conductive rubber glue?

Dec 21, 2004 18 Replies

The more I think about this the longer a shot it appears likely to be, but here goes anyway:



I have a car radio with button switches that don't work. Buttons for bands, memories, that sort of thing.



The switches are a plastic button, a printed circuit with two traces, and a kind of black rubber doughnut with a tit in the middle. The tit sticks out a bit more from the bottom of the assemble, so it hits one pc board trace, the joint between the tit and the ring flexes, then the ring hits the other pc trace, and the switch is closed.



Many of these little rubber things have broken where the tit is joined to the dougnut. I'm off to another car radio repair place tomorrow - at the really good electronics place that I go to first the guy just shook his head, so I don't have much hope of finding new bits. This radio is old and foreign.



Is there a conductive flexible rubber glue?


I got some Nickel Coat (Kote?) from Bainsville Electronics, Baltimore. Get that or whatever they have.

Kevin Gallimore

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There is something called a remote control kit for fixing the buttons. This is an adhesive conductive coating that is painted on to the buttons to make them conductive again. It is formulated to stick to the type of silicon rubber that the pad buttons are made out of. Regular contact cement, and the others will not stick to the pad buttons.

Many of the electronic parts suppliers can supply this kit for servicing the pad buttons.

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See .

Another option: Aluminum tape. Used for furnace ductwork; purchased at the hardware store in a roll like duct tape. It's thin metal foil with strong adhesive on the back. A great fix for membrane keys that've lost their conductivity.

Richard

That looks like a great product. However, on the same site sits

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I personally liked the phone line powered car battery charger. That's gotta take a long time to work.

Yup, that's the fix-it kit I remember. Used to have a general electronics supply place in town that had it on the shelf. TV parts places are an endangered species anymore, it'll probably have to come by the big brown buggy now, HAZMAT stickers and all. A very temporary fix can be implemented if you have some rubber roller conditioner, this kind of dissolves the outer-most layer of the contact area on the button and gets some fresh material exposed, the stuff I have will also take off any markings on the other side, really nasty solvents in it. Some of these keypads use a carbon-rich harder plastic contact embedded in the rubber, these tend to wear the PC board contact area away after hard use, in that case, you need some nickel print PC board paint to fix it and it probably won't wear very well. Face it, most consumer electronic equipment these days isn't meant to be fixed. If you get 6 months or a year out of it, you'll be lucky. Start saving your pennies for a new one.

Stan

I have used this on a membrane key pad. Don't put on a thick coating, or it will flake off.

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There is also a two part conductive epoxy, but I don't remember the brand name.

Randy

Aluminum is a poor choice. When exposed to air it forms a non-conductive layer of aluminum oxide. Tin or Gold-plated or even Copper foil would work far better.

That tape seems to remain pretty shiny over time, it may not be pure aluminum.

Sounds good. So where can these adhesive backed foils be easily purchased at a reasonable price?

| > Richard H. wrote: | >

| > >Another option: Aluminum tape. Used for furnace ductwork; purchased at | > >the hardware store in a roll like duct tape. It's thin metal foil with | > >strong adhesive on the back. A great fix for membrane keys that've lost | > >their conductivity. | >

| > Aluminum is a poor choice. When exposed to air it forms a | > non-conductive layer of aluminum oxide. Tin or Gold-plated | > or even Copper foil would work far better. | | That tape seems to remain pretty shiny over time, it may not be pure | aluminium.

I believe it has a coating of lacquer over a VERY thin film of aluminium, so that's another reason to avoid it.

N

| >Richard H. wrote: | >

| >>Another option: Aluminum tape. Used for furnace ductwork; purchased at | >>the hardware store in a roll like duct tape. It's thin metal foil with | >>strong adhesive on the back. A great fix for membrane keys that've lost | >>their conductivity. | >

| >Aluminum is a poor choice. When exposed to air it forms a | >non-conductive layer of aluminum oxide. Tin or Gold-plated | >or even Copper foil would work far better. | | Sounds good. So where can these adhesive backed foils be easily | purchased at a reasonable price?

Copper foil is used for crafts but may be too thick.

N

I read in sci.electronics.design that James Sweet wrote (in ) about 'conductive rubber glue?', on Tue, 21 Dec 2004:

What happens is that an oxide film forms almost instantaneously, but it is exceedingly thin and has a very low breakdown voltage. So unless you want a good contact for millivolt-level signals, aluminium will work reasonably well. But gold is better, and consequently costs more.

And shielding, sticky copper tape is readily available.

I find though that those keypads don't really lose conductivity, they simply become saturated with skin oils. A good scrub of the membrane and circuit board with liquid dish detergent has fixed every one I've encountered yet.

Very possible it is tin, considering it's been aging in my shop for about 10 years before I put it to use... and still shiny.

It may be vacuum deposited aluminium with lacquer over it.

N

Hmm ... check your local electronics hobby store for the kind of tape used to build up "printed circuit" boards, instead of the more common etching away of the unwanted copper from a fully copper clad board.

Enjoy, DoN.

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