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How to analyze the organic contamination in the soft Ni/Au plate bath

In the soft(bondable) Ni/Au plate, the photo resist(dry file) is used to pattern plate. The plated golden surface has discolouration from time to time. I doubt the Ni or Au plate bath is organic contamination. How can I check the bath if it is organic contamination. My Au plate bath is Cyanide.

Henry Zhu
engineer - Guangdong, China
2007

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2007

Henry,
Soft bondable Au plating formulations are usually of a neutral ph and referred to as neutral golds. You will throw responders off by calling your Au a cyanide Au. The Au salts (for Au metal) can be potassium gold aurocyanide. These salts are also used in acid golds as well. If it was a Cn bath you would have free Cn in the make-up. The photo resist would likely break down if it was.
Because organic contamination can stem from so many different causes, a person with a organic chemistry doctorate would have trouble finding it. The best way I know how is by running efficiency tests on the plating bath in a lab setting. For a given current density and time you should achieve a given thickness, providing all the other parameters are in spec such as gold concentration, temperature, ph, conducting salts, etc. If you see a drop in efficiency it usually means you have either organic or inorganic contamination. It is natural to have a small amount of organics in the bath. When the cyanide is oxidized at the anode (from the Au salt) during plating it forms cyanate, which is an organic. Regular carbon polishing with carbon filter tubes keeps the organics at bay. The frequency would depend on production from the bath of course. Your gold supplier can give you a treatment schedule based on your production. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York