SMTA International Conference Proceedings

In House Dross Recovery- Do You Know What You Are Putting Back in Your Solder Bath?

Authors: Mitch Holtzer and Jason Fullerton
Company: Alpha
Date Published: 9/27/2015   Conference: SMTA International

Abstract: Over the last 3 years, several large OEMs and CEMs have purchased inexpensive equipment to melt entrapped metal from solder dross skimmings, and returning this material to their wave soldering or selective soldering systems. This results in a significant reduction in the volume of bar solder consumed. With the still increasing trend towards lead free utilization and higher pot temperatures, dross management becomes a greater issue.

In this process, small ingots of solder are produced by using pressure to separate liquid metal from the oxide/metal mixture skimmed from the solder bath. After the entrapped metal is removed, the remaining oxides are returned to solder suppliers for further recovery. Analysis of these ingots show that there is a significant change in the ratio of tin/silver in SAC alloys, and the ratio of tin/lead in Sn63 alloys. This means that the ratio of tin to silver and tin to lead may be changing in the wave or selective soldering pots.

Analysis of the amount of dross included in the ingots produced using this method was compared to a number of commercially available brands of bar solder. Data indicates that the lack of post treatment of this recycled material results in an order of magnitude increase in the amount of included dross.

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