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

Abstract

Some new issues concerning the contacting and positioning of small electrical microelectromechanical systems (MEMS) probes based on multiple, flexible microcantilevers are presented here. A tilt error, associated with the lateral probe roll, means that contact touchdown occurs sequentially in different cantilevers upon increasing probe overtravel. To understand the relationship between probe overtravel, tip skate, tip planarity, tip tangency, and contact force in the different contacts, the relationship between mechanical bending and torsion of the flexible cantilevers needs to be accounted for. The study reveals the conditions for achieving contact planarity and desired contact force, as well as the identification of a new ‘differential skate error’ contact misalignment associated with such MEMS probes based on multiple, flexible microcantilevers. This misalignment leads to a ‘differential contact force error’ which has implications for electrical contact quality. An experimental scale model probe based on three cantilevers is used to test the modelling—the results agree well with the predictions of the model. Interestingly, the experiments revealed an effect not accounted for in the modelling; this ‘twist error’ resulted in the cantilever lead edge not being parallel to the touchdown plane. The findings may be useful for engineers involved with the automatic control positioning of such emerging miniature probes, especially in terms of the impact of probe positioning errors.