Problems with thick Electroless Nickel Plating (>40µm)

A. If it is not feasible to electroplate economically, try thermal spray technique. There are job-shops providing the service.

A. Pinhole free high phosphorus type EN coatings are possible, but require that the substrate also be free of defects (like pores and inclusions) that will initiate pinholes or other coating defects.

EN coatings of 250 - 300 µm are commonly plated for salvage of worn or mismachined parts without difficulty. With these thick coatings it is helpful to mechanically agitate the parts during plating, along with general air agitation of the solution.

A. As properly stated by Mr. Duncan pin holes generally come from existing superficial defects. Also, from gas bubbles that adhere to the plated surface (then they look bottom-rounded and bright), from solid particles in the bath due to improper filtration, poor chemistry or poor processing practices. In general, if the corrective measures are not taken, the same results may be expected from an electrolytic NiP process.

A. Over 1.5 mils of EN, though quite possible, is not very common. Brass is also not a very common substrate either. It is not catalytic to the reaction for it is more electropositive than the nickel ion. So, you need to start it first to attain good adhesion. A professional and reliable start would be to preplate strike your parts in a conventional Watts bath. Alternatively, a brief electric kick as soon as the parts get into the EN bath using an inert anode may work. Something else, if your substrate has lead, its presence over the surface may also be a problem.

A. John, you do not say what sort of brass you are using - if it is free machining brass it probably contains lead and this can cause lead smear and problems in coverage. I am surprised you have to go as thick as 30 microns to get a continuous coating - I would normally expect to get a continuous coating in about 5 microns of electrolytic nickel and perhaps a bit more (up to 10 microns in electroless), especially if the bath isn't agitated and gas bubbles removed. However, there are so many variables with these processes, it is difficult to generalise. Brass is not easy to initiate for electroless nickel, so you may need to give it a gentle poke by starting it with some gentle cathodic polarisation; once the electroless nickel bath is going, it will keep doing so. I do not fully understand why you need such thick electroless nickel - perhaps you may want to consider using electrolytic nickel, which is quicker and cheaper. Furthermore, you can plate directly onto brass once it has been correctly cleaned and activated.

A. Pores or pitting is sometimes an issue with simple low cost EN formulations, more so when plating thick layers. Review what Mr. Crichton pointed out but also check for a pore free formulation with your actual chemicals vendor or go out for shopping somewhere else.

A. Talk to your vendor's tech services! You should be able to plate 42 with no problem with a proper bath and proper plating operation. You can expect to run into a few problems when you try to go over 50 and a lot of problems with a simple bath at over 60.
Get the vendor involved. They tend to get real interested when you say that you will have to switch to another vendor if they can not solve the problem. If you do not like what they say, talk to another vendor and see what they will guarantee.

A. The Wood's Nickel could be contaminated with organic materials. In this case you will have to filter with activated carbon.

A. Hi John,
What is the thickness that you are aiming for? There are other methods to coat nickel which can give a thickness above 50 microns.

A. A lot more detail of your set up is necessary to get a meaningful answer from this site.

What are your pre-treatments?
What is the typical plating rate?
What is the analysis of the tank like? Are you seeing high variations in nickel and/or pH?
How many metal turnovers (MTO) do you run to?
What sort of filtration and agitation do you have?

Pinholes can be caused by many things such as poor agitation, lack of wetting agent, pH imbalance...

Roughness is usually caused by inclusions in the coating, such as dust or nickel "seeds".

Take some time to give more detail and I'm sure you will get something to help you.

A. Brian gave a very complete answer for the information given.
The chemistry is something that you should be maintaining a tight control over. With that as a given, improving the filtration should help. Improving the agitation will definitely help.
The "nickel seeds" intrigued me. How often do you strip your tank?

A. A huge amount of this depends on the company that manufactures the EN solution and what their ops sheet calls for.
My experience with 2 high P EN would say that your temp is a wee bit low, and your plate rate is a bit low. Our pH was a tiny bit lower than yours, but it all depends on the formula for the EN.

Oil less air agitation would probably give you more metal turn overs and probably a better plate rate. It is not that expensive and it is mandatory for some formulations as well as beneficial for any formulation that I have heard of.

We could plate to 45 micron with no problems, but had some problems over 55 microns. (skip plating)

A. Nickel strike is a must for good adhesion.

In order to be able to plate a thick deposit, you MUST operate your solution with a slow plating rate like 4-5 microns per hour.

To prevent pitting use a wetter. Ask your vendor for an appropriate wetter.

A. Sara and I have been at this site a long time and we rarely disagree, but I will this time.
First, ideal plate rate depends on the chemistry of the solution.
On the 2 high P EN solutions that I used, the bath would try to self destruct at that plate rate. The costs of the extra time for labor, lab, electricity and etc would make it very expensive.
The lowest that we used was about 15 per hour and typical was 25 per hour with zero problems to about 50 microns.

A. Jim,
It is rare to plate 50 microns when the plating speed is 15-25 microns per hour.

The plating rate is not only a function of chemistry. You can lower the plating rate by lowering the pH, temperature and Nickel concentration.

A. I guess that our tanks were like bumble bees which do not know that aerodynamically, they cannot fly, so they do.

We rarely plated less than 30 and normally 45 thickness and did it at 20 to 25 per hour.

Drip additions, lots of air, good temp control and pH control.