Keyboards Switch Assembly With Multilayer Pattern Contact Means

Abstract

Keyboards for use in calculators, control equipment and the like, and which include a circuit board supporting electrical pathways, an insulator separator having openings registerable with portions of the pathways, a non-conductive elastomeric layer supporting a plurality of non-selfsupporting flexible conductive members or pathways and contactors thereon, said flexible conductive circuit contactors registerable with said openings whereby pressure applied to said elastomeric layer causes one or more of said contactors to extend through one or more openings to make electrical contact with portions of one or more circuit pathways supported by said board.

Description

BACKGROUND OF THE DISCLOSURE

This invention is directed to new improved keyboards for converting key depression to a coded electrical output and is more particularly directed to flexible conductive plastics formed into a plurality of selectively interconnected flexible and non-selfsupporting contactors and pathways joined to and supported by an elastomeric layer for making electrical contact with selected portions of a circuit board supported circuit pattern of the keyboard.

Small and inexpensive keyboards have become an integral part of personal calculators. As the price of calculators have rapidly decreased, keyboards of the type shown in U.S. Pat. Nos. 3,721,778 and 3,699,294 have become less attractive for use because of their cost.

Since a significant portion of the cost of a keyboard is due to the cost of the thick self-supporting resilient conductive plastic (elastomeric) filled with electrically conductive particles used as a contactor it became imperative that a keyboard be developed with a less expensive contactor.

This invention provides a low cost contactor which now permits a keyboard manufacturer to remain competitive as calculator prices continue to fall.

The present invention provides further advantages in certain situations in that a keyboard manufacturer can form the contactor in a manner so as to add another layer of circuitry for performing logic thus permitting further cost reductions.

With this invention material cost savings of 70% or more in comparison with conventional contactors of the prior art is estimated.

BRIEF SUMMARY OF THE DISCLOSURE

This invention discloses in combination with a circuit board having a plurality of electrically conducting pathways, a separator layer having a plurality of openings in register with portions of said pathways, the improvement of an elastomeric non-conductive layer supporting a plurality of non-selfsupporting flexible electrically conductive plastic contactors selectively interconnected by a plurality of non-selfsupporting flexible conductive plastic pathways. The flexible contactors and pathways may be made by using a non-elastomeric plastic such as polyamides, polyesters, polycarbonates, polyacetates, polystyrenes, epoxies, etc., filled with electrically conductive particles such as silver, carbon, etc., dispersed therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a keyboard according to the invention;

FIG. 2 is an enlarged sectional view taken along line 2--2 in FIG. 1 which includes the elastomeric, contactor structure of FIG. 4;

FIG. 3 is an enlarged sectional view taken along linne 3--3 in FIG. 1;

FIG. 4 is a bottom view of an elastomeric layer supporting electrically conductive circuit pathways and contactors;

FIG. 5 is a sectional view taken along line 5--5 in FIG. 4;

FIG. 6 is a sectional view taken along line 6--6 in FIG. 4;

FIG. 7 illustrates in a sectional view a plunger member used as a key for applying pressure to the elastomeric layer; and

FIG. 8 illustrates an alternate view of circuit pathways and contactors formed on a portion of an elastomeric layer.

DETAILED DESCRIPTION OF THE DISCLOSURE

Reference should now be had to FIGS. 1-8 for a description of the preferred embodiments of the disclosure.

The keyboard comprises a frame 10 preferably of insulator material, more preferably of a plastic, e.g., A.B.S. (a high impact polystyrene) or polyethelene. The frame 10 is provided with a plurality of divider members which form the walls of windows 12 extending through the frame 10.

The underside of the frame includes a plurality of rods 13 (preferably formed at the same time as the frame, i.e., by molding (see FIG. 2) which extend downwardly as shown in FIG. 3.

Reference may be had to U.S Pat. No. 3,721,778 for a further description of the frame, rods and the construction of a keyboard.

The rods 13 may be softened by heat to form heads 13a to hold the keyboard assembly together as shown in FIG. 3. Alternatively the rods may be threaded and nuts may be used to hold the keyboard assembly together.

Positioned directly below the frame member 11 is a thin plastic insulator layer 14, e.g., of Mylar which has indicia applied thereto. Instead of the layer 14 with indicia which functions as keys of the keyboard, buttons having indicia thereon may also be used as keys such as shown in U.S. Pat. No. 3,721,778 or U.S. Pat. applications Ser. No. 297,721 filed Oct. 16, 1972 now U.S. Pat. No. 3,780,237 or Ser. No. 297,636 filed Oct. 16, 1972 now U.S. Pat. No. 3,773,998 or as shown in FIG. 8.

Positioned below the layer 14 is a non-electrically conductive elastomeric layer 15. The elastomeric layer 15 may comprise any of the well known elastomeric and resilient materials such as silicone rubber or fluoro silicone rubber, nitrile rubber, natural rubber, etc.

Positioned below the elastomeric layer 15 and joined, coupled, adhered or bonded thereto is a plurality of flexible electrically conductive plastic contactors 16a selectively connected together with a plurality of flexible electrically conductive plastic pathways or interconnecting members 16b. The contactors and pathways are relatively thin in comparison with the conductive elastomeric layers of the prior art and rely upon the elasticity of the non-conductive self-supporting elastomeric layer to which they are attached for movement. The contactors and pathways are so thin that they are non-selfsupporting and would not properly function without being coupled to the elastomeric layer.

In addition, since each of the contactors and pathways are separated from each other and are coupled together as shown, there is a large saving in costly conductive plastic in comparison with the aforementioned patents.

A backing, e.g., the elastomeric layer to which they are joined is necessary to maintain their physical separation of the contactors and pathways and to prevent them from curling up or distorting.

At 16c there is also shown a connecting member of a flexible conductive plastic for coupling to a pin (see FIG. 2) used to provide the same potential to the contactors 16a and the pathways 16b.

The parts 16a-16c may be formed of either flexible non-elastomeric or elastomeric plastics such as plastic adhesives or by a flexible conductive plastic layer joined or attached to the elastomeric layer by a flexible plastic adhesive.

In particular, contactors 16a, pathways or members 16b and members 16c may be formed from flexible plastic (non-elastomeric) materials such as polyamides (e.g. Versalon 1140 polyamide resin by General Mills), polycarbonates (e.g. Lexan by General Electrical), polyester (e.g.Mylar), epoxy (Carvel by Polymer Corp.) polyacetate, polystyrene, etc., unmodified or modified if needed by plastisizers as will be apparent to those skilled in the art, to obtain the desired flexibility for the parts 16a-16c to flex with the layer 15 and not separate or break away therefrom after continuous prolonged use.

The parts 16a-16c also contain electrically conductive particles dispersed therethrough such as silver particles, carbon particles and other well know conductive particles such as shown in U.S. Pat. Nos. 3,140,342 and 3,576,387.

The amount of electrical particles may vary with particles in the amount of 20 to 40 volume percent being preferred although in this application the amount may vary over a wide range e.g., 10 80 volume percent.

In the preferred embodiment the layer 15 is preferably of a thickness t.sub.a of between 5 to 200 mils with 5 to 100 mils being more preferred and 20 - 50 mils being most preferred.

The parts 16a-16c are preferably of a thickness of t.sub.a between 5 microns (0.197 mil) to 2.0 mils with a thickness of 10 microns (0.394 mil) to 25 microns (0.984 mil) being more preferred and a thickness of 10 microns (0.394 mil) to 20 microns (0.788 mil) being most preferred.

In the preferred embodiment the layer 15 is a nitrile rubber layer made by combining Hycar 1042(NBR) (B.F. Goodrich) 100 parts by weight with zinc oxide 1 part by weight, hydrated silica (HI-SIL 215), 40 parts by weight, Dicumyl peroxide 5 parts by weight and then curing. The parts 16a-16c was made by mixing about 63 percent by volume of Versalon 1140 (a polyamide adhesive) with 37 percent by volume of silflake 135, and then coating it on the elastomeric layer 15 after it is formed e.g., by using an artists air brush and a screen or template having openings of the shape of the desired parts 16a- 16c. Solvents such as toluene and 1-propanol as in example 7 may be added to the Versalon 1140 and Silflake 135 solvents such as shown in U.S. Pat. 3,576,387 may be added to permit easy spraying or coating e.g., by a knife. The solvents are then permitted to evaporate in air. The conductive pattern (parts 16a-16c) can also be formed using printing techniques with the above composition. It is preferred, in order to carry out the screening process more effectively to replace toluene with a higher boiling point solvent such as Aromatic 150, Butyl Carbitol, etc., conductive inks well known in the art can also be used.

The layer 15 and parts 16a-16c are positioned over an insualtor plastic layer 17 e.g., of Mylar, acting as a separator and having a plurality of openings or windows 17a extending therethrough in alignment with windows 12. The rods 13a also extend through holes 17b in layer 17 to locate the layer 17 within the frame 10. See the aforementioned patents for further disclosure of the separator layer.

Below the layer 17 is a typical circuit board 18 e.g., of Bakelite having a plurality of electrically conductive contacts or pathways 13a formed thereon. See U.S. Pat. Nos. 3,705,276 and 3,721,778 for an illustration of various possible circuit configurations.

The circuit pattern may be formed conventionally from copper which is etched, etc., as is well known in the printed circuit art or by other well known printing techniques.

The electrical pathways are at least in part aligned with the windows 17a so that the application of pressure (by a finger) to the key or force applying layer 14 can push selected portions of the layer 15 and the contactor 16a through the windows 17a against the pathways 18a. In this manner electrical contact is made between the contactors 16a and the pathways 18a.

When the force is withdrawn the resilience of the elastomeric layer 15 causes it to withdraw pulling the flexible contactors 16a back with it and breaking electrical contact between contactors 16aand the pathways 18a. Most preferably the thickness of the layer 15 is at least 5times that of parts 16a-16c.

In order to make electrical contact with the electrically conductive parts 16a -16c as well as the pathways 18a, there are provided pins 20a- 20b retained with connector supports 21a and 21b respectively with pin 20a in contact with part 16c and pin 20b in contact with pathway 18a.

It should be understood that while preferred dimensions are given for the layer 15 be just sufficient to provide the elasticity to pull the parts 16a-16c back with after being depressed while the parts 16a-16c should be preferably as thin as physically possible to save as much money as possible so long as it provides good electrical conductivity for use as contactors and pathways, and does not flake off or separate (e.g. pull off) from the elastomeric layer under these dynamic conditions.

The volume resistivity of the conductive parts 16a-16c is preferably less than 10 ohm centimeters, more preferably less than 1 ohm centimeter and most preferably less than 0.5 ohm centimeters. As used herein the term nonselfsupporting means that the layer unless backed as shown would curl up and not be useful for its intended purpose i.e., as keyboard contactors and pathways.

In FIG. 7 there is shown a button 30 preferabvly of non-conductive plastic supported in a redesigned frame 31 and held in its undepressed condition by a spring 32. The remainder of the keyboard members are identical with that of FIGS. 1-5 and are so numbered. Upon depression of the key 30 by a finger, the conductive contactor 16a is brought into contact with the pathway 18a.

FIG. 8 discloses another configuration for the contactors, pathways, an interconnecting members and pin connecting members attached to an elastomeric layer. In this embodiment, the elastomeric layer is shown at 40 and supports flexible plastic contactors 41 which are interconnected in a selected manner by flexible conductive plastic pathways 42 to generate a coded output at flexible conductive plastic pin interconnecting member 43.

Pins are coupled to the member 43 as shown in FIG. 2. In this manner the logical capability of the keyboard device may be expanded by providing another layer of logic circuitry in addition to the logic circuitry provided on the circuit board.

Claims

We claim:

1. In a keyboard the combination of a circuit board supporting a plurality of electrically conductive pathways, a separator positioned upon the top of said board and conductive pathways and having a plurality of openings in register with selected portions of said pathways, the improvement comprising an elastomeric layer having adhered thereto and supported thereby for movement therewith a plurality of nonselfsupporting flexible conductive plastic contactors, said conductive plastic contactors comprising a plastic binder and electrically conductive particles dispersed therein, said contactors positioned over said openings so that pressure selectively applied to said elastomeric layer forces selected ones of said contactors through selected openings into contact with said selected portions of said pathways and release of said pressure permits the elastomeric layer to return to its original shape while pulling the contactors adhered thereto away from the pathways.

2. In a keyboard according to claim 1 in which a plurality of non-selfsupporting flexible conductive plastic interconnecting members are adhered to and supported by the elastomeric layer and are coupled to selected ones of said contactors.

3. In a keyboard according to claim 2 in which the conductive plastic is of a non-elastomeric material.

4. In a keyboard according to claim 3 in which the conductive plastic has silver particles dispersed.

5. In a keyboard according to claim 2 in which the interconnecting members are at least partially out of register with said openings.

6. In a keyboard according to claim 2 in which the thickness of the contactors and interconnecting members is at least about 5 times less than the thickness of the elastomeric layer.

7. In a keyboard according to claim 6 in which the contactors and interconnecting members are less than 0.788 mil in thickness and in which the elastomeric layer is between 5 to 200 mils in thickness.

8. In a keyboard according to claim 7 in which the conductive plastic is of a non-elastomeric material.

9. In a keyboard according to claim 1 in which a plurality of said contactors are electrically connected together by a non-selfsupporting flexible conductive plastic interconnecting element means adhered to and supported by said elastomeric layer, said plastic interconnecting element means comprising a plastic binder and electrically conductive particles dispersed theren.

10. In a keyboard according to claim 1 in which the plastic binder is a polyamide resin and silver particles are dispersed therein.

11. In a keyboard according to claim 9 in which the plastic binder is a polyamide resin and silver particles are dispersed therein.

12. In a keyboard which includes an insulator board having circuit pathways thereon, insulator means having a plurality of windows therethrough in alignment with selected portions of the pathways, a plurality of nonselfsupporting contactors spaced apart and each positioned for passage through one of said windows and supported by an elastomeric layer to which it is adhered, said contactor means comprising a flexible electrically conductive plastic material physically adhered to said elastomeric layer, said conductive plastic material comprising a plastic binder and electrically conductive particles dispersed therein and pressure application means for forcing said contactors through said windows to cause said contactors to electrically contact portions of said pathways, said elastomeric layer being thick enough to keep said contactors away from said pathway portions in the absence of pressure applied to pressure application means and for pulling said contactors away with it from said pathways after application and the release of pressure to said pressure application means and said contactors being thick enough to provide electrical conductivity while not being so flexible to separate from the elastomer layer upon being flexed in continuous use.

13. In a keyboard according to claim 12 in which the contactors are non-elastomeric.

14. In a keyboard according to claim 13 in which the contactors are 0.197 mil to 1.0 mils in thickness.

15. In a keyboard according to claim 14 in which the elastomeric layer is 5 to 200 mils in thickness.

16. In a keyboard according to claim 13 in which the contactors are 0.197 to 1.969 mil in thickness.

17. In a keyboard according to claim 16 in which the elastomeric layer is 10 to 100 mils in thickness.

18. In a keyboard according to claim 12 in which the contactors are of a lesser thickness than the non-conductive elastomeric layer with the elastomeric layer being of a thickness at least about 5 times that of the conductive layer to provide the elasticity to pull the contactors back with it after being depressed and the contactors being thick enough to provide electrical conductivity.

19. In a keyboard according to claim 18 in which the contactors are of a thickness less than 1 mil.

20. In a keyboard according to claim 18 in which said binder is polyamide resin and said particles are silver.

21. In a keyboard according to claim 12 in which the contactors are of a thickness less than 0.788 mil.

22. In a keyboard according to claim 12 in which the volume resistivity of the contactors is less than 10 ohm centimeters.

23. In a keyboard according to claim 22 in which the volume resistivity is less than 1 ohm centimeter.

24. In a keyboard according to claim 23 in which the volume resistivity is less than 0.5 ohm centimeters.

25. In a keyboard according to claim 12 including a plurality of flexible conducting plastic members adhered to said elastomeric layer and selectively coupled to at least two said plurality of contactors.

26. In a keyboard according to claim 25 in which the contactors and the interconnecting members are of a nonelastomeric material.

27. In a keyboard according to claim 25 in which said binder is polyamide resin and said particles are silver.

28. In a keyboard according to claim 12 in which said binder is polyamide resin and said particles are silver.