Fickian Diffusion Kinetics and Desorption Times for Molded Packages
Fickian desorption calculations use temperature-dependent diffusivity to determine exact package bake times, preventing reflow popcorning and structural delamination.
Preconditioning Profile
Thermal Exposure
Moisture sensitivity classification dictates the schedule of temperatures and time durations applied to electronic components before surface mount assembly. A preconditioning profile determines how a component simulates the life cycle of shipping and storage to trigger potential popcorn failure or delamination. This thermal sequence pushes internal moisture to vapor pressure levels that stress the plastic housing or package seal.
Failure Mechanics
Delamination occurs when a preconditioning profile drives thermal expansion differentials between disparate materials within the component body. Heat induces mechanical strain on the interface between silicon, lead frames and molding compounds. Exposure to extreme temperature cycles often exposes weaknesses in the structural integrity of the seal, allowing ambient moisture to compromise internal connections before the board reaches reflow.
When moisture content remains above acceptable levels during the application of this thermal sequence, the resulting pressure gradients cause internal cracks or package bulging.
Compliance Requirements
Standards dictate that non-hermetic parts undergo this specific sequence prior to reliability testing or destructive analysis. Industry documentation defines the duration and temperature set points based on the moisture sensitivity level assigned to the component by the manufacturer. These values account for the known thermal tolerance of the assembly materials and the moisture absorption characteristics of the polymer matrix.
Compliance relies on the application of the defined thermal history to ensure that subsequent electrical performance represents the actual integrity of the device under real environmental conditions.