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Pits in Nickel/Gold Plating

+++++++

Hi to All,
We encountered PITS AND NODULE here in our plant although all the parameters are in the target range. We change our carbon filter every other day, we had an air agitation in the line, We performed dummy plate before the production, we add wetting agent regularly (as per tds), the bath concentration are all in the target range (as per supplier or tds specification) before the production proceed. The hullcell test appearance have pits in the High Current Density. If we make some hullcell test labscales by adding wetting agent, the pits in the hullcell test was eliminated but when the production qualify, the parts or the circuits HAD PITS.
Can anyone give some idea or suggestions how to eliminate or get free from the pits? How and where pits occur? Is pits and nodule had a relationship? Is there any prevention that can suggest to eliminate the pits aside from the above mention?

Regards,

Joy De Luna
engineer - Philippines


+++++++

Have you considered ditching the carbon filters? They'll remove the wetters, and may be a source of nodules if the filter quality is poor. You might try going to a plain polypropylene filter with no or removed sizing. Make sure that the filter is suitably fine for your operation...I never used filters coarser than 10 micron absolute.

totter James Totter, CEF
- Tallahassee, Florida


+++++++

Hello Joy,
Pitting can be caused by different factors. Usually caused by hydrogen gassing or oil / grease introduced to the solution, or poor cleaning. If it is a hydrogen gas bubble, the pit will usually have a tail (from the gassing). This is most noticeable in the high current density area. Certain measures can be taken.
1) Use an air blower, not compressed air for agitation. If compressed air, it should be oil free.
2) Check above the tank, make sure no grease or oil can drop into tank. Be sure no oil is floating on pre - plate tanks (drag-in possible).
3) Be sure anode bags are clean, come up above the solution level, and tied around the anode hooks.
4) If you are still using air agitation, check with your supplier to be sure you are using the proper wetting agent. The wetter varies from air agitation to solution agitation.
5) Investigate your cleaning cycle, do a water break test after cleaning.
Nodules are normally caused by poor filtration whereby particulate matter is suspended in solution. Nodules and pitting are not related.
It sounds like you are running a lot of carbon packs in the bath. Carbon polishing should only be done periodically. You could be filtering out an additive that you need. Good Luck!

Mark Baker
Process Engineer - Syracuse, NY USA


+++++++

Hi Mark/James,

I have some followed up comments or condition about this pits in nickel sulfamate plating line. What is the effect in the bath if addition of antipitting agent is in excess of required amount? Because during our labscale the amount required as per tds is not enough to eliminate the pits in the line.

Did the organic contaminants cause of pits? If any, what is the major one?

Regards and thank you,

Joy de luna
- Philippines


+++++++

Joy,
The main cause of pitting is hydrogen gas adhering to the surface during plating.
Make sure you have adequate bath agitation, and are employing the proper current density. Also make sure the boric acid concentration is within range. Organic contamination generally is not the cause of pitting. Is your supplier helping you with this problem?

Mark Baker
Process Engineer - Syracuse, New York


+++++++

Hi Mark

Thank you for the immediate respond.

Yes, our supplier help us in this pits issue.

Our boric acid concentration is on control range(43- 47g/L), this was base on the supplier specs. Right now, we minimize the pits in the line, the adjustment we've done were increase the agitation(FYI, we use mechanical agitation), increase the addition of antipitting agent(base on labscale) due to continuous carbon filtration.

Mark, as the result of our mapping, we have more pits on the bottom of the bath compare to the top (this was done without adding antipitting agents). By the way, the appearance of the pits is like shinny small circle.

We don't have acid cleaner because were processing flextronics black cover coat, is this ok? Continuous carbon filtration is our preventive action in cracking issue. What can you suggest?

Joy De Luna
- Philippines


First of two simultaneous responses -- +++++++

Joy,
James Totter had a good point in his response back on October 26th. I agree with him on his filter advice. I also believe that carbon polishing (filtering) should only be done periodically. Mechanical agitation is ok, but you also may need more adequate solution agitation, along with good filtering methods. Carbon filtering should not be used as a method to remove particulate matter. I have seen some cases where the same carbon packs were used too long, and carbon granules escaped into the bath causing pits. Because the pits are round with no gas swirls I would suspect particulate matter. You also have to have clean anode bags tied up above the solution level. Let us know how you make out.

Mark Baker
Process Engineer - Syracuse, New York


Second of two simultaneous responses -- +++++++

Hi,

also strong over dose or dis-balance between organic additives, especially the secundary brightener can cause pits. Also, if you observe that the main area of pits is the bottom line check also the inlet of your pump (maybe sucks somewhere air) and also, if you have air agitato, check in which direction the air agitation is. Recommended is a pipe which has holes in an angle of 45° degrees in direction of the bottom. Be aware that the agitiation is not going to affect close to the anodes.

Saludos,
Dominik

Dominik Michalek
- Mexico City, Mexico
+++++++

Hi Mark/James,

Until now we don't have any problem on the line and we already control the pits although some times it appears but we don't take it risk before we make action. We use 7 microns of carbon filter and the carbon polishing is now periodically ( 3x per week).
The big factor that I think it was a big help for us your advice. Thank you for that.

What do you mean by adequate solution agitation? What particulate matter do you pointing out? Is there any way to determine the particulate matter? How did it occur?
In mechanical agitation, Can you please give me some advice, what required parameters can we use to improve our plating line (ex. Flowrate, power pump, etc.)

Again, thank you for your respond.

Regards,

Joy De Luna
- Philippines


+++++++

Specific recommendations on filtration/mechanical agitation depend upon the physical plant as much as the process and parts involved. I still kind of think 3/week carbon polish is somewhat excessive, but that would depend upon exactly how you do it and how big the tank is, etc.

Some small rules of thumb I've used: You need to size pumps to provide about 4 tank turnovers per hour. I've generally used about a 3 cm stroke for mechanical part agitation, and sufficient air to raise the solution level 3 cm (air might/might not be appropriate, depends on the wetters).

James Totter, CEF
- Tallahassee, Florida

February 1, 2008

I understand that without the Carbon filter, the plating parts will have crack issue which normally result from organic contamination. However, doing Carbon treatment will not only remove the contamination but also the wetting agent as well.

However, there is a carbon filter that removes organics selectively. It will only remove the contamination while still retain your wetting agent and brightener. This product is from Japan.

You can try to use the special carbon filter continuously to remove the organic contamination while still maintaining the additive and wetting agent. This filter works well with some products but you will need to test it out with yours.

Note that wetting agent only help to prevent the pit issue, you will still need to consider the agitation and other factors too.

Robin Chua
chemical supplier - Singapore


December 10, 2009

Hello.

This response (inquiry) is a bit late but here it is anyway.

Sir Robin Chua: Do you happen to know the maker of that carbon filter that selectively removes organic contamination only, and not the additives?

We're planning to set a frequency of carbon filtering our plating solution - was looking for ideas and found this thread.

All the best.

Melchor Gapayao Jr.
Semiconductors - Laguna, Philippines


December 11, 2009

Hi, Robin; hi, Melchor. Even better would be to get a patent number or an explanation of what they are claiming. Some brighteners are removed by conventional carbon filtration, some are not; some breakdown products are removed, some are not. It would be great to get a technical handle on what we're talking about here. Thanks.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

December 13, 2009

Hi Melchor,

This product is manufactured by Japan.

I am not too familiar of the theory of this specific cartridge but it is supposed to remove a specific range of organics. Although this product is designed to selectively remove organic contaminants, it will still remove some good organics (brightener) in your solution. This product is normally used only in the Nickel plating process.

Good Luck.

Robin Chua
freelance advisor - Singapore

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