Measurement Methodologies for Acoustic Noise Induced by Multilayer Ceramic Capacitors of Power Distribution Network in Mobile Systems

In this article, acoustic noise of printed circuit board (PCB) introduced by multilayer ceramic capacitors (MLCCs) on power distribution network (PDN) is studied. The correlation of PDN power rail noise, MLCCs and PCB dynamic characteristics, and PCB acoustic noise is demonstrated on a real mobile product through electrical, vibrational, and acoustic measurements. Two measurement methodologies are proposed to identify the problematic MLCCs on the power rail. One method analyzes the board and MLCCs vibration properties with the external electrical signal applied on the power rail on a product board. Other measurement detects the problematic MLCCs based on the coherence value between the power rail signal during product operation and MLCC vibration characteristics. By replacing the identified original MLCCs with low acoustic noise ones, the PCB vibration is clearly reduced. With the MLCCs' influence on PCB vibration studied, a measurement methodology is also proposed to analyze the PCB intrinsic vibration properties. The intrinsic modal response of PCB is applied to predict the MLCC-induced PCB vibration. The obtained modal response can also provide design guidelines for MLCC placement to reduce the level of PCB vibration.