Process for making contact bands on substrates, especially on panes, and panes made by this process.

p0001The invention relates to a method for the manufacture of contact strips on substrates, and in particular slices of mineral glass, with an electrically conductive surface coating, which is coated on the side facing away from the substrate with at least a surface layer of a dielectric material.

p0002The products of such a process are used, especially when the substrates are made of mineral glass, often. As front or rear windows of motor vehicles The electrically conductive surface coating, which thereby usually consists of a thin metal layer having high transparency in the visible region of the light spectrum may be used as a heating resistor, to defrost icing and vaporize deposits of condensed water. It is therefore necessary to provide the resistive layer with corresponding terminal contacts that ensure uniform distribution of the heating over the entire substrate surface and prevent local Oberhitzung immediate post area.

p0003Particularly, it is additionally desirable in automotive glazing, that the surface coating the longer wavelength portion of the spectrum of the sunlight reflected, the so-called heat radiation. This thermal radiation is particularly undesirable in modern passenger cars with slanted and therefore large windshield and rear window, because they can heat the interior of the motor vehicle to unbearable temperatures.

p0004Discs, including those made of mineral glass, with a corresponding spectral transmission and reflection behavior by the EP-PS 35 906, DE-OS 33 07 661 and EP-OS 104 870 known. In the known discs is a silver layer having on one or both sides of a diffusion barrier made of a thin metal layer sandwiched between two oxide layers, one of which is a surface layer which protects the metal layers against chemical and / or mechanical attacks. While the metallic layers, in particular the silver layer, a sufficient electrical conductivity to serve as a heating resistor can (at least as long as the disc is not heated to temperatures above 150 ° C), the oxide surface layer of a pronounced insulator represents the prevents contact of the underlying metal layer or metal layers. It is extremely troublesome to remove the relatively hard, oxide surface layer in a defined thickness in order to provide the underlying metal layer having contact paths can.

p0005The invention is therefore based on the object of specifying a method for the manufacture of contact strips on substrates of the kind described above, which leads to a reliable and stable contact between the electrically conductive surface coating.

p0006The solution of the stated problem is accomplished according to the invention in the method mentioned at the outset by applying to the surface layer (of a dielectric material) applying a precious metal suspension in a liquid in accordance with developments of the contact strips and exposes the substrate to a heat treatment at least 100 ° C until through the conductive surface coating by means of the contact paths, a reduced total resistance occurs.

p0007Such noble metal suspensions are commercially available, for example under the name "conductive silver 200" by the company Demetron in Hanau / Germany.

p0008It is through the book by Dr. AF Bogenschütz "surface technology and electroplating in the electronics", Eugen G. Leuze Verlag in Saulgau / Württemberg, edition 1971, page 298, known to use pasty suspensions of finely divided silver powder in a lacquer substance to on produce insulating electrical contacts. It is by the same reference also known that the conductivity due to thermal aging can still be significantly improved. When conductive silver is in Lack colloidally dissolved silver which is coated and dried. An alternative possibility is to suspend silver powder in a casting resin (Araldite), to improve the adhesive strength.

p0009Such suspensions are also suitable for the inventive purpose. However, it was überraschend.festgestellt layer on a package of the kind described above the application of such a precious metal suspension, that the precious metal, especially silver, diffuses due to the temperature treatment by the dielectric layer and into the electrically conductive surface coating (such as silver), and with the layers mentioned an intimate connection or tooth comes in, not only ensures a stable current transfer, but also leads to an excellent adhesion of the respective contact paths.

p0010It is understood that the thermally induced diffusion process proceeds more rapidly the higher the temperature is. However, experience has shown that at about 100 ° C, a lower limit is achieved, below which the diffusion process takes an uneconomically long time. However, the diffusion process takes place in an extremely short time when using a substrate made of mineral glass, the temperature treatment is carried out at the softening temperature of the mineral glass. This softening temperature is 640 ° C in a conventional float glass such as a sodium silicate glass.

p0011A heat treatment at such a high temperature brings the further advantage that the entire glass sheet can be plastically deformed even after the application of the contact paths, in order to bring an automotive disc into its final, optionally strongly curved shape. This advantage is especially not to be underestimated in the production of laminated glass sandwich construction. In such laminated glazing is - without air inclusion - between two thin slices of mineral glass, a viscoelastic intermediate layer of a plastic (eg, polyvinyl butyrate). The two (outer) Mineral glass sheets lying one bent together generally, what also with the complete package of layers and the contact paths is possible in the invention, the layer package and the contact paths are in the separation gap between the two discs. It is now only necessary - and this process step is prior art - to introduce between the two mineral glass, the intermediate layer of the visco-elastic plastic and bond the wafers by a thermal process under vacuum together. It is understood that in this case the contact strips also can be provided with leads before this compound, which protrude from the both side plate edges outward.

p0012The statement that the heat treatment is continued until the conductive surface coating by means of the contact paths, a reduced total resistance occurs is not to define a measurement or control process during manufacturing. There may be a final measurement method also, by the parameters (temperature and duration) during the heat treatment to be determined empirically. This means that the transition resistance between the applied contact strips and the conductive surface coating itself has become negligibly small compared to the resistance of the conductive surface coating, and thus a stable and uniform current flow is ensured.

p0013Without such a sufficient temperature treatment, a very unstable current flow indicated by the arrangement and an obviously quite high transition resistance.

p0014In order to enable thereby the best possible diffusi-on of the precious metal, particularly silver, by the dielectric surface layer is in a particularly advantageous manner for the surface layer is an oxide of at least one of the metals from the group of tin, zinc, indium, tantalum, titanium, zirconium , nickel and chromium is used. These metal oxides already allow sufficient diffusion, even if the oxide surface layer has been produced by vapor deposition. Insofar as a coating method for the oxide surface layer, a reactive sputtering method is applied, which is preferable for reasons of process control, the group of oxides or oxide-forming metals can significant he be panded because the sputtering method obviously leads to a layer structure for a is the noble metal diffusion process more suitable for the contact paths. Also this advantage of Katodenzerstäubungsverfahrens was surprisingly found.

p0015The invention also relates to a transparent pane with a substrate having at least one electrically conductive surface coating, which is coated on the side facing away from the substrate with a surface layer of dielectric material. To achieve the same object at least two metallic contact strips are arranged, starting extend of which metal atoms by diffusion into the electrically conductive surface coating on the surface layer.

p0016Further advantageous embodiments of the subject invention will be apparent from the remaining dependent claims.

p0017The inventive method is also suitable, and particularly for contacting discs, as produced by the process of the unpublished DE-OS 3543 178.4.

p0018An embodiment of the inventive method is explained in detail with reference to Figures 1 to 4. FIG.

p0019Show it:<ul><li>Figure 1 is a plan view of a heated windscreen of a passenger car,</li><li>2 shows a section through the article of Figure 1 along the line II-II,</li><li>Figure 3 shows a section through a laminated pane, and</li><li>Figure 4 is a diagram showing the timing of the change in the total resistance "contact sheet - dielectric - leitfänige surface coating - dielectric - contact path" by increasing doping of dielectrics by the noble metal from the suspension.</li></ul>

p0020In Figure 1, a disc 1 is drawn from a mineral glass, such as is typically used for automobile windows. In the edge region of the two narrow sides of two contact paths 2 and 3 are arranged, which have been prepared by the present process and are connected to lead-out lead wires 4 and 5. FIG. The arrangement of the contact paths 2 and 3 it is achieved that the intervening surface is flowed through substantially uniformly from the heating current.

p0021The arrangement need not be performed necessarily so, as shown in FIG. 1 There are also other geometric configurations of the contact paths possible being only necessary to ensure that the total heating power is distributed evenly over the entire surface lying between the contact paths in about.

p0022In Figure 2, a substrate 6 is shown, which is the supporting element of the entire disc. The substrate 6 carries firstly a first layer 7 which, in the present case consists of an oxide of tin oxide dielectric. On this base layer is an electrically conductive second layer 8, which can be composed of several metallic layers, which is the simplicity not graphically highlighted sake. In the present case, the second layer 8 consists of a total of three layers, namely a central layer of silver, the low thickness between two layers is embedded nickel. The layer 8 is electrically conductive, the conductivity is still increasing by a tempering process. It is a surface coating, which coats the entire surface of the substrate 6 substantially.

p0023On the electrically conductive layer 8 in turn is a third layer, namely, a surface layer 9 which serves as a protective layer against mechanical and chemical influences. The surface layer 9 is like the layer 7 of tin oxide with a thickness of about 30 nm. In this surface layer by brush or brush capable precious metal suspension in a solvent and a binder ( "conductive silver 200") was applied. After drying and after the heat treatment these precious suspension formed the contact web 2 (see also Figure 1).

p0024By the thermal treatment process, the metal of the contact web 2 is penetrated by atomic diffusion into the electrically conductive surface coating 8, which is indicated by the dashed area between the contact strip 2 and the surface coating eighth By this diffusion process, the original dielectric or oxide with the noble metal of the suspension, with silver, is doped in the present case, so that a current flows between the electrically conductive Flächänbeschichtung 8 and the contact strip 2 (and of course analogous to the contact path 3) can flow. The contact strips can be connected to the leads 4 and 5 in their turn, for example, by a soldering process.

p0025Figure 3 shows a composite disc, which was made by bending an arrangement according to FIG. 2 For this purpose, the substrate 6 with its layer package 10, which is here representative of the layers 7, 8 and 9 of Figure 2, and with the contact paths 2 and 3 has been bent, of which only the contact track 2 is shown here. The bending process was carried out together with another, uncoated pane 11 so that the contacting surfaces of the substrate 6 and the washer 11 have a geometric virtually identical course. The film package 10 and the contact paths 2 and 3 may here be disregarded since they are negligibly thin in comparison to the thickness of the substrate 6 and the washer eleventh Between the substrate 6 or its layer package 10 and the contact tracks 2 and 3 on the one hand and the disc 11 on the other hand, a film is 12 from a tough elastic plastic (Polyvenylbutyrat). The free surface 13 of the substrate 6 is - in relation to the vehicle interior - outer surface or weather side, while the free surface 14 of the disc 11 facing the vehicle interior. This results in that the package of layers 10 is on the inside of the outer pane or the substrate. 6

Example:

p0026A substrate 6 according to Figure 2 was coated by the application of the layers 7, 8 and 9 by magnetron cathodes in a Katodenzerstäubungsanlage Leybold-Heraeus GmbH, Type A 1100 Z3H / 4, followed by painting a conductive paste of the "conductive silver 200" provided in accordance with the surface pattern in figure 1 with two contact paths. 2 and 3 Subsequently, the entire assembly of substrate 6, the layers 7, 8 and 9 and the conductor tracks 2 and 3 in flat state in air to a uniform temperature of 150 ° C was heated to and held for a period of 60 minutes at this temperature , During this time, the total resistance between the contact paths 2 and 3 was measured. After about 2^- Minutes joined dine marked decrease of the total resistance between the contact paths 2 and 3, wherein the action after 20 minutes came to a halt. The time course of change in resistance is shown in FIG. 4 The high values ​​(less than 4 minutes) comprise high transition resistances between the contact paths (2, 3) and the conductive surface coating (8), the horizontal portion is essentially for the no longer ver änderlichen resistance of the surface coating (8). At the inlet of the measured values ​​in the horizontal portion of the doping process is essentially completed and the temperature of treatment can be discontinued.

Example 2:

p0027The example according to figure 1 was repeated but with the difference that the substrate 6 is heated with the layers 7, 8 and 9 and with the contact paths 2 and 3 in air uniformly to a temperature of 640 ° C and bent in the same heat ie was plastically deformed. The reduction of the total resistance between the contact paths 2 and 3 was carried out before reaching the final temperature of 640 ° C, so that it could be assumed that the diffusion process had the electrically conductive layer 8 already fully achieved.

p0028The graph applies only to a specific layer system and a specific treatment temperature, but it has for other coating systems and temperatures similar or analogous profile.