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The causes of possible failures of MEMS microphones during guided free fall tests are investigated through top-down, multiscale finite element numerical simulations. Focusing at the micro-scale, the role of the travelling stress waves in the solid, transferred as relative displacement imposed motion histories at the microphone anchors, is clarified. The system including the thin silicon membrane (i.e. the microphone), a holed backplate and the substrate is modelled and studied by including the (different) motions at every support combined with the air over-pressure on the membrane, as captured by fluid dynamics analyses at the higher scale. We show that several failure mechanisms can alternatively occur, involving the membrane or (more likely) the backplate, depending on the phase balance between the two loading history signals. The numerical results help to get insight into the experimental behaviour during guided free fall tests, which instead would appear random and evidence only a rupture/not rupture output.

Impact effects on thin silicon MEMS membranes attached to dummy devices, as observed through guided free fall tests, are investigated through three-dimensional, finite element numerical simulations. Accounting for the different scales involved, a multiscale top-down approach is followed: fluid dynamics and solid mechanics macro-scale simulations are first carried out, to provide input histories for fluid (air) pressures and relative displacements for the thin silicon membrane anchors at the micro-scale. Then, a mechanical analysis is carried out for each membrane to judge whether possible failures arise in a given guided free fall test. It is found that in some cases possible failures actually depend from the combination of the fluid-induced and of the solid-induced input transferred to the MEMS membrane, and not from a single domain-induced loading condition.

Failures on MEMS microphones placed on dummy smartphone are observed during a guided free fall test. The instants before and after the first impact are registered with a high-speed camera and the displacement/velocity signals are used as input for three-dimensional finite element analyses at different scales to obtain insights at local level to judge whether possible ruptures arise. The numerical procedure follows a multi-scale, top-down approach and it can adopt both fluid-structure interaction and purely mechanical analyses. Finally, two loadings are transferred at the micro-scale to the thin silicon membrane representing the microphone: it is found that, in some drop cases, failures depend from the combination of the fluid-induced (air over-pressure) and of the solid-induced input (relative displacements at the anchors), and not from a single domain loading condition.