Dross, a byproduct of wave soldering, is often thought of as waste, a residue that forms on the surface of a metal from oxidation that looks bubbly and is filled with metal impurities. This mass of solid impurities floating on molten metal in wave solder machines can be removed from the process, and recycled by shipping to the recycling site of an outsourced processor or in-house using specialized equipment. With the use of lead-free alloys, the need to recycle now has a monetary consideration as well. EVS International's Simon Norman gives a concise comparison of in-house or outsourced considerations based on the experience of TT electronics plc.
There are a lot of companies that provide help with dross. EVS solder recovery systems (www.solder-recovery.com) are said to be able to recover as much as 75% of solder from dross by weight in a 10-minute cycle. Since a clean wave system is the goal, this is one way to add efficiency and eliminate waste. And there are others as well.
Greeley, Colo.-based FCT Recovery (www.fctrecovery.com) works with customers on recovering metals from dross. Customers ship leaded and lead-free dross to FCT and the processor pays them a competitive price for this recyclable scrap.
Los Angeles, Calif.-based P. KAY Metals (www.pkmetals.com) has a material called MS2 that does not mix with solder, but is added to the solder to eliminate dross formation. This is said to substantially lower waste formation.
Other factors affect the amount of dross produced. Denis Barbini, Ph.D., of Vitronics Soltec (www.vitronics-soltec.com) explains that optimizing the wave solder operation so that pot temperature and wave turbulence are in spec creates less dross in the first place. He adds that this should always be the first step in dross control. The less dross produced, the lower the waste recycling need.
Other experts mentioned excessive flux on the PCB, which is carried into the wave, contributing to dross production. A nitrogen blanket over the solder pot also helps control dross creation by lowering oxidation. There are many ways to attack the problems related to dross, so how could I leave out the literary method?
Limerick to Dross
EMS had a problem with dross,
Which caused a considerable loss.
Outsourced or inside,
Where the problem resides,
Must act like a rolling stone that will carry no moss.
Gail Flower, editor-in-chief
See comments on this article from dross expert Ray Chartrand, in his letter to the editor. Click Here