Classification:
Prologue:
Epilogue:

You'll need to test your application yourself, as every application is unique;
but, here's some thoughts;

If both surfaces have immersion Au over Ni and if the keyboard is sealed in
construction, and the contacts are just pressure contacts, and the electronic
circuits can handle significant increaces in resistance (up to say 10's of
ohms) you'll probably be OK.  Increace in resistance from corrosion would be
your biggest concern.  Most comercial keypads I've torn apart use either Carbon
printed contacts or Silver based printed contacts.

With the thick Ni you will not have to worry about Au migrating into the Cu.
and since you don't have a wiping system typically, you may transfer Au back
and forth between the two contact surfaces, but there is no place to wear it
away to.

Jim Herard
IBM Microelectronics
Quality Engineering




        TechNet-request @ ipc.ipc.org
        03-21-97 03:44 PM


To: TechNet @ ipc.org@internet
cc: ddriscol @ mgln.com@internet
Subject: Immersion gold for keypad contacts

To all Technetters,

I think this topic has been covered before and I apologize if this is so
but I will ask the question again.

I want to use immersion gold over nickel for my PCB.  While this is not
unusual in itself, I'm more concerned with the use of the gold as keypad
contacts.  Since the gold is very thin to begin with (around 4-5
microinches), will this degrade over time to where there is no more gold
present on the contact pad?

I have read varying articles that state that it is or isn't a problem and
would like to know what others have experienced with this alternative
surface finish.

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