Measurement Investigation on Acoustic Noise Caused by "Singing" Capacitors on Mobile Devices

Acoustic noise from mobile devices can he annoying for customers. Multilayer ceramic capacitors (MLCCs) soldered on printed circuit board (PCB) are known to be a main source of acoustic noise. The PCB in these devices feature hundreds of MLCCs. In this paper, a measurement methodology to identify the major vibrating MLCCs on board is presented. Laser Doppler vibrometer scanning result is used to find the dominant MLCC source. The correlation between board vibration and acoustic noise is confirmed with microphone probe. As a result of the piezoelectric properties of MLCCs, the root cause of the vibration is analyzed from an electric point of view. The problematic MLCCs are find to share the same power line which renders the same noise peaks as in the vibration and sound pressure measurements. After replacing the vibrating MLCCs with low acoustic noise MLCCs, the board clearly shows decreased level of vibration.