Corrosion caused by incorporation of drag-out?

A. More likely corrosion of the underlying nickel through porosity in the gold. A somewhat thicker gold layer may solve the problem. Jeffrey Holmes, CEF Spartanburg, South Carolina A. Hello Steve, It sounds as though you did your homework on this problem. Yes, I have seen solution entrapment cause this very problem. The plater I was working with at the time had to install air agitation ⇦ huh? spargers in the bottom of the 2 rinse tanks after Ni plate and drag out rinse. They then went into a Ni activator, double cascade rinse, pure Au strike, then Au plate. It's important that the post Ni rinses are of a cascading type to minimize Ni concentration. Low current density areas on the bellows shaped part may also be low in Au plating thickness causing a porosity problem. Are the spots confined to one specific area on the parts, or are they sporadic? If they are sporadic I would suspect rinsing practices. Good luck! Mark Baker process engineer - Malone, New York A. Dear Steve, This may be due to diffusion. Increase thickness of Gold layer. If it is economically viable, try to plate a flash under coat with palladium as a barrier layer. If you think it is due to entrapped Ni soln., then try to introduce a final DM water rinse with continuous flow and vigorous air agitation. Also increase the rinse time in this tank Regards T.K. Mohan plating process supplier - Mumbai, India

Q. Thanks for all the insights. if I'm looking at incorporation of drag-out (i.e. particularly the low pH chlorinated nickel solution), is it possible that porosity of the nickel could be reduced such that the only significant drag-out is superficial and easy to rinse off? how does one increase density / reduce porosity in a sulfamate nickel?

A. Hello again Steve, Incorporation of a Ni dragout rinse couldn't hurt. To answer the second part of your question, as long as you are not co-depositing contaminant metals on the Ni deposit and rinsing practices are adequate, corrosion should be nonexistent. The porosity you are experiencing is coming up through the Gold layer. The least expensive way to tackle this is to improve rinsing, and as mentioned already by respondents, is to increase the gold thickness to reduce porosity. In the unlikely event that none of this works, a pure gold strike under the final gold plate will help reduce porosity as well. Good luck! Mark Baker Process Engineer - Syracuse, New York A. Steve It is not that the nickel layer is porous but the gold layer is porous. Please read and understand all the answers carefully. Regards T.K. Mohan plating process supplier - Mumbai, India Q. The nickel is in fact porous. I've seen it. Pressurizing this part without the external gold yields a pin-cushion effect ... hundreds of tiny holes. Adding a gold layer seals the part, apparently by plugging the holes in the nickel. What has yet to be addressed is the possibility of incorporation of low pH chlorinated plating fluid within the apparently open lattice of the nickel layer, and whether any resulting reaction between this fluid and the metallic nickel can produce hydrous nickel chloride on exposure to air. Secondarily, what process changes (e.g. additive / current density) might yield a denser nickel without the intragranular spaces which (hypothetically) might be trapping plating fluid? Steve Yon [returning] - San Diego

Although I am not familiar with your gold/nickel/copper/nickel electroforms, I am familiar with single layer nickel electroforms and nickel-cobalt electroforms that successfully test for helium tightness let alone air tightness. So if these bellows are like pincushions until the gold plating, it does seem to indicate faulty electroforming

Luck & Regards

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Hi again Steve,
You speak of hydrated Ni Chloride in the lattice. Firstly, Sulfamate Ni does not contain Ni Chloride. What type of bath is used for the bellows type electroforming? If it is sulfamate Ni, keeping the pH on the low end will improve ductility of the deposit, but the current efficiency drops off some. Get the facts from the Ni bath supplier regarding the use of leveling and wetting agents. You are not giving us accurate information on the plating chemistry that is used, so it is difficult for us to help you.

uses of leveling agents, wetters, etc

Mark Baker
Process Engineer - Syracuse, New York

Q. The manufacturer tells me that small amounts of chlorine are added. This is to aid dissolution of the anode material. Additionally, Schlesinger & Paunovic ⇦ on on Amazon or eBay [affil links] clearly state (pg. 173) that without chlorine, a sulfamate solution requires sulfur-containing anode material to avoid anodic oxidation of sulfamate anions. I've had enough materials experience to know that sulfur incorporated into the electroform produces undesirable mechanical properties.

The 'Nickel Plating Handbook' published by the OMG group states (and this is mirrored in Schlesinger and Paunovic) that HYDRATED NICKEL CHLORIDE can be present at up to 10% of the sulfamate concentration. If you don't know the answer to this question, fine, but please don't impugn my understanding of the chemistry or physics.

The Sulfamate Nickel How-To Guide
by David Crotty, PhD & Robert Probert

Nobody impugned your knowledge of chemistry or physics, but your response to a very knowledgable plater, who DOES know and is trying to help you is out of line, Steve! Four electroplating experts are telling you that your understanding might be wrong but that there aren't enough facts on the table yet to be sure. Nickel sulfamate plating baths often have no chlorine in them and rely on sulfurized nickel anodes for anode corrosion (although organic sulfur compounds sometimes used as brighteners may be incorporated into the deposit, this elemental sulfur is not).

Unfortunately it can be difficult to deduce the nature of a plating problem solely from a description of some of the features of the finished product.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Very well put Ted, thank you. Steve, I respect the knowledge that you have and the material you have resourced. When you mentioned hydrated Ni chloride and "low pH chlorinated solution", this leads me to believe it was a nickel sulphate solution that was being used. I admit I don't have all the answers, I just try to help fellow platers utilizing the information that is furnished in the inquiry. I hope you solve the problem. Mark Baker Process Engineer - Syracuse, New York A. Steve/Mark/Ted Steve wrote You can possibly incorporate low pH (other than the pH of the plating bath, in the plating bath) plating fluid. If at all it is possible, then you have to incorporate it on the outside of the plated surface.It can be Nickel chloride and HCl mixture which will give lower pH. As such a reaction is probably not possible to produce hydrous NiCl2 on exposure to air to fill in the pore. All these sound good as hypothetical answer to your hypothetical question. Regards, T.K. Mohan plating process supplier - Mumbai, India

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