Relationship Between Leaching Behavior Of Metal Elements From Solder Alloy And Electrochemical Property

As connecting material, Sn-based solders are commonly used in electronic packaging industry. During the landfill treatment, metal elements will leach from discarded electronic devices and could result in the contamination of groundwater and environment. With the trend of miniaturization of electronics, the amount of bump is becoming larger. Spontaneously, the effect of joint on the corrosion property of solders can’t be ignored. Therefore, it is important to research the corrosion behavior of solder and its joint with substrate in simulated soil solution.In this paper, the corrosion behavior of Sn-0.75Cu solder and Sn-0.75Cu/Cu joint in3.5%NaCI,1%NaCl-2%Na2SO4and simulated soil solution of1%NaCl-2%Na2SO4-0.6%Na2CO3was investegated by leaching and potentiodynamic polarization methods. After corrosion testing, the morphology and phase composition of samples surfaces were observed by SEM and XRD. The effects of the composition of solution and Cu substrate on the corrosion of Sn-0.75Cu solder were analyzed. And the relationship between leaching behavior of Sn and characteristic parameters of electrochemical corrosion was discussed. The following conclusions were obtained:(1) The leaching behavior of Sn element from Sn-0.75Cu solder and Sn-0.75Cu/Cu joint suggested that the leaching amount of Sn was increased with the increase of leaching time. Largest leaching amount of Sn from Sn-0.75solder and Sn-0.75Cu/Cu joint was detected in1%NaCl-2%Na2SO4-0.6%Na2CO3and3.5%NaCl solution, respectively. In the investigated solutions, the leaching amount of Sn from Sn-0.75Cu/Cu joint was larger than that of Sn-0.75Cu solder. Thick and loosen corrosion products formed on the surface of Sn-0.75Cu solder and Sn-0.75Cu/Cu joints, where the leaching had severely occurred. Moreover, the corrosion products were composed of large amount of Sn4(OH)6Cl2and small amount of SnO and SnCl2.(2) The polarization curves indicated that the corrosion resistance of Sn-0.75Cu solders in the3.5%NaCl and1%NaCl-2%Na2SO4solution was better than that in the1%NaCl-2%Na2SO4-0.6%Na2CO3solution. After polarization testing in the3.5%NaCl and1%NaCl-2%Na2SO4solution, needle-like or fossa-like Sn3O(OH)2Cl2was observed on the Sn-0.75Cu surface, however, no product was found on the Sn-0.75Cu solder after it was polarized in the1%NaCl-2%Na2SO4-0.6%Na2CO3solution.(3) The influence of Cu substrate and temperature on the corrosion behavior of Sn-0.75Cu solder was studied-taking the3.5%NaCl solution as example. It was found that galvanic cell formed between Cu substrate and Sn-0.75Cu solder, and the corrosion rate of Sn-0.75Cu solder was accelerated by Cu substrate. Consequencely, large amount of Sn leached from Sn-0.75Cu/Cu joint. Within the temperature of35-65℃, there was no obvious change in the resistance of Sn-0.75Cu solder, however, the corrosion rate of Sn-0.75Cu solder increased rapidly with the increase of temperature. And the activation energy of corrosion was about37.2kJ/mol.(4) The leaching result of Sn-0.75Cu solder was in accordance with the corrosion current density that obtained from polarization curves. In particular, the fastest leaching rate of Sn meant higher corrosion current density in1%NaCl-2%Na2SO4-0.6%Na2CO3solution.