Wave Solder Dross Contamination

We have a problem with out tin/lead wave soldering system.Dross particles are sticking to the PCB and some are not found during visual inspection, but detected during in-circuit test. The solder pot has a turbulentwave and a laminar wave and no nitrogen supply is used. The system has a wax cage to protectpump shafts. The wax cage uses specialmineral oil. What could be the cause of the contamination and how can we prevent it?

H.R.

Expert Panel Responses

Several process issues could cause dross sticking to the board. One being solder pot maintenance, dross may form on the walls orat hot spots in the solder spot or the impeller region. So here regular cleaning of the solder pot can reduce dross frombeing carried out of the pot via the impeller system. Temperature should be keep to lower limits if possible in 63/37the limits are 465-500F for lead-free it is 510-540F. Lower temperatures create less dross within the pot and impellersystem. Using solder withlower impurities levels also helps since some elements enhance dross formation.Regular analysis is recommended.

Peter Biocca
Senior Market Development Engineer
Kester

Mr. Biocca was a chemist with many years experience in soldering technologies. He presented around the world in matters relating to process optimization and assembly. He was the author of many technical papers delivered globally. Mr. Biocca was a respected mentor in the electronics industry. He passed away in November, 2014.

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