Why multilayer ceramic capacitors leak electricity
Published time: 2018-09-21
Let's look at the basic structure of ceramic capacitors
The most basic structure used by capacitors to store electrical charge consists of a pair of electrodes separated by a dielectric, as is shown in Fig. 1 below.
One of the indicators used to express the performance of a capacitor is how much electrical charge it can store.
And in the case of a multilayer ceramic capacitor, by repeating the same structure shown in Fig. 1 level after level, the amount of charge it can store is increased.
Fig. 2 shows the basic structure that results.
Overview of articles
Although MLCC(multilayer ceramic capacitors) is simple in function, it is widely used in electronic products such as smart phones.
Once it fails, it will lead to circuit failure, abnormal function, and even a series of safety problems such as product burning and explosion.
MLCC's failure mode is the focus of quality-testing engineers, and ensuring that MLCC works effectively is an important part of their work
Jotrin Electronics will tell you about it:
In many failure modes, the most common type of failure is the leakage of capacitors (low insulation impedance).
The main reasons can be divided into the internal factors in manufacturing process and the external factors in the process.
1.The internal factors of leakage of multilayer ceramic capacitors
1.1 The leakage of multilayer ceramic capacitors due to formation of void
The inner foreign body of the capacitor volatilizes during sintering, thus forming a Void.
The Void can lead to short circuits and potential electrical failure between electrodes.
If the Void is enough large, it will not only reduce IR but also reduce the effective capacitance.
When plugged in the power supply, it is possible to cause the hollow local heat, reduce the insulating properties of ceramic media and aggravate the leakage of electricity, which can lead to cracking, explosion, combustion, etc
1.2 Ceramic capacitor (MLCC) leakage due to sintering crack
The Sintering cracks generally occur due to rapid cooling during sintering and appear perpendicular to the sides of the electrodes.
Therefore, when using a capacitor, we should pay attention to whether the capacitor has sintering cracks.
1.3 Layered Delamination
The delamination is often generated after the stacking, due to poor lamination or poor drainage, insufficient sintering, air is mixed between the layers, and external impurities appear jagged lateral cracking.
It is also possible that the thermal expansion mismatch after mixing different materials.
2.The external factors of leakage of multi-layer ceramic capacitors
2.1 Capacitors (MLCC) leak electricity due to thermal shock
Thermal shock mainly occurs during wave peak welding, and the temperature changes sharply, causing cracks between the internal electrodes of the capacitor.
Generally, it needs to be found through measurement, and after grinding, it is usually a small crack, which needs to be confirmed by a magnifier. In rare cases, visible cracks will appear.
In this case, it is recommended to use reflow soldering, or to slow down the temperature change during wave soldering (not exceeding 4~5 °C/s), and control the temperature below 60 °C before cleaning the panel.
2.2 External mechanical stress
Because the main component of MLCC is ceramic, in the process of placing components, dividing plates, and screws.
It is likely that the capacitor is crushed and broken due to excessive mechanical stress, resulting in potential leakage failure.
The crack at this time is generally oblique, and is cracked from the joint of the terminal and the ceramic body.
3.3 Solder transfer
Soldering in a high-humidity environment may cause solder migration at both ends of the capacitor, which together cause a leakage short circuit.
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