Scott,
The approach you describe is lower risk application for Silver
contact.  The contact only has electrical bias applied at the moment of
switch contact.

dw

At 11:56 AM 1/20/2005, Roger Stoops wrote:
>Scott,
>
>On some of our products we built some years ago we used carbon as an
>alternate for Au for LCD and switch contacts.  We had no reported
>problems, either from assembly or the end-user.
>
>Dwight made a good point in his email.  Interesting side point to his
>comments: when we needed to build our own keypad, the contact layer was
>silver on mylar sealed to a pcb with PSA adhesive (pcb contacts were
>ENIG).  Even though there were no apparent openings and no vents, to our
>dismay the contacts oxidized rather quickly (found sulfur and moisture in
>enclosed areas).  The vendor suggested a thin layer of carbon ink over the
>silver.  Worked like a charm.  You may find it helpful to find out what
>ink your vendor is using and specify it on your print.
>
>Question for anyone: Has anyone used IAg as a board finish with carbon ink
>over any desired areas?  Seems like it might work for a keypad with parts
>on one side and contacts on the other...
>
>Rgds,
>
>Roger
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Scott Lefebvre
>Sent: Thursday, January 20, 2005 2:37 PM
>To: [log in to unmask]
>Subject: [TN] Carbon Keypad
>
>
>Currently we use gold for all of our keypads.  I want to reduce the cost
>of a product and thought about switching to a carbon keypad.  I am not
>familiar with the process and wanted to know a few things.  We mostly use
>a water-soluble process and our entire product is washed.  Some boards are
>a mixed technology using SnPb currently.
>
>?  Are there any Reflow solder concerns I should be aware of?
>?  Are there any Wave solder concerns I should be aware of, like masking
>pads during wave solder?
>?  Are there any other concerns period that I should be addressing.
>
>Thank you,
>
>Scott
>
>
>
>
>
>
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