MLCC is widely used in electronic products such as smart phones. If it fails, it will cause the circuit to malfunction, the function is not normal, and serious problems such as burning and explosion of the product may occur. Therefore, the reason for its failure is also very worthy of attention.
Capacitor leakage is the most common type of failure mode. The main reason for MLCC leakage can be divided into internal factors in the manufacturing process and external factors in the production process.
Intrinsic factors that cause MLCC leakage:
1, Void
The foreign matter inside the capacitor volatilizes the void formed during the sintering process. The void will cause short circuit between the electrodes and potential electrical failure. If the cavity is large, the IR will be reduced and the effective capacitance will be reduced. When power is on, there may be leakage causing local heating of the cavity, reducing the insulation of the ceramic medium, accelerating leakage, and causing cracking, explosion, and combustion.
2, Crack
The cause of the occurrence of sintering cracks is generally rapid cooling during the sintering process, which occurs in the vertical direction of the electrode side.
3, Delamination
The delamination is often caused by poor lamination or debinding, and insufficient sintering after stacking. The air is mixed between the layers and the external impurities are jagged laterally cracked. It is also possible that thermal expansion mismatches occur after mixing different materials.
External factors that cause MLCC leakage:
1, thermal shock
Thermal shock mainly occurs during wave soldering, and the temperature changes abruptly, causing cracks between the internal electrodes of the capacitor. Generally, it is found through measurement that it is observed after grinding, usually a small crack, which needs to be confirmed by a magnifying glass, and in a few cases, it will be visible to the naked eye. Crack.
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. External mechanical stress
Because the main component of MLCC is ceramic, in the process of placing components, sub-plates, screws, etc., 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. 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.