Analysis of the causes of squeaking of MLCC (sMD) capacitors (I)

MLCC capacitors, commonly known as multilayer ceramic capacitors, are commonly referred to as chip capacitors. During the actual debugging and use, there may be a small partner who hears the MLCC capacitor emitting an annoying hum. Before the specific development, first introduce a noun: piezoelectric effect (specific Baidu), piezoelectric effect includes positive piezoelectric effect and inverse piezoelectric effect. The so-called positive piezoelectric effect refers to the fact that some materials generate electric charge under the action of external force; the inverse piezoelectric effect means that the object will deform under the applied voltage.

The sound originates from the vibration of the object, and when the frequency of the vibration is between 20 Hz and 2 kHz, it can be heard by the human ear. Back to our theme, the MLCC capacitor hums, that is, the MLCC capacitor undergoes a large deformation (visible on the micro), and the frequency of the vibration is within the hearing range of the human ear, so we hear a click. So the remaining question is why the MLCC capacitor vibrates? Combined with the theory of the front bedding, it is found that there is an inverse piezoelectric phenomenon, that is, the MLCC capacitor is mechanically vibrated in the case of externally applied alternating current, thereby making a buzzing sound.

As people's demand for electronic devices has become calmer, the "howling" problem caused by capacitor vibration has not been paid attention to in the power circuits of various applications such as notebook computers, mobile phones, and digital cameras (DSCs). Become a design issue.

The sound originates from the vibration of the object, and the sound wave with a vibration frequency of 20 Hz to 20 kHz can be recognized by the human ear. The MLCC emits a howling sound, that is, the MLCC undergoes a large amplitude vibration under the action of a voltage (a microscopically large, less than 1 nm).

Why does MLCC vibrate?

We must first understand a natural phenomenon - electrostriction.

Under the action of an external electric field, all substances will undergo telescopic deformation - electrostriction.

For some high dielectric constant ferroelectric materials, the electrostrictive effect is intense, called the piezoelectric effect.

Piezoelectric effects include positive and negative piezoelectric effects.