Carl: The elastomeric to tin/lead(HASL)contact switch will work fine for
your prototype.
Over time the tin/lead forms an oxide layer that raises the contact
resistance resulting in an intermittent connection that can gradually
deteriorate to an open. However at normal conditions it can take years to
form a thick enough oxide layer to cause problems.

If you can live with something in a 20-30 ohm/sq contact resistance on the
board you may want to consider a carbon polymer thick film (PTF). It will
retain the same contact resistance over time. Your quick turn shop may
offers this. Also if this is applicable to the finished design it might  be
cheaper than gold; depending on the gold type, thickness and process.

Over the years we have used all three; tin/lead, PTF and gold for a variety
of applications with elastomeric switches.


Regards

Michael Barmuta

Staff Engineer

Fluke Corp

Everett WA

425-446-6076

-----Original Message-----
From: Carl VanWormer [mailto:[log in to unmask]]
Sent: Wednesday, June 19, 2002 1:56 PM
To: [log in to unmask]
Subject: [TN] Not gold fingers on prototype conductive elastomer switch


I am making a prototype handheld unit that uses a conductive elastomeric
button to short out an interdigitated pattern as a switch (just like in your
TV remote).  The quick turn prototype house I will be using does not offer
gold plating in their fast/cheap process, so I plan to live with the HASL
finish for this switch.  Have any of you guys tried this before?  How short
will the useful life be, when compared to the standard elastomer on gold?

Thanks,
Carl



Carl Van Wormer
Cipher Systems
1815 NW 169th Place, Suite 5010
Beaverton, OR  97006
Phone (503)-617-7447    Fax (503)-617-6550

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