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.
Static Path Resistance
Electrical Property
Ohmic value of a conductive circuit measured at a constant temperature provides the fundamental metric for electrical integrity. The static path resistance represents the total opposition to current flow through conductors and vias. It is measured under steady state conditions where no external thermal or mechanical loads are applied.
Baseline Value
Establishing this number is the first step in any reliability or qualification test. Measuring the static path resistance requires high-precision probes to avoid contact errors. Engineers use a micro-ohmmeter to record the resistance of a daisy chain or a specific net after fabrication.
This measurement provides the control against which all future changes are compared. A stable initial reading suggests that the plating and bonding are uniform across the test coupon. It provides a reference point for subsequent environmental stress screening.
Acceptance Limit
Deviation from the nominal design value indicates a manufacturing error or a material defect. Nominal static path resistance must be calculated based on copper weight and trace length. If the result exceeds the calculated threshold, the board is flagged for inspection.
Most standards allow for a small tolerance to account for plating thickness variations. Excessive resistance often points to under-plating in the barrels of the plated through holes. Calculated values for the net are compared to the measured static path resistance to ensure plating consistency.