Abstract:
A method for manufacturing low cost electroluminescent (EL) illuminated membrane switches is disclosed. The method includes the steps of die cutting, embossing or chemically etching the metal foil surface of a metal foil bonded, light transmitting flexible electrical insulation to simultaneously form one or more front capacitive electrodes, membrane switch contacts and electrical shunt, electrical distribution means and electrical terminations that together form a flexible printed circuit panel. This continuous flexible printed circuit substrate is then used with a precisely positioned indexing system.

Description:
The Divisional of application Ser. No. 09/942,339 Filed on Aug. 30, 2001 U.S. Pat. No. 6,698,085. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present field of the invention relates to membrane switches, and more particularly to a method for manufacturing membrane switches that are illuminated using electroluminescent lamps. 
   2. Description of the Prior Art 
   Present membrane switches are typically made from flexible plastic insulators that contain two layers of opposing electrically conductive surfaces isolated from one another by an air gap such that, when one surface is mechanically deformed by applied pressure, that deformed surface makes mechanical contact against the opposing stationary surface and completes an electrical current path between them. This current path may carry either signal or power electrical charge, or both. By positioning an insulating mask between these two surfaces, effective mechanical isolation ensures that unwanted electrical contact is avoided. Adding illumination to such membrane switches can create both complicated and bulky assemblies tat are unsuitable for many electronics product applications. Illuminated membrane switch assemblies made using this method contain three or more individual layers of electrically conductive and isolating materials that require precise alignment for their successful application. 
   An alternative construction consists of a rigid circuit board having on its upper surface a pair of electrical switch contacts. Positioned above this surface is an isolating mask layer that is typically a plastic film with openings positioned in alignment with the contact pairs. Above that is placed a second plastic film with a deformable electrical shunt surface oppositely positioned in alignment with the isolation mask&#39;s opening and the printed circuit board&#39;s switch contact pairs. When this outermost shunt layer is mechanically deformed by pressure, the shunt is driven past the isolating mask layer opening such that the shunt may then make contact to the printed circuit board&#39;s switch contacts, thus creating a current path. Illuminating this switch constructions may take the form of an overlaying elastomeric actuating structure that is edge-lit illuminated by externally mounted lamps or alternatively via light emitting diodes (LED&#39;s). Application of an additional layer of electroluminescent lamp construction may also be used to provide illumination to the elastomeric structure. Such constructions typically require an additional rigid framework to keep the various layers in alignment. 
   An alternative to this s construction is to form the elastomeric actuating structure into an integrated system that begins with a positioning flange that rests on top of the printed circuit board and surrounds the switch contact pair. Projecting from this flange structure is an elastomeric spring member that then supports an actuating key. In the open gap formed by this structure, a typically cylindrical shaped protrusion extends down from the actuating key and is supported above the switch contacts. The end of this protrusion may alternatively be coated with a conductive surface to provide the electrical shunting effect, or a “pill” of conductive elastomer is attached to the protrusion to provide this function. Thus, the actuating key may be pressed, allowing the shunting surface of the protruding conductor to mechanically contact the switch contacts below to from an electrical current path between them. If an additional insulating layer, constructed with electroluminescent lamp elements that surround an opening in the insulation corresponding to the location of the shunting protrusion of the elastomeric actuating structure, is placed between the elastomeric actuating structure and the surface of the switch bearing side of a printed circuit board, a ring of illumination surrounds the actuating key. Additionally, a rigid framework must also be provided to keep the surfaces and structures in alignment. 
   In the above alternative methods, only signal level electrical charge may be switched by key actuation. Additionally, these structures are also bulky, and require great care in their design and manufacture in order to make them successful for many electrical and electronic applications. 
   To provide a pleasing tactile “snap” to the above constructions, a layer of formed metal foil shapes may also be applied to replace the shunt layer. These shapes are typically convey on their outer surface and concave on their interior surface. By placing the formed metal foil shapes above the isolating mask layer opening, opposite a switch contact pair, applied mechanical pressure causes the shapes to temporarily invert, thus making contact between the switch contacts. This method allows both signal and power electrical charges to be passed between switch pairs. As this construction also requires individual layers to be assembled, including illuminated actuating elastomeric structures and frames, a bulky and complex assembly results. 
   Application of electroluminescent lamp as an illumination scheme to the above methodologies provides a thinner structure, however there are still numerous individual layers and actuators to be applied and aligned to complete an illuminated membrane switch assembly. An example of this process is referenced in U.S. Pat. No. 5,680,160 (the &#39;160 patent), wherein LaPointe describes such an application consisting of screen-printed illumination and electrical contacts arranged in a pattern such as might be used for a map as a teaching tool in geography. However, this method only provides illumination during switch contact, and is also limited in the amount of electrical current the switch contacts may carry. The use of conductive inks as switch elements also severely limits their useful life cycle. Additionally, this method does not provide electrical circuit separation between the switch portion and the illumination circuit portion without introducing an additional switch contact and shunt set with attendant construction and isolation layers. Thus, high voltage alternating current may add electrical interference to the switch circuit. As the switch circuit may also make contact for voltage sensitive semiconductor devices, this lack of isolating circuits may cause both electrical interference to, and failure of such devices. 
   In U.S. Pat. No. 5,667,417, Stevenson teaches a method of producing low cost metal foil based electroluminescent lamps of potentially complex graphic pattern by using a precise indexing system that applies well known flexible circuit technology to a cost-effective continuous production process. Application of this process to the manufacture or illuminated membranes switches can result in switch assemblies that are both low-cost, plus electrically and mechanically superior to those described in the &#39;160 patent. 
   Thus, there is a need for low profile illuminated membrane switch assemblies that provide all the elements of individually addressable illuminated areas, electrically separated switch and illumination circuitry, plus robust current carrying switch contacts and shunting means. Further, there is a need to provide such a low profile membrane switch assembly that may be made from a single flexible substrate material applied to an automated manufacturing system. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method of manufacturing EL illuminated membrane switches incorporating some of the processes used in the manufacture of flexible printed circuit boards. 
   In an exemplary embodiment of the invention, the method of the present invention includes the following steps. In the first step, a light transmissive process carrier film having metal foil bonded to its surface is prepared for further process by die cutting or chemically etching the bonded metal foil to from the desired front capacitive electrode bus, membrane switch contacts and electrical shunt, power input distribution elements and associated electrical contacts to produce a planar flexible circuit board. Following this, the basis flexible circuit board carrier film is placed onto a commercially available transport system that incorporates an optical registration system to precisely position the image area, for the remaining print and die cutting process cycles. This method allows the precise (+/−&lt;0.002″ in X, Y and θ axis) physical positioning of the basis carrier film without deleterious effect upon the positioning reference means. Using this positioning method allows practically unlimited numbers of print layers to be applied, and final die cutting of the completed product, without concern for layer-to-layer alignment. 
   The third stop consists of printing a light transmissive, electrically conductive ink to precisely form a capacitive front electrode. Through precise, optically registered positioning the capacitive front electrode ink is allowed minimal bleed onto the front capacitive electrode bus. 
   In the fourth step a high dielectric, hygrophobically compounded EL phosphor ink is printed over the front electrode ink to further define the illuminated area. Precise, optically registered positioning of the basis carrier film allows precision phosphor application onto the front capacitive electrode element. Following this, in the fifth step, a layer of capacitive dielectric ink is applies to cover the EL phosphor layer, completely isolating the front capacitive electrode, phosphor layers and their associated power distribution elements. The capacitive dielectric layer ink is allowed to bleed beyond the EL phosphor layer and front electrode elements and power distribution elements to provide this electrical isolation. 
   Next then, in step six, a rear electrode layer of electrically conductive ink is applied to further define the precise illuminated area. This layer is allowed to bleed onto the rear electrode power distribution element, providing an electrical path to input power. 
   In step seven; a polyester film or ultraviolet activated dielectric coating is applied to the entire metal foil surface of the process carrier film. Openings in this layer are made allowing exposure of the metal foil layer to precisely define membrane switch contacts and electrical shunt, plus isolated electrical power contact termination areas. 
   Steps eight and nine comprise the printing of an isolation element and an actuating element from thick film elastomeric ink. The isolation element is printed as a frame shape surrounding the shunt portion, while the actuating element is printed as a hemispherical bump on top of the dielectric coating and is centered over the EL rear electrode. 
   Following this step, the complete EL lamp and membrane switch subassembly is then cut from the basis carrier film, then folded into three layers comprising the switch contact layer, the shunt layer and the illuminated actuator layer to which mechanical force may be applied to operate the switch. 
   A first embodiment of an EL illuminated membrane switch manufactured by the method of the present invention comprises a light transmissive, single-sided flexible printed circuit substrate containing both switch and EL lamp elements, electrical distribution elements and electrical input and output terminations. The EL lamp layers are progressively applied beginning with the front electrode light transmissive, electrically conductive ink, followed by hygrophobically compounded electroluminescent phosphor ink to define the illumination pattern, then capacitive dielectric ink to electrically isolate the front electrode and phosphor layers, followed by an electrically conductive ink layer that defines the rear capacitive electrode, finishing with an electrically insulted and environmentally isolated encapsulation layer that is patterned to protectively insulate all EL portions while leaving exposed all switch elements and electrical contacts. Flexible, thick-film elastomeric ink is then applied to create both a switch isolation mask pattern located around the switch shunt portion and a mechanical actuator bump on the rear surface of the EL lamp portion. The. EL illuminated membrane switch is then die-cut from the surrounding substrate material, folded into three layers that comprise switch, shunt and illuminated portions to complete the assembly. 
   In a second preferred embodiment, a double-sided flexible circuit substrate with switch contacts and switch shunt, associated electrical distribution elements and electrical contact terminals formed on one surface; EL lamp rear electrode and front capacitive electrode bus elements, electrical distribution elements and electrical input contact terminals are formed upon the opposite surface. EL lamp layers are sequentially applied in order of a first capacitive dielectric layer isolating the rear electrodes and associated electrical distribution elements from the front electrode bus; application of hygrophobically compounded electroluminescent phosphor ink on top of the capacitive dielectric layer to precisely define the illuminated pattern; application of electrically conductive, light transmissive ink over the EL phosphor layer and bridging onto the front capacitive electrode power distribution bus to create a front capacitive electrode; then, application of a light transmissive, electrically insulated and environmentally isolated encapsulation layer that is patterned to protectively insulate all EL portions while leaving exposed all EL lamp portion electrical contacts. The EL illuminated membrane switch subassembly is then die-cut and forming from the surrounding substrate material, creating an embossed portion surrounding the switch shunt acting as a spring element, thus isolating the shunt; then folded into three layers that comprise switch, shunt and illuminated portions to complete the assembly. 
   In a third preferred embodiment, a double-sided flexible circuit substrate with switch contacts and switch shunt, (the shunt element positioned approximately opposite the EL lamp rear capacitive electrode center), electrical distribution elements and electrical contacts formed on one surface; EL lamp rear capacitive electrode and front capacitive electrode power distribution bus elements, electrical distribution elements and electrical input contact terminations arc formed upon the opposite surface. EL lamp layers are sequentially applied in order of first capacitive dielectric layer to isolate the rear capacitive electrodes and their associated electrical distribution elements from the front capacitive electrode bus; application of hygrophobically compounded electroluminescent phosphor ink on top or the capacitive dielectric layer to precisely define the illuminated pattern; application of electrically conductive, light transmissive ink over the EL phosphor layer bleeding onto the front capacitive electrode power distribution bus to create a front capacitive electrode; then application of a light transmissive, electrically insulated and environmentally isolated encapsulation layer that is patterned to protectively insulate all EL portions leaving exposed all EL lamp portion electrical contact terminals. The EL illuminated membrane switch is then die-cut and formed from the surrounding substrate material, creating an embossed portion that acts as a spring element surrounding an aperture opening isolating the shunt from the switch contacts; finally then, folded into three layers that comprise switch portion, isolation layer portion, shunt and illuminated portion to complete the assembly. 
   The method of the present invention provides the ability to manufacture EL illuminated membrane switches at a cost fractional of that of comparable conventional construction. Additionally, these lower-cost EL illuminated membrane switches can be manufactured on readily obtainable automated production equipment. Further features and advantages of the present invention will be appreciated by a review of the following detailed description when taken in conjunction with the following drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein like numerals denote like elements and in which: 
       FIG. 1  is a top view diagram illustrating the process subassembly of first exemplary electroluminescent illuminated membrane switch  100  constructed in accordance with the present invention; 
       FIG. 2  is a cross-sectional view of a first exemplary electroluminescent illuminated membrane switch  100  Constructed in accordance with the present invention; 
       FIG. 3  is a schematic diagram of an equivalent circuit of a first exemplary electroluminescent illuminated membrane switch  100 ; 
       FIG. 4  is a top view diagram illustrating the process subassembly of a second exemplary electroluminescent illuminated membrane switch  200 ; 
       FIG. 5  is a cross-sectional view of electroluminescent illuminated membrane switch  200  of  FIG. 4 ; 
       FIG. 6  is a schematic diagram of an equivalent circuit of electroluminescent illuminated membrane switch  200  of  FIG. 4 ; 
       FIG. 7  is a top view diagram illustrating the process subassembly of a third exemplary EL lamp electroluminescent illuminated membrane switch  300 ; 
       FIG. 8  is a cross-sectional view of electroluminescent illuminated membrane switch  300  of  FIG. 7 ; 
       FIG. 9  is a schematic diagram of an equivalent circuit of electroluminescent illuminated membrane switch  300  of  FIG. 7 ; 
       FIGS. 10(   a ) &amp; ( b ) are isometric views of the process subassembly of electroluminescent illuminated membrane switch  100 , showing alternative electrical termination locations; 
       FIGS. 11(   a ) &amp; ( b ) are isometric views of electroluminescent illuminated membrane switch  100  in folded form, showing alternative electrical termination locations; 
       FIG. 12  is an isometric view of an electroluminescent illuminated membrane switch  100  installed inside of a keypad switch enclosure assembly  400 ; 
       FIG. 13  is an isometric blow-apart view of keypad switch enclosure assembly  400  of  FIG. 12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following exemplary discussion focuses upon the manufacture of an electroluminescent illuminated membrane switch. The electroluminescent illuminated membrane switch produced by the method of the present invention is suitable for a variety of electronics, electrical and other lighted switch applications. 
   Referring to  FIG. 1 , a top view diagram illustrating a preferred electroluminescent illuminated membrane switch subassembly made in accordance with the present invention is shown. In the first step of the method, typically an approximately 0.001 inch thick metal foil is die cut or chemically etched to form one or more front capacitive electrode power distribution bus elements  132 , rear capacitive electrode power distribution bus  140 , electrical power contacts  124 ,  126 ,  148  and  150 , switch contact elements  116  and  118 , switch shunt  12 l, electrical distribution elements  128 ,  130 ,  152  and  154  that are all permanently bonded to a light transmissive plastic film core stock  102 . Alternatively, the metal foil can be embossed onto plastic film core stock  102  from a separate metal foil supply. 
   Alternatively, front capacitive electrode power distribution bus elements  132 , rear capacitive electrode power distribution bus  140 , electrical power contacts  124 ,  126 ,  148  and  150 , switch contact elements  116  and  118 , switch shunt  120 , electrical distribution elements  128 ,  130 ,  152  and  154  may be printed in electrically conductive ink upon the surface of plastic film core stock  102 . Additional alternate construction includes the use of a patterned conductive polymer layer to substitute for the metal foil layer of plastic film core stock  102 . The typical thickness of plastic film core stock  102  is approximately 0.005 inch. The die cutting or chemical etching process can be performed by any of numerous conventional means. Additionally, the plastic film core stock  102  may be coupled to a conventional optically registered flat stock indexing feed mechanism (not shown) to facilitate automated production. 
   In the next step, a layer of electrically conductive, light transmissive ink is applied over front capacitive electrode power distribution bus elements  132  to create a front capacitive plate  134 . In an alternative step, the electrically conductive, light transmissive ink layer forming front capacitive electrode  134  may be augmented or replaced by a conductive metal oxide layer such as indium tin oxide (ITO). In another alternative step, the front capacitive electrode  134  may be augmented or replaced by a conductive, light transmissive polymer layer such as PEDOT, (Poly-3,4-Ethyelenedioxithiophene). 
   In the following step, a layer of hygrophobically compounded EL phosphor ink  136  is applied over the front capacitive plate  134  providing a precisely defined illumination pattern. Following this, hygrophobically compounded capacitive dielectric ink  138  is applied over phosphor layer  136 . The capacitive dielectric ink  138  is allowed to bleed approximately 0.020 inch beyond the edges of the front capacitive electrode power distribution bus element  132 , and up to the inside edge of rear capacitive power distribution bus  140 , thereby electrically insulating front electrode  134 , phosphor layer  136  and power distribution element  154 . Additionally, the dielectric ink may also extend well beyond the rear electrode pattern so as to provide a positive aesthetic appearance to the final assembly. Additionally, the dielectric ink may be dyed or imbued with pigmentation to provide for illuminated and non-illuminated color effects. 
   An electrically conductive ink layer is then applied over capacitive dielectric ink layer  138  defining a rear capacitive electrode  142 . The electrically conductive ink layer  142  is allowed to blood beyond the capacitive dielectric layer  138  and onto rear capacitive power distribution bus  140 , completing electrical connection therebetween and providing a means to address electrical answer to rear capacitive electrode  142 . The use of an optically registered flat stock indexing feed mechanism allows the distribution of capacitive dielectric ink, El phosphor ink and electrically conductive inks to be specifically limited to those areas which are to be illuminated. For example, complex graphical patterns such as circles within circles, text, or individually addressable EL lamp indicia elements may be created. 
   As shown in  FIG. 1 , the rear capacitive electrode  144  and the EL phosphor layer  138  define a rectangular area of illumination. However, the specific shape of the area of illumination is not limited to simple rectangles, circles and polygons. Any pattern with which the rear capacitive electrode  104  may be made and any pattern that may be printed in EL phosphor ink may also define the area of illumination. Similarly, the shapes of switch contacts  116  and  118 , and the switch shunt  120  may also be defined as shapes other than simple rectangles, squares or circles. 
   Continuing with  FIG. 1 , a polyester film is applied over the entire lamp surface to provide electrical and environmental encapsulation layer  144 . Typical application of environmental encapsulation layer  144  leaves electrical power contacts  124 ,  126 ,  148  and  150 , switch contact elements  116  and  118 , and switch shunt  120  exposed. Ordinarily, environmental encapsulation layer  144  is approximately 0.0005-0.010 in thickness, depending upon the level of isolation desired for specific applications. An alternative to polyester film environmental encapsulation  144  is polycarbonate, or any other plastic film or sheet suitable for specific illuminated switch applications. An alternative construction also allows use of screen-printable, or flood-coated, ultraviolet light activated encapsulating inks as environmental encapsulation  144 . 
   In the next step, spacer  122  and switch actuator  146  are printed using thick film elastomer ink. Spacer  122  surrounds switch shunt  120  providing mechanical and electrical isolation. Switch actuator  146  is printed as a hemispherical bumps on top of encapsulation layer  144  located in relation to the center of rear capacitive electrode  142 . Alternatively, spacer  122  and switch actuator  146  may also be printed thick film adhesive. Another alternative construction of spacer  122  and switch actuator  146  may be adhesively mounted, molded or die cut plastic forms. 
   Upon completion of all printing and lamination processes, plastic core stock  102  is, further trimmed via die cutting to form a subassembly of flexible elements that define operating surfaces of the finished EL illuminated membrane switch. These elements consist of stationary switch contact plane  104 , hinge portion  106 , switch shunt plane  108 , hinge portion  110 , EL illuminated actuator plane  112 , and electrical connector tab  114 . 
   In an alternative first step, the metal foil may be replaced boy a metal plated surface that is patterned into front capacitive electrode power distribution bus element  132 , rear capacitive electrode power distribution bus  140 , electrical power contacts  124 ,  126 ,  148  and  150 , switch contact elements  116  and  118 , switch shunt  120 , and electrical distribution elements  128 ,  130 ,  152  and  154 . 
   In another alternative first step, an electrically conductive plastic film that has been die cut or chemically modified to create the above referenced electrical elements may replace the metal foil. In addition, a plastic dielectric film imbued with EL phosphors may replace the EL phosphor ink layer  136 . Similarly, the conductive ink front capacitive electrode  134  may be replaced or augmented by a plating of ITO or other metal/metal oxide light transmissive, electrically conductive layer applied over the front capacitive electrode power distribution bus elements  132 . 
   Plastic core stock  102  may be replaced any variety of flexible non-conducting materials such as a thin fiber reinforced plastic or plastic laminated paper. 
   Referring now to  FIG. 2 , a cross-sectional view of the construction of a first exemplary EL illuminated membrane switch  100 , constructed in accordance with the  FIG. 1  method is shown. EL illuminated membrane switch  100  includes plastic core stock  102 ; stationary switch contact plane  104 ; hinge portion  106 ; switch shunt plane  108 ; hinge portion  110 ; EL illuminated actuator plane  112 ; electrically isolated switch contacts  116  and  118 ; mechanical spacer  122  that defines isolation space S; front capacitive electrode power distribution bus  132 ; light transmissive, electrically conductive front capacitive electrode  134 ; electroluminescent phosphor layer  136 ; capacitive dielectric layer  138 ; rear capacitive electrode power distribution bus  140 ; rear capacitive electrode  142 ; environmental encapsulation layer  144 ; and switch actuator  146 . 
   When suitable alternating (AC), or pulsed direct current (DC) voltage is applied to power distribution buses  132  and  140 , electrical energy is transferred to capacitive electrodes  134  and  142  causing EL phosphor layer  138  to fluoresce with visible light. 
   Hinge portion  106  is positioned such that switch shunt actuator plane  108  substantially parallels stationary switch contact plane  104 , locating switch shunt  120  directly opposite switch contacts  116  and  118 . Spacer  122  isolates switch shunt  120  from switch contacts  116  and  118 , creating an opening defining isolation space S. Hinge portion  110  is positioned such that EL illuminated actuator plane  112  substantially parallels stationary switch contact plane  104 , locating EL lamp elements  132 ,  134 ,  136 ,  138 ,  142 , and switch actuator  146  approximately centered above switch shunt  120  such that, when mechanical pressure is applied to EL illuminated actuator plane  112 , said mechanical force is transferred throughout all intervening layers to the interface between switch actuator  114  and switch shunt actuator plane  108 . Switch shunt actuator plane  108  is thus deformed such that switch shunt  120  is forced against switch contacts  116  and  118 , thereby creating an electrical current path between switch contacts  116  and  118 . 
   Referring again to  FIG. 2 , note that capacitive dielectric insulation layer  138  is allowed to fill the gap between the rear capacitive electrode power distribution bus  140  and front capacitive electrode  134 . Also note that EL phosphor layer  136  is not allowed to bleed outside of front capacitive electrode power distribution bus  132 . Note also that capacitive dielectric layer  138  provides complete isolation of both front capacitive electrode  134  and EL phosphor layer  136  from rear capacitive electrode  142 . Additionally, electrically conductive layer  134  contacts the front capacitive electrode power distribution bus  132  making electrical connection therebetween. Rear capacitive electrode  142  is allowed to bleed onto rear capacitive power distribution bus  140 , thus forming electrical contact therebetween. Polyester film environmental encapsulation  144  bleeds beyond all previous layers and extends onto plastic core stock  102 , providing both electrical safety isolation and ant environmental attack resistant encapsulating envelope. Finally, switch actuator  146  is designed such as to minimize unwanted flexing of the EL illumination layers, while it is also large enough to provide ample pressure to force switch shunt  120  against switch contacts  116  and  118 . 
   In an alternative construction, switch shunt  120  and switch shunt actuator plane  108  may be embossed to form a snap action shape. Switch shunt  120  may be shapes s a concave surface bounded by spacer  122 , while switch shunt actuator plane  108  is shaped as a convex surface inboard of spacer  122  that mechanically interfaces actuator  146 . This construction provides a satisfying tactile “snap” when force is applied by actuator  146 . 
     FIG. 3  provides an electrical schematic diagram of the various elements of preferred embodiment  100 . When force is applied to actuator  146 , shunt  120  bridges contacts  116  and  118 . Electrical current path is then made beginning at terminal  124 , carried by distribution path  128  to contact  116  bridging through shunt  120  to contact  118 , carried by distribution path  130  to terminal  126 . In a separate portion of this schematic diagram, alternating current  156  is applied to electrical terminations  148  and  150 . Current flow from electrical termination  148  is carried by distribution element  152  to rear capacitive electrode power distribution bus  140 , and hence to rear capacitive plate  142 . Oppositional AC current  156  is applied to electrical contact  150 , carried by distribution element  154  to front capacitive electrode power distribution bus  132 , and thence to front capacitive plate  134 . Capacitive dielectric layer  138  isolates electroluminescent phosphor  136  and, together these layers form a light emitting capacitor dielectric. Front capacitive plate  134  is light transmissive, allowing visible light to escape the construction. 
   This isolated construction method allows the electroluminescent lamp portion to be independently addressed relative to the switch functions. However, by series connections of the switch portion to the electroluminescent lamp portion and the AC power source  156 , successful switch contact actuation may be confirmed by concurrent EL lamp illumination. 
     FIG. 4  is a top view diagram illustrating a second preferred embodiment of an electroluminescent illuminated membrane switch  200  in accordance with the present invention. In the first step of the method, typically an approximately 0.001 inch thick metal foil is die cut or chemically etched to form one or more rear capacitive electrodes  232 , front capacitive electrode power distribution bus  234 , electrical power contacts  244  and  246 , electrical distribution elements  248  and  250  that are all permanently bonded to one surface of a plastic film core stock  202 . An approximately 0.001 inch thick metal foil is die cut or chemically etched to form switch contacts  216  and  218 , switch shunt  220 , electrical power contacts  226  and  228 , electrical distribution elements  230  and  232  that are all permanently bonded to the opposite surface of core stock  202 . 
   Alternatively, the metal foil can be embossed onto plastic film core stock  202  from a separate metal foil supply. Alternatively, front capacitive electrode power distribution bus elements  234 , rear capacitive electrode  232 , electrical power contacts  226 ,  228 ,  244  and  246 , switch contact elements  216  and  218 , switch shunt  220 , electrical distribution elements  230 ,  232 ,  248  and  250  may be printed in electrically conductive ink upon the opposing surfaces of core stock  202 . The typical thickness of plastic film core stock  202  is approximately 0.005 inch. The die cutting or chemical etching processes can be performed by any of numerous conventional means. Additionally, the plastic film core stock  202  may be coupled to a conventional optically registered flat stock indexing feed mechanism (not shown) to facilitate automated production. 
   In the next step, a layer of capacitive dielectric ink  236  is applied over rear capacitive electrode  232 , bleeding approximately 0.020 inch beyond rear capacitive electrode  232 , extending well over electrical distribution element  250  and also up to the inside edge of front capacitive electrode power distribution bus  234 , thereby insulating rear capacitive electrode  232 . Additionally, the dielectric ink may also extend well beyond the rear electrode pattern so as to provide a positive aesthetic appearance to the final assembly. Further, the dielectric ink may be dyed or imbued with pigmentation to provide for illuminated and non-illuminated color effects. 
   Further in  FIG. 2 , a layer of hygrophobically compounded EL phosphor ink  238  is applied over the dielectric layer  236  providing a precisely defined illumination pattern. Next is to print front capacitive plate  240  using electrically conductive, light transmissive ink that is allowed to bleed onto power distribution bus  234 . In an alternative step, the electrically conductive, light transmissive ink layer forming front capacitive electrode  240  may be augmented or replaced by a conductive metal oxide layer such as indium tin oxide (ITO). 
   The use of an optically registered flat stock indexing feed mechanism allows the distribution of capacitive dielectric ink, El phosphor ink and electrically conductive inks to be specifically limited to those areas which are to be illuminated. For example, complex graphical patterns such as circles within circles, text, or individually addressable EL lamp indicia elements may be created. 
   As shown in  FIG. 4 , the rear capacitive electrode  232  and the EL phosphor layer  238  define a circular area of illumination. However, the specific shape of the area of illumination is not limited to simple rectangles, circles and polygons. Any pattern with which the rear capacitive electrode  232  may be made and any pattern that may be printed in EL phosphor ink may also define the area of illumination. Similarly, the shapes of switch contacts  216  and  218 , and the switch shunt  220  may also be defined as shapes other than simple rectangles, squares or circles. 
   Continuing with  FIG. 4 , a light transmissive polyester film is applied over the entire lamp surface to provide electrical and environmental encapsulation layer  242 . Typical application of environmental encapsulation layer  242  leaves electrical power contacts  244  and  246  exposed. Ordinarily, environmental encapsulation layer  242  is approximately 0.0005-0.010 in thickness, depending upon the level of isolation desired for specific applications. An alternative to polyester film environmental encapsulation  242  is polycarbonate, or any other plastic film or sheet suitable for specific illuminated switch applications. An alternative construction also allows use of screen-printable, or flood-coated, ultraviolet activated light transmissive encapsulating inks as environmental encapsulation  242 . 
   Upon completion of all printing and lamination processes, plastic core stock  202  is further trimmed via die cutting to form flexible elements that define operating surfaces of the finished EL illuminated membrane switch. These elements consist of stationary switch contact plane  204 , hinge portion  206 , switch shunt plane  208 , hinge portion  210 , EL illuminated actuator plane  212 , and electrical connector tab  214 . During the die cutting process, an area of stationary switch contact plane  204  is embossed to create serpentine spring member  222  and switch actuator portion  224 . Spring member  222  surrounds switch shunt  220  providing mechanical and electrical isolation. Switch actuator portion  224  is defined as the area inboard of spring member  222 . 
   In an alternative first stop, the metal foil of either surface of core stock  202  may be replaced by a metal plated surface that is formed into front capacitive electrode power distribution bus elements  234 , rear capacitive plate  232 , electrical power contacts  226 ,  228 ,  244  and  246 , switch contact elements  216  and  218 , switch shunt  220 , and electrical distribution elements  230 ,  232 ,  248  and  250 . 
   In another alternative first step, a double sided, electrically conductive plastic film that has been die cut or chemically modified to create the above referenced electrical elements may replace the metal foil. In addition, a plastic dielectric film imbued with EL phosphors may replace the EL phosphor ink layer  236 . Similarly, the conductive ink front capacitive electrode  238  may be replaced or augmented by a plating of ITO or other metal/metal oxide light transmissive, electrically conductive layer applied over the front capacitive electrode power distribution bus elements  234 . 
   Plastic film core stock  202  may be replaced any variety or flexible non-conducting materials such as a thin fiber reinforced plastic, or alternately a plastic coated paper. 
   Referring now to  FIG. 5 , a cross-sectional view of the construction of second exemplary EL illuminated membrane switch  200 , constructed in accordance with the  FIG. 4  method is shown. EL illuminated membrane switch  200  includes plastic core stock  202 ; stationary switch contact plane  204 ; hinge portion  206 ; switch shunt plane  208 ; hinge portion  210 ; EL illuminated actuator plane  212 ; electrically isolated switch contacts  216  and  218 ; spring member  222  and switch actuator portion  224  defining isolation space S; front capacitive electrode power distribution bus  234 ; light transmissive, electrically conductive front capacitive electrode  240 ; electroluminescent phosphor layer  238 ; capacitive dielectric layer  236 ; front capacitive electrode power distribution bus  234 ; rear capacitive plate  232 ; environmental encapsulation layer  242 ; and switch actuator portion  224 . 
   When suitable alternating (AC), or pulsed direct current (DC) voltage is applied to rear capacitive plate  232 , and via power distribution bus  234  to front capacitive plate  240 , EL phosphor layer  238  fluoresces with visible light. 
   Hinge portion  206  is positioned such that switch shunt actuator plane  208  substantially parallels stationary switch contact plane  204 , locating switch shunt  220  approximately opposite switch contacts  216  and  218 . Spring member  222  and switch actuator portion  224  isolate switch shunt  220  from switch contacts  216  and  218 , creating an opening that defines isolation space S. Hinge portion  210  is positioned such that EL illuminated actuator plane  212  substantially parallels stationary switch contact plane  204 , locating EL lamp elements  232 ,  234 ,  236 ,  238 , and  240  approximately centered above switch shunt  220  such that, when mechanical pressure is applied to encapsulation layer  242 , said mechanical force is transferred between intervening layers to the interface between EL illuminated actuator plane  212  and switch actuator portion  224 , and thence switch shunt  220 . Switch shunt actuator portion  224  is thus deformed such that switch shunt  220  is forced against switch contacts  216  and  218 , thereby creating an electrical current path between switch contacts  216  and  218 . 
   Referring again to  FIG. 5 , note that capacitive dielectric insulation layer  236  is allowed to fill the gap between the front capacitive electrode power distribution bus  234  and rear capacitive plate  232 . Also note that EL phosphor layer  238  is not allowed to bleed outboard of rear capacitive electrode  232 . Note also that capacitive dielectric layer  238  provides complete isolation of rear capacitive plate  232 , thus electrically isolating EL phosphor layer  238 . Additionally, electrically conductive layer  240  contacts the front capacitive electrode power distribution bus  234  making electrical connection therebetween. Polyester film environmental encapsulation  242  bleeds beyond all previous layers and extends onto plastic core stock  202 , providing both electrical safety isolation and an environmental attack resistant encapsulating envelope. 
   In an alternative construction, switch shunt  220  and switch shunt actuator portion  224  may be embossed to form a snap acting shape. Switch shunt  220  may be shaped as a substantially concave surface bounded by serpentine spring member  222 , while switch shunt actuator portion  224  is shaped as a substantially convex surface that mechanically interfaces with illuminated actuator plane  212 . This construction provides a satisfying tactile “snap” when mechanical force is applied by actuation of illuminated actuator plane  212 . 
     FIG. 6  provides an electrical schematic diagram of the various elements of preferred embodiment  200 . When force is applied to switch actuator portion  224 , shunt  220  bridges contacts  216  and  218 . Electrical current path is then made beginning at terminal  226 , carried by distribution path  230  to contact  216 , bridging through shunt  220  to contact  218 , carried by distribution path  232  to terminal  228 . In a separate portion of this schematic diagram, alternating current  252  is applied to electrical terminations  244  and  246 . Current flow from electrical termination  246  is carried by distribution element  250  to rear capacitive plate  232 . Opposition AC current  252  is applied to electrical contact  244 , carried by distribution element  248  to front capacitive electrode power distribution bus  234 , and thence to light transmissive front capacitive plate  240 . Capacitive dielectric layer  236  isolates electroluminescent phosphor  238 , and, together these layers form a light emitting capacitor dielectric. 
   This isolated construction method allows the electroluminescent lamp portion to be independently addressed relative to the switch functions. However, by series connection of the switch portion with the electroluminescent lamp portion and to the AC power source  252 , successful switch contact actuation may be confirmed by concurrent EL lamp illumination. 
     FIG. 7  is a top view diagram illustrating a third preferred embodiment of an electroluminescent illuminated membrane switch  300  in accordance with the present invention. In the first step of the method, typically an approximately 0.001 inch thick metal foil is die cut or chemically etched to form one or more rear capacitive plates  336 , front capacitive electrode power distribution bus  338 , electrical power contacts  348  and  350 , electrical distribution elements  352  and  354  that are all permanently bonded to one surface of a plastic film core stock  302 . An approximately 0.001 inch thick metal foil is die cut or chemically etched to form switch contacts  316  and  318 , switch shunt  320 , electrical power contacts  328  and  330 , electrical distribution elements  332  and  334  that are all permanently bonded to the opposite surface of core stock  302 . Alternatively, the metal foil can be embossed onto plastic film core stock  302  from a separate metal foil supply. Alternatively, front capacitive electrode power distribution bus elements  338 , rear capacitive plate  336 , electrical power contacts  328 ,  330 ,  348  and  350 , switch contact elements  316  and  318 , switch shunt  320 , electrical distribution elements  332 ,  334 ,  352  and  354  may be printed in electrically conductive ink upon the opposing surfaces of core stock  302 . The typical thickness of plastic film core stock  302  is approximately 0.005 inch. The die cutting or chemical etching can be performed by any of numerous conventional means. Additionally, the plastic film core stock  302  may be coupled to a conventional optically registered flat stock indexing feed mechanism (not shown) to facilitate automated production. 
   In the next step, a layer of capacitive dielectric ink  340  is applied over rear capacitive electrode  336 , bleeding approximately 0.020 inch beyond rear capacitive plate  336 , extending well over electrical distribution element  354  and also up to the inside edge of front capacitive electrode power distribution bus  338 , thereby insulating rear capacitive plate  336 . Additionally, the dielectric ink may also extend well beyond the rear electrode pattern so as to provide a positive aesthetic appearance to the final assembly. Additionally, the dielectric ink may be dyed or imbued with pigmentation to provide for illuminated and non-illuminated color effects. 
   Following this, a layer of hygrophobically compounded EL phosphor ink  342  is applied over the dielectric layer  340  providing a precisely defined illumination pattern. Next is to print front capacitive electrode  344  using electrically conductive, light transmissive ink that is allowed to bleed onto power distribution bus  338 . In an alternative step, the electrically conductive, light transmissive ink layer forming front capacitive plate  344  may be augmented or replaced by a conductive metal oxide layer such as indium tin oxide (ITO). 
   The use of an optically registered flat stock indexing feed mechanism allows the distribution of capacitive dielectric ink, El phosphor ink and electrically conductive inks to be specifically limited to those arrears which are to be illuminated. For example, complex graphical patterns such as circles within circles, text, or individually addressable EL lamp indicia elements may be created. 
   As shown in  FIG. 7 , the rear capacitive plate  336  and the EL phosphor layer  342  define a circular area of illumination. However, the specific shape of the area of illumination is not limited to simple rectangles, circles and polygons. Any pattern with which the rear capacitive plate  336  may be made and any pattern that may be printed in EL phosphor ink may also define the area of illumination. Similarly, the shapes of switch contacts  316  and  318 , and of switch shunt  320  may also be defined as shapes other than simple rectangles, squares or circles. 
   Now continuing with  FIG. 7 , a light transmissive polyester film is applied over the entire lamp surface to provide electrical and environmental encapsulation layer  346 . Typical application of environmental encapsulation layer  346  leaves electrical power contacts  348  and  350  exposed. Ordinarily, environmental encapsulation layer  346  is approximately 0.0005-0.010 in thickness, depending upon the level of isolation desired for specific applications. An alternative to polyester film environmental encapsulation  346  is polycarbonate, or any other plastic film or sheet suitable for specific illuminated switch applications. An alternative construction also allows use of screen-printable, or flood-coated, ultraviolet activated light transmissive encapsulating inks as environmental encapsulation  346 . 
   Upon completion of all printing and lamination processes, plastic core stock  302  is further trimmed via die cutting to form flexible elements that define operating surfaces of the finished EL illuminated membrane switch. These elements consist of stationary switch contact plane  304 , hinge portion  306 , isolation plane  308 , hinge portion  310 , EL illuminated actuator plane  312 , and electrical connector tab  314 . During the die cutting process, an area of isolation plane  308  is embossed to create serpentine spring member  322  and aperture opening  324 . Spring member  322  surrounds aperture opening  324  providing mechanical and electrical isolation between switch contacts  316  and  318 , and switch shunt  320 . 
   In an alternative first step, the metal foil of either surface of core stock  302  may be replaced by a metal plated surface that is formed into front capacitive electrode power distribution bus elements  338 , rear capacitive plate  336 , electrical power contacts  328 ,  330 ,  348  and  350 , switch contact elements  316  and  318 , switch shunt  320 , anus electrical distribution elements  332 ,  334 ,  352  and  354 . 
   In another alternative first step, a double sided, electrically conductive plastic film that has been die cut or chemically modified to create the above referenced electrical elements may replace the metal foil. In addition, a plastic dielectric film imbued with EL phosphors may replace the EL phosphor ink layer  342 . Similarly, the conductive ink front capacitive plate  344  may he replaced or augmented by a plating of ITO or other metal/metal oxide light transmissive, electrically conductive layer applied over the front capacitive electrode power distribution bus elements  338 . 
   Plastic film core stock  302  may be replaced any variety of flexible non-conducting materials such as a thin fiber reinforced plastic or plastic coated paper. 
   Referring now to  FIG. 8 , a cross-sectional view of the construction or third exemplary EL illuminated membrane switch  300 , constructed in accordance with the  FIG. 7  method is shown. EL illuminated membrane switch  300  includes plastic core stock  302 ; stationary switch contact plane  304 ; hinge portion  306 ; isolation plane  308 ; hinge portion  310 ; EL illuminated actuator plane  312 ; electrically isolated switch contacts  316  and  318 ; serpentine spring member  322  and aperture opening  324  defining isolation space S; rear capacitive plate  336 ; front capacitive electrode power distribution bus  338 ; light transmissive, electrically conductive front capacitive electrode  344 ; electroluminescent phosphor layer  342 ; capacitive dielectric layer  340 ; and environmental encapsulation layer  346 . 
   When suitable alternating (AC), or pulsed direct current (DC) voltage is applied to rear capacitive plate  336 , and via power distribution bus  338  to capacitive plate  344 , EL phosphor layer  342  fluoresces with visible light. 
   Hinge portion  306  is positioned such that isolation plane  308  substantially parallels stationary switch contact plane  304 , locating aperture opening  324  approximately opposite switch contacts  316  and  318 . Serpentine spring member  322  projects from isolation plane  308  and is substantially centered opposite of switch contacts  316  and  318 . Further, spring member  322  forms a frame outboard of switch contacts  316  and  318 , and in conjunction with aperture opening  324  creates an opening that defines isolation space S. Aperture opening  324 , slightly larger in size than the profile of switch shunt  320  forms an access path for switch shunt  320  to make connection with switch contacts  316  and  318 . Hinge portion  310  i s positioned such that EL illuminated actuator plane  312  substantially parallels stationary switch contact plane  304 , locating switch shunt  320  approximately opposite aperture  324  and switch contacts  316  and  318 . EL lamp elements  336 ,  340 ,  342 , and  344  arc essentially centered above switch shunt  320  such that, when mechanical pressure is applied to encapsulation layer  346 , mechanical force is transferred between intervening layers to switch shunt  320 . Switch shunt  320  and serpentine spring element  322  are thus compressively deformed such that switch shunt  320  is forced against switch contacts  316  and  318 , thereby creating an electrical current path between switch contacts  316  and  318 . Upon release of mechanical pressure applied to encapsulation layer  346 , spring element  322  returns to its relaxed mechanical state, forcibly separating switch shunt  320  from switch contacts  316  and  318  thus recreating isolation space S. 
   Again referring to  FIG. 8 , note that capacitive dielectric insulation layer  340  is allowed to fill the gap between the front capacitive electrode power distribution bus  338  and rear capacitive plate  336 . Also note that EL phosphor layer  342  is not allowed to bleed outboard of rear capacitive plate  336 . Note also that capacitive dielectric layer  340  provides complete isolation of rear capacitive plate  336 , thus electrically isolating EL phosphor layer  342 . Additionally, electrically conductive layer  344  contacts the front capacitive, electrode power distribution bus  338  making electrical connection therebetween. Polyester film environmental encapsulation  346  bleeds beyond all previous layers and extends onto plastic core stock  302 , providing both electrical safety isolation and an environmental attack resistant encapsulating envelope. 
   In an alternative construction, switch shunt  320 , EL illuminated actuator plane  312  and EL lamp elements  336 ,  340 ,  342 , and  344  may be embossed to form a snap action shape. Switch shunt  320  may be shaped as a substantially concave surface approximating the size of aperture  321 , while EL illuminated actuator plane  312  and EL lamp elements  336 ,  340 ,  342 , and  344  are formed as a substantially convex surface. Additionally, serpentine spring member  322  may be eliminated as it becomes redundant for this construction. This alternate construction provides a satisfying tactile “snap” when mechanical force is applied to encapsulation layer  346  at a point approximating the centerline of switch shunt  320 . 
     FIG. 9  is an electrical schematic diagram of the various elements of preferred embodiment  300 . When mechanical force is applied to EL illuminated actuator plane  312 , shunt  320  bridges contacts  316  and  318 . Electrical current path is then made beginning at terminal  328 , carried by distribution element  332  to contact  316 , bridging through shunt  320  to contact  318 , carried by distribution element  334  to terminal  330 . In a separate portion of this schematic diagram, alternating current (AC)  356  is applied to electrical terminations  348  and  350 . Current flow from electrical termination  350  is carried by distribution element  354  to rear capacitive plate  336 . Oppositional AC current  356  is applied to electrical contact  348 , carried by distribution element  352  to front capacitive electrode power distribution bus  338 , and thence too eight transmissive front capacitive plate  344 . Capacitive dielectric layer  340  isolates electroluminescent phosphor  342  and, together these layers form a light emitting capacitor dielectric. 
   This isolated construction method allows the electroluminescent lamp portion to be independently addressed relative to the switch functions. However, by series connection of the switch portion with the electroluminescent lamp portion and to the AC power source  356 , successful switch contact actuation may be confirmed by concurrent EL lamp illumination. 
     FIG. 10(   a ) is an isometric view of the subassembly manufacturing process plane of first exemplary EL illuminated switch  100 , constructed in accordance with the method of  FIG. 1 . Herein, connector tab  114  extending from stationary switch contact plane  104 , and supporting electrical connection terminals  124 ,  126 ,  148  and  150 , is shown in a position that approximates the centerline between switch contacts  116  and  118 . 
     FIG. 10(   b ) is an isometric view of the subassembly manufacturing process plane of first exemplary EL illuminated switch  100 , constructed in accordance with the method of  FIG. 1 . Herein, connector tab  114  extending from EL illuminated actuator plane  112 , and supporting electrical connection terminals  124 ,  126 ,  148  and  150 , is shown in a position that approximates the centerline of actuator  146 . 
     FIG. 11(   a ) illustrates an isometric view of first exemplary EL illuminated switch  100 , constructed in accordance with the method of  FIG. 10(   a ) in the completed assembly folded condition. Herein, connector tab  114  extending from stationary switch contact plane  104 , and supporting electrical connection terminals  124 ,  126 ,  148  and  150 , is shown whereby electrical connection terminals  124 ,  126 ,  148  and  150  are facing toward the EL illuminated actuating plane  112 . 
     FIG. 11(   b ) illustrates an isometric view of first exemplary EL illuminated switch  100 , constructed in accordance with the method of  FIG. 10(   b ) in the completed assembly folded condition. Herein, connector tab  114  extending from EL illuminated actuator plane  112 , and supporting electrical connection terminals  124 ,  126 ,  148  and  150 , is shown whereby electrical connection terminals  124 ,  126 ,  148  and  150  are facing toward the stationary switch contact plane  104 . 
   Together,  FIGS. 10(   a ) &amp; ( b ) and  11 ( a ) &amp; ( b ) demonstrate the reversibility of electrical connection terminal planes, facilitating the utility of the invention in various electrical and electronic illuminated membrane switch applications. 
     FIG. 12  illustrates an isometric view of first exemplary EL, illuminated switch  100 , constructed in accordance with the method of  FIG. 1  installed within a housing, creating an illuminated keypad switch  400  with connector tab  114  protruding from a side. Keypad switch  400  consists of a lower housing  402 , an upper housing  404  and a light transmissive actuator key  406 . Although keypad switch  400  as illustrated herein is a cube shape for clarity, any shape convenient to an end use may be made within the scope of the present invention. Further, although the light transmissive actuator key  406  is illustrated as a cylindrical shape, any shape convenient to end use function may be employed. Such shapes may include, but not be limited to geometric forms; characters; letters; numerals; or indicia. 
     FIG. 13  is an isometric blow-apart view of keypad switch  400 , illustrating the individual components that comprise the completed switch assembly. Lower housing  402  consists of walls  408  that are approximately perpendicular to switch support surface  416 , walls  408  having interior surfaces  410  and exterior surfaces  412 , and an opening  414  corresponding in size to connector tab  114  of EL illuminated membrane switch  100 . Interior surfaces  410  are approximately perpendicular to switch support surface  416 , and together these elements create a cavity that intersects opening  414 . 
   Upper housing  404  consists of walls  418  that are approximately perpendicular to keypad actuator support surface  426 , walls  418  having interior surfaces  422  and exterior surfaces  420 , and a tab  424  that extends planar to walls  418 . Tab  424  corresponds in size to opening  414  of lower housing  402 , and is of an engaging length equal to the depth of lower housing  402  walls  408  less the thickness of switch  100  connector tab  114 , compressively locking connector tab  114  against switch support surface  416 . Interior surfaces  422  are approximately perpendicular to keypad actuator support surface  426 , and together these elements create an interior cavity with an aperture  428  for access of key  406 . 
   Continuing with  FIG. 13 , light transmissive key  406  is comprised of a flange portion  430  that rests upon tho illuminated surface of switch  100 , and shaft  432  rising approximately perpendicularly from flange  430 , then terminating in surface  434 . The combined length of key  406  is such that shaft  432  protrudes through aperture  428  in order that mechanical pressure applied to surface  434  is transferred to flange  430  thus actuating switch  100 . When applied mechanical pressure is released from surface  434 , key  406  returns to its original position s a result of stored spring force in switch  100 . 
   Surface  434  may be planar, textured, hemi-spherically domed, printed, painted or otherwise decorated with characters, numerals, indicia, etc. Additionally, shaft  432  and aperture  428  may be correspondingly shaped as polygons, numeral, indicia, etc. to provide uniqueness of application. 
   Again referring to  FIG. 13 , the open terminating edges of walls  408  and  418  are permanently mated together, confining key  406  and switch  100  within the cavity formed by walls  408  and  418 , support surface  416  and keypad actuator support surface  426 . This then completes the assembly of illuminated keypad switch  400 . Thus, the method of the present invention provides an automated means to manufacture high volumes of electroluminescent illuminated membrane switches at minimal labor cost, and minimal constituent raw material wastage. Additionally, EL illuminated membrane switches produced by the method of the present invention consume low power, and generate little waste heat. Further, the EL illuminated membrane switches produced by the method of the present invention are significantly more robust than those of conventional manufacture, and may be connected to power sources and other controlling electrical circuitry via processes typically reserved for ordinary flexible printed circuit board products. 
   The forgoing description includes what are at present considered to be preferred embodiments of the invention. However, it will be readily apparent to those skilled in the art that various changes and modifications may be made to the embodiments without departing from the spirit and scope of the invention. Accordingly, it is intended that such changes and modifications fall within the scope of the invention, and that the invention be limited only by the following claims.