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Why has lead content of solder bath increased?

We have a solder bath facility in our PCB making shop. The bath was prepared on Apr 2010.
At that time the solution has 17 g/l of tin, 11 g/l of lead. We do use 63:37 Tin lead anodes. The anode area is 684 Sq cm each. Total six anodes are used totaling 4104 Sq cm. The anodes were immersed even during non operation. We operate 8 hrs X 5 days per week.

We didn't operate the bath for about a month in April. After that we analyzed the solution , We found Tin(Sn++) is around 18 g/l(Total Tin content is 34 g/l) & the lead is 17.56 g/l.

Whether keeping the anodes immersed always will increase the lead to this level due to galvanic difference ?

The bath capacity is 250 l .

Saravanan R
Employee - Trivandrum, Kerala, India
May 13, 2011

Are you sure no-one has made any additions to the tin-lead bath? It is most unusual for a bath to go from a 63/37 to a 50/50 tin/lead. Is there any evidence of the anodes dissolving and if so, what do they look like?

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
May 16, 2011

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