WO2008066490A1

WO2008066490A1 - 'ielk' (intelligent el keytop)

Info

Publication number: WO2008066490A1
Application number: PCT/SG2006/000374
Authority: WO
Inventors: Jit Ming Bryan Lim
Original assignee: Sinco Technologies Pte Ltd
Priority date: 2006-12-01
Filing date: 2006-12-01
Publication date: 2008-06-05
Also published as: TW200805408A

Abstract

A keypad (10) for a mobile telephone or the like. The key pad (10) has a key top surface (501) upon a transparent base substrate (502), and an electroluminescent lamp (whether 2 layer or 3 layer) formed directly upon the transparent base substrate (502). The EL lamp is provided by forming a transparent front electrode layer (504) upon a bottom side of the transparent substrate (502) opposite the top side, and forming a light-emitting layer (505) upon the transparent front electrode (504). In turn, a dielectric layer (506) is formed upon the light-emitting layer (505), and a rear conductor (507) is formed upon the dielectric layer (506). The need for a separate EL lamp module is thus avoided, improving design options for non-planar configurations of the keypad (10), as shown in Fig. 5a & 5b.

Description

"IELK" (INTELLIGENT EL KEYTOP)

Technical Field

The present invention relates to an electroluminescent keypad module and a method of constructing such a module, in particular for a mobile or cellular telephone.

Background of the Invention

Mobile telephones are an extremely widespread wireless communication appliance allowing portable use. Mobile telephone design may comprise a single piece or bar- type phone with exposed key buttons, a flip-type phone, a folding phone or a swinging type compact mobile phone having improved portability.

There exists a desire to provide for mobile telephones which are small in size, to improve user convenience in carrying the telephone. For example, folding telephones have been developed to provide a mobile telephone of shorter length when in the folded position than single-piece mobile telephones, while maintaining sufficient separation between speaker and microphone when unfolded and in use. Such folding mobile telephones may have a length (or height) of around 80-90mm. However the thickness (or depth) of folding telephones may be somewhat greater than single piece mobile telephones, for example a folding telephone may have a thickness of around 25-30 mm. On the other hand, while single piece mobile telephones may have a length of the order of 100-120 mm, the thickness or depth of single piece mobile telephones may be around 20 mm. Depending on user or application, such distinctions in device size and proportion can be of much importance.

In the interests of reducing the size of mobile telephones, much effort has been put into minimising the dimensions of all components of the telephone, while maintaining or improving functionality. However, normal usage of mobile phones involves relatively robust treatment, and device size minimisation must not reduce robustness of the telephone to a point where it can not withstand the rigours of normal use. Mechanical and electrical strength and durability of the telephone must therefore be maintained while pursuing the goal of device size minimisation.

Mobile telephones include a keypad to allow user input and user control of device functions. The keypad is usually an assembly of a number of individual parts stacked up together, and has numeric and alphabetical characters and / or symbols that can be actuated by being depressed or touched by the user. Individual keys of the telephone keypad should have electrical and mechanical switch contact closure points which ensure electrical contact and which are resistant to fatigue. The required press force for actuation of each key should be low for ease of use, while being sufficiently high to avoid the key being actuated in error by small or accidental contact.

Further, the mobile telephone as a whole, and the mobile telephone keypad in particular, should withstand typical forces experienced in normal usage, such as compression forces, bending forces or delamination forces, such as may be experienced in a user's pocket or bag or during other use.

Still further, for aesthetic purposes the mobile telephone keypad should have a construction which permits a broad range of colours to be printed upon the key-top layer, and permits selection from a wide variety of key-top designs. The telephone construction should also provide a key-top layer which is resistant to discolouration, print delamination, and the abrasion to which it is subjected during use.

It can further be desirable to provide an electroluminescent lamp "panel", such a lamp panel being a single sheet including one or more luminous areas, wherein each luminous area is an electroluminescent "lamp". An electroluminescent lamp is essentially a capacitor having a dielectric layer between two or three conductive electrodes, at least one of which is transparent. The dielectric layer can include a phosphor powder, or there can be a separate layer of phosphor powder adjacent the dielectric layer. Application of an alternating current (AC) voltage across the electrodes generates a changing electric field within the phosphor which causes the phosphor to emit light. For most electroluminescent lamps, an inverter is used as a power source. An inverter is a direct current to alternate current (DC-AC) converter which typically generates around 60-115 V alternating current (AC) at 50-1000 Hertz.

A modern (post- 1990) electroluminescent lamp typically includes a transparent substrate of polyester or polycarbonate material having a thickness of about 7.0 mils (0.178 mm.). A transparent front electrode of indium tin oxide or indium oxide is vacuum deposited onto the substrate to a certain thickness. A phosphor layer is screen printed over the front electrode and a dielectric layer is screen printed over the phosphor layer. A rear electrode is screen printed over the dielectric layer. It is also possible to deposit the layers by roll coating.

The inks used for screen printing or roll coating include a binder, a solvent, and a filler, wherein the filler determines the nature of the printed layer. A typical solvent is dimethylacetamide (DMAC). The binder is typically a fluoropolymer such as polyvinylidene fluoride/hexafluoropropylene (PVDF/HFP), polyester, vinyl, epoxy or Kynar 9301, a proprietary terpolymer sold by Atofina.

A phosphor layer is typically screen printed from a slurry containing a solvent, a binder, and zinc sulphide particles. Phosphors are powders made of materials such as zinc sulphide which are designed to phosphoresce at characteristic wave lengths

(colors). The color can be defined during the manufacturing of the phosphor, or can be achieved by blending phosphors of different colors to achieve the composite color. The particle size of the phosphor powder is selected to provide the highest efficiency of light emission.

A dielectric layer is typically screen printed from a slurry containing a solvent, a binder, and particles of titania (TiO₂) or barium titanate (BaTiO₃). A rear electrode is typically screen printed from a slurry containing a solvent, a binder, and conductive particles such as silver or carbon. Because the solvent and binder for each layer are chemically the same or similar, there is chemical compatibility and good adhesion between adjoining layers.

To date, these demands have resulted in the stacking process for fabrication of mobile telephones and the like utilizing at least two keypad modules to form a keypad which meets such requirements. Figures 6a and 6b illustrate such a two-part keypad assembly 600, with Figure 6a being a perspective view of the key top element 610, comprising a web adapted to provide a desirable tactile feel. The switch layer element 620 of the two-part keypad assembly is shown in Figure 6b. A further or alternative element may be provided in such assemblies in the form of a layer of metal domes to provide a desired tactile response to depression of each key. Such two-part or multiple-part keypad assemblies generally have a thickness of no less than 1.8 mm. Further, the adoption of such a multiple-part keypad assembly introduces the risk of mechanical mismatch between the two components, particularly where the separate components are addressed by different designers, engineers, buyers or suppliers. Even matched elements of a keypad assembly can raise the risk of mis-keying or human error.

The EL lamp panel is one of several such keypad component modules which may be used in constructing a multiple module keypad.

Moreover, a panel constructed in accordance with the preceding techniques is relatively stiff even though it is typically only seven mils thick, making it difficult to mold into a three dimensional surface, for example. Layer thickness and stiffness are not directly related. The material from which the layer is made affects stiffness. Typically, electroluminescent lamps are made from the materials mentioned above, which produces an undesirable stiffness. Simply reducing thickness does not provide the desired flexibility.

These and similar considerations apply to other portable electrical devices comprising a keypad, such as portable digital assistants. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Summary of the Invention

According to a first aspect the present invention provides a method of manufacturing a single module keypad, the method comprising: providing a key top surface upon a top side of a transparent substrate; providing a transparent front electrode layer upon a bottom side of the transparent substrate opposite the top side; forming a light-emitting layer upon the transparent front electrode; forming a dielectric layer upon the light-emitting layer; and forming a rear conductor upon the dielectric layer.

According to a second aspect the present invention provides a single module keypad, the keypad comprising: a key top surface upon a top side of a transparent substrate; a transparent front electrode layer upon a bottom side of the transparent substrate opposite the top side; a light-emitting layer upon the transparent front electrode; a dielectric layer upon the light-emitting layer; and a rear conductor upon the dielectric layer. Thus, in embodiments of the first and second aspects of the invention, the keypad comprises a single module keypad, and further includes an electroluminescent lamp layer. Such embodiments of the invention may thus eliminate the need for a multiple- module keypad in a mobile telephone, and may permit a keypad of reduced thickness to be provided, while nevertheless providing for EL lighting of the keypad. Moreover, by forming an EL lamp, whether two layer or three layer, directly upon the key top substrate, the present invention provides for the keypad to take a moulded shape defined by the key top substrate, with the EL lamp layers conforming to whatever shape may be desirable. Such embodiments of the invention thus provide for a single module EL keypad which may be molded to a desired shape.

The light-emitting layer, the dielectric layer and the rear conductor may each be formed by screen printing or roll coating.

The keypad module may further comprise a second dielectric layer formed upon the rear conductor, and a second rear conductor formed upon the second dielectric layer, so as to provide a three layer EL lamp. Such embodiments may provide for improved yield and device reliability.

The key top surface may comprise a UV cured layer presenting a desired facade or appearance of the keypad module.

The transparent base substrate may comprise a polyester film, preferably a heat stabilised print treated polyester.

The transparent front electrode layer may comprise an indium tin oxide layer screen printed upon the transparent base substrate. Alternatively, the transparent front electrode layer may comprise a conducting polymer layer coated upon the transparent base substrate. In still further alternative embodiments of the invention, the transparent front electrode layer may comprise conductive translucent ink applied to the transparent base substrate. A non-transparent conductive bus bar or mesh may be formed upon the transparent front electrode layer to improve current supply to the front electrode. For example, a pattern of silver bus bars or meshes may be formed upon the transparent front electrode layer.

The keypad module may further comprise one or more of, and preferably comprises all of: a strengthening layer formed of a substantially rigid electrically conductive material; a switch layer comprising a plurality of switches; and a plunger sheet comprising a plurality of plungers for transferring applied force from the key top layer to the switch layer to switch said switches. The key top layer, EL lamp layers, the strengthening layer, the switch layer and the plunger sheet are preferably laminated together to form a single module.

By providing a strengthening layer which is substantially rigid and electrically conductive, such embodiments of the present invention provide for an electrical grounding function to be served by the strengthening layer. In preferred embodiments of the first and second aspects of the invention the strengthening layer is a mesh. The strengthening layer is preferably formed of metal.

Still further embodiments preferably comprise a flexible printed circuit layer, adapted to pass signals from the switches to a mobile telephone processor, and adapted to pass power from a mobile telephone power supply to the EL lamp layer.

In preferred embodiments of the invention, the switches of the switch layer comprise dome switches. When force is applied to and released from the switches, the switches preferably provide a tactile response for user perception of switch action.

In preferred embodiments of the invention, the keypad has a thickness of less than 1.65 mm. In preferred embodiments the keypad may be for a mobile phone. Or₅ the keypad may be adapted for another type of device, such as a personal digital assistant or the like.

According to a third aspect the present invention provides an electrical device having a keypad in accordance with an embodiment of the second aspect of the invention.

Brief Description of the Drawings

An example of the invention will now be described with reference to the accompanying drawings, in which:

Figs. Ia and Ib are a front left perspective view and a front right perspective view, respectively, illustrating a single module keypad assembly in accordance with a first embodiment of the present invention;

Figure 2 is a partial exploded side view of the keypad assembly module stack;

Figures 3a, 3b and 3c are photographs of an actual keypad assembly comprising the combination of layers illustrated in Figures 2;

Figures 4a and 4b are a side view and a partial side view, respectively, of a formed keypad assembly in accordance with the present invention;

Figures 5 a and 5b illustrate a configuration of a three layer and two layer electroluminescent lamp in-mold keypad; and

Figures 6a and 6b illustrate a prior art two part keypad assembly.

Description of the Preferred Embodiments

An embodiment of the invention will now be described having the purpose to minimize the mass, volume and size of the keypad device, so that the structure is lighter, smaller and thinner than existing keypads, while nevertheless providing an electroluminescent lamp in-mold keypad. Providing such a thinner keypad is important in improving the tactile feel of the keypad, improving light transmission from the EL layer through the transparent base substrate to the user, and in ameliorating issues of marking by a user's finger nails. The present embodiment further provides a single module keypad and thus reduces the number of steps in the assembly process compared to assembly of multiple-module keypads. The present embodiment provides a thin, flexible and light weight keypad having surface illumination which can be tailored for complex shapes for a variety of backlighting and sign applications, especially in cellular phone. There are many potentially advantageous applications of such an electroluminescent (EL) in- mold keypad (IMK). For example, reduced power consumption, lower heat generation in operation, permitting use of a cost effective screen printing process, and minimizing the thickness of the keypad produced.

Figs. Ia and Ib are a front left perspective view and a front right perspective view, respectively, illustrating a single-module keypad assembly 10 for a mobile telephone, in accordance with a first embodiment of the present invention. The assembly 10 comprises a printed electroluminescent lamp key top layer 11 having a second surface printing for aesthetic and abrasion resistance purposes. The key top Layer 11 can have a metallic appearance (as shown in the embodiment of Fig. 3 c) and/or can be provided with any of a wide range of colors. The metallic appearance of the key top layer in the embodiment of Fig. 3 c is created by a method which avoids the use of a conventional electro-plating process which can be harmful to the environment. In alternative embodiments, the key top layer 11 can have different types of surface textures such as spin line, brush hair line and/or a three dimensional surface finish. The printed electroluminescent lamp consists of a sandwich structure containing an appropriate substrate, a rear electrode, an insulating layer, the phosphor layer, a transparent or translucent front electrode and a protective layer on in-mold keypad.

The lamp may be terminated by a silver conductor, and crimped connectors (or other means) to allow connection to the power source. Care must be taken in providing a connection with good integrity. Conductive adhesive layer 12 provides electrical energy, and can act to ground electro-static discharge from the layer 14. A double sided adhesive layer 13 bonds the lamp layer 11 and metal mesh strengthening layer 14 together.

A metal mesh acts as the strengthening layer 14. This layer 14 is the main structure to provide flatness or desire shape to the entire stack 10, and can provide an ergonomic and tactile feel to the user by defining shape and/or configuration of the key top layer 11. The metal mesh strengthening layer 14 is a most important layer in the module 10, as it acts as a stiffener in providing the basic support to the entire stack, as well as controlling the flatness and the shape of the entire module, for example in order to suit hand phone design. Further, the metal mesh may be formed by a plurality of holes etched into the metal sheet, and the etched holes may be patterned to influence the form of the key top layer 11, so as to provide a particular tactile feel of the keypad to the user. Still further, the strengthening layer 14 is formed of a conductive metal, and thus provides an electro static discharge (ESD) path by being grounded.

In the present embodiment, the strengthening layer 14 is grounded by the conductive adhesive layer 15, which electrically connects the metal mesh 14 to a flexible printed circuit board 19, to thus ground electro-static discharge from the metal mesh layer 14.

Assembly 10 further comprises a plunger sheet layer 16. As shown in more detail in Figures 4a and 4b, plunger sheet layer 16 has a plurality of bosses 171 protruding from the plunger sheet layer 16, each boss 171 positioned against a contact of the printed circuit board layer 19. The position of each boss 171 also corresponds to a key position of the key top layer 11. Depression of a key of the key top layer 11 causes a boss 171 of the plunger sheet layer 16 to bear upon a dome of dome layer 18, as shown in Fig. 4b. The dome of layer 18 provides a desired tactile response when a key is pressed, and acts as a contact to provide an electrical input to the printed circuit of layer 19. The printed circuit board layer 19 has a plurality of such stationary contacts with corresponding movable contacts of the dome switch layer 18. Each of the key tops of the key top layer 11 are printed with numeral and/or character display to indicate where a user should apply pressure far given commands, that pressure being transmitted through the assembly 10 to the printed circuit of layer 19. Printed circuit layer 19 further comprises a flexible connector 201 shown in Figure 3 a, which enables electrical signals and power to be passed between the keypad assembly 10 and a mobile telephone upon which it is to be mounted.

Figure 2 is a partial exploded side view of the keypad assembly module stack 10. The function of each layer is as described above, with the present embodiment having layer components and materials as follows. Key top layer 1 is formed of molded liquid UV urethane with PC or PET Film, to provide an aesthetic look. Layer 2 is provided by industry available substance supplied by Adhesive Research, and bridges the power supply from the flexible printed circuit board 9 and 201 to the lighting layer 11. Layer 3 is also provided by industry available substance supplied by 3 M, and serves to bond the EL keypad layer 1 to the metal mesh layer 4.

Metal mesh strengthening layer 4 is formed of a SUS 304FH steel sheet with chemically etched holes through the sheet. Layer 4 serves to maintain the planar form or other desired shape of the key-top configuration, and acts as a physical support for the entire assembly 10. Layer 4 further provides for electro static grounding (ESD) of the electrically conductive layers to which it is connected. Notably, the layer 4 enables provision for various types of tactile feel by varying hole diameter, hole distribution, and/or hole shape.

Conductive adhesive layer 5 is also provided by industry available substance supplied by Adhesive Research, and has the purpose of providing an electrostatic discharge grounding connection between the flexible printed circuit board layer 9 and the metal mesh layer 4. Plunger sheet 6 is formed of molded liquid UV urethane with PC or PET film, and transfers applied pressure from the key top to the metal dome of each contact. Layer 7 is the adhesive plunger to dome layer, provided by industry available substance supplied by 3 M, Layer 7 adheres the plunger layer 6 to the metal dome layer 8.

Metal dome layer 8 is an industry available part supplied by Fujikura Dome, and serves to provide a tactile feeling when a user applies and releases force to the keypad assembly 10, while also acting as a circuitry switch with printed circuit board layer 9. The flexible printed circuit board is a customized part with the purpose of transmitting electrical signals to the main board of the telephone, providing electrical power to the EL printed keypad layer 1, and providing for electrostatic grounding.

Finally, adhesive layer 10 is provided by industry available substance supplied by 3 M, and bonds the entire assembly 10 to a mobile telephone housing.

Figures 3 a, 3b and 3 c are photographs of an actual keypad assembly comprising the combination of layers illustrated in Figure 2, and illustrating the flexible connector 201. Fig 3b in particular illustrates the thin profile of the assembly, having a total stack thickness of 1.641 mm.

Experiments conducted to date have revealed that the single module keypad of the present invention enables a keypad to be constructed having integrated mechanical and electronic layers and a thickness of as little as 1.2 mm. Thus, the present invention provides an electroluminescent lamp keypad assembly comprising a single module, which integrates different layers of mechanical and electronic components together as a total keypad solution that substantially differs from the conventional keypad. The assembly can maintain a slim profile of reduced thickness, as well as assisting in ease of manufacture, reducing the amount of human resources involved. Further, the assembly may be formed into different geometries that can suit the various hand phone designs. Figure 5 a is a schematic diagram of a three layer electroluminescent lamp keypad. Three layer electroluminescent lamps are preferred for optimum yield and reliability. This embodiment of invention in which an UV cured layer of keypad layer 501 is the front appearance of keypad, in-mold keypad is provided by industry available substance supplied by Meiwa. UV cured layer 501 acts as a protective layer to provide protection from moisture and electrical isolation for safety reasons. The layer beneath in-mold keypad acts as transparent base substrate. Polyester film with silk screen printed artwork lies beneath the film. Next, the same polyester film layer 502, printed with indium tin oxide (ITO) or coating with a conducting polymer layer 504, can be used as the front electrode. Alternatively, a screen printed conducting translucent ink can be used on a clear base substrate. The build sequence printed on beneath is simply phosphor layer 505, and then three layer electroluminescent lamps, or alternatively two layer electroluminescent lamps. It is advisable to use a heat stabilized, print treated polyester (PET) for in-mold keypad. The next approach is to screen-print the polyester film with indium tin oxide (ITO), a transparent conductive material that serves as the lamp's outer electrode. Alternatively, over the indium tin oxide coated sided of this polyester, a bus bar (generally silver) is printed to ensure maximum current to the coating.

Next, a light-emitting phosphor layer 505 is printed down on polyester (PET) film layer 502. There should be printed directly onto the printed indium tin oxide (ITO) layer 504 side of the polyester. To obtain uniform illumination, it is essential that sufficient phosphor ink be deposited at this step. The amount of phosphor ink required is around 10 mg/cm² if a polyester screen is used it is recommended to begin with 62T mesh (wires/ cm) with 20-25 μm emulsion. If a mesh with insufficient open area is used, a double wet pass will improve the particle packing density and results in more uniform light when powered up. A printed thickness in the range 30-40 μm (dry) should be achieved, which represents coverage of approximately 100 mg²/ g of wet phosphor ink. Phosphors can be divided into two types of choices, encapsulated phosphor and unencapsulated phosphor. Encapsulated phosphors have each microscopic phosphor particle surrounded by a glass-like protector. This acts as moisture barrier to the phosphor, providing reasonable protection from moisture. Hence, encapsulation offers additional protection during manufacturing and lamination.

After layer 505 is printed, it is followed by a dielectric insulating layer 506 of barium titanate. Printing through a 62T (wires/ cm) polyester screen is suggested as a starting point. This should give a film thickness of approximately 10 μm (dry). Three separate dried layers are preferred as illustrate in Fig 5 a and 5b, to prevent shorting and total thickness of around 25 μm should be maintained. This represents a total laydown of 20 mg / cm². If voids are observed due to large underlying phosphor, double- wet passes or extra layers may be necessary.

The conductive layer 507, comprising an electrically active ink layer can be an electrophoretic material, and comprises, for example, bi-chromal particles having opposite electrical charges, suspended in a medium or encapsulated in a microsphere containing a medium that allows the particles to migrate. The particles, having electrically charged surfaces, migrate when a voltage differential is applied to them. Selectively applying a voltage differential at various points on the layer causes the particles at those points to migrate toward opposite electrodes, and being bi-chromal, show a different color at that point. The voltage differential is experienced between the conductive layer 507, rear conductive layer 509 and transparent conductor layer 504. The transparent conductor layer can be a layer of, for example, indium tin oxide (ITO).

A dielectric layer 508 in Fig 5a is printed down onto conductive layer 507. Layer 509 is a rear conductive layer of silver or conductive carbon ink, which serves as the second electrode, and is then printed onto dielectric layer. The lamp is completed with a final layer of rear insulator layer 510. The remainder of the keypad module stack illustrated in Figure 2 may then be constructed.

Figure 5b shows a configuration of a two layer electroluminescent lamp in-mold keypad. Two layer electroluminescent lamps give a brighter lamp but may reduce the yield and reliability. First layer 501 is initially UV cured of in-mold keypad with artwork printed onto polyester (PET) film. Indium tin oxide (ITO) layer 504 is printed down onto artwork printed polyester (PET) film layer 503, and phosphor layer 505 is printed down onto indium tin oxide (ITO) layer 504, whereupon, dielectric layer 506 is printed down onto layer 505. Rear conductive layer 509 is printed down onto layer 506, and finally a rear insulator layer 510 is printed down on rear conductive layer.

By forming the EL lamp layer directly upon the key top transparent substrate, the present embodiment of the invention enables elimination of usage of PET film (with minimum thickness 0.025mm) and EL adhesive (with minimum thickness 0.05 mm). By eliminating such previously essential parts of the EL module the present invention not only provides for a single module keypad assembly but further permits thinner EL keypad modules to be constructed.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A method of manufacturing a single module keypad, the method comprising: providing a key top surface upon a top side of a transparent substrate; providing a transparent front electrode layer upon a bottom side of the transparent substrate opposite the top side; forming a light-emitting layer upon the transparent front electrode; forming a dielectric layer upon the light-emitting layer; and forming a rear conductor upon the dielectric layer.

2. The method of claim 1 wherein the light-emitting layer is formed by screen printing.

3. The method of claim 1 wherein the light-emitting layer is formed by roll coating.

4. The method of any one of claims 1 to 3 wherein the dielectric layer is formed by screen printing.

5. The method of any one of claims 1 to 3 wherein the dielectric layer is formed by roll coating.

6. The method of any one of claims 1 to 5 wherein the rear conductor is formed by screen printing.

7. The method of any one of claims 1 to 5 wherein the rear conductor is formed by roll coating.

8. The method of any one of claims 1 to 7 further comprising forming a second dielectric layer upon the rear conductor, and forming a second rear conductor upon the second dielectric layer, to provide a three layer EL lamp.

9. The method of any one of claims 1 to 8 wherein the key top surface comprises a UV cured layer presenting a desired appearance of the keypad module.

10. The method of any one of claims 1 to 9 wherein the transparent base substrate comprises a polyester film.

11. The method of claim 10 wherein the transparent base substrate comprises a heat stabilised print treated polyester.

12. The method of any one of claims 1 to 11 wherein the transparent front electrode layer comprises an indium tin oxide layer.

13. The method of any one of claims 1 to 11 wherein the transparent front electrode layer comprises a conducting polymer layer.

14. The method of any one of claims 1 to 11 wherein the transparent front electrode layer comprises conductive translucent ink.

15. The method of any one of claims 1 to 14 further comprising forming a non- transparent conductive bus bar upon the transparent front electrode layer to improve current supply to the front electrode.

16. The method of any one of claims 1 to 15 further comprising: providing a strengthening layer formed of a substantially rigid electrically conductive material; providing a switch layer comprising a plurality of switches; providing a plunger sheet comprising a plurality of plungers for transferring applied force from the key top layer to the switch layer to switch said switches; and laminating the key top layer, the strengthening layer, the switch layer and the plunger sheet together to form a single module.

17. The method of claim 16, wherein an electrical grounding function is served by the strengthening layer.

18. The method of claim 16 or claim 17, wherein the strengthening layer is a mesh.

19. The method of any one of claims 16 to 18, wherein the strengthening layer is formed of metal.

20. The method of any one of claims 16 to 19, further comprising providing a flexible printed circuit layer, adapted to pass signals from the switches to a mobile telephone processor, and adapted to pass power from a mobile telephone power supply to the front and rear electrode layers.

21. The method of any one of claims 16 to 20, wherein the switches of the switch layer comprise dome switches.

22. The method of any one of claims 16 to 21, wherein the switches provide a tactile response for user perception of switch action.

23. The method of any one of claims 16 to 22, wherein the keypad has a thickness of less than 1.65 mm.

24. The method of any one of claims 16 to 23, wherein the keypad is for a mobile phone.

25. A single module keypad comprising: a key top surface upon a top side of a transparent substrate; a transparent front electrode layer upon a bottom side of the transparent substrate opposite the top side; a light-emitting layer upon the transparent front electrode; a dielectric layer upon the light-emitting layer; and a rear conductor upon, the dielectric layer.

26. The keypad of claim 25 wherein the light-emitting layer is a screen printed layer.

27. The keypad of claim 25 wherein the light-emitting layer is a roll coated layer.

28. The keypad of any one of claims 25 to 27 wherein the dielectric layer is a screen printed layer.

29. The keypad of any one of claims 25 to 27 wherein the dielectric layer is a roll coated layer.

30. The keypad of any one of claims 25 to 29 wherein the rear conductor is a screen printed layer.

31. The keypad of any one of claims 25 to 29 wherein the rear conductor is a roll coated layer.

32. The keypad of any one of claims 25 to 31 further comprising a second dielectric layer upon the rear conductor, and a second rear conductor upon the second dielectric layer, to provide a three layer EL lamp.

33. The keypad of any one of claims 25 to 32 wherein the key top surface comprises a UV cured layer presenting a desired appearance of the keypad module.

34. The keypad of any one of claims 25 to 33 wherein the transparent base substrate comprises a polyester film.

35. The keypad of claim 34 wherein the transparent base substrate comprises a heat stabilised print treated polyester.

36. The keypad of any one of claims 25 to 35 wherein the transparent front electrode layer comprises an indium tin oxide layer.

37. The keypad of any one of claims 25 to 35 wherein the transparent front electrode layer comprises a conducting polymer layer.

38. The keypad of any one of claims 25 to 35 wherein the transparent front electrode layer comprises conductive translucent ink.

39. The keypad of any one of claims 25 to 38 further comprising a non-transparent conductive bus bar formed upon the transparent front electrode layer to improve current supply to the front electrode.

40. The keypad of any one of claims 25 to 39 and further comprising: a strengthening layer formed of a substantially rigid electrically conductive material; a switch layer comprising a plurality of switches; and a plunger sheet comprising a plurality of plungers for transferring applied force from the key top layer to the switch layer to switch said switches; wherein the key top layer, the strengthening layer, the switch layer and the plunger sheet are laminated together to form a single module.

41. The keypad of claim 40, wherein an electrical grounding function is served by the strengthening layer.

42. The keypad of claim 40 or claim 41 , wherein the strengthening layer is a mesh.

43. The keypad of any one of claims 40 to 42, wherein the strengthening layer is formed of metal.

44. The keypad of any one of claims 40 to 43, further comprising a flexible printed circuit layer, adapted to pass signals from the switches to a mobile telephone processor, and adapted to pass power from a mobile telephone power supply to the EL lamp layer.

45. The keypad of any one of claims 40 to 44, wherein the switches of the switch layer comprise dome switches.

46. The keypad of any one of claims 40 to 45, wherein the switches provide a tactile response for user perception of switch action.

47. The keypad of any one of claims 40 to 46, wherein the keypad has a thickness of less than 1.65 mm.

48. The keypad of any one of claims 40 to 47, wherein the keypad is for a mobile phone.

49. An electrical device having a keypad in accordance with any one of claims 25 to 48.