Resistance Isolation
Measurement of low electrical resistance values in printed circuit boards or solder joints requires a method that separates the current excitation path from the voltage measurement path to eliminate test lead errors. Utilizing four-point kelvin probing allows test equipment to determine the true resistance of a conductor by ensuring that virtually no current flows through the sensing leads. This approach eliminates the influence of contact resistance and lead impedance, which would otherwise skew the measurement of sub-milliohm features.
Lead Cancellation
Contact resistances between the test probes and the copper trace pads often exceed the actual trace resistance being measured. By using two dedicated probes to source a known current and a separate pair of probes to measure the voltage drop directly across the target, the voltage meter draws negligible current, meaning that any resistance in the sensing leads does not affect the reading. This configuration is standard in automated in-circuit testing machines that inspect high-reliability power boards or fine-pitch traces where micro-cracks might exist.
The accuracy achieved with this technique is vital for detecting partial solder joint cracks.
Contact Design
Mechanical alignment of the dual probe tips is carefully managed to maintain consistent contact spacing on small test pads. Automated fixtures ensure repeat measurements are precise.
