DE29800924U1 - Membrane buttons with key surface illumination - Google Patents

Description

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Application for a utility model/patent

Date:12.01.1998

Company:

Place of business;

Phone:

Fax:

WIKO Technology

Walter Winterfeld

Borseistrasse 3, 22 765 Hamburg

040 391728

040 392920

Representative: Karsten Sievers Dipl.Ing. (FH) Residence: Richard-Drews-Weg 1, 25335 Elmshorn Telephone: 04121 10934

Main class:
Subclass:

HOlH 9/18 HOlH 13/48

Description: Membrane switch with key surface illumination

Description

In order to create the interface between man and machine, the input technology of a membrane keyboard is increasingly used, as this combines various advantages, such as individual design options, low installation height, long service life and also price advantages in series production.

In order to display the status of a button, it is often important to provide information about it using optical signal elements.

This is done very effectively with lights that indicate the current operating status via buttons.

This already shows the problem of integrating a light source into a membrane keyboard, which can only accommodate the smallest components due to its small spatial dimensions, in such a way that this also enables surface illumination.

Thanks to SMT components, a wide range of lighting devices with sufficient performance and minimal dimensions are already available on the market.

Nevertheless, it was only possible to integrate the components in such a way that the requirements for partial surface illumination and low construction height were rarely met, which meant that considerable cost and design effort were required.

The dilemma arises when it comes to whether the light source should be placed in the center, meaning the switch arrangement should be decentralized, or the light source should be decentralized and the switch contact should be centrally placed.

In the first case, the problem could be partially solved with an expensive, specially manufactured snap disk (hole in the center).

In the second variant, it would be difficult to achieve a surface illumination because the radiation maximum is in the edge area of the key

The invention relates to a membrane keyboard with separately controllable illumination of the key with tactile feedback.

Illuminated membrane keyboards of the conventional design (DE 3133779 Al) have, as does most of this design, the

by laminating the individual film layers (lower adhesive film, switching films, fixing layers for snap-on disks and decorative film) a 'sandwich construction' is created.

In order to meet the requirements for low overall height, low cost, and design freedom with unrestricted switching characteristics, the structure was designed as follows:

1. Variant: (Fig.1+2)

The first film layer (3) contains the electrical wiring of the LEDs, which is produced using state-of-the-art screen printing and silver conductive paste, as well as the single/multi-colored SMT LEDs (7), which are mounted using conductive adhesive. This is followed by a spacer layer made of colored Plexiglass (9) (or other composite/fiber boards such as FR4 material), which has openings for the LEDs at the appropriate points in order to achieve a flat finish with the upper edge of the LEDs.

The switching package (2) is now applied to the Plexiglas plate (9) in a conventional construction method using one or two-level technology. The corresponding adhesive layer consists of a carrier material, which is slightly opal in color and has no openings in the LED area.

This ensures that the brightest point in the paraxial area of the LED extends over a larger area.

Contact is made using a standard snap-on disk available on the market, which is located on the edge of the button on the diagonal and is rotated by 45° to make the structure more compact in the X-Y plane.

The two films that follow (spacer and contact guide) ensure that the snap-on disk is fixed and also have no openings in the LED area.

To mechanically implement the pressure force by the operator's triggering finger, a specially milled opal disk (1), which can take on a wide variety of external shapes (round, rectangular, square), is placed with its geometric center point over the center of the LED (7).

This opal disc (1) has at least two incorporated elevations of different heights.

These small 'nubs ¹ also ensure that the largest possible gap is created between the underside of the opal key and the light exit plane,

which prevents the light from being refracted unnecessarily early in the opal, thereby reducing the effectively illuminated area.

In particular, the use of SMT LEDs with their opening angle of typ. 12 0-150° and the opal material, with its ability to conduct light without creating sharp-edged contours, allows for high-intensity illumination with a small structure. (Installation height: 4mm overall > 12xl2mm illuminated area)

The flatter elevation (1.1) is located exactly above the center of the snap disk, the other higher elevation (1.2) is then located diametrically opposite on the switching package.

The reason for the different heights of the elevations lies in the fact that the snap disk protrudes from the switching package.

A carrier (6), preferably made of aluminum, for example, is milled on both sides to accommodate the decorative foil on the front and the switch package (2) described above on the back. The opal keypads are located under the translucent customer-specific foil print and are located in the openings in the aluminum carrier, which are the same shape but have a slight oversize, and are guided in the X-Y direction at the same time.

Since the opal key only rests on two raised points, it must be and is held in the plane by the decorative foil (8) in order to prevent it from tipping over.

If the construction is carried out exactly as described, the snap discs can be operated perfectly by finger pressure in 80% of the effective key surface. (Fig. 5)

If the number of support points is increased to three (Fig. 5), the actuation area is reduced for geometric reasons, although the opal touch surface then shows a lower tendency to tip over even without the supporting effect of the decoration.

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2. Variant (Fig.4)

The structure is basically identical to the above structure, only here the LED level, the spacer material and the switching level are replaced by an FR4 circuit board (10) with at least 2-sided copper plating (2 layers).

The SMT LED (7) is soldered/glued on the underside and the housing of the LED is placed in a hole in the circuit board, and its light output is directed towards the decoration.

On the top of the board is the wiring■via the conductor tracks to the circuit matrix.

This design is best suited for use with solderable plug/socket connections.

In this case, defective lamps can also be replaced by repair.

The aluminum carrier prevents crosstalk of the lighting to neighboring keys thanks to the individual key cutouts.

This structure places few limits on creative freedom.

In both variants, all freely defined embossing geometries (as used in conventional membrane keyboards) can be easily implemented.

This design was also provided with insert strips, which allow the customer to label the keys individually and at a later date.

A refinement of the radiation characteristics with a concentric grid print with increasing grid density towards the center of the key enables an even more improved, more uniform surface illumination.

All materials used in this construction are commercially available as standard goods at low cost.

All materials used can be manufactured and processed using standard production machines.

The impetus for the development of this design are various requests from the industry, which require a flat input unit with a practical and decorative illumination of the individual keys, a cost-effective structure, the advantages of the membrane keyboard

(as mentioned at the beginning) but have not found it yet.

All reasonable key arrangements can be implemented, provided the key area does not fall below 10 x 10 mm.

Key surfaces that are larger than approx. 18 x 8 mm can be created by carefully arranging several LEDs below a key.

In the images shown here, only a single key is visible, but more complex key fields with a wide variety of geometric dimensions can of course also be implemented.

For explanation:

(1) Opal touch disc

(2) Foil switch package (2.1) Flex connection

(3) Foil switching level for SMT LEDs (3.1) Flex connection

(4) Plug/socket

(5) Mounting surface (shown only in section)

(6) Support for the keypads

(7) SMT LED

(8) Decorative foil (here unembossed)

(9) Distance material

(10) FR4 circuit board as an alternative to the foil circuit package

(11) conventional snap spring washer

Claims (6)

Protection claims 1. Membrane keyboard, for installation in/on operating devices such as handheld terminals, with a closing function per key, which has a single/multi-coloured full-surface key surface illumination with a minimum installation height to display the operating modes, characterized in that due to the special structural design, no additional guide, joint and support elements are required to carry out the switching operation, since this function is carried out by a specially processed opal acrylic disc (1), with at least two worked support points (Fig. 5), which are also provided by a light source attached to the rear (7) is illuminated/transilluminated across the surface. 2. Membrane keyboard according to claim 1, characterized in that the decorative film (8) guides the opal touch surface in the Z direction in order to prevent the opal disc resting on at least two support points from tipping over. 3. Membrane keyboard according to claim 1 and 2, characterized in that the resulting lever of the specially processed opal disc with at least two elevations reduces the switching path in such a way that even non-raised key surfaces in the decor ensure a perfect switching function. 4. Membrane keyboard according to claim 1 - 3, characterized in that the use of commercially available single- or multi-colored SMT LEDs in conjunction with the opal disk positioned in this way creates a desired distance between the light source and the disk (Fig. 6), which prevents premature breaking of the light cone in the optically denser medium (opal disk), in order to achieve even more extensive illumination. 5. Membrane keyboard according to claims 1-4, characterized in that the connecting adhesive layer consists of a slightly opal colored adhesive carrier that contains no openings above the light exit area in order to achieve a more even intensity distribution of the light cone at this point. 6. Membrane keyboard according to claims 1-5, characterized in that the snap disk (11) for making electrical contact is located on the edge of the key on the key diagonal and rotated by 45°.