A Study on Measuring Contact Resistance of Ball Bonds on Thin Metallization

Contact resistance measurement configurations for the evaluation of ball bond reliability on thin metallizations are studied. Samples with symmetrical and asymmetrical four-wire probe configurations are analyzed and compared with a calibrated finite-element model. It is found that the measured contact resistance strongly depends on the geometric placement of the probe wires, and the value closest to the true value is obtained from a probe placement that is opposite and away from high-current-density regions on the metallization. Probes should also be placed as close as possible to the contact interface. Sheet resistance components contributed by intermediate thin metallizations are of the same order of magnitude as the unaged reported R-C. Therefore, they are considered. Symmetrical current distributions yield a more homogeneous potential drop across the bond interface being probed, but also capture a larger component of metallization sheet resistance. Experimental samples were aged, and the contact resistance increase was measured. The impacts of various probe placements on the sensed R-C were studied.