Un'i'ted States Patent Office 31308,253 3,308,253 DIAPHRAGM SWITCH HAVING A DIAPHRAGM SUPPORTED ON AN INCOMPRESSIBLE LAYER AND AN ELASTOMER OVERLAYING THE DIAPHRAGM Morris Krakinowski, Ossining, N.Y., assignor to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Ffled Mar. 25, 1965, Ser. No. 442,758 8 Claims. (Cl. 200-@-46) This invention relates to electrical switching elements and more particularly to pressure-sensitive diaphragm switching elements. While pressure-sensitive switches have been in existence for some time, their field of application has been limited by such factors as their size, cost, and lack of sensitivity to very slight pressures. One way in which such limitations have been overcome is to form the switch by use of thin film techniques. In doing this, a first conducting segment or strip is laid down on a substrate, a iion-conductive spacer layer placed over this with an opening over the conducting segment, and a diapbragm having a conductin,@ segment positioned adjacent to the ,condticting segment on the substrate positioned over the spacer@ layer. With such an arrangement, the conducting segments are brought into contact with each other by applying pressure to deform the diaphragm. Since thin film techniques are employed in constructing these switches, the size of ihe switch may be made quite small and their cost kept low. However, there are still practi@cal limitations on their usefulness. One disadvantage is that if a fairly pointed stylus such as a pencil or a pen is being used as the actuating element, as would often be the case in many applications of such switches, a thin diaphragm tends to puncture or to at least sustain permanent deformati4on on the point where pressure is applied due to the hi.@h stress concentration. The deformation may occur in the diaphragm itself and/or in the conducting segment atta@ched to the diaphragm, and may occur after only a short number of switching cycles. This problem may be overcomb to some extent by using a thicker diaphragm. However, when this is done, the permissible switch density (i.e. switches per unit area) is severely restricted. In applications of such switches, suich as in a punched card reader, an embossed card reader, or aconstrained handwriting recording device, the limitation on the swit@h density becomes a seri-ous problem. Also, with a thick Jiaphragm, the amount of force required to energize the switch is increased. In addition to the shortcomings mentioned above, most diaphragm switches have a limited contact area which is largely determined by the surface area of the actuating device and its alignment with the plane of the switch. The contact resistance and the current density at the point of contact between the twoconducting segments is inversely proportional to the area of contact between these two segments. Heating at this junction is directly proportional to both the current density and the resistance, and therefor6 the smaller the contact area, the greater the heating at the junction. This causes evaporation of contact material and material transfer, which ultimately results in a failure of the switch. The limited contact area and the resulting heating problem therefore seriously reduces the current cartying capacity of the sw@itch. Another problem with diaphragm switches is contamination of the conducting surfaces by organic molecules and other dirt in the atmosphere which causes a thin film to form over the -contacts. Such a film, unless broken, prevents good contact from being made, leadPatented Mar. 7. 1967 2 ing to erroneous indications from the.switch. It is therefore important that the switch be designed to prevent contamination -of the contacts as much as possible and to piere@ such film as may exist in ordbr to establish good contact in every instance. A diaphragm switch should also be designed to have a minimum stroke so as to have a short response time and to be capable of being stacked so as to provide multi-pole isolated switching elements that can be acti10 vated by a single actuator. It is therefore a primary object of this invention to provide an improved pressure responsive electrical switching element. A more specific object of this invention is to provide 15 an improved diaphragm, pressure-responsive switching element. Another object of this invention is to provide a diaphragm switching element which is capable -of operating for a very large number of switching cycles, even with 20 a relatively pointed actuating element, without having the diaphragm puncture or become permanently deformed. A further object of this invention is to provide a diaphragm switching element which provides a larger con25 tact area at the terminals than the area of the pressureapplying element. Still anotber object of this invention is to provide a pressureresponsive diaphragm switch which is capable of switching relatively large currents. 30 A still ftirther object of this inventi6n is to provide a pressure-responsive diaphragm switch which allows a very dense array of switching points to be constructed.. Another object of this invention is to provide a pressureresponsive diaphragm switch which requires a mini35 mum actuating force to cause @contact closure. Another object of this invention is to provide a pr essure-responsive diaphragm switching element, several of which may be stacked together to provide multipole isolated switching elements that can be activated by a single 40 actuator. Still another object of this invention is to provide a pressure-responsive diaphragn-i switch with a very small stroke and therefore very short response time. A still ftirther object of this invention is to provide a 45 pressure-responsive diaphragm switch which is easy and inexpensive to fabricate. Another object of this invention is to provide a pr essure-responsive diaphragm switch which is nearly maintenance free and therefore extremely inexpensive to operate. 60 A feature of this invention is the provision of a pressure-responsive diaphragm switch, the terminals of which op-en and close with an inherent rolling acti'on which helps penetrate any contaminant fil-m on the contacting surfa-ces, 55 Another feature of this invention is the provision of a pressure-responsive diaphragm switch which is inherently sealed and which may easily be hermetically sealed so as to be capable of operating under adve'rse envirbnrnental conditions. 60 In accordance with these objects, this invention provides a switching element which includes a first terminal which is fixed on a substrate, a diaphragm-carried second terminal wliich is adjacent to the first terminal, a (j5 spacer fok normally separating the terminals, and a layer of elastomeric aiaterial over the diaphragm. The spacer has an opening in it so that when pressure is applied to the elastomeric material, the elastomeric material and the diaphragm are deformed to bring the terminals into 70 contact with each other. The individual switching ele-

3,308,253 ments may be arranged in an array for performing any desired function. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodi5 ment of the invention, as illustrated in the accompanying drawihgs. In the drawings: FIG. 1 is a sectional side view of a single switching element of this invention in its open condition. 10. FiG. 2 is a' secti'onal sid6 view of the switching element shown in FIG. 1 in its closed condition. , FIG.. 3 is a partially cutaway perspective view of an array of switching elements of the type shown in FIGS. l and 2. 15 Referring now to FIGS. 1 and 2, it is seen that the preferred embodiment of the switching element of this invention has a laminar structure. The individual lamina of this struciure are (1) a substrate 10, having a segment of conductive material 12 plated on its upper sur20 face; (2) a layer of insulating material 14 overlaying or plated on substrate 10, the insul@ting material being incompressible and having an opening 16 in it in the area of conducting segment 12; (3) a diaphragm 18 positioned on, top of the insulating material 14; (4) a segment 20 25 of conducting material fixed to the underside of diaphragm 18 in the area of opening 16; (5) a layer 22 of elastomeric material resting on diaphragm 18; and (6) a layer of lubricant 24 between diaphragm 18 and elastomeric material 22. While the particular materials em- 30 ployed for the various layers shown in FIGS. I and 2 a I nd the relative thicknesses of these layers are a matter of choice and will vary, with the application to which the switch is being put, the following materials and relative dimensions have been found to give satisfactory 35 results: The substrate is of copper-clad glass or - paper-filled epoxy laminate and is 0.060" thick, with I oz. copper. Separator 14 is of Mylar 1 and is 0.001 to 0.005" thick. Diaphragm 18 is of a Mylar-copper laminate and is 40 0.003 to 0.006" thick with one-half to 1 oz. copper. Contacts 12 and 20 are of gold and are 25 to 30 x 10-6" thick. Cover sheet 22 is of neoprene, Hypalon, Viton film rubber, a urethane synthetic rubber, or of any other. clastomer and -may vary. in-@ thickness from 0.005 . to 45 O@030",@ d6p6ndi on the applicatio ,pg n to whicli the switch is being 7 piit.' In t@e 'discussi6n td f6llow, cover' 22 will be referred to as being mad,e of either an elastomer or an elastomeric material. Lubricant 24 is a silicbne grease. 50 Referring now to FIG. 2, it is seen that when pressure is applied to the upper surface of elastomer cover sheet 22, the single component of pressure P in the downward direction is converted by the elastbmer into a component of pressure Pd in the downward direction and compo-, 55 nents of pressure Pr which radiate out in all directions in a plane parallel to that Of substrate -10. This effecI " tively widens the area over which pressure is applied, to dia ragm 18 causing a larger area, D, of conductive . ph I segment 20 to be brought in contact with conductive seg60 ment 12, then the area, d, of actuating stylus 26. The relatively large contact area, D, reduces the contact resistance and the current density so that the switch is capable of handling relatively large currents of a magnitude approaching I amp@ without overheating. With 65 lower currents of a magnitude in the milliamp range, the switch is capable of operating for an, almost unlimited number of cycles without breakdown. The con-. tact-making ability of the switch is further enhanced by . 70 the inherent rolling actiofi which occurs as the center of segment 20 first touches segment 12 followed by adjacent sections of this segment making contact until contact is made over the entire area D. A reverse unrolling action :1 A trademark of the Du Pont Corporation. 75 4 occurs when contact is broken. The initial point contact causes a high pressure td be momentarily applied over a small area to physically puncture any contaminant filrn which may have accumulated on the conducting segment surfaces and also causes a high contact resistance and current density to exist for a short period of time. This latter condition exists long enough for any contaminant film to be burned away but not long enough to do any damage to the condticting surfaces. From FIG. 1, it can be seen also that the stroke(s) wit of the s ' ch is very sffiall (0.003 to 0 030" with theillustrative dimensions previously stated) so that the response time of the switch is good and the force required to activate it low. The silicone grease 24 between diaphragm 18 and cover sheet 22 reduces the friction which would otherwise occur as these two sheets move relative to each other, thereby further reducing the energizingi force required and improving the response time of the switch. The fact that only the relatively thin diaphragm 18 must move into opening 16 permits opening 16 to be relatively small and therefore allows a relatively dense array of switching points to be constructed@ 'lh ord6r to provide a fuller understanding of the invention, the pbysical sequence of events which occurs when pressure is applied to@a small area, having a diameter d, near the center of the switch will now be described in detaili The pressure P applied to the elastomeric layer 22 is initially transmitted through the elastomeric layer to deform the diaphragm with a very small radius of curvature, resulting in a point contact betweeii conducting segments 12 and 20. The small radius of curvature of the diaphraam results from the fact that it is being rigidly supported at the walls of the opening as it is being poked and stretched into the opening by the pressure applied to it. Once contact is made, additional pr6ssure applied to the switch results in a flattening of the clastomer material. However, since an elastomer is substantially incompressible, the flattening @of the elastomer causes ma. terial to be forced out all around the per'phery of the actuator@ Lubricant 24 provides low friction between diaphragm 18 and elastomer 22 which permits the forced. out material to move freely. Since the elastomer is, at this time, wedged into the deformation in the diaphragnl, the elastomer material forced out around the periphery by the:@ffattening thereof, causes radial pressures Pr to be applied to the diaphragin which further deforni the diaphragm towqrd the walls of -the opening. @ This further deformation of the diaphragm iner6ases the radius of curvature thereof, and therefore increases the contact@ area between segments 12 and 20. The rolling action described above is in this manner achieved. FIG. 3 is a partially cutaway view of an array of the Pressure-responsive diaphra,-m switches of this invention. This array may, for example, be used as part of a punched card reader or to give a series of x-y coordinates when used as part of a curve or character reading device. In this array,, the layers 10, 12, 14, 18, 20 and 22 are clamped in a frame 28 to dvoid: gross -relative shift of the separate layers. For purpo of illustration, segments se 12 have been shown as being continuous strips oriented in one direction, and segments 20 have been shown as continuous strips oriented in a direction perpendicular to that of the strip 12. A line 30 is connected to each of the strips 12 and a line 32 to each of the strips 20. As an example,of how the array shown in FIG. 3 may be operated, assume that a stylus is moved across the top of sheet 22. As the stylus comes over each opening 16, diaphragm 18 and an associate strip 20 are forced through the opening into contact with a strip 12. By succeedingly applying a signal to the lines 30 and sensing on which of the lines 32 an output occurs, it is possible to determine which of the openings 16 the stylus is positioned over at any given time. It can be seen that the array shown in FIG. 3 may be easily fabricated by use of known thin film techniques

5 such as phot&-etching and that the d6st per switching point for a switching array may be made extremely low by use of such techniques. Such tecbniques also provide an extremely thin switching array as may be observed from the illustrative layer thickness previously stated. Further, the frame 28 forcing the various layers togetber, provides an inherent sealing action which enables the array to operate under adverse conditions of temperature, humidity and contamination without ill effect. Should further security against adverse environmental conditions be desired, the entire array may be hei)metically sealed. Any contamination of the coritacts which still exists is taken care of by the inherent rolling action previously described. It should also be noted that a sheet of paper or similar material may be placed over layer 22 and written on without in any way hampering the switching action of the array so that a visual record of what is being recorded may be obtained at the same time that it is being electrically recorded. While in FIG. 3, segments 12 and 20 have been shown as being strips of conducting material oriented perpendicular to each other and the switching points oriented in a matrix array, the array may also be constructed by, for example, coating the entire underside of diaphragm 18 with conducting material or using a diaphragm of conducting -material and providing an individual conducting segment 12 for each index position. A single Iead would be connected to the conducting layer under the diaphragm and an individual output lead would @be provided for each of the segments. 12. The array could then be laid Out in any desired fashion. Where it is desired to provide a multi-pole isolated switching element which may be activated by a single actuator, segment 12 is mounted on the upper surface of a second diaphragm with the underside of the diaphragm having a conducting segment 20. This second conducting segment 20 has a separator layer 14, a conductor segment 12, and a substrate 10 associated with it, thereby providing a two-layer stacked diaphragm switch, the upper layer of which closes first and opens last wben pressure is applied to cover sheet 22. A tbird and possibly a fourth layer of stacked switch could likewise be provided in this manner. While the invention has been particularly shown and described with reference to -a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in for@m and detail may be made therein without departing from the spirit and scope of the invention. What is