Damage of Stainless Steels by Erosion in Molten Pb-free Solder

The damage of stainless steels in molten lead-free solder was investigated by the cross sectional observation of damaged area of stainless steel. The damage is caused by dissolution and reaction between molten solder and solid stainless steel. The inhomogeneous damage was observed in cross sectional observation, therefore, the maximum damage depth was defined as the maximum erosion. The increase of the immersion time enhanced the maximum erosion. The dissolution rate of Sn-Ag based lead-free solders were almost three times higher than in the conventional Sn-Pb eutectic. The addition of Cu, In and Bi to Sn-Ag gives only a little effect on the erosion. The use of Sn-Zn system lead-free solder enhanced the maximum erosion. SUS 309S with higher Cr and Ni was found to reduce erosion to some extent. The eco-design of flow soldering bath is considered