Abstract:Leaching behavior of Sn from Sn-3.5Ag-0.75Cu solder alloy and its joints with Cu substrate in three types of simulated soil solutions, namely NaCl, NaCl-Na2SO4 and NaCl-Na2SO4-Na2CO3 was investigated. It was found that serious leaching of Sn in the NaCl-Na2SO4-Na2CO3 solution was observed for the Sn-3.5Ag-0.75Cu solder, while for the Sn-3.5Ag-0.75Cu/Cu joint the largest leaching amount of Sn was realized in the NaCl solution. Thick and loosen corrosion products formed on the surface of solder and its joints where the leaching had severely occurred. From the XRD analysis, it revealed that the corrosion products were mainly composed of SnO, SnO2 and Sn4(OH)6Cl2. Based on the potentiodynamic polarization plots, it was proposed that the galvanic corrosion between solder alloy and Cu substrate was responsible for the leaching difference between solder and its joint.