Impact of NaCl Contamination and Climatic Conditions on the Reliability of Printed Circuit Board Assemblies

The effect of climatic conditions and ionic contamination on the reliability of printed circuit board assembly has been investigated in terms of leakage current (LC) and electrochemical migration susceptibility. The change in LC as a function of relative humidity (RH) and temperature was measured using single components (size 0805) and surface insulation resistance comb patterns precontaminated with sodium chloride at levels adjacent to levels used in the IPC J-STD-001 standard.

The potential bias of 5–10 V was applied during experiments, and the climatic conditions were in the range 60%–98% RH and 15 $^{\circ}\hbox{C}$ –65 $^{\circ}\hbox{C}$. The variation of RH at the surface of the test specimens was imposed by 1) increasing the RH of the surrounding air and 2) reducing the temperature of the printed circuit boards using a cooling stage, while maintaining a constant climatic condition in the chamber.

A considerable increase in LC was observed at sodium chloride concentrations above 1.56 $\mu\hbox{g}\cdot \hbox{cm}^{-2}$, as the RH on the surface was close to the critical RH for sodium chloride. Prolonged exposure to conditions close to condensation resulted in the formation of tin whiskers and hillocks growing from the component electrodes due to corrosion of the electrodes freeing the whisker growth.