Ron: We have used both gold and conductive carbon, typically called PTF
(polymer thick film)for years. They both work well and have their own pluses
and minuses. The PTF should do the job for you replacing gold for key/touch
pads if you can live with it's higher contact resistance. It also does not
have the photo definition of plated gold. PTF is normally screen printed
onto the substrate so spaces/traces below about 15 mils are difficult to
achieve.

As to life cycle testing a lot depends on your PTF and mating membrane
design. I've always felt that claims like 5 million cycles was a bit
optimistic. We done our own life cycle testing and have easily exceeded 1
million cycles. Note: It will not give you these type of life cycles if used
for a rotary switch.

We have millions of instruments in the field with PTF contacts, many with
15+ years in all kinds of service conditions.

Take a look in the TechNet archives there is considerable information on
this topic.



Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076



-----Original Message-----
From: Miswald, Ron [mailto:[log in to unmask]]
Sent: Thursday, March 04, 2004 7:07 AM
To: [log in to unmask]
Subject: [TN]


Hi all

I am looking for experiences with conductive carbon coating used in a touch
pad.  We currently use gold, but are looking to reduce costs.  Unfortunately
we still need a couple years of service.  For carbon I do have a data sheet
which claims 5 million cycles with no wear - there is no information on
environment or type of cycles.  At the bottom of that page is a paragraph
full of legalese negating everything above.

What type of experiences have members here had?  Duty cycles?  Length of
service?

TIA
Ron

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