Metal finishing Q&As since 1989
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Nodules in Electroless Plating
2005
What are the main reasons for formation of the nodules in Electroless nickel-plated parts?
We have been dealing with this problem for over a year now. First time this problem appeared year ago when nodules were observed on parts made from two different machine shops but plated at the same plating shop. This is an intermittent problem that comes and goes. We have tried to duplicate the problem on purpose to understand the root cause but do not have any success.
We need help in understanding reasons behind formation of nodules and what types of precautions should be taken to eliminate them. Our intent is to understand the mechanism and create a specification for our plating suppliers.
Our main business is designing of semiconductor test equipments and we have very limited experience with plating processes.
Semiconductor test equipment manufacturer - Petaluma, California, USA
First of two simultaneous responses --
You do not say what the parent material is. A cause would be microscopic burrs on the surface. If it was grit blasted, I would suspect embedded particles. A caustic soak will remove some of the aluminum oxide, but will take longer to get the really deep larger particles. Note that caustic soak will not attack sand or silicon carbide.
James Watts- Navarre, Florida
2005
Second of two simultaneous responses -- 2005
Dear Mr. Desai,
Nodule formation is a common feature in electroless plated deposits. The rapid formation of nuclei and subsequent growth of the electroless nickel deposit promotes the nodular feature. When the plating rate is high, nodule formation is quite evident. This is due to the fast supply of atoms which enables the nodules to grow preferentially in the
Z-direction than the X- and Y-directions. Besides, the surface diffusion of adatoms could also be inhibited to a certain extent by the rapidly arriving atoms.
I believe that the problem is not with the machine shop (assuming that the pretreatment and activation stages are similar in both cases) but mostly with the plating bath and accelerators and stabilizers in the plating bath.
It has been reported in some research reports that electroless Ni-P coatings obtained with the use of lead acetate is very smooth.(Caution: Lead-containing plating baths are being phased out).
Try to reduce the plating rate - It will help to avoid the nodule formation to some extent.
T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
(ed.note Nov. 2017: The good doctor has a fascinating blog at https://advancementinscience.wordpress.com)
2005
Narayanan's reply is somewhat misleading. Nodules in EN do not form on their own. There will be particle of something at its center that has initiated it. The particles can come from many different sources: dirt and debris from the air, blasting or grinding media, machining damage, tank plateout, dirty water, NiP particles from an overactive or old bath, poor cleaning, etc.
You should try to identify the source. Cross sectioning a nodule on a part is difficult, but may show the source, especially if you have access to EDAX. If the nodules are all on upper surface, it is called shelf roughness and usually due to particles from the bath settling out on the parts. If the nodules are all over the surface, they probably originated with the parts before they entered the bath.
Good luck!
Ron Duncan [deceased]
- LaVergne, Tennessee
It is our sad duty to note Ron's passing on Dec. 15, 2006. A brief obituary opens Episode 13 of our Podcast.
Hi Desai, I agree with Ron Duncan there are many reasons for roughness which may lead to nodules depending on your thickness. Have you tried to plate a bent 90 degree panel for shelf roughness.
Sridhar Bushigampala- Toronot, ON, Canada
2005
2005
Dear Mr Desai,
There are two aspects one has to consider.
1. You have mentioned that the nodule formation on the part - intermittent one.
Is the nodule formed was microscopic or macroscopic. Since once a while you are facing this problem, I will suspect only the component. In this I agree with Dr. Ron Duncan.
2. When the nodule has been observed microscopically, that means it is due to bath composition, pH and operating temperature. As Dr Naryanan rightly pointed out deposition rate plays an important role and it depends on the bath constituents. There are some stabilizers like Thiourea [on
eBay or
Amazon], lead compounds, arsenic in ppm level may inhibit the nodule formation.
Wish you all the best.
- Bangalore, Karnataka, India
I am having an issue with multiple outside vendors. We manufacture a core coil that is a low mag iron (12L14) that has an id of .049". And due to cost restrictions, we must barrel plate the items. We have been receiving this parts back from our customer with the following rejection:
Parts have nodules/nickel particles through inside diameter.
So far we have tried cleaning the parts even better here to ensure no particles left inside parts. We have done 100% visual inspection on all pieces and the vendor even tried wiring to no avail.
What would be the cause of this and how and what are my options to help alleviate this issue as I barely make any money on the part as it is!
Thanks in advance for your comments/suggestions!
Swiss Machining - Palmdale, California
March 24, 2011
De-magnetize the parts prior to plating. Improve bath filtration.
G. Marrufo-Monterrey, Mexico
Monterrey, NL, Mexico
First of two simultaneous responses -- March 27, 2011
Assuming that your parts are clean and that the plating bath is well filtered, then the likely source of the particles is nickel plate that has deposited on the interior of the barrel or dangler and then has broken off from the tumbling of the parts.
A visit to your supplier and visual inspection of the danglers and the barrel interior should reveal if this is the source, or not.
consultant - Cleveland Heights, Ohio
Second of two simultaneous responses -- March 28, 2011
We are starting to see the nodules that this post is referring to on some of our Electroless Nickel plated parts per ASTM B733 Cls 4 SC3 on Aluminum 6061-T651. We also use several outside processors. We have a variety of ways we deburr these parts prior to the electroless nickel plating process. We use glass beads during a wet blast and we also process via vibratory tumbler using plastic composite media and urea formaldehyde. From the responses I have read, it sounds like I may have a cleaning issue with both the way we clean prior to platers and with the way the platers are processing. We are seeing imbedded and easily dislodged nodules in varying sizes and locations.
Julie Derby- Yankton, South Dakota, USA
November 10, 2011
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