EP0124862A2 - Keyboard - Google Patents

Abstract

The keypad has switching contacts (2, 3) on a base plate (1) with conductor tracks (8, 9), which are electrically connected to the conductor tracks. A switching film (5) has a contact surface (6) opposite and facing the switching contacts, which electrically connects the assigned switching contacts (2, 3) to one another when the switching film is mechanically bent. An intermediate insulation layer (4) serves as a spacer for the switching film (5) and thus also separates the contact surface (6) from the switching contacts (2, 3). This intermediate insulation layer (4) has recesses (10) in the area of the switch contacts. The intermediate insulation layer (4) is applied to the base plate, preferably by means of screen printing technology.

Description

The invention relates to a keypad according to the preamble of claim 1 and to a method for producing the same according to the preamble of claim 8.

Such keypads are commercially available and are characterized by their flat design and low manufacturing costs.

In order to prevent accidental closing of the respective switches on the keypad, there is flexibility between the base plate with conductor tracks and switch contact surfaces le switching film, which has a coating of electrically conductive material (contact surface) opposite the switching contacts, an intermediate insulating layer in the form of a film is provided which has openings in the area of the switching contacts only. The switch contact foil thus serves as a spacer between the switch contacts and the contact surface. To actuate the respective switch, mechanical pressure is exerted on the switching film, so that the contact surface attached to it reaches through the cutout in the insulating layer and touches the associated switching contacts and thus electrically connects them to one another.

A disadvantage of this known keypad is the intermediate insulation layer described in the form of a film. It must be manufactured with separate tools, correctly aligned when installing the keypad and secured against slipping during operation by special measures.

These disadvantages are to be eliminated with the present invention.

The object of the invention is therefore to improve the keypad of the type mentioned and the method for its production in such a way that the production is simplified and the operational reliability is increased.

This object is achieved by the features specified in the characterizing part of claims 1 and 8, respectively.

An advantageous embodiment and development of the invention can be found in the subclaims.

The invention takes advantage of the fact that, in the production of keypads of the type mentioned at the outset, certain layers are in any case firmly applied to the base plate with the conductor tracks, which is done by photolithography techniques or by screen printing technology. In particular, these are insulation layers in the area of interconnect bridges or crossings. Simultaneously with the application of these insulation layers, which are in any case necessary, those insulation layers which are realized in the known keypad through the foil with openings are also applied in the invention.

• Figur 1 eine schematische Schnittansicht des Tastenfeldes nach der Erfindung im Bereich eines Schaltkontaktes (Schnitt entlang Linie I-I der Figur 2)
• Figur 2 eine Draufsicht auf den Ausschnitt der Figur l;
• Figur 3 eine abgewandelte Ausführungsform gemäß Figur l;
• Figur 4 a ein Muster einer ersten Isoliationsschicht;
• Figur 4 b ein Muster einer zweiten Isolationsschicht, die auf die erste Isolationsschicht der Figur 4 A aufgebracht wird; und
• Figur 4 c. ein Muster einer elektrisch leitfähigen Schicht, die auf die beiden Isolationsschichten gemäß Figur 4 A und Figur 4 B aufgebracht wird.

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing. It shows:

• 1 shows a schematic sectional view of the keypad according to the invention in the area of a switching contact (section along line II of FIG. 2)
• Figure 2 is a plan view of the detail of Figure 1;
• FIG. 3 shows a modified embodiment according to FIG. 1;
• FIG. 4 a shows a pattern of a first insulation layer;
• FIG. 4b shows a pattern of a second insulation layer which is applied to the first insulation layer of FIG. 4A; and
• Figure 4 c. a pattern of an electrically conductive layer which is applied to the two insulation layers according to Figure 4 A and Figure 4 B.

The same reference numerals in the individual figures denote the same parts.

1 to 3 show the section of a base plate (1) made of electrically insulating material, such as hard paper or plastic, to which switch contacts (2 and 3), which form a pair of switch contacts, are applied. The switch contacts (2 and 3) exist, for example from an electrically conductive carbon layer, which are applied by screen printing. In plan view, these switching contacts are usually semicircular, their mutually facing edges (12) being at a distance (7) from one another.

An intermediate insulation layer (4) is arranged around a pair of switch contacts (2, 3) so that it partially overlaps the two switch contacts (2 and 3) of a pair at their outer edges. The intermediate insulation layer (4) thus has the shape of a disk in plan view, which has an essentially circular central recess (10), as a result of which certain areas of the switch contacts (2 and 3) are not covered and are therefore accessible from above. A switching film (5) made of electrically non-conductive and flexible material now lies over the structure described so far, this switching film (5) in the region of the cutout (10) of the intermediate insulation layer (4) being an electrically conductive layer, in the following contact surface (6) called, carries. This contact surface (6) can be a carbon layer, for example, which is printed on the film.

In the embodiment of Figure 1, the diameter of the contact surface (6) is smaller than the diameter of the recess (10). Thus, only the switching film (5) lies on the edges of the intermediate insulation layer (4), while the contact surface (6) protrudes completely into the recess (10). It can be seen that the intermediate insulation layer (4) serves as a spacer, also called spacer in technical jargon, and thus prevents the switch from being inadvertently closed.

In the exemplary embodiment in FIG. 3, on the other hand, the diameter of the contact surface (6) is larger than the diameter of the recess (10), so that the outer edges of the contact surface (6) rest on the edge of the intermediate insulation layer (4) surrounding the recess (10). This is the distance between the contact surface (6) and the switching contacts (2 and 3) is somewhat larger than in the exemplary embodiment in FIG. 1.

The switching contacts (2 and 3) of a pair of switching contacts are each electrically connected to a conductor track (8) or (9), as is generally known in the prior art. The switch contacts in the transition area between the straight edges (12) and their circular outer contour are also beveled, as can be seen from FIG. 2 at reference number (11).

The respective switch is actuated in that a mechanical force is exerted on the switching film (5) in the region of a pair of switching contacts. As a result, the contact surface (6) is moved so far down with sufficient force that it touches both switching contact surfaces (2 and 3), so that an electrical connection is established, which ultimately leads to the conductor tracks (8 and 9) being electrically connected to one another are connected. The contact surface (6) is also flexible to a certain extent so that there is no risk of cracks or breaks.

A small cavity is shown in FIGS. 1 and 3 in the transition area between the outer circumference of the switch contacts (2 and 3) and the intermediate insulation layer (4). In practice, this cavity does not exist. Rather, it will be filled by the intermediate insulation layer.

It is also shown in Figures 1 to 3 that the intermediate insulation layer (4) partially covers the switch contacts (2 and 3). According to a variant of the invention, the recess (10) of the intermediate insulation layer (4) can also be so large that there is no such overlap. Of course, the layer thickness of the intermediate insulation layer (4) must be greater in this case than the layer thickness of the switch contacts (2 and 3) so that the intermediate insulation layer (4) can fulfill its function as a spacer.

According to the method of the invention, the intermediate insulation layer (4) made of insulating varnish is applied, preferably printed on by means of screen printing. FIGS. 4 a to 4 c show print samples of a specific exemplary embodiment. FIG. 4 a shows the print pattern for a first intermediate insulation layer (13) which is printed on a base plate provided with conductor tracks. This pattern has different cutouts for switch contacts and for bridges. Two substantially circular cutouts (14 and 15) for switching contacts and rectangular cutouts (16 and 17) for interconnect crossings or bridges are designated by way of example, the two cutouts (16 and 17) lying exactly over sections of two interconnects which are later through a bridge should be connected. A recess (19) is also provided, which leaves solder connection points free. Finally, an alignment mark (18) is shown, which enables the further layers to be aligned in subsequent printing processes. Otherwise, the first intermediate insulation layer (13) completely covers the base plate and the conductor tracks applied thereon. After this first intermediate insulation layer (13) has been applied, a second intermediate insulation layer according to FIG. 4b is applied. This intermediate insulation layer on the one hand forms further spacers (24 and 25) around the cutouts (14 and 15) in FIG. 4 a and on the other hand is additionally printed in areas where printed circuit bridges are later printed. The section of the second insulation layer designated by reference number 26 then covers the region of the first insulation layer (13) lying between the openings (16 and 17). Correspondingly, the section of the second insulation layer designated 27 covers the section of the first insulation layer (13) that lies between the recess (17) and the recess lying to the right with FIG. 4 a.

In a third printing process, the pattern of FIG. 4 c made of electrically conductive material, for example in the form of a carbon layer, is then printed on. The two switch contact pairs (34 and 35) are then pressed into the openings formed by the spacers (24 and 25) and the recess (14 and 15), while the section 36 the recesses (16, 17 and 20) and thus the ones lying underneath Interconnects connects.

Analogously to the adjustment point (18), the layers in FIGS. 4b and 4c also have corresponding adjustment points (28 and 38).

Instead of the two layers of FIGS. 4 a and 4 b, a single layer with either the shape of FIG. 4 a or the shape of FIG. 4 b can also be printed on. However, this must then be thicker than the two layers described in FIGS. 4 a and 4 b. However, it is nevertheless advantageous to apply the two intermediate insulation layers of FIGS. 4 a and 4 b, since small defects, for example due to dust grains, can occur in the area of the conductor track bridges when only one intermediate insulation layer is applied, which then destroy the insulation, which is caused by subsequent formation the conductor bridge can lead to short circuits.

Although it is preferred to apply the individual layers by screen printing, other known application methods can also be used, preferably photolithographic methods, in which the entire surface is first coated with a photosensitive, electrically insulating lacquer, then covered with a mask and exposed, and then is developed so that during the development process the unexposed or the exposed, ie those covered by the mask or not covered areas are removed, so that the pattern of FIG. 4a is ultimately created.

Instead of printing, the intermediate insulation layers can also be glued on, for example by means of self-adhesive insulation layers which have the configuration of FIG. 4a or that of FIG. 4b.

In practice, the thickness of the intermediate insulation layer is approx. 30µ. In the embodiment of Figure 4, the first intermediate insulation layer (13) also serves as a "solder stop". During the later soldering process, it is prevented in a manner known per se that the solder penetrates into areas that are covered by the intermediate insulation layer.

All technical features shown in the claims, the description and the drawing can be essential to the invention both individually and in any combination with one another.

Claims (10)

1. Keypad with a base plate, with switch contacts attached to it, which are arranged in pairs at a distance from each other and are each electrically connected to a conductor track, with an intermediate insulation layer that has recesses at least in the area of the switch contacts, and with a switching film that is opposite the switch contacts has a coating of electrically conductive material (contact surface), characterized in that the intermediate insulation layer (4) is firmly applied to the base plate (1). 2. Keypad according to claim 1, characterized in that the intermediate insulation layer (4) is applied by means of photolithography technology (photoetching technology, photoresist technology) or screen printing technology. 3. Keypad according to claim 1 of 2, characterized in that the intermediate insulation layer (4) is arranged annularly around the switch contact pairs (2, 3). 4. Keypad according to claim 3, characterized in that the intermediate insulation layer (4) overlaps the switch contact pairs (2, 3) in the region of their outer edges. 5. Keypad according to one or more of claims 1 to 4, characterized in that the recesses (10) of the intermediate insulation layer (4) for the switch contacts have a smaller opening width than the outer diameter of the contact surface (6). 6. Keypad according to one or more of claims 1 to 5, characterized in that the intermediate insulation layer (4) consists of two layers (13, 24-26) which are applied in succession, the second layer being ring-shaped around the switch contact pairs (2, 3) is arranged around and serves as a spacer between the contact surface (6) attached to the switching film (5) and the associated switching contact pair (2, 3). 7. Keypad according to claim 6, characterized in that the first layer (13) of the intermediate insulation layer (4) covers the base plate with conductor tracks substantially over the entire surface with the exception of recesses (14, 15, 16, 17, 19) for switch contacts, connections " for solder joints and connections "for interconnect bridges, and that the second layer (24-26) only covers annular areas (24, 25) around the switch contacts and areas (26, 27) which are to be insulated for the formation of interconnect bridges. 8. A method for producing keypads in which an intermediate insulation layer is applied to a base plate with conductor tracks and switching contact points, characterized in that the intermediate insulation layer is firmly applied to the base plate. 9. The method according to claim 8, characterized in that the intermediate insulation layer is printed by screen printing from insulating varnish, sprayed or glued. 10.The method according to claim 8 or 9, characterized in that a first intermediate insulation layer is applied to the base plate provided with conductor tracks, which has recesses only in the area of switch contacts, connections for solder joints and for conductor track bridges, that then a second insulation layer in a ring around the Cutout for the switch contact points and on areas of the conductor bridge is printed, and then a conductive layer, preferably carbon layer for the conductor bridges and the switch contacts is applied, preferably printed using screen printing technology.

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