Reduction of dross formation during wave soldering using lead-free solders

To reduce the dross formation rate during wave soldering, the addition of trace elements in to lead-free solder and the development of a new equipment have been investigated. The dross formation test was conducted by using a small wave solder bath maintained at 250/spl deg/C and also the test was performed on a wave soldering machine for production line scale. The small addition of germanium and also phosphorous reduced the dross formation rate of Sn-3.5Ag. Chemical analysis of dross revealed that the trace elements added concentrated in the dross, about 2/spl sim/9 times higher than the added amount for germanium and more than 4.5 times for phosphorus. The main oxide of dross was found to be SnO, and the oxygen content of dross is about 5 at %; that is about 90% of dross is constituted from metal. To reduce the dross during wave soldering operation, a new instrument attachable to wave soldering machine was evaluated. About 50% reduction of weight of dross was achieved by using this instruments.