WO2008002269A1

WO2008002269A1 - Keypad module

Info

Publication number: WO2008002269A1
Application number: PCT/SG2006/000184
Authority: WO
Inventors: Jit Ming Bryan Lim
Original assignee: Sinco Technologies Pte. Ltd
Priority date: 2006-06-30
Filing date: 2006-06-30
Publication date: 2008-01-03
Also published as: TW200802452A

Abstract

A keypad for a mobile telephone or the like. The key pad has a key top layer, and a strengthening layer formed of a substantially rigid electrically conductive material. Also, 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, the strengthening layer, the switch layer and the plunger sheet are laminated together to form a single module.

Description

"Keypad module"

Technical Field

The present invention relates to a keypad module and a method of constructing a keypad module, and in particular a keypad module 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.

To date, these demands have resulted in the stacking process for fabrication of mobile telephones utilising at least two keypad modules to form a keypad which meets such requirements. Figures 5 a and 5b illustrate such a two-part keypad assembly 500, with Figure 5a being a perspective view of the key top element 510, comprising a web adapted to provide a desirable tactile feel. The switch layer element 520 of the two- part keypad assembly is shown in Figure 5b. 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.

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 keypad, the method comprising: providing a key top layer; 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.

According to a second aspect the present invention provides a keypad, the keypad comprising: a key top layer; 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.

Thus, in embodiments of the first and second aspects of the invention, the keypad comprises a single module. 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.

By providing a strengthening layer which is substantially rigid and electrically conductive, the present invention provides 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.

In further preferred embodiments, a back lighting layer may be provided beneath the key top layer in order to provide back lighting of the key top layer. The back lighting layer is preferably laminated to and electrically connected to the strengthening layer by a conductive adhesive.

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 back lighting 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. Or, 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;

Figures 2a and 2b are partial exploded side views 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 2a and 2b;

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; and

Figures 5a and 5b illustrate a prior art two part keypad assembly.

Description of the Preferred Embodiments

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 key top layer 11 having a second surface printing for aesthetic and abrasion resistance purposes. The key top Layer 1 can have a metallic appearance (as shown in the embodiment of Fig. 3c) 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. 3c is created by using metallic, holographic or tinted foil, metallic ink or mirror ink, and thus adopts a method which avoids the use of a conventional electro-plating process which can be harmful to the environment, hi 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 assembly 10 further comprises a lamp layer 12 to provide back lighting of the key top layer 11. Conductive adhesive layer 13 provides electrical energy to the lamp layer 12, and can act to ground electro-static discharge from the layer 15. A double sided adhesive layer 14 bonds the lamp layer 12 and metal mesh strengthening layer 15 together.

A metal mesh acts as the strengthening layer 15. This layer 15 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 15 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 15 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 15 is grounded by the conductive adhesive layer 16, which electrically connects the metal mesh 15 to a flexible printed circuit board 20, to thus ground electro-static discharge from the metal mesh layer 15.

Assembly 10 further comprises a plunger sheet layer 17. As shown in more detail in Figures 4a and 4b, plunger sheet layer 17 has a plurality of bosses 171 protruding from the plunger sheet layer 17, each boss 171 positioned against a contact of the printed circuit board layer 20. 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 17 to bear upon a dome of dome layer 19, as shown in Fig. 4b. The dome of layer 19 provides a desired tactile response when a key is pressed, and also acts as a contact to provide an electrical input to the printed circuit of layer 20.

Turning to Figure 2b, it is further noted that the thickness dl of the plunger layer

17 without bosses 171 is, in the present embodiment, 0.025 mm. As seen in Fig 2a, the plunger layer 17 is formed by a PET film of 0.025 mm thickness. This extremely thin layer is made possible by the keypad module structure provided by the present embodiment of the invention, and it is noted that previous to the present invention the thinnest dimension of prior plunger layers which could be achieved was of the order of 0.2 mm. The structure of the present invention thus provides for a significant module thickness reduction by reducing the thickness of the plunger layer 17. Height d2 of the bosses 171 can be user defined, and in the present embodiment is 0.4 mm. The printed circuit board layer 20 has a plurality of such stationary contacts with corresponding movable contacts of the dome switch layer 19. 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 for given commands, that pressure being transmitted through the assembly 10 to the printed circuit of layer 20. Printed circuit layer 20 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 11 is formed of molded liquid UV urethane with PC or PET Film, to provide an aesthetic look. Back lighting lamp layer 12 is an industry available part supplied by Rogers Corp., and provides back lighting for some or all keys of the key top layer 11.

Layer 13 is also provided by industry available substance supplied by Adhesive Research, and bridges the power supply from the flexible printed circuit board 20 and 201 to the lighting lamp layer 12. Layer 14 is also provided by industry available substance supplied by 3M, and serves to bond the backlighting lamp layer 12 to the metal mesh layer 15.

Metal mesh strengthening layer 15 is formed of a SUS 304FH steel sheet with chemically etched holes through the sheet. Layer 15 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 15 further provides for electro static grounding (ESD) of the electrically conductive layers to which it is connected. Notably, the layer 15 enables provision for various types of tactile feel by varying hole diameter, hole distribution, and/or hole shape. Conductive adhesive layer 16 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 20 and the metal mesh layer 15. Plunger sheet 17 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 8 is the adhesive plunger to dome layer, provided by industry available substance supplied by 3M. Layer 8 adheres the plunger layer 17 to the metal dome layer 19.

Metal dome layer 19 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 20. The flexible printed circuit board is a customised part with the purpose of transmitting electrical signals to the main board of the telephone, providing electrical power to the back lighting layer 12, and providing for electrostatic grounding. Finally, adhesive layer 21 is provided by industry available substance supplied by 3M, and bonds the entire assembly 10 to a mobile telephone housing

Figures 3a, 3b and 3c 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 a 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. 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 keypad, the method comprising: providing a key top layer; 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.

2. The method of claim 1, wherein an electrical grounding function is served by the strengthening layer.

3. The method of claim 1 or claim 2, wherein the strengthening layer is a mesh.

4. The method of any one of claims 1 to 3, wherein the strengthening layer is formed of metal.

5. The method of any one of claims 1 to 4, wherein a back lighting layer is provided beneath the key top layer in order to provide back lighting of the key top layer.

6. The method of claim 5, wherein the back lighting layer is laminated to and electrically connected to the strengthening layer by a conductive adhesive.

7. The method of any one of claims 1 to 6, 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 back lighting layer.

8. The method of any one of claims 1 to 7, wherein the switches of the switch layer comprise dome switches.

9. The method of any one of claims 1 to 8, wherein the switches provide a tactile response for user perception of switch action.

10. The method of any one of claims 1 to 9, wherein the keypad has a thickness of less than 1.65 mm.

11. The method of any one of claims 1 to 10, wherein the keypad is for a mobile phone.

12. A keypad comprising: a key top layer; 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.

13. The keypad of claim 12, wherein an electrical grounding function is served by the strengthening layer.

14. The keypad of claim 12 or claim 13, wherein the strengthening layer is a mesh.

15. The keypad of any one of claims 12 to 14, wherein the strengthening layer is formed of metal.

16. The keypad of any one of claims 12 to 15, further comprising a back lighting layer beneath the key top layer, which provides back lighting of the key top layer.

17. The keypad of claim 16, wherein the back lighting layer is laminated to and electrically connected to the strengthening layer by a conductive adhesive.

18. The keypad of any one of claims 12 to 17, 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 back lighting layer.

19. The keypad of any one of claims 12 to 18, wherein the switches of the switch layer comprise dome switches.

20. The keypad of any one of claims 12 to 19, wherein the switches provide a tactile response for user perception of switch action.

21. The keypad of any one of claims 12 to 20, wherein the keypad has a thickness of less than 1.65 mm.

22. The keypad of any one of claims 12 to 21, wherein the keypad is for a mobile phone.

23. An electrical device having a keypad in accordance with any one of claims 12 to 22.