Metal finishing Q&As since 1989

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Acid copper plating on zinc die castings equals stardust pitting

May 6, 2009

Hi, I'm having a problem with my plating. I am getting a stardust pitting look over the whole casting after acid copper. I've pretty much ran out ideas on how to fix it.

I can't tell you whats causing it (obviously) but I can tell you whats not causing it. Its definitely not the casting itself, because the pitting is on all the castings. It doesn't look like pits in casting either. It looks like a contamination issue, but I can't feel anything with my finger. I've also eliminated all washing and acid activator issues that could cause it.

More agitation in acid Cu seemed to help today. I am also wondering if the copper cyanide strike chemistry could cause it.

Any advice is appreciated!

Albert Puchany
Plater - Bend, Oregon

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First of two simultaneous responses -- May 8, 2009

Albert,
It is always helpful to know all the steps up to and including the problem phase.

How does the part look after the cyanide copper stage?

You say increased agitation helps, are you sure you are not burning instead of getting stardust? It might also be that the increased agitation is reducing the tendency for for solid matter in the tank to first settle on then come off the part.

Since the information is so limited here are some "standard" areas to look at:

1. Tank should be filtered through a 20 micron or less polypropylene media with flow rate of 2 tank turnovers per hour or more. Note that when the tubes start to cake the flow rate is reduced.

2. Anodes should be bagged with either woven or napped polypropylene bags that have been leached in advance.

3. You should be using low pressure air from a blower. Check and see that the filter on the blower has been properly maintained. Use a sparger design that spreads air evenly (as much as possible) over the tank area without impinging on the work. The idea is to move solution that is in contact with the work surface and the anode surface, not to "boil" the solution.

4. Periodically carbon filter solution.

5. Bath may be low in make up additive. (have vendor check or run hull Cell)

6. Bath may be high in chloride - have vendor test and run a full analysis of bath

7. High maintenance brightener - contact vendor, carbon filter add dilute hydrogen peroxide as recommended by vendor.

Without seeing parts these are the areas I think you should be investigating. Also look and see if debris is falling into the tank from the ceiling or if a tank lining is crumbling.

Gene Packman
process supplier - Great Neck, New York

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Second of two simultaneous responses -- May 9, 2009

DEAR SIR,
REFERRING TO YOUR PLATING PROBLEM, I SUGGEST POTASSIUM BASED CYANIDE COPPER WITH ROCHELLE SALT [on eBay or Amazon] INSTEAD OF SODIUM
BASED.

SUNIL GADHIA
- RAJKOT, GUJARAT, INDIA

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Hi Albert,

Probably time to run some Hull cels and start skipping some steps. 1st run an as is cell with your strike the acid copper and see if you can reproduce it on a panel. I'm guessing from the limited info you gave that your acid copper is contaminated. Talk to your vendor and see, but in my experience they are about the easiest bath to clean up with carbon or peroxide/carbon

Godd Luck

Trent Kaufman
electroplater - Galva, Illinois
May 11, 2009

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May 17, 2009

Dear Albert,

try to give a flash of dull nickel before copper plating, increase the concentration of wetter or just go for mild buffing after copper plating if you are not looking for bulk production.

Regards,

Shafiuddin A. Mohammed
metal coating shop - Dubai, United Arab Emirates