With the introduction of lead-free assemblies, many sources of lead bearing material have to be eliminated from the wave soldering process. OSP coating over bare copper are quickly becoming a replacement for traditional hot air solder leveled (HASL) board finishes resulting in a trade off between a potential source of lead contamination and a potential source of copper contamination. As lead-free wave soldering becomes more widespread, questions have been raised over increased solder pot maintenance brought about by the high copper dissolution rates of lead-free alloys.

During long periods of operation, some lead-free alloys begin to show sluggish behavior in the solder pot. This is caused by a buildup of a copper-tin inter metallic (CuSn) that forms at the bottom of the solder pot. The problem didn't exist with standard tin-lead wave soldering because the copper-tin inter metallic floats and can be easily removed.

In a standard tin-lead wave pot, as impurities such as copper build up them form inter metallic with the tin. Reducing the temperature of the solder pot, allowing the pot to sit idle for a few hours, and skimming the top surface can easily remove the inter metallic. The method works quite well since the density of the copper-tin inter metallic (CuSn) is 8.28, and tin-lead (SnPb) is 8.80, allowing the copper-tin inter metallic to float. Periodic maintenance of a tin-lead solder pot can easily maintain copper levels between acceptable ranges of 0.15-3.0%. With the increased use of tin-copper or tin silver-copper lead-free wave solder alloys, the situation changes since the density of both alloys is less than that of tin-lead As a result, instead of floating on the surface where it can be easily removed, the copper-tin inter metallic sink in lead-free alloys and are dispersed throughout the solder pot.

In addition, some lead-free alloys dissolve copper at a faster rate than tin-lead. The effect can be a higher rate of copper build-up and contamination of the solder pot. The result can be the need to dump the solder pot more often, or a complete changeover of the pot. Studies suggest that solder pots containing lead-free alloys may have to be dumped when the copper contamination levels reach 1.55%. Above this point most lead-free alloys become sluggish and above 1.9 to 2.0% damage can result to the impeller, baffles and solder pot. Practice has shown many lead-free alloys because corrosion to the base metals used for solder pots, impellers and baffles because of aggressive nature of tin at high temperatures. The surface of many base metals such as stainless steel or cast iron generally show signs of pitting and start to dissolve after prolonged contact with lead free alloys. This leaching process releases iron (Fe) particles resulting in increased iron content and contamination of the solder alloy.