Thin-film encapsulation
Thin-film encapsulation provides conformal insulating barriers, micrometers thick or thinner, to protect flexible, high-density devices that cannot house a rigid hermetic can. Materials include organic layers (parylene C, polyimide) and inorganic ones (silicon carbide, silicon dioxide and nitride, aluminium oxide), often stacked into multilayer organic/inorganic nanolaminates so that pinholes and cracks in one layer do not line up with those in the next, defeating continuous water pathways.
The fundamental caveat is that no polymer is a perfect water barrier — water molecules eventually permeate any thin organic film — so the practical figure of merit is water-vapor transmission rate and projected service lifetime rather than absolute hermeticity. Devices are therefore validated by long-term soak testing rather than a leak-rate pass/fail, and the goal is to keep leakage below the threshold at which traces corrode or short over the required years.
A silicon array insulated with silicon carbide or atomic-layer-deposited alumina is soak-tested in warm saline; the time-to-impedance-failure at an elevated temperature is extrapolated to body temperature using an Arrhenius model to project years of service.
For thin films the question is not whether water gets in, but how slowly.