Comparison between beryllium-copper and tungsten high frequency air coplanar probes

High frequency air coplanar probes using tungsten tips are now available for silicon wafer probing with aluminum pads. A comparative study of the beryllium-copper and tungsten behavior is presented in terms of contact resistance values, stability and reproducibility. The contact theory is summarized for practical purposes and probe cleaning methods are exposed. Finally, tungsten is demonstrated to be the best material for breaking the aluminum oxide over the pad to enable accurate high frequency probing.