US3657690A

US3657690A - Miniature variable-resistance device with flexible disk contact

Info

Publication number: US3657690A
Application number: US62419A
Authority: US
Inventors: Radovan Tavzes; Jelko Koron; Evgen Kansky
Original assignee: INST ZA ELEKRONIKO IN VAKUUMSK
Current assignee: INST ZA ELEKRONIKO IN VAKUUMSK
Priority date: 1969-08-11
Filing date: 1970-08-10
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: FR2056808A5; YU32406B; YU206969A; GB1322218A; DE2039886B2; DE2039886A1

Abstract

A potentiometer comprising a body of homogeneous vitreous material in which a plurality of wire leads are embedded flush with a surface of the vitreous body which is received in a metal frame. A cup-shaped housing encloses the flush surface of the body and engages the frame while receiving a rotatable plug having a boss with a screwdriver slot extending through this cover. An arcuate contact strip is applied, e.g. by vacuum depositing to the surface while a thin deformable plate yieldably overlies the contact strip in spaced relation therewith, the contact strip being angularly fixed upon rotation in the plug, a spring-loaded ball presses a limited region of the disk against the contact strip to form the wiper.

Description

United States Patent Tavzes et al.

[54] MINIATURE VARIABLE-RESISTANCE DEVICE WITH FLEXIBLE DISK CONTACT {72] Inventors: Radovan Tavzes; Jelko Koron; Evgen Kan- 21 Appl. No.: 62,419

[30] Foreign Application Priority Data Aug. 11, I969 Yugoslavia ..P-2069/69 [52} US. Cl ..338/154, 338/174 [51] Int. Cl ..H0lc 9/02 [58] Field ofSearch ..338/96,118,154,157,162l64,

[56] References Cited UNITED STATES PATENTS 7 3,516,041 6/1970 Estlick ..338/96 X 1 Apr. 18, 1972 Primary Examiner-Laramie E. Askin Assistant Examiner-Gerald P. Tolin Att0rneyl(arl F. Ross 57 ABSTRACT A potentiometer comprising a body of homogeneous vitreous material in which a plurality of wire leads are embedded flush with a surface of the vitreous body which is received in a metal frame. A cup-shaped housing encloses the flush surface of the body and engages the frame while receiving a rotatable plug having a boss with a screwdriver slot extending through this cover. An arcuate contact strip is applied, eg by vacuum depositing to the surface while a thin deformable plate yieldably overlies the contact strip in spaced relation therewith, the contact strip being angularly fixed upon rotation in the plug, a spring-loaded ball presses a limited region of the disk against the contact strip to form the wiper.

10 Claims, 3 Drawing Figures Patented April 18, 1972 'FIG.I

E Y WWW. RN T KK m V N mE win REE F l G 2 ATTORNEY MINIATURE'VARlABLE-RESISTANCEDEVICE WITH FLEXIBLE DISK CONTACT It is an object of the present invention to provide a miniature thin-film potentiometer which is particularly suitable forv use in printed circuits.

According to the invention, the mechanism of the miniature potentiometer is built into a can which is moistureand waterproof, welded or soldered to the header. The can protects the potentiometer mechanism against external influences or damages and transmits the dissipated heat from the interior to the ambient. The can is electrically connected to the mass lead in order to prevent the influence of I electromagnetic perturbances on the resistance film of the potentiometer. Through an opening in the can there protrudes an extension of an insulating plug for adjusting the potentiometer resistance. This extension has a slot for a screw driver, or is adapted to receivean adjusting knob. The header consists of a metal ring intowhich wire leads are sealed with the aid of aglass or ceramic plate. One of the wire leads is welded to the metal ring for ground connection, the remaining wire leads are connected to the ends of the resistance film and to the resilient contact plate. The materials for the header, i.e. glass or ceramic, metal rings and wire leads are so chosen that their coefficients of thermal expansion are matched in a broad temperature range of use. Moreover, the glass orceramic must meet severe requirements regarding vacuumdepositing of metal segments and the resistance film.

According v to present invention the resistance film is vacuum-deposited directly upon the polished upper surface of the glass or ceramics substrate. After being sealed, the wire leads are worked together with the glass or ceramics surface so that the entire upper surface of the substrate is highly smooth and even and that the ends of the wire leads are flush with the upper surface of the substrate. The resistance film has the shape of a cut-out ring or a circular horseshoe and is so oriented that the ends of the film are connectedto the wire leads. These connections are made with the aid of metal segments vacuum-deposited on the ends of the wire leads and the surrounding surface of the substrate. In this way a better reliability of the connections of the wire can be obtained.

The resistance film is made of one or more layers. Its design depends upon the required value of the resistance and other properties required, such as the temperature coefficient of resistance, mechanical stability, contact properties and other. The single-layer film is usually made of ametal alloy, e.g. Ni- Cr, and can be used for resistances of up to 1,000 ohms. In the case of a two-layer film, the lower layer is made of a material with a predominantly negative temperaturecoefficient of resistance, i.e. of the semiconductor type, such as are combinations of oxides and metals, e.g. cermets; the upper layer is of a metal having a prevailingly positive temperature coefficient of resistance. This upper metal layer is continuous for resistance ranges between 1 and 100 kiloohms, while for higher resistance values the layer is mosaic-shaped and has a high layer resistance.

in the middle of the upper substrate surface, a conductive metal layer is also vacuum-deposited and connected to the central wire lead. A little round resilient contact plate is concentrically fixed to this layer. This plate is made of a resilient metal with a durable contact surface. This small plate can-be fastened by ultrasonic soldering or by gluing with a conductive adhesive. This small plate is so shaped that its edge overlaps the resistance film and touches it only in that point where a spring lever of the tumable plug, preferably having the shape of a steel ball and a helicoidal spring, which are placed in an eccentric groove of the tumable plug, presses against the resistance film. A pressure on the plate creates an electrical contact between the selected point of the resistance film and the central wire lead through said plate and the central vacuumdeposited conductive layer. It follows therefrom that the resilient plate and the spring-loaded eccentric metal ball pressing the plate against the resistance film, perform the function of a wiper. The resilient'plate prevents wear of the resistance film because it does not slide upon the resistance film, but it only adheres to it when it is pressed. In this way a good contact is reached with the resistance film without risk of wear and tear or damage, as well as without displeasing noise and crepitation when the potentiometer resistance is being adjusted.

In the middle of its upper part, the tumable insulating plug has an extension protruding through the can and faciliating turning of the plug and thus the variation of the potentiometer resistance. A ring-shaped gasket embraces the extension and provides for vacuum tightness between the can and the plug. Further, the plug comprises a tooth for the limitation of the turning angle so that the plug is allowed to turn only by a determined angle. On its lower side, the plug has two bores into which the helicoidal spring-loaded metal balls are placed; the eccentrically positioned ball presses the resilient contact plate against the selected point of the resistance film. The can is hermetically closed by welding or soldering to the metal ring of the header.

For depositing metal segments, any vacuum procedure is suited which provides for a quick deposition of a solid and homogeneous thin metal layer having a low surface resistance and a good adhesiveness to the substrate, preferentially evaporation from a boat or a helix, flash evaporation or sputten'ng. The procedure mentioned requires a vacuum of at least 10 3 torr. The surface to which the metal segment should be applied must be thoroughly cleaned and heated. During the procedure,- the header temperature should be maintained constant and enough high, the speed of deposition and the composition of the deposited material should also be kept constant. For depositing resistance films procedures are suitable which allow for the creation of highly homogeneous and strictly defined thin layers so by the structure as well as by the composition and by electric properties. Before all, we can use flash evaporation, sublimation and sputtering. Still more severe requirements than for depositing metal segments apply for depositing resistance films.

During deposition and composition of the layer deposited on the substrate can be varied from a metallic substance throughout to semiconductor materials simply by adding reactive gases to the residual atmosphere. The sequence of metal and/or semiconductor layers results in high quality resistance film for high resistance with a low temperature coeflicient. Sputtering, however, also allows for depositing substances which otherwise are evaporated with difiiculty.

By introducing a reactive gas also in this procedure, the deposition of subsequent layers of different compositions may be controlled similarly as in the case of evaporation.

Thin layers deposited can be artificially stabilized by continuous or cyclic heating in air, vacuum, or under a protective atmosphere. A very usual procedure for the stabilization of layers consists in a long storage of headers with resistance film deposited at an increased temperature. Before all, it is important to obtain the stabilization of electrical properties of the resistance film.

The potentiometer according to the invention differs from known embodiments by the following essential advantages. The resistance layer is extremely even and smooth warranting for a very low-noise level when setting the value of resistance. Due to smoothness of the film any transfer of material between the contact plate and the film is avoided. The smoothness of the film and the special design of the wiper by the small contact plate described also allows for a high contact pressure resulting in a reliable contact so that the potentiometer is resistant against vibrations and mechanical shocks. This design gives a long useful life of the potentiometer according to the invention. Thin layers evaporated in differing compositions result in a very low temperature coefficient ofresistance, the relatively short resistance film has a low inductance particularly when compared with wire-wound potentiometers. In addition the stray capacitance is low because the resistance trace is distant also from metal parts.

An embodiment of the miniature potentiometer according to the present invention will be described in detail with reference to the accompanying drawing, in which FIG. 1 shows a longitudinal cross-section of the potentiometer,

FIG. 2 shows a plan view of the potentiometer according to FIG. 1, and

FIG. 3 shows a plan view of a header with deposited contact segments and the resistance film.

The miniature potentiometer according to FIGS. 1 and 2 has a metal can 1 equal to the standard cans for transistors of type TO 5.

Wire leads 3, 4, 5 are sealed into a metal ring 2 with the aid of homogeneous glass, while the ground lead 6 is welded to the metal ring 2. The upper surface of the glass substrate 7 is evenly ground and optically polished. The resistance film 8 having the shape of a cut-out ring of a thin layer of resistive substance is then deposited on said upper surface. The ends of the resistance film 8 are electrically connected to wire leads 3, 5. A good contact between the ends of the resistance film 8 and the wire leads 3, 5 is warranted by metal contact segments 8 shown in FIG. 3. Usually the contact segments 8' are deposited below the resistance film 8. In some cases it is more suitable to design the contact segments in the form of two layers, one being deposited below the resistance film and the other layer above it. In the middle of the upper surface of the glass substrate 7 and separated from the resistance film 8, a contact metal segment 8" is deposited. A small round resilient plate 9 is soldered to the segment mentioned, which warrants for a good electrical connection between the plate 9 and the wire lead 4. The middle part of plate 9 is impressed so that the plate becomes the shape of a saucer with a round even bottom and a ring parallel to the bottom and raised above the bottom plane. The surface of said small plate is smooth, corrosionproof and has good contact properties. This plate is made of resilient copper and is gold-plated. The bottom of the small The resistance film and metal contact segments are vacuum-deposited onto the glass substrate with the aid of adequately shaped screening masks. The resistance film has a thickness of about 0.1 um, whereby it fully adheres to the polished surface and is highly smooth. The film is hard, strong and firmly adhering to the substrate. The electrical and physical properties are artificially stabilized with time. Moreover, the resistance film has a low temperature coefficient of electric resistance and a surface with good contact properties. Depending upon the desired resistance value, the resistance film is made of different materials and. with various structures. Low-resistance films up to about 1,000 ohms are made preferentially of metal alloys of a homogeneous composition contact plate 9 is firmly soldered to the contact segment 8".

Thereby this plate is stiffly connected to the glass substrate 7 concentrically with the resistance film 8. The edge of this plate protrudes over the outer border of the resistance film and does not touch it when no pressure is applied to the plate. To the glass substrate 7 with-the metal ring 2, a metal can 1 is fixed containing a turnable plug 10, a gasket 11, two helicoidal springs 12 and 12' and two

balls

13 and 13'. The upper surface of can 1 is provided with a central round opening, through which protrudes a concentric extension 10' for turning the plug 10 by two helicoidal springs 12 and 12' and two

balls

13 and 13. The upper surface of can 1 is provided with a central round opening, through which protrudes a concentric extension 10' for turning the plug 10 with the aid of a slot 14. An indent 15 for the limitation of turning the plug 10 is impressed on the edge of the can. A ring-shaped gasket is inserted between the plug 10 and the top of the can, hermetically separating the interior of the potentiometer from the ambient atmosphere. The gasket is made of a heat-resistant elastomer. The plug 10 is made of insulating and heat-resistant material, having the shape of a low cylinder with obliquely cut bottom.

On the upper side, the plug 10 comprises a tooth 16 on its border for limiting the rotation. On the bottom side, the plug 10 also comprises two bores 17 and 17. The bore 17 is placed in the center of the plug and is stepped. The bore 17' is eccentrically positioned. Into the bores 17, 17 two helicoidal springs l2, l2 and two

steel balls

13 and 13' are inserted. The spring 12 presses the plug 10 against the can 1 and the ball 13 against the bottom of contact plate 9. The spring 12 presses with the aid of ball 13' the small contact plate 9 onto the resistance film 8, thereby establishing an electric contact between the resilient contact plate and the resistance film. By turning the plug by 270, the resistance film can be moved. A step in the central bore 17 of plug 10 protects the contact plate, because with an excessive external pressure the ball 13 rests on the step, thereby preventing that the plug 10 should touch the plate 9.

throughout. The films up to about 50 kiloohms are made of two or several layers; the lower layer is of a semiconductor type, e.g. cermet SiO Cr, or Cr Ce o and similar, and covered by an upper metal layer. The upper metal layer reduces the temperature coefficient of electric resistance and improves contact properties of the resistance film. For still higher resistance values the film is a multi-layer film, but the upper metal layer is composed of single separated mosaic-like metal islets so that it is not continuous.

For still higher resistance values, the resistance film consists of several layers with continuous or sudden changes in its composition and/or structure. The interior of the potentiometer is hermetically separated by the gasket 11 on one side, and on the other side by the lower edge of can 1 being hermetically sealed to the metal ring 2 of the header.

We claim:

1. A miniature variable resistance device comprising a body of homogeneous vitreous material. having a ground opticallypolished surface; a plurality of conductive leads embedded in said body and terminating flush with said surface; an arcuate contact strip vacuum-deposited upon said surface and conductively connected with said leads; a resiliently deflectible conductive disk overlying said surface and normally spaced above said strip while being angularly fixed with respect to said body; and a rotatable member disposed above said surface and provided with an element bearing upon said disk and deflecting same into engagement with said strip, said disk being electrically connected with one of said leads.

2. The device defined in claim 1 wherein said element includes a ball mounted in said member for movement toward and away from said surface and a helicoidal spring in said member resiliently biasing said ball against said disk over a limited region of the latter.

3. The device defined in claim 2, further comprising a cupshaped can surrounding said surface and provided with a central opening; said member being formed as a plug rotatably received in said can and having a boss extending into said opening for rotation of said member.

4. The device defined in claim 3, further comprising a sealing gasket surrounding said opening and bearing upon said member around said boss.

5. The device defined in claim 4, further comprising mutually engageable formations on said can and on said member for limiting rotation of said member within said can.

6. The device defined in claim 1 wherein said strip is a resistance film of homogeneous composition.

7. The device defined in claim 1 wherein said strip consists of a metallic layer and a semi-conductor layer disposed one above the other.

8. The device defined in claim 1 wherein said strip is formed with discrete mosaic-like metal islets.

9.. The device defined in claim 1, further comprising vacuum-deposited metallic contact segments electrically connecting said strip with said leads.

10. The device defined in claim 1 wherein said strip is a circular arc segment connected at its ends to two of said leads, said potentiometer further comprising a central contact layer deposited on said surface and electrically connected to another of said leads between the ends of said strip, said disk being dished and having a convex portion bearing upon said layer, said member being constituted as a rotatable plug having a central pivot ball seated in said convex portion and,

.limiting rotation of said plug within said can, said element including a spring-loaded ball carried by said plug and bearing against said disk, and a frame in conductive relationship with one of said leads and surrounding said body and engaged by said can, said body being composed of glass.

iii!

Claims

1. A miniature variable resistance device comprising a body of homogeneous vitreous material having a ground optically-polished surface; a plurality of conductive leads embedded in said body and terminating flush with said surface; an arcuate contact strip vacuum-deposited upon said surface and conductively connected with said leads; a resiliently deflectible conductive disk overlying said surface and normally spaced above said strip while being angularly fixed with respect to said body; and a rotatable member disposed above said surface and provided with an element bearing upon said disk and deflecting same into engagement with said strip, said disk being electrically connected with one of said leads.

3. The device defined in claim 2, further comprising a cup-shaped can surrounding said surface and provided with a central opening; said member being formed as a plug rotatably received in said can and having a boss extending into said opening for rotation of said member.

9. The device defined in claim 1, further comprising vacuum-deposited metallic contact segments electrically connecting said strip with said leads.

10. The device defined in claim 1 wherein said strip is a circular arc segment connected at its ends to two of said leads, said potentiometer further comprising a central contact layer deposited on said surface and electrically connected to another of said leads between the ends of said strip, said disk being dished and having a convex portion bearing upon said layer, said member being constituted as a rotatable plug having a central pivot ball seated in said convex portion and spring loaded thereagainst, a can surrounding said plug and provided with a central opening, a gasket surrounding said opening and sealingly engaging said plug, said plug having a boss provided with a screw driver slot projecting through said opening, cooperating formations on said can and said plug for limiting rotation of said plug within said can, said element including a spring-loaded ball carried by said plug and bearing against said disk, and a frame in conductive relationship with one of said leads and surrounding said body and engaged by said can, said body being composed of glass.