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Specific gravity reduction of silver solution

2004

My company does leadframe electroplating that uses silver cyanide solution for the main plating chemical. The silver solution supply system has developed with circulation process (2000L silver solution involved). For your info, herewith contents composition for our process
[Ag] >= 100grm/L
Free cyanide 4-5 gram/L
Temperature 65 °C

In order to maintain silver and FCN contents, we are using S-940 Replenisher chemical and silver cyanide. Other non-silver chemicals are leveler, conducting salt and brightener. Those chemical additions are fully based on condition. Now, we have a problem about specific gravity (SG) rising which is making our plating times tend to be longer; then our machine runs at low speed and low machine utilization. In normal condition with above contents composition is about 1.20-1.23. However, it grew to 1.28-1.30. Based on my experience, another impact of this condition was crystalizing tendency when the temperature drops. During my observation, higher SG contents came from accumulating foreign material into the solution. So, we we're trying to partially treat those silver solutions as follows:
- Concentrated solution with heat up
- Crystallization and separation between crystal & supernatant
- Dilution those silver crystal
- Analysis with HULL CELL test method
- Peroxide 20% (2mL/L solution) 2 hr - activated carbon 5 micron 4 hr filtration and sediment final filtration.

But the SG reduction is not significant. Could you please to give us another/alternative method for SG reduction?

Dave Marindra
Electroplating - Lobam, Bintan Island, Indonesia

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Dave

The possibility of carbonate Build up exists which tends to slow down plating and push up density. Carbonates crystallise out of solution when temp is reduced by chilling to any level below 7 °C. Use a chiller , and cool down say 20 percent of the solution in a separate tank or drums. .m When the temp is below 7 Centigrade , hold it there for an hour so all the carbonate crystallises out. Retn the sol'n to the bath or to a separate tank. repeat the exercise. You will end up with a lower density and enhanced sol'n efficiency. Check your supplier is not selling you carbonates in the silver salts used too.

Regards,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
2004