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Hard gold plating efficiency drop

December 1, 2010

Hello to all,

I assist a reel-to-reel connector plating company and we noticed an interesting problem.
The connectors are plated with Co-alloyed hard gold.
It is important to reduce process variation as much as possible, in order to be able to plate at the lowest possible average value, still guaranteeing the required CpK for the gold layer thickness.
We notice that during a production run, the efficiency of a typical acid oxalate based hard gold bath gradually drops over time, although [Co], T, [Au] and pH are kept constant and no contaminants are analysed. To give you an indication, we nearly have to double the amperage within days.
What is puzzling is that after a day of not using the electrolyte, the efficiency comes back to the original starting level.
Anyone having an idea what could be the cause and, more important, what can be done to keep the efficiency a constant level?
Thank you for your help,

Harry van der Zanden
- Budapest, Hungary

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December 2, 2010

Harry, here are a couple of suggestions:

1. Make sure that the specific gravity of the plating solution is also held constant.
2. Check the anodes and make sure that there is no gold on the anodes as this will reduce the efficiency
3. check for stray currents - make sure the rectifier output terminals are floating and not grounded

Hope this helps

Pat Mentone
St Paul, Minnesota

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December 5, 2010

Hi Pat,

Thank you for your reaction, please allow me to comment.
1. Make sure that the specific gravity of the plating solution is also held constant.
--> Over the few days this phenomenon occurs, the Be is constant.
2. Check the anodes and make sure that there is no gold on the anodes as this will reduce the efficiency.
--> We use platinised Ti.
3. check for stray currents - make sure the rectifier output terminals are floating and not grounded.
--> This is the case, no stray currents, no grounding.

Any more suggestions are welcome, maybe it has something to do with dissolved oxygen / hydrogen?, but I hope someone has besides the theoretical explanation also some practical remedy.

Best regards,

Harry.

Harry van der Zanden
- Budapest, Hungary