“Singing” Multilayer Ceramic Capacitors and Mitigation Methods: History
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Subjects: Engineering, Electrical & Electronic
Contributor:
Corina Covaci
,
Aurel GONTEAN

Multilayer Ceramic Capacitors (MLCC) have a major role in modern electronic devices due to their small price and size, large range of capacitance, small ESL and ESR, and good frequency response. Unfortunately, the main dielectric material used for MLCCs, Barium Titanate, makes the capacitors vibrate due to the piezoelectric and electrostrictive effects. This vibration is transferred to the PCB, making it resonate in the audible range of 20 Hz–20 kHz, and in this way the singing capacitors phenomenon occurs. This phenomenon is usually measured with a microphone, to measure the sound pressure level, or with a Laser Doppler Vibrometer (LDV), to measure the vibration. Besides this, other methods are mentioned in the literature, for example, the optical fiber and the active excitation method. There are several solutions to attenuate or even eliminate the acoustic noise caused by MLCC. Specially designed capacitors for low acoustic levels and different layout geometries are only two options found in the literature. To prevent the singing capacitor phenomenon, different simulations can be performed, the harmonic analysis being the most popular technique. This paper is an up-to-date review of the acoustic noise caused by MLCCs in electronic devices, containing measurements methodologies, solutions, and simulation methods.

  • singing capacitors
  • MLCC
  • acoustic noise
  • electronics design
  • PCB acoustics measurement methods
  • simulation
  • analysis
  • IoT sensors

1. Introduction

Capacitors are passive electronic components found in various shapes and using different materials [1]. Numerous ceramic capacitors, especially multilayer ceramic capacitors (MLCC), are used on a modern printed circuit board (PCB). They have a major role in resonant circuits, power supply bypass, and filters [2]. This makes them indispensable in all modern electronic devices, including but not limited to wearable smart sensors, environmental monitoring, agriculture, and food control, to name a few. Due to their popularity, the global market of MLCCs was valued at USD 5315 million in 2017 and it is predicted to increase to USD 7833 million by 2024 [3,4].
As presented in Figure 1, MLCCs are composed of three main elements: inner electrode, outer electrode, and ceramic dielectric material, mainly made of nickel, silver, and palladium [5].
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Figure 1. MLCC Structure.
The main advantages of the MLCCs are their small size and price [6]. Despite their small size, they have large capacitance and favorable electrical characteristics. These characteristics are small equivalent series inductance (ESL), small equivalent series resistance (ESR), good frequency response, a wide range of capacitance value, and their ability to be used for long periods at high temperature or in high-voltage applications [7,8,9].
All of these MLCCs advantages are due to the high-level permittivity dielectric material, Barium Titanate (BaTiO3), they are made of [10,11,12]. Ironically, the two main electro-mechanical properties of the BaTiO3 cause one of the newest problems in electronic devices: the singing capacitors phenomenon [13]. These properties are piezoelectricity and electrostriction. When an AC voltage is applied to the MLCC, the capacitor starts to vibrate due to the piezoelectricity. At the same time, the electric field generated between the inner electrodes creates electrostrictive vibration whose level is similar to the piezoelectric vibration level. Furthermore, the nonlinear phenomenon of the electrostriction also makes a second harmonic frequency vibration of the applied voltage [13]. In recent years, the thickness of the hundreds of dielectric layers present in an MLCC has decreased to achieve a large capacitance in a small package size [1]. Therefore, both properties must be taken into consideration, as the vibration generated by the piezoelectric effect is proportional to the electric field, and the vibration generated by the electrostriction is proportional to the square of the electric field [8].
Besides the piezoelectric and electrostrictive effects, the converse magnetoelectric effect also influences the MLCCs behavior. An induced electric polarization that appears under an applied magnetic field characterizes the magnetoelectric effect. On the contrary, the converse magnetoelectric effect is characterized by an induced magnetization under an external electric field [14]. When driven near resonance frequency, the converse magnetoelectric coefficient reaches the maximum [15]. The resonance frequency of the MLCC vibration is in the range of MHz, therefore we should not be able to hear anything. However, as the MLCCs are surface-mount devices (SMD), the induced vibration is transferred to the PCB via solder joint [1,16]. When an AC voltage is applied to the MLCC, the dielectric material expands in the direction of the electric field and contracts in the direction perpendicular to the electric field, causing the deformation of the board, as shown in Figure 2 [4]. Therefore, the PCB starts to vibrate with the MLCC, and the frequency can reach the audible range of 20 Hz–20 kHz [10].
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Figure 2. The mechanism for singing capacitor phenomenon.
We can conclude that the singing capacitor phenomenon is caused by three major factors [2]:
  • the MLCC itself—the capacitor acts as an excitation source;
  • the mounting situation—the solder joint is the vibration transfer path;
  • the PCB—the board is the acoustic noise resonator.

In this paper (https://doi.org/10.3390/s22103869), a review of the literature information about the singing capacitors phenomenon is presented. In Section 2, we will show how to detect the problematic MLCCs on a PCB. In Section 3, the solutions for singing capacitors found in the literature will be presented, while in Section 4, we will present types of simulation and analysis to prevent audible noise on PCB. We will end with a short discussion about the paper’s highlights and findings.

References

  1. Kim, D.; Kim, W.; Kim, W.-C. Dynamic Analysis of Multilayer Ceramic Capacitor for Vibration Reduction of Printed Circuit Board. J. Mech. Sci. Technol. 2019, 33, 1595–1601. [Google Scholar] [CrossRef]
  2. Ko, B.-H.; Park, H.-G.; Kim, D.; Park, N.-C.; Park, Y.-P. Reduction of Multilayer Ceramic Capacitor Vibration by Changing the Cover Thickness. Microsyst. Technol. 2016, 22, 1375–1380. [Google Scholar] [CrossRef]
  3. Johnson, W.L.; Kim, S.A.; Quinn, T.P.; White, G.S. Nonlinear Acoustic Effects in Multilayer Ceramic Capacitors. AIP Conf. Proc. 2013, 1511, 1462–1469. [Google Scholar] [CrossRef]
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  6. Wang, Y.-Q.; Ko, B.-H.; Jeong, S.-G.; Park, K.-S.; Park, N.-C.; Park, Y.-P. Analysis of the Influence of Soldering Parameters on Multi-Layer Ceramic Capacitor Vibration. Microsyst. Technol. 2015, 21, 2565–2571. [Google Scholar] [CrossRef]
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  8. Ko, B.; Jeong, S.; Kim, D.; Park, N. Identification of the Electromechanical Material Properties of a Multilayer Ceramic Capacitor. Int. J. Appl. Ceram. Technol. 2017, 14, 424–432. [Google Scholar] [CrossRef]
  9. Sun, Y.; Zhang, J.; Yang, Z.; Hwang, C.; Wu, S. Measurement Investigation on Acoustic Noise Caused by “Singing” Capacitors on Mobile Devices. In Proceedings of the 2019 IEEE International Symposium on Electromagnetic Compatibility, Signal & Power Integrity (EMC+SIPI), New Orleans, LA, USA, 22–26 July 2019; pp. 505–510. [Google Scholar] [CrossRef]
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  11. Kim, H.; Kim, D.; Park, N.-C.; Park, Y.-P. Acoustic Noise and Vibration Analysis of Solid State Drive Induced by Multi-Layer Ceramic Capacitors. Microelectron. Reliab. 2018, 83, 136–145. [Google Scholar] [CrossRef]
  12. Margielewicz, J.; Gąska, D.; Litak, G.; Wolszczak, P.; Trigona, C. Nonlinear Dynamics of a Star-Shaped Structure and Variable Configuration of Elastic Elements for Energy Harvesting Applications. Sensors 2022, 22, 2518. [Google Scholar] [CrossRef]
  13. Ko, B.-H.; Kim, D.; Park, N.-C.; Park, Y.-P. Study on Effective Piezoelectric Coefficient for Finite Element Analysis of Multi-Layer Ceramic Capacitor. In Proceedings of the 2015 Joint IEEE International Symposium on the Applications of Ferroelectric (ISAF), International Symposium on Integrated Functionalities (ISIF), and Piezoelectric Force Microscopy Workshop (PFM), Singapore, 24–27 May 2015; pp. 64–66. [Google Scholar] [CrossRef]
  14. Jia, Y.; Luo, H.; Zhao, X.; Wang, F. Giant Magnetoelectric Response from a Piezoelectric/Magnetostrictive Laminated Composite Combined with a Piezoelectric Transformer. Adv. Mater. 2008, 20, 4776–4779. [Google Scholar] [CrossRef]
  15. Wu, Z.; Xiang, Z.; Jia, Y.; Zhang, Y.; Luo, H. Electrical Impedance Dependence on the Direct and Converse Magnetoelectric Resonances in Magnetostrictive/Piezoelectric Laminated Composites. J. Appl. Phys. 2012, 112, 106102. [Google Scholar] [CrossRef]
  16. Kim, D.; Park, N.-C.; Park, Y.-P. Analysis of High-Pitched Noise from Solid-State Drives Generated by Multilayer Ceramic Capacitors. Microsyst. Technol. 2016, 22, 1367–1374. [Google Scholar] [CrossRef]

This entry is adapted from the peer-reviewed paper 10.3390/s22103869

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