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Nodules in Nickel Sulfamate Electroforming
adv.
September 3, 2008
Q. Hi,
We are playing around with manufacturing electroformed nickel stencils. We have had some very good success with the process to a point. However we have come across a problem that we are unable to solve.
Some details :
MacDermid BARRETT SNR-24
S-Rounds for Anodes
Mandrel = Brushed Aluminum SHIM ( type unknown )
The solution is filtered through 10 micron filters.
The Nickel is plating to the mandrel, it is fairly uniform and we are pleased with the
plating, we plate to about 0.005" We get no premature de-lam or blisters. And the Nickel
Peels from the flat mandrel very nicely. We are very happy with the surface that was against the mandrel.
The problem is that the plated surface, is getting "nodules" forming on the surface, it seems to happen fairly quickly within the first hour of plating. These nodules continue
to plate as the time goes on (obviously). And we don't know where they are coming from.
Please help me as best you can, I really need to solve this issue. My knowledge of electroplating is moderate at best. I'm fairly experienced with PCB manufacture and the plating that involves, but the nickel is new to me.
Do we need to filter more?
There seems to be a relation between the current and the amount of nodules that form. The higher the current the MORE there are / not necessarily bigger, but definitely more.
The mandrel does not show any of these nodules, before plating, or anything that would cause them. They are well brushed and cleaned before dry film, expose and develop.
They are also disposable so it's not that.
Any ideas anyone?
Regards
Richard
Plating Shop Manager - Auckland, New Zealand
A. Nodules in electroforming are a real pain... The most common reason is inadequate filtration - I would recommend filtering through
1 micron or even 0.5 micron filters and have a tank turnover rte of about 10 TT/hr. You must also keep your environment clean, there is no sense in filtering if the atmosphere is full of dust - clean the atmosphere!
You say the nodules are on the surface of the electroform - are they on the edges of the photoresist or are they in the middle of the nickel deposit? If they are in the middle, it is almost certainly a filtration issue, but if they are on the edge of the resist, it could be due to poor imaging and rough edges. Perhaps a couple of photos would help...
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
September 5, 2008
A. In addition to what Trevor said, there is a possibility that the brushed surface is raising tiny post like stumps in the prep steps as some of the material is removed. A dummy part that you could closely check with a 10X glass would prove or disprove this thought.
I love filtration. If you go to a 1 micron filter, you will need to significantly increase the filter area and a major increase in the HP of the pump.
You will need a pressure gauge and pressure/flow charts to determine what your true flow is. Filter companies rate their equipment with a new filter and water, so do not believe the ratings on the box. As the filter plugs up, the flow rate drops drastically. I will guess that you do not have a true 10 turnovers an hour.
- Navarre, Florida
September 9, 2008
Q. Hi,
Thanks for your reply, we found that the problem went aways with double bagging the anodes. I think the ones supplied we're not filtering the nickel deposists enough. Double bagging solved the problem. :)
On another issue now, we are trying to improve distribution of the plating across the sheet.
Are there any tips to improve distribution? We are finding the end further aways from the jig is plating at a faster rate than the end connected to the jig. We rotate this half way in order to try balance this, but still find that one end gets thicker than the other.....
Plating Shop Manager - Auckland, New Zealand
September 12, 2008
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A. Your jig is acting as a thief or robber. Insulating it would allow that end to plate more, but then you have to find out how much of a dog bone effect you will get. A true robber or shields properly placed will even out the plate. Increasing agitation will also help to reduce the dog bone effect. Eductors work well for this. James Watts- Navarre, Florida September 15, 2008 A. I have to admit I am having a problem visualising your problem - perhaps you could submit a diagram or photograph of what you mean. The most common reason for for differential plating thicknesses or rates is a difference in localised current densities. This can be controlled or modified by using screens or robbers to divert the current flux and give a more uniform thickness. However, it is also possible to have differential plating thickness by having different rates of solution agitation on the workpiece. By the way, if the workpiece has differential distances between it and the anode, you will also see differential plating thicknesses. Trevor Crichton R&D practical scientist Chesham, Bucks, UK September 15, 2008 |
Q. I am currently experiencing a nodule problem with our Nickel forming process - Watts type formulation. Chemical balances are in order with appropriate filtration, electrolytic purification and Carbon treating. pH is maintained @ 3.8-4.2
we are plating about 0.5 mm to 5.00 mm thickness
- Bangalore, Karnataka, India
February 6, 2012
A. Hi Sathya,
Please check article below regarding pits and nodule because sometimes these two defects are related to each other or can solve in the same troubleshooting.
www.finishing.com/468/18.shtml
regards,
- philippines
April 19, 2012
A. Sathya, clearly something is not right. Nodules are caused by a variety of reasons, including poor filtration, bath contamination, incorrect bath conditions (e.g., too high pH, too high current density). My best guess would be too high current density and poor filtration, so start with those and then systematically work through the other options. What happens if you use the electroforming solution in a clean beaker [beakers on eBay or Amazon] in the lab?
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
May 1, 2012
adv.
"The Sulfamate Nickel How-To Guide"
by David Crotty, PhD
& Robert Probert
published Oct. 2018
$89 plus shipping
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