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Error in analysis of total cyanide in citrate gold bath




We are trying to control the cyanide in our citrate gold bath. The analysis shows less than actual value. We tried analysing total KCN in a 200 gpl citrate water mixture. We got a value of 5 gpl. Is the citrate reacting with citrate and no CN radical is left? adding more KOH in titration does not change the result.

Anil Kher
Plating shop PCBs - Goa, India
July 21, 2009



Anil,
When you refer to a citrate gold bath, do you mean hard acid gold bath? These baths do contain potassium citrate and citric acid . Is the bath cobalt or nickel brightened (hardened)? These baths are commonly used on printed circuit boards and in some cases pure gold is used. If the bath is a hard acid gold, analysis of total cyanide is not necessary. The gold salts contain cyanide (potassium gold aurocyanide). When you plate the gold out, a lot of the cyanide is oxidized at the anode. When this particular bath is made up, no free cyanide is needed. Also, free cyanide would raise the ph of the bath and break down the plating resist, if the bath comes in contact with it. Let me know if you are using a different bath than I mentioned.

Mark Baker
Fellow Plater - Syracuse, NY, USA
July 30, 2009




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