Study of Interaction Between Reflow Solder Flux and Humidity in Relation to Failures in Electronics

This paper shows the humidity interaction between different reflow solder flux chemistry and effect on corrosion driven failures using a custom-designed test PCBA, which simulate dummy “component” mounted at a known standoff distance from the base PCB. Five reflow solder flux systems were exposed to a standardized harsh climate profile after reflow soldering on the PCBA, and changes in surface insulation resistance (SIR) is measured during exposure. Trends in SIR measurements were correlated with other properties of the flux residue such as moisture absorption, released ionic contamination, and activator chemistry. Results showed that the higher the flux activity (driven by both overall quantity of Weak Organic Acids used, and proportion of more active Glutaric acid used as activator), in combination with higher moisture-absorbent polymer tackifier compounds (like Poly(Isobutene:Isoprene) and Synthetic Polyterpenes that spread and “opened up” more to release contained activator compounds) resulted in lowered SIR values. The study provides an insight into climatic reliability-based performance of different flux systems based on the properties of various chemical constituents by developing a methodology of solder paste flux analysis.