Wafer probing is a testing process to inspect semiconductor wafers before packaging for defects by checking the electrical conductivity via 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 have 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 is analyzed with a nonlinear finite element analysis. The comparison between fixed mount and floating mount technologies is a part of the analyses. The geometry of a vertical probe needle is optimized to minimize the stress that occurs during the overdrive process, while maintaining adequate force for proper contact with the wafer. Effects of major overall dimensions of probe needle on the maximum stress and contact force is analyzed first, and then curvature of the probe needle body is optimized by employing a constrained minimization function, fmincon, in MATLAB. The maximum stress in the vertical probe pin at 125 µm overdrive is effectively reduced from 1339 MPa to 972 MPa by applying floating mount technology over the fixed mount, and further reduced to 666 MPa by applying the optimization scheme. The final optimized design induced the contact force of 5.217 gf, which is in the range of the required contact force of 5 to 8 gf. Fatigue life increased from 19,219 cycles to 108,129 by applying floating mount over fixed mount, and further increased to 830,596 for the optimized design.
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Shape Optimization of Vertical-type Probe Needle Integrated with Floating Mount Technology
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