Fatigue Life Estimation of Vertical Probe Needle for Wafer Probing

Wafer probing is a core inspection process to detect defects in a wafer prior to packaging. Since probe card requires over a million touchdowns on wafers, service life of the probe needle is a critical factor in probe card design. For the prediction of service life, fatigue life estimation model should be developed first through fatigue testing with actual probe needles. However, standard fatigue test method cannot be adopted due the complexity in the mounting method and the geometry of probe needles. In this paper; a new fatigue test method for vertical probe needle with floating mount technology is proposed. By applying the method to the fatigue tests with actual probe needles, a stress-lift estimation model is developed as a probe card design reference. The maximum Mises stress is determined as a primary variable of the model using a nonlinear finite element analysis simulation that considers both material and geometrical nonlineariy. The simulation results are verified by comparing the reaction forces from experiments and FEA. The fatigue fracture surfaces are observed with scanning electron microscopy to understand the fatigue failure mechanism in the probe needle.