Impact of Process-Related Flux Contamination on the Electronics Reliability Issues Under Detrimental Climatic Conditions

The reliability issues faced by modern electronic devices are inherently related to the non-optimized manufacturing process, which leaves behind a substantial amount of soldering residues of an aggressive nature. The use of flux systems for soldering purposes is vital, however, upon exposure of the device to harsh climatic conditions, it can result in the compromised corrosion reliability of the Printed Circuit Board Assembly (PCBA) due to the corrosive nature of the flux system. In this paper, the behavior of reflow process-related solder flux residues was investigated. The evolutions of potentially corrosive flux components from the soldered pads exposed to high humidity and temperature conditions was studied as a function of exposure climate and solder paste type using the acidity indication gel test. Changes in the filmformer morphology due to the climatic exposure were visualized using light optical and scanning electron microscopy, and correlated to the observations from the gel test. Quantification of the residue level was performed using the conductivity measurements. Results show that evolution of acidic residues from the reflow-soldered pads occurs upon exposure to high temperature and humidity levels. The exposure time defines the extent of evolution, and it was found to be typically directly proportional.