PCBA Tech - Device packaging problems in PCB design

MLCC temperature characteristics are determined by EIA specifications and JIS specifications. The classification table, as shown in the figure above, 5U/Y5V and Z5U/Z5V have also been changed to the second category. In fact, many scenarios are no longer used. Therefore, general MLCC can be roughly divided into class I (low permittivity series, paramagnetic) and class II (high permittivity series, ferroelectric). This kind of capacitor has stable electrical performance and basically does not change with temperature, voltage and time. It is a super stable and low loss capacitor material type. It is suitable for high frequency, ultra-high frequency PCB and very high frequency circuits which require high stability and reliability.

The second category includes X5R, X8R, X6S, Y5V, etc. The main material is barium titanate, but the precious metals added are different. X7R dielectric Because X7R is a strong dielectric, it can produce capacitors with larger capacity than NPO dielectric. This kind of capacitor has relatively stable performance, and its unique performance does not change significantly with the change of temperature and voltage time. It belongs to the type of stable capacitor material, and is used in straight isolation, coupling, bypass, filter circuit and high reliability requirements of medium and high frequency circuit. Y5V dielectric capacitors with high dielectric constant are often used to produce large capacitors with large specific volume and high nominal capacity. However, its capacity stability is worse than X7R, and its capacity and loss are more sensitive to temperature, voltage and other test conditions. It is mainly used in oscillating, coupling, filtering and bypass circuits in electronic whole machines.

MLCC commonly used specifications are C0G (NP0), X7R, Z5U, Y5V and so on, different specifications have different characteristics and uses.

C0G capacitors have high temperature compensation characteristics and are suitable for bypass capacitor and coupling capacitor

X7R capacitors are temperature stable ceramic capacitors suitable for less demanding industrial applications

Z5U capacitors are characterized by their small size and low cost, which are especially suitable for decoupling circuits

Y5V capacitors have poor temperature characteristics but large capacity, which can replace low volume aluminum electrolytic capacitors

The main difference between C0G, X7R, Z5U and Y5V is their different filling media. In the same volume due to different filling medium composed of capacitors capacity is different, followed by the capacitor dielectric loss, capacity stability is also different, so in the use of capacitors should be based on the role of capacitors in the circuit to choose different capacitors.

C0G (NP0) capacitor

C0G is a commonly used MLCC with temperature compensation characteristics. Its filling medium is rubidium, samarium and some other rare oxides. C0G is stable in capacitance and dielectric loss, and has a wide range of operating temperature. The capacitance variation is 0±30ppm/ degree Celsius at temperature from -55 degree Celsius to +125 degree Celsius, and the capacitance variation with frequency is less than ±0.3 δ C. The drift or lag of C0G capacitance is less than ±0.05%, which is negligible compared to the film capacitance greater than ±2%. The typical change in capacity relative to service life is less than ±0.1%.

The capacitance and dielectric loss of C0G capacitors vary with the packaging type, and the frequency characteristic of large package size is better than that of small package size. C0G capacitors are suitable for bypass capacitors in oscillators, resonators, and coupling capacitors in high-frequency circuits.

In the figure below, the capacitance value of the 1206 package, C0G temperature characteristic, 25V withstand voltage, 0.22μF capacitor varies with temperature. The capacitance values are 0.21996μF and 0.22016μF in the temperature range required by all specifications. The error is very small.

X7R capacitor

X7R capacitor is called temperature stable ceramic capacitor. The temperature characteristic of X7R capacitor is inferior to that of C0G. When the temperature is from -55 degree Celsius to +125 degree Celsius, its capacity change is 15%. It should be noted that the capacitor capacity change is nonlinear at this time.

The capacity of X7R capacitors is also different at different voltages and frequencies, and it varies with time by about 1% δ C per 10 years, representing a change of about 5% per 10 years.

X7R capacitors are mainly used in low-requirement industrial applications, and the capacity variation is within an acceptable range when the voltage changes. The main characteristic of X7R is that the capacity can be relatively large under the same volume.

X5R and X7R are mainly upper temperature is not so high, but also a lot of use.

Is the capacitance value of the 1206 package, X7R temperature characteristic, 25V withstand voltage, 0.22μF capacitor as a function of temperature. In the temperature range required by all specifications, the capacitance value is 0.204μF, 0.224μF, the error is an order of magnitude larger than C0G, but the temperature performance is very good.

Z5U capacitors

Z5U capacitors are called "universal" ceramic monolithic capacitors. It should be noted here that the temperature range of Z5U is from +10 degree Celsius to +85 degree Celsius, the capacity variation is from +22% to -56%, and the dielectric loss is 4%. Z5U capacitors are mainly characterized by their small size and low cost. For the two MLCC mentioned above, Z5U capacitors have capacitance at the same volume, but its capacitance is greatly affected by the environment and working conditions, and its aging rate can decrease by 5% every 10 years.

Although its capacity is not stable, its small size, low equivalent series inductance (ESL) and equivalent series resistance (ESR), and good frequency response make it have a wide range of applications, especially in decoupling circuits.

In some manufacturers have not found the corresponding selection specifications. The following figure shows the comparison curves of temperature characteristics of NP0, X7R, Y5V and Z5U.

Y5V capacitor

Y5V capacitor is a universal capacitor with a certain temperature limit, and the dielectric loss of Y5V is 5%. Capacitance of Y5V material, temperature stability is not good, temperature change will cause a large change in capacity, design must be taken into account, in the range of -30 degree Celsius to 85 degree Celsius, its capacity change can reach +22% to -82%, Y5V will gradually be replaced by X7R, X5R good temperature characteristics. In some manufacturers have not found the corresponding selection specifications. The following figure shows the measured data of netizens.

The temperature characteristics and reliability of C0G, X7R, Z5U and Y5V decrease in turn, and the cost decreases in turn. In the selection, if the operating temperature and temperature coefficient requirements are very low, you can consider using Y5V, but in general to use X7R, higher requirements must choose C0G. Under normal circumstances, MLCC is designed to make the capacitance of X7R and Y5V material near the room temperature. The change trajectory of the capacity relative to temperature is a downward opening parabola. As the temperature rises or falls, the capacity will decrease.

And the dielectric constant of C0G, X7R, Z5U, Y5V medium is also reduced in turn, so the same size and pressure, the capacity can be made is also reduced in turn. In practical application, the development and design engineers of many companies calculate according to the theory, but do not know the actual production status of MLCC manufacturers, and often list some specifications that seldom produce or even do not exist, which not only causes the purchase cost to rise but also affects the delivery time. For example, you want to use a 0603/C0G/25V/3300pF capacitor, but the 0603/C0G/25V MLCC is generally only 1000pF.