Pits on ground electroless nickel plating
Q. We are plating an Inconel 718 shaft with electroless nickel to 0.0035-0.0040" thickness. The part is then ground to 32 microinch finish to a specified runout tolerance. The plating looks good as-plated but we have numerous pits(<0.050" diameter) after grinding. These pits sometimes have "comet tails" after grinding. We have tried some of the following "back to the basics" techniques: vertical shaft orientation in the bath, Scotch Brite after vaporhone, de-smut nickel strike anode, remove Cu contamination from strike bath, lacquer over edge of tape mask, change EN tank liner, higher air pressure into EN air bubbler manifold, and bumping the rack every 15 minutes.
Any suggestions?Steve [last name deleted for privacy by Editor]
Let me recommend getting a copy of "Electroless Plating" Edited by Mallory and Hajdu. It has numerous reference pages on pits and pitting. Obtain thru American electroplaters and surface finishers society. They have a link on this site.
To me, it sounds like inclusions, IE: not enough filtering or not fine enough filtering. As I understand, it has no pits after plate. Does it have very tiny bumps. You will have to look very close for these. After grind, do the swirls have tails up or to the side from the agitation? Without seeing the parts and the operation, it is really hard to troubleshoot
Why are you grinding after EN? You should be able to control EN to a tenth, or two at the worst. If you start out with a little bit better than a 32 finish, the EN should give a 32.
Why so much EN? Not knowing the engineering reason , it seems unnecessary, especially over 718. Better product and less cost by tight initial machining tolerance and then plate to size and finish. Less plating cost and it deletes a second machining. You have to have a very good bath and take excellent care of it, to not get pits in the surface after plate, when you put on 0.005 per side, especially when you "push" the rate to the high side of the bath's plate rate.James Watts
- Navarre, Florida
A. The most back to basics I can get, when I hear "comet tails" is the surface tension of the solution. Gas pitting can occur at an inclusion in the steel, where the hydrogen overvoltage allows gassing, perhaps until the nickel can sneak up around the hole and fill it from the side. Then maybe the adhesion is not great, and it pops off in grinding?
What is the surface tension of the solution?
A. What kind of EN are you using, high,mid or low phosphor? For thick deposits I would recommend a mid phophor DULL EN. The bright ones tend more to pit.
I agree with Jim that filtering is very important. Also pay attention to quality of water used.
chemical process supplier
August 25, 2017
We are fabricating semiconductor parts and we using copper as raw material. Then after machining, it will proceed to plating process PS 1033 Electroless nickel plating, the target Plating thickness is .0015-.002" thick.
Our problem is massive pits after plating. Can you give us recommendation for this?
- calamba city, philippines
August 25, 2017
A. Hi Jovelyn,
First things I look for when I hear pitting are filtration and agitation. What's your filter bag size, pump's turnover/hour, and what's your schedule for changing bags? Are you currently using air agitation? There is definitely an art to dialing in the proper amount of agitation.
Two mils is a lot of nickel and you can run into some coating issues when you get that high. You can try running the bath at a slightly lower pH or activity to slow the plating rate down a bit. This more controlled deposition can alleviate some pitting issues. Word of caution if you need to go this route: it will most likely increase your phos content. Double check your spec to make sure its acceptable.
- Springfield, Massachusetts USA
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