Elastomer Strips

[John10b]

Never heard of this stuff before, i only learned about it after looking at the thread on repairing a Fluke Multimeter.
How many ways are there to connect electrical items together I wonder?
Cheers
John

[Graham G3ZVT]

I had to look it up, but then realised that I know well what they are, but I've always called them Zebra strips.
You find them in digital clocks, thermometers and meters, the filling in the sandwich twixt PCB and LCD

[John10b]

Thanks, I learn something every day!
Cheers
John

[stuarth]

As I understand it, the elastomer strip has many fine wires running from one side to the other, much finer pitch than the two things you’re connecting together, so the “two things” must be accurately aligned to each other, but the alignment of the elastomer strip is not critical.

Stuart

[ajgriff]

I'm not at all sure as to the nature of the conductive threads. It looks like something similar to carbon or graphite. Anyone know?

Alan

[David G4EBT]

Here you go, according to Wiki ('instant erudition for the hard of thinking'!), possibly carbon, gold or silver, depending on the application.

'Zebra Strip' isn't a colloquialism - it's a trade mark, which is perhaps why they're better known by that term.

https://en.wikipedia.org/wiki/Elastomeric_connector

Odd that some Fluke meters seem to be afflicted by the 'fading display' phenomenon when meters costing a tenth of the price seem to be immune to it.

[John10b]

Thank you that David.
If I may expand by asking what type of connectors are used in aviation, with there many displays etc.
Cheers
John

[ajgriff]

Thanks David. Now you've highlighted it I seem to remember reading somewhere that Fluke upgraded the specification to gold at some point, presumably in an attempt to resolve the display issues. My guess would be that it was originally carbon which would also explain why the pencil rubber I used when cleaning my zebra strips turned black.

Hope they would use gold for a 'plane John!

Alan

[John10b]

Took a look at pdf of Zebra connectors, in it they say for use in Aviation and Military etc etc.
A long way from the days of me using Plessey connectors!
Cheers
John

[stuarth]

Whether you use carbon, silver or gold in the elastomer strip depends on the material used on the contact material it’s used with. Gold will not always be the best option.

I once had to resolve a problem where a piece of kit was very very slightly intermittent, so slightly that when the kit was brought back to the factory, it invariably worked perfectly, and resisted all attempts to make it fail. The problem was finally found (by careful examination of a faulty unit undisturbed on a customer site) to be a plug-in IC with gold plated pins in a tin plated socket. The device spec called for tin plated pins, our goods inward folk accepted gold as it was “better” than tin, so must be OK. Beware of dissimilar metals!

Stuart

[John10b]

Thank you Stuart, Interesting how the non technical stores inward department overruled the technical specification!
I have encountered suppliers officers trying to overrule a technical officers on grounds of cost, it got very heated!!
Cheers
John

[ajgriff]

Interesting point about galvanic corrosion. Gold plated audiophool phono plugs anyone?

I also note that elastomeric connectors/strips (the generic description apparently) are manufactured in large quantities. They come in all sorts of shapes, sizes and styles for a variety of applications particularly in relation to modern vehicle display modules. However, there doesn't seem to be much of a retail market, although strips can be bought wholesale with minimum order lengths of 50m plus, which is not very useful for people like us.

Alan

[emeritus]

I understand that early ICs that used Gold metallisation suffered from the "Purple Plague" , an inter-metallic gold compound that led to failure of chips that suffered from it.

[Craig Sawyers]

Originally Posted by ajgriff

Interesting point about galvanic corrosion. Gold plated audiophool phono plugs anyone?

Well, gold on gold is fine - so gold plated phono plugs AND sockets are just fine. As stated, it is dissimilar contact metals that are likely to cause a problem.

Of course, what is commonly forgotten is that the base metal is either brass or phosphor bronze, and there is always an adhesion layer between the base metal and the gold - usually nickel or chromium.

All things that audio connector manufacturers omit to mention

FWIW NPL chose connectors in which the base metal is copper, and then pay to have the platings chemically stripped - so in particularly DC calibration work all connections are copper/copper. And they use Van Damme cheapo cable - again they choose a cable in which the core and screen are both high purity copper.

They only use esoteric aerospace teflon insulated cable for internal wiring inside cryostats and for wiring standards immersed in warm oil, both environments being unsuitable for any other insulation.

Craig

[dseymo1]

The issue with combining gold-plated and base metal contacts is quite well known in relation to computer memory modules too. Logically, there's little point in using gold (whatever its perceived advantage) on only one side of a contact pair anyway.

[stuarth]

Gold inside the package, and gold outside the package are quite different things.

IIRC, some early processes used gold doping to improve switching speed. But gold killed the gain of other processes. You couldn't run both processes in the same fab without the gold from one contaminating the other.

Then there was the purple plague mentioned by emeritus which was a problem with gold bond wires.

But if you keep wafers away from gold until they are passivated, you can use gold for the packaging.

Stuart

[MotorBikeLes]

I had never heard of "gold plague", but 55+ years ago in our "colours" lectures (Ceramic Technology) we were acquainted with the fact that colloidal gold when finely dispersed was purple, and referred to as "Purple of Cassius".
If you look carefully at a gold lined cup or saucer, you will probably see the purple if the gold is very thin at the edge.
I would assume this is the same purple.
Les.

[stuarth]

We've drifted a bit off topic. I'd just like to say that gold on contacts is not necessarily a good thing, and if anyone has some gold which is causing them problems, I'd be happy to take it off their hands and dispose of it safely.

Meanwhile on topic, the connections in the elastomer strip, whatever they are made of must not be rigid, as the name implies they must be elastic, they must be compressible to take up variations in the spacing between the two things they are supposed to connect together.

Stuart

[Refugee]

Surely they must be a stack of conductive rubber and insulating layers all stacked together.

[John10b]

Thank you all for your very informative and interesting answers, how about a couple of suggestions to my original post #1?