Summary for brown spots over gold plated ss Discussion
Brown spots over gold plated SS parts were reported on SS-303 connector parts plated with bright nickel and a thin gold topcoat, with the discoloration appearing after a few days and not on every batch. P. Gurumoorthi’s first guess was that the nickel underlayer was too thin and porous. Anders Sundman later suggested that a neutralising dip and better passivation of the nickel could help, because brown spots may come from atmospheric corrosion aided by trapped moisture and chemicals, and he pointed to porosity in the gold deposit as a likely issue. In a later related exchange, Celso de Souza described gold over sulphamate nickel and noted the plating was outsourced, while Sara Michaeli added a key practical point: stainless steel needs a gold strike when plating on SS. Overall, the thread points to substrate preparation, nickel porosity/passivation, and proper strike layers as the main areas to check.
2004
Q. We are one of the connector manufacturers in India and do gold plating (0.6 microns) over SS-303 parts as per the customer spec. with a under coat of Bright Nickel of 7-8 microns.
We observe after few days, a brown growth / spot in the gold deposit, which increasing /grows day by day.
Also this problem is not existing in all the batches.
The process sequence, we follow is
1. Caustic soak for 2 hrs. (60-65 °C)
2. Anodic (10-12 V) for 10 minutes.
3. Cathodic (10-12 V) for 5 minutes.
4. sulfuric etch, anodic (10-12 V) for 3 minutes
5. Wood’s Nickel strike
6. Bright Nickel
7. Gold plate
Can any one suggest what went wrong and remedial solutions and advise where we need to concentrate? Thanks
DHANASEKAR. D
Connector Manufacturer – CHENNAI, TAMIL NADU, INDIA
A. From this distance and vantage point, all I can do is play the odds. First guess is the nickel plating is too thin and porous.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
2004
A. From the description of your problem it appears that there is porosity in your Nickel Deposit which is showing up, look at the possibility of plating a 0.2 micron deposit of Palladium prior to gold plating, this should help solve the problem. Also I hope you are using a Acid Hard gold process which uses Cobalt or Nickel as hardener.
Best of Luck,
P. Gurumoorthi
electroplating process chemicals – Chennai, Tamilnadu, India
2004
A. Mr Dhanashekar
The following may help.
1) A neutralising dip using a proprietary product.
2) Porosity in gold deposit needs closing and the Nickel below needs passivation so that the brown spots don’t occur due to atmospheric corrosion aided by left over entrapped dampness and chemicals.
We can be of help if you wish.
Regards,
Asif Nurie [deceased]
– New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
2004
Q. We have been finding the same issue, but with BeCu C173. Could it be the same root cause?
Celso de Souza
– Danbury, Connecticut
March 15, 2013
A. Hello Selso,
Before we can help you it would be beneficial if you could list your process steps. We wouldn’t be able to tell if the Ni is too thin without knowing what current density and plating time you are using, or known deposit thickness. It would also help if you could let us know if a full analysis on the Ni bath has been completed recently including Fe and Cu contamination levels. Please advise.
Mark Baker
Process Engineer – Mesa, Arizona, USA
March 19, 2013
A. Hi,
It’s migration.
The porous thin nickel layer is the problem.
To get a thin layer without migration, use pyrophosphate copper as a strike.
Regards
Anders Sundman
4th Generation Surface Engineering
Consultant – Arvika,
Sweden
March 23, 2013
March 27, 2013
Q. Hi Mark and Anders;
Mark;
We use 30 to 50 microinches of gold (MIL-G-45204) over 10 to 20 microinches of Sulphamate Nickel electroplated. It is a customer requirement and it is been used for many years. In terms of plating process I do not have the details, since we outsource all plating processes. The plating bath supplied by our source did not show issues.
Anders;
I heard about “Migration” before, but I’m not sure what it means in terms of electrochemical process; I’m a mechanical engineer, not really familiar with the plating processes.
Just as a note, I was on the phone with Sweden when I got the notification about your reply.
Thanks, guys, for your help.
Celso de Souza
– Danbury, Connecticut, USA
A. You need a gold strike when plating on SS.
Sara Michaeli
Tel-Aviv-Yafo, Israel
April 3, 2013
adv.
