At 2:47 PM  -0400 5/20/96, [log in to unmask] (Jerry Cupples) wrote:

>Doug McKean asked:
>
>>          Green Cu oxide shows up on socket pins after about three

I believe copper oxide is black not green.  Sounds like it could be a
copper chloride.

>>          months in the field.  Very little shows up before assembly,
>>          or shipment.
>
>Regarding copper, the Merck Index says: "...in moist air, gradually becomes
>coated with green basic copper carbonate" Most copper salts are blue or
>blue-green. I think that the salts tend toward a bright blue. As a wild
>guess, if the color is bluish, it could be an artifact of halide
>contamination. Straight green, OTOH is normal after environmental exposure
>to water vapor. A real chemist might disagree.

Well I'm not a real or psuedo chemist but pure water won't hurt you.  It's
little traces of nasty things like chlorides in the water which hurt.   A
simple view of corrosion is you need three things for it to occur: a
corrodent (chloride (Cl) for example), water (H2O) and something to corrode
(the copper).  Take away one of the three and nothing happens.

[...]
>
>Also, if you are putting a tin-lead plated lead into a gold plated socket
>(or vice-versa) you have set up a galvanic couple which can accelerate
>corrosion between the socket and the mating lead, regardless of the
>cleanliness level you have reached. In that case, the socket plated finish
>should be changed to match that of the lead to be inserted.

Also watch out for fretting corrosion if you have this type of contact
metallurgy (tin-lead contacting gold) and the end application experiences
some low level vibration (like a cooling fan in a computer).  The residues
in this case would be black or grey oxides of tin at the contact interfaces.

A failure analysis would be helpful with your problem and could determine
a) what the green residue is, b) whether your sockets or device contacts
are plated as you expect.  This information can assist you in where you
need to take corrective action.

Regards,
Gregg Klawson
GTE Government Systems Corp
Taunton, MA, USA
email: [log in to unmask], telephone: +1.508.880.1822

my views are my own.