Electrochemical migration behavior of Lead-free solders

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Dr. Illés Balázs György
Department of Electronics Technology

In normal operating conditions, if a moisture condensation occurs or a thin water film formes on the cunductor-dielectric-conductor surface, the electrochemical migration (ECM) phenomenon can cause a short failure in the electronic circuits. The model of classical ECM has been known a long time ago, but this phenomenon get more importance with the miniaturization trends in the electronic industry.

Under certain conditions the metal ions can migrate from anode to cathode and the metal ions forming dendrites after metal deposition. The dendrites can cause short-circuit between the cathode and the anode. A lot of factor have a significant impact on the process of electrochemical migration such as contaminants or magnitude of potential gradient.

The ECM susceptibility was investigated on six lead-free solder alloys (SAC305, SAC405, SAC0807, SAC0307, Sn42Bi58, Sn42Bi57,6Ag0,4). The investigation were carried out by water drop test, where NaCl and Na2SO4 solutions were used as electrolytes, hence these salt solutions are the most common contaminants in the electronic circuits. The ranking of ECM susceptibility of the investigated lead-free solder alloys was determined. Furthermore Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy investigations were carried out on dendrites. The detailed results of SEM-EDS and ECM susceptibility rankig of the lead-free solder alloys were preseted in this document.


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