Consumption of Soldering Iron by Pb-Free Solder

The consumption of a soldering iron by Pb-free solder is examined and the kinetic analysis of the reaction between the solder and the soldering iron is discussed. The consumption of the soldering iron increases with prolonged contact time between the solder and the soldering iron. No thick reaction layer is detected at the solder/soldering iron interface at the position where fused solder is removed by compressed air cleaning. However, at the position where fused solder remains, a thick reaction layer is formed. In particular, a thick FeSn2 reaction layer is observed when fused solder sticks on the surface of the soldering iron for a long time. On the basis of the reaction kinetics, the growth rate of the reaction layer is demonstrated to be controlled by iron diffusion through the reaction layer. The mechanism of soldering iron consumption by Pb-free solder is as that a ~30$ nm-thick layer is formed during one soldering process and then flaked off from the surface of the soldering iron during compressed air cleaning.