Permeation Rate
Water molecule migration through package seals quantifies humidity ingress potential over operational sensor lifespans. Measuring moisture vapor transmission evaluates how effectively organic polymers, gaskets, and potted enclosures prevent water vapor from entering internal sensor cavities. Water vapor diffuses through polymer matrices under partial pressure gradients between external environments and dry sensor interiors.
Penetration of moisture causes corrosion of metallization traces, dielectric breakdown of insulating layers, and gain drift in sensitive electronic front ends. Standard test methods like ASTM E96 measure water vapor transmission rates in grams per square meter over twenty-four-hour periods under controlled temperature and humidity conditions.
Polymeric Diffusion
Diffusion coefficients dictate the speed at which water molecules navigate polymer cross-link networks. Material density, filler content, and curing temperature govern overall permeability in sealing materials. Glass transition temperatures mark changes in diffusion rates across operational thermal ranges.
Gravimetric testing measures mass change in film samples over extended test durations.
Signal Degradation
Internal relative humidity buildup degrades high-impedance electrical paths on sensor substrates. Stray leakage currents cause zero-offset shifts and increase sensor output noise floors. Condensation during thermal cycling creates transient short circuits across fine-pitch IC leads.
Seal selection relies on permeation rate limits derived from lifespan testing.
Test Protocol
Standardized testing uses gravimetric dish methods or electrolytic sensors to detect transmitted moisture. Sealed test chambers maintain ninety percent relative humidity at thirty degrees Celsius. Test records define maximum allowable vapor permeability values for package designs.
