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Characteristics of chip capacitor dielectrics
Date: 2024-08-23
The full name of chip capacitors is multilayer ceramic capacitors, which are equivalent to insulators. They can interrupt the function in DC circuits and are one of the most commonly used electronic components in the SMT processing industry. Chip capacitors are mainly divided into NPO capacitors, X7R capacitors, X5R capacitors and Y5V capacitors based on dielectrics (materials). The difference between them is mainly the difference in filling dielectrics (materials). Under the same volume, the capacity of capacitors composed of filling dielectrics is also different. The resulting dielectric loss and capacity stability of capacitors are also different.
Therefore, when using capacitors, different ones should be selected according to the different functions of the capacitors in the circuit. The characteristics of NPO, X7R, X5R, and Y5V capacitor dielectrics (materials) are explained.
1. NPO capacitors
NPO is the most commonly used monolithic ceramic capacitor with compensation characteristics. Its filling dielectric is composed of some rare oxides. It is one of the capacitors with the most stable capacitance and dielectric loss. When the temperature ranges from -55℃ to 125℃, the capacitance becomes 0±30ppm/℃, and the capacitance changes with frequency by less than 0.3△C. The drift or hysteresis of NPO capacitors is less than 0.05%, which is negligible compared to film capacitors with a value greater than 2%. The service life change of its typical capacity is less than 0.1%. The capacitance and dielectric loss of NPO capacitors vary according to the different packaging forms and the frequency characteristics. The frequency characteristics of large packaging sizes are better than those of small packaging sizes.
2. X7R capacitors
X7R capacitors are called temperature-stable ceramic capacitors. When the temperature drops from -55℃ to 125℃, its capacitance changes by 15%. It should be noted that the capacitance change of the capacitor is nonlinear at this time. Its capacitance is different under different voltage and frequency conditions. It also changes with time, changing by about 1%ΔC every 10 years, which is expressed as a change of about 5% in 10 years.
X7R capacitors are mainly used in industrial applications with low requirements, and when the voltage changes, its capacitance change is acceptable. Its main feature is that the capacitance can be made larger at the same volume.
3. X5R capacitors
X5R capacitors are called general-purpose ceramic monolithic capacitors. The first thing to consider here is the temperature range of use. X5R capacitors are mainly small in size and low in cost. Among the three types of ceramic monolithic capacitors mentioned above, X5R capacitor has the largest capacitance at the same volume. However, its capacitance is greatly affected by the environment and working conditions, and its aging rate can reach a maximum decrease of 5% every 10 years.
Although its capacitance is unstable, it has a wide range of applications due to its small size, small equivalent series inductance, low equivalent series resistance, and good frequency response. Especially in the application of decoupling circuits.
IV. Y5V capacitor
Y5V capacitor is a general-purpose capacitor with certain temperature limitations. Its capacitance change can reach -82% in the range of -30℃ to 85℃. The high dielectric constant of Y5V allows the manufacture of 4.7μF capacitors in smaller physical sizes.
Causes of chip capacitor leakage
(1) The surface of the chip capacitor is dirty, resulting in a decrease in surface insulation. The leakage current is not large, generally in the microampere level. The insulation value will increase when hot air is blown;
(2) Internal cracks, cracks caused by welding, and cracks caused by poor manufacturing of MLCC. The leakage current caused by this crack increases, and in severe cases, local explosions and fires occur;
(3) When the chip capacitor has a large capacity, external stress and thermal shock will cause cracks, resulting in large leakage current;
Chip capacitor leakage test method
It is difficult to measure leakage on the circuit board. The main reason is the influence of other components in the circuit, resulting in inaccurate measurement. If other circuits need to be disconnected, leakage can be measured. Sometimes it is possible to test whether its DC operating point is normal. If the leakage is serious, the DC operating voltage will drop.