Geometry design of vertical probe needle using mechanical testing and finite element analysis

In wafer probing, probe needles provide the physical contact between the wafers and the probe card. During the contact process, the shape of the probe needle and the mounting configuration onto the probe card has large influences on the stresses and contact force that the probe needles experience. In this paper, static performance of a vertical-type probe needle integrated with floating mount technology was analyzed with a nonlinear finite element analysis. The geometry of a vertical probe needle was optimized in order to minimize the stress that occurs during the overdrive process, while maintaining adequate force for proper contact with the wafer. Maximum stress and contact force were formulated using the coefficients of 4th order polynomial representing the shape of cobra body, and then curvature of the probe needle body was optimized by applying the constrained minimization function to these functions. The maximum stress in the vertical probe pin at 125 μm overdrive was reduced from 972 MPa to 666 MPa by employing the probe needle with optimized geometry. The optimized design also induced the contact force of 5.217 gf, which is in the range of the required contact force of 5 to 8 gf.