Corrosion investigations on a lead-free solder alloy contaminated by NaCl using different concentrations

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Supervisor:
Dr. Medgyes Bálint Károly
Department of Electronics Technology

The goal of the MSc degree’s work is the corrosion investigation of two type of lead-free solders, a micro-alloyed lead-free (90.95% tin – 3.8% silver – 0.7 % copper -3% bismuth – 1.4% antimony – 0.15% nickel) and a reference (96.5% tin – 3% silver – 0.5% copper) which have been widely used in the electronic industries. The electrochemical measurements were carried out in a cell with three electrode (working electrode, Pt counter electrode and a calomel electrode as a reference) in various concentrations of sodium chloride. The corrosion properties of the samples (solder alloys) were investigated by potenciodynamic polarization measurements. Measurements were carried out at 25 degree of Celsius and under atmospheric pressure. I prepared ingots from the solder paste for the investigation. I polished and cleaned their surface before and after the polarization test. From the potentiodynamic polarization curves different corrosion parameters (such as corrosion potential, corrosion current density, passivation and critical current density) can be obtained. According to the latter parameters, I have made comparison from the corrosion point of view at various concentrations of solutions. Samples were also investigated by scanning electron microscope, which show the morphological changes on the surface and the cross-section. Finally, I have also carried out some energy-dispersive x-ray spectroscopy (EDS) to determine the elemental composition of the corroded layers.

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