Corrosion investigation of lead-free solder alloys

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Supervisor:
Dr. Medgyes Bálint Károly
Department of Electronics Technology

The work aims to investigate corrosion behavior of different micro-alloyed lead-free solders [(99Sn-0,3Ag-0,7Cu-0,05Ni (SACxPlus0307) 98,4Sn-0,8Ag-0,7Cu-0,1Bi (SACx0807), 98, 5Sn-0,8Ag-0,7Cu-0,05Ni (SACxPlus0807) 90,95Sn-3,8Ag-0,7Cu-3Bi-1,4Sb-0,15Ni (InnoLot) and the 96,5Sn-3Ag-0,5Cu (SAC305)] as refrence used in the electronics industry. The electrochemical measurements were carried out with a three-electrode (working electrode, Pt counter electrode and calomel reference electrode) cell, in a 3.5 wt% sodium chloride medium to simulate the sea water. The corrosion properties of the samples (solders) were investigated by open circuit potential (OCP) and potentiodynamic polarization test methods at different scan rates (30, 60 and 300 mV / min). Each measurements were carried out at 25 ° C and under atmospheric pressure. From the potentiodynamic polarization curves different corrosion parameters (such as corrosion potential, corrosion current density, passivation and critical current density) could be obtained. The corrosion ranking established, was based on the passivation current density. InnoLot showed the highest passivation current dendsity, while SACxPlus0307 showed the smallest current density using the scan rate of 300 mV/min. In case of 30 and 60 mV/min scan rate Innolot also showed the highest passivation current density. However, SACxPlus0807 showed the lowest value in case of 30 and 60 mV/min. According to the Tafel equation InnoLot has shown the highest corrosion rate at each scan rates. In other words Innolot showed the highest susceptibility for corrosion compared to other microalloyed solders including SAC305 (reference) as well. Scanning electron microscope method was also applied to investigate the surface changes of the solders caused by corrosion.

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