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topic 0061

Passivating an electroless nickel tank

A discussion started in 1995.
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Hello,   I'm in charge of electroless nickel/immersion gold line in a PCB shop. I've some problem with Ni plate-out after running the bath for few days. We are using stainless steel tank with a sump tank for heating up & circulating the bath. We also install some sort of anodic protection for the tank. My questions are:  

1) How to minimize or prolong the onset of the plate-out?

2) What is the best way to leach & passivate the tank? With nitric acid, what should be the desirable strength & at what temperature. What about the rinsing after the leach?  

Well appreciate your advise & help. Thanks.   Regards,

Bab Hui
Process Engineer 

The purpose of the anodic protection unit is to prevent plate-out onto the tank, and it should have detailed instructions for how to set the current to do so.

Such units are, I believe, available from Atotech and Palm International.

The usual idea behind leaching is to expose the tank material to a solution which has the same capability for absorbing contaminants as the working solution will have, but for the leaching solution to not introduce any new contaminants to the working solution. So room temp or slightly warmer nitric acid sounds good to me--but why not just go ahead and follow a QQ-P-35 [link is to free spec at Defense Logistics Agency,] nitric acid passivation procedure on the tank itself.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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