Failure of MEMS Microphones During Impact Tests: the Role of Anchor Imposed Motion

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.