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How do I make citric copper plating smooth

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Q. I am using citric copper plating solution to plate copper film on a CVD copper film. the citric copper solution are mainly made of trisodium citrate and copper sulphate, pH is controlled between 4-5 by NaOH and H2SO4. the deposited film is very rough. how do I make this film smooth. thank you very much in advance.

Jingjia Ji
- Sydney New South Wales
March 10, 2023

A. Hi Jingjia. I've seen a couple of articles and patents, plus a number of youtube videos, dealing with citric acid based copper plating ... but I've never seen it actually used for serious purpose. I'm not saying you don't have a good reason, but can I ask why you are using this home-brew rather than a conventional copper sulphate based copper plating solution?

If the plating is very rough I'd guess that you are plating at too high a current density -- what voltage and amperage per square inch are you using? But there are other causes for roughness like lack of anode bags, lack of filtration, inadequate agitation, or lack of brightener. Do you happen to have a Hull Cell to enable testing your plating solution across a range of current densities? Thanks.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. Dear Ted,

Thank you very much for your kind reply. I am developing a less corrosive copper plating solution than sulphate based copper plating solution. it seems Citric base copper solution is a good alternative. However, I don't get film property what I wanted, or too rough surface to be useful. Do you know any brighteners may be applied in the citric based copper plating solution?

thank you very much.

Jingjia

Jingjia Ji [returning]
- Sydney New South Wales
March 10, 2023

Miralax

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A. Hi again Jingjia. Hobbyists in youtube videos often suggest polyethylene glycol (Miralax) →
as a brightener for citric-based copper and other plating, but if you are doing serious development work on a marketable plating solution, you should probably do a detailed patent search, plus a thorough technical database search as a starting point.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Dear Ted,

Thank you very much for your suggestions.

Jingjia Ji [returning]
- Sydney New South Wales
March 10, 2023

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