductive pattern may be heated by infrared radiation or microwave radiation for its metallization and sintering. For this purpose, the manufacturing line may comprise an infrared radiation source or a microwave radiation source.

After the heat treatment step the graphite substrate and the electrically conductive pattern are cooled down to at least 170°C. It is possible that the electrically conductive pattern is cooled to even lower temperature, such as 100°C or room temperature. For example, nitrogen gas can be used to protect the surface of the metal layer during cooling.

In some cases it may be necessary that the electrically conductive pattern must be rolled after the reduction step in order to achieve a suitable thickness, rigidity and strength. The electrically conductive pattern can be rolled while it remains on the carrier substrate and hence, a high production speed is achieved. The rolling can also be performed while the sintered/reduced copper foil is still hot, i.e. at a temperature of over 300°C, in which case the formation of the electrically conductive pattern on the carrier substrate and the sintering/reduction and rolling can all be carried out on the same production line.

Another process step, which is not necessary in all cases is a passivation step in which copper is passivated in such a manner that oxidation is prevented. The passivation step is usually performed by using suitable chemicals.

In the next process step, the electrically conductive pattern is heated and transferred to the application substrate. A temperature difference may be created between the carrier substrate and the electrically conductive pattern in order to obtain a situation in which the electrically conductive pattern is warmer than the carrier substrate. The heated electrically conductive pattern melts the adhesive on the surface of the application substrate while the carrier substrate is in a lower temperature and cannot melt the adhesive. Another option is that both the carrier substrate and the electrically conductive pattern are substantially at the same temperature but due to differences e.g. in the porosity of materials or surface roughness the electrically conductive pattern can be detached from the carrier substrate. The characteristics of the adhesive are naturally selected to correspond the temperature conditions so that the above described process can be carried out. The specific heat of the material of the carrier substrate shall be greater than that of the electrically conductive pattern in order to effect the temperature difference between the carrier substrate and the electrically conductive pattern. In regard to the specific heats, graphite and copper are very suitable materials to be used together. The basic material of the application substrate is preferably a flexible continuous web, for example a polyester, polyethylene, polypropylene or paper web, which is provided with an adhesive layer on its surface. The adhesive layer comprises hot melt adhesive. The adhesive on the surface of the web receives the electrically conductive pattern, and the pattern is released from the carrier substrate. Another alternative is that the basic material is a thermoplastic material, which softens adequately when it is in contact with the heated electrically conductive pattern. Heating of the electrically conductive pattern can be accomplished by induction heating or by a heated roll. For example, when a continuously working process line is used the heated roll can be pressed and rolled against successively advancing graphite plates in such a manner that the electrically conductive patterns and the application substrate move forward between the roll and the plate. The roll heats the electrically conductive patterns and softens the surface of the application substrate. In that way successive patterns adhere to the continuous application substrate.

A practical process for transferring the electrically conductive pattern from the carrier substrate to the application substrate is described next. The process utilizes the substantially porous structure of the electrically conductive pattern. In the process, the electrically conductive pattern is heated to a first temperature, which is between 30 and 60°C, for example 40°C, in order to transfer the electrically conductive pattern to the application substrate. The first temperature is high enough to make the adhesive on the application substrate adherent to the electrically conductive pattern but not yet adherent to the carrier substrate. The adhesive is preferably based on the EVA. When the electrically conductive pattern has been transferred to the application substrate the electrically conductive pattern is heated to a second temperature, which is between 80 and 150°C, for example 100°C. In such a manner the adhesive penetrates to the electrically conductive pattern and the electrically conductive pattern is firmly attached to the application substrate. The device used for heating may be a pair of rolls forming a nip. At least one of the rolls is heated. A release paper or the like may be required when the electrically conductive pattern is treated in the second temperature in order to prevent the adhesive to stick to the rolls.

After the transfer of the electrically conductive pattern has happened the application substrate can be reeled up and conveyed to another production line, or the process can be continued on the same production line in such a manner that practically all the process steps required to get sequential ready transponders on a continuous web are conducted on the same production line. However, also intermediate forms of the process may exist. In one embodiment of the invention, it is possible to attach the chip on the carrier substrate and transfer it with the electrically conductive pattern to the application substrate. In another embodiment, conductive leads of modules can be formed by the method of the invention.

The graphite substrate is led to reuse after the electrically conductive pattern is removed. First it is abraded to remove remnants of metal and after that follows a washing and drying sequence after which it is ready to be printed again.

By this method, it is also possible to produce multi-layer conductor structures. For example, on top of a first layer is formed a second layer from an electrically conductive material. To allow the superimposed electrically conductive patterns to be at different potentials during use, an electrically insulating dielectric layer is formed on the first layer, and a second layer is only then formed on the dielectric layer. The second layer may be formed from the same material or a different material than the underlying first layer. The material of the second layer may be selected from the following group: copper, silver, gold, platinum, palladium, oxides of copper, silver, gold, platinum, palladium or mixtures of these. The second layer is formed before the metallization and sintering of the first layer, in other words, while the lower electrically conductive pattern remains in an oxidic form. A prerequisite for this embodiment is that the dielectric layer resists high temperatures. Alternatively, the second layer may be formed after the metallization and sintering of the first layer. The second layer is preferably formed in the same way as the first layer. The metal foil structure may comprise several electrically conductive layers one upon the other, separated by a dielectric layer.

In another example, the copper foil forms an electrically conductive pattern for a circuit board, and the application substrate onto which the electrically conductive pattern is transferred is a rigid circuit board substrate.

As previously mentioned, in addition to the circuitry pattern, i.e. antenna, also other electrically conductive parts of the transponder, such as capacitor plates and leads, can be formed by the method of the invention.

In the second embodiment of the invention, a foil, which is on a surface of an adhesive layer on a first substrate, is etched to form an electrically conductive pattern, or an electrically conductive pattern is created on a surface of an adhesive layer by additive techniques. The electrically conductive pattern is heated in order to release it from the substrate above the glass transition temperature of the adhesive for example by electromagnetic radiation. Another adhesive layer formed on a second substrate is brought into contact with the electrically conductive pattern, and the electrically conductive pattern is adhered to the adhesive layer on the surface of the second substrate. The adhesive layers are selected in such manner that the adhesive layer on the surface of the initial substrate melts in a lower temperature that the adhesive layer on the surface of the second substrate. When the electrically conductive pattern cools down the adhesive on the surface of the second substrate crystallizes first and thus it is firmly attached to the second substrate before the adhesive on the surface of the first substrate solidifies. In such a manner the electrically conductive pattern can be released from the first substrate and transferred to the second substrate. The first substrate can be for example polypropylene and the second substrate can be a fibrous substrate, such as paper. The used adhesives are hot melt adhesives.

In the third embodiment of the invention, an electrically conductive pattern is first formed on a conductive substrate by plating. Areas, which are not intended to be plated are covered with a resist. In the next process step, a second substrate, which has adhesive on its surface, is brought into a contact with the electrically conductive pattern, which is heated above the glass transition temperature of the adhesive by a suitable energy source in such a manner that the adhesive melts when it is in contact with the electrically conductive pattern. The electrically conductive pattern adheres to the adhesive and when the adhesive cools down, the joint between the electrically conductive pattern and the adhesive becomes firm. The conductive substrate can be an aluminium foil and the second substrate can be a fibrous substrate, such as paper. The adhesive is a hot melt adhesive. The electrically conductive pattern is preferably of copper.

In the fourth embodiment of the invention, an electrically conductive pattern is first formed on a surface of a plating drum. In the next process step, a second substrate, which has adhesive on its surface, is brought into a contact with the electrically conductive pattern, which is heated before contacting the second substrate above the glass transition temperature of the adhesive by a suitable energy source in such a manner that the adhesive softens when it is in contact with the electrically conductive pattern. The material of the second substrate can be paper, polyester or polypropylene. The adhesive is a hot melt adhesive. When the electrically conductive pattern is contacted with the second substrate, the electrically conductive pattern starts to cool, and the adhesive crystallizes. As a consequence, the electrically conductive pattern adheres to the second substrate. The second substrate is preferably in a web form, which makes it is easy to convey successive electrically conductive patterns from the plating drum along the web.

In the fifth embodiment of the invention, an electrically conductive pattern is formed of a metal foil, preferably copper foil. The electrically conductive pattern is for instance punched or cut by laser but it continues its travel with the rest of the metal foil supported by a belt or a like. The metal foil may be heated selectively in such a manner that only the temperature of the electrically conductive pattern rises above the glass transition temperature of the adhesive. Another option is that the whole metal foil is substantially at the same temperature. In the next process step, a second substrate, which has adhesive on its surface, is brought into a contact with the electrically conductive pattern. The electrically conductive pattern adheres to the second substrate firmly when the adhesive starts to cool. The material of the second substrate can be paper, polyester or polypropylene. The adhesive is a hot melt adhesive.

According to the sixth embodiment of the invention, an electrically conductive pattern is formed of a laminate comprising a metal foil and a non-metallic web. The laminate serves as an application substrate. The metal foil is preferably of aluminium and the non-metallic web preferably comprises polyethylene terephtalate. The metal foil and the non — metallic web are attached together by using an adhesive, preferably a hot melt adhesive. The hot melt adhesive is preferably based on ethylene vinyl acetate (EVA). The melting point of EVA can be adjusted by adjusting the amount of ethylene. Besides EVA, many other adhesives can be used.

The electrically conductive pattern is punched in such a manner that the metal foil is cut but the non-metallic web remains untouched. Suitable punching methods are for example mechanical punching or punching by laser.

After punching the laminate may be heated selectively in such a manner that those parts of the laminate, from which the metal foil is due to be removed, are heated. The heating softens the adhesive and thus the foil can be removed, and the punched electrically conductive patterns remain in their places. The great advantage of this embodiment compared to prior art methods is that the metal foil can be removed as a continuos web. It is also possible that the whole laminate is substantially at the same temperature.

The method according to the sixth embodiment of the invention is best suitable for manufacturing of the UHF antennas.

Example 1.

A graphite plate and a circuitry pattern on a surface of the graphite plate were heated by induction heating approximately 10 seconds. Temperatures were measured every second during the heating period. The induction heating step was accomplished by an induction coil. The output capacity of the coil was 500 W and the used frequency 400 - 450 kHz. The distance between the induction coil and the graphite plate was 28 mm.

As seen from the results in table 1 , in the end of the heating period the temperature difference between the circuitry pattern and the graphite plate was almost 3°C.

Table 1. Temperature difference created between the circuitry pattern and the graphite plate.

Example 2.

A graphite plate and a circuitry pattern on a surface of the graphite plate were heated by induction heating approximately 10 seconds. Temperatures were measured every second during the heating period. The induction heating step was accomplished by an induction coil. The output capacity of the coil was 500 W and the used frequency 400 - 450 kHz. The distance between the induction coil and the graphite plate was 31 mm.

As seen from the results in table 2, in the end of the heating period the temperature difference between the circuitry pattern and the graphite plate was almost 3°C.

Table 2. Temperature difference created between the circuitry pattern and the graphite plate.

Example 3. A borium nitride plate and a circuitry pattern on a surface of the borium nitride plate were heated by induction heating approximately 10 seconds. Temperatures were measured every second during the heating period. The induction heating step was accomplished by an induction coil. The output capacity of the coil was 500 W and the used frequency 400 - 450 kHz. The distance between the induction coil and the borium nitride plate was 5 mm.

As seen from the results in table 3, in the end of the heating period the temperature difference between the circuitry pattern and the graphite plate was 7.5 °C.

Table 3. Temperature difference created between the circuitry pattern and the borium nitride plate.

Example 4.

A borium nitride plate and a circuitry pattern on a surface of the borium nitride plate were heated by induction heating approximately 10 seconds. Temperatures were measured every second during the heating period. The induction heating step was accomplished by an induction coil. The output capacity of the coil was 500 W and the used frequency 400 - 450 kHz. The distance between the induction coil and the borium nitride plate was 2 mm.

As seen from the results in table 3, at its highest the temperature difference between the circuitry pattern and the graphite plate was 20.2 °C.

Table 4. Temperature difference created between the circuitry pattern and the borium nitride plate.

In Fig. 1 is shown an example about a transponder. The transponder comprises an application substrate 1 , a circuitry pattern 2, an integrated circuit on a chip 3 and an electrically insulating pattern 4, which is formed between electrically conductive leads to prevent short circuits. The circuitry pattern is in this example a coil antenna but antennas based on dipole antenna technique are as well possible. The chip 3 can be attached directly to the application substrate, or it can be attached to the application substrate with a module comprising the chip 3.

In Fig. 2 is shown a part of a process line according to the first embodiment of the invention. A web comprising hot melt adhesive on its surface is unwound from a roll 5, and brought into contact with an application substrate. The application substrate is in this case a heat resisting plate 7, for example a graphite plate or a borium nitride plate. On the surface of the plate there is at least one circuitry pattern, which is heated in such a manner that the circuitry pattern reaches a higher temperature than the heat resisting plate. A device (not shown), which is used for heating, can be for example an induction coil.

In Fig. 3 is shown a part of a process line, which covers in principal the second, third and the fifth embodiment of the invention. A web comprising hot melt adhesive on its surface is unwound from a roll 5, and brought into contact with an application substrate. The application substrate is in this case a web 8, which advances forward continuously. The web 8 can be for example of the type described in Figs. 5a and 5b, but it can also be a metallic foil from which circuitry patterns are cut in a continuous manner. For the webs of the latter type the belt arrangement comprising an endless belt 9 rotating around two rolls 10 is advantageous because the belt 9 supports the circuitry patterns from underneath. For the webs shown in Figs. 5a and 5b a simple counter roll forming a nip N1 with the roll 6 is in most cases sufficient. Each circuitry pattern is heated to a temperature, which exceeds temperatures of the surrounding material or materials. A device (not shown), which is used for heating, can be for example an electromagnetic radiation source.

In Fig. 4 is shown a part of a process line according to the fourth embodiment of the invention. Circuitry patterns are formed on a surface of a plating drum 11.

In Fig. 5a is shown a cross section of a web 8 according to the second embodiment of the invention. A multilayer web comprising a copper foil 12, a hot melt adhesive layer 13 and a backing web 14 of polypropylene is first etched in such a manner that circuitry patterns are formed.

In Fig. 5b is shown a cross section of a web 8 according to the third embodiment of the invention. A resist coating 16 is formed on the surface of an electrically conductive foil, such as an aluminium foil 17, except an area determined by a shape of a circuitry pattern 15. The circuitry pattern is formed to that uncoated area by plating. The circuitry pattern 15 is preferably of copper.

In Fig. 6 is shown a process line according to the sixth embodiment of the invention. A metal foil, for example an aluminium foil having a thickness of 9 μm, is unwound from a roll 21. A non-metallic web, such as a heat stable web having a thickness of 50 μm and comprising polyethylene terephtalate (PET), is unwound from a roll 22. An adhesive, for example a hot melt adhesive comprising ethylene vinyl acetate (EVA), is applied on the surface of the non-metallic web. The amount of adhesive is between 2 and 20 g/m², typically between 25 and 8 g/m². The manner of the application can be any suitable method, such as the extrusion, the roll application, or the blade coating. In Fig. 6 there is an extruder 23. The metal foil and the non-metallic web are attached together in a nip N2 which is formed by two rolls. The metal foil, the adhesive and the non-metallic web forms a laminate which serves as an application substrate.

Electrically conductive patterns are separated from the metal foil in a nip N3 by a die cutting method. It is possible that between the nips N2 and N3 there are other process steps but their contents depend on the desired end products.

In the nip N3, one of the rotating rolls forming the nip is provided with a punching tool. The punching tool punches the metal foil in such a manner that the non-metallic foil remains untouched. The die cutting process has a servo-assisted steering. Besides the mechanical punching it is possible to use for example the laser cutting. The laminate comprising the punched metal foil, the adhesive and the non-metallic web is led to the next process step in which the excess metal foil is removed. In other words, the electrically conductive patterns remain on the surface of the non-metallic web and the rest of the metal foil is removed. That takes place around a nip N4. One of the rolls forming the nip N4, preferably the upper roll 25 (the metal foil conducts heat well), is heated by an infra-red lamp 24. Instead of the infra-red lamp 24 and the roll 25 can be used a heated engraved oil- filled roll which produces more even heat distribution but the technical solution is more expensive. The heated surface of the roll 25 increases the temperature of the adhesive. The roll 25 has engraved portions on its surface in such a manner that the electrically conductive patterns meet the engraved portions when the electrically conductive patterns are not heated (the engraved roll 25 has the negatives of the electrically conductive patterns on its surface). The engraved portions can be manufactured by using the techniques which are known in connection with the devices used for the rotogravure printing. Another possibility is to make protrusions on those areas which are intended to be heated. Still another option is to use a roll having an ordinary smooth surface without any height differences; This option is suitable for simple patterns. The roll 25 has a servo control. When the adhesive is selectively heated it is easy to peel the excess metal foil from the laminate. The excess metal foil is wound to a roll 26 and the ready web comprising the electrically conductive patterns is wound to a roll 27.

In Fig. 6 the process is shown as a single process line but it is possible that for example the laminate is first manufactured on a separate process line, wound to a roll, transferred to another process line and unwound.

The invention is not restricted to the above-mentioned embodiments. Some process steps, devices and materials included into the invention may be combined differently to form a new embodiment belonging to the scope of the invention. The adhesive layer, which receives the electrically conductive pattern, is not necessarily a hot melt adhesive but can be as well another thermoplastic material, which softens adequately when heated. Such materials are for example amorphous polyester terephthalate (APET), ethylene vinyl acetate (EVA), low density polyethylene (LDPE) and high density polyethylene (HDPE). The above mentioned materials can form alone an application substrate without any excess backing material.

Claims

Claims:

1. A method for processing an electrically conductive pattern (2) comprising i - forming the electrically conductive pattern on a non-adhesive surface of a carrier substrate (7, 11 , 17), or forming the electrically conductive pattern by separating the electrically conductive pattern from a carrier substrate (8) consisting of a metallic foil,

• heating the electrically conductive pattern (2), and

- transferring the electrically conductive pattern (2) to an application substrate (1), which comprises material, which softens when the heated electrically conductive pattern is brought into contact with the application substrate, thus causing the electrically conductive pattern to adhere to the application substrate (1 ).

2. The method according to claim 1 , characterized in that the application substrate comprises thermoplastic material.

3. The method according to claim 1 or 2, characterized in that the application substrate comprises hot melt adhesive.

4. The method according to any preceding claim, characterized in that the electrically conductive pattern is heated by heat convection, heat conduction, electromagnetic radiation, or magnetic or electric field induced heating.

5. A method for processing an electrically conductive pattern (2) comprising

- forming the electrically conductive pattern by cutting a metal foil forming the outmost layer of an application substrate, which is a laminate (28) comprising the metal foil, an adhesive and a non-metallic web, the adhesive being of material which softens when heated, - heating the application substrate, and

- removing the rest of the metal foil (29).

6. The method according to claim 5, characterized in that the application substrate comprises hot melt adhesive.

7. The method according to claim 5 or 6, characterized in that the rest of the metal foil is heated by heat convection, heat conduction, electromagnetic radiation, or magnetic or electric field induced heating.