Permeability Rate
Material physics in a reliability study describe how water molecules migrate through a substance at a molecular level. In electronic assemblies, moisture diffusion affects the dielectric properties of circuit boards and the mechanical stability of plastic packages. The process is driven by the difference in partial pressure between the inside of the material and the surrounding environment.
Temperature Effect
Heating a material increases the energy of the water molecules and the free volume within the polymer matrix. This leads to a faster rate of ingress during humid storage or faster egress during a dry bake. Cooling the material can trap moisture inside where it may condense and cause corrosion.
Impact Assessment
Accumulated water reduces the glass transition temperature of epoxy resins and increases the risk of conductive anodic filament growth. Sensors may experience a shift in capacitance or resistance as the moisture levels change. Barrier coatings and hermetic seals are used when high reliability is required in damp conditions.
Absorption Profile
Different polymers and resins have varying degrees of resistance to water vapor penetration. High density materials generally slow the movement of molecules but rarely block them entirely over long periods. The thickness of the material directly determines the time it takes for moisture to reach sensitive internal interfaces.
Total absorption follows a predictable curve until saturation occurs.
