| Summary: | 碩士 === 明志科技大學 === 機械工程系機械與機電工程碩士班 === 104 === This study developed a theoretical and experimental model for a high-aspect-ratio probe, applying the technique to a semiconductor chip of decreasing spacing and a system that required a high-density probe. Buckling strain exerted on high-aspect-ratio probes during testing was examined to explore the optimal parameters for evaluating the probe durability and reliability. Specifically, beryllium copper (BeCu) and tungsten alloy were adopted through an initial examination of theories on linear static stress in solid mechanics, and the strain of the probe tip was designated as a cantilever beam model. Moreover, the theory of elasticity was employed to simplify the three-dimensional strain condition of the material into a two-dimensional plane stress condition. The finite element method (FEM) was adopted to establish the strain condition; additionally, ANSYS software was used to stimulate the von Mises equivalent stress. If the resulting stress is found to be less than the fatigue strength, the adopted probe can be applied to conduct a considerable amount of routine probe testing, whereas if the stress value is greater than the fatigue strength, several modification methods should be used to decrease the stimulated stress and investigate the optimal aspect ratio. For instance, the output force should be decreased (i.e., the designated force distribution should be lower than the listed maximum value); the probe tip diameter should be slightly increased to enhance the inertia force (with consideration of the breadth of the test kit); and the probe tip length should be shortened to decrease the bending stress (with the high aspect ratio of the probe maintained).
First, a geometric method was employed to analyze the strain condition of the contact between the probe tip and test kit. The fatigue strength of the BeCu and its influential factors were examined to determine an acceptable working stress for probe testing. Next, a static stress analysis was conducted using the stress formula for the bending moment of the cantilever beam. The equivalent concentrated stress on the probe tip, derived through theoretical calculations, was converted into the force distribution therein and subsequently applied as the numerical input into the FEM ANSYS software.
Through a three-dimensional stress analysis of Mohr’s circle, the three-dimensional principal stress was derived and subsequently converted into von Mises equivalent stress. This value needed to be smaller than the fatigue strength of the tested material, and was applied to the conversion formula for plane stress to acquire another principal stress. The obtained principal stress was verified to be the same as that of the three-dimensional Mohr’s circle. Finally, the buckling theory of cylinders was used to demonstrate how the critical load limited by the probe tip length, suggesting that the deformation observed in over-extended tips can lead to failure in probing performance. Finally, the FEM stimulation revealed that tip length varied in its limitations with respect to tip material, diameter, or angle; the limitations ensure that the designated force of the probe output remains within the permissible working stress for the tip.
Simulated and actual probe testing revealed several findings:
(1) When the same tip diameter and probing angle were given, a longer probe tip was observed to be less tolerant of distributed force.
(2) The resultant bending deformation of the BeCu tip may generate interference in electrical transmission.
(3) At a 60° probing angle, plastic deformation caused by bending stress may occur prior to buckling.
Keywords：beryllium-copper probe、stress analysis、buckling.
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