Anne;

Where the Cu is exposed, and how much will affect reliability.  Also the type
of mating connector design and type will affect this.

Here's the scenario;

the Cu corrodes, forming various compounds with sulfur and oxygen, and
Chlorine.  Cu Chlorides "plume" so they are among the worst (ie they grow).
These compounds are hard to break through for the mating connector, also, they
have a higher resistance than the Au.  The result is an open circuit or an
increase in the resistance between the two contacts.  The higher the change in
resistance, the greater the probability that it will eventually go full open,
even if only in a sporadic mode.

Except for the comoning tails beveled edge, we allow no exposed Cu greater than
a few mils of an inch in its largest dimension, in the wear track critical
contact area as defined by the connector supplier (for a wiping connector).

We've done a lot of Mixed Flowing Gas testing on connectors.  Exposed Cu is
bad.  Not at time zero, but  a few years down the road, and you've got a
problem.  Environments with higher humidity and temperature accelerate the
problem. A lot of the time, what happens is the corrosion products build up
near the mated contacts but not exactly between them.  given some shock and
vibration the contacts move a bit, land on the corrosion products, and well,
you've got yourself an open contact in the field.

Battell Labs (sp? lost their card)  Has performed a lot of this type of testing
also.

One other "bad" point.  Cu and Au adjacent to each other can create a galvanic
cell in the presence of certain fluids (particularly enchants).  So, the
interface area of the copper etches away very quickly when it is exposed right
next to Au.  This can cause etched off circuits.


(technical fanatics and chemists, please forgive my layman's explanations)

Jim Herard
KBL, Product Quality Engineering
IBM Microelectronics Endicott
t/l 857-7026

---------------------- Forwarded by Jim Herard/Endicott/IBM on 08-06-97 06:41 PM
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Subject: [TECHNET] Exposed Copper on Gold Fingers Reliability

     Hi.

     I am looking for some leads or information about reliability data/concerns
     with exposed copper on gold fingers.  Please share what you have available.

     Thank you,
     Anne Trujillo