Permittivity Shift
Change in the ability of a material to store electrical energy in an electric field. A dielectric constant alteration affects the signal propagation speed and impedance of a printed circuit board. High frequency circuits are particularly sensitive to these variations.
Moisture Absorption
Water molecules entering the substrate increase the overall capacitance of the dielectric material. A dielectric constant alteration often occurs when hygroscopic resins are exposed to high humidity. This increases the delay of the signal and can lead to timing errors in digital logic.
The effect is measured by comparing the dry permittivity to the saturated state.
Thermal Variance
Temperature changes modify the molecular alignment and density of the insulator. The dielectric constant alteration is usually non linear across a wide temperature range. Engineers must account for this drift during the design of radio frequency filters and antennas.
Calibration at the operating temperature ensures the circuit performs as expected.
Signal Integrity
Impedance mismatches arise when the dielectric constant varies across different layers or regions. The dielectric constant alteration can cause reflections that degrade the quality of high speed data transmission. Designers specify materials with low loss tangents to minimize these effects.
Measurement of the alteration is verified using a network analyzer.
