|
letter 061
Passivating an electroless nickel tank
-----
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 our supporting
advertisers 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-35C [link is to spec at TechStreet]
nitric acid passivation procedure on the tank itself.
|
|

Ted Mooney, P.E.
finishing.com
Brick, New Jersey
|
-
-
 |