"N_Cook" wrote in message
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Anyone any insight on this. Failure of 34 year old TTL chip, in unpowered
storage. Just 1 of 50 chips on a board, TTL,4000, analogue, memory etc.
Only this one had silver tarnish looking appearance of black silver
sulphide on the pins. This make of TTL did for a while have silver plating
aded to the pin frame , for a period.
I cracked open the device and no obvious tarnish on internal frame metal.
Anyone know what the failure process was? was silver plating found to be
problematic?

There have been problems in the past where gold plated IC pins have
developed a microscopic insulating layer - but I don't know about silver
plated.

Silver plating develops black silver sulphide after long exposure to air,
with NOS parts you'd just clean it off and solder as normal. Silver is a
component of several types of solder alloys. So I don't think it should
cause any problems.