Chip capacitor performance introduction

Crystal oscillator

Quartz Oscillator 3225 20M OSC

The chip capacitor has the characteristics of large capacity, small size, easy chipping, etc. It is one of the most used components in today's mobile communication devices, computer boards and home appliance remote controls. In order to meet the needs of miniaturization, large capacity, high reliability and low cost of electronic devices, chip capacitors are also rapidly developing: the types are increasing, the volume is shrinking, the performance is continuously improved, and the technology is constantly Progress, materials are constantly updated, thin and light series products have become more standardized and generalized. Its application is gradually infiltrating and developing from consumer devices to investment devices.

In addition, chip capacitors are still moving in a diversified direction:
1 In order to meet the needs of portable communication tools, chip capacitors are developing in the direction of low voltage, large capacity, ultra small and ultra thin.
2 In order to adapt to the development of some electronic complete machines (such as military communication equipment), high voltage, high current, high power, ultra high Q value, low ESR type medium and high voltage chip capacitors are also an important development direction.
3 In order to meet the requirements of highly integrated circuits, multi-functional composite chip capacitors are becoming a hot research topic.

1 chip laminated ceramic dielectric capacitor

The most widely used chip capacitors are chip laminated ceramic dielectric capacitors.
A chip-type multilayer ceramic capacitor (MLCC), referred to as a chip-type multilayer capacitor (or simply a chip capacitor), is formed by disposing a ceramic dielectric film printed with electrodes (internal electrodes) in a misaligned manner. The high-temperature sintering forms a ceramic chip, and then the metal layer (outer electrode) is sealed on both ends of the chip to form a monolith-like structure, so it is also called a monolithic capacitor.
The chip type monolithic ceramic capacitor is a multi-layered structure which is substantially a parallel body of a plurality of simple parallel plate capacitors. Therefore, the capacitance calculation formula of the capacitor is
C=NKA/t
Where C is the capacitance; N is the number of electrode layers; K is the dielectric constant (commonly known as K value); A is the relative electrode coverage area; t is the electrode spacing (media thickness).
From this formula, it can be seen that in order to realize the requirements of large capacity and small volume of the chip laminated ceramic capacitor. As long as N is increased (the number of layers is increased), the capacitance can be increased. Of course, it is also possible to use high-k materials (reducing the stability), increasing A (increasing the volume), and decreasing t (reducing the voltage withstand capability).
Here, in particular, the dielectric constant K value depends on the ceramic material filling the medium in the capacitor. The ambient temperature, operating voltage and frequency used by the capacitor, as well as the time of operation (stability of long-term operation), can have different effects on different media. Generally, the larger the dielectric constant (K value), the worse the stability, reliability, and durability.
The main components of the commonly used ceramic medium are MgTiO3, CaTiO3, SrTiO3 and TiO2, and then added with an appropriate amount of rare earth oxides. It is characterized by large dielectric coefficient, low dielectric loss, small temperature coefficient, wide application range of ambient temperature and good high-frequency characteristics. It is used in high-demand applications (class I ceramic capacitors).
The other type is low-frequency high-molecular materials called ferroelectric ferroelectric ceramics, which are often used as dielectrics for class II ceramic capacitors. Ferroelectric ceramics with BaTiO3 as the main component are characterized by a high dielectric constant of thousands, even Tens of thousands; however, the dielectric constant varies nonlinearly with temperature, and the dielectric constant also has a nonlinear relationship with the applied external electric field.

At present, there are three types of multilayer ceramic capacitor media commonly used: COG or NPO is an ultra-stable material with a K value of 10 to 100; X7R is a relatively stable material with a K value of 2,000 to 4,000; Y5V or Z5U is a general purpose. The material has a K value of 5,000 to 25,000. In China's standards, it is divided into Class I ceramics (CC 4 and CC41) and Class II ceramics (CT4 and CT41). Among the above materials, COG and NPO are ultra-stable materials, and the capacity change of the capacitor does not exceed ± 30 ppm/°C in the range of -55 ° C to + 125 ° C.
The rest of the material is named according to the range of its operating temperature and the rate of change of capacitance.
Among the dielectric materials of several commonly used chip capacitors:
X7R stands for a temperature range of -50 ° C to +125 ° C; the capacitance change in this range can reach ± ​​15%.
Z5U represents a temperature range of +10 ° C to +85 ° C; the capacitance in this range varies from -56% to +22%.
Y5V represents a temperature range of -30 ° C to +85 ° C; the capacitance within this range varies from -82% to +22%.
These relationships indicate that in practical use, the choice of chip capacitors cannot be considered only in terms of volume and price. If there is an environmental temperature problem, attention should also be paid to the change in capacitance caused by the capacitor's medium. Figure 2 plots the capacitance of different material capacitors and the dielectric loss as a function of temperature.

The following are the performance and application of capacitors of different materials:
1NPO capacitor
NPO capacitors are the most stable capacitors for capacitance and dielectric loss. Its filling medium consists of ruthenium, osmium and some other rare oxides. The capacity change is 0±30ppm/°C at temperatures from -55°C to +125°C, and the capacitance varies very little with frequency and relative service life.
Depending on the package type, the capacitance and dielectric loss vary with frequency, and NPO capacitors with large package sizes have better frequency characteristics than small package sizes.
NPO capacitors are suitable for use in oscillators, tank tank capacitors, and coupling capacitors in high frequency circuits.
2X7R capacitor
The X7R capacitor is called a temperature stable ceramic capacitor. When the temperature changes from -55 ° C to +125 ° C, its capacity changes to 15%. It should be noted that the capacitor capacity change is nonlinear at this time.
The capacity of the X7R capacitor is different under different voltage and frequency conditions, it also changes with time, but much better than the Z5U and Y5V capacitors.
X7R capacitors are mainly used in less demanding industrial applications, and their capacity changes are acceptable when the voltage changes. Its main feature is that the capacitance can be made larger under the same volume.
3Z5U capacitor
Z5U capacitors are called "universal" ceramic chip capacitors. Its main advantages are small size and low cost. For the three chip capacitors already mentioned, the Z5U capacitor has the largest capacitance at the same volume. However, its capacitance is greatly affected by environmental and working conditions, and the dielectric loss can reach 3%.
Despite its unstable capacity, this capacitor is characterized by its small size, low equivalent series inductance (ESL) and low equivalent series resistance (ESR), and good frequency response. Applications, especially in the application of decoupling circuits.
4Y5V capacitor
The Y5V capacitor is a general-purpose capacitor with a certain temperature limit. The capacity variation can reach +22% to -82% in the range of -30 ° C to +85 ° C, and the dielectric loss can reach 5%. However, the high dielectric constant of Y5V allows capacitors of up to 4.7μF to be fabricated in smaller physical sizes.

The following are the main technical indicators to illustrate the performance of chip capacitors:
1 Capacity and error: The maximum deviation range allowed by the actual capacitance and the nominal capacitance.
Commonly used capacitors have the same level of accuracy as resistors. Expressed by letter: D grade: ±0.5%; grade F: ±1%; grade G: ±2%; grade J: ±5%; grade K: ±10%; grade M: ±20%.
2 rated working voltage: Capacitor can work stably and reliably for a long time in the circuit, and the maximum DC voltage it bears, also known as withstand voltage. For devices with the same structure, medium and capacity, the higher the withstand voltage, the larger the volume.
3 Temperature coefficient: The relative change value of the capacitance for every 1 °C change in temperature within a certain temperature range. The smaller the temperature coefficient, the better.
4 insulation resistance: used to indicate the size of the leakage. Generally, a small-capacity capacitor has a large insulation resistance of several hundred megaohms or several gigaohms. The insulation resistance of electrolytic capacitors is generally small. Relatively speaking, the larger the insulation resistance, the better the leakage is.
5 Loss: The energy consumed by a capacitor to generate heat per unit time under the action of an electric field. These losses are mainly due to dielectric loss and metal loss. Usually expressed by the loss tangent value.
6 Frequency characteristics: The nature of the electrical parameters of the capacitor as a function of the frequency of the electric field. In a capacitor operating under high frequency conditions, since the dielectric constant is smaller at a high frequency than at a low frequency, the capacitance is also reduced accordingly. Losses also increase with increasing frequency. In addition, when operating at high frequencies, the distribution parameters of the capacitor, such as the resistance of the pole piece, the resistance between the lead and the pole piece, the inductance of the pole piece, the inductance of the lead, etc., all affect the performance of the capacitor. All of this limits the frequency of use of the capacitor.

In actual use, in addition to paying attention to the influence of environmental temperature changes on the capacitance change of the capacitor, it is also necessary to pay attention to the influence of the operating voltage and storage time on the capacitance change of the capacitor.
1 The voltage of the capacitor has an influence on the capacitance of the capacitor. The medium with low stability will greatly reduce the capacity after the rated operating voltage is applied, so that the effect cannot be achieved. This must be paid attention to when selecting the capacitor ( Can not blindly pursue large capacity and small volume, must have sufficient room for capacity and use voltage).
2 storage time also has an impact on the capacity of the capacitor. For ultra-stable capacitors, such as COG and X7R, the capacitor capacity does not change much with time. However, the capacitance of Z5U/Y5V increases with time, and the change in capacitance for 1 000 hours can be as high as 5% to 10% or more. However, the ageing of such capacitors is reversible. Each time the capacitor temperature is raised to 125 ° C, the aging process begins again. Therefore, when the storage capacity of such capacitors exceeds 1000 hours, the low capacity phenomenon does not belong to the quality problem of the product, and its characteristics are in line with international standards. A general solution for capacitors with low capacity is to preheat the capacitor for 1 hour in an environment of around 150 °C. Its capacity will return to normal.

2 Chip capacitors in the electromagnetic interference suppression of equipment The main applications of chip capacitors in general electronic circuits are: filtering, coupling, decoupling, bypass, resonance, time constant (timing) and feedback. among them:
1 Filtering: Parallel between the positive and negative poles of the power supply circuit to remove the useless AC in the circuit (or filter the AC component in the rectified one-way ripple voltage to make the unidirectional pulsation become smooth DC).
2 Decoupling: Connected between the positive and negative poles of the circuit power supply wiring to prevent mutual interference caused by the internal resistance of each part of the circuit (and parasitic oscillations in severe cases).
3 Bypass: Connected to both ends of the resistor or directly from a point to the common potential point to set a path for the AC or pulsation signal in the AC/DC signal to prevent the AC component from generating a voltage drop when passing through the resistor.
The electromagnetic interference suppression of chip capacitors in equipment is actually only one aspect of the application of chip capacitors in circuits.
The power line filtering and decoupling described above is also part of the device's electromagnetic interference suppression application. In addition, there are common mode filtering of signal lines, radiation suppression of signal lines and power lines, and the like.
In order to make the effect of chip capacitor interference suppression more obvious, it is sometimes used in combination with chip beads and chip inductors. There is also a chip laminate composite device that combines capacitors and inductors in one component, making it easier to use and better.

3 chip capacitor line form
1) The chip capacitor of the two-terminal type of chip type two-terminal capacitor is the most commonly used chip capacitor. Here, the product of Murata Manufacturing Co., Ltd. is taken as an example.
Murata's chip capacitors are extremely versatile, with general decoupling and filtering capacitors (multiple specifications, large capacity, and high-capacity products), as well as capacitors for frequency control, tuning and impedance matching (with temperature compensation), high speed and High-frequency circuit decoupling capacitors (low inductance and low resistance), medium and high voltage conversion capacitors (high voltage, large capacity), capacitors for AC circuits (in compliance with safety regulations), and capacitors for automotive transmission and safety equipment. Users can choose the right capacitor according to different needs.
Below is the chip capacitor of the GRM15/18/21/31 series from Murata Manufacturing Co., Ltd.
1GRM18/21/31 series chip capacitors are suitable for wave crest and reflow soldering; GRM15 series chip capacitors are only suitable for reflow soldering.
2GRM1 5/18/21/31 series chip capacitors are available in a variety of sizes including length × width × thickness 1.0 × 0.5 × 0.5mm to 3.2 × 1.6 × 1.6mm .
The applicable voltages of the 3GRM15/18/21/31 series chip capacitors include 6.3V, 10V, 16V, 25V, 50V, and 100V. Multiple grades such as 200V and 500V; depending on the dielectric material used, there are a variety of chip capacitors such as COG to Y5V.
The 4GRM15/18/21/31 series of chip capacitors can be used in general-purpose electronic equipment.
Murata also produces a type of capacitor with 2 to 4 capacitors in a single device, making it ideal for use on a microcontroller bus.

2) Chip type three-terminal capacitors The ceramic wafer capacitors we usually use as bypass capacitors can short-circuit high-frequency interference to the ground to achieve anti-interference. However, the lead inductance of the capacitor and the residual inductance inside the capacitor limit its high frequency characteristics.
The insertion loss of the capacitor initially increases with increasing frequency until the self-resonant frequency (the series resonance of the equivalent inductance and capacitance) is reached, and the insertion loss also reaches a maximum. Thereafter, as the inductive reactance of the equivalent inductance increases, the insertion loss begins to decrease.
In order to have a good bypass function at high frequencies, the self-resonant frequency of the bypass capacitor must also be high, so the lead of the capacitor must not be long. In addition, the bypass capacitor is not as large as possible, the capacitance is large, and the frequency of self-resonance is low. Therefore, the best way is to select the appropriate capacitor by experiment, and try to make the interference frequency to be suppressed consistent with the self-resonance point, so as to maximize the insertion loss caused by the filter capacitor.
Since the common two-terminal capacitor has a lead inductance, the total residual inductance is large and the self-resonance point is also low. In order to improve the self-resonance of ordinary leaded capacitors and the low self-resonance frequency, Murata has developed a lead-type three-terminal capacitor. Compared to the capacitance at both ends, the upper lead of this capacitor is turned into two (so the three-terminal capacitor has three leads). The two upper leads of the three-terminal capacitor are part of the signal transmission line, so the lead inductance and the capacitor become an "LC" filter. It is the three-terminal capacitor that cleverly utilizes the lead inductance, so that the three-terminal capacitor has better suppression of interference. Three-terminal capacitors also have self-resonance problems. To minimize this problem, the length of this pin that is grounded to the three-terminal capacitor should be limited.
It should be said that the appearance of a chip type two-terminal capacitor is very advantageous for improving the self-resonance problem of a conventional lead type capacitor because the lead length of the chip type two-terminal capacitor is minimized. However, due to the internal structure of the capacitor, the residual inductance of the internal electrode cannot be eliminated, so that when the frequency is such that the capacitive reactance XC of the capacitor is equal to the absolute value of the residual inductance XL, the two-terminal capacitor still generates self-resonance. Due to the existence of the self-resonant frequency, when the frequency band of the noise exceeds the self-resonant frequency, the suppression effect of the noise rapidly drops. However, compared with the conventional leaded two-terminal capacitor, there is still a great improvement.