BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to electrical bus bars on transparent or non-transparent substrates, and more particularly, to a method of applying the bus bars to substrates using vapor deposition processes such as sputtering, cathodic arc process, ion plating process and vacuum evaporation. ^

Electrical bus bars applied to glass for automobile windshields for example, is well known in the art. Typically electric current is passed through a transparent electro- conductive coating or film via the bus bars to heat the coating to de-ice, defog, or defrost a glass surface.

For example, U.S. Patent No. 4,743,741 to Ramus discloses an electrically heated windshield having a pair of electrically conductive bus bars applied to one of the surfaces of the windshield. The '741 Patent is incorporated by reference herein.

Another example of electrically heated windows is found in U.S. Patent No. 4,778,732 to Hasegawa, et al. Hasegawa discloses an electrically conductive glass sheet used as a fog resistant automotive window. The glass sheet comprises a pair of bus bars and an electrically conductive, transparent

thin film. The '732 patent is also incorporated by reference herein.

Ramus and Hasegawa as well as others (see also, U.S. Patent No. 4,847,472 to Koontz) have applied their electrically conductive bus bars to the glass substrates using a silver ceramic material which is silk screen printed on the selected surface of the glass and then heated to a temperature as high as 600°F or more to bond the silver ceramic material to the glass. This is disclosed in Column 4, Lines 10-15 in Ramus. In Column 2, Lines 18-30 of Hasegawa, it states that the bus bars are formed on the glass by printing electrically conductive paste by the silk screen printing process, and baking the paste. It goes on to say that the paste may be of a needed mixture of glass powder (frit) of a low melting point containing metal particles such as Ag, Cu, or Pd, for example, and an organic solvent or a binder. Others have used inks, lacquers, or UV paint for the bus bars (see U.S. Patent No. 4,830,876 to Dietrich, et al.)

There are many disadvantages to the above methods for applying the bus bars. For one, they use volatile solvents with various pigments. Secondly, the result is a relatively thick coating of silver from 0.001 to 0.002 inches. Since bus bars are usually at or near the edges of the glass, thick bus bars between laminated panes of glass will cause the panes of glass to have less intimate contact over their entire surfaces inducing stresses in the glass. Third, high

temperature firing or baking causes excessive thermal stress and weakness in the glass. Fourth, the material cost of silver is high.

The present invention has many advantages over the above described methods. With the present invention, very thin, durable and reliable bus bars which require no firing or baking process are provided. Therefore, the glass is not stressed as much as with previous methods. The bus bars may be thinner resulting in close and intimate contact over the entire mating surfaces of glass panes laminated together. In addition, using the present invention, the material cost of the bus bars is lower and they are applied with greater ease in conjunction with current window fabrication processes and techniques.

Although the example thus far has concerned automobile windshields, there are many other applications for the present invention. The present invention will be useful in automotive vehicle windows, including rooftop windows, aircraft windows, marine craft windows, architectural windows, mirrors, various electronic applications including computer screens and display panels, food heating or warming devices, ceramics, metal substrates, silicon substrates, electrochromic devices, as well as many other glass, plastic, and other transparent substrates, and non-transparent substrate applications.

In the present invention, the bus bars are conductive paths for applying electrical energy, either AC or DC to the extent that a uniform flow of current takes place between the bus bars through a conductive medium. The medium could be a transparent or non-transparent coating or film, many electro-conductive materials such as wires (currently used in automobile rear window defoggers), and other metal or even non-metal conductive devices. A uniformally developed heating pattern may be established between the bus bar system through the conductive coating or other conductive material. The bus bars of the present invention may also be used in an electrochromic device to distribute electrical power over a large surface area. Flat or bent substrates can be used. The bus bars of the present invention are applied by any one of the vapor deposition processes mentioned above. Various layers of metals (for example Cr-Cu ^' -Cr) form the bus bar and are applied on the substrate to arrange a bus bar system for carrying electrical heating currents through the transparent conductive coating or other conductive material.

The bus bars may be applied to a window pane border portion after a dark coating has been applied to the window border portion. This may be done to conceal the bus bars from view.

The foregoing and other objects and advantages will become more apparent when viewed in light of the accompanying drawings and following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is an elevational view of an automobile windshield having the bus bars of the present invention;

FIGURE 2 is a cross sectional view of the windshield of FIGURE 1;

FIGURE 3 is a cross section of a bus bar of the present invention in use on a single pane of glass, plastic, or other transparent substrate and in contact with a transparent electro-conductive coating;

FIGURE 4 is a cross section of another embodiment of a bus bar of the present invention having two layers on a substrate;

FIGURE 5 is a cross section of a bus bar of the present invention applied to a substrate without a transparent coating;

FIGURE 6 is a cross section of a bus bar of the present invention applied to a non-transparent substrate;

FIGURE 7 is a cross section of a bus bar of the present invention applied to a substrate and in contact with a non-transparent electro-conductive heating element;

FIGURE 8 is a cross section of a bus bar of the present invention for use in another application involving two panes of glass with an air or gas filled space between them;

FIGURE 9 is a cross section of a bus bar of the present invention applied to a dark coating that has been applied to a transparent substrate;

FIGURE 10 is a cross section of another embodiment of a bus bar of the present invention having four layers applied to a substrate; and

FIGURE 11 is a cross section of yet another embodiment of a bus bar of the present invention having five layers applied to a substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSS)

Referring to FIGURE 1, there is shown a typical automobile windshield 20. The windshield 20 is comprised of a glass substrate 22. Also shown are a pair of electrically conductive bus bars 24, 26 applied to one of the surfaces of the substrate 22.

Typically, a windshield 20 will be made of a laminated construction in which two sheets of glass 22, 28 are used to form the windshield 20. The two sheets of glass 22, 28 may be united by an inner layer of plastic (polyvinyl butyral) 30 in a manner known to those skilled in the art. As shown for example in FIGURE 2, there may be six different surfaces 32, 34, 36, 38, 40, 42 upon which the bus bars 24, 26 could be applied but usually the bus bars 24, 26 are applied to the inner surface 34 of the outside sheet 22 or the outer surface

40 of the inside sheet 28. The shape and configuration of the bus bars in FIGURE 1 is just one way of arranging the bus bars 24, 26. Many other shapes and arrangements could also be used effectively.

In other applications, a single substrate sheet 44 may be desired and the bus bars 24, 26 could be applied to either surface 46, 48 of the substrate 44 as shown in FIGURE 3. The significance of FIGURE 3 is that the bus bars may be applied to many other substrates besides automobile windshields.

The bus bars 24, 26 may be positioned on the substrate 22 in order to achieve generally equal distance between the bus bars 24, 26. Generally, the bus bars 24, 26 are applied near the top 50 and bottom 52 edges of the substrate 22 but other arrangements could be employed to achieve the same results in an appropriate application. After the bus bars 24, 26 are applied, a transparent conductive coating 54 may be applied to the substrate 22 between the bus bars 24, 26. Using vapor deposition processes for applying the conductive coating 54 is well known in the art. However, using vapor deposition processes to apply the bus bars 24, 26 to a substrate 22 has heretofore never been successfully accomplished to the knowledge of the present inventors.

To apply the bus bars 24, 26 to a substrate 22 using a vapor deposition process at least one problem must be overcome. The bus bars 24, 26 should adhere to the substrate 22 so that they will be durable and will not tend to peel off

(for example, when electrical wires are soldered onto the bus bars 24, 26). For durability of the bus bars 24, 26, the substrate 22 should first be thoroughly cleaned. This may be done by washing the substrate 22 with water and detergent then rinsing the detergent off. Another rinse with deionized water should follow. Then, warm blown filtered air directed at the substrate 22 will dry it. The substrate 22 may then be placed in a vacuum chamber (not shown) and glow discharge cleaned using a wet gas technique as is known in the glass cleaning art.

The substrate 22 may be left in the same vacuum chamber for the vapor deposition of the bus bars 24, 26 if the particular vacuum chamber in use is suited for this. An initial metal layer may be deposited onto the substrate 22 as the first layer or bond layer 58 of the bus bars 24, 26. The next layer deposited onto the bond layer 58 is a conductive metal layer 60.

In FIGURE 2 a cross section of the windshield 20 of FIGURE 1 is shown. In FIGURES 2-11 only a single bus bar cross section is shown for clarity but it should be recognized that in most applications two or more bus bars applied at separate locations on a substrate, would be needed. The bond layer 58 of the bus bar 24 may be deposited directly to the inner surface 34 of the outside glass sheet 22 or the outer surface 40 of the inside glass sheet 28. The conductive layer 60 of the bus bar 24 is deposited onto the

bond layer 58. A protective layer 62 may then be deposited onto the conductive layer 60 to form a three layer bus bar 24. In the example as shown in FIGURE 2 a transparent electro-conductive coating 54 is deposited onto the protective layer 62 and the coating 54 will substantially cover the windshield 20. Various coatings may exhibit the combination of transparency and electroconductivity to serve as the heating element for a windshield 20 or the like, which is known to those skilled in the art. Continuing in reference to FIGURE 2, a plastic (polyvinyl butyral) layer 30 and an inside glass sheet 28 are added and the entire assembly 64 is laminated together.

Referring again to FIGURE 1, electrical connections 66, 68 to the windshield bus bars 24, 26 may be made at the lower edge 70, center portion 72 thereof. But, the connections 66, 68 could be placed elsewhere along the bus bars 24, 26 and function effectively. In the embodiment described above, a small portion of the protective layer 62 of the bus bars 24, 26 should be removed, by acid etching for example, so that an electrical connection 66, 68 can be made directly to the conductive metal layer 60 of the bus bars 24, 26. For the electrical connection, wire leads (not shown) may be bonded to the conductive layer 60 by, for example, soldering, welding, brazing, diffusion bonding, physically clamping, or other like methods.

FIGURE 5 is an example of a bus bar 74 arrangement without a transparent electro-conductive coating which may not be necessary in some applications. Most any conductive material (not shown) could be applied to the substrate 76 to contact the bus bar 74. FIGURE 4 shows another embodiment 78 of the bus bars of the present invention in two layer form. In this embodiment 78 a bond layer 80 is deposited onto the transparent substrate 82 in the same manner as described above for a windshield. A conductive layer 84 is next deposited onto the bond layer 80. In some situations this two layer bus bar 78 may be sufficient.

FIGURE 6 is an example of another embodiment 86 of the bus bars of the present invention applied to a non-transparent substrate 88 such as ceramics, plastics, metal oxides, silicon, etc. In this embodiment 86 the conductive layer 90 may be a heating layer. The heating layer 90 has a resistor material, for example nichrome (NiCr) in place of a conductor. In this example, the bus bars could be used for heating mirrors, food trays or other containers, heating elements in heaters for buildings, and many other examples too numerous to mention wherein a substrate would be heated.

FIGURE 7 is yet another example wherein the bus bar 92 is deposited on a substrate 94 and in this case a non- transparent electro-conductive heating element 96 is in contact with the bus bar.

FIGURE 8 is another application for the bus bars 97 of the present invention. Insulated windows for architectural use and freezer or refrigerator door windows, for example, typically have two transparent substrates 98, 100 (usually glass) separated by a dead air or gas filled space 102. The layers 104, 106, 108 of the bus bar 97 could be deposited onto a portion of the inner surface 110 of one of the substrates 98 using the method of the present invention. A transparent electro-conductive coating 112 may then be applied over the substrate 98 and in contact with the bus bar 97 so that the substrate 98 can be heated to defrost, defog or de-ice it, for example.

FIGURE 9 shows a laminated window assembly 114 mμch like that shown in FIGURE 2 except the bond layer 116 of the bus bar 118 is deposited onto a dark or opaque border 120. The dark border 120 may be applied to the substrate 122 to conceal the bus bar 118.

FIGURE 10 is a view of another embodiment of the present invention in which a four layer bus bar 124 is deposited onto a substrate 126. In this bus bar 124, a bond layer 128 is first applied. Then a first conductive layer 130 is deposited onto the bond layer 128. This first conductive layer 130 could be a metal such as copper. A second conductive layer 132 is deposited over the first conductive layer 130. This second conductive layer 132 could be a

different metal such as aluminum. Finally, a protective layer 134 is deposited onto the second conductive layer 132.

FIGURE 11 is a view of yet another embodiment of the present invention in which a five layer bus bar 136 is deposited onto a substrate 138. In this embodiment, a bond layer 140 is deposited onto a surface 142 of the substrate 138. Then a first conductive layer 144 is deposited onto the bond layer 140. An intermediate layer 146 is next applied to act as a stress reliever for differences in thermal expansion between the conductive layers 144, 148 and the substrate 138 or as an adhesive layer for the second conductive layer 148. A second conductive layer 148 is then deposited onto the intermediate layer 146 and finally a protective layer 150 is applied. A second conductive layer 148 offers extra power capacity in an appropriate application.

It should be recognized that many other embodiments and examples could have been shown. Six or more layer bus bars may be needed in a given application. Countless uses for the bus bars of the present invention could be shown. However, for the sake of demonstrating the many variations of the bus bars of the present invention it is believed the FIGURES above will cover the basic embodiments. Particular embodiments and uses not shown should be evident from reading this specification.

The protective metal layer and the bond layer may be the same metal or different metals. The protective metal

composition and bond metal composition will come from the group chromium, tungsten, titanium, molybdenum, nickel, tantalum, stainless steel, zirconium, hafnium, aluminum, and mixtures and alloys of any of these metals. The conductive metal layer composition will come from the group copper, silver, gold, aluminum, and mixtures and alloys of these metals. The conductive layer should be a good electrical conductor having low resistance. The layer in contact with a transparent conductive coating in the application such as an electrically heated windshield or an electrochromic device should be chemically and metallurgically compatible with the coating.

Each layer may be sequentially applied by sputtering in a vacuum system without exposing the substrate to the atmosphere between application of layers. Using this process, bus bars can be applied to flat or bent/curved surfaces. The sputtering process of the present invention uses argon gas under a process pressure of preferrably 1-50 millitorr (3-10 millitorr may be most preferred) and a maximum temperature need not exceed 250°F. Electrical conductivity laws dictate the minimum thickness of a bus bar depending upon the electric current carried by the bus bar plus its length and width. Total bus bar thickness may be as low as 1000 Angstroms in a particular application.

As mentioned above, other vapor deposition processes can be used besides sputtering. The fact that a vapor deposition

process of any kind can be used to apply bus bars to a substrate resulting in a durable bus bar is a surprising achievement. Furthermore, making an electrical connection to vapor deposited bus bars by soldering, for example, is also surprising. Previously, it was believed that this would not be feasible, because the bus bars would peel off once they were soldered to. The novel method of applying bus bars of the present invention provides a durable bus bar and overcomes many disadvantages of previously used methods for applying bus bars.

It is thought that the method and improved bus bars of the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes can be made in the form and construction of the components thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely preferred or exemplary embodiments thereof.