CA1098946A

CA1098946A - Electrical switch

Info

Publication number: CA1098946A
Application number: CA299,973A
Authority: CA
Inventors: Richard H. Zimmerman; Richard M. Wagner
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1977-04-25
Filing date: 1978-03-29
Publication date: 1981-04-07
Also published as: JPS53133775A; IT1094377B; NL7803802A; DE2817950A1; FR2389217A1; US4143253A; IT7822350A0; ES469075A1; SE7804659L; GB1567731A; BE866109A; FR2389217B1

Abstract

ABSTRACT

In an electrical switch comprising a first sheet of transparent electrically insulating material having at least one electrical conductor on a surface thereof;
a second sheet of transparent electrically insulating material having at least one electrical conductor on a surface thereof; and a spacer sheet of electrically insulating material having at least one hole therethrough r the first, second and spacer sheets being arranged in superposed relationship with the first and second sheets on opposite sides of the spacer sheet with the conductors on the first and second sheets adjacent to the spacer sheet and each aligned with at least one hole in the spacer sheet whereby by the application of pressure to the first sheet, conductors on the first and second sheets can be urged into contact through a hole in the spacer sheet, the first and second sheets are of cellulose acetate material, the conductors having been formed on the surfaces thereof by electro-deposition.

Description

This invention relates to an electrical switch, and particularly to an opt.ically clear electrical switch of the type used with vi.sual display devices.
Known switches of thls ~ype comprise a first sheet of transparent electrically insulating materlal having at least one electrical conductor on a surEace thereof; a second sheet of transparent electrically insula~in~ material having at least one electrical conductor on a suxEace thexeof; and a spacer sheet of electrically insulating material havlng at least one hole therethrough r the fixst, second and spacer sheets being arranged in superposed relationship with the first and second sheets on opposite sides of the spacer sheet with the conductors on the flrst and second sheets adjacen~ to the spacer sheet and each align~d with at least one hole in the spacer sheet whereby by the application of pressure to the first sheet conductors on the first and second sheets can be urged into contact through a hole in the spacer sheet.
According to this invention, in a switch of the type set out above, the first and second sheets are of cellulose acetate materia.l, the conductors having been formed on the surfaces thereof by electro-deposition.
Preferably the first and second sheets are of cellulo~e tri-acetate, although cellulose acetate butyrate, or cellulose di~acetate can otherwise be used.
This invent~on will now be described by way of

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example~ with reference to the drawings, in which:-Figure 1 is a plan view of a switch in accordance with the invention;
Figure 2 is an exploded view of the switch of S Figure l;
Figure 3 i9 a cross-sec~ional view o a conductor of the switch of Figure l;
Figuxe 4 is a cross-sectlonal view of the switch of Figure 1, with a filter disposed over its surface;
and Figure 5 is a fragmentary view of the switch of Figure 1, with an integral grid of shieldlng conductors formed thereon.
Referring first to Figures 1 and 2, the switch here shown comprises a substantially optlcally transparent laminate formed of first, second and spacer sheets o~
cellulose tri-acetate material 1, 2 and 3, respectively.
The three sheets are bonded to each other along their edges, and the spacer shee~ 3 i5 provided with a plurality of through holes 4 which define individual switch sites.
Vertically extending (as seen in Figure 1) hairline conductors 5 are provided on the inner surface of the first sheet 1, that is the su.rface which is adjacent the spacer sheet 3, and similar horizontally extending conductors 6 are provided on the corresponding inner surface of the second sheet 2. The conductors 5 and 6 cross each o~her at the holes 4 as shown, ~ut are .

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normally spaced from each other by the spacer sheet 3, but can be brought into engagemenk at a particular switch site by simply pressing on the outer surface of the first sheet l over the hole 4 at that site.
The conductors 5 have integral leads 7 which extend to the lower (as seen in Figure l~ edge of the first sheet l where they terminate in terminal portio~s 8 which axe relatively wider than the conductors 5 and the leads 7. Similarly, the ~onductors 6 have integral lo leads 9 which extend along the second sheet 2, and which terminate in terminal portions lO which are relatively wide. As shown in Figure 2, some of the adjacent terminal portions lO are separated by isolated relatively wide conductors ll which can be bonded to the terminal portions 8 of the conductors 7 on the first sheet l.
The conductors are deposited on the sheets l and 2 hy the following process.
Each sheet is advantageously of ahout five mils in ~hickness, and is prepared first by immersion in a suitable detergent capable of removing any residual oils or other forelgn matter on the surface of the sheet. One suitable detergent which has been found to be satisfactory is a cleaning agent containing wetting agents~ having a p~ of 7, and which is sold under the trademark Neutra Clean 6~. This ma~erial is used in a one to~one aqu~ous solution at room temperature, the sheet being immersed in the solution for about on~ minute. After a hot water :

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~ 8970 rinse (55C) the sheet is immersed in a solutlon containing hydrazine, sodium hydroxide~ and triethanolamine for about thirty seconds.
; It is believed that the hydrazine treatment attacks and slightly softens the surface in a very mild manner to prepare it for reception of palladium as described below but it does not effect the optical characteristics of the sheet~ This hydrazine treatment contributes si~nificantly to the good adhesion which is obtained in the finished product as will be described below~
Followin~ the hydrazine traatment the sheet is immersed in a weak sodium hydroxide solution followed by immersion in a dilute HCl solution. Thereafter, the surface is catalyzed by contacting with a PdC12-SnC12 solutionO This step is followed by immersion in an ammonium bifluoride solution to dissolve any residual stannous ions on the surface of the sheet.
Thereafter, a blanket plating of electroless copper is provided over the entire surface of the sheet to a thickness of about two or three micro-inches. While this blanket plating covers the entire surface, it is relatively thin~ and in order to prevent an~ attack of the cellulose tri-acetate sheet, an additional fifty micro-inches of copper are elec~rolytically plated over the entire surface from a CuS0~ bath9 the bath temperature bein~ about 43 to 4gC. The electroless copper serves ..
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~98~6 8970 as a bus to ensure electrolytic p]ating over the entir~
exposed surface.
The sheet is then subjected to a cold water spray rinse, and is dried at about 75C for a brief interval~
A suitable resist such as AZ-340 is then applied to the entire surface, dried r and the film is baked at 75C for ten minutes. The resist is then exposed along the lines of the conductors r developed, and rinsed 50 that the lines which define the conductors are not covered by the resist. Copper is then electro-plated on the exposed areas to a thickness o about 250 micro-inches and after sui~able cleaning and an acid dip~ a thin plating (25 micro-inches3 of nickel is deposited over the copper and about 30 micro-inches of gold is electro-deposited over the nic]cel. Alternatively, Pd, Ag or other etch resistant metal may be plated over the copper conductors. The resist is then stripped, and the copper blank~t ~s etched away by a FeC13 spray.
From the above brief description, it will he apparent that both surfaces of the sheet are subjected to the process steps described, and that a re.sist is applied to the entire surface on which the conductors are not belng produced. Under some circums~ances, it is desirable to provide a grld of shielding conductors as shown at 12 in Figure 5 on the outer surface of the sheet 1, and such sh~elding conductors can be produced on this surface by exposing ~he resist on the surface, . ~:

~ 970 selectively developing and removing the resist, and then electro-depositing copper on the shielding conductor lines while the conductors are being electro-deposited on the downwardly facing surface. Suitable shielding can be provided by producing 2 mil conductors on 100 mil centre lines, ten lines per inch.
Figure 3 shows a cross-section of a conductor 5 on the surface of the sheet 1. Electro-deposited copper 13 constitutes the bulk of the conductor, and the thin layers of nickel 14 and gold lS extend beyond the sides of the copper 13 as a result of und~rcutting during the etching process.
It will be appreciated that in the drawings, the width of the conductors is exag~erated, the actual widths 1~ ~eing approximately 5 mils as mentioned previously.
Thus, the shielding conductors 12 and the conductors 5 and 6 would, in an actual switch, be much less obvious - than they are shown in Figure 5, the width of the conductors not being sufficient to interfere with an observer's view of a display area beneath the switcho Figure 4 diagrammatically illustrates the use of the switch of Figures 1 and 2 on the upper side of an array of light emitting diodes 16, there heing a polarising filter member 17 coverin~ the outer surface of the sheet 1.
As mentioned previously, the treatment of the sheets with a hydrazine-sodium hydroxide- trie~hanolamine ~; ~

~ 8970 solution is believed to cause a chemical attack and softening of the cellulose surface, this resulting in the formation of a gel on the surface. It is also probable ~ha~ some complex species are entrapped in this gel, speciflcally a sodium alcoholate along with some sodium hydroxide and some hydrazine. It is additionally believed that othex species migh~ be present, which might be formed with the acetyl groups on the surface, such as acetyl hyrazide and acetate salts. Some of these entrapped species serve as catalytic agents for the deposition of palladium on the surface, particularly since the hydrazine can serve as a reducing agent to xeduce the colloidal palladium ions to metallic palladium.
It has been found that when conductors are provided on cellulose acetate sheets as described above r the optical clarity of the sheets will not be significantly affected. ShePts which have conductors thereon will generally have about 90~ light txansmlssion and the condwctors will have a metal adhesion of about 5 pounds peel strength per linear inch.
~s previously mentioned, the swltch can be used with a polarising filter (17 in igure 4) and the cellulose acetate shee~s will not depolarise light upon passage therethrough. By virtue of this fact, swltches in accordance with the invention can be equipped with filters and used in ordinary daylight conditions.
Following are specific examples of processes ;', .
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8g70 followed to produce conductors on a sheet of Gellulose tri-acetate.
EXAMPLE I
A 12 inch square sheet of cellulose tri-acetate having a thickness oE S mils was cleaned of all surface oils and other foreign matter by immersion for ~0 seconds in a aqueous detergent solution. The sheet was then washed under a 55C hot water spray, and was then immersed for about 35 seconds in a solution composed of 70 parts of an 85~ hydra2ine hydrate solution, 25 parts of a 25%
sodium hydroxide solution and 5 parts of triethanolamine.
The sheet was ~hen again rinsed under a hot water spray (55C), and then immersed in a 1~ sodium hydroxide solution for 30 seconds, and then again rinsed under a hot water spray. It was then immersed in a 25% HCl solution for 30 seconds. The surface of the sheet was then catalyzed by immersion for 90 seconds in a commercially available palladium-tin colloidal solution containing 0.67 gm/1 of PdC12, 42 gm/l of SnC12 and 250 ml/l of HC1. Thereafter, ~he sheet was washed in a cold water spray, and immersed in an aqueous solution of ammonium bifluoride for 90 seconds. The sheet was then washed again under a cold water spray and dried in an oven for 5 minutes at a tempera~ure of 60C. A
blanket coating of electroless copper having a thickness of about 3 to 5 micro-inches was provided on the sheet by 1mmersion or 10 minutes in an electroless copper g _ ~ 970 plating bath containing a soluble copper saltl a compl~xing agent to keep the copper in solution, sodium hydroxide to render the solution alkaline, and formaldehyde as a reducing agent. After removal of the sheet from this electroless platin~ bath, it was rinsed under a cold water spray, dried by an air blast, and placed in an oven at 60C for 3 minutes. The sheet was then placed on a rack and an additional blanket plating of 50 micro-inches of copper was deposited electrolytica]ly from an acid copper sulfate bath. The sheet was then washed under a cold water spray, air dried and placed in an oven at 75C for two minutes. The sheet was then coated by immersion in a liquid photo resist sensitive to ultra violet light, dried at room temperature or 10 minutes and baked at 75~C for 10 minutes. The pattern was developed by selective exposure to ultra violet l~ght and immersion in a developing solution. The sheet was then rinsed in a cold water spray and racked for elec~ro-plating of the circuitry. The surface was activated by mild sponging with a detergent solution and washed under a cold water spray. Thereaf$er, the rack was dipped in a ten percent sulfuric acid solution for 5 seconds, rinsed under a cold water spray, and electroplated to a ~hickness of 300 micro-inches in an acid copper sulfate bath. After this electroplating step, the sheet was rinsed under a cold water spray, it was again dipped in a 10 percent sulfuric acid solution ~: . . :-: ' ' ~. ~' ' ~970 for 5 seconds, and again rinsed under a cold water spray.
25 micro-inches of nickel were then electroplated over the copper from a nick~l sulfamate bath. The sheet was then washed under a cold water spray, dipped in a 10 percent sulfuric acid for 5 seconds, and again washed under a cold water spray. ~ bright gold plating having a thickness of about 32 micro-inches was thsn electroplated over the nickel from a neutral cyanide gold bath. The sheet was then washed under a cold water spray, ~he resist was stripped from both surfaces of the sheet and the blanket copper plating was etched away by - spraying with a ferric chloride etchant. The sheet was then again rinsed under a colcl water spray and dried under an air blast.
After stripping of the blanket plating, the sheet was observed to have a light transmission of about 92%o The conductors had an adhesion in the range of 4 to 5 pounds per linear inch.
EXAMPLE II
A sheet of cellulose tri-acetate having a thickness of 5 mils was cleaned of all surface oils and other foreign matter by immersion for 30 seconds in an aqueous detergent solution. It was then washed under a hot water spray ~55C) and immersed for 30 seconds in a solution made up of 70 parts of an 85~ hydrazine solution, 25 parts of a 25~ NaOH solution and 5 parts triethanolamine. It was then immersed for 30 seconds ln a 1% NaOH solution, ~8~ 970 washed in a hot water spray ~55C) and then immersed in a 25% HCl solution for 15 seconds. Thereaf~er, the surface of the film was catalyzed by immersion for 60 seconds in a palladium-tin colloidal solution containing 0.67 gm~l of PdC12, 42 ~m/l of SnC12 and 250 ml/l of IICl, washed under a cold water spray and immersed for 60 seconds in an aqueous solution of ammonium bifluoride as described in Example I. It was then washed in a cold water spray and baked in an oven at 60C for about 5 minutes. A blanket coatiny of electro~ess copper was provided as described in Example I, the immersion time bein~ 10 minutes. The sheet was then again washed under a cold water spray, dried under a,n air blast, baked at a temperature of 60C for 3 minutes. The steps outlinad in Example I beginning with an electro-depositlon of the blanket coating were then followed. After stripping of the blanket plating, the sheet had substantially the same characteristics as the sheet of Example I.
In the examples presen~ed above, both surfaces f the sheets of cellulose acetate are provided with blanket coatings of copper. Ordinarily, the resist material will be applied to the surface of the sheet on which conductors are not being provided and this blanket coating will be removed at the time of etchin~.
As shown in Figure 4 t and as mentioned previously.
it is desirable under some circumstances, to provide shielding conductors 12 on the upwardly facing surface .~ ~ , : ~ , .
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~ 6 ~970 of the sheet 1, and these can be produced by simply selectively developiny the blanket coating on the upwardly facing surface of the sheet 1, and electro-depositing the shielding conductors thereon.
Cellulose acetate materials other than cellulose tri-acetate can be used.
For example, conductors have been provided on cellulose acetate butyrate by the procedures outlined above in Examples I and II with minor changes. In general, when conductors are being provid2d on cellulose ace~ate butyrate, the sheet should be baked a~ 120C
for about S minutes before electroless deposltion and the sheet should be treated in the hydrazine solution for 90 seconds or more. After the electroless metallization step, the sheet should ~hen be baked again at 120C for about 5 minutes. In other respects, the procedures discussed above can be followed.
~ cellulose acetate butyrate sheet having a thickness of 15 mils was provided with conductors as described above, and was suitable or use as the sheet 2 of the switch. A relatively thinner sheet is desirable for the shee~ 1 since this sheet must he flexible, Cellulose di-ace~ate can also be used, A distinct advantage of the ahove described process is that the use of an adhesive as is r~quired in processes in which a laminate ~metal to plastics sheet) produced by bonding me~al foil to the sheet, is etched, is avoided.

When the la~inate is produced by bonding thin metal film to plastics sheet, an adhesive mu~t be used to bring about the bond of the metal to the plastics sheet. The use of an adhesive causes derogation of the optical properties of the sheet to the extent that switches produced by such processes are far from satisfactory. The adhesive is, of course, not removed when the etching step is carried out, so that it remains on the surface of the sheet as an extra layer through which light must pass, a layer, lo moreover, which will usually have inferior light transmission characteristics and will have an index of refraction which is different from that of the sheet.
It will thus be apparent that the presence of an adhesive layer can only cause misch~ef in an optically clear switch.
Switches in accordance with the invention also have the advantase that the electro-deposited and etched conductors can be made extremely narrow ~about 5 mils or less) as compared with conductors on plastics sheats, which are conventionally produced by silk screen printing operations~ Silk screen printed conductors usually have a minimum width of about 10 mils, and conductors of this width may interfere with the view of the display through the switch. rrhe narrow conductors also permit extremely precise loca~ion of each switch site at the geometric centre of a hole 4, such precise location being desirable ln that it facilitates miniatuxlsation of the switch.
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Claims

The embodiments of the invention for which an exclusive property or privilege is claimed are as follows:-

1. An electrical switch comprising a first sheet of transparent electrically insulating material having at least one electrical conductor on a surface thereof;
a second sheet of transparent electrically insulating material having at least one electrical conductor on a surface thereof; and a spacer sheet of electrically insulating material having at least one hole therethrough, the first, second and spacer sheets being arranged in superposed relationship with the first and second sheets on opposite sides of the spacer sheet with the conductors on the first and second sheets adjacent to the spacer sheets and each aligned with at least one hole in the spacer sheet whereby by the application of pressure to the first sheet, conductors on the first and second sheets can be urged into contact through a hole in the spacer sheet, in which switch the first and second sheets are of cellulose acetate material, the conductors having been formed on the surfaces thereof by electro-deposition.

2. A switch as claimed in Claim 1, in which the first and second sheets are of cellulose tri-acetate.

3. A switch as claimed in Claim 1, in which the first and second sheets are of cellulose acetate butyrate.

4. A switch as claimed in Claim 1, in which the first and second sheets are of cellulose di-acetate.

5. A switch as claimed in Claim l, including a grid of shielding conductors on the outer surface of the first sheet.

6. A switch as claimed in Claim 1, including a polarising filter member covering the outer surface of the first sheet.

7. A switch as claimed in Claim l, in which the conductors have been formed on the surfaces of the sheets by a process involving rendering the surfaces of the sheets conductive by electroless deposition of a metal blanket coating on the surfaces; coating the blanket coatings with a resist material coating; removing the resist material coating along lines defining the conductors; depositing metal plating along the lines defining the conductors; removing the exposed resist coating; and etching away the blanket coating from the surfaces to leave the conductors thereon.

8. A switch as claimed in Claim 7, in which each conductor comprises a layer of copper covered by a layer of nickel, in turn covered by a layer of etch resistant contact metal.