Environmental Exposure
Transient migration of water molecules through a protective barrier defines the rate of internal humidity change over time. The dynamic moisture ingress rate determines the lifespan of sensitive electronic components within a non-hermetic enclosure. Diffusion coefficients vary with temperature and external vapor pressure according to the specific chemistry of the sealant.
Kinetics Analysis
Fickian diffusion governs the movement of water through polymers or potting compounds. In dynamic moisture ingress, the concentration gradient drives the flow until the internal cavity reaches equilibrium with the outside environment.
Sensing Methodology
Capacitive humidity sensors or surface acoustic wave devices track the internal change in real time. Standardised tests for dynamic moisture ingress involve high-temperature storage and humidity cycling to accelerate the migration process.
Qualification Limit
Performance data informs the calculation of the moisture sensitivity level for the assembly. Protection fails when the dynamic moisture ingress allows the internal humidity to reach the point for corrosion or delamination. Corrective actions include thicker coatings or more hydrophobic materials.
Verification of the ingress rate occurs during reliability testing where the internal atmosphere is sampled or monitored during exposure to a 85 percent relative humidity environment. Failure to meet the ingress limit results in the redesign of the seal geometry or the selection of a material with a lower permeability coefficient.
