Electroluminescent display and method of making same
TECHNICAL FIELD 
     The present invention relates, in general, to electroluminescent devices and, in particular, to (1) a method for applying the conductors and leads through which electricity is supplied to excite the electroluminescent material, and (2) the product made by this method. 
     BACKGROUND ART 
     In the past, electroluminescent displays were fabricated by carefully depositing electroluminescent material layers of prescribed thicknesses at designated locations on a substrate and selectively placing electrical conductors, which carry electricity to excite the electroluminescent material, on both sides of the electroluminescent material. These displays presented little risk to short-circuiting the electrical conductors when electrical leads, through which power is supplied, were mechanically fastened to their respective electrical conductors. The designer of the electroluminescent display had sufficient flexibility in shaping, sizing and positioning the electrical conductors and their associated electrical leads, so that they would not overlap at the connection points and create a short-circuit as connections were made and the connecting components might pierce through the display. 
     Recently, electroluminescent sheets and rolls have become available and have received widespread acceptance. Typically, electroluminescent sheets and rolls are relatively thin and are composed of a substrate coated with the electroluminescent material and a transparent conductor covering the electroluminescent material. Panels of desired size and shape are cut from the electroluminescent sheet or roll and then selectively coated with conductors, so that selected segments of the electroluminescent material are excited to produce the desired display when the conductors are energized. 
     It is apparent that producers of electroluminescent displays, when using electroluminescent sheets and rolls, are spared the problem of handling electroluminescent material and depositing this material over accurately defined areas in layers of prescribed thicknesses. They have a simpler task of selectively applying conductors to a panel cut from an electroluminescent sheet or roll to selectively energize the electroluminescent material. 
     However, connecting the electrical leads, through which power is supplied to the electroluminescent panel, to conductors disposed on opposite sides of the electroluminescent material can be a costly and time-consuming step in the fabrication of these electroluminescent displays. Care must be taken to assure that the components, such as copper clips, which press the electrical leads into good electrical contact with their respective conductors do not penetrate the relatively thin panel and short-circuit the conductors through these components. The risk of a short-circuit exists because the transparent conductor, which is part of the electroluminescent sheet or roll, extends across the entire face of the panel. A connecting component, applied to a conductor on the opposite side of the panel from the transparent conductor, will make contact with the transparent conductor if it penetrates through the panel. 
     DISCLOSURE OF THE INVENTION 
     An electroluminescent display is fabricated, according to the present invention, by providing an electroluminescent panel having an electroluminescent material on a first surface of a non-conducting substrate and a transparent conductor covering the electroluminescent material. A mask, resistant to etching solvent, is produced on the transparent conductor to cover selected areas of the transparent conductor and corresponding areas of the electroluminescent material lying beneath the masked areas of the transparent conductor. Each masked area is composed of a unitary display segment and lead segment. After applying an etching solvent to unmasked portions of the transparent conductor, unmasked portions of the transparent conductor are etched away resulting in selected regions of layered electroluminescent material and transparent conductor. Each such region is composed of a unitary display segment and lead segment. Next, a metallic conductor is applied to selected areas of a second surface of the substrate opposite from the first surface. Each selected region of metallic conductor is composed of a unitary display segment and lead segment. The etched electroluminescent panel, with the metallic conductor applied, then is enclosed within a non-conducting envelope having a transparent surface extending over the regions of layered electroluminescent material and transparent conductor. A first set of terminals is connected to the lead segments of the transparent conductor and a second set of terminals is connected to the lead segments of the metallic conductor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings: 
     FIGS. 1A through 1E are sectional views which illustrate the sequence of steps for producing an electroluminescent display in accordance with the present invention; 
     FIG. 2 is a top view of one electroluminescent display constructed in accordance with the present invention; 
     FIG. 3 is a sectional view taken along line 3--3 of FIG. 2; and 
     FIG. 4 is a sectional view taken along line 4-4 of FIG. 3. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The drawings illustrate the fabrication of an electroluminescent dot-matrix display in accordance with the present invention. It will be apparent that other formats can be produced according to the present invention. 
     Referring to the drawings, an electroluminescent display, fabricated in accordance with the present invention, includes an electroluminescent panel 10 having an electroluminescent material 12 on a first surface 14a of a non-conducting substrate 14 and a transparent conductor 16 covering electroluminescent material 12. An electroluminescent panel is cut to the desired shape and size from a relatively thin layered sheet or roll composed of the substrate, the electroluminescent material, and the transparent conductor. The electroluminescent coating can be any of a variety of phosphorescent materials, for example, copper activated or copper manganese activated zinc sulfide. The substrate can be a polyester such as mylar. Transparent conductor can be indium tin oxide. 
     Next, a mask, resistant to etching solvent, is produced covering selected areas of transparent conductor 16 and corresponding areas of electroluminescent material 12 lying beneath the masked areas of the transparent conductor. The masking of transparent conductor 16 corresponds to the desired display format which is to be produced. 
     The masking of transparent conductor 16 can be accomplished in a number of ways. One preferred method is to lay a stencil 18 on transparent conductor 16 and deposit a mask of transparent ultraviolet ink 20 on those portions of transparent conductor 16 exposed through openings in stencil 18 which correspond to the desired format of the display. The deposits of ultraviolet ink 20 are hardened by radiating the ultraviolet ink with an ultraviolet light. Ultraviolet ink 20 may be a clear acrylic base ultraviolet curable material. 
     After stencil 18 is removed, an etching solvent such as methyl ethyl ketone is applied to the unmasked portions of transparent conductor 16 to etch away unmasked portions of the transparent conductor. As shown in FIG. 1C, this produces selected regions of layered electroluminescent material 12 and transparent conductor 16. It is not necessary to remove unmasked portions of electroluminescent material 12 because the unmasked portions of electroluminescent materials can not be energized after the transparent conductor is removed. 
     As shown in FIG. 2, each discrete region of layered electroluminescent material and transparent conductor is composed of a unitary display segment 22a  and lead segment 22b. Display segments 22a form a part of the desired electroluminescent display, while lead segments 22b serve to conduct electricity to the display segments. For the dot-matrix display shown in FIG. 2, each display segment 22a is a straight line of prescribed width spaced from an adajcent display segment 22a by a prescribed distance. 
     Next, a metallic conductor 24 is applied to one or more selected areas of a second surface 14b of substrate 14 opposite from surface 14a. A selected region of metallic conductor is composed of a unitary display segment 24a and lead segment 24b. A display segment 24a forms part of the desired electroluminescent display, while a lead segment 24b serves to conduct electricity to the display segment. For the dot-matrix display shown in FIG. 2, in which a plurality of selected regions of metallic conductor are provided, each display segment 24a is a straight line of prescribed width spaced from an adjacent display segment 24a by a prescribed distance and disposed perpendicular to display segments 22a. The application of metallic conductor 24 can be done by conventional selective coating techniques, such as by a silk screen process, which involves masking the surface to be coated and applying a metal, such as silver, according to the mask. 
     The etched and coated electroluminescent panel then is enclosed within a non-conducting envelope having a transparent surface extending over regions of layered electroluminescent material and transparent conductor. This can be accomplished by placing a pair of transparent sheets 26 and 27 on opposite sides of the etched and coated panel with the edges of transparent sheets 26 and 27 extending beyond the edges of the panel and heat-sealing the edges. Then the envelope is trimmed to the desired size and shape as shown in FIG. 2. 
     A first set of terminals 28 is attached to lead segments 22b and a second set of terminals 30 is connected to lead segments 24b. These terminals can be connected to the associated lead segments either before the application of transparent sheets 26 and 27 or afterwards by penetrating the transparent sheets. 
     When electricity is applied to selected ones of terminals 28 and 30, the electroluminescent material between the intersections of the display segments associated with the selected terminals is excited. Electroluminescent material beneath lead segments 22b or above lead segments 24b is not excited because there is no metallic conductor or transparent conductor on the opposite side of the electroluminescent material. Lead segments 22b of the transparent conductor lie outside the area defined by the outermost portions of display segments 24a of the metallic conductor and lead segments 24b of the metallic conductor lie outside the area defined by the outermost portions of the display segments 22a of the transparent conductor. 
     The ultraviolet ink, being transparent, need not be removed from the areas over which it is deposited. However, if other masking material is used which is opaque, it must be removed after the etching step. 
     The foregoing has set forth an exemplary and preferred embodiment of the present invention. It will be understood, however, that various alternatives will occur to those of ordinary skill in the art without departure from the spirit and scope of the present invention.