Electric Contact Arrangement for Liquid Crystal Display Cells

The invention relates to an electric contact for liquid crystal display cells. The contact arrangement described in German Pat. No. 2,910,779 consists of part mounts comprising a bottom part and side walls, from the upper ends of which two mutually parallel strips (projections) begin which reach over the display device. A display cell representing a single digit is pushed into the clamping seat thus formed. A fluorescence plate can then be provided between the holder bottom and the display cell. In the holder bottom, an integrated electronic circuit is embedded which is electrically connected to the terminal pins protruding from the holder bottom and to the contact pins located in the side walls. The contact pins are curved towards the display cell and, with connection surfaces extending across the end face of the display cell, form a spring-loaded electric contact for the electrodes. If the contact is unsatisfactory, the contact pins can be soldered to the connection surfaces. For the representation of several display symbols, a corresponding number of part holders is connected by means of snap closures.

The known contact arrangement can be exchanged only with great difficulty, even if the contact pins are not soldered to the connection surfaces. The display device to be provided with contacts cannot be operated in transmitted light. With the exception of a fluorescence plate, artificial illumination is difficult. In addition, the number of terminal pins for the representation of many display symbols is considerable. Using this contact arrangement, it is difficult to provide large display cells with contacts.

It is one of the objects of invention to provide an electric contact arrangement for liquid crystal display cells, which is suitable for both transmissive and reflective displays, which can easily be exchanged, and which allows good electrical contacting of the display cell. It is a further object to provide a device which is also suitable for display cells of any desired shape, and which has few external electrical terminals and is of space-saving design.

The advantages obtained by the invention are essentially that the electric contact arrangement, due to the counter-contacts, represents a good and stable electrical connection to the display cell and nevertheless, for example in the event of a malfunction of the integrated circuit, can readily be exchanged. Since the contact arrangement is located outside the display and illumination zone, it is particularly suitable for displays which are operated in transmitted light. Moreover, the outlay on connections, which is otherwise conisderable, using auxiliary prints, part holders and "chip-on-glass" technology is minimised.

The invention is explained below in more detail by reference to examples illustrated in the drawing in which:

FIG. 1 shows a liquid crystal display cell with an electrical contact arrangement according to the invention;

FIG. 2 shows another liquid crystal display cell with another electric contact arrangement according to the invention;

FIG. 3 shows a section of the contact arrangement according to FIG. 2 along the line A--A';

FIG. 4 shows a liquid crystal display cell with another electric contact arrangement according to the invention;

FIG. 5 shows a section of the contact arrangement according to FIG. 4 along the line B--B', and

FIG. 6 shows a cascade connection of two integrated circuits.

Two contact arrangements according to the invention with L-shaped multi-point connectors 1 are shown in FIG. 1. The counter-contacts held in the multi-point connector 1 and the external terminals are formed by contact tabs 2 and contact pins 3. The two contact arrangements are plugged into the side of a liquid crystal display cell 4 which has electrode segments 5 for digits and decimal points. The contact arrangement is mounted on a print plate 6 by means of soldering the contact pins 3.

Two further electric contact arrangements according to the invention with L-shaped multi-point connectors 1 are shown in FIG. 2. The designation is here the same as in FIG. 1. In this case, the two contact arrangements are plugged into the same side of a large-area liquid crystal display cell 4. The cell forms a speedometer display for cars, and it has digits and other display symbols. The contact pins 3 are arranged in the center of the multi-point connector 1 and are pushed into a plug 7. The socket in turn is connected via a flat band cable 8 to a voltage supply and control electronics (not shown).

FIG. 3 shows a section along the line A--A' of FIG. 2. Contact tabs 2 which are connected via tracks 5' to the electrode segments 5 (not shown here) are provided on the display cell 4 in contact with contact surfaces 2'. The contact tabs 2 and the contact pins 3 are connected via electric lines 9', 9" (gold or aluminium wires) to an integrated electronic circuit 10 embedded in the multi-point connector 1. The electric lines 9', 9" are likewise located within the multi-point connector 1. Since the integrated circuit is in the immediate vicinity of the counter-contact, namely the contact tabs 2, the electric lines 9', 9" are very short. The electrical losses and hence also the outlay on connections are thus substantially reduced. At the upper end of the multi-point connector 1, a projection 11 is provided opposite the contact tabs 2 with the display cell 4 resting on the projection 11 and being laterally adjusted by guides provided therein. As shown in broken lines, the contact pins can also protrude laterally from the contact arrangement.

In FIG. 4, another embodiment of the invention is shown. The contact arrangement here consists of an essentially cuboid multi-point connector 1, into which the liquid crystal display cell 4, namely a matrix display with punctiform electrode segments 5, is plugged in.

FIG. 5 is a section along the line B--B' of FIG. 4. On its upper surface, the multi-point connector 1 has a U-shaped slot with a row of spring contacts 12 (counter-contacts) on both sides. The ends of the slot are surrounded by the multi-point connector 1, so that the plugged-in display cell 4 is adjusted. The spring contacts 12 here form a regular grid. On the lower surface of the cuboid multi-point connector 1, a (narrower) U-shaped slot surrounded by the multi-point connector is likewise provided, wherein a row of contact bushes 13 (external terminals) is arranged. The integrated circuit 10 is again embedded in the multi-point connector 1 and is connected via electric lines 9', 9" located within the multi-point connector 1 to the spring contacts 12 and to the contact bushes 13. The plugs 14 which are plugged into the contact bushes 13 are in turn located on a multi-point connector. On the display cell 4, contact surfaces 2' are provided on both sides, in order to enlarge the number of contacts. The contact surfaces 2' located on the outer side of the display cell 4 are here connected via the end face to the corresponding tracks 5'.

When two integrated circuits 10 are provided in one multi-point connector 1, a cascade arrangement according to FIG. 6 is particularly suitable. The part located in the multi-point connector 1 is indicated in broken lines. In this way, the number of external connections 3 is minimised. The two integrated circuits 10 form a so-called "master-slave" relationship, in which the left-hand circuit represents the master and the right-hand circuit represents the slave. This arrangement is excellently suitable for both symbol displays and point-matrix displays. The electrical connections between the two integrated circuits 10, the counter-contacts 2 and the external terminals 3 are made without cross-overs or by means of a film which is coated on both sides with metal tracks and which is anyway required for making the contacts with the integrated circuits 10.

The conventional display cells have a standardised length. The following four standard lengths are most suitable for use with the contact arrangement according to the invention: ##EQU1##

The smallest standard length given is, due to the conventional grid for the contact tabs 2 (FIG. 3) or spring contacts 12 (FIG. 5), still just technically feasible. The largest standard length given is limited due to the number of terminals of the integrated circuit 10. As a standard grid for the contact tabs 2 or spring contacts 12, there are the following possibilities: 2.54 mm (0.1 inch), 1.905 mm (0.075 inch), 1.27 mm (0.02 inch) and 1.00 mm. The standard grid here gives the distance between the center lines of two adjacent contact tabs 2 or spring contacts 12. For the contact tabs 2 or spring contacts 12 made as metal springs, the smallest indicated grid of 1.00 mm cannot be further reduced because of the width of the contact tabs or spring contacts.

In Table 1, examples of integrated circuits as drivers for the display cells are listed; these are particularly suitable for the contact arrangements according to the invention. The number, the manufacturer, the type designation, the number of selectable segments Z.sub.seg, the selection type A and the number of counter-contacts Z.sub.int and external terminals Z.sub.ext are listed.

In Table 2, the most favourable combinations of integrated circuits, length of the display cell L in mm, number of counter-contacts Z.sub.int, grid constant of the counter-contacts R.sub.int in mm, segment number Z.sub.seg and selection type A are indicated.

In the illustrative embodiment described in FIG. 1, two integrated circuits of type PCE 2100 from Philips have been used. The display cell 4 is 51 mm long and 22 mm wide. The number of contact tabs 2 is 20 on each side, with a grid constant of 2.54 mm. The number of contact pins 3 is 6 on each side, the grid constant being 2.54 mm for each group of three. The contact pins 3 are soldered to the print plate 6, so that a very stable electrical and mechanical connection to the contact arrangements and hence also to the display cell 4 is formed. The total number of the selected electrode segments 5 is 72.

In the illustrative embodiment indicated in FIG. 2, two integrated circuits of the type PCE 2111 from Philips have been used. The large-area display cell 4 is 70 mm long and 70 mm wide. The number of the contact tabs 2 of one contact arrangement is 34, with a grid constant of 1.00 mm. The number of the contact pins 3 of each contact arrangement is 6, with a grid constant of 2.54 mm, and they are connected via the plug 7 to the flat band cable 8. The number of the selectable electrode segments 5 is 128 in this case. The display cell 4 is mounted in a frame (not drawn), in order to ensure good mechanical stability.

The manufacture of the contact arrangements, according to the invention, with multi-point connectors 1 is similar to the production of integrated circuits with plastic housings. For this purpose, the track pattern is stamped from a metal web (copper) and glued to a flexible film. When two integrated circuits 10 have been arranged in cascade, a second track pattern is stamped and glued to the other side of the film. The conventional margin around the track pattern is then stamped out and the integrated circuit or circuits 10 and, for example, the contact tabs 2 and the contact pins 3 are bonded to the tracks by means of gold or silver wires. The housing is then fitted around this structure by means of an appropriate process, such as transfer moulding, that is to say two multi-point connector halves are locally heated and the flexible film with the integrated circuit 10, the contact tabs 2 and the contact pins 3 is pressed in between the two halves.

For the contact tabs 2, the contact pins 3, the spring contacts 12 and the contact bushes 13, preferably nickel-silver, beryllium or--and this is particularly economical--brass is selected. The sheet thickness is between 0.1 and 0.3 mm, and is preferably 0.2 mm. The outer parts are provided with superficial copper-plating or tin-plating.

It is to be understood that the counter-contacts and the external terminals can be formed by any desired plug systems. The contact arrangements according to the invention are also applicable with particular advantage for a modular plug-in system.