Bare Board Insulation Resistance Testing Thresholds
Bare board insulation resistance testing requires minimum 100MΩ thresholds at 100V DC under IPC-9252B Class 3 to prevent electrochemical migration escapes.
Dielectric Absorption Current
Insulation Response
Insulation resistance testing protocols require a stabilization period to account for the delayed polarization of the resin system. A dielectric absorption current represents the decaying energy that remains stored in the pcb laminate after the initial capacitive charging is complete. This phenomenon causes a voltage to reappear on a capacitor or trace after it has been briefly discharged.
Testing Procedure
Resistance meters measure the leakage over a specific time to distinguish between different types of current flow. When a high voltage is applied to the circuit, the dielectric absorption current decreases exponentially as the molecular dipoles align with the electric field. Technicians wait for this current to stabilize before taking a final insulation resistance reading.
If the reading is taken too early, the apparent resistance will be lower than the true value of the material. Reliable measurement is essential for high impedance circuits where even tiny amounts of stored charge can disrupt signal precision.
Material Property
Different resin systems like epoxy or polyimide exhibit varying levels of molecular relaxation. High performance substrates are selected for low dielectric absorption current to prevent signal memory effects in precision analog applications. The choice of glass reinforcement also affects how much charge the board retains over time.