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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