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Poor coverage of copper parts in stannous sulfate tin bath

My problem involves poor coverage of copper parts in our stannous sulfate tin bath.The problem seems to have come on quite suddenly but perhaps this is because we don't use this bath on a daily basis.

Our parts are rack plated and there seems to be tin throwing to the lower portion of the parts but bad or none to the upper, especially around the contact point of the rack and parts. I am suspecting we need to add a brightener or some type of additive, but don't have information on analysis to determine type and amount(s) of additives. All of our known analysis information shows no problems. Your help would be greatly appreciated.

THANKS!

Benigna Skorobogatiene
electrical components mfgr. - San Jose, California

A hull cell panel will tell you plating range of the bath. It will also tell you if something is interfering with the throw. Once you know the range the tank is plating best in try adjusting the current density. Check your Copper level...it will rise rapidly from dropped parts and start to poison the bath.

Jim Conner
- Salisbury, Maryland

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