GB2052871A - Switch with wetted contacts - Google Patents

Abstract

A switch with mercury-wetted contacts, comprises two plane electrical conductors (2, 3) fixed to an insulating substrate (1), and having contacting portions treated for retaining by wettability drops of mercury (6), and a moveable plate (7) with a non-conductive surface, the plate (7) being movable, e.g. by a piezoelectric transducer 8, towards the mercury (6) to cause it to bridge the conductors (2, 3). <IMAGE>

Description

SPECIFICATION Relay with wetted contacts and flat circuit incorporating such a relay The present invention relates to electromechanical relays used for switching currents between several circuits under the action of a control voltage.

The known relays generally have two fixed conducting connections and a moving conductor member constituting the control switching circuit. Known relays also have a motor means actuating the moving conductor member constituting the control device, which is itself provided with conducting connections for applying the control voltage.

In a known construction of such relays two elastic ferromagnetic blades are used in a magnetic circuit provided with a control coil.

When a voltage is applied to this coil the magnetic field produced brings about the contacting of the two blades, thus closing the switching circuit. In their contact area the blades are coated with a metal such as gold, rhodium or palladium or are wetted by a conductive liquid such as mercury. They are protected by a tightly sealed enclosure in the form of a bulb under a controlled atmosphere.

The coil and the bulb are generally placed in a box or case having outgoing connections.

However, these devices have the serious disadvantage of excessive overall dimensions for existing uses and more specifically for the miniaturisation of electronic circuits, particularly when the circuits are produced on cards.

It is also pointed out that the principle of such relays housed in a bulb uses the elasticity of the blades forming the contacts as the restoring force, requiring a precise adjustment of the displacement of the blades in the factory as a function of the core characteristics and leads to high prices for mass-produced articles.

Finally the presence of a reserve supply of mercury whose quantity, indispensable for the operation, subjects it to gravity, makes it necessary to construct with the bulb in the vertical position and with limited tolerances of approximately + 20".

It has also been proposed to replace the magnetic motor means by a less cumbersome piezoelectric means. However, the very low amplitudes inherent in the latter type of motor have, under practical conditions pproved to be incompatible with those of the elastic blades when wishing to maintain a control voltage range below 100 volts.

Movement amplification systems which have been conceived for utilizing this type of control have the disadvantage of adding to the overall dimensions due to their very presence.

The relay according to the invention does not have these disadvantages.

Fundamentally it utilizes a piezoielectric motor means, whose flat shape satisfies the requirements of limited overall dimensions imposed by the use on a flat circuit. However, it overcomes the amplitude limitations inherent in this type of motor by replacing the moveable elastic blades constituting the elements ensuring on the one hand the switching and on the other the elastic restoring force by a predetermined volume of electrically conductive liquid, the restoring force then being supplied by the surface tension forces characterizing such liquid. The liquid is placed between two parallel planar surfaces, whereof one carries the two fixed conducting connections and the other is moveable under the action of the piezoelectric motor.Through the choice of a very small volume of said liquid very small displacement amplitudes of the moving surface are sufficient for copiously spreading the liquid over the two planar surfaces and for establishing contact between the two conducting connections. Thus, due to the surface tension forces the operation is completely satisfactory, no matter what the orientation.

As a result the invention advantageously satisfies a number of desired objects in the field of switching relays.

One of these objects is to provide a very flat relay, whose overall dimensions are small compared with existing relays.

Another object is the possibility of integrating into the flat printed circuit, the printed connections serving directly as switching conducting strips or areas. Combinations and concentrations of relays within a restricted space become possible.

Another object satisfied by the invention is the possibility of easy large-scale manufacture as compared with the prior art. This is because the relay according to the invention has no moving mechanical member to be adjusted for ensuring contact.

Moreover the arrangement of the switching strips or areas can be brought about by conventional means using photosensitive masks permitting the precise reproduction of parts in large numbers.

Another object of the invention is to permit the possibility of a substantially zero electric power consumption in operation through the direct use of a motor means having piezoelectric properties.

Another object of the invention is to provide a relay able to operate with any random orientation.

In its basic construction the relay according to the invention has a switching circuit, supported by a flat, non-conductive substrate constituted by at least two electrically conductive strips or connections respectively having facing portions.

A predetermined quantity of an electrically conductive liquid such as mercury is placed on the substrate in the vicinity of said portions, whereby the quantity is such that, as a result of surface tension molecular forces it does not establish electrical contact between them.

Thus, it is the crushing of a drop of conductive liquid which brings the two ends of the electrically conductive strips fixed to the substrate into electrical contact, due to the deformation of the geometry of said drop causing its spreading over the substrate. When pressure on the drop is at an end the surface tension forces restore the initial geometry of the conductive liquid and with the device in its initial state the relevant ends of the conductive strips are no longer electrically connected. Thus, there are no longer fine and precise adjustments and controls of the amplitude and elasticity of the contact blades, the former being limited to the choice of the liquid volume and the latter being included in the surface tension forces fixed by the choice of mercury.

It is pointed out that as in relays with flexible blades the conductive region of the contacts must be given a physico-chemical treatment so that they can be wetted by the conductive liquid.

The substrate can be treated so that it is wettable by the conductive liquid outside the said area or strips in order to improve the operation of the relay according to the invention, whilst retaining a larger quantity of the liquid. Conversely the portions of the substrate and the conductive strips not to be wetted by the conductive liquid can be given another special treatment in order to make them unwettable.

More specifically the present invention relates to a relay with wetted contacts incorporating two electrical conductors fixed to an insulating substrate, wherein it incorporates a moveabie plate facing the two conductors and which can occupy two positions, respectively remote from and close to the substrate, and a conductive liquid kept between the substrate and the plate by its surface tension and which, in the position close to the latter, ensures the electrical contacting of the two conductors due to its predetermined volume.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and with reference to the drawings, wherein show: Figure i-a relay according to the invention in a partly open perspective view in two operating phases (a) and (b).

Figure 2-in perspective a substrate for relays according to the invention provided with two areas or strips, whose contact regions are in the form of concentric circles.

Figure Sin perspective a substrate provided with two strips, whose contact regions are in the form of combs fitted into one another.

Figure 1 in perspective a relay according to the invention ensuring a changeover function.

Figure Sin perspective a relay according to the invention ensuring the simultaneous switching of two circuits.

Figure 6-in perspective a relay arrangement according to the invention incorporating a grid for providing the external connections.

Fig. 1 is a sectional view of a relay according to the invention for the two operating phases (a) and (b). It comprises a plate-like substrate 1 constituted by a material which does not conduct electricity such as glass, epoxy glass or ceramic.

This substrate has conductive areas or strips 2 and 3 made from a conductive material such as copper, forming the switching circuit.

These strips can be constituted by a deposit obtained by vacuum evaporation. They can also be made from other electrically conductive materials such as metal alloys or superimposed layers of various materials, whereof at least one is conductive.

The metal thicknesses deposited, which are a function of needs, can for example be between 35 and 70 microns.

The facing switching circuit contact strips 4 and 5, are treated so as to be wettable by a conductive liquid, for example mercury. A known treatment can consist of heating in the presence of mercury. Conversely other portions of said strips can be treated to make them completely inwettable by mercury, by using methods known in the production of liquid contact switches, for example the selective deposition chromium. Other parts of the substrate outside the said strips can also be treated in one or other of the senses referred to hereinbefore in order to facilitate the operation of the relay.

One or more drops 6 of the conductive liquid are placed on the portions treated to be wettable therewith. These drops are covered by a plate 7, whose face which is in contact with the conductive liquid does not conduct electricity. A piezoelectric transducer 8 is placed on a fixed support 9 and rests on the moving plate 7.

The connections 10 and 11 used for applying the control voltage to the piezoelectric transducer are connected by means of weld points to the conductive strips deposited on the substrate and constituting the control circuit.

Support 9 can advantageously be in the form of a box or protective cover and, according to a variant, can be tightly seaied by welding to the substrate with a glass cord or strand with for example a low melting point.

Thus, it is possible to obtain a switching device operating under a controlled atmosphere by welding the cover in an enclosure filled with a chemically neutral gas such as nitrogen, or a reducing gas such as hydrogen.

In operation the movement of the plate towards the substrate 1 has the effect, starting from position (a), of crushing the conductive liquid drop or drops 6 and spreading them in plane of the substrate on strips 2 and 3 forming the switching circuit and thereby establishing the electrical contact between them, as indicated at (b).

The piezoelectric transducer is shown at 8 and its expansion causes the crushing of the conductive liquid drops and therefore the electrical contacting of strips 2 and 3.

Fig. 2 shows an embodiment of the contact strips fixed to the relay according to the invention. The contact strips are fixed on either side of the substrate of a double-faced printed circuit and are in the form of two concentric circular strips.

Fig. 3 shows another embodiment in which the two contacting strips have, at the switching point, the shape of rakes or combs fitted into one another.

Fig. 4 shows in examplified manner an association of two switching devices ensuring the changeover function. Two piezoelectric motors 1 7 and 1 8 control the switching of circuits 1 9 and 20. A common cover covers the complete device, which is not shown in the drawings for reasons of clarity. Motors 1 7 and 1 8 have control wires 10, 11 and 22, 23 connected to the strips 24, 25 and 26, 27 supplying the control circuit. Depending on whether strip 1 9 or strip 20 is closed, it is possible to branch the current from strip 21 either towards strip 1 9 or towards strip 20 or towards both of these strips at once.

Fig. 5 shows another embodiment of the relay according to the invention. Two separate circuits, represented by strips 2 and 3 on the one hand and 28, 29 on the other are simultaneously controlled by the same control element, represented here by a piezoelectric motor 8 acting simultaneously on two drops of mercury and connected by conductor wires 10 and 11 to strips 25 and 24 forming the control circuit. The device of Fig. 5 thus makes it possible to simultaneously switch two separate circuits, the whole assembly being covered by a cover, which is not shown in the drawing for reasons of clarity.

Fig. 6 shows an arrangement procedure according to the invention by encapsulation. It utilizes the system of mounting on a grid known in the integrated circuit field as grid circuit mounting. The relay has a ceramic support plate 1 to which are fixed conductive strips or areas 2, 3 forning the switched circuit, and 24, 25 forming the control circuit.

The switching device is covered by a tightly sealing cover 9. Strips 2, 3 and 24, 25 are electrically connected by a gold wire welded to the clips 35, 36 and 37, 38 of a thin metal plate 30, which has openings giving it the shape of a grating.

The relay is coated with a moulded resin block 40, shown by dotted lines for reasons of clarity, using procedures known in the manufacture of electronic components. The emergent parts of grid 30 are then cut off to electrically separate the relay outputs 35, 36, 37, 38.

It is pointed out that the relay according to the invention, whose preferred embodiment has been described in the case of a piezoelectric transducer, can be realised by using another type of motor, such as an electromagnetic or electrostatic motor, when the dimensional problem is not vital. The only fundamental requirement is the moving planar surface spreading a given volume of conductive liquid.

A particularly simple embodiment of the invention can be obtained in the form of a direct appliation of the muscular force of the user's finger to the moving plate, which in particular makes it possible to form typewriterlike keyboards with keys. The capiilary forces resulting from the liquid bring about the contact without any significant displacement of the key, so that very flat keyboards can be produced.

It should also be noted that the relay according to the invention has been described in the case where the contact is established by applying the control voltage constituting a closing relay. However, the inventive scope also covers the opposite case, namely where the contact is interrupted by applying said voltage, constituting an opening relay.

It should also be noted that the invention makes it possibly by displacing the moving plate in rotary manner about a median axis parallel to its plane to provide a switching relay having three conductors, contact being obtained in a random manner between a median contact and, alternately, one of the two other conductors. It is then only necessary to have a single motor means and act on one of the ends of the pivoting plate, or the motor means can be duplicated, each of them acting on end of the plate.

Finally, the piezoelectric motor according to the invention has been described in the case of a single bar. However, any other piezoelectric motor construction, such as for example a dimorphic torsion construction also falls within the scope of the invention.

Claims (9)

1. A relay with wetted contacts, comprising firstly at least two electrical conductors fixed to an insulating substrate, each of them having contacting regions and secondly a moveable plate facing said regions by an insulated surface, and which, under the action of a motor means can occupy two positions, respectively remote from and close to the substrate, and thirdly, a conductive liquid made of mercury maintained by its surface tension between the substrate and the plate, and which in the position close to the latter ensures, due to its given volume, the electrical contacting of said regions, wherein said regions are plane, and are given a physicochemical treatment ensuring their wettability.

2. A relay according to Claim 1, wherein, with the exception of their respective contacting regions, the electrical conductors receive a treatment ensuring their non-wettability.

3. A relay according to Claim 1, wherein the respective contacting portions are shaped like concentric circles.

4. A relay according to Claim 1, wherein the respective contacting regions are shaped like combs with teeth fitted into one another.

5. A relay according to Claim 1, wherein the motor means is of the piezoelectric type.

6. A relay according to Claim 1, wherein the motor means is a muscular bearing force directly applied to the plate.

7. A relay according to Claim 6, wherein a plurality of plates is arranged in keyboard-like manner.

8. A flat electric circuit, wherein it comprises a relay according to any one of the preceding Claims.

9. A relay substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.