Dynamic Kelvin Resistance Screening Mechanics for High Density Circuit Boards
Dynamic four-wire Kelvin screening uses thermal current pulses and flexure to isolate latent microvia cracks that pass static continuity tests.
Dynamic Resistance Test
Diagnostic Procedure
Continuity measurement during thermal or mechanical stress identifies intermittent failures in a conductive path. A dynamic resistance test monitors the ohmic value of a circuit while the substrate undergoes physical change. This procedure targets defects that separate under load.
Capture Mechanism
Electrical monitoring occurs at high sampling rates to catch millisecond events. By analyzing the dynamic resistance test data, technicians can pinpoint the temperature at which the crack opens. High-speed data acquisition systems record the voltage drop across the net while a thermal cycle or vibration profile is applied to the assembly.
If a micro-fracture exists, the expansion of the dielectric material pulls the copper interfaces apart. This separation results in a spike that a conventional multimeter might miss due to slow integration times.
Acceptance Boundary
Pass criteria usually depend on the maximum allowable change from the initial baseline measurement. The dynamic resistance test monitors this threshold during environmental stress to identify intermittent failures. Standard IPC guidelines often set a ten percent increase in resistance as the limit for failure.
When the circuit returns to its original state after the stress is removed, the fault often disappears. This repeatability confirms the presence of a latent defect.