Flip-chip MEMS microphone package with small front-volume and large back-volume

This paper describes a new packaging technology for bottom port micro-electromechanical system (MEMS) microphones in detail. The package combines the advantages of a small front-volume of 0.2 mm³ to avoid resonances in the acoustic frequency range and a large back-volume of 3.4 mm³ to increase the signal to noise ratio (SNR). The microphone package is built on a high temperature cofired ceramic substrate by flip-chip technology and closed by a metal lid. Front-volume and back-volume are separated by a new process applying polymer foil lamination and laser ablation. To achieve a signal to noise ratio of up to 66 dB (A) a double backplate transducer chip is used. To calculate the microphone response a lumped element simulation model was extended to integrate the second backplate structure. The simulation model is used to show the influence of the front-volume and the back-volume. The comparison with measurements showed considerable agreement.