Patent Publication Number: US-8110765-B2

Title: Electroluminescent lamp membrane switch

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/438,182, filed May 22, 2006 now U.S. Pat. No. 7,186,936 and entitled “Electroluminescent Lamp Membrane Switch”; which application is a continuation of U.S. patent application Ser. No. 11/148,216 filed Jun. 9, 2005, and now U.S. Pat. No. 7,049,536, issued May 23, 2006. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to membrane switches, and more particularly to an integrated electroluminescent lamp system and membrane switch which reduces labor costs and cycle time in membrane switch manufacturing. 
     BACKGROUND 
     Conventional membrane switches are typically manufactured individually by laminating several independent elements with interposed double-sided adhesive sheets. The steps of die cutting, lamination, and assembly are repeated multiple times during manufacturing leading to a labor intensive and slow process. The typical elements of a conventional membrane switch include a graphic layer, laminating adhesive, embossed electrical contactors, spacer, electrical contact, laminate adhesive, and backing. These elements are individually manufactured, individually die cut and assembled layer by layer. Additionally, in many cases additional steps are required when adding an electroluminescent lamp and/or LED to backlight the switches. Additional steps are required to provide tactile feel using metal domes, poly domes, or magnetic switches. Indicator lights, and digital or alphanumerical displays are also often used either as a part of the membrane switch or adjacent to the switch. 
     Referring to  FIG. 1 , an exploded view of a conventional membrane switch using electroluminescent lamp technology is illustrated, and is generally identified by the numeral  20 . Layer  22  is a substrate with a printed graphic element  24 . A typical substrate layer  22  is made of polyester or polycarbonate with thicknesses of 3 to 7 mils. The graphic element  24  is usually on the bottom face so that substrate  22  will protect the graphic element  24 . Typically, graphic printing is completed in a batch process. The printing flow is broken up by the operation of die cutting. This cut out piece that typically includes substrate layer  22  and graphic element  24  is called a graphical overlay. 
     Layer  26  is an electroluminescent lamp printed on an Indium Tin Oxide (ITO) sputtered substrate. The substrate is typically polyester or polycarbonate, 3 to 5 mils thick. The substrate is sputtered with ITO. The ITO sputtered substrate is screen printed with the following layers: Silver ink bus bars 0.5 to 1.0 mils thick, Phosphor 1 to 1.5 mils thick, Dielectric layer containing barium titanate 0.2 to 0.6 mils thick, back electrode of silver or graphite filled inks 0.5 to 1 mils thick, insulating layer 2 to 6 mils thick. Once the lamp layer  26  has been successfully printed, it is die cut from the substrate. 
     Layer  22  and the lamp layer  26  are joined together in a laminating step. Layer  28  is a double-sided laminating adhesive and is die cut to the same size as the layer  22  and lamp layer  26 . The double-sided laminating adhesive layer  28  attaches the lamp layer  26  to the layer  22 . Alignment and removal of air bubbles are critical in lamination steps and are serious sources of defects. 
     A conductive contact element layer  30  is used to actuate the switches. This layer may include metal domes, polymer domes coated with a conductive layer or flat electrical contactors. The electrical contactors are used when a simple electrical contact is needed. The purpose of metal domes and poly domes is to give a tactile response when the switch is depressed. Conductive layer  30  is connected to lamp layer  26  using an adhesive layer  32 . 
     Layer  34 , the electrical circuit and contact points for the switch, is composed of a substrate of polyester or polycarbonate 3 to 7 mils thick. A first layer of conductive ink is printed on the substrate. These inks are often made with silver or graphite as the conductive elements. If more than one conductive layer is needed, an insulating layer is printed next to protect the first conductive layer. A second conductive layer is then printed. After successfully completing these steps the circuit layer  34  is then die cut. 
     A spacer layer  36  is also die cut. The spacer layer  36  is approximately the same thickness as the metal domes and has adhesive on both sides. After die cutting the spacer layer  36 , layer  36  and the circuit layer  34  are laminated together. Metal domes  38  are then placed in the holes  40  of the spacer layer  36  either manually or by a pick and place machine. Conductive layer  30  is applied over the spacer layer  36  and laminated into place. 
     The metal domes  38  and electrical circuit layer  34  are laminated to the conductive layer  30  using a double-sided laminating adhesive layer  36 . Adhesive layer  36  is die cut to the proper size before the lamination step. 
     A final laminating adhesive layer  42  is applied to circuit layer  34 . The laminating adhesive layer  42  is die cut into the desired shape and is applied to the back of the electrical circuit layer  34 . A release liner layer  44  is left on the laminating adhesive until the finished membrane switch  20  is applied to its final location on a circuit board or electronics enclosure. 
     In addition to the labor necessary to assemble these many different layers ( FIG. 1 ) there are significant quality and manufacturing issues that arise from the lamination steps required to produce a conventional membrane switch. These include, but are not limited to, die cut registration, alignment of the various layers, and removal of air trapped in the lamination process. Because the membrane switches are die cut each individual membrane switch must be processed one at a time. 
     Moreover, the placement of discreet lighting elements such as light emitting diodes, the connection of these elements to electrical traces with the use of conductive polymers, and the curing of these polymers are all very labor intensive operations. These operations steps may not be part of the membrane switch manufacturer&#39;s process. Hence, the manufacturer may outsource these operations to a third party vendor resulting in a disruption of the normal manufacturing flow. 
     When electroluminescent lamp lighting is used it is advantageous to place both the graphic and the lamp behind the deformable substrate. The deformable substrate is typically composed of either polyester or polycarbonate material that is very rugged and durable to environmental conditions. Common sources of electroluminescent lamp lighting do not allow graphics to be printed directly between the substrate and the optically transmissive conductive layer of the lamp nor do they permit graphic layers to be printed between the ITO and other layers of the lamp. This is because the graphic layers interfere with the electrical connection to the ITO conductive layer often used on the substrate and/or the graphic layer may contaminate other clear conductive layers that may be used instead of ITO. 
     Therefore, a need exists for combining electroluminescent lamp technology and membrane switch elements into a continuous manufacturing process that eliminates the conventional batch process used for lamination steps and the labor required to assemble the layers of the switch while protecting the graphics. 
     SUMMARY 
     The present disclosure addresses the above-described problems by printing layers of a membrane switch and an electroluminescent lamp in a single continuous process, layer after layer, without the need to stop and die cut and assemble these layers. As the layers are laid down and cured, they join by co-valent bonding, creating one monolithic structure. In an embodiment, the layers are screen printed primarily with UV-curable inks. When these inks are deployed in layer form and exposed to UV radiation, the inks cure quickly, thus improving process cycle time and leading to a continuous process. In other embodiments, inks cured by other means, such as thermal energy or electron beam radiation, could be used. 
     The continuous process is defined by the ability to cure each layer in seconds on a conveyor system and to print one layer right after the previous layer without taking the in-process membrane switch components to other steps such as die cutting and assembly. In addition, the switches are processed on sheets each containing multiple switches where all switches on any given sheet receive the same process steps simultaneously. The layer shape is formed during screen printing thus eliminating the need for the process steps of die cutting and assembly. There is no need to stop this process between the graphics layers, the lamp layers, the electrical elements of either, electrical contactors or circuits, insulating layers, spacer layers (if any) and contact adhesive layers (if any); these can all be printed in one continuous process. There is a reduction in cycle time due to the elimination of the die cutting and expensive labor intensive lamination steps. There is an optimization of handling time through the use of a continuous system because each layer now prints and cures in seconds. The membrane switches are processed on sheets containing many switches instead of processing each switch individually. In addition, the number of die cutting operations is reduced to just one or two, or none, if the switch and lamp are printed as one monolithic object; that is, with inseparable printed layers. Manufacturing is significantly optimized over traditional die cutting, lamination and assembly processes for individual lamps. 
     The reduction in cycle time and the elimination of the die cutting step and assembly steps can transform a batch processing to a continuous process. The process may involve curing on conveyor systems between printing stations as is well known in the art. There is a reduction in cycle time by the elimination of the die cutting and expensive labor intensive lamination steps, because each layer now can be printed and cured in seconds; there is an optimization of handling time through the use of a continuous system. Accordingly, a technical advantage of the present disclosure is that cycle times for the inventive membrane switch manufacturing processes are dramatically reduced. 
     In accordance with the present disclosure, a depressable substrate is coated with a graphical layer and in a continuous process further coated with an electroluminescent lamp having a polyurethane insulation layer formed on the graphic layer. This structure provides the benefit of the graphic layer and the electroluminescent lamp being protected behind the substrate. The polyurethane insulating layer also protects the sensitive electroluminescent layers from contamination from the graphical inks. 
     Graphical layers and electroluminescent lamp lighting may also be advantageously combined to form display elements. These display elements can be used to convey information such as status, numerical or alphanumerical data. The marginal cost of providing these display elements is very low because they can be printed simultaneously with the lamp and graphics without adding additional process steps. 
     The process just described results in a reduction of the total number of layers and the substrates contained in those layers and in the elimination of multiple assembly steps through a continuous printing and UV curing process. This reduction not only decreases the overall thickness of the membrane switch in the final device but also reduces the cost and process time to produce. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the following Description of the Preferred Embodiments taken in conjunction with the accompanying Drawings in which: 
         FIG. 1  is an exploded perspective view illustrating the construction of a conventional membrane switch that includes an electroluminescent lamp; 
         FIG. 2  is a cross-sectional view of the present electroluminescent lamp membrane switch; 
         FIG. 3  is a cross-sectional view of an additional embodiment; 
         FIG. 4  is a cross-sectional view of an additional embodiment; 
         FIG. 5  is a cross-sectional view of an additional embodiment; 
         FIG. 6  is a cross-sectional view of an additional embodiment; 
         FIG. 7  is a cross-sectional view of an additional embodiment; 
         FIG. 8  is a cross-sectional view of an embodiment illustrating the construction of an electroluminescent lamp and portions of a membrane switch; 
         FIG. 9  is a cross-sectional view of an embodiment illustrating the construction of an electroluminescent lamp and portions of a membrane switch; 
         FIG. 10  is a cross-sectional view of an embodiment illustrating the construction of an electroluminescent lamp and portions of a membrane switch; 
         FIG. 11  is a cross-sectional view of an embodiment illustrating the construction of an electroluminescent lamp and portions of a membrane switch; 
         FIG. 12  is a cross-sectional view of an embodiment illustrating the construction of an electroluminescent lamp and portions of a membrane switch; 
         FIG. 13  is a cross-sectional view of preferred embodiment illustrating the construction of a monolithic electroluminescent lamp and membrane switch; 
         FIG. 14  is an illustration of a graphic display used with the disclosed embodiments. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 2 , the present continuously printed electroluminescent lamp membrane switch combination is illustrated, and is generally identified by the numeral  50 . Switch  50  includes an electroluminescent lamp membrane system, generally identified by the numeral  52 , a membrane switch, generally identified by the numeral  54  and a graphics layer  56 . Lamp system  52  includes a top insulating layer  58  and a bottom insulating layer  60 . Top layer  58  has a front surface  58   a  and a back surface  58   b . Bottom insulating layer  60  includes a front surface  60   a  and a back surface  60   b . Disposed between insulating layers  58  and  60  is an electroluminescent lamp  62 . Lamp  62  includes various layers which will subsequently be described with respect to  FIG. 8 . Lamp  62  may comprise, for example, the electroluminescent lamp shown and described in U.S. Pat. No. 5,856,030, which disclosure and drawings are hereby incorporated by reference. 
     Top insulating layer  58  of lamp system  52  is directly imprinted on graphics layer  56 . Graphics layer  56  may include, for example, alpha numeric indicia which may be printed using a wide variety of inks, such as, for example, UV-cured polyurethane inks. No die cutting or lamination is required to form the combined graphics layer  56  and insulating layer  58  of lamp system  52 . Insulating layers  58  and  60  may comprise, for example, UV-curable polyurethane ink, inks cured by other means. 
     Various components of membrane switch  54  are illustrated in  FIGS. 8-13 . Membrane switch  54  may be constructed in a continuous printing process, as described above, so that no layers need to be cut out or receive manual handling, thus creating a monolithic switch fabricated as a single structure. In this case, a layer  120  is printed into the switch between first and second conductive layers or traces  86   a ,  90  for sensing actuation of the switch  54 . The layer for sensing actuation  120  may be a sensor for a change in capacitance (such as created by a user&#39;s finger approaching the switch), or a change in resistance due to pressure imparted by a user, or by detection of a magnetic field, such as that of a magnetic stylus. An illustration of the preferred embodiment is depicted in  FIG. 13 . 
     The layer for sensing actuation  120  of the monolithic membrane switch may be a curable polymer such as a urethane, epoxy, unsaturated and saturated acrylics and silicones in base resin compounds. Depending on the method of actuation desired, the polymer to print the layer for sensing actuation  120  would then include, for example, carbon-impregnated powdered rubber, indium, indium-tin oxide, carbon powder, nano-carbon powder, or nano-silver powder for resistance-change sensing; silver-coated coppers, coated iron particles, or low-carbon steel particles for magnetic sensing; and ferro-electric compounds such as barium titanate for capacitance-change sensing, and in all cases, the equivalents thereof. 
     Referring now to  FIG. 3 , switch  50  is illustrated as being integrally formed on a deformable substrate  66  which may comprise, for example, a layer of polycarbonate or polyester. Graphics layer  56  is directly printed on substrate  66  and is followed by insulating layer  58 . Substrate  66  provides a surface for a user to actuate switch  54  by depressing a portion of the deformable substrate  66 . Graphics layer  56  is protected by deformable substrate  66  since graphics layer  56  is disposed between deformable substrate  66  and insulating layer  58 . 
     Alternatively, as illustrated in  FIG. 4  graphics layer  68  may be imprinted on the outer surface of deformable substrate  66 . 
     Multiple layers of graphics may be included in switch  50 , as illustrated in  FIG. 5 , wherein both graphic layers  56  and  68  are used and are imprinted on the inner and outer surfaces of deformable substrate  66 . In this manner, multiple graphic indicia may be used with switch  50  and illuminated utilizing lamp system  52 . As previously indicated, graphic layers  56  and  68  may include various indicia, and may further include various multicolored graphic designs. 
       FIG. 6  further illustrates an additional embodiment of switch  50  in which insulating layer  58  is eliminated and lamp  62  is directly imprinted on deformable substrate  66 . 
       FIG. 7  illustrates a further embodiment of switch  50  in which deformable substrate  66  is disposed between lamp system  52  and membrane switch  54 . 
     Referring now to  FIG. 8 , an illustrative example of an electroluminescent lamp  62  is illustrated, it being understood that lamp  62  is shown for illustrative purposes only, and not by way of limitation. Lamp  62  includes a bus bar  74  that is printed on insulating layer  58 . A transparent electrically conductive front electrode  76  is then printed onto insulating layer  58 . A phosphor layer  78  is printed and is disposed on front electrode  76 . A high dielectric constant layer  80  is then printed onto layer  78 . Layer  80  may contain, among other compositions, for example, barium titanate. A rear electrode  82  is imprinted on layer  80 . Electrode  82  may include electrically conductive ink, typically containing silver or graphite. The inks used to print the various layers of lamp  62  may include UV curable inks. Insulating layer  60  is printed onto electrode  82  to complete the lamp system  52 . Power is supplied to electrodes  74  and  82  from a power supply  84 . 
       FIG. 8  also illustrates a component of membrane switch  54  including conductive pads  86  which are imprinted on insulating layer  60 . 
       FIGS. 9-13  further illustrate components within membrane switch  54 .  FIG. 9  illustrates an insulating layer  88  disposed on insulating layer  60  and between a conductive layer (typically a trace)  86   a  which is part of an electrical switch circuit. An additional conductive layer (typically a pad)  90  is illustrated and is the other half of the switch circuit and is disposed opposite trace  86   a .  FIG. 10  illustrates the further use of spacer elements  92  within switch  54 . (Note that spacer elements  92  are not required in monolithic switches printed by a continuous process). 
     As shown in  FIG. 11 , disposed between spacer elements  92  is a snap dome  94  which provides tactile feedback to the user of the switch  50 . 
       FIG. 12  illustrates the addition of adhesive layers  96  to spacers  92 . Adhesive layers  96  function to attach the remaining outer layer  100  ( FIG. 13 ) of switch  54 . (Note that the monolithic embodiment of the membrane switch  54  does not have an adhesive layer, since no separately-manufactured layers are assembled to create it.) 
       FIG. 13  illustrates a completed monolithic switch  54  and electroluminescent lamp  62 , according to the preferred embodiment. Closure of switch  54  is accomplished by a user  102  applying pressure from the deformable substrate  66 , which, in the case of a layer for sensing actuation  120  of the switch comprising a resistance change, caused actuation of the switch by a conventional sensing circuit (not shown). In other embodiments, the layer for sensing actuation  120  comprises material for sensing a change in capacitance, or a change in a magnetic field, as discussed above.  FIG. 13  shows the layer for sensing actuation  120  as having optionally areas of particular sensitivity  125  for separate switching circuits within the same monolithic switch  54 . 
       FIG. 14  illustrates an example of graphic indicia which may be included in graphics layers  56 ,  68  and  62 . A display  104  includes a numeric display  106  and an alpha display  108 . Display  104  also includes the necessary electronic circuitry for illuminating segments within display  106  and  108 . Display  104  also includes an indicator light  110 . 
     Since those skilled in the art can modify the specific embodiments described above, we intend that the claims be interpreted to cover such modifications and equivalents.