DE3316616A1 - KEYPAD - Google Patents

Description

description

The invention relates to a keypad according to the preamble of claim 1 and to a method for Production of 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 the end.

In order to prevent unintentional closing of the respective switches on the keypad, there is a space between the base plate with conductor tracks and switch contact surfaces and the flexible

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le switching foil, which has a coating of electrically conductive material (contact surface) opposite the switching contacts, an intermediate insulating layer is provided in the form of a foil which has openings only in the area of the switching contacts. The switch contact foil thus serves as a spacer between the switch contacts and the contact surface. To operate the respective switch, mechanical pressure is exerted on the switching foil, so that the contact surface attached to it reaches through the said IQ recess in the insulating layer and touches the associated switching contacts and thus connects them electrically to one another.

The disadvantage of this known keypad is the described intermediate insulation layer in the form of a film. she must namely be made with separate tools, be correctly aligned when assembling the keypad and secured by special measures against slipping during operation.

These disadvantages are to be eliminated with the present invention.

The object of the invention is therefore to provide the keypad of the type mentioned at the beginning and the method for its production to the effect that production is simplified and operational reliability is increased.

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

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

In the invention, the fact is used that in the manufacture of keypads of the type mentioned anyway, certain layers are firmly applied to the base plate with the conductor tracks, which is achieved by photolithography

techniques or by screen printing. In particular these are insulation layers in the area of conductor track bridges or crossings. At the same time with the application of these insulation layers, which are necessary in any case, are now also those insulation layers in the invention applied, which are realized in the known keypad through the film with openings.

In the following the invention is explained in more detail by means of exemplary embodiments in connection with the drawing explained. It shows:

Figure 1 is a schematic sectional view of the keypad according to the invention in the area of a switching contact (Section along line I-I of Figure 2)

FIG. 2 shows a plan view of the detail from FIG. 1;

FIG. 3 shows a modified embodiment according to FIG. 1;

Figure 4 a. a pattern of a first insulating layer;

FIG. 4b shows a pattern of a second insulation layer which is applied to the first insulation layer of FIG. 4A will; and

FIG. 4 c shows a pattern of an electrically conductive layer which is applied to the two insulation layers according to FIG .Figur 4 A and 4 B is applied. 30th

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

In Figures 1 to 3, the section of a base plate (1) made of electrically insulating material such as hard paper or plastic is shown, on which switching contacts (2 and 3), which form a pair of switching contacts, are applied. The switching contacts (2 and 3) exist for example

made of an electrically conductive carbon layer that is applied by screen printing. In the top view these are Switching contacts usually semicircular, with their mutually facing edges (12) at a distance (7) from one another lie.

There is an intermediate insulation layer around a pair of switching contacts (2, 3) (4) arranged in such a way that they connect the two switching contacts (2 and 3) of a pair to the outer one Edges partially overlapped. The intermediate insulation layer (4) thus has the shape of a disk in plan view, which has a substantially circular central recess (10), whereby certain areas of the switching contacts (2 and 3) not covered and therefore accessible from above are. A switching foil (5) made of electrically non-conductive material now lies over the structure described so far and flexible material, this switching foil (5) in the region of the recess (10) of the intermediate insulation layer (4) carries an electrically conductive layer, hereinafter referred to as contact surface (6). This contact surface (6) For example, it can be a layer of carbon that is printed onto the film.

In the exemplary embodiment in FIG. 1, the diameter of the contact surface (6) is smaller than the diameter of the recess (10). Thus, only the switching foil (5) rests 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 insulating layer (4) serves as a spacer, also known as a spacer ^ in technical jargon, preventing the unintentional closing of the Switch prevented.

In the exemplary embodiment in FIG. 3, however, the diameter of the contact surface (6) is greater than the diameter the recess (10) so that the outer edges of the contact surface (6) on the edge surrounding the recess (10) the intermediate insulation layer (4) rests. This is

the distance between the contact surface (6) and the switching contacts (2 and 3) somewhat larger than in the exemplary embodiment in FIG. 1.

The switching contacts (2 and 3) of a switching contact pair are each electrically connected to a conductor track (8) or (9), as is generally known in the prior art. Also, the switch contacts are tapered contour in the transition area between the straight edge (12) and its circular outer IQ, as can be seen from Figure 2 at the reference numeral (11).

The actuation of the respective switch takes place in that in the area of a switching contact pair a mechanical Force is exerted on the switching foil (5). As a result, the contact surface (6) will move so far if there is sufficient force moved down so that it touches both switch contact surfaces (2 and 3), so that an electrical connection is made becomes, which ultimately leads to the fact that the conductor tracks (8 and 9) are electrically connected to one another. the The contact surface (6) is also flexible to a certain extent, so that there is a risk of cracks or breaks is excluded.

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

Furthermore, FIGS. 1 to 3 each show that the intermediate insulation layer (4) is the switching contacts (2 and 3) partially covered. According to a variant of the invention, the recess (10) of the intermediate insulation layer (4) also be so large that no such overlap occurs. Of course, the layer thickness must be the Intermediate insulation layer (4) must be larger in this case

than the layer thickness of the switching contacts (2 and 3), so that the intermediate insulation layer (4) does its job as a spacer can meet.

According to the method of the invention, the intermediate insulating layer (4) Applied from insulating varnish, preferably printed on by means of screen printing. In Figures 4 a to 4c print samples of a specific embodiment are shown. Figure 4 a shows the print pattern for a first intermediate insulation layer (13) which is printed onto a base plate provided with conductor tracks. This pattern has different recesses for switching contacts and for bridges. Exemplary are essentially two circular recesses (14 and 15) for switching contacts and rectangular recesses (16 and 17) for track crossings or bridges, the two recesses (16 and 17) exactly over sections of two conductor tracks that are later to be connected to one another by a bridge. Farther a recess (19) is provided which leaves solder connection points free. Finally there is an alignment mark (18), which enables the additional layers to be aligned during subsequent printing processes. Otherwise the first intermediate insulation layer (13) completely covers the base plate and the conductor tracks applied to it. After this first intermediate insulating layer (13) has been applied, a second intermediate insulating layer is applied applied according to Figure 4b. On the one hand, this intermediate insulation layer forms around the cutouts (14 and 15) of Figure 4 a further spacers (24 and 25) and is also used in such areas printed on, on which conductor track bridges will later be printed. The designated with the reference numeral 26 The section of the second insulation layer then covers the area between the openings (L6 and 17) first insulation layer (13). Correspondingly, the section labeled 27 of the second insulation layer covers the Section of the first insulation layer (13) between

the recess (17) and the recess located to the right of it with FIG. 4 a.

In a third printing process, the pattern in FIG. 4c is then made of electrically conductive material, for example printed in the form of a layer of carbon. The two pairs of switching contacts (34 and 35) are then in the through the spacers (24 and 25) and the recess (14 and 15) formed openings impressed while the section 36 connects the recesses (16, 17 and 20) and thus the conductor tracks lying underneath.

Analogously to the adjustment point (18), the layers in FIG. 4 b and FIG. 4 c also have corresponding adjustment points (28 b2w. 38).

Instead of the two layers of FIGS. 4 a and 4 b, a single layer with either the shape of the Figure 4a or the shape of Figure 4b can be printed.

However, this must then be thicker than the two layers described in FIG. 4 a and FIG. 4 b. However, it is it is nevertheless advantageous to apply the two intermediate insulation layers of FIG. 4 a and FIG. 4 b, since in particular Small imperfections in the area of the conductor track bridges when only one intermediate insulation layer is applied, for example, dust particles can occur, which then destroy the insulation, which is the case with subsequent Formation of the conductor track bridges 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 are used, preferably photolithographic processes, in which first the entire surface with coated with a photosensitive, electrically insulating lacquer is, is then covered with a mask and exposed and then developed so that the Development process the unexposed or the exposed, d. H. those covered or not covered by the mask

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covered areas are removed, so that then ultimately the pattern of FIG. 4a is produced.

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

In practice, the thickness of the intermediate insulation layer is approx. 30 / t. In the embodiment of the figure the first intermediate insulation layer (13) also serves as a "solder stop". During the later soldering process, in is known to prevent the solder from penetrating into areas which are from the interlayer insulation are covered.

All of the 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)

Claims ( 1.) Keypad with a base plate, with switching contacts applied to it, which are arranged in pairs at a distance from one another and are each electrically connected to a conductor track, with an intermediate insulation layer that has recesses at least in the area of the switching contacts, and with a switching foil, which is opposite has a coating of electrically conductive material (contact surface) on the switching contacts, 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) by means of photolithography technology (Photo etching technique, photoresist technique) or Screen printing technology is applied. 3. Keypad according to claim 1 of 2, characterized in that the intermediate insulating layer (4) is annular is arranged around the switching contact pairs (2, 3). 4.'Tastenfeld according to claim 3, characterized in that the intermediate insulation layer (4) overlaps the pairs of switching contacts (2, 3) in the area 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 switching 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 one after the other, the second Layer is arranged in a ring around the switching contact pairs (2, 3) and as a spacer between the on the switching foil (5) attached contact surface (6) and the associated switching contact pair (2, 3) is used. 7. Keypad according to claim 6, characterized in that the first layer (13) of the intermediate insulation layer (4) the base plate is essentially covered over the entire surface with conductor tracks with the exception of recesses (14, 15, 16, 17, 19) for switch contacts, connections "for soldering points and connections" for conductor track bridges, and that the second layer (24-26) only annular areas (24, 25) around the switching contacts and areas (26, 27), which have to be insulated for the formation of conductor track bridges. 8. Process for the production of keypads, in which on a base plate with conductor tracks and switching contact points an intermediate insulation layer is applied, characterized in that the intermediate insulation layer is firmly attached to the base plate. 9. The method according to claim 8, characterized in that the intermediate insulation layer is printed, sprayed or glued on by means of screen printing from insulating varnish will. 10. The method according to claim 8 or 9, characterized in that that on the base plate provided with conductor tracks first a first intermediate insulation layer is applied, which is only in the area of switch contacts, connections for soldering points and for conductor track bridges Has recesses that then a second insulation layer is ring-shaped around the recess for the switching contact points and on Areas of the conductor track bridges is printed, and that then a conductive layer, preferably a carbon layer applied for the conductor track bridges and the switching contacts, preferably by means of screen printing technology is printed.