Re-Evaluating Radiated Emissions and Exposure for Potted Transmitter Housings
Encapsulating transmitters alters dielectric loading, detuning antennas and shifting RF exposure boundaries, demanding re-evaluation of emissions and SAR compliance.
Encapsulation Resin
Meaning
Liquid polymers provide a barrier against moisture and mechanical shock for sensitive circuit assemblies. The use of encapsulation resin ensures that individual components remain isolated from environmental contaminants such as salt spray or dust. This material fills the voids around semiconductors and capacitors to prevent oxidation.
Material Selection
Two part systems involve a base resin and a hardener mixed immediately before use. Epoxy or silicone versions of encapsulation resin offer different levels of flexibility and thermal conductivity. Selection depends on the glass transition temperature and the expected mechanical load.
High stiffness prevents lead breakage under vibration.
Thermal Dissipation
Heat transfer occurs through the bulk of the material toward the external housing. While standard encapsulation resin acts as an insulator, filled versions contain ceramic particles to improve conductivity. This modification allows the assembly to shed heat while maintaining electrical isolation.
Total thermal resistance dictates the maximum power rating of the module. Conduction through the resin prevents hot spots that would degrade delicate silicon junctions.
Process Control
Vacuum degassing removes air bubbles that might otherwise cause electrical arcing in high voltage circuits. The curing of encapsulation resin requires controlled ramp rates to avoid internal voids. Cracking occurs if the material cools too quickly.
Consistent thickness is necessary for repeatable results. Precise weighing of components ensures the chemical reaction reaches completion. Handling time is limited by the pot life of the mixture.
Technicians monitor the ambient humidity to prevent moisture from reacting with the hardener. Automatic dispensing systems maintain the correct volume for every unit on the production line.