Leaching Behavior Of Solder Alloys And Their Joints

Solder is normally used for electronic packaging, as a result this has produced an ever-increasing electronic waste (E-waste) stream, which has generated concerns regarding the E-waste's potential for adversely impacting the environment. Electronic waste, including discarded electronic equipment, concerns have been posed on the high toxicity of Pb, while sufficient concern should be paid on other heavy metal elements in solders, if the heavy metal elements in electronic waste were corroded, they will migrate with the leaching solution, finally arrive into the environment. Studying leaching of toxic substances in electronic waste in landfill is important to the assessment of their potential impact on the environment.Leaching behavior of heavy metal elements from Sn-3.5Ag-0.5Cu, Sn-9Zn, and Sn-37Pb solder and their joints were investigated in typical acid, alkaline and saline corrosive solutions. It was found that a large leaching amount of Sn was observed for Sn-9Zn and Sn-37Pb solder joints in each testing solution and significant leaching of Sn could only be detected for Sn-3.5Ag-0.5Cu solder joint in NaCl solution. The amount of Zn and Pb leached into the solutions were much more than that of Ag and Cu.When the samples were treated in 3.5%NaCl solution, it was found that the corrosion resistance of Sn-9Zn solder was the worst of all, the corrosion resistance of Sn-3.5Ag-0.5Cu solder was the best. When the samples were treated in NaOH solution, it was found that the corrosion resistance of Sn-37Pb solder was the worst of all, the corrosion resistance of Sn-3.5Ag-0.5Cu solder was the best. When the samples were treated in H2SO4 solution, it was found that the corrosion resistance of Sn-37Pb solder was the worst of all, the corrosion resistance of Sn-3.5Ag-0.5Cu solder was the best.The leaching kinetics of Sn in liquid solutions for solders and their joints at periodic in the range 15-60 days were investigated. The leaching amounts increased as periods increasing, but increasing rate constant tended to decrease.In order to investigate the corrosion mechanism of solders, M342 electronical testing systems was used to obtain the polarization curves of solders in corrosive solutions. Electrochemical test results validate the leaching test results, and electrochemical test results show that when the Sn-37Pb, Sn-9Zn, Sn-3.5Ag-0.5Cu alloys were treated in 3.5%NaCl solution, there were passive phenomenon, wider range of passivation at low temperature, while active dissolution in the acid and alkaline solution. By using SEM and XRD, the morphology and phase composition of the corrosion product on the solder surface were analysed. The corrosion products on the surface of solders and their joints are composed of oxide, oxide hydroxide and oxychloride of the component element. And the products of the samples treated in NaCl solution are found to be thicker than that in NaOH and H2SO4 solutions.