Parallel Plate Capacitance Testing for Packaging Core Dielectrics
Parallel plate capacitance testing extracts packaging core permittivity from 100 Hz to 1 GHz by applying guarded electrodes to etched, preconditioned coupons.
Parallel Plate Fixture
Sensor Design
Material testing instrumentation utilizes opposing metal electrodes to measure the dielectric properties of substrate samples under controlled electric fields. This arrangement, known as a parallel plate fixture, establishes a uniform electric field through the thickness of the material under test. It connects directly to an impedance analyzer or an LCR meter, allowing the operator to extract capacitance and dissipation factor values at specified frequencies.
Electrode Arrangement
To achieve high precision, the fixture must minimize the errors caused by edge capacitance and stray fields. Modern designs feature a guard electrode that redirects the outer fringing field lines away from the main sensing area, leaving only the uniform field lines to pass through the specimen. This configuration allows for the accurate measurement of thin sheets of dielectric material such as epoxy, polyimide, polyester and PTFE.
Testing requires applying a constant force to the plates to eliminate air gaps between the electrodes and the sample, as even a microscopic air layer will cause a severe reduction in the measured capacitance.
Calibration Requirement
Standardization is maintained by performing open-circuit and short-circuit calibration routines prior to inserting the dielectric sample. The parallel plate fixture is then zeroed to compensate for the residual inductance and resistance of the lead wires.