Contact Force Experiments and Deformation Analyses of a Cobra Needle Used in Vertical Wafer Probe Card

Abstract

Wafer testing requires a probe card with a mass of microprobes as a contact medium between the prober and the wafer. Electric characteristics of the examined welding pads are tested by direct contacts between the microprobes and pads. These needles are subject to deflection or buckling resulting from the contact test, and might lose their original strength. To understand the loading state and deformation process of the needle, this study develops a microprobe testing platform for analyzing a vertical cobra needle. Testing parameters which affect the contact force were investigated, such as the probing overdrive, approaching speed, and probing time. Needle deformation during probing was observed by a computer vision system and evaluated by image processing methods. Furthermore, the finite element model of a palladium alloy cobra needle was established to simulate its contact behaviors in wafer probing for obtaining a wafer probe card with correct test and robust performance.