GB2192307A

GB2192307A - Push-button keyboard switch unit

Info

Publication number: GB2192307A
Application number: GB08710152A
Authority: GB
Inventors: Masami Fukushima; Kazutoki Tahara
Original assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Polymer Co Ltd; Shin Etsu Chemical Co Ltd
Priority date: 1986-05-02
Filing date: 1987-04-29
Publication date: 1988-01-06
Anticipated expiration: 2007-04-29
Also published as: GB8710152D0; GB2192307B; DE3714382A1; DE3714382C2

Description

1 GB 2 192 307 A 1

SPECIFICATION greatly increased production costs.

Push-Button Keyboard Switch Unit The object of the present invention therefore is to provide a push-button keyboard switch unit, which The present invention relates to push-button is free from the above described problems and keyboard switch units comprising a printed circuit 70 disadvantages in the prior art push-button keyboard board having a plurality of pairs of contact points switch units and is suitable forthe manufacture of and push-buttons for making electrical contact many different switch units in relatively small lots.

between the points of each pair. According to one aspect of the invention, a push In push-button keyboard switch units of the above button keyboard switch unit comprises:

mentioned type, it is usual that the keyboard 75 (a) a printed circuit board having a plurality of covering member is shaped of a rubbery material pairs of contact points on a base board or on a base with a plurality of dome-like raised portions forming board assembly, made of an electrically insulating the push-buttons and the base parts thereof all material; and integrally molded. A conventional molding process (b) a plural number of push-button units made of of such a covering member is as follows. Namely, a 80 an electrically insulating rubber, each unit including metal mold for the rubber molding is provided with a push-button with a contacting portion on the inner a plurality of cavities each to conform with the surface thereof to confront the nair of contact points configuration of the dome-like raised portion of the on the printed circuit board or assembly, whereby finished covering member. Pieces of vulcanised pressing of the push- button effects electrical contact electroconductive rubber to serve as movable 85 between the pair of contact points, each push contact points are put each on the bottom of one of button being bonded by an adhesive to a peripheral the cavities and then a sheet of unvulcanised zone around the pair of contact points.

insulating rubber is spread thereon followed by The adhesive may be, for example, a silicone-based compression-molding with simultaneous rubber adhesive or a pressure- sensitive adhesive.

vulcanisation of the rubber sheet with heating to 90 In one embodiment, the pairs of contact points are given an integral covering member of rubber on the base board and are both fixed and the usually having a large number of the dome-like contacting portion of each push-button is a movable push-button portions and the base thereof, each contact point made of an electroconductive rubber dome-like portion bearing a movable contact point. fixed to the inner surface of the push-button.

In the above described molding process of a 95 In the above defined pushbutton keyboard switch keyboard covering member, a metal mold of unit, the rubber covering member used in different design must be prepared in order to mold a conventional units is formed by a combination of a covering member different from the other with any plural number of the push-button units each directly slightest modification in respect of the configuration bonded to a peripheral zone of the fixed contact or arrangement of the dome-like push-button 100 points using an adhesive.

portions. Preparation of a new metal mold is of The printed circuit board may, however, be of the course very expensive because the dimensions so-called membrane type and the push-button units thereof should be carefully selected in a trial-and- are then adhesively bonded to the membrane.

error manner taking into account the shrinkage of Thus, with this form of printed circuit board, the rubbery material by the vulcanization and 105 according to another aspect of the invention, a contraction or expansion of the covering member push-button keyboard switch unit comprises:

during use. The disadvantage due to the (a) a printed circuit board having a plurality of expensiveness of the metal mold rapidly increases fixed contact points on a base board made of an in geometric progression with the increase in the electrically insulating material; dimensions of the covering memberwhen 110 (b) a membrane made of an electrically insulating comparison is made, for example, between small- rubber mounted on the printed circu ' it board and sized ones of 5 cm by 10 cm dimensions and large- having an electroconductive contact portion on the sized ones of 20 cm by 50 cm dimensions, if not to surface facing the printed circuit board; mention the costs for a big press machine. (c) an electrically insulating spacer intervening While it is sometimes required in recent years that 115 between the printed circuit board and the one or several of the dome-like push-button membrane; and portions in a rubber-made keyboard covering (d) a plural number of push- button units made of member should have a different color from the an electrically insulating rubber, each unit including others, in addition, such a covering member must a push-button, bonded by an adhesive to the be prepared by putting two or more of unvulcanized 120 membrane at such a position that each push-button rubber sheets of different colors as desired confronts one of the fixed contact points on the simultaneously in the metal mold followed by printed circuit board with the membrane compression molding with heating. A serious intervening therebetween.

problem in such a molding process is that no clear- Two examples of switchboard units in accordance cut demarcation can be formed at the boundary of 125 with the invention will now be described with the zones of different colours since two kinds of the reference to the accompanying drawings in which:

unvulcanised rubbers on both sides of the colour FIGURES 1 and 2 are each a perspective view of a boundary are more or less intermixed with each conventional rubber-made push-button keyboard other so that the yield of acceptable product is covering member formed as an integrally molded sometimes quite unsatisfactory consequently with 130 body.

2 GB 2 192 307 A 2 FIGURES 3 and 4 are each a vertical cross buttons.

sectional view of the inventive push-button A plural number of the pushbuttons 1 or push keyboard switch unit showing only one push button button units each having at least two push-buttons directly bonded to the printed circuit board using an as described above are mounted on a printed circuit adhesive. 70 board 3 and bonded thereto at the base 2 by using FIGURE 5 is a perspective view of the inventive an adhesive or pressure- sensitive adhesive 5 push-button keyboard switch unit partially therebetween to give a push- button keyboard disassembled into parts. switch unit of the invention. The printed circuit FIGURE 6 is a vertical cross sectional view of the board 3 has a plural number of pairs of fixed contact inventive push-button keyboard switch unit, in 75 points 4 each of which should confront the movable which the push button is adhesively bonded to the contact point 11 on the dome-like portion of the membrane mounted on the printed circuit push-button 1 keeping a suitable space for stroke board. therebetween. The printed circuit board 3 may be a FIGURE 7 is a perspective view of the membrane- conventional one such as flexible circuit boards type push-button keyboard switch unit of the 80 made of polyimide films, polyester films, glass-fiber invention as illustrated in FIGURE 6 disassembled reinforced epoxy resin films and the like, into parts. paperboard-based copper-foiled laminates, glass based copper-foiled laminates, composite-based DETAILED DESCRIPTION OFTHE PREFERRED copper-foiled laminates, multiwire- circuiting

EMBODIMENTS 85 boards, ceramic-substrated boards, composite In the conventional push-button keyboard switch boards and the like without particular unit of the prior art illustrated in FIGURES 1 and 2, limitation.

the keyboard covering member 9, which is mounted The adhesive or pressuresensitive adhesive used on a printed circuit board (not shown in the figures) for adhesively bonding the push-buttons 1 or push is integrally shaped of an electrically insulating 90 button units to the printed circuit board 3 may be rubber and the membrane 9 is formed of a base part conventional without particular limitations.

8 and a plural number of the dome-like raised push- Exemplary of suitable pressure-sensitive adhesives button portions 7 or a combination of two or more are rubber-based ones formulated with natural groups of push-buttons 7 and 7a having different rubber, SBR, reclaimed rubber, polyisobutylene, dimensions or colors. Each of the push-buttons 7 95 block rubbers and the like, copolymers of an acrylic and 7a is provided with a movable contact point ester as the main component with a made of an electroconductive rubber on the inner copolymerizable monomer such as acrylic acid, surface of the dome-like push-button just at the top methacrylic acid, acrylamide, vinyl acetate, styrene thereof to confront the fixed contact point below. and the like, and silicone-based ones composed of a In the inventive push-button keyboard switch unit 100 silicone rubber and a silicone resin obtained by the illustrated in FIGURE 3 by a cross section, the condensation reaction of a hydrolyzate of configuration of each push-button 1 may be organochlorosilanes, and so -n.

conventional in a dome-like form raised on the base The adhesives may be of a non-curable part 2. The material of the push-button 1 may also thermoplastic type, heat-curable type or room be conventional and is preferably an electrically 105 temperature-curable type. The heat-curable insulating rubber including natural rubber and adhesives are exemplified by those compounded various synthetic rubbers such as diene-based with a thermosetting urethane resin, phenolic resin, synthetic rubbers, e.g. polybutacliene, polyisoprene, resorcin- formaldehyde resin, epoxy resin, SBR and polychloroprene, ethylene-propylene polyisocyanate and silicone rubber while the copolymeric rubbers, polyurethane-based rubbers, 110 thermoplastic adhesives are exemplified by those polyester-based rubbers, silicone rubbers and the formulated with a polyvinyl chloride, polyvinyl like. Silicone rubbers are preferred in respect of their acetal, polyvinyl alcohol, polymer of an acrylic acid excellent heat resistance, weatherability and electric ester or methacrylic acid ester, polycyanoacrylate, insulation. A movable contact point 11 made of, polyamide, polyester, polyamideimicle, preferably, an electroconductive rubber is integrally 115 polybenzimiclazole and polyimicle. Adhesives of a attached to the inner surface of the push-button 1 at composite type are also suitable including those the top thereof. Each of the push-buttons 1 may be compounded with a polyvinyl acetal and phenolic shaped by molding separatelyfrom the others as is resin, a rubber and phenolic resin, an epoxy resin illustrated in FIGURE 5 or a plural number of the and nylon, and so on.

push-buttons are shaped by molding in an integrally 120 Although the pressure-sensitive adhesive is combined sheet to form a unit of push-buttons. advantageous in respect of subsequent Such push-button units can be prepared by a replaceability, the adhesives are preferred in respect conventional molding method for rubbers including of the higher adhesive bonding strength than the compression molding, injection molding, transfer pressure-sensitive adhesives to prevent subsequent molding and the like. It is optional that a large 125 displacement of the push-buttons and absence of number of the push-buttons are molded in one shot surface tackiness consequently with less deposition into an integrally connected sheet form of the push- of dust. Silicone rubber-based adhesives are buttons and the integral sheet is cut apart into the particularly preferred since a silicone rubber may individual push-buttons or into several push-button serve also as a resist material.

units each having a plural number of the push- 130 While silicone rubbers are curable by several 3 GB 2 192 307 A 3 different mechanisms for crosslinkformation ring-wise groove 12 on the base 2 of the push including those cured by the free-radical reaction, button 1 when the push-button 1 is mounted on the addition reaction and condensation reaction, the printed circuit board 3 to give a tailing effect. The silicone rubber used as an adhesive in the invention line protrusion 13 should be bonded to the ring-wise is not particularly Hmitative in this regard, although 70 groove 12 by using an adhesive 5 as an intervening the silicone rubber composition curable by the layer. This type of the push-button 1 is addition reaction is preferred. Such a composition is advantageous in respect of the increased accuracy compounded with an organopolysiloxane having of positioning of the push- button 1 relative to the silicon-bonded vinyl groups, an fixed contact point 4 on the printed circuit board 3 organohydrogenpolysiloxane and a platinum 75 although the model illustrated in FIGURE 3 is catalyst and curable by heating within a relatively advantageous in respect of the versatility of the short time in addition to the advantage of relatively push-button units which may be a conventional one high initial tackiness in an uncured condition so that used in the prior art push-button covering members.

the push-buttons or push-button units can be FIGURE 5 schematically illustrates a perspective temporarily bonded to the printed circuit board with 80 view of the inventive push-button keyboard switch sufficient strength and improved accuracy of unit which is on a halfway of assembling of the positioning as well as safety in transportation from push-buttons 1 on a printed circuit board 3 having the step of temporary bonding to the step of curing 16 pairs of fixed contact points 4 in a 4 rows by 4 with heating. The composition as cured is freed columns arrangement. The push-buttons 1 are from surface tackiness. It is optional thatthe silicone 85 mounted and bonded adhesively each to the rubber composition may be admixed with a silane peripheral zone of one of nine pairs of the fixed coupling agent ortitanate coupling agent with an contact points 4 while remaining seven pairs of the object to increase the adhesive bonding strength. fixed contact points 4 are left unworked with the When the push-buttons or push-button units are push-buttons 1.

bonded adhesively to the printed circuit board by 90 FIGURE 6 illustrates a cross sectional view of using the above described silicone rubber-based another model of the inventive push-button adhesive followed by curing of the adhesive, the keyboard switch unit which is of the so-called adhesive bonding strength is much higher than with membrane type. Namely, each of the push-buttons a pressure-sensitive adhesive so that the inventive has no movable contact point but serves to push push-button keyboard switch unit can be used in 95 down a membrane having a movable contact point any hard practical service withoutthe danger of to confrontthe fixed contact point or a pair of fixed displacement of the push-buttons even after a large contact points on the printed circuit board. Thus, a number of key strokes so that the durability of the rubber-made membrane 14 is mounted on the inventive keyboard switch unit is just as high as that printed circuit board 3 bearing a plural number of of conventional keyboard switch units having an 100 fixed contact points 4 with a spacer 6 therebetween integrally molded keyboard switch covering to make a space between the membrane 14 and the member. It is also optional that, with an object to printed circuit board 3 for stroke. The membrane 14 further increase the adhesive bonding strength, the is provided on the lower surface thereof with a surfaces of the base of the push-button and/orthe plural number of movable contact points 11 at printed circuit board are coated and treated 105 positions justto confront the fixed contact points 4 beforehand with a primer containing a silane on the printed circuit board 3. The printed circuit coupling agent or titanate coupling agent. board 3, spacer 6 and membrane 14 should be In the step of applying the adhesive to the printed integrally bonded together. A plural number of circuit board 3, it is essential that the surface of the push-buttons 1 are mounted on the membrane 14 fixed contact points 4 is never contaminated with 110 each at such a position that the center top of the the adhesive 5 outflowing from proper areas. In this push-button 1 is just above a pair of the contact regard, it is advisable that the fixed contact points 4 points 4 and 11 on the printed circuit board 3 below are masked in advance before application of the and the membrane 14 so that, when the push-button adhesive 5 to the surface of the printed circuit board is pushed down at the center top, the downward 3 by the rnethod of casting, topping, printing, 115 protrusion on the lower surface of the center top of transferring or the like so that the adhesive is spread the push-button 1 pushes the membrane 14 to such on the peripheral zone of each pair of the fixed an extent that the movable contact point 11 on the contact points 4 alone. The coating thickness of the membrane 4 is brought into contact with the fixed silicone rubber-based adhesive should be in the contact point 4 below to close an electric circuit range from 0.005 to 2 mm or, preferably, from 0.01 120 therebetween. In this inventive unit, the push to 0.3 mm on both of the printed circuit board 3 and buttons 1 are not in the form of an integral keyboard the lower surface of the base 2 of each push button covering member as in conventional keyboard 1. switch units but the push-buttons are separated into FIGURE 4 illustrates a cross sectional view of a individual ones or into a plural number of push- somewhat modified embodiment of the inventive 125 button units each having at least two push-buttons push-button keyboard switch unit. In this model, the 1. The push-buttons 1 or push-button units should lower surface of the base 2 of the push-button 1 is be bonded to the membrane by means of an not flat but provided with a ring-wise groove 12 adhesive or a pressure- sensitive adhesive as an while the printed circuit board 3 is provided with a intervening layer 5 between the base 2 of the push- rib-like line protrusion 13 which should fit to the 130button 1 and the upper surface of the membrane 14.

4 GB 2 192 307 A 4 FIGURE 7 illustrates a perspective view of such a Preparation by compression molding at 170'C under push-button keyboard switch unit of the invention a pressure of 50 kg/cm' except that the insulatin V as disassembled, in which the membrane 14 is an rubber compound was formulated with 100 parts of integral sheet member with the printed circuit board an ethyl ene-p ropylene copolymeric rubber (EPDM 3. Namely, an insulating sheet member 3-14 is 70 501 A, a product by Sumitomo Chemical Industry bent in a U-shaped configuration and the fixed Co.), 40 parts of calcium carbonate filler, 3 parts of contact points 4 are provided on one of the U-bent dicumyl peroxide, 1 part of vulcanization legs 3 while the other U-shaped leg serves as the accelerator, 0.5 part of a red pigment and 40 parts of membrane 14. The two U-shaped legs 3 and 14 are a paraffin-based softener and the movable contact integrally bonded together with a spacer sheet 6 75 points were formed by pad printing. The integrated therebetween. The spacer sheet 6 has openings push-button sheets were cut apart along the thinned each at a position corresponding to one of the fixed dividing lines into 480 individual push-buttons each contact points 4 on the printed circuit board 3. The having a 13 mm by 15 mm rectangular base.

dimensions of the openings should be large enough so that the movable contact point on the lower 80 Push-button Preparation 3 surface of the membrane 14 can be brought into The formulation of the insulating rubber contact with the fixed contact point 4 below when compound and the conditions of compression the membrane is pushed down by pushing the molding were substantially the same as in the above push-button at the center top with a finger tip. described Preparation 1 excepting replacement of In the following, the push-button keyboard switch 85 the white pigment with a black pigment. Each of the unit of the invention is described in more detail by push-buttons molded in an integrated sheet form way of examples as preceded by the description of containing 26 pushbuttons had dimensions preparation of push-buttons or push-button units. In including an outer diameter of 14.4 mm, inner the following description, the term of "parts" diameter of 10.0 mm, inner diameter of the dome- always refers to "parts by weight". 90 like portion of 13.4 mm, height thereof of 6 mm and wall thickness thereof of 0.8 mm and the movable Push-button Preparation 1 contact points each having a diameter of 4.0 mm An electroconductive silicone rubber composition were integrally molded using the same was prepared by compounding 70 parts of a electroconductive rubber compound. Ten sheets commercially available silicone rubber compound 95 were prepared in this manner and cut apart into 260 (KE 742U, a product by Shin-Etsu Chemical Co.) with individual push- button each having a circular base parts of acetylene black and 0.5 part of dicurnyl of 18.4 mm diameter.

peroxide. The silicone rubber composition was shaped by compression molding under a pressure Push-button Preparation 4 of 50 kg/cm' at 170'C into stud-like forms of 4.0 mm 100 The formulation of the insulating rubber diameter to serve as the movable contact points. compound and the molding conditions were The stud-like movable contact points were placed substantially the same as in the preceding each at the proper position in the cavity of a metal Preparation excepting replacement of the black mold for molding 48 push-button in one shot, on pigment with a blue pigment. Each of the push- which a sheet of an electrically insulating silicone 105 buttons molded in an integrated sheet form rubber composition prepared from a commercially containing 76 push- buttons had dimensions available silicone rubber compound (KE 951 U, a including an outer diameter of 8.0 mm, inner product by Shin-Etsu Chemical Co.), 1.5 parts of diameter of 5.0 mm, inner diameter of the dome-like dicurnyl peroxide and 0.5 part of a white pigment portion of 7.4 mm, height thereof of 3.0 mm and was mounted and compression-molded under a 110 wall thickness thereof of 0.7 mm and the movable pressure of 50 kg/CM2 at 1-700C to give a push- contact points each having a diameter of 4.0 mm buttons in an integral sheet to each of which the were integrally molded using the same movable contact point was integrally bonded electroconductive rubber compound. Each of the 76 together. Each push-button had dimensions individual push-buttons was surrounded by the A including an outer diameter of 9.5 mm, inner 115 thinned dividing lines running at intervals of 10 mm diameter of 5.0 mm, inner diameter of the dome-like in the down direction and 12 mm in the across portion of 8.7 mm, height of the dome-like portion of direction. Ten sheets were prepared in this manner 3.3 mm and wall thickness of 0.8 mm and was and cut apart into units each containing 6 push surrounded by thinned dividing lines running at buttons in a row.

intervals of 13 mm in the across direction and 15 120 mm in the down direction. Ten sheets of such EXAMPLE 1 integrated push-buttons were prepared and cut Pairs of fixed contact points, each contact point apart along the thinned dividing lines into 480 being in a semicircular form having a diameter of individual push-buttons each having a i3 mrn by 15 3.5 mm oppositely facing anotherto form a pair, mm rectangular base or into units each containing 3 125 were formed on a polyester film having a thickness push-buttons in a row. of 0.100 mm by printing with a silver paste and each contact point was overcoated with an Push-button Preparation 2 electroconductive carbon layer in a diameter of 4.0 Integrated push-button sheets were prepared in mm. The thus prepared flexible printed circuit board substantially the same manner as in the preceding 130 having 16 digit- form electrodes at a pitch of 17 mm GB 2 192 307 A 5 in the across and down directions and lead-out switch unit which could withstand a durability test electrodes was coated with a layer of an addition- of 10,000,000 times of repeated key strokes.

curable silicone rubber composition (KE 180ORTV ABC, a product by Shin-Etsu Chemical Co.) in a EXAMPLE 3 thickness of 0.03 mm simultaneously to serve as a 70 A printed circuit board was prepared by resist and as an adhesive by screen printing with the subjecting a copperfoiled, glass cloth-based epoxy digit-form electrodes masked with a patterned resin laminate having a thickness of 1.00 mm to masking sheet. form a circuit pattern and 12 digit-form electrodes in In the next place, 8 pieces each of the push- a 4 rows by 3 columns arrangement at a pitch of 15 buttons prepared in the Push-button Preparations 1 75 mm followed by gold plating and the board was and 2 described above were put each to cover one of coated with an epoxy resin as a resist followed by the 16 digit-form electrodes to have the base of the curing with the electrodes masked.

push-button in contact with the zone around the Separately, a doublecoated pressure-sensitive electrode and heated together in an oven at 150'C acrylic adhesive sheet protected on both surfaces for 30 minutes to cure the silicone rubber 80 with sheets of release paper (#500, a product by composition so that the push-buttons were firmly Nitto Denko Co.) was punched to be provided with bonded by adhesion to give a push-button keyboard 12 openings of 8.0 mm diameter in a 4 rows by 3 switch unit which could withstand a durability test columns arrangement at a pitch.of 15.0 mm and one of 1,000,000 times of repeated key strokes. of the release paper sheets was peeled off. This 85 pressure-sensitive adhesive sheet was mounted on EXAMPLE 2 the printed circuit board with the adhesive layer A copper-foiled, paper-based phenolic resin contacting the board at such a disposition that each laminate having a thickness of 1.58 mm was of the electrodes appeared in one of the openings in subjected to an etching workto form a circuit the adhesive sheet and the pressure-sensitive pattern and 36 digit-form electrodes in 4 parallel 90 adhesive layerwas transferred on to the circuit rows, one atthe upper end having 6 electrodes at a board followed by peeling of the remaining release pitch of 12 mm and the otherthree each having 10 paper. Thereafter, 4 push-button units each electrodes at a pitch of 19 mm, followed by gold containing 3 push- buttons prepared in Push-button plating to give a printed circuit board. The board Preparation 2 were mounted on the layer of the was coated with a primer (Primer No. 4, a product by 95 pressuresensitive adhesive and pressed down to be Shin-Etsu Chemical Co'.) followed by drying with the adhesively bonded at such a disposition that the electrodes masked. base of the push-buttons was on the zones Separately, a polyester film having a thickness of surorunding the electrodes. The thus prepared 0.075 mm was provided with a topping layer having push-button keyboard switch unit could withstand a a thickness of 0.06 mm of an addition-curable, low 100 durability test by repeating 1,000,000 times of key temperature-curable silicone rubber compound (KE strokes.

167, a product by Shin-Etsu Chemical Co.) and further overlaid with a polypropylene film having a EXAMPLE 4 thickness of 0.025 mm as a covering film to give a A printed circuit board was prepared by laminate. Then, 36 circular openings were formed in 105 subjecting a copper-foiled polyimide laminate this laminate using a cutter blade in 4 parallel rows, having a thickness of 0.08 mm to an etching workto one at the upper end having 6 openings of 7.0 mm form a circuit pattern and 6 digit-form electrodes in diameter at a pitch of 12 m m a nd the other th ree 2 parallel rows each containing 3 electrodes at a each having 10 openings of 13.0 mm diameter at a pitch of 20 mm followed by gold plating and coating pitch of 19.0 mm followed by peeling of the 110 with and curing of an epoxy resin as aresist layer polypropylene film. with the electrodes masked.

The laminate thus provided with the openings Six push-buttons prepared in Push-button was mounted on the printed circuit board with the Preparation 2 were coated each with 0.06 g of an a silicone rubber layer contacting the board at such a cyanoacrylate-based adhesive on the bottom disposition that each of the electrodes on the board 115 surface of the base and mounted on the printed appeared in one of the openings in the laminate and circuit board at such a disposition that the base the silicone rubber layer was transferred on to the thereof surrounded one of the electrodes. After a printed circuit board to simultaneously serve as a while, the push- buttons were firmly bonded by resist and as an adhesive followed by peeling of the adhesion to the printed circuit board to give a pushpolyester film. Thereafter, a push-button unit 120 button keyboard swich unit which could withstand a containing 6 push-buttons in a row prepared in durability test by repeating 5,000,000 times of key Push-button Preparation 4 and 30 individual push- strokes.

buttons prepared in Push-button Preparation 3 were mounted on the adhesive layer of silicone rubber at EXAMPLE 5 such a disposition that the base of the push-button 125 A membrane-type printed circuit board as is on the zone surrounding the electrode and heated illustrated in FIGURE 7 was prepared. Thus, 16 fixed together in an oven at 1 OO'C for 60 minutes to cure and 16 movable contact points were formed on a the silicone rubber composition so that the push- polyester film having a thickness of 0.10 mm by first buttons were firmly bonded by adhesion to the printing with a silver paste in a diameter of 3.5 mm printed circuit board to give a push-button keyboard 130 followed by overcoating with a conductive carbon 6 GB 2 192 307 A 6 layer in a diameter of 4.0 mm in a 4 rows by 4 to the same printed circuit board as used in Example columns arrangement at a pitch of 20 mm in both 6 at such a disposition that the center of each down and across directions together with lead-out opening was just above a pair of the contact points electrodes. A silicone rubber composition was followed by peeling of the remaining release paper.

applied to the board in a thickness of 0.04 mm 70 The same push-buttons as used in Example 6 were excepting the surface of the contact points and the mounted thereon and bonded thereto by means of board was bent in a U-shaped form in such a the pressure-sensitive adhesive sheet to give a manner that the movable contact points on one leg push-button keyboard switch unit which could just confronted the fixed contact points on the other withstand a durability test by repeating 1,000,000 leg with the silicone rubber layer sandwiched 75 times of key strokes.

between the legs followed by curing of the silicone rubber composition to give a membrane-type EXAMPLE 8 printed circuit board. A membrane-type printed circuit board as An addition-curable self-bonding silicone rubber illustrated in FIGURE 7 was prepared. Thus, 78 fixed composition (KE 180ORTV ABC, a product by Shin- 80 and 78 movable contact points of 4.0 mm diameter Etsu Chemical Co.) was applied to the surface of the in parallel 7 rows, three thereof a group each membrane-type printed circuit board on the areas containing 6 points at a pitch of 12 mm and the other surrounding the spots just opposite to the movable four a group each containing 15 points at a pitch of contact points in a thickness of 0.03 mm by screen 20 mm, were formed on a polyester film having a printing to serve as an adhesive layer. Six white 85 thickness of 0.075 mm by using a carbon-silver push-buttons and six red push-buttons prepared in paste followed by coating with and curing of a the same manner as in Push-button Preparations 1 silicone rubber composition and the film was bent in and 2 excepting omission of the movable contact U-shape sandwiching the cured silicone rubber points were mounted on the thus adhesive-coated layer of 0.05 mm thickness as a spacer between the circuit board at such a disposition that the center 90 legs to give a membrane-type printed circuit board axis of each push-button is just above the movable with the contact points on both legs just to confront contact point on the lower surface of the membrane each other. The surface thereof was coated with a and heated together in an oven at 1500C for 30 primer (Primer No. 4, a product by Shin-Etsu minutes to cure the silicone rubber adhesive so that Chemical Co.) followed by drying on the area where the push-buttons were firmly bonded by adhesion 95 push-buttons were to be mounted.

to the circuit board to give a push-button keyboard A polyester film having a thickness of 0.075 mm switch unit which could withstand a durability test having a topping layer of an addition-curable, low by repeating 10,000,000 times of key strokes. temperature-curable silicone rubber composition (KE 167, a product by Shin-Etsu Chemical Co.) in a EXAMPLE 6 100 thickness of 0.04 mm to serve as an adhesive was A membrane-type printed circuit board as applied and bonded to the primercoated surface of illustrated in FIGURE 7 was prepared. Thus, 10 fixed the circuit board and the silico.-e rubber layer was and 10 movable contact points of 4.0 mm diameter transferred thereto followed by peeling of the in 2 rows each containing 5 points were formed on a polyesterfilm.

copper-foi led polyimide laminate having a thickness 105 Three pushbutton units each containing 6 push- of 0.08 mm by etching followed by gold plating and buttons and 60 individual push-buttons prepared in the laminate was bent in U-shape sandwiching a the same manner as in Pushbutton Preparations 4 spacer film of 0.15 mm thickness double-coated on and 3, respectively, excepting omission of the both surfaces with a pressure-sensitive adhesive movable contact points were mounted on the and provided with openings of 4.2 mm diameter 110 surface coated with the silicone rubber adhesive at between the legs to give a membrane-type printed such a disposition that the center axis of each push circuit board. button was just above one of the pairs of the contact Ten push-buttons prepared in the same manner points and heated in an oven at 100'C for 60 minutes as in Push-button Preparation 2 excepting omission to cure the silicone rubber adhesive so that the of the movable contact points were coated each 115 push-buttons were firmly bonded by adhesion to with 0.05 g of an a-cyanoacrylate-based adhesive on the printed circuit board to give a push-button the bottom surface of the base and mounted on the keyboard switch unit which could withstand a circuit board at such a disposition that the center durability test by repeating 10,000,000 times of key axis of each push-button was just above the pair of strokes.

the contact points. After awhile, the push-buttons 120

Claims

were firmly bonded by adhesion to the circuit board CLAIMS to give a

push-button keyboard switch unit which 1. A push-button keyboard switch unit which could withstand a durability test by repeating comprises:

5,000,000 times of keystrokes. (a) a printed circuit board having a plurality of 125 pairs of contact points on a base board or on a base EXAMPLE 7 board assembly, made of an electrically insulating The same double-coated pressure-sensitive material; and adhesive sheet as used in Example 3 was punched (b) a plural number of push-button units made of to form 10 openings of 8.5 mm diameter in 2 rows an electrically insulating rubber, each unit including each containing 5 openings and applied and bonded 130 a push-button with a contacting portion on the inner 7 GB 2 192 307 A 7 surface thereof to confront the pair of contact points (b) a membrane made of an electrically insulating on the printed circuit board or assembly, whereby rubber mounted on the printed circuit board and pressing of the push-button effects electrical contact having an electroconductive contact portion on the between the pair of contact points, each push- surface facing the printed circuit board; button being bonded by an adhesive to a peripheral 25 (c) an electrically insulating spacer intervening zone around the pair of contact points. between the printed circuit board and the
2. A switch unit according to Claim 1, in which the membrane; and adhesive is a sUicone-based rubber adhesive or a (d) a plural member of push-button units made of pressure-sensitive adhesive. an electrically insulating rubber, each unit including
3. A switch unit according to Claim 1 or Claim 2, in 30 a push-button, bonded by an adhesive to the which the pairs of contact points are on the base membrane at such a position that each push-button board and are both fixed and the contacting portion confronts one of the fixed contact points on the of each push-button is a movable contact point printed circuit board with the membrane made of an electroconductive rubber fixed to the intervening therebetween.

inner surface of the push-button. 35 5. A switch unit according to Claim 4, in which the
4. A push-button keyboard switch unit which adhesive is a silicone-based rubber adhesive or a comprises: pressure-sensitive adhesive.

(a) a printed circuit board having a plurality of 6. A switch unit according to Claim 1, substantially fixed contact points on a base board made of an as described with reference to Figures 3 to 5 or electrically insulating material; 40 Figures 6 and 7 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Courier Press, Leamington Spa, 1188. Demand No. 8991685. Published by the Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.