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Ionic residues resulting from the soldering process is an important parameter in connection with humidity robustness of Printed Circuit Board Assemblies (PCBAs) due to their ability to enhance moisture absorption and surface conductivity. For reflow process, residues are trapped under the components, and the morphology of the residues can change with humidity exposure resulting in the release of ionic components. In this work, trapped residues below the components from reflow process of several commercial PCBAs were characterized before and after exposure to humidity conditions. PCBAs used for the analysis had undergone multiple reflow heating profiles by single and double reflow plus additional passes to understand heating effects. The morphology change of the trapped residues under components upon humidity exposure was observed using optical and scanning electron microscopy. The conductivity of the localized extracted solutions was measured and NaCl equivalency was determined. The solder paste materials were analysed for their water sorption property, while the effect of humidity on electrical property was assessed using electrochemical impedance spectroscopy using test PCBs. The results show that the change in morphology and level of activator release of residues were a function of the flux type, PCBA characteristics such as component standoff height and number of reflow cycles. Water layer formation upon humidity exposure and electrical properties on test PCBs are correlated with water sorption of the flux part. [ABSTRACT FROM AUTHOR]

A common concern with electronics packaging is the reduction of moisture ingress into the devices. One option to consider is the use of water absorption desiccant. Its criteria for selection should be its water capacity property, while its regeneration temperature has to be taken into account. Electronic devices are exposed to all kinds of harsh cyclic environments, and assuring a low level of humidity inside the devices implies the replacement of the desiccant once its saturation content is reached. This may not be applicable, or the frequency of replacement may represent a high cost. Using the dissipated heat from the electronic devices during the “ON” time may be a low-cost process for the regeneration of the desiccant, therefore increasing its lifetime. This article presents the experimental investigation of the performance of different desiccants on water absorption and regeneration. Analysis and test results show that the desiccant system continuously maintains a lower humidity inside the electronic enclosures over the tested time of cyclic exposure if they can be regenerated using device self-heating. [ABSTRACT FROM AUTHOR]