Skate, overtravel, and contact force of tilted triangular cantilevers for microcantilever-based MEMS probe technologies

Abstract

Microfabricated chip-edge microcantilevers are commonly used as surface probes, e.g. in near-field microscopy. Such probes normally function in the low-deflection regime, where their behaviour is very well understood and documented. In contrast, when microcantilevers are used for applications such as electrical testing probes, their deflection can be somewhat higher, taking them into the less well understood high-deflection regime of microelectromechanical systems (MEMS). Here, a scalable model for the relationship between the skate, overtravel, and resulting tip contact force in tilted triangular cantilevers—which are bending with high deflection and in contact with a flat surface—is presented. The model is tested experimentally using macroscopic triangular cantilevers—the experimental results agree well with the proposed model. The findings enable a practical solution for zero-skate in tapered MEMS probes to be suggested. It is hoped that the findings may be of use for probe engineers involved with on-wafer testing and designers of emerging MEMS micro cantilever-based probes.

Tilt-related alignment issues in miniature micromechanical on-wafer electrical probes composed of multiple flexible microcantilevers

“…This situation is shown in figure 4(h) where the tip skate of the red cantilever has gone beyond the horizontal blue line (the tangency skate of the red cantilever). In this case, increasing the overtravel beyond the tangency overtravel value [15,16] may cause the tips to leave the surface, jeopardizing electrical contact quality.…”

“…The thickness of the polystyrene was measured to be 1.45 ± 0.01 mm using a precision thickness gauge (Mitutoyo, Japan) having a resolution of 1 μm. The Young's modulus of and Poisson coefficient the polystyrene has been determined by the author to be 1.754 ± 0.071 GPa and 0.33 [16,17]. The design dimensions of the scale model probe are: L = 100 mm, 75 mm, and 50 mm, w = 25 mm, and g = 15 mm.…”

“…The design dimensions of the scale model probe are: L = 100 mm, 75 mm, and 50 mm, w = 25 mm, and g = 15 mm. The details of the fabrication of such objects can be found in previous publications [16,17]. Following fabrication, the width of the cantilevers and the gap length were measured from photographs using software [24].…”

“…This is particularly important in terms of the impact of positional errors on optimum electrical contact [6]; something that has been studied in rigid commercial probes [7][8][9][10][11][12][13][14]. In contrast, the micromechanical behaviour (bending and twisting) of miniature microcantilever-based probes must be taken into account for optimum probe contacting [15][16][17]. The author has previously discussed the relationship between skate and overtravel in rectangular [15], triangular, and trapezoid [16] shaped probes based on flexible microcantilevers.…”

“…In contrast, the micromechanical behaviour (bending and twisting) of miniature microcantilever-based probes must be taken into account for optimum probe contacting [15][16][17]. The author has previously discussed the relationship between skate and overtravel in rectangular [15], triangular, and trapezoid [16] shaped probes based on flexible microcantilevers. The impact of tilt error on a probe composed of a single flexible microcantilever has also been described by the author [17].…”