Scott,
Initially, it sounds like a candidate for Cu diffusion through the
Ni to the surface, especially as you say that you were finding trace
amount of copper in the bad connectors, and that those bad parts have
a thinner plated layer. However, do you have the facility to look at
the surface with something like an AES (Auger Electron Microscope),
XPS (Xray Photo Spectrocopy, (sometimes called ESCA)) or any of the
other low penetration techniques?
In a previous job I used to get a similar problem, with parts being
returned for a black layer over the complete Ni-P plating (I thought
it kind of pretty but the customer did'nt agree) and these parts could
be returned from anything within 2 days to 10 months. This drove me
nuts for almost 4 months as I could find no obvious reason, At first
glance SEM/EDX showed that there was a trace of Cu in the bulk plated
layer, and I immediatly jumped at the Cu diffusing through and
oxidising. I increased the plating layer, to increase the diffusion
distance as this effectively removed the Cu and I still got a problem
when running trials. Management were unwilling to spend the money on
some serious analysis so the problem continued until it suddenly
stopped, it was subsequently assumed that it was related to the DBC
batches as the problem stopped when the batch ran out, but it returned
4-5 weeks later.
I could go on for hours about the trials ran on this, but the crux
of it was that the DI water in the final rinse stage was reacting with
Ni-P layer. I used to live in the North East of the UK where the
water is real hard (Calcium etc), and ion exchange columns in the DI
plant used to last three weeks and not the predicted 6 months. Due to
the crap logistics from our materials guys, I eventually found that we
had to run exchange columns for a couple of weeks after their normal
replace time, and that we were washing in a mildly corrosive DI water.
This was attacking the Ni-P and subsequently leaving it open to
attack during service. If the ion columns are old enough you can wash
a clean Ni-P layer and make it go black immediatly!
I dont know if this is the same thing for you, but, take a look at
the quality of the DI in your tanks, and the frequency of the ion
columns changes, see if there is a pattern with the occurance of the
problem. A chemist friend said that it could be sulphides on the Ni
making the black tarnish, so the low penetration analysis techniques
could pick them up, or at least indicate other possible sources
(failing that, tell the customer its a cosmetic feature at no extra
cost, the random nature nature could make it a kind of collectors
edition, and actually increase sales)
Good luck
Roger
(PS. Mr Fenner, the joys of the old days while working at the "Wely",
alas sadly no more)
Roger Massey
Materials Technologist - Europe
Motorola AIEG
______________________________ Reply Separator _________________________________
Subject: [TN] Oxidation on a Connector
Author: "TechNet E-Mail Forum." <[log in to unmask]> at #email
Date: 12/04/99 09:02
Hi All,
We have a BNC connector that is put through reflow and wave solder with
water washes after each soldering operation. The customer has been
returning some product because the BNC connectors are turning black in
the field.
Cross-sectional and SEM/EDS analysis show that the connector has a
ferrous base-metal with copper overplate. Nickel is plated on top that
contains about 5%phosphorous. The "bad" connectors have a Ni thickness
of 0.1mil and the "good" connector has Ni thickness of 0.2mil. A trace
of copper was detected on the "bad" connectors (about 1%).
What could be causing the black oxide? Could it be copper oxide from
solid state diffusion of the copper through the nickel barrier? Other
ideas?
Some of the units were in the field for 6 months to a year.
Thanks
Scott
************************************************************************
*****************************
Scott M. Severson
QA/FA Lab Manager "Space and
Time
are not
conditions in which we live,
Benchmark Electronics Inc. but modes in which we
think."
4155 Theurer Blvd.
Winona, MN
55987
---Albert Einstein
(507)452-8932
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