Effect of ionic contamination on climatic reliability of printed circuit board assemblies

The effect of NaCl and weak organic acids (WOAs) in “no-clean” wave solder flux residues was studied on electrochemical migration (ECM), leakage current, and corrosion on surface mount chip capacitors using a test printed circuit board assembly (PCBA) substrate having known chip components. The investigations were performed under environmental conditions varying from non-condensation with 60% RH at 25°C to near to condensation with 98% RH at 25°C, and full condensation conditions.

Near to condensation and full condensation conditions have been established by (i) lowering the temperature of PCBA while keeping the temperature and relative humidity constant inside the climatic chamber and (ii) applying single micro-droplets of water on the surface mount chip capacitors. Water layer formation on the PCBA was observed in-situ by introducing a video camera inside the climatic chamber.

The ECM probability testing under droplet condition showed dependency on the type and amount of ionic contamination. Climatic testing of the test PCBAs pre-contaminated with NaCl and solder flux residues showed the importance of hygroscopic nature of ionic contamination to corrosion and leakage current due to water adsorption on the surface.