CH659428A5 - METHOD FOR RELAXING AND / OR STABILIZING AGAINST THE DEVELOPMENT OF TENSION CRACKS OF AN AT LEAST PARTIAL OBJECT OF A POLYMER. - Google Patents

Description

The present invention relates to a method of treating objects which are at least partially made of polymer with radiation in order to reduce stresses occurring in the polymer and / or to protect the polymer against cracks occurring as a result of stress. The method is of particular interest in order to relax a polymer material very quickly in the manufacture of printed circuits or to protect it against the formation of stress cracks.

It is known to electroplate various plastics such. B. for decorative purposes by using strong oxidizing agents such as e.g. Chromic acid, chemically pretreated. The plastics suitable for this include acrylic-nitrile-butadiene-styrene copolymers (ABS), polyphenylene oxides (PPO), polysulfones, polyether sulfones, polycarbonates and nylon. Some of these plastics do not withstand the usual soldering temperatures of around 260 ° C. So ABS has z. B. at room temperature only a bond strength of 1N mm "1 and a softening point, which is 80 to 100 ° C. A printed circuit board made of ABS is consequently not resistant to the temperature required for soldering.

The use of thermoplastics as a base material for printed circuits has found only limited use, since many of the inexpensive materials are unable to cope with the chemical stresses of the pretreatment and plating baths used for the production of printed circuits. Often it is not these chemical processes themselves, but the stresses when attaching the components, when soldering and then removing the excess solder with solvents, as well as when cleaning with detergents, which preclude the use of the materials in question. A thermoplastic suitable for printed circuits should be able to withstand the chemical stresses that occur during its manufacture, to be processed with existing machines, to be soldered and easy to clean, and to be a useful dielectric.

Many extruded or cast high temperature resistant thermoplastic polymer films, sheets or other objects have to be relaxed after each mechanical treatment step. So z. B. drilling, machining and edge trimming can cause the polymer to bubble or crack.

Because of the great processing difficulties and the high price, the use of high temperature resistant thermoplastics such as. B. with copper coated polyetherimide plates as the base material for printed circuits found no widespread use.

The present invention relates to an improved method for the above-mentioned purpose, which is defined in claim 1.

The method is suitable for the treatment of objects made of a high-temperature-resistant thermoplastic material which has an aromatic backbone, such as aromatic ones

Polyether polymers. It allows relaxation without annealing the polymer and without mounting it between support plates and without its physical deformation. The method also permits the treatment of objects which have a polymer surface laminated or glued to a base material.

In the context of this invention, the formulation “aromatic polyether polymers” comprises thermoplastic polymers which are characterized by repeating aromatic and ether units, such as, for example, B. polyetherimides and polyether ether ketones.

The term “high-temperature-resistant thermoplastic polymers” encompasses polymers with an aromatic backbone that do not liquefy at the temperature mentioned. The polymer has a heat resistance of at least 170 ° C. In order to achieve the aforementioned object of the invention, to relax an object made entirely or partially of a polymer, this is subjected to a method in which it is treated with electromagnetic radiation of one or more frequencies in the microwave, infrared or ultraviolet range, which can be absorbed by the object. This process relieves the stresses, with neither softening, liquefaction or deformation of the polymer occurring in the period of time required to relax or stabilize the polymer.

The article can consist of a high temperature resistant thermoplastic polymer which can be extruded or cast and can be in the form of a sheet, blank, foil or in any other geometrical form. Stress cracks in the material can result from extrusion, casting, metal plating, mechanical treatment, swelling or etching, or from one of the other chemical treatment steps described below.

It has been found that when polymers are relaxed by treatment with infrared, UV and / or microwave rays, no appreciable heat development occurs, and the effect of the treatment is therefore not based on such. Since no heat is generated in the relaxation method according to the invention, there is neither softening or liquefaction nor physical deformation of the polymer, which is why the process can be carried out without the use of supporting and holding devices, etc., as must be used in known processes.

The present invention also enables improved manufacturing of circuit boards, metal-coated insulating boards, printed circuits, etc.

The polymer should have a thickness of at least 75 µm and preferably at most 6.250 µm.

The present invention describes a simple and inexpensive method for producing an insulating base material, which is a high temperature resistant thermoplastic polymer such. B. includes an aromatic polyether polymer and has a surface that can be provided by electroless metal deposition with a layer or pattern of metal. The process for producing the circuit board or the base material made of the polymer includes the following steps:

(1) Treating the polymer film, the film or the plate with electromagnetic radiation in one or more frequency range (s) which can be absorbed by the material mentioned and which is suitable for relaxing it without any heat-related softening or Liquefaction of the material occurs and for a sufficiently long period of time to ensure the energy absorption required to relax the polymer and to protect it from cracking by stresses, the electromagnetic radiation being selected from the microwave, infrared or UV range;

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(2) mechanical treatment of the polymer film, the film or the plate to produce holes;

(3) repetition of the irradiation after the aforementioned and all subsequent mechanical processing steps;

(4) chemical treatment of the surface of the polymer film, the film or the plate with a polar solvent which is suitable for swelling this outer surface;

(5) Treat the surface of the polymer film, sheet or plate with a strong oxidizing solution or other agent or with plasma at a temperature and for a period of time sufficient to anchor the surface to it electrolessly and / or to prepare galvanically deposited metal layer.

The present invention also includes a method of making laminates for printed circuit boards. This method involves laminating a radiation-treated polymer film or sheet of uniform thickness, preferably greater than 75 µm, to a sheet of reinforced thermosetting material, either by using an adhesive layer between the two layers, or by applying pressure and temperature, or both together ; and further the treatment of the laminate in order to produce one or more holes by mechanical or other means and the treatment of said laminate with electromagnetic radiation of one or more frequency ranges, so that the polymer film or the plate can absorb a sufficient amount of energy to relax it, in order to be protected against stress-related cracking without the material being deformed by softening or liquefying under the influence of heat in the time required for this.

According to the present invention it is also possible to manufacture plates for multilevel printed circuits, this method, starting from a carrier plate with a circuit pattern on at least one side, including the following steps;

(1) laminating a high temperature resistant thermoplastic polymer film or sheets to the metal coated base material surface;

(2) making one or more holes in the laminate;

(3) Treatment of said polymer film or film with infrared or UV radiation in one or more frequency ranges, which can or can be absorbed by the polymer in order to relax it, without any significant heating occurring, which leads to Deformation of the polymer material through softening or liquefaction; the irradiation takes place over a period of time sufficient to relax and / or stabilize the polymer film or film against cracking;

(4) treating the polymer surface with a solvent and an oxidizing agent to make them microporous and hydrophilic;

(5) repeating said irradiation step;

(6) Form a second circuit pattern by metal deposition on the treated surface and in the holes.

In a preferred embodiment, the thermoplastic polymer film or film should have a thickness of at least 75 (xm.

The second conductor pattern can be made by electroless plating, which may or may not follow electrodeposition, or by another known method.

Aromatic polyether polymers are high-temperature-resistant thermoplastic polymers that have an aromatic backbone and do not liquefy or decompose after 5 seconds at a temperature of approx. 245 ° C.

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The relaxed polymeric workpieces to be used in the context of the present invention can be processed further.

the aromatic polyether polymers include polyetherimides. In the case of manufacturing printed circuits and polyether ether ketones. the holes can be made by drilling or punching

It has turned out that records and films are getting high.

temperature-resistant polymers of lengthy tempering processes. 5 A microwave treatment according to the present invention.

gears are required to prevent stress cracking. So dung can also be used instead of in the previously known method. B. known, the polyetherimide after gluing a second annealing used with equally good results

Require an annealing time of 2 to 4 hours at 200 ° C. Des be applied. The prefabricated workpiece can be determined by further that materials of the type of the aroma- the microwave radiation are relaxed, z. B. for table polyether after the mechanical manufacturing steps io a 1.6 mm thick layer an irradiation time of 30 min and before the electroless metal deposition is required. The treatment according to the invention makes it necessary to avoid the formation of stress cracks due to the workpiece being dimensionally stable and resistant to excessive swelling and the oxidation process. subsequent chemical and necessary for metallization

Tensions in the polymer plates also occur during the drilling of the treatment steps and thus dispense with the

holes close to each other, such as those used for 15 long annealing processes.

modern, highly integrated circuits are required, where 7 to In another embodiment of the invention

20 holes of 1 mm diameter with a distance of the process is infrared radiation, such as z. B. for curing

Hole centers of 2.54 mm are drilled. , of masks in the manufacture of printed circuits

When solvent treatment is used to swell the surface, to relax the polymeric material, stress corrosion occurs in the polymer plate, which is used to 20.

Cracks in the plate or to break them apart For this purpose the polymer can lead to infrared treatment. This can result in additional voltages being exposed in an infrared continuous furnace. Because of the brief fact that the polymer body occurs during the swelling in the period of the infrared radiation according to the invention,

Racks or held with brackets. If, unlike the previously known baking processes, the

Pour the rest of the workpiece or the rest of the workpiece due to mechanical stress and this does not have to be between

Tension not removed before swelling accelerates which are clamped by metal plates. With infrared radiation the brackets generated additional tension the voltage will cause the polymer material to be irradiated in the wavelength range

corrosion. range between 2.5 and 50 [xm, preferably between 6 and

It has been found that the stress corrosion at a thin 20 | xm, over a period of at least 35 seconds at a

Polyetherimide layers of e.g. B. 0.4 mm substantially pronounced 30 1.6 mm thick polymer material. The irradiation time is ter than for thicker layers of z. B. 1.6 to 3.2 mm. Thin also depends on the thickness of the treatment

Layers break and tear under the influence of the polymer material, whereby thicker materials have longer exposure times.

Stress corrosion much easier than thicker ones. Require different delivery times.

Type of stress cracking is the appearance of fine. In another embodiment of the present invention

Surface cracks that only appear after the surface has been provided are irradiated with UV.

surface with a layer of metal. These cracks During the treatment according to the invention generally only show up in the metal layer and make it possible to use it either with infrared, ultraviolet or microwave radiation.

impossible as a metallic conductive surface. There are exceptions to this.

As already mentioned, in the prior art methods, printed circuit boards are e.g. According to the so-called technology, an additional lengthy baking process is produced using 40 so-called “semi-additive” processes. The insulating material - the machining of the material and before the plate for the plate according to the present invention is cut - the subsequent metal deposition is necessary and requires microwave, infrared or UV with a wave. The advantages of irradiating rigid, cast aromatic poly lengths, which can be absorbed by the polymer, are of great importance for the users who are strict. Then holes in the plate will have to be met by drilling, punching or high-frequency application requirements Process manufactured. Alternatively, the holes can be sen. In such cases, the material is ideally suited to being present in the untreated panel. However, since one requires the complex baking processes in order not to be able to pre-process such a pre-perforated plate. consequently, it does not have to be subjected to the process before the polymer treated according to the new process is relaxed. After the relaxed and / or stabilized so that it is provided with holes 50 holes, the plate is irradiated with microwaves, infra and then the various oxidation and swelling agents with suitable red or UV rays, which by tel- Solutions, etc. can be exposed without chip being absorbed by the polymer. Then the cracking occurs. In addition to the very quick relaxation plate pre-treated for metallization, such as. B. Dipping in and stabilizing the polymer, there is an additional advantage of a dimethylformamide solution for 3 to 6 min and subsequent present invention in that the risk of deforming the etching at 55 to 65 ° C. results in a strong oxidizing agent in the workpieces is largely excluded. Solution for 3 min. Through these treatment steps, the

According to one embodiment of the present invention, the surface of the plate is previously matt and the workpiece is formed from aromatic polyether polymer. Micro-spots that form a firm mechanical and / or chemical process

Wave frequencies of more than 1,900 megahertz, preferably core of the subsequently deposited metal layer, ensure

those in the range from IO8 to 1016 Hertz, in a microwave oven.

exposed oven to relax it. In contrast to the prior art, a thin metal layer is then de-energized on the th method, the microwave treatment reduces the temperature of the plate surface and the deformations caused by the door on the perforated walls, and makes use of and then on the plate provided with the metal layer

Metal plates, etc., as printed on the circuit patterns which are usually desired when they are baked out for fixing, either and are necessary, are superfluous. The duration of the microwave exposure after the photoresist process or by applying the treatment is relatively short and is between 1 and 60 min, with negatives of the circuit pattern in the screen printing process. The

30 minutes for a material thickness of 1.6 mm are typical; it changes circuit pattern then becomes galvanic with copper or copper depending on the material thickness. After the microwave treatment and another metal to the desired layer thickness

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reinforced. Then, if desired, the circuit pattern can be tinned. The masking varnish is then removed and the thin, electrolessly deposited metal layer thus exposed is removed by etching.

In the present method, the base material can also have continuous catalytic properties, namely if e.g. B. in the manufacture of the thermoplastic surface Sim suitable materials are built into this. In the context of the present invention, the polymers defined above are referred to as base material or laminate.

In one embodiment of the invention, the carrier materials provided with a thermoplastic surface layer according to the invention can organic or inorganic materials such as. B. glass, ceramics, porcelain, resins, paper, fabrics, etc. The base materials used for printed circuits include thermosetting resins, thermoplastic resins and mixtures thereof, and glass fiber material, impregnated paper, etc.

The present invention is explained in more detail below with reference to the drawings, which illustrate some embodiments of the invention.

1 to 3 illustrate methods of making printed circuit boards from insulating material in accordance with the teachings of the present invention.

Figure 1A shows the catalytic base material 10 consisting of an aromatic polyether polymer such as e.g. Polyetherimide or polyetheretherketone. The polymer base material is sensitized for electroless metal deposition. Before drilling the holes, the base material 10 is irradiated with microwaves at a frequency of more than 1.960 megahertz for 30 minutes.

In Fig. 1B, the base material 10 is provided with the holes 16 and 18.

After the holes have been made, the plate 10 is again irradiated with microwaves, as described above, then immersed in a solvent and then in a solution of 20 g / 1 Cr03,500 mg / 1 H2S04 and 25 g / 1 NaF at a temperature between 45 and 65 ° C chemically treated to expose the catalytic material and make the surface microporous and hydrophilic (Fig. IC).

A permanent photo mask 24 is applied to the base material 10 and covers those areas that should not be copper-plated (FIG. 1D).

Subsequently, copper is electrolessly deposited on the hole walls of holes 16 and 18 as well as on the exposed parts of the surface by generally known methods, whereby the conductor pattern 22 is formed (FIG. IE). A solder mask 30 is applied in FIG. 1F.

2A to 2E illustrate the use of the full additive process for the production of printed circuit boards, FIG. 2A showing the base material 10 consisting of a polyetherimide polymer.

2B, the base material 10 is provided with a hole 16. Before and after the hole 16 is made, the plate 10 is irradiated with microwaves, depending on the thickness of the material and the frequency used, for 1 to 25 minutes, as described in connection with FIG. 1. As a result, the base material 10 is relaxed without significant heat being generated, which could lead to the deformation of the polymer. The base material 10 and the walls of the hole 16 are pretreated as described above and then completely coated with a copper complex 20 that can be reduced by UV radiation and dried (FIG. 2C).

By briefly projecting or contact printing, an image of the conductor pattern is brought onto the surface made so sensitive to radiation with UV light. The unexposed areas of the layer 20 are then washed off and the image 22 is fixed by briefly immersing it in an electroless copper depositing bath (FIG. 2D).

The copper conductor pattern including the walls of the hole 16 thus formed is reinforced by electroless copper deposition to the desired layer thickness of the conductor pattern 28.

5 In FIGS. 3A to 3F, the metal is electrodeposited, the base material plate 10 consisting of polyether ether ketone being shown again in FIG. 3A. Both before and after the holes have been made, the base material 10 is irradiated for 1 min or shorter with infrared of a wavelength between 2.5 and 40 Jim in order to relax it without significant heat generation and consequently without deformation or liquefaction of the polymer. The duration of the infrared radiation depends on the thickness of the base material 10. The base material 10 is then pretreated for about 3 to 6 minutes in dimethylform-15 amide and for about 3 minutes at 35 to 70 ° C. in a strong oxidizing agent solution or a strongly oxidizing gas phase. As a result, the previously shiny surface of the base material 10 becomes matt and spots are formed which guarantee firm mechanical and / or chemical anchoring 20 of a subsequently deposited metal layer.

In order to sensitize the pretreated base material 10 for electroless metal deposition, it is immersed in a solution containing the reaction product of SnCl2 and PdCl2 at room temperature for 1 to 3 minutes. During this treatment 25, catalytically active germs 20 (FIG. 3B) are formed on the entire surface, including the perforated walls (not shown).

According to a known method, a metal layer 22 is electrolessly deposited on the entire surface including the hole wall (not shown) fertilizing the base material 10 (FIG. 3C).

After the photoresist process, a desired conductor pattern is printed on the metal layer 22. A light-sensitive coating 24 is applied to the entire surface of the base material 10 and exposed to UV; a mask 26 is formed which leaves the areas corresponding to the conductor pattern to be produced free (FIG. 3D). The conductor pattern thus produced is galvanically built up with copper 28 until the desired layer thickness is reached (FIG. 3E). The protective mask is then removed and the then exposed thin, electrolessly deposited copper layer is etched off (FIG. 3F).

The following examples show some embodiments of the present invention.

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example 1

An extruded polyetheretherketone film 1 mm thick

50 is treated as follows:

(1) Two mounting holes are drilled to hold the film in place during processing;

(2) the film is irradiated with microwaves of 2.450 megahertz for 1 min in the microwave oven;

55 (3) the film is immersed in a bath of a dimethyl-water mixture (specific density between 0.955 and 0.965) for 3 to 6 min;

(4) the film is immersed in a 1% aqueous solution of an anionic wetting agent, such as, for example, nonylphenol

60 nylpolyäthoxyphosphat, at a temperature of 35 to 45 ° C for 5 to 60 sec;

(5) the film is immersed in a solution of 100 ml / l phosphoric acid, 600 ml / l sulfuric acid and 0.05% of an anionic perfluoroalkyl-sulfonate at 55 ° C for 5 min;

65 (6) then the film is treated for 5 min in a solution of 400 g / 1 Cr03, 250 ml / 1 sulfuric acid, 50 ml / 1 phosphoric acid and 0.5 g / 1 of an anionic perfluoroalkyl sulfonate at 70 ° C and in a water basin rinsed;

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(7) the film is immersed in a solution of 40 ml of 35% hydrogen peroxide and 10 ml of 96% sulfuric acid and rinsed in water;

(8) the film is treated with an alkaline cleaner and rinsed again in water;

(9) the film is successively immersed in a tin (II) chloride-sodium chloride solution and an activator solution of tin (II) chloride and palladium (II) chloride, then rinsed in water and in an accelerator solution made of 5% fluoro -treated boric acid;

(10) Copper is deposited without current up to a layer thickness of 2.5 [xm;

(11) the copper-plated film is rinsed in water and dried at 125 ° C for 10 min.

Thus, the copper-plated extruded film shown in Fig. 3C is produced.

A copper layer to a thickness of 35 μm was deposited galvanically on the pre-coppered film, the peel strength of which was 2.6 N / mm. After a solder bath float test at 288 ° C for 20 seconds, the surface showed neither blistering nor detachment of the copper layer.

Example 2

The procedure of Example 1 is repeated with an extruded polyetherimide film 1.6 mm thick. The peel strength was 1 N / mm and the sample survived a solder bath float test at 260 ° C for 10 seconds.

Example 3

Panels are cast from polyetherimide, which contains 0.12% titanium dioxide as a pigment to make the board opaque. For some boards, 10% glass fiber filler was added to the material, while for other boards, a mineral filler was added in addition to the glass fiber filler to reinforce the base material. The cast base plates were treated in accordance with the process steps given in Example 1, the exposure time being reduced to 3 minutes in process step (6).

In accordance with the process according to CH-PS 587 352, a printed circuit diagram was applied to the surface, the copper conductor strips of which had a thickness of 35 μm. The plates were dried for 1 hour at 160 ° C. The values measured for the peel strength are in the following table compiled:

Base material composition Peel strength

Polyetherimide + 0.12% Ti02 1.75 N / mm Polyetherimide + 0.12% Ti02

+ 10% glass fiber filler 1.40 N / mm polyetherimide + 0.12% Ti02

+ 10% glass fiber filler + mineral filler 1.20 N / mm

Example 4

A printed circuit was produced on an extruded polyetherimide using the semi-additive method. The plate was first cut to the desired size, relaxed according to the present invention and then provided with the hole pattern. The plate was then treated in accordance with process steps (2) to (11) from Example 1. After applying a plating mask corresponding to the negative of the desired conductor pattern by one of the known printing processes, copper was electrodeposited to the desired thickness in the areas not covered. After the mask was removed, the exposed, thin, electrolessly deposited copper layer was removed, and the desired conductor pattern including the perforated wall metallization was thus produced. The peel strength of the copper layer was 1 N / mm.

Example 5

The starting material used was an epoxy glass laminate laminated on both sides with a copper foil 35 μm thick, on which a conductor pattern was first produced in a known manner using the printing and etching technique.

A polyetherimide adhesive was prepared by dissolving polyetherimide granules in methylene chloride and a 75 [in the thick polyetherimide film was coated on one side with this adhesive and with a roll laminator with heated silicone rubber rolls at 75 ° C., a pressure of 15 N / mm board width and a throughput speed of 20 mm / min are laminated onto the side carrying the conductor pattern. The holes were then produced, the walls of which are metallized in the finished record, the laminate being irradiated with infrared with a wavelength of 2.5 to 40 μm for 35 seconds in an infrared reactor both before the holes were made and afterwards according to the invention so as to relax the polyetherimide film. The plate was then treated in accordance with Example 1 and a multilevel circuit was produced, the exposure time being reduced to only 2 minutes in step (6).

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Claims (15)

659 428 PATENT CLAIMS 1. A method for relaxing and / or stabilizing against the formation of stress cracks from an object consisting at least partially of a polymer, characterized in that the polymer is a thermoplastic and the 5 object is electromagnetic radiation from the microwave, infrared or UV range is exposed in such a way that one or more frequencies of the radiation are or are absorbed by the thermoplastic, as a result of which the object is relaxed and / or stabilized without causing significant heating and thus softening of the thermoplastic. 2. The method according to claim 1, characterized in that the object is such as is obtainable by extrusion or in the casting process from a thermoplastic with an aromatic framework, the liquefaction or decomposition temperature of which is above 245 ° C. 3. The method according to claim 2, characterized in that the thermoplastic is selected from aromatic polyether polymers, e.g. made of polyetherimides or polyether clays - 20 tones. 4. The method according to claim 2 or 3, characterized in that the object is provided with perforations and openings. 5. The method according to any one of the claims 3, 25, characterized in that the object is exposed to infrared radiation of a wavelength between 2.5 and 40 [im. 6. The method according to claim 2 or 3, characterized in that the object is a polymer film, a polymer sheet or a polymer carrier of certain dimensions. 30th 7. A process for the production of supports for printed conductor arrangement, characterized in that an object obtained by the process according to claim 6 is provided with perforations, that the treatment with electromagnetic radiation is repeated thereupon, that the surface of the thermoplastic with 35 send polar solvent and then treated with a strong oxidizing agent so as to make the surface microporous and wettable and thus suitable for firmly mechanical and / or chemical anchoring of a metal layer on it. 40 8. A process for producing a laminate for printed circuit boards, characterized in that a film obtained by the process according to claim 6 is applied to a carrier, so that a laminate is formed, that the laminate is provided with a perforated pattern, and that the film 45 or the laminate is then subjected to the radiation treatment again. 9. The method according to claim 8, characterized in that the film has a thickness of at least 75 jtm. 10. The method according to claim 8 or 9, characterized in that the carrier consists of a hardened synthetic resin or of a laminate containing such a synthetic resin. 11. The method according to any one of claims 8 to 10, characterized in that the film is laminated under the influence of heat and pressure. 12. A method for producing a printed multilevel printed circuit board, characterized in that firstly a carrier is provided with a conductor pattern on at least one side, and then its surface (s) including the conductor pattern is covered by applying a film made of a thermoplastic that a hole pattern is then produced and then the laminate is exposed to the process according to one of the claims 1 to 3, that the surface is then treated with a solvent and then with a 65 etchant in order to use it for the solid Prepare the anchoring of a metal covering, that the radiation treatment is repeated thereon and then that Surface (s) including the perforated walls are provided with a metal layer. 13. The method according to claim 12, characterized in that the entire surface is provided with the metal layer and this is then converted into a conductor pattern. 14. The method according to claim 12, characterized in that the metal layer is applied in the form of the corresponding conductor pattern. 15. The method according to any one of claims 12 to 14, characterized in that the steps from laminating the film to producing the corresponding conductor pattern are repeated in accordance with the desired number of levels.