Moisture Absorption Kinetics in Epoxy Molding Compounds
Epoxy molding compounds absorb moisture according to temperature-dependent diffusion rules, requiring strict MSL floor life management to avoid popcorning during reflow.
Langmuir Model
Monolayer Adsorption
Theoretical descriptions of gas-surface interactions describe how gas molecules occupy specific binding sites on a solid substrate at constant temperature. The mathematical framework of the langmuir model assumes that adsorption occurs on a uniform surface with no interaction between the adsorbed molecules. This simplifies the prediction of gas coverage as a function of partial pressure and has direct application in sensor calibration and surface science.
Sorption Behavior
Sensing layers in gas and moisture sensors often show response curves that fit this simple adsorption mechanism. Under the langmuir model, as pressure increases, the sensor output approaches a saturation limit as all available binding sites become occupied. This non-linear behavior is used by designers to program the linearization tables within sensor microcontrollers.
The model allows for a clear definition of the sensor operating range. This keeps the sensor in its most responsive region.
Model Calibration
Calibration of this model relies on recording the sensor output across a broad range of reference gas concentrations in a controlled flow chamber. The resulting data points are fitted using regression analysis to extract the binding affinity and saturation constants of the sensing material. If the measured response diverges from the curve, it indicates that the sensor surface has multiple classes of binding sites.
This test ensures calibration accuracy across the range.
Model Limitation
The assumed simplicity of the model makes it inaccurate when gas molecules form multiple layers or interact with each other on the surface. For these complex cases, alternative models must be used to prevent calibration errors.