Ultrasonic Impedance Discontinuity Phase Inversion Limits in Baked Plastic Packages
Acoustic phase inversion limits in baked plastic packages occur when thermal gap shrinkage creates sub-wavelength contact that suppresses echo reversal.
Plastic Encapsulated Microcircuits
Package Classification
Semiconductor devices utilizing synthetic resin to protect the internal die and wire bonds represent the most common form of electronic packaging. Modern high volume production relies on plastic encapsulated microcircuits to provide a lightweight and cost effective alternative to ceramic or metal hermetic packages. The resin protects the delicate circuitry from mechanical shock and chemical contaminants encountered during handling.
These components are used extensively in consumer and industrial applications where extreme hermeticity is not required.
Material Composition
The epoxy molding compound contains various fillers to manage thermal expansion. Proper selection of these materials prevents the package from cracking during the high temperatures of reflow.
Failure Mode
Moisture absorption is a primary concern for these packages because the resin is not completely impermeable to water vapor. If moisture enters the package, it can expand rapidly during soldering and cause the package to burst or the internal layers to separate. Manufacturers assign a moisture sensitivity level to help users determine the safe storage and handling requirements.
Proper baking and vacuum sealing are necessary to prevent damage before the assembly reaches the reflow oven. The package integrity depends on the quality of the bond between the lead frame and the molding compound.