# Patent

## Title
Metal dome sheet in mobile communication terminal and keypad thereof

## Abstract

A keypad for a mobile communication terminal is provided. The keypad includes a sheet having contacts which deflect so as to switch contact point pairs on a printed circuit board on and off. The contacts may be formed as hemispherical domes to facilitate use. The sheet may also include band parts covering the contacts and an insulting sheet having at least one pair of semicircular openings which expose portions of the contacts. The insulating sheet is preferably made of a light-reflecting material/color which disperses light to illuminate keys of the keypad.

## Background
This is a Continuation Application of application Ser. No. 10/372,083 filed on Feb. 25, 2003 now U.S. Pat. No. 6,909,063, the entirety of which is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a contact structure in an electronic device such as but not limited to a mobile communication terminal.
2. Background of the Related Art
Most mobile communication terminals have keypads for inputting characters or symbols, and the keypads usually have a contact sheet. In a related art terminal, the sheet is attached to a surface of a PCB (printed circuit board) having a plurality of keypad switches ringed thereon. The sheet includes a plurality of metal domes made of a metal based material (e.g., stainless steel) and the domes are attached onto the keypad switches respectively.
In operation, when a user presses a key (e.g., a character key), pressure is placed on the metal dome beneath the pressed key. This pressure causes the key to move and thus become distorted in a downward direction. As a result, the corresponding keypad switch is pressed by such distortion to bring about switch operation. The metal dome is useful because it gives a user's finger a feeling of click when pressed by the user, and also protects the corresponding keypad switch beneath the metal dome.
A related art keypad includes a plurality of keys (character keys) formed by injection molding of synthesized resin such as acryl or the like. The keys have various characters or symbols formed thereon so that they may be distinguished from each other. Over time, a character or symbol printed on a surface of the key wears out and thus is hardly recognizable. To overcome this drawback, a specific color is coated on an inner face of the key using pigments. This color is partly removed to display a character or symbol. This method is widely used.
More specifically, in the foregoing keypad the character (symbol) is depicted by stripping off a portion of the colored surface using a laser. The portion representing the character is the stripped portion from which the color is removed, and it is transparent to allow for leakage of light emitted from inside. Hence, the user is able to distinguish and select keys conveniently. Also, it is noted that keypad switches are placed beneath the keypad to generate electric signals corresponding to the pressed keys. Once the key is pressed, the keypad switch is operated to generate the corresponding electric signal.
As previously discussed, a metal dome is frequently placed between the key and keypad switch to provide a “click” feeling to a user as well as to protect the switch. The keypad is formed from a plurality of the keys and an insulating sheet is usually attached to support a plurality of metal domes. An insulating sheet having metal domes attached thereto may be referred to as a metal dome sheet
FIGS. 1 and 2 show different views of a metal dome sheet according to the related art. The metal dome sheet 10 includes a thin plate type insulating sheet 15 and metal domes 1 attached to the insulating sheet. Each metal dome 1 is made of a substantially hemispherical stainless steel plate. More specifically, each metal dome formed like a contact lens by cutting a portion of a sphere.
The insulating sheet 15 is mainly made of a white plastic sheet, and the number of the metal domes coincides with the number of keys to be placed on the metal domes. A plurality of holes 2 are formed between the metal domes. Light emitted from LEDs installed on a PCB (printed circuit board) having keypad switches, passes through the holes.
Problems may arise as a result of using the metal dome sheet of the related art when used in communications terminals. In these terminals, the keys (keyboard) have a tendency to be too small to use. Hence, key size has to be increased.
As the size of the keys (keyboard) increases, so does a display portion for each number or character as well as width of each character style. However, if the size of the key or the width of the character or symbol increases, the corresponding metal dome beneath the key is seen externally through the wider and larger character potion of the key (keyboard).
A cut portion (numeral and character portion) of the key, which is cut by a laser, becomes dark due to the color of the corresponding metal dome. As a result, the light leaking through the key becomes hazy. Moreover, the metal dome protrudes out of the surface of the sheet to form a dome shape and blocks the light-propagating space to inhibit the flow of light. In FIG. 1, a light path is partially shown by a cutting line to show that light emitted from LED is blocked by the metal domes. Consequently, use of the metal domes inhibits bright illumination of the keys of the keyboard. Moreover, the metal domes are basically made of an opaque material, which thereby worsens the illumination problem.
A need therefore exists for an improved contact sheet which enables light to be evenly applied to a keypad, and which also prevents the color of the contacts from being exposed naturally.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a contact sheet in an electronic device such as but not limited to a mobile communication terminal that substantially obviates one or more of the problems of the related art.
Another object of the present invention is to provide a contact sheet in a mobile communication terminal and a keypad thereof which enables light to be evenly applied to a keypad and which also prevents the color of the contacts on the sheet from being exposed to view by a user.
To achieve these and other objects and advantages, the present invention provides a contact sheet attached to a surface of a printed circuit board having keypad switch contact point pairs formed thereon. The contact sheet includes a plurality of contacts which are preferably in the form of hemispherical metal domes which are used to turn on/off the keypad switch contact point pairs of the printed circuit board, respectively. The contact sheet also includes a plurality of bands covering the metal domes respectively, an insulating sheet having at least one pair of semicircular openings formed at both sides of each of the band parts to expose an edge of each of the metal domes, and an adhesive agent layer inserted between a bottom of the insulating sheet and top surfaces of the metal domes and PCB to attach the metal domes and PCB to the insulating sheet. Preferably, a plurality of LED holes are formed in the insulating sheet so that light of at least one LED installed on the printed circuit board passes through the LED holes. Also, the metal dome sheet may further include an elastic plastic film coated on the insulating sheet and the metal domes exposed by the openings. The insulating sheet may be a white sheet having a property of diffused reflection, although any light-reflecting color may be used.
In another aspect of the present invention, a keypad in a mobile communication terminal includes a printed circuit board having a plurality of switch contact point pairs formed thereon, a plurality of hemispherical metal domes to connect the switch contact point pairs, respectively, a plurality of band parts covering the metal domes, respectively, and an insulating sheet having at least one pair of semicircular openings formed at both sides of each of the band parts to expose an edge of each of the metal domes.
Preferably, the keypad further includes an adhesive agent layer inserted between a bottom of the insulating sheet and top surfaces of the metal domes and PCB to attach the metal domes and PCB to the insulating sheet. A plurality of LED holes are formed in the insulating sheet so that light of at least one LED installed on the printed circuit board passes through the LED holes. Also, the keypad may include an elastic plastic film coated on the insulating sheet and the metal domes exposed by the opening. Preferably, the insulating sheet is a white sheet having a property of diffused reflection.
In a further aspect of the present invention, in a mobile communication terminal, the mobile communication terminal includes a keypad having a printed circuit board having a plurality of switch contact point pairs formed thereon, a plurality of hemispherical metal domes to connect the switch contact point pairs, respectively, a plurality of band parts covering the metal domes, respectively, and an insulating sheet having at least one pair of semicircular openings formed at both sides of each of the band parts to expose an edge of each of the metal domes.
Preferably, the mobile communication terminal further includes an adhesive agent layer inserted between a bottom of the insulating sheet and top surfaces of the metal domes and PCB to attach the metal domes and PCB to the insulating sheet, a plurality of LED holes formed in the insulating sheet so that light of at least one LED installed on the printed circuit board passes through the LED holes, and an elastic plastic film coated on the insulating sheet and the metal domes exposed by the openings, wherein the insulating sheet is a white sheet having a property of diffused reflection.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a layout of a metal dome sheet according to a related art for showing that LED light is blocked;
FIG. 2 illustrates a bird's-eye view of a metal dome sheet according to a related art;
FIG. 3 illustrates a cross-sectional view of a keypad bisected along a cutting line V—V in FIG. 7;
FIG. 4 illustrates a layout of a keypad according to the present invention for shoving a contact point;
FIG. 5 illustrates a PCB layout of a keypad according to the present invention.
FIG. 6 illustrates a layout of a metal dome sheet according to the present invention; and
FIG. 7 illustrates a bird's-eye view of a metal dome sheet according to the present invention;



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 3, a contact sheet included in a mobile communications terminal according to the present invention is inserted between a keypad 58 and a printed circuit board (PCB) 52. The keypad has a plurality of keys 59 arranged thereon, the PCB 52 has keypad switch contact points 56 and 57 disposed under the corresponding key 59. The keypad 58 may be made of, for example, an elastic plastic material.
The PCB 52 may also include a plurality of LEDs 22a formed on the PCB 52 for providing improved keypad illumination. Lines are also printed for connecting the switch contact points and the LEDs, as well as the key switch contact points 56 and 57.
The contact sheet 20 includes a plurality of contacts 21 and an insulating sheet 25 which covers the metal domes in order to attach them to the PCB 52. The contacts 21 are illustratively shown as being in the shape of metal domes, however other shapes may be used if desired.
Each of the metal domes is capable of being distorted by a force pressing a corresponding key 59. When this occurs, the metal dome will deflect downwardly to establish an electrical connection between the first and second contact points 56 and 57. The first and second contact points 56 and 57 thus serve as a key switch contact point pair, which thereby plays a role in turning on the key switch electrically as well as protecting the key switch contact points from external environmental influences such as dust, moisture, and the like.
The metal domes are made of a conductive material such as, for example, stainless steel plate, and the sheet may be made of an insulating synthesized resin based material. An edge of the metal dome is in contact with the second contact point 57. In operation, when a central portion of the metal dome is pressed, it is distorted in a downward direction to establish contact with the first contact point 56, thereby electrically connecting the first and second contact points 56 and 57 to each other. See FIGS. 4 and 5.
Referring to FIGS. 6 and 7, at least a portion of a top of the metal dome is covered with the insulating sheet, i.e., a band part 23. Openings 21a in the insulating sheet 25 expose edges of the metal dome. More specifically, two portions of the insulating sheet 25 are removed to provide a pair of half-moon-shaped openings 21a. While two openings 21a are preferably provided over each metal dome, those skilled in the art can appreciate that one or more openings in the insulating sheet 25 may be provided for each metal dome.
Referring to FIGS. 3 and 7, the insulating sheet 25 includes a band part 23 covering a substantially hemispherically shaped metal dome to connect the key switch contact points to each other, and a pair of the openings 21a at both sides of the band part 23 are provided to expose edges of the metal dome. While the openings are shown as being semicircular, those skilled in the art can appreciate that these openings may have any shape desired. The openings are advantageously formed to facilitate the distortion of the metal dome since the insulating sheet 25 has small elasticity. The insulating sheet 25 may further include an adhesive agent layer (attached to the insulating sheet and not shown in the drawing) between its bottom and tops of the metal dome 21 and PCB 52.
A plurality of LED holes 22 are formed in the insulating sheet 25 so that the light of the LEDs 22a on the PCB passes through the holes 22. See FIGS. 6 and 7.
An elastic thin plastic film 24 may be coated on entire surfaces of the insulating sheet 25 and each top of the metal domes exposed by the openings 21a. The plastic film 24 may be formed of vinyl coating or some other material. Such a film 24 plays a role in building the metal dome sheet in one body and protects the under structures from dust, moisture, and the like.
The insulating sheet 25 is preferably formed of a sheet having a light color such as but not limited to white. A light color is preferably for the insulating sheet 25 because such a color posses the property of diffused light reflection. It is a matter of course that various colors are applicable to the sheet for implementing various colors of the keypad.
A keypad according to the present invention therefore includes a PCB 52 having a plurality of switch contact points 56 and 57 formed thereon, at least one hemispherical metal dome 21 for connecting a switch contact point pair when the dome is deflected, at least one band part 23 covering the metal dome, an insulating sheet 25 having at least one pair of openings 21a (preferably semicircular) for exposing a pair of edges of the metal dome, and a keypad 58 having at least one key 59 arranged thereon in alignment over the corresponding metal dome. While such a keypad is suitable for inputting character or symbol signals into a mobile communication terminal, those skilled in the art can appreciate that the keypad may be used in any type of electronic device.
The present invention is advantageous in a number of respects. For example, since each of the metal domes is directly covered with at least part of the sheet, the color of the metal domes fails to be seen externally between the keys or through the symbol portions of the keys. Instead, the color of the sheet is seen externally all the time.
Also, because light from the LEDs is reflected from the sheet uniformly, the characters or symbols can be distinguished or recognized with relative ease compared with the related art. For example, as shown in FIG. 6, light from the lens incident on the sheet on the metal dome is reflected therefrom at a point where a cutting line indicates a light path in part. Accordingly, the metal dome sheet according to the present invention prevents the metal dome from being seen through the numeral or character of the key. And, the LED light is transferred uniformly to illuminate the entire area of the keypad effectively.
Moreover, the metal dome sheet according to the present invention is modified from that of the related art in various ways, thereby being applicable to a mobile communication terminal to increase the product value as well as providing long endurance and convenience of use.
The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.
For example, while the metal domes (or conductive contacts) of the present invention have substantially a semicircular shape, alternative embodiments of the invention may correspond to a contact structure having contacts 21 in other shapes, including but not limited to, rectangular or box shapes, conical or truncated conical shapes, as well as other shapes

## Claims

1. A keypad, comprising:
a printed circuit board including at least one contact point;
at least one contact corresponding to the at least one contact point; and
a sheet at least partially covering the at least one contact so as to allow light to diffuse through an opening portion formed in the sheet.

2. The keypad of claim 1, wherein the sheet is an insulating layer.

3. The keypad of claim 1, further comprising a transparent layer.

4. The keypad of claim 3, wherein the transparent layer is disposed on the sheet.

5. The keypad of claim 1, wherein the sheet has at least one light hole.

6. The keypad of claim 1, wherein the contact has a dome shape.

7. The keypad of claim 1, wherein the printed circuit board includes at least one light emitting device.

8. A terminal including the keypad of claim 1.

9. A keypad, comprising:
at least one key switch; and
at least one contact structure adjacent the key switch, wherein the contact structure comprises:
at least one contact; and
a light diffusing layer configured to at least partially cover the at least one contact.

10. The keypad of claim 9, wherein the light diffusing layer is an insulating layer.

11. The keypad of claim 9, further comprising a transparent layer.

12. The keypad of claim 11, wherein the transparent layer is disposed on the light diffusing layer.

13. The keypad of claim 9, wherein the light diffusing layer includes at least one light hole.

14. The keypad of claim 9, wherein the light diffusing layer includes at least one opening portion.

15. The keypad of claim 14, wherein the at least one opening portion is configured to expose at least a portion of the at least one contact.

16. The keypad of claim 9, wherein the contact has a dome shape.

17. The keypad of claim 9, wherein the printed circuit board includes at least one light emitting device.

18. A terminal including the keypad of claim 9.