Doug McKean asked:

>          Green Cu oxide shows up on socket pins after about three
>          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.

>          Is this as simple as the wash not being monitored properly?

Possibly. Sometimes it is very difficult to remove flux or dilute flux
rinse solution from washing from under or within molded plastic DIP
sockets, but it may be no more than a normal "corrosive" process you see
(normal from the view it is not a matter of chemical attack).

>          I'll listen to anything as technical as anyone wants to get
>          from proper p.c. fab methods to the chemistry behind it.

It won't hurt my feelings a bit if you don't.

Are these sockets tin-lead or gold plated? I would question the protective
plating itself, review the cleaning process, and perhaps look at an "open
frame" version of the socket so that the cleaning difficulty is reduced -
more water can enter the contaminated area, and the dilution of the flux
activators would be increased.

Another opinion is that you should have a mondo-power turbine air knife on
your water cleaner (as powerful as your ears can stand) which would blast
most all the water from the board as the boards exit the cleaner.
Effectively this is a physical removal of residual water which is still a
dilute solution of your flux activator. My rule of thumb is that I should
be able to tap the edge of the board firmly and see no visible water come
from beneath any parts as the boards come off the conveyor. I advise you to
run your wash conveyor as slowly as you can tolerate for the rate of
production you have.

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.


regards,

Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com/