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.
Epoxy Dielectric
Meaning
Thermosetting polymers act as non-conductive layers to prevent electrical leakage between conductive planes in multilayer boards. Application of epoxy dielectric provides the necessary isolation in high density interconnects. The material adheres to copper foil through a combination of chemical bonding and surface roughness.
Electrical Performance
Voltage breakdown happens when the electrical field exceeds the rating of the insulating layer. The thickness of epoxy dielectric determines the capacitance between adjacent power and ground planes. Signal integrity depends on the dissipation factor and the relative permittivity of the resin.
Lower loss tangents allow for higher frequency operation. Frequency response remains stable across the rated temperature range.
Mechanical Strength
Tensile force is resisted by the crosslinked structure of the cured board. Using epoxy dielectric in a prepreg form allows for the inclusion of glass fibres to increase rigidity. These reinforcements prevent warping during subsequent assembly steps.
Dimension stability ensures that microvias remain aligned across multiple layers. Load distribution is managed by the resin matrix.
Environmental Stability
Moisture absorption causes a change in the electrical properties of the insulator over time. When epoxy dielectric is exposed to high humidity, the dielectric constant can shift and lead to impedance mismatches. Reliable designs account for these shifts by selecting low moisture absorption grades.
Chemical resistance to soldering fluxes is also a requirement.